Title of Invention	AN IMPROVED PROCESS FOR THE BENEFICIATION OF HIGH PHOSPHORUS MANGANESE ORES.
Abstract	High phosphorus manganese ores grounded and subjected to magnetic separation. The magnetic fraction was mixed with 5 - 20% by wt. of salt of sodium and roasted at a temperature ranging 600 - 850°C to get dephosphorized manganese ore.

Full Text

This invention relates to an improved process for the beneficiation of manganese ores. Particularly it relates to beneficiation of high phosphorus manganese ores by dephosphorization. India is one of the major producers of manganese ores in the world with a total reserve of about 156 million tonnes comprising all grades of ore. Except for a few mines in the Madhya Pradesh-Maharashtra belt of Central India and in northern region of Orissa (Keonjhar-Bonai belt) the manganese ores of India are generally medium to low grade (38-20% Mn) with iron or silica or both constituting the major impurities. While both siliceous and ferruginous ores can toe berieficiated to a grade suitable for use in the production of ferromangaraese, ferruginous ores with low silica and alumina contents can be used directly in the production of pig iron by the conventional blast furnace process. However, of all the impurities in the manganese ores phosphorus is considered to be the most deliterious. This is because phosphorus goes into the metal phase during smelting as Fe-P compound which accumulates at the grain boundaries, thereby deteriorating the mechanical strength of steel, particularly during cold-rolling processThe presence of both high silica and phosphorus as impurities tends to reduce the price of the ore to such an extent that its mining becomes virtually uneconomical. The high phosphorus manganese ores of southern Orissa are located mainly in the districts of Rayagada, Koraput and Bolangir. The ore belt is related to feldspathic quartette occurring in close association with calc- silicates in the khondolite group. High grade ores occurring in few pockets and ferruginous medium grade ores occurring widely are usually hard and massive. On the other hand, weathered low grade ores are relatively friable and porous due to superf ene alterations. Cryptowefane, psitemelane and pyrolusite are the major manganese minerals, while goeihite and hematite are the primary iron bearing minerals. Phosphorus occurs in all these minerals almost uniformly. In the neighbouring Andhra Pradesh, manganese ore deposits occur mainly in the Srikakulum and Viaanagaram districts in association with ealc-granulites or calc-silicates of kodurite group. Indeed, the ores of this region form part of the broad belt of Eastern Ghat super group. The ores are generally low to medium grade, porous, fragile and disintegrates even when placed in water. Extensive weathering has resulted in the enrichment of both iron and silica. Pyrolusite, psitemefane, cryptometane, jacobsite constitute the major manganese minerals while Hraonitic iron ore and goethite constitute the iron minerals. Quartz, feldspar, garnet, kaolirtite etc. are the main accessory minerals. In these ores phosphorus also occurs almost uniformly in manganese, iron and accessory minerals. The purpose of giving these detailed introductory informations is to demonstrate that not only the complex mineralogy of mawfauese opes of this region, but also the complex nature of association of pbosphmis with these minerals render the task of beneficiation and tepHHsphiorization of these ores very difficult and indeed a challenging one. Many attempts have been raade earlier in this direction especially on Andhra Pradesh ores, the mining of which started in the beginning of this century. Narayanan and Subrahmanyarn have doccumented and reviewed the earlier work carried out particularly in NML, Jamshedpur. (p.l.A. Narayanan and N.N. Subrahmanyam, Beneficiation of the low grade manganese ores of India, CSIR, New Delhi, 1959.J The authors concluded that jigging followed by tabling show lower recovery than that of magnetic separation. Subsequent investigations by several authors indicate that while the Mn content could be increased by about 10-15% by using the conventional ore dressing methods, attempts to reduce the phosphorus content were by and large unsuccessful. A. Narasinghrao, Studies on the beneficiation of low grade manganese ores from Srikakulum and Vizianagaram districts with special reference to the reduction of phosphorus content. J. Miiaes Metals & Fuels. February, 1965, pp 55-59. R.S. Narasimharao and K. Kameswararao, Processing of manganese ore dumps of Garbham, Vizianagaram, Proc. 9th National Convention of Chemical Engineers, held at Visakhapatnam, Jannuary 5-7, 1993, pp 352-354. Research work on the high phosphorus manganese ores of southern Orissa, however, started at much later period. From 1968 to 1974 extensive investigation was carried out at R.R.L. Bhubaneswar on the chemical method of beneficiation, particularly on the dephosphorization of manganese ores of this region as these ores are also not amenable to beneficiation by any physical method of beneficiation. The work on alkali-roast leaching method was initiated during that period. A reference can be made to the following documents. 5.6. Kanungo and B.R. Sant, Reduction of phosphorus content of manganese ores. Indian J. Technol. 9. 1991, pp 432-434. S.B, Kanungo and B.R. Sant, Reduction of phosphorus content from high phosphorus manganese ores of India by sodium carbonate roasting. J. Mines Metals & Fuels. December 1971, pp 364-368. S.8. Kanungo, B.R. Sant and G.S. Chowdhury, Improvements in or relating to the reduction of phosphorus content from high phosphorus manganese ores: Indian Patent. 128381 Appl. September 11, 1970. S.B. Kanungo, Removal of phosphate by lime from aqueous solution. Indian J Techonol. 13 (1975) pp 524-527. S.B. Kanungo, Removal of silicate and aluminate by lime from aqueous solution containing alkali, Indian J. Technol 15 (1977) pp 34-38. S.B. Kanungo and B.R. Sant, A process for the recovery of alkali from aqueous solutions containing alkali carbonates, hydroxides, phosphates, silicates and aluminates : Indian Patent 134972, Appl. February 28, 1972. In abroad, most of the investigations on the dephosphorization of high phosphorus manganese ores were carried out in the erstwhile Soviet Union. The nature of occurrence of phosphorus in some of the manganese ores of Chiatura and Nikopal mines in the Ural region of Ukraine are closely similar to those of southern Orissa and Andhra Pradesh. For such ores where phosphorus does not occur in the form of discrete mineral grains, alkali-roast leaching method has been found to be effective as indicated in the following references. S.I. Khuzik, M.I. Sasik and A.G. Kucher. Low phosphorus manganese concentrate and hydrometallurgical method of production. Ghorn. Zh. No.9, 1966, pp 66-69, Chem. Abstr. 66 (1967) Abstr. No. 31119. S,l. Khirik, A.G. Kucher, Rogachar, 1.P. and Yu. V. Lagunov. Effect of particle size, composition of initial concentrates and sinters on the completeness of etimiwation of phosphorous and SiO2 during dephosphortzation of manganese concentrates. Met. Koksokhim. No.11, 1968 pp80-84, Chem. Abstr. 70 (19691 Abstr. No. 59817. Consequently, actetaited mineralogical investigation is considered to be essential before undertaking the beneficiation work. The results of the foregoing studies indicate that white the low grade ore can be upgraded to a certain extent by using the eoiwentional ore dressing methods phosphorus content can not be reduced below 0.3%. Further, the low grade ores of AP. are so fragile in nature that considerable amount of fines are generated during mining and subsequent bulk handling, there are only a few or limited options left for the selection of beneficiation methods, such as high intensity magnetic separation, hydrocyclone, floatation. However, it has been observed that floatation gives not only poor grade, but also low recovery as the extremely fine particles of both ferromanganese oxides minerals and silicate gangue minerals exhibit self-floatation. Therefore, only high intensity mapietic separation and hydnocyclone have been selected for the feenefinatton of A.P. ores. However, for ferruginous ares no prebeneficralien step has been envisaged and therefore treated directly for deplsssphorizatcon. The following are the essential steps r-equired for the low grade fragile ores of Andhra Pradesh and southern Ortssa. (1) Cnashing the ore in a secondary crusher (e.g. roll crasher) to a size finer than 3 mm only. During this step a substantial quantity of fines (- 105 mm) are also generated. (2) Wet grinding of the crushed ore to -150 mm size in a rod mill for 10-15 minute to avoid over-grinding in case of A.P. ores. For high or medium grade ores of southern Orissa a longer period is necessary. However, when a close circuit grinding is used the over size is fed continuously to the mill. (3) The undersize is made into a slurry of about 10-15% (weight/volume) suitable for use as feed for wet high intensity magnetic separation which was carried out at field strength of 1.2-1.6 tesla. Magnetic fraction was separated after demagnetizing the-electro-magnet and washing out the magnetically attracted material from within the interpolar grid spaces. (4) The suspensions containing both the products of magnetic separation were allowed to settle, the supernatants were deeanted off and the thickened slurry containg the magnetic fraction was filtered and the residue was dried at 110°C. (5) The thickened slurry containing the non-magnetic fraction was stored until a sufficient quantity was accumulated for hydrocyetene separation. The solid content in the thickened slurry was determined and a fresh slurry containing 15-20% of solid |w/v) was prepared by diluting with the requisite quantity of water. (6) The fresh suspension of non-magnetic fraction thus prepared was subjected to hydrocyclone classification at suitabfe or optimum operational parameters depending upon the size of the cyclone used. (7) The underflow obtained from the hydrocyelone separation was a§aw subjected to wet high intensity magnetic separation at the fietel strength of 1.3 -1.5 tesla. The magnetic fraction thus obtained was allowed to settle and filtered and the residue was dried. This was mixed with the bulk magnetic fraction obtained from step (3) and the recovery of the he overflow obtained from step (6) and the non-magnetic fraction of step (7) were cconcentrate was 75-77% by weight of the feed ore. (8) The overflow obtained from step (6) and the nonmagneticfraettew of step (7) were combined together and rejected. This amount is afeout 23-28% by weight of the feed ore. (9) The overall concentrate was thoroughly mixed with either sodium carbonate or a combination of sodium carbonate and sodium cnloride in suitable proportion, preferably in a blender. (10) The mixture was transfesaed to a stainless steel boat and the boat was heated in a muffle furnace for a suitable period of time at temperature ranging from 600° to 800°C. (11) After the requisite period of roasting the boat was taken out of the furnace, allowed to cool to about 100°-150°and the material content of the boat was transferred to a beaker containing water. The contents were leached for 30-60 minutes at 90°C in a constant temperature water bath. The pulp density was varied from 10-20%. The residue was filtered, washed, dried and analysed. (12) The filtrate and the initial 2-3 washings were preserved for the recovery of alkali. The solution was analysed for phosphate, silicate and aluminate contents and stoichiometric quantity of lime required to convert these anions to their calcium salts was added to the solution. (13) After 36 - 48 h of equilibration at ambient temperature with intermittent stirring, the suspension was filtered. The filtrate was free from all these anions without the loss of any alkalinity. Indeed there should be more alkali in the solution due to the formation of sodium hydroxide in the solution by double decomposition reactions of calcium hydroxide with sodium salts of carbonate, phosphate, silicate and aluminate. (14) The recovered alkali in the filtrate is suitably concentrated and recycled at least partially during subsequent roasting. Steps (9) to (14) are common for dephosphorization for all grades of high phosphorus manganese ores of southern Orissa-A.P. region. Accordingly, the present invention provides an improved process for the beneficiation of high phosphorus manganese ores characterized in that mixing the magnetic fraction of ore with 5- 20% by wt. a salt of sodium and roasting at 600 to 850°C,which comprises grinding manganese ores to -150µm, subjecting to conventional magnetic separation then subjecting to conventional hydrocyclone separation followed by high intensity magnetic separation, mixing the magnetic fraction with 5-20% by wt. a salt of sodium such as carbonate, chloride or mixture thereof and roasting at 600 to 850°C for 30 to 120 minutes followed by washing with water to get beneficiated ore as residue drying and if desired recycling the alkalies obtained in washing. 30 to 120 minutes followed by washing with water to get beneficiated ore as residue drying and if desired recycling the alkalies obtained in washings. The manner in which the invention has to be performed is illustrated by the following examples which should not however be construed to limit the scope of the invention. Example 1 About 500 gm of ground manfpanese ore (-150 mm) from the mines in and aroynd Garividi region of Vizianagaram district A.P. and analysed as Mn 22.9%, Fe 11%, P 0.492%, acid insol. 26.4% was suspended in 3 litres of water. The uniform suspension was fed through S.S. grid spacing placed between the potes of an electromagnet, the field strength of which was varied by allowing constant flow of current (10 amp.). The actual field strength was obtained from the calibration curves provided with the instrument (Box Mag Rapid, U.K.) for different grid spacings and current strength used. The late of flow of suspension was maintained at 150-200 ml/min. After the suspension was passed about one litre of water was allowed to flow through the grid to wash the magnetic fraction free from adhering slimy particles. The electromagnet was demagnetized by switching off the current. The attracted material was dislodged or separated from the grid spacings with the help of water jet. The suspensions containing both magnetic and nonmagnetic fractions were allowed to settle, the thickened suspensions were filtered and dried. The product was analysed as Mn 31.5%, Fe 15.1%, P 0.34%, acid insoluble 15%. About 6 kg of non-magnetic fraction generated after a number of wet high intenstty magnetic separation expewroents, was resuspended in 40 litres of water in the slurry tank of a 'Mozley' (U.K.) hydeoeyetene test tig. The cyclone {5 cm internal diameter) was run for a few minutes at the requisite or desired pressure (1.5 bar) for stabittzatton after writeh the overflow and underflow samples were collected simultaneously for a fixed period (4-5 sees.). The other operational conditions were: Vortex finder 14.3 mm, apex nozzle 6.3 mm. The solid content in the underflow was estimated either by measuring density of the suspension or by evaporating a known volume of suspension to dryness and noting the weight of the sotid residue. Knowing the solid content the concentration of the suspension was readjusted to 10-1 5% (w/v). The suspension was subjected to high intensity magnetic separation according to the procedure given under example 1 . An average recovery of 17-18% with respect to original feed weight in the magnetic fraction was observed. This was mixed with the original magnetic fraction obtained from the experiment described under example 1. The overall recovery thus becomes 75-77% by weight and henceforth regarded as the total Twenty gms of total concentrate having the composition of Mo 33.0%, Fe 15.0%, P 0 382% and acid insolubles 14.0% was thoroughly mixed with 15-20% (weight/weight) of anhydrous sodium carbonate. The mixture was placed in a stainless steel boat and roasted at 700°-750°C in a muffle furnace for 60 minutes. The boat was allowed to cool at ambient temperature and its contents were transferred to a beaker containing 140 ml of water. The suspension was teatned at 80°C over steam bath for 45-60 min., filtered, washed 2-3 times using 50 ml of water each time. The fillrate and the washings were preserved separately for the recovery of alkali. The residue on drying was analysed as follows : Mn 33.0%, Fe 14.5%, P 0.158%, acid insolubies 11.0%. Example 2 Twenty grams of -200 mm ferruginous manganese ore from Nishikhal mine, Rayagada district, Orissa and analysed as Mn 30.2%, Fe 24.3%, P 0.645% and acid insoluble 6.7% was mixed with 3 gm of Na'Cf and 1 gm of anhydrous Na2O3- The mixture was raasted at 750°C for 90 min, cooled at ambient temperature and leached in water according to the procedure given under the example 3. The dry residue was analysed as Mn 44.4%, Fe 17.6%, P 0.126% and acid insoluble 6.0% suggesting that for Nishikhal 'ore there is a considerable improvement in the grade of the product by the above treatment, besides reduction in phosphorus content. Example 3 Twenty gm of -200 mm high grade manganese ore from Kuttinga, Rayagada district Orissa and analysed as Mn 49 8%, Fe 8.3%, P 0.43%, acid insoluble 2.5% was thoroughly mixed with 2 gm of anhydrous Na2CO3 and roasted at 720°C for 90 minutes. The mixture was cooted and teached in water at 80°-85°C for 1 hr. The suspension was filtered, washed and dried. The final product was analysed as fellpws: Mn 55.4%, Fe 3,63%, P 0.12% The following are the advantages of the invention: 1. The high phosphorus manganese ores of southern Orissa and Andhra Pradesh which are not amenable to dephosphorization fey conventional ore dressing methods or even simple acid leaching method are amenable to alkali roast-leaching method. 2. For high grade manganese ores (> 45% Mn) containing low iron, silica and alumina, e.g., high grade ore of Kuttinga, Rayagada district, Orissa for which no pre-beneficiation is necessary, the method shows excellent results. 3. For low to medium grade ferruginous ores of Nishikhal, (Rayagada district, Orissa) where phosphorus occurs in very large quantity (> 0.660%) roasting with a mixture of NaCI (10-15% ore) and Na2CO3 (5% of ore) and subsequent leaching in water brings down phosphorus content in the ore to 0.125%. This not only reduces the cost of raw material but also enhances the Mn content of the final product by about 14,5% and decrease the iron content by about 8%. 4. For highly metamorphosed and weathered ores of Andhra Pradesh having high gangue mineral content, pre-benefieiation of the ore using the combination of wet high intensity magnetic separation and hydroeyelone classification gives an excellent overall recovery of 75-77% by weight of the feed ore and 90% of total manganese value. No other method can give such high recovery values. 5. The entire alkali can easily be recovered by a simple treatment with lime at ambient temperature. We Claim: 1. An improved process for the beneficiation of high phosphorus manganese ores characterized in that mixing the magnetic fraction of ore with 5- 20% by wt. a salt of sodium and roasting at 600 to 850°C, which comprises grinding manganese ores to -150µm, subjecting to conventional magnetic separation then subjecting to conventional hydrocyclone separation followed by high intensity magnetic separation, mixing the magnetic fraction with 5-20% by wt. a salt of sodium such as carbonate, chloride or mixture thereof and roasting at 600 to 850°C for 30 to 120 minutes followed by washing with water to get beneficiated ore as residue drying and if desired recycling the alkalies obtained in washing. 2. An improved process as claimed in claim 1 wherein amount of sodium salt added ranges from 5 - 10%. 3. An improved process for the beneficiation of high phosphorus manganese ores substantially as herein described with reference to the examples.

Documents:

282-del-1999-abstract.pdf

282-del-1999-claims.pdf

282-del-1999-correspondence-others.pdf

282-del-1999-correspondence-po.pdf

282-del-1999-description (complete).pdf

282-del-1999-form-1.pdf

282-del-1999-form-19.pdf

282-del-1999-form-2.pdf

282-del-1999-form-3.pdf