Title of Invention	"A PROCESS FOR THE MANUFACTURE OF SLOW-RELEASE FERTILIZERS"
Abstract	A process for preparation of slow release cationic micronutrient fertilizers, which processes comprises heating at such as herein described 1east one micronutrient metsl or a compound thereof^ with or such as herein described without additives^ with phosphoric acid ti11 the resultant (the correspondir mixture is mostly homogenous, further heating, to form metal, polyphosphates of such a degree of polymerisation that they are still soluble in dilute mineral acids and complexants, treating said metal polyphosphates with a basic compound and finally obtaining a dried powder.

Title of Invention

"A PROCESS FOR THE MANUFACTURE OF SLOW-RELEASE FERTILIZERS"

Abstract

A process for preparation of slow release cationic micronutrient fertilizers, which processes comprises heating at such as herein described 1east one micronutrient metsl or a compound thereof^ with or such as herein described without additives^ with phosphoric acid ti11 the resultant (the correspondir mixture is mostly homogenous, further heating, to form metal, polyphosphates of such a degree of polymerisation that they are still soluble in dilute mineral acids and complexants, treating said metal polyphosphates with a basic compound and finally obtaining a dried powder.

Full Text	-2- FIELD OF INVENTION This invention relates to a process for the manufacture of slow-release fertilizers of cationic micronutrients such as zinc, copper,iron, manganese, cobalt or magensium, either as single nutrient or as multinutrient formulations. BACKGROUND OF INVENTION Compounds which are widely used today as micronutrient fertilisers, are soluble salts or organic chelated forms eg., zinc, copper, manganese or iron sulphates, and EDTA, complexes of the same. Liquid fertilizers such as micronutrients dissolved in condensed phosphoric acid or ammonium polyphosphates are also used (V. Sauchel1i, 1967, Chemistry and Technology of Ferti1izers, Reinhold, New York; G-H. Col1ins, 1955, Commercial Fertilizers, McGraw Hill, New York). The synthesis of slow-release fertilizers based on phosphate glasses known as frits, have been described. Such frits are usually prepared by fusing ammonium or sodium dihydrogen -3- phosphates with micronutrient salts to produce a melt, at temperatures between 8ØØo and 14ØØoC and then rapidly cooling the liquid by pouring on to a cold plate (G.J. Roberts, 1973, Am. Ceram, Soc-Bull., Vol 52, p.. 383, ibid idem, Vol. 54, p 1Ø69, Austrian Patent No. 32616Ø of 1975 US Patent No- 3574531 of 1971, US Patent No. 2713536 of 1974. Apart from phosphate glasses, other phosphate compounds have also been proposed as slow-release fertilizers. These include micronutrients added to metaphosphates of potassium or calcium prior to reaction. Volfkovich et al. , (S.I. Volfkovich, A.S. Cherepanova, I.A. Grishina & G.A. Bitko, 197Ø, D. Zh. Nauki Kaz SSP (Russian? p. 3) added various metal oxides to potassium metaphosphate melts. Volfkovich reviewed the work done by the Russian school in the filed of metaphosphate based fertilizers (S.I. Volfkovich, 1372, J. Appl- Chem (USSR), Vol. 45, p.2479). A Russian patent (Su of 1986 127Ø148 / describes the production of such mixed o metaphosphate based fertilizers produced at 55Ø - -4- o of 199Ø 88Ø C. Two Indian Patents (Nos. 1728ØØ/and 1772Ø5 of 1391) describe the processes for production of zinc and copper fertilizers based on low molecular weight polyphosphates. The chemistry of zinc and copper phosphate polymerisation and the chemical nature of these fertilizers have also been described (S.K. Pay, C. Varadachari & K. Ghosh, 1993, Ind. Eng. Chem. Pes., Vol. 32, p. 1218; S.K.Ray, C1 Varadachari & K. Ghosh, 1997, J. Agric. Food Chem., Vol-, 45, p. 1447) . The major drawbacks of using soluble salts (such as sulphates), as micronutrients fertilizers are, leaching losses, chemical transformation losses, ground water contamination and low ferti1izer-use efficiency. On the other hand, micronutrlent fertilizers having slow-release properties do not suffer any of these disadvantages. However,, both the existing types of slow-release fertilizsrs incorporating micronutrients, are not commercially successful so far. The major disadvantage of the first group of compounds viz. the phosphate glass frits, is that -5- the process for their production is not commercially viable; the reaction conditions, in the melting of phosphates, are so corrosive that very expensive material have to be used for furnace construction thereby limiting large scale production and increasing product costs. The major disadvantage of the second group of compounds viz the long chain metaphosphates is; their excessive insolubility particularly in complexants, which renders, the t micronutrient ions mostly unavailable for plants. The most important factor here is that both these two types of phosphate based slow release fertilizers are essentially macronutrient (N, P or K) fertilizers containing micronutrients as supplements. There is no process available as yet for making a slow-release fertilizer that is essentially a source of micronutrients and which can thereby replace the conventional water-soluble micronutrient fertilizers. -6- OBJECTS OF THE INVENTION An object of this invention is to propose a procese for the manufacture of slow release fertilizers of cationic micronutrients having a substantial reduction in production time for the initial reaction stage between phosphor ic acid and micronutrient compounds. Another object of this invention is to propose a process for the manufacture of slow release fertilizers of cationic micronutrients and which has a simple method of assessing the upper limit of polymerisation whereby the process is rendered extremely flexible as regards choice of temperature for polymerisation and components in reacting mixture. Yet another object of this invention is to propose a process for the manufacture of slow release fertilizers of cationic micronutrients and wherein a wide range of starting materials may be used in widely ranging proportions and the -7- polymerisation can be carried out at any convenient temperature. Still another object of this invention is to propose a process for the manufacture of slow release fertilizers of cationic micronutrients which is simple, requirs lower energy inputs than all previous processes and is readily adaptible to a wide range of micronutrient formalations. DESCRIPTION OF THE INVENTION According to this invention there is provided a process for the preparation of slow-release cationic micronutrient fertilizers, which comprises in heating at least one micronutrient metal or a compound thereof, with or without additives, with phosphoric acid till the resultant mixture is nearly homogeneous, further heating to form metal polyphosphates of such a degree of polymerisation that they are still soluble in dilute mineral acids and complexants, treating said metal polyphosphates with a basic compound and finally obtaining a dried powder. Compound of the micronutrient element such as their oxides, hydroxides, carbonates, sulphates or chlorides are mixed with phosphoric acid and heated to a temperature T above 1 o 15ø to remove excess water and allow completion of reaction. This reaction may also be carried out under vacuum, at o temperature lower than 15ø . The dihydrogen phosphates are then -8- further heated to 3 temperature T which is above temperature T 2 1 till polyphosphates of the desired degree of polymerisation are produced as observed by their solubility characteristics or average chain length estimates. The polyphosphates are subsequently neutralised with bases like ammonia, lime, sodium or potassium hydroxide. The product is dried at low temperature powdered and sieved, (i) Zinc Fertilisers Starting materials include zinc oxide (containing upto 79% Zn) , zinc metal (containing upto 99.99% Zn), zinc ash (containing zinc oxide and metallic zinc in variable amounts), zinc sulphate (containng up to 4Ø.5% Zn) or zinc chloride (containing upto 47.9% Zn). The zinc raw material is added to phosphoric acid (containing not more than 6Ø% P Ø ) so that the 2 5 molar ratio of Zn:P in the mixture is at least 1x2 (weight ratio Zn:P is at least 1.Ø5:1). The optimum molar ratio of Zn:P is 1:2. With P levels higher than this the initial reaction is faster but at the same time more acid groups will remain in the polyphosphate and this will requrie more base for neutralisation. Almost any grade of acid can be used for the reaction. However, fertilizer grade phosphoric acids containing about 3ø -6ø % P Ø 2 5 are suitable and since acid containing about 5ø% P O is 2 5 the most commonly available this is preferred for the : 9 : reaction. The mixture of zinc compounds and phosphoric acid is taken in a porcelain crucible or a tray made of SS 316L , placed in a muffle furnace and heated at any temperature above 15ø C.At higher temperatures evaporation is faster. The optimum temperature is determined by the nature of the equipment used for evaporation. Thus, in a muffle furnace 17ø oC is optimum; in commercial driers like a spray drier input temperatures of about 4ø oC may be needed but the duration of heating is very small -snd product temperatures donot exceed 2 ø ØoC. When evaporation is done under partial vacuum reaction temperatures may be reduced. After the reaction, the product contains mostly zinc dihydrogen phosphate; some sulphate or chloride may also be present if such raw materials have been used. This product is further heated at o any temperature above 19Ø C for polyphosphates to form. Here again, the temperature used for polymerisation depends on the o equipment used for the reaction. In a muffle furnace 35 ø C is o optimum. If a fluidised bed furnace is used 4 ø ø C is preferred-Heating is done till a polyphospate of the desired degree of polymerisation is obtained. When such reaction is carried out in o trays or similar vessels about 6Ø min is required at 35Ø C furnace temperatures. When the reaction is done in a fluidised o bed furnace only about 15 min is required at 4øø C furnace temperatures, the product is tested at periodic intervals for 1Ø z solubility in ø.1 N HCI , ø.33 M citric acid, ø.ØØ5 M DTPA. Polymerisation may be stopped at any stage wherein the product retains its solubility in the aforesaid reagents; the product will be observed mostly to dissolve in these reagents within 3Ø min. The optimum polymerisation stage is that prior to the formation of a product which is significantly insoluble in the acids and complexants mentioned above; in other words, the product has reached the upper limit of its solubility in these reagents. Subsequently, the reaction product is cooled to room, temperature, made into a slurry with water and mixed with ammonia solution, CaO (lime), CaCo3 (limestone), sodium carbonate (soda ash), potassium carbonate, sodium hydroxide or potassium hydroxide. Enough bases are added to raise the pH of the slurry to between 3 and 4. Too little base will result in a hygroscopic product. Too much of base has no particular advantage and may precipitate of some of the zinc ions. After neutralising, when o the pH has stabilised, the material is dried at (1øø C, o o preferably at 6Ø -8Ø C. It is then ground and sieved, preferably to (1øø mesh B.S. (ii) Copper fertilizers Starting materials include the hydroxide carbonate, sulphate or chloride of the cupric ion containing up to 49.9%, 51-4%, 25.4% and 47.Ø% Cut respectively- The copper raw material 11 is added to phosphoric acid (containing up to 6Ø% of P Ø ) so 2 5 that the molar ratio of Cu: P is 1:2 or higher (weight ratio of Cu:P is at least 1.ø 2:1). The optimum molar ratio of Cu:P is 1:3. With P ratios lower than this the cupric potyphosphate tends to insolubilise so rapidly that reaction control may be difficult. This problem is overcome at the Cu:P = 1.3 ratio. Higher . ratios of P may also be used but are of so particular advantage. all other stages of manufacture are as described above for the zinc fertiliser. Polymerisation temperature and period of heating are equipment dependant, generally lower temperatures are required than for the zinc compounds. When the reaction is carried out in o o a muffle furnace 25ø -3øø C i s optimum. Polymerisation is stopped before insolubilisation in the acids and complexants occurs. ( i i i ) Iron fertilizers Starting materials include oxides (eg.hematite), oxyhydroxides (eg.goethite), sulphate or chloride form of ferric iron, iron metal (eg.iron filings), ferrous sulphate or ferrous chloride containing up to 69.9%, 62.8%, 27.9%, 34.4%, 99-9%, 36.7% or 44.9% Fe respectively. The iron raw material is added to phosphoric acid ( containing up to 6Ø% P Ø ) so that the molar 2 5 ratio of Fe:P is at least 1:3 (weight ratio 1:1.67) where ferric compounds are used and at least 1:2 (weight ration 1:1.11) where iron metal or ferrous compounds are used. The optimum molar ratio of Fe:P in the case of ferric compounds is 1:3 and in case ; 12 : of ferrous compounds it is 1 :2,. All other reaction parameters art broadly as described for the zinc fertilizers. Polymerisation, however, occurs at s lower temperature than with the zinc phosphates and the polyphosphate formed is also more insoluble in dilute acids and complexants. Iron fertilizers prepared with additives have improved properties; magnesium oxide is best suited for this purpose. The optimum molar ratio of Fe :Mg is i :3, When MgO additive is used, the amount of phosphoric acid is also increased. Thus, for every mole of Mg, at least 2 moles of phosphoric sc id are to be added (Mg s P=1 :2) . The mixture of iron salt, magnesium oxide and phosphoric acid is heated at above 15ø C as described for the zinc fertilizer- Reaction is continued at least till a viscous gel is obtained and little unreacted material remains. This material is subsequently polymerised, by o heating at any temperature above 2ØØ C, whereupon iron magnesium polyphosphate is obtained. reaction is optimum at 25ø C, o whereupon iron magnesium polyphosphate is obtained reaction is o optimum at 25Ø C, However, depending on the nature of reaction and heat contact period, reactions may also be carried out at higher temperatures. The polyphosphate with maximum solubi1ity in the testing reagents (ø.1 N HC1 , ø.33 M citric acid, ø.ØØ5 M DTPA) is chosen. It is subsequently neutralised with ammonia solution or with magnesium oxide in the presence of sufficient water to allow the neutralisation reaction to occur. Any basic : 13 compound may be used but magnesium oxide gives the best results; the final pH of the slurry should be between 4.5 and 6; the optimum pH. is 5.4. The neutralised material is then dried, at o o o temperatures lower than 1Ø C (preferably at 6Ø -8 Ø C) , finally, it is ground to a powder which passes through a 1 Ø Ø mesh BS sieve. Starting materials include managanese dioxide or manganous oxide or sulphate which may contain up to 63.4%, 77.4% or 36.4% Mn respectively. The manganese raw material is added to phosphoric acid such that the molar ratio 4+ of Mn:P is at least 1:4 (weight ratio Mn :P 1 :2.26) when Mn is used out. The optimum 4+ 2+ molar ratio of Mn;P is 1:4 All other reaction parameters are as described for the zinc fertilizer. The manganese salt (preferably manganese dioxide), o is mixed with phosphoric acid and heated at 15 Ø C or above, under vacuum or under normal atmospheric pressures until at least a thick viscous material is formed. This may contain a small amount of unreacted particles. At this stage, manganese dihydrogen phosphate is formed. Further heating of this compound o at temperatures above 2 Ø Ø C produces manganese polyphosphates. o Optimally, the reaction is carried out at 3 Ø Ø C. Polymerisation is allowed to proceed till the compound retains its solubility in the testing reagents. Manganese polyphosphates have high water 14 solubility. To reduce water solubi1ity and improve physical characteristics of the product, manganese polyphosphate is further neutralised with a basic compound such as lime, ammonia, magnesium oxide, etc. to a pH between 5 and 6. Best results are obtained with magnesium oxide and a neutral i sat ion pH of 5:3-Following neutralisation, the product is dried and sieved. Apart from iron, which is a micronutrient, the fertilizer also contains nitrogen or magnesium, both of which are also micronutrients and add to the value of the fertilizer. ( v) Cobalt fertilizers Starting materials include cobaltous oxide, sulphate or 2+ chloride which may contain upto 78-6%, 38-Ø% and 45.3% Co respectively. The cobalt raw material is added to phosphoric such that the molar ratios of Co:P is at least 1:2 (weight ratio Co:P - 1:1. Ø 5). The optimum molar ratio of Co:P is 1:2. All other reaction parameters are as described for zinc fertilizers. (vi) In an embodiment of this invention, additives such as alkali or alkaline earth metal compounds are used for improving the solubility of the micronutrient polyphosphates in acids and Complexants. Additives are useful in improving the solubility i5 characteristics of a polyphosphate, particularly those of the 3+ trivalent and tetravalent metals. Thus Fe polyphosphates repidly form highly insoluble polyphosphates end arresting the reaction at the desired stage may be difficult. In such cases the use of additives is advocated. Starting materials are any of the materials described earlier. To these, magnesium oxide or carbonate, potassium hydroxide or carbonate or sodium hydroxide or carbonate is added such that the molar ratio of the metal ion, M : additive is at any level from 1: Ø or higher. The micronutrient compound and the additive are added to phosphoric acid whose proportion is in excess of that described in sections (i) to (v). This excess amount is in order to compensate for the additive. Thus, optimally, for each mole of divalent cation additive, 2 moles of P is added in excess as phosphoric acid; similarly for each mole of monovalent cation as additive 1 mole of P is added in excess. The reaction is carried out as described earlier for zinc ferti1izers. (vi i) In a further embodiment of this invention fertilizers are prepared containing multiple micronutrient formulations. Two or more types of micronutrient starting materials 16 are taken in any desired proportion- Additives are also added as described in section (vi). These sre added to phosphoric acid which is taken in a proportion as mentioned in sections (i) to (vii). The reaction is then carried out as described in section (i ) . The principle underlying the production of slow-release micronutrient fertilizers according to the process of the present invention, is that when metals and their oxides, hydroxides or carbonates are heated with phosphoric acid, and water is removed from the reacting mixture, the dihydrogen orthophosphates are produced. When sulphates or chlorides of the metal ions are used for reaction, heating results in loss of water and some sulphuric or hydrochloric acid leaving a residue of mixed sulphates/chlorides and orthophosphates. On further heating the polyphosphates, linear polyphosphate chains are formed which have -P-O-F-O-P iinkages. The negatively charged Ø atoms on the P-O-P 2+ chains are the sites to which micronutrient cations like Zn , 2+ 3+ + CU , Fe , etc. or H ion is attached. The cations with double or triple charges may also cross-1ink adjacent p-O-P chains to form a 3-D structure which may have low solubility in acids and complexants. For this reason additives like Mg , Na , K etc. help in reducing the number and bond ^strength of such cross-linkages of P-Ø-P chains and thereby improving solubility characteristics. Polymerisation is not allowed to proceed up to 17 the stage where very long chain metaphosphates are formed since such compounds are highly insoluble and the micronutrients in them are not avail able to plants. Polymerisation is stopped when the polyphosphates are not fully polymerised and the products show good solubility in dilute acids and complexants. Polyphosphates with these solubili ty parameters contain nutrients in a form that is available for plant uptake. However such polyphosphate which are of incompletely Pplymerised are hygroscopic and acidic. Both these undesirable characteristics are due to the presence of hydrogen ions on the partially polymerised polyphosphate chain, Neutralisation of such acid groups with bases, renders the product non-hygroscopic as well as non-acidic. It also reduces the water solubility of the polyphosphate. This invention presents a substantial improvement over previous processes for the production of slow-release micronutrient fertilizers. In this process, the initial reaction between metal compounds and phosphoric acid is carried out at o temperatures above 15Ø C to speed up the reaction and remove o moisture. Since 15 Ø is close to the boiling point of phosphoric acid evaporation is very slow and, therefore, for purposes of o commercial production temperatures above 15Ø are more sppropri ate since the process is significantly faster.This invention a 18 includes the new concept that, the extent to which any micronutrient phosphate should be polymerised is limited by the solubility of the polyphosphate product in dilute acids and solutions of complexants. Thus any suitable temperature above o 15 Ø C may be chosen for producing the polyphosphate and the reaction is stopped at any stage before insolubilisation in the aforesaid reagents. Accordingly, this invention provides a process for the production of slow-release fertilizers of all cationic micronutrients, in single- or multinutrient forms. The products have low water solubility but the nutrients are in a form available to plants. The fertilizers are also non-toxic, non-hygroscopic , easy to apply and exhibit improved fertilizer-use efficiency. The main advantage of this process is the significant reduction in production time for the initial reaction stage between phosphoric acid and micronutrient compounds. Another advantage of this process is the simple technique of assessing the upper limit of polymerisation whereby the process is rendered extremely flexible as regards choice of temperature for polymerisation and components in reacting mixture. Thus, a wide range of starting materials may be used in widely ranging proportions and the polymerisation can be carried out at any 19 convenient temperature; the polymerisation is stopped once a simple test reveals that the upper limit of polymerisation, is reached. Lastly, the process on the whole is simple requires lower energy inputs than all previous processes and is readily adaptable to a wide range of micronutrient formulations. The invention will now be explained in greater detail with the help of the following non-limiting examples. Examples for zinc fertilizer Example 1 Phosphoric acid (containing 52% P Ø was taken in a 2 5 stainless steel tray. To 16 Ø g of the acid 5 Ø g of zinc ash (containing 72.1% Zn) was added. The material was allowed to stand for 3Ø min for frothing to subside. Frothing is due to the reaction of metallic zinc with acid. The mixture was then put o into a muffle furnace at 17 Ø C and heated until a mostly dried product was formed which is mostly Zn(H PO ) . The temperature 2 4 2 o of the furnace was increased to 35 Ø C and the material was further heated for 6 Ø mm. Preliminary trials had shown that heating beyond this period to 7Ø min and more results in the formation of polyphosphates which are not completely soluble in Ø.1N HCI, Ø.33M citric acid and Ø. ØØ5 M DTPA. The solubility of the polyphosphate was tested in these reagents ; Ø.5g of the polyphosphate dissolved in 15Ø ml Ø.1N HCI, 4Ø ml Ø.33 M citric acid and 35Ø ml Ø. ØØ5 M DTPA within 15 min- The average chain length (n) of the polyphosphate was 2.5, - 2Ø- The polyphosphate was allowed to cool to ambient temperature it was made into a paste with water and 58.5 ml of 25% NH solution 3 was added to it. The pH after neutralisation was 4.Ø. The slurry o was stirred and dried in an oven at 8Ø C. The dried material was ground in a mortar and sieved through 1ØØ mesh B. S. The material thus obtained had the composition 21% Zn , 19.1% P and 5.1% N.In Ø.1 N HCI, Ø.33 M citric acid and Ø-ØØ5 M. DTPA, the Zn in it is almost 1ØØ% soluble. About 7.5% of the' Zn in it was soluble in water. The fertilizer remained undissolved in water for several months- Field trials with the fertilizer showed that 1.14 kg Zn added as this slow-release fertilizer increased the yield of paddy by 4ØØ-6ØØ kg/ha in the first crop and to a similar extent in the second crop (residual effect). The requirements of this zinc fertilizer are about one-fifth to two-fifth the normal recommended dose for zinc sulphate. This fertilizer is also very effective in soils where zinc sulphate shows little response. Example II The entire process was the same as in example 1 except that during neutralisation 82 g CaCO was used instead of ammonia. The composition of this sample was 19.5% Zn, 18% P and 9.6% Ca. - 21- Example III The entire process was the same as in Example I except that during neutralisat ion 46 g KOH dissolved in about 8Ø ml water was used instead of ammonia solution. Example IV The entire process was the same as in Example I except that zinc oxide ( contain ing 78% Zn) was used instead of zinc ash as the starting material. 1ØØ g of the zinc oxide was reacted with 324 g phosphoric acid containing 52% P Ø . The composition 2 5 of the fertilizer obtained was as follows 22.9% Zn, 25.Ø% P and 4.7% IM. Example V The entire process was the same as Example 1 except that metal lie zinc was used instead of zinc ash, as the starting material. 1ØØ g of zinc dust was reacted wi th 4Ø9 g of phosphoric acid containing 52% P Ø . 2 5 Example VI Phosphoric acid containing 23% P Ø was taken in a 2 5 stainless steel tray. To 37Ø g of the acid 5Ø g of zinc ash (containing 72-1% Zn) was added. It was allowed to stand for about 3Ø min for the frothing to subside. This was subsequently o put into a muffle furnace and heated at 2ØØ C till the product was almost dry. The furnace temperature was then increased to o 3ØØ C and the sample heated for 9Ø mm. solubility of the : 22 : polyphosphate in Ø.1 N HCI, Ø.33 M citric acid and Ø.ØØ5 M DTPA was tested. The polyphosphate dissolved in these reagents within 15 min. After cooling to ambient temperature it was made into a paste with about 3Ø ml water and 58.5 ml of 25% ammonia solution, was added to it. The pH after neutralisation was 4.Ø. The material was dried in an area at 6Øo C ground and sieved through 1ØØ mesh B.S. The material thus obtained had the composition ^-^ 2Ø.9% Zn, 18-9% P and 5.5.% N. Other characteristics were similar to the fertilizer described in Example 1. Example for copper fertilizer Example VII 1Ø g cupric hydroxide (containing 53.6% Cu) was taken in a porcelain dish. To this 38 g phosphoric acid [containing 46.4% P Ø (w/w)] was added. The molar ratio of Cu:P was, thus, 2 5 o 1;3. The mixture was placed in a muffle furnace at 18Ø C till a clear viscous material was obtained. This was further heated at o 25Ø C for 6Ø min. The cupric polyphosphate was tested for its solubility. It was observed to be soluble in Ø.1N HCI, Ø.33 M c itric acid and Ø.ØØ5 M DTPA wi thin 3Ø min. The sample was made into a slurry with a few ml water and neutralised to pH 4.Ø with 1Ø% NH solution (about 8 ml). It was then dried in an oven at 3 o 8Ø C, ground and sieved through 1ØØ mesh B.S. The fertilizer had the composition 13.6% Cu, 19.6% P -23- and 16.3% N. It had an average chain length (n) of 2.65 and 5-2H of total Cu was soluble in water. The material remained stable in contact with water for several months. It was completely soluble in the dilute acids and complexants mentioned above. Plant growth trials with paddy showed significant increase in yields over the control at dosages as low as 2.Ø kg/ha Cu; at this level copper sulphate does not result in any yield increase. Example VIII 1Ø g cupric chloride (containing 36.5% Cu) was taken in a porcelain crucible. Phosphoric acid (containing 5##% P Ø ) was 2 5 added such that the molar ratio Cu:P was 1:3 (24.5 g acid added). o The crucible was put into a muffle furnace at 17Ø C and heated till a dried substance, was obtained having a light green colour. o This was again heated at 2ØØ C for 3Ø min. During this period samples of the polyphosphate were periodically taken and tested for their solubility in Ø.1 N HCl, Ø.33 M citric acid and Ø.ØØ5 M DTPA. The sample was removed from the furnace at that stage when the material begins to solubilise slowly (within 3Ø min) but insoluble materials are not yet formed. The average chain-length (n) of the polyphosphate was 2.5. The polyphosphate was cooled to room temperature, made -24- into a slurry with a few drops of water and then neutralised with 1Ø% ammonia solution upto a pH of 4.Ø, This was dried in an oven o at 7Ø C, powdered and sieved through 15Ø mesh B.S. Example IX To 1Ø g cupric carbonate (cDntainig 5Ø.Ø% Cu) 24 g of phosphoric acid (46-4% P O) was added so that the molar ratio of 2 5 o CusP = 1:2. This was placed in a muffle furnace at 18Ø C and heated till almost dry. This was further heated at 225 C for 49 min. The remaining procedure is the same as that described in Examp1e VII. Samples for iron fertiliser Example X The starting material was synthetic qoethite [a-FeØ(ØH)] containing 6Ø%. To 175Ø g of phosphoric acid (containing 39.7% w/w of P Ø ), 1ØØg goethite and 13Øg magnesium oxide were 2 5 added and the mixture was stirred. The amount of phosphoric acid taken was such that the Fe:P molar ratio was 1:3 plus an excess amount such that the Mg:P molar ratio was 1:2. This was placed in o a muff1e furnace in flat trays iss 316L ) and heated at 18Ø C till it was almost dry. The temperature of the furnace was o subsequently increased to 25Ø C and the sample was heated for 1Ø min. Solubility of the sample was tested at periodic intervals, in Ø.1N HCl, Ø.33 M citric acid, and Ø.ØØ5 M DTPA- Solubility of the polyphosphates in these reagents increases with period of 25 heating, reaches a maximum and declines again. The ideal palyphosphate would be around the region of the maximum- Water solubility of the polyphosphste and the material after neutralisat ion were also tested; polyphosphates having lowest water solubility are preferred. Thus, al though the polyphosphate o obtained after heating at 25Ø C for 1Ø min and 2Ø min ,have similar solubi1ities in acids and complexants, the neutralised products of the former has much lower water solubi1ity than that o of the latter. Therefore the material obtained at 25Ø C after 1Ø min heating was preferred. The weight loss of the polyphosphate at this stage is afoout 9g/1ØØg H PO in the reaction mixture. 3 4 This corresponds to 53% polymerisation. The polyphosphste is cooled to ambient temperature, made into a paste with water and neutralised with dilute ammonia solution (containing about 12,5% NH ) bill the pH of the slurry was around 5,4, This required I.751 of 12-5% ammoni a solution. o The slurry was stirred and dried in an oven at 7Ø C, it was hand ground and sieved through 8Ø mesh E The entire process was the same as in Example X except that magnesium oxide was used for neutralisation instead of 26 ammonia solution. In this case the pH of the solution was raised to 4.5 by addition of MgO (about 55Ø g)- The suspension was heated to 6ØoC and stirred for one hour- It was subsequently processed as described earlier. The product contained 3.7% Fe, 45. 4% P Ø and 25.3% Mo It had a water solubi1ity of around Ø.1%. Other parameters were the same as for Example X. Example X.II The process is essentially the same as in Example X and XI except that natural goethite (containing 45% Fe) is used instead of synthetic goethite. 1ØØg natural goethite, 95g magnesiunr oxide and 152Øg phosphoric acid (containing 39-7% P Ø ) were mixed and processed as described in Example X. o Polymerisation, in this case, was carried out at 2ØØ C for 25 roin till a weight loss of about 7g/1ØØg H PO in the reaction 3 4 mixture, was obtained. The polyphosphate was neutralised with ammonia solution (12.5%, 1.65 1) to a pM of around 5.4 and subsequently processed as in Example X. The properties of the two materials were similar. Example XIII 1ØØg niaqnanese dioxide (pyrolusite) containing 63-4% Mn was mixed with 5ØØg of phosphoric acid containing 51% P Ø (Mn;F3 2 5 ratio in the mixture = 1:4). This was taken in a poreelain : 27 : o crucible and heated at 17Ø C till a thick gel-like material was o formed. The temperature of the furnace was raised to 3ØØ C and the crucible was kept in it for 5Ø min. Thereupon a dark purple, hard solid was formed, which had the maximum solubility in the testing reagents. The corresponding weight loss was 15.4g/1ØØg H PO in the reaction mixture, which produces about 55% 3 3 polymerisation. The polyphosphste was cooled to ambient temperature, made into a paste with water and neutralised with mactnesium oxide to a pH of about 5.3. About 4ØØ g MgO was required; after o addition the slurry was stirred at 6Ø C for about one hour for o completion of the reaction. The material was dried at 7Ø C, ground and sieved through 1ØØ mesh BS. The fertilizer contained 7.5% Mn, 35.3%P Ø and 29% MG . Solubility in water was about Ø.1% 2 5 but in Ø.1 N HC1 and Ø.33M citric acid it was soluble to the extent of about 9Ø-95%. Example XIV 1Øg cobalt oxide was mixed with 51g phosphoric acid of 5Ø% strength to give a Co:P ratio of 1:3. To this 67.7g potassium hydroxide and a further 17Øg phosphoric acid were added to give o K:Co=1Ø:l and KsP-l:l- The slurry was heated at 13Ø C till dried- o This was further heated at 25Ø C for 3Ø min to obtain the mixed 28 polyphosphate of potassium snd cobalt. The polyhosphate was cooled to ambient temperature, made to a paste with water and neutralised with potassium hydroxide to pH 5. Subsequently it was ground with a hand mortar and sieved through 1ØØ mesh. The fertilizer was completely soluble in Ø.1N HC1 and Ø.33 M citric acid . Example XV 1ØØg natural goethite and 1ØØq manganese dioxide were mixed with 1 .541 phosphoric acid (containing 4Ø% P Ø ). The mixture was put into a muffle furnace and heated at 2ØØ C for 5Ø min whereupon a mostly homogenous gel was obtained. The o temperature of the furnace was raised to 35Ø C and the sample was heated for 3Ø min. Optimum polymerisation was tested as described in the previous Examples. Subsequent processing was done as described in Example XIII except that 9ØØ g of magnesium oxide was required for neutralisation of the polyphosphate. This fertiliser containing both iron and msganese, has low water solubi1ity (about 2%) but high solubi1ity in dilute acids and comp1exants. WE CLAIM -29- 1 . A process for- preparation of slow release cationic micronutrient fertilizers, which processes comprises heating at such as herein described least one micronutrient metal or a compound thereof^ with or such as herein described without additives^ with phosphoric acid till the resultant the correspondir mixture is mostly homogenous, further heating, to farm Ametal, polyphosphates of such a degree of polymerisation that they are still soluble in dilute mineral acids and complexants, treating -said metal polyphosphates with a basic compound and finally obtaining a dried powder. 2Aprocess as clamid 1.wherein thephosphoric acid used hasu concentration upto 6Ø% P O by weight; 2 5 3. The process as claimed in claim 1, wherein the phosphoric acid used has a concentration of 3Ø to 6Ø*/. P Ø by weight 4. The process as claimed in claim 1, wherein said micronutrient metal is selected from zinc, copperiron, maganese, cobalt. 5, The process as claimed in claim 1, wherein the micronutrient metal of the axide,hydroxide, chloride or sulphate the of micronutrient metal is used for the reaction with phosphoric acid. - 3Ø- 6. The process as claimed in claim 1, wherein various additives such as the oxides, hydroxides, or carbonates of magnesium, calcium, potassium or sodium may also be added to the reaction mixture before heating with phosphoric acid. 7. The process as claimed in claim i, wherein the ratio of metal cation: additive cation is, at least 1:Ø. 8. The process as claimed in claim 1 , where in Ø5 the moler ratio of metal cation: additive cation is in the range 1 :2 to 1:1Ø. 9. The process as claimed in claim 1 , wherein the amount of phosphoric acid used for the first step of heating with the micronutrient metal or a compound thereof, is sufficient to produce the dihydrogen phosphates of the cations present, 1Ø. The process as claimed in claim 1, wherein for every n + mole of metal ion, m , in the reaction mixture, the molar proportion of phosphoric acid is at least n times that of the metal, where n denotes the valance of the metal ion. 11. A process as claimed in claim 1, wherein during the first step of heating with phosphoric acid for every mole of divalent cation present, phosphoric acid containing at least 2 moles P is added for every mole of trivalent cation present, phosphoric acid containing at least 3 moles P is added, and for : 31 : every mole of tetravslent cation present, phosphoric acid containing at least 4 moles P is added. 12. A process as claimed in claim 1, wherein during the f irst step of heating with phosphoric acid, if an additive is used then an additional n+ amount of phosphoric acid is added in- quantities such that M :P is at least 1 :n or more; where n is A n+ the valance of the additive cation, M A 13- A process as claimed in claim 1, wherein the first step of heating with phosphoric acid is carried out at any temperature o above 15Ø C under mostly ambient pressure. 14. A process as claimed in claim 1, wherein the first step of heating with phosphoric acid is csrried out at any temperature o above or below 15Ø C under vacuum. 15. A process as claimed in claim 1, wherein step of further heatirvg, to form the metal polyphosphates is carried out o at temperatures above 2ØØ C. 1.6. A process as claimed in claim 15, wherein, the step of further heating to form the metal polyphosphate is carried out at o o a temperature in the range of 25Ø and 35Ø C. 17- A process as claimed in claim 1, wherein the step of : 32 : further heating to form the metal polyphosphate is carried out till polymerisation occurs and the compound shows reduced solubility in water. 18. A process as claimed in claim 1, wherein the step of further heating to form the metal polyphosphstes is carried out till the product shows high solubility in dilute acids and complexants. 19. A process as claimed in claim 1, wherein the step of further heating to form the metal polyphasphstes is carried out upto the point where the upper limit of its solub^l ity, in dilute acids and complexants is reached. 2Ø. A process as claimed in claim 1, wherein the solubility of the metal polyphosphate is tested using Ø.1 N hydrochloric acid, Ø.33 M citric acid and/or Ø.ØØ5 M DTPA (diethylene triamine pentaacetic acid). 21 . A process as claimed in claim 1, wherein for the step of neutralisation, a basic compound such as ammonia, lime, magnesium oxide, potassium hydroxide is used. 22. A process as claimed in claim 1, wherein the neutralisation is. carried out after addition of water to form a paste or slurry. 33 23. A process as claimed in claim 1, wherein for the step of neutralisation the pH of the slurry is above 4. 24. A process as claimed in claim 1, wherein the pH of neutralisation is between 4.5 and 5.5. 25. A process as claimed in claim 1, wherein for the step of neutralisation using water-insoluble bases such as magnesium oxide or lime, the reaction mixture is stirred and warmed. 26. A process as claimed in claim 25 , wherein the reaction o mixture is warmed to 6Ø C 27. - A process as claimed in claim 1, wherein the product from the step of neutralisation is dried till it is essentially free of moisture. 28. A process as claimed in claim 1, wherein the product from the step of neutral isati on is dried at temperatures below o 1ØØ C. 29. A process as claimed in claim 1, wherein the dried product is ground to a powder. 3Ø. A process as claimed in claim 1, wherein the product is- ground to pass through a 1ØØ mesh BS sieve. 31. A process for the manufacture of slow-release micronutrient fertilizers substanti ally as herein described and as illustrated in the examp 1 es (5) . A process for preparation of slow release cationic micronutrient fertilizers, which processes comprises heating at such as herein described 1east one micronutrient metsl or a compound thereof^ with or such as herein described without additives^ with phosphoric acid ti11 the resultant (the correspondir mixture is mostly homogenous, further heating, to form metal, polyphosphates of such a degree of polymerisation that they are still soluble in dilute mineral acids and complexants, treating said metal polyphosphates with a basic compound and finally obtaining a dried powder.

Full Text

-2-
FIELD OF INVENTION
This invention relates to a process for the manufacture of slow-release fertilizers of cationic
micronutrients such as zinc, copper,iron, manganese, cobalt or magensium, either as single nutrient or as multinutrient formulations.
BACKGROUND OF INVENTION
Compounds which are widely used today as micronutrient fertilisers, are soluble salts or organic chelated forms eg., zinc, copper, manganese or iron sulphates, and EDTA, complexes of the same. Liquid fertilizers such as micronutrients dissolved in condensed phosphoric acid or ammonium polyphosphates are also used (V. Sauchel1i, 1967, Chemistry and Technology of Ferti1izers, Reinhold, New York; G-H. Col1ins, 1955, Commercial Fertilizers, McGraw Hill, New York). The synthesis of slow-release fertilizers based on phosphate glasses known as frits, have been described. Such frits are usually prepared by fusing ammonium or sodium dihydrogen

-3-
phosphates with micronutrient salts to produce a

melt, at temperatures between 8ØØo and 14ØØoC and
then rapidly cooling the liquid by pouring on to a cold plate (G.J. Roberts, 1973, Am. Ceram, Soc-Bull., Vol 52, p.. 383, ibid idem, Vol. 54, p 1Ø69, Austrian Patent No. 32616Ø of 1975 US Patent No- 3574531 of 1971, US Patent No. 2713536 of 1974.
Apart from phosphate glasses, other phosphate compounds have also been proposed as slow-release fertilizers. These include micronutrients added to metaphosphates of potassium or calcium prior to reaction. Volfkovich et al. , (S.I. Volfkovich, A.S. Cherepanova, I.A. Grishina & G.A. Bitko, 197Ø, D. Zh. Nauki Kaz SSP (Russian? p. 3) added various metal oxides to potassium metaphosphate melts. Volfkovich reviewed the work done by the Russian school in the filed of metaphosphate based fertilizers (S.I. Volfkovich, 1372, J. Appl- Chem
(USSR), Vol. 45, p.2479). A Russian patent (Su
of 1986 127Ø148 / describes the production of such mixed
o metaphosphate based fertilizers produced at 55Ø -

-4-
o of 199Ø
88Ø C. Two Indian Patents (Nos. 1728ØØ/and 1772Ø5 of
1391) describe the processes for production of zinc and copper fertilizers based on low molecular weight polyphosphates. The chemistry of zinc and copper phosphate polymerisation and the chemical nature of these fertilizers have also been described (S.K. Pay, C. Varadachari & K. Ghosh, 1993, Ind. Eng. Chem. Pes., Vol. 32, p. 1218; S.K.Ray, C1 Varadachari & K. Ghosh, 1997, J. Agric. Food Chem., Vol-, 45, p. 1447) .
The major drawbacks of using soluble salts (such as sulphates), as micronutrients fertilizers are, leaching losses, chemical transformation losses, ground water contamination and low ferti1izer-use efficiency. On the other hand, micronutrlent fertilizers having slow-release properties do not suffer any of these disadvantages. However,, both the existing types of slow-release fertilizsrs incorporating micronutrients, are not commercially successful so far.
The major disadvantage of the first group of compounds viz. the phosphate glass frits, is that

-5-
the process for their production is not commercially viable; the reaction conditions, in the melting of phosphates, are so corrosive that very expensive material have to be used for furnace construction thereby limiting large scale production and increasing product costs. The major disadvantage of the second group of compounds viz the long chain metaphosphates is; their excessive insolubility
particularly in complexants, which renders, the
t micronutrient ions mostly unavailable for plants.
The most important factor here is that both these two types of phosphate based slow release fertilizers are essentially macronutrient (N, P or K) fertilizers containing micronutrients as supplements. There is no process available as yet for making a slow-release fertilizer that is essentially a source of micronutrients and which can thereby replace the conventional water-soluble micronutrient fertilizers.

-6-
OBJECTS OF THE INVENTION
An object of this invention is to propose a procese for the manufacture of slow release fertilizers of cationic micronutrients having a substantial reduction in production time for the initial reaction stage between phosphor ic acid and micronutrient compounds.
Another object of this invention is to propose a process for the manufacture of slow release fertilizers of cationic micronutrients and which has a simple method of assessing the upper limit of polymerisation whereby the process is rendered extremely flexible as regards choice of temperature for polymerisation and components in reacting mixture.
Yet another object of this invention is to propose a process for the manufacture of slow release fertilizers of cationic micronutrients and wherein a wide range of starting materials may be used in widely ranging proportions and the

-7-
polymerisation can be carried out at any convenient temperature.
Still another object of this invention is to propose a process for the manufacture of slow release fertilizers of
cationic micronutrients which is simple, requirs lower energy
inputs than all previous processes and is readily adaptible to a

wide range of micronutrient formalations.
DESCRIPTION OF THE INVENTION
According to this invention there is provided a process for the preparation of slow-release cationic micronutrient fertilizers, which comprises in heating at least one micronutrient metal or a compound thereof, with or without additives, with phosphoric acid till the resultant mixture is nearly homogeneous, further heating to form metal polyphosphates of such a degree of polymerisation that they are still soluble in dilute mineral acids and complexants, treating said metal polyphosphates with a basic compound and finally obtaining a dried powder.
Compound of the micronutrient element such as their oxides, hydroxides, carbonates, sulphates or chlorides are mixed
with phosphoric acid and heated to a temperature T above
1 o 15ø to remove excess water and allow completion of reaction.
This reaction may also be carried out under vacuum, at
o temperature lower than 15ø . The dihydrogen phosphates are then

-8-
further heated to 3 temperature T which is above temperature T
2 1
till polyphosphates of the desired degree of polymerisation are
produced as observed by their solubility characteristics or average chain length estimates. The polyphosphates are subsequently neutralised with bases like ammonia, lime, sodium or potassium hydroxide. The product is dried at low temperature powdered and sieved, (i) Zinc Fertilisers
Starting materials include zinc oxide (containing upto 79% Zn) , zinc metal (containing upto 99.99% Zn), zinc ash (containing zinc oxide and metallic zinc in variable amounts), zinc sulphate (containng up to 4Ø.5% Zn) or zinc chloride (containing upto 47.9% Zn). The zinc raw material is added to
phosphoric acid (containing not more than 6Ø% P Ø ) so that the
2 5 molar ratio of Zn:P in the mixture is at least 1x2 (weight ratio
Zn:P is at least 1.Ø5:1). The optimum molar ratio of Zn:P is 1:2. With P levels higher than this the initial reaction is faster but at the same time more acid groups will remain in the polyphosphate and this will requrie more base for neutralisation. Almost any grade of acid can be used for the reaction. However,
fertilizer grade phosphoric acids containing about 3ø -6ø % P Ø
2 5 are suitable and since acid containing about 5ø% P O is
2 5 the most commonly available this is preferred for the

: 9 :
reaction. The mixture of zinc compounds and phosphoric acid is taken in a porcelain crucible or a tray made of SS 316L , placed in a muffle furnace and heated at any temperature above 15ø C.At

higher temperatures evaporation is faster. The optimum

temperature is determined by the nature of the equipment used

for evaporation. Thus, in a muffle furnace 17ø oC is optimum; in

commercial driers like a spray drier input temperatures of about 4ø oC may be needed but the duration of heating is very small -snd product temperatures donot exceed 2 ø ØoC. When evaporation is done under partial vacuum reaction temperatures may be reduced. After the reaction, the product contains mostly zinc dihydrogen phosphate; some sulphate or chloride may also be present if such
raw materials have been used. This product is further heated at
o any temperature above 19Ø C for polyphosphates to form. Here
again, the temperature used for polymerisation depends on the
o equipment used for the reaction. In a muffle furnace 35 ø C is
o
optimum. If a fluidised bed furnace is used 4 ø ø C is preferred-Heating is done till a polyphospate of the desired degree of
polymerisation is obtained. When such reaction is carried out in
o trays or similar vessels about 6Ø min is required at 35Ø C
furnace temperatures. When the reaction is done in a fluidised
o bed furnace only about 15 min is required at 4øø C furnace
temperatures, the product is tested at periodic intervals for

1Ø z
solubility in ø.1 N HCI , ø.33 M citric acid, ø.ØØ5 M DTPA. Polymerisation may be stopped at any stage wherein the product retains its solubility in the aforesaid reagents; the product will be observed mostly to dissolve in these reagents within 3Ø min. The optimum polymerisation stage is that prior to the formation of a product which is significantly insoluble in the acids and complexants mentioned above; in other words, the product has reached the upper limit of its solubility in these reagents. Subsequently, the reaction product is cooled to room, temperature, made into a slurry with water and mixed with ammonia solution, CaO (lime), CaCo3 (limestone), sodium carbonate (soda ash), potassium carbonate, sodium hydroxide or potassium hydroxide. Enough bases are added to raise the pH of the slurry to between 3 and 4. Too little base will result in a hygroscopic product. Too much of base has no particular advantage and may
precipitate of some of the zinc ions. After neutralising, when
o the pH has stabilised, the material is dried at (1øø C,
o o preferably at 6Ø -8Ø C. It is then ground and sieved, preferably
to (1øø mesh B.S.
(ii) Copper fertilizers
Starting materials include the hydroxide carbonate, sulphate or chloride of the cupric ion containing up to 49.9%, 51-4%, 25.4% and 47.Ø% Cut respectively- The copper raw material

11
is added to phosphoric acid (containing up to 6Ø% of P Ø ) so
2 5 that the molar ratio of Cu: P is 1:2 or higher (weight ratio of
Cu:P is at least 1.ø 2:1). The optimum molar ratio of Cu:P is 1:3. With P ratios lower than this the cupric potyphosphate tends to insolubilise so rapidly that reaction control may be difficult. This problem is overcome at the Cu:P = 1.3 ratio. Higher . ratios of P may also be used but are of so particular advantage. all other stages of manufacture are as described above for the zinc fertiliser. Polymerisation temperature and period of heating are equipment dependant, generally lower temperatures are required

than for the zinc compounds. When the reaction is carried out in
o o
a muffle furnace 25ø -3øø C i s optimum. Polymerisation is stopped
before insolubilisation in the acids and complexants occurs. ( i i i ) Iron fertilizers
Starting materials include oxides (eg.hematite), oxyhydroxides (eg.goethite), sulphate or chloride form of ferric iron, iron metal (eg.iron filings), ferrous sulphate or ferrous chloride containing up to 69.9%, 62.8%, 27.9%, 34.4%, 99-9%, 36.7% or 44.9% Fe respectively. The iron raw material is added to
phosphoric acid ( containing up to 6Ø% P Ø ) so that the molar
2 5 ratio of Fe:P is at least 1:3 (weight ratio 1:1.67) where ferric
compounds are used and at least 1:2 (weight ration 1:1.11) where iron metal or ferrous compounds are used. The optimum molar ratio of Fe:P in the case of ferric compounds is 1:3 and in case

; 12 :
of ferrous compounds it is 1 :2,. All other reaction parameters art broadly as described for the zinc fertilizers. Polymerisation, however, occurs at s lower temperature than with the zinc phosphates and the polyphosphate formed is also more insoluble in dilute acids and complexants. Iron fertilizers prepared with additives have improved properties; magnesium oxide is best suited for this purpose. The optimum molar ratio of Fe :Mg is i :3, When MgO additive is used, the amount of phosphoric acid is also increased. Thus, for every mole of Mg, at least 2 moles of phosphoric sc id are to be added (Mg s P=1 :2) . The mixture of iron salt, magnesium oxide and phosphoric acid is heated at above 15ø C as described for the zinc fertilizer- Reaction is continued at least till a viscous gel is obtained and little unreacted
material remains. This material is subsequently polymerised, by
o heating at any temperature above 2ØØ C, whereupon iron magnesium
polyphosphate is obtained. reaction is optimum at 25ø C,
o whereupon iron magnesium polyphosphate is obtained reaction is
o optimum at 25Ø C, However, depending on the nature of reaction
and heat contact period, reactions may also be carried out at higher temperatures. The polyphosphate with maximum solubi1ity in the testing reagents (ø.1 N HC1 , ø.33 M citric acid, ø.ØØ5 M DTPA) is chosen. It is subsequently neutralised with ammonia solution or with magnesium oxide in the presence of sufficient water to allow the neutralisation reaction to occur. Any basic

: 13
compound may be used but magnesium oxide gives the best results; the final pH of the slurry should be between 4.5 and 6; the
optimum pH. is 5.4. The neutralised material is then dried, at
o o o
temperatures lower than 1Ø C (preferably at 6Ø -8 Ø C) , finally,
it is ground to a powder which passes through a 1 Ø Ø mesh BS
sieve.
Starting materials include managanese dioxide or manganous oxide or sulphate which may contain up to 63.4%, 77.4% or 36.4% Mn respectively. The manganese raw material is added to

phosphoric acid such that the molar ratio 4+ of Mn:P is at least 1:4
(weight ratio Mn :P 1 :2.26) when Mn is used out. The optimum
4+ 2+
molar ratio of Mn;P is 1:4 All other reaction parameters are as described for the zinc
fertilizer. The manganese salt (preferably manganese dioxide),
o is mixed with phosphoric acid and heated at 15 Ø C or above, under
vacuum or under normal atmospheric pressures until at least a thick viscous material is formed. This may contain a small amount of unreacted particles. At this stage, manganese
dihydrogen phosphate is formed. Further heating of this compound
o at temperatures above 2 Ø Ø C produces manganese polyphosphates.
o Optimally, the reaction is carried out at 3 Ø Ø C. Polymerisation
is allowed to proceed till the compound retains its solubility in the testing reagents. Manganese polyphosphates have high water

14
solubility. To reduce water solubi1ity and improve physical characteristics of the product, manganese polyphosphate is further neutralised with a basic compound such as lime, ammonia, magnesium oxide, etc. to a pH between 5 and 6. Best results are obtained with magnesium oxide and a neutral i sat ion pH of 5:3-Following neutralisation, the product is dried and sieved. Apart from iron, which is a micronutrient, the fertilizer also contains nitrogen or magnesium, both of which are also micronutrients and add to the value of the fertilizer. ( v) Cobalt fertilizers
Starting materials include cobaltous oxide, sulphate or
2+ chloride which may contain upto 78-6%, 38-Ø% and 45.3% Co
respectively. The cobalt raw material is added to phosphoric such that the molar ratios of Co:P is at least 1:2 (weight ratio Co:P - 1:1. Ø 5). The optimum molar ratio of Co:P is 1:2. All other reaction parameters are as described for zinc fertilizers.
(vi) In an embodiment of this invention, additives such as alkali or alkaline earth metal compounds are used for improving the solubility of the micronutrient polyphosphates in acids and
Complexants.
Additives are useful in improving the solubility

i5
characteristics of a polyphosphate, particularly those of the
3+ trivalent and tetravalent metals. Thus Fe polyphosphates
repidly form highly insoluble polyphosphates end arresting the reaction at the desired stage may be difficult. In such cases the use of additives is advocated.
Starting materials are any of the materials described
earlier. To these, magnesium oxide or carbonate, potassium
hydroxide or carbonate or sodium hydroxide or carbonate is added such that the molar ratio of the metal ion, M : additive is at any level from 1: Ø or higher. The micronutrient compound and the additive are added to phosphoric acid whose proportion is in excess of that described in sections (i) to (v). This excess amount is in order to compensate for the additive. Thus, optimally, for each mole of divalent cation additive, 2 moles of P is added in excess as phosphoric acid; similarly for each mole of monovalent cation as additive 1 mole of P is added in excess. The reaction is carried out as described earlier for zinc ferti1izers.
(vi i) In a further embodiment of this invention
fertilizers are prepared containing multiple micronutrient formulations.
Two or more types of micronutrient starting materials

16
are taken in any desired proportion- Additives are also added as described in section (vi). These sre added to phosphoric acid which is taken in a proportion as mentioned in sections (i) to (vii). The reaction is then carried out as described in section
(i ) .
The principle underlying the production of slow-release
micronutrient fertilizers according to the process of the present invention, is that when metals and their oxides, hydroxides or carbonates are heated with phosphoric acid, and water is removed from the reacting mixture, the dihydrogen orthophosphates are produced. When sulphates or chlorides of the metal ions are used for reaction, heating results in loss of water and some sulphuric or hydrochloric acid leaving a residue of mixed sulphates/chlorides and orthophosphates. On further heating the polyphosphates, linear polyphosphate chains are formed which have
-P-O-F-O-P iinkages. The negatively charged Ø atoms on the P-O-P
2+ chains are the sites to which micronutrient cations like Zn ,
2+ 3+ +
CU , Fe , etc. or H ion is attached. The cations with double
or triple charges may also cross-1ink adjacent p-O-P chains to form a 3-D structure which may have low solubility in acids and complexants. For this reason additives like Mg , Na , K etc. help in reducing the number and bond ^strength of such cross-linkages of P-Ø-P chains and thereby improving solubility characteristics. Polymerisation is not allowed to proceed up to

17
the stage where very long chain metaphosphates are formed since such compounds are highly insoluble and the micronutrients in them are not avail able to plants. Polymerisation is stopped when the polyphosphates are not fully polymerised and the products show good solubility in dilute acids and complexants. Polyphosphates with these solubili ty parameters contain nutrients in a form that is available for plant uptake. However such polyphosphate which are of incompletely Pplymerised are hygroscopic and acidic. Both these undesirable characteristics
are due to the presence of hydrogen ions on the partially polymerised polyphosphate chain, Neutralisation of such acid groups with bases, renders the product non-hygroscopic as well as non-acidic. It also reduces the water solubility of the polyphosphate.
This invention presents a substantial improvement over previous processes for the production of slow-release micronutrient fertilizers. In this process, the initial reaction
between metal compounds and phosphoric acid is carried out at
o temperatures above 15Ø C to speed up the reaction and remove
o moisture. Since 15 Ø is close to the boiling point of phosphoric
acid evaporation is very slow and, therefore, for purposes of
o commercial production temperatures above 15Ø are more
sppropri ate since the process is significantly faster.This invention a

18
includes the new concept that, the extent to which any micronutrient phosphate should be polymerised is limited by the solubility of the polyphosphate product in dilute acids and
solutions of complexants. Thus any suitable temperature above
o 15 Ø C may be chosen for producing the polyphosphate and the
reaction is stopped at any stage before insolubilisation in the aforesaid reagents.
Accordingly, this invention provides a process for the production of slow-release fertilizers of all cationic micronutrients, in single- or multinutrient forms. The products have low water solubility but the nutrients are in a form available to plants. The fertilizers are also non-toxic, non-hygroscopic , easy to apply and exhibit improved fertilizer-use efficiency.
The main advantage of this process is the significant reduction in production time for the initial reaction stage between phosphoric acid and micronutrient compounds. Another advantage of this process is the simple technique of assessing the upper limit of polymerisation whereby the process is rendered extremely flexible as regards choice of temperature for polymerisation and components in reacting mixture. Thus, a wide range of starting materials may be used in widely ranging proportions and the polymerisation can be carried out at any

19
convenient temperature; the polymerisation is stopped once a simple test reveals that the upper limit of polymerisation, is reached. Lastly, the process on the whole is simple requires

lower energy inputs than all previous processes and is readily adaptable to a wide range of micronutrient formulations.
The invention will now be explained in greater detail with the help of the following non-limiting examples. Examples for zinc fertilizer Example 1
Phosphoric acid (containing 52% P Ø was taken in a
2 5 stainless steel tray. To 16 Ø g of the acid 5 Ø g of zinc ash
(containing 72.1% Zn) was added. The material was allowed to stand for 3Ø min for frothing to subside. Frothing is due to the
reaction of metallic zinc with acid. The mixture was then put
o into a muffle furnace at 17 Ø C and heated until a mostly dried
product was formed which is mostly Zn(H PO ) . The temperature
2 4 2 o of the furnace was increased to 35 Ø C and the material was
further heated for 6 Ø mm. Preliminary trials had shown that heating beyond this period to 7Ø min and more results in the formation of polyphosphates which are not completely soluble in Ø.1N HCI, Ø.33M citric acid and Ø. ØØ5 M DTPA. The solubility of the polyphosphate was tested in these reagents ; Ø.5g of the polyphosphate dissolved in 15Ø ml Ø.1N HCI, 4Ø ml Ø.33 M citric acid and 35Ø ml Ø. ØØ5 M DTPA within 15 min- The average chain length (n) of the polyphosphate was 2.5,

- 2Ø-
The polyphosphate was allowed to cool to ambient temperature it
was made into a paste with water and 58.5 ml of 25% NH solution
3 was added to it. The pH after neutralisation was 4.Ø. The slurry
o was stirred and dried in an oven at 8Ø C. The dried material was
ground in a mortar and sieved through 1ØØ mesh B. S.
The material thus obtained had the composition 21% Zn , 19.1% P and 5.1% N.In Ø.1 N HCI, Ø.33 M citric acid and Ø-ØØ5 M. DTPA, the Zn in it is almost 1ØØ% soluble. About 7.5% of the' Zn in it was soluble in water. The fertilizer remained undissolved in water for several months- Field trials with the fertilizer showed that 1.14 kg Zn added as this slow-release fertilizer increased the yield of paddy by 4ØØ-6ØØ kg/ha in the first crop and to a similar extent in the second crop (residual effect). The requirements of this zinc fertilizer are about one-fifth to two-fifth the normal recommended dose for zinc sulphate. This fertilizer is also very effective in soils where zinc sulphate shows little response.
Example II
The entire process was the same as in example 1 except that during neutralisation 82 g CaCO was used instead of ammonia. The composition of this sample was 19.5% Zn, 18% P and 9.6% Ca.

- 21-
Example III
The entire process was the same as in Example I except that during neutralisat ion 46 g KOH dissolved in about 8Ø ml water was used instead of ammonia solution. Example IV
The entire process was the same as in Example I except that zinc oxide ( contain ing 78% Zn) was used instead of zinc ash as the starting material. 1ØØ g of the zinc oxide was reacted
with 324 g phosphoric acid containing 52% P Ø . The composition
2 5
of the fertilizer obtained was as follows 22.9% Zn, 25.Ø% P and
4.7% IM. Example V
The entire process was the same as Example 1 except that metal lie zinc was used instead of zinc ash, as the starting material. 1ØØ g of zinc dust
was reacted wi th 4Ø9 g of phosphoric acid containing 52% P Ø .
2 5 Example VI
Phosphoric acid containing 23% P Ø was taken in a
2 5 stainless steel tray. To 37Ø g of the acid 5Ø g of zinc ash
(containing 72-1% Zn) was added. It was allowed to stand for
about 3Ø min for the frothing to subside. This was subsequently
o put into a muffle furnace and heated at 2ØØ C till the product
was almost dry. The furnace temperature was then increased to
o 3ØØ C and the sample heated for 9Ø mm. solubility of the

: 22 :
polyphosphate in Ø.1 N HCI, Ø.33 M citric acid and Ø.ØØ5 M DTPA
was tested. The polyphosphate dissolved in these reagents within
15 min. After cooling to ambient temperature it was made into a
paste with about 3Ø ml water and 58.5 ml of 25% ammonia solution,
was added to it. The pH after neutralisation was 4.Ø. The
material was dried in an area at 6Øo C ground and sieved through
1ØØ mesh B.S. The material thus obtained had the composition ^-^
2Ø.9% Zn, 18-9% P and 5.5.% N. Other characteristics were similar
to the fertilizer described in Example 1.
Example for copper fertilizer Example VII
1Ø g cupric hydroxide (containing 53.6% Cu) was taken in a porcelain dish. To this 38 g phosphoric acid [containing
46.4% P Ø (w/w)] was added. The molar ratio of Cu:P was, thus, 2 5
o 1;3. The mixture was placed in a muffle furnace at 18Ø C till a
clear viscous material was obtained. This was further heated at
o 25Ø C for 6Ø min. The cupric polyphosphate was tested for its
solubility. It was observed to be soluble in Ø.1N HCI, Ø.33 M c itric acid and Ø.ØØ5 M DTPA wi thin 3Ø min. The sample was made into a slurry with a few ml water and neutralised to pH 4.Ø with
1Ø% NH solution (about 8 ml). It was then dried in an oven at
3 o 8Ø C, ground and sieved through 1ØØ mesh B.S.
The fertilizer had the composition 13.6% Cu, 19.6% P

-23-
and 16.3% N. It had an average chain length (n) of 2.65 and 5-2H of total Cu was soluble in water.
The material remained stable in contact with water for several months. It was completely soluble in the dilute acids and complexants mentioned above. Plant growth trials with paddy showed significant increase in yields over the control at dosages as low as 2.Ø kg/ha Cu; at this level copper sulphate does not result in any yield increase.
Example VIII
1Ø g cupric chloride (containing 36.5% Cu) was taken in
a porcelain crucible. Phosphoric acid (containing 5##% P Ø ) was
2 5 added such that the molar ratio Cu:P was 1:3 (24.5 g acid added).
o The crucible was put into a muffle furnace at 17Ø C and heated
till a dried substance, was obtained having a light green colour.
o This was again heated at 2ØØ C for 3Ø min. During this period
samples of the polyphosphate were periodically taken and tested for their solubility in Ø.1 N HCl, Ø.33 M citric acid and Ø.ØØ5 M DTPA. The sample was removed from the furnace at that stage when the material begins to solubilise slowly (within 3Ø min) but insoluble materials are not yet formed. The average chain-length (n) of the polyphosphate was 2.5.
The polyphosphate was cooled to room temperature, made

-24-
into a slurry with a few drops of water and then neutralised with
1Ø% ammonia solution upto a pH of 4.Ø, This was dried in an oven
o at 7Ø C, powdered and sieved through 15Ø mesh B.S.
Example IX
To 1Ø g cupric carbonate (cDntainig 5Ø.Ø% Cu) 24 g of
phosphoric acid (46-4% P O) was added so that the molar ratio of
2 5
o CusP = 1:2. This was placed in a muffle furnace at 18Ø C and
heated till almost dry. This was further heated at 225 C for 49 min. The remaining procedure is the same as that described in

Examp1e VII.
Samples for iron fertiliser
Example X
The starting material was synthetic qoethite [a-FeØ(ØH)] containing 6Ø%. To 175Ø g of phosphoric acid (containing
39.7% w/w of P Ø ), 1ØØg goethite and 13Øg magnesium oxide were
2 5 added and the mixture was stirred. The amount of phosphoric acid
taken was such that the Fe:P molar ratio was 1:3 plus an excess
amount such that the Mg:P molar ratio was 1:2. This was placed in
o a muff1e furnace in flat trays iss 316L ) and heated at 18Ø C till
it was almost dry. The temperature of the furnace was
o subsequently increased to 25Ø C and the sample was heated for 1Ø
min. Solubility of the sample was tested at periodic intervals, in Ø.1N HCl, Ø.33 M citric acid, and Ø.ØØ5 M DTPA- Solubility of the polyphosphates in these reagents increases with period of

25
heating, reaches a maximum and declines again. The ideal
palyphosphate would be around the region of the maximum- Water
solubility of the polyphosphste and the material after
neutralisat ion were also tested; polyphosphates having lowest
water solubility are preferred. Thus, al though the polyphosphate
o obtained after heating at 25Ø C for 1Ø min and 2Ø min ,have
similar solubi1ities in acids and complexants, the neutralised
products of the former has much lower water solubi1ity than that
o of the latter. Therefore the material obtained at 25Ø C after 1Ø
min heating was preferred. The weight loss of the polyphosphate
at this stage is afoout 9g/1ØØg H PO in the reaction mixture.
3 4 This corresponds to 53% polymerisation.
The polyphosphste is cooled to ambient temperature, made into a paste with water and neutralised with dilute ammonia solution (containing about 12,5% NH ) bill the pH of the slurry
was around 5,4, This required I.751 of 12-5% ammoni a solution.
o The slurry was stirred and dried in an oven at 7Ø C, it was hand
ground and sieved through 8Ø mesh E The entire process was the same as in Example X except that magnesium oxide was used for neutralisation instead of

26
ammonia solution. In this case the pH of the solution was raised to 4.5 by addition of MgO (about 55Ø g)- The suspension was heated to 6ØoC and stirred for one hour- It was subsequently
processed as described earlier.

The product contained 3.7% Fe, 45. 4% P Ø and 25.3% Mo

It had a water solubi1ity of around Ø.1%. Other parameters were
the same as for Example X.
Example X.II
The process is essentially the same as in Example X and
XI except that natural goethite (containing 45% Fe) is used
instead of synthetic goethite. 1ØØg natural goethite, 95g
magnesiunr oxide and 152Øg phosphoric acid (containing 39-7% P Ø )
were mixed and processed as described in Example X.
o Polymerisation, in this case, was carried out at 2ØØ C for 25 roin
till a weight loss of about 7g/1ØØg H PO in the reaction
3 4 mixture, was obtained. The polyphosphate was neutralised with
ammonia solution (12.5%, 1.65 1) to a pM of around 5.4 and subsequently processed as in Example X. The properties of the two materials were similar. Example XIII
1ØØg niaqnanese dioxide (pyrolusite) containing 63-4% Mn
was mixed with 5ØØg of phosphoric acid containing 51% P Ø (Mn;F3
2 5 ratio in the mixture = 1:4). This was taken in a poreelain

: 27 :
o
crucible and heated at 17Ø C till a thick gel-like material was
o formed. The temperature of the furnace was raised to 3ØØ C and
the crucible was kept in it for 5Ø min. Thereupon a dark purple, hard solid was formed, which had the maximum solubility in the
testing reagents. The corresponding weight loss was 15.4g/1ØØg

H PO in the reaction mixture, which produces about 55%
3 3
polymerisation.

The polyphosphste was cooled to ambient temperature, made into a paste with water and neutralised with mactnesium oxide
to a pH of about 5.3. About 4ØØ g MgO was required; after
o addition the slurry was stirred at 6Ø C for about one hour for
o completion of the reaction. The material was dried at 7Ø C,
ground and sieved through 1ØØ mesh BS. The fertilizer contained
7.5% Mn, 35.3%P Ø and 29% MG . Solubility in water was about Ø.1%
2 5 but in Ø.1 N HC1 and Ø.33M citric acid it was soluble to the
extent of about 9Ø-95%. Example XIV
1Øg cobalt oxide was mixed with 51g phosphoric acid of 5Ø% strength to give a Co:P ratio of 1:3. To this 67.7g potassium
hydroxide and a further 17Øg phosphoric acid were added to give
o K:Co=1Ø:l and KsP-l:l- The slurry was heated at 13Ø C till dried-
o This was further heated at 25Ø C for 3Ø min to obtain the mixed

28
polyphosphate of potassium snd cobalt. The polyhosphate was cooled to ambient temperature, made to a paste with water and neutralised with potassium hydroxide to pH 5. Subsequently it was ground with a hand mortar and sieved through 1ØØ mesh. The fertilizer was completely soluble in Ø.1N HC1 and Ø.33 M citric acid . Example XV
1ØØg natural goethite and 1ØØq manganese dioxide were mixed with 1 .541 phosphoric acid (containing 4Ø% P Ø ). The
mixture was put into a muffle furnace and heated at 2ØØ C for 5Ø
min whereupon a mostly homogenous gel was obtained. The
o temperature of the furnace was raised to 35Ø C and the sample was
heated for 3Ø min. Optimum polymerisation was tested as described in the previous Examples. Subsequent processing was done as described in Example XIII except that 9ØØ g of magnesium oxide was required for neutralisation of the polyphosphate. This fertiliser containing both iron and msganese, has low water solubi1ity (about 2%) but high solubi1ity in dilute acids and comp1exants.

WE CLAIM -29-
1 . A process for- preparation of slow release cationic
micronutrient fertilizers, which processes comprises heating at
such as herein described least one micronutrient metal or a compound thereof^ with or
such as herein described without additives^ with phosphoric acid till the resultant
the correspondir mixture is mostly homogenous, further heating, to farm Ametal,
polyphosphates of such a degree of polymerisation that they are
still soluble in dilute mineral acids and complexants, treating
-said metal polyphosphates with a basic compound and finally
obtaining a dried powder.
2Aprocess as clamid 1.wherein thephosphoric
acid used hasu concentration upto 6Ø% P O by weight;
2 5
3. The process as claimed in claim 1, wherein the phosphoric acid used has a concentration of 3Ø to 6Ø*/. P Ø by weight
4. The process as claimed in claim 1, wherein said
micronutrient metal is selected from zinc, copperiron, maganese, cobalt.
5, The process as claimed in claim 1, wherein the micronutrient metal of the axide,hydroxide, chloride or sulphate the of micronutrient metal is used for the reaction with phosphoric acid.

- 3Ø-
6. The process as claimed in claim 1, wherein various additives such as the oxides, hydroxides, or carbonates of magnesium, calcium, potassium or sodium may also be added to the reaction mixture before heating with phosphoric acid.
7. The process as claimed in claim i, wherein the ratio of
metal cation: additive cation is, at least 1:Ø.
8. The process as claimed in claim 1 , where in Ø5 the moler
ratio of metal cation: additive cation is in the range 1 :2 to
1:1Ø.
9. The process as claimed in claim 1 , wherein the amount
of phosphoric acid used for the first step of heating with the micronutrient metal or a compound thereof, is sufficient to produce the dihydrogen phosphates of the cations present,
1Ø. The process as claimed in claim 1, wherein for every
n + mole of metal ion, m , in the reaction mixture, the molar
proportion of phosphoric acid is at least n times that of the metal, where n denotes the valance of the metal ion.
11. A process as claimed in claim 1, wherein during the
first step of heating with phosphoric acid for every mole of
divalent cation present, phosphoric acid containing at least 2
moles P is added for every mole of trivalent cation present,
phosphoric acid containing at least 3 moles P is added, and for

: 31 :
every mole of tetravslent cation present, phosphoric acid containing at least 4 moles P is added.
12. A process as claimed in claim 1, wherein during the f irst step of heating with phosphoric acid, if an additive is used then an additional n+ amount of phosphoric acid is added in-
quantities such that M :P is at least 1 :n or more; where n is
A
n+

the valance of the additive cation, M
A
13- A process as claimed in claim 1, wherein the first step
of heating with phosphoric acid is carried out at any temperature
o above 15Ø C under mostly ambient pressure.
14. A process as claimed in claim 1, wherein the first step
of heating with phosphoric acid is csrried out at any temperature
o above or below 15Ø C under vacuum.
15. A process as claimed in claim 1, wherein step of
further heatirvg, to form the metal polyphosphates is carried out
o at temperatures above 2ØØ C.
1.6. A process as claimed in claim 15, wherein, the step of
further heating to form the metal polyphosphate is carried out at
o o a temperature in the range of 25Ø and 35Ø C.
17- A process as claimed in claim 1, wherein the step of

: 32 :
further heating to form the metal polyphosphate is carried out till polymerisation occurs and the compound shows reduced
solubility in water.
18. A process as claimed in claim 1, wherein the step of
further heating to form the metal polyphosphstes is carried out
till the product shows high solubility in dilute acids and
complexants.
19. A process as claimed in claim 1, wherein the step of
further heating to form the metal polyphasphstes is carried out
upto the point where the upper limit of its solub^l ity, in dilute
acids and complexants is reached.
2Ø. A process as claimed in claim 1, wherein the solubility
of the metal polyphosphate is tested using Ø.1 N hydrochloric
acid, Ø.33 M citric acid and/or Ø.ØØ5 M DTPA (diethylene triamine
pentaacetic acid).
21 . A process as claimed in claim 1, wherein for the step of neutralisation, a basic compound such as ammonia, lime, magnesium oxide, potassium hydroxide is used.
22. A process as claimed in claim 1, wherein the neutralisation is. carried out after addition of water to form a paste or slurry.

33
23. A process as claimed in claim 1, wherein for the step
of neutralisation the pH of the slurry is above 4.
24. A process as claimed in claim 1, wherein the pH of
neutralisation is between 4.5 and 5.5.
25. A process as claimed in claim 1, wherein for the step
of neutralisation using water-insoluble bases such as magnesium
oxide or lime, the reaction mixture is stirred and warmed.
26. A process as claimed in claim 25 , wherein the reaction
o mixture is warmed to 6Ø C
27. - A process as claimed in claim 1, wherein the product
from the step of neutralisation is dried till it is essentially
free of moisture.
28. A process as claimed in claim 1, wherein the product
from the step of neutral isati on is dried at temperatures below
o 1ØØ C.
29. A process as claimed in claim 1, wherein the dried
product is ground to a powder.
3Ø. A process as claimed in claim 1, wherein the product is-
ground to pass through a 1ØØ mesh BS sieve.
31. A process for the manufacture of slow-release
micronutrient fertilizers substanti ally as herein described and
as illustrated in the examp 1 es (5) .
A process for preparation of slow release cationic
micronutrient fertilizers, which processes comprises heating at
such as herein described 1east one micronutrient metsl or a compound thereof^ with or
such as herein described without additives^ with phosphoric acid ti11 the resultant
(the correspondir mixture is mostly homogenous, further heating, to form metal,
polyphosphates of such a degree of polymerisation that they are still soluble in dilute mineral acids and complexants, treating said metal polyphosphates with a basic compound and finally obtaining a dried powder.

Documents:

0010-cal-1999 abstract.pdf

0010-cal-1999 claims.pdf

0010-cal-1999 correspondence.pdf

0010-cal-1999 description(complete).pdf

0010-cal-1999 description(provisional).pdf

0010-cal-1999 form-1.pdf

0010-cal-1999 form-2.pdf

0010-cal-1999 form-3.pdf

0010-cal-1999 form-5.pdf

0010-cal-1999 pa.pdf

10-CAL-1999-(17-05-2012)-ASSIGNMENT.pdf

10-CAL-1999-(17-05-2012)-CORRESPONDENCE.pdf

10-CAL-1999-(17-05-2012)-PA.pdf

10-CAL-1999-(29-06-2012)-ASSIGNMENT.pdf

10-CAL-1999-(29-06-2012)-CORRESPONDENCE.pdf

10-CAL-1999-(29-06-2012)-OTHERS.pdf

10-CAL-1999--(17-05-2012)-CORRESPONDENCE-1.pdf

10-CAL-1999--(17-05-2012)-FORM-1.pdf

10-CAL-1999--(17-05-2012)-FORM-13.pdf

10-CAL-1999--(17-05-2012)-PA-1.pdf

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Patent Number

194747

Indian Patent Application Number

10/CAL/1999

PG Journal Number

30/2009

Publication Date

24-Jul-2009

Grant Date

29-Jul-2005

Date of Filing

06-Jan-1999

Name of Patentee

CHANRIKA VARADACHARI

Applicant Address

4A,RATNABALI,7A,JUDGES,COURT ROAD,ALIPORE, CALCUTTA-700027,

Inventors:

#	Inventor's Name	Inventor's Address
1	CHANDRIKA VARADACHARI	4A,RATNABALI,7A,JUDGES,COURT ROAD,ALIPORE, CALCUTTA-700027,

PCT International Classification Number

C05B 11/10 C05C 3/00

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA