Title of Invention

An Improved process for the preparation of high pure Iron oxide of ferrite Grade

Abstract

An improved process for the preparation of high-pure iron oxide of ferrite grade by treating the complex iron solution with air-ammonia mixture to effect copre-cipitation of impurities with hydrated iron(III) oxide, filtering and pressing the residue to expel the mother liquor, treating the filtrate along with the recovered mother liquor with hydrated yellow iron(III) oxide, filtering and pressing the residue to expel the mother liquor, repeating the above treatment successively, as required, treating the resultant filtrate with hydroxy-lamine hydrochloride, passing mixture of air and ammonia to precipitate iron oxide, filtering and washing the precipitate with demineralised water containing hydroxylamine hydrochloride, followed by drying, roasting and powdering of the roasted precipitate to obtain high-pure iron oxide.

Full Text

This invention is related to an improved process for the production of high pure iron oxide of ferrite grade. High purity synthetic iron oxides find a large number of applications : catalysts, ferrites, flare compositions etc. Iron oxides required for ferrite should have a minimum purity of 99.9% and a particle size of less than 1 micron. Also, they should satisfy the specifications as laid down in Table 1. TABLE 1. (Table Removed) synthetic iron oxides of high purity required for ferrites are generally made by the following methods: I. To a solution of iron(II) salt, an alkali is added and the resulting precipitate is filtered and washed. Then the precipitate is redissolved and reprecipitated The process is repeated as many times as desired to remove all impurities. The final precipitate is oxidised to iron(III) oxide which on filtration, washing, drying, roasting and pulverisation, gives the desired product. The method is tedious in the sense that the final product is obtained after a series of precipitation-dissolution-precipitation operations. Also, the precipitate is slimy and offers considerable resistance to filtration and washing. 2. Iron(III) chloride (anhydrous) is vapourised and in the vapour state steam-hydrolysed to produce pure and fine iron oxide powder. This method involves preparation of anhydrous iron (III) chloride, its vaporisation and steam hydrolysis in vapour state. The method requires sophisticated apparatus and controls. In our Indian Patent No. 167581, we have described and claimed a method for the preparation of High-Pure Synthetic Iron(III) oxide(HPIO) of ferrite grade. The patent No. 167581 deals primerely with the removal of silica which is detrimental for ferrite making. As per the specification on HPIO for soft ferrites, the silica content of the HPIO should not exceed 0.02%. The raw materials envisaged in this patent generally contain 0.1% to 0.2% silica which is brought down to below 0.02%. Other impurities amount to a maximum of 0.9%. Thus, the raw material delt with, has a purity of 99% with respect to iron(III) oxide content. STEPS IN THE PROCESS OF PATENT NO. 167581: 1. Treatment of the iron(II) salt solution with air + ammonia mixture to precipitate 20% of the iron present in the solution as yellow hydrated oxide at room temperature. 2. Filtering the precipitate of step (1) and pressing the cake to recover maximum volume of mother liquor. 3. Treating the filtrate with air + ammonia mixture till all iron present is precipitated as yellow or brownish yellow hydrated iron(III) oxide. 4. Filtering the product of step (3) and washing it with demineralised water till free from chloride or sulphate. 5. Drying the residue of step (4) in an air-oven to remove all free water. 6. Roasting the product of step (5) at 500-800°C to get anhydrous high pure iron(III) oxide. 7. Powdering the HPIO of step (6) to the required size. In case of raw material of 85-90% purity with respect to iron(III) oxide content, certain difficulties arose which are described below: The raw material used in the present invention is a mixture of iron(H) and iron(III) chlorides. When spray-roasted, the iron(III) oxide formed has the composition given in Table 2. TABLE 2 Analysis of spray-roasted iron(IH) oxide. (Table Removed) The specifications for HPIO for soft ferrites are given in Table 3 TABLE 3 (Table Removed) The first step in patent no.167581 was to precipitate 20% of the iron present in the raw material as hydrous iron(III) oxide to bring down the impurites. When this step was applied to the present raw material, the purity of HPIO was far from satisfactory. Increasing the precipitation to 80% gave a HPIO with the composition given in Table 4. TABLE 4_ Analysis of HPIO after removal of impurities at 80% precipitation level (Table Removed) The results show that eventhough other impurities are under control, the silica content far exceeds the specification. The main object of the present invention is to provide an improved process for the preparation of high-pure iron oxide (HPIO) of ferrite grade which obviates the draw backs of the hitherto known processes. Another object is to provide a process for the preparation of HPIO with silica content below 0.02%. Accordingly, the present invention provides an improved process for the preparation of high-pure iron oxide of ferrite grade which comprises : (i; treating the complex iron solution with air-ammonia mixture to effect coprecipitation of impurities with hydrated iron(III) oxide, (ii) filtering and pressing the residue to expel the mother liquor, (iii) treating the filtrate along with the recovered mother liquor with hydrated yellow iron(III) oxide, (iv) filtering and pressing the residue to expel the mother liquor, repeating the above treatment successively, as required, (v) treating the resultant filtrate with hydroxylamine hydrochloride, (vi) passing mixture of air and ammonia to precipitate iron oxide, (vii) filtering and washing the precipitate with demineralised water containing hydroxylamine hydrochloride, followed by drying, roasting and powdering of the roasted precipitate to obtain high-pure iron oxide. The process may be effected at room temperature. The complex iron solution used may be such as leach liquor from synthetic rutile industries The pressed residues may be processed to prepare red oxide. The steps involved in the process are, therefore: Precipitation of 60% of the iron present in the starting raw material with air + ammonia mixture to remove major part of the impurities at room temperature. Filtration and pressing the cake to remove as much mother liquor as possible. Processing the cake for red oxide preparation. Treating the filtrate along with the recovered mother liquor in three successive operations with hydrated yellow iron (EI) oxide to remove silica. Filtering the precipitate and pressing the cake each time to remove as much mother liquor as possible. Processing the combined yellow cakes for red oxide preparation. Treating the filtrate from the 3rd successive operation from step(4) along with recovered mother liquors with hydroxylamine hydrochloride. Precipitating the remaining iron as hydrated iron(III) oxide with a mixture of air + ammonia at room temperature. Filtering the precipitate and washing the precipitate with demineralised water containing hydroxy 1 amine hydrochloride, followed by demineralized water. Collecting the precipitate and rejecting the washings. Drying the precipitate. Roasting the precipitate. Powdering the precipitate. The present invention uses hydrated yellow iron (HI) oxide, added externally to remove especially silica. The yellow oxide is a commercial product sold under the names, ferrite yellow and yellow oxide pigment. This product invariably contains adsorbed impurities like silica, calcium, magnesium, potassium, sodium etc. which are the same impurities considered as objectionable for HPIO. These impurities get released into the process solution and find their way into HPIO. To eliminate this possibility, the yellow oxide is first boiled with sufficient water (20 g per 100 ml) for a few hours and then filtered, washed with demineralised water till the filtrate passes colour test for silica. One should note here that the silican can be extraneous also. For example, it may come from the reactor walls where mild steel vessels are used or from dust in the environment. All purification efforts will be a waste if silica enters from reaction system and from dust. It is, therefore, essential that all-synthetic-material (e.g. polyethylene) reactor system must be used. The reaction system should be a closed one so that reactants do not come into contact with the dust in the environment. The novelty of the process, therefore, lies in removing the silica by the yellow oxide added externally and preventing the co-precipitation of the manganese with the final precipitate by using hydroxylamine hydrochloride and using the same during washing also. The results are given in Tables 5 and 6 TABLE 5 (Table Removed) TABLE 6 Analysis of 60% precipitated, yellow oxide treated HPIO. precipitated in the presence of hydroxylamine hydrochloride (Table Removed) Step (4) of the new process is specially ment for the removal of silica though it removes other left-over minor impurities also. Tables 4 and 5 illustrate the function of step (4). Step (6) involves roasting the externally added yellow oxide with its adsorbed impurities to good grade red oxide of iron, which is a valuable commercial product. This step is very essential for the economy of the process. The red oxide of iron (III) obtained is one of the best products available in the market and helps to reduce the cost of HPIO, making it competitive in the market. Step (7) is essential to keep the manganese at bay. This is illustrated by Tables (5) and (6). We now illustrate the invention with the help of suitable examples which prove the workability of the process. EXAMPLE-1 Two liters of the liquor under investigation were treated with air + ammonia mixture at room temperature till 60% of the iron present in the solution was precipitated. The precipitate of the hydrated iron(IH) oxide was then filtered. The filtrate was treated with 12 grams of processed yellow oxide, stirred slowly for two hours and allowed to equilibriate for 4 hours. The precipitate was filtered. The filtrate was used to prepare HPIO by precipitation with air + ammonia etc. The HPIO thus prepared was analysed for silica. The process was repeated by increasing the treatment with yellow oxide twice and thrice. The results; are given in Table 7. TABLE 7 Analysis of HPIO for SiO2 (yellow treatment Sl.No. Single stage Double stage Triple Stage 1. 0.4% 0.06 0.013% From these results it is evident that single or double treatments with yellow oxide do not remove silica completely but three successive treatments are required. EXAMPLE-2 Two liters of the liquor under investigation were treated with air + ammonia till 60% of the iron present in the solution was precipitated. Filtered and the filtrate was treated with 12 gram portions of the yellow oxide successively three times. The filtrate from the last yellow treatment was used for the precipitation of high pure iron(IH) oxide (HPIO). The hydrated oxide was filtered, washed, dried and roasted to get HPIO. The result of analysis is presented in Table 5. From this table it is evident that manganese may still be a problem. EXAMPLE-3 Two liters of the liquor under investigation were treated with air + ammonia mixture till 60% of the iron present in the solution was precipitated. Filtered and the filtrate was treated with 12 gram portions of the yellow oxide successively three times. The filtrate from the last treatment was treated with hydroxylamine hydrochloride and hydrated iron(IH) oxide was precipitated by air + ammonia mixture. The precipitate was filtered, washed, dried and roasted. The HPIO was analysed. Table 6 shows the results. It shows that the desired HPIO produce has been obtained. EXAMPLE-4 This experiment was carried out on a larger scale (50 liters of iron chloride solution) with all the improvements incorporated and illustrates amply the utility of the new invention for complex iron salt solutions. Fifty liters of the complex iron chloride liquor was filled into the special reactor fabricated for this purpose. Air + ammonia mixture was introduced into the reactor at the rate of 200 liters per minute for a pre-determined period at room temperature, to precipitate 60% of iron. The contents of the reactor were transfered to a decantai ion tank and allowed to equilibriate overnight. The supernatent liquor was decanted and preserved. The remaining slurry was filtered and pressed to recover as much mother liquor as possible and the filtrate thus obtained was mixed with the decantant preserved earlier (F-l). The residue (R-l) was transferred to a cylindrical mild steel vessel, sufficient water was added, stirred, neutralised and filtered. The residue was washed with water till the filtrate was free from chloride, dried in an air oven (110 ± 10°C) to remove all free water and roasted at 800°C for 2 hours. The roasted mass was powdered to the required size. The yield was 3.25 Kg primer grade red oxide. Alternately, the residue, R-l is transferred to a M.S. reactor, dissolved in sufficient concentrated Hydrochloric Acid, the Fe2+: Fe'+ ratio is adjusted to 0.5 by adding scrap iron or air as the case may be and stirred without passing air for two hours to get iron oxide black. This, on filtration, washing, drying and roasting at 350°C gives magnetic brown oxide which on roasting at 800°C gives good grade red oxide of iron. The filtrate (F-l) was transferred to the reactor, the volume was made up to fifty liters and stirred with 300 grams of the processed yellow oxide for two hours and allowed to equilibrate for 4 hours. The residue was then filtered under vacuum and pressed to recover as much mother liquor as possible. The residue was preserved and the filtrate was treated along with its recovered mother liquor with 300 grams of the processed yellow oxide as described above. This procedure was repeated again. The three yellow residues thus obtained were combined (R-2) and were taken into a cylindrical mild steel vessel, sufficient water was added and neutralised with liquor ammonia to pH 7. The whole slurry thus obtained was filtered, washed free from chloride, dried at 110 ± 10°C and roasted at 800°C for one hour to get 1.03 Kg of good grade red oxide pigment of iron. The filtrate (F-2) from yellow treatments was transferred to the reactor, hydroxylamine hydrochloride in the form of a solution containing 50 grams of the salt was added. The volume was adjusted to fifty liters. Air + ammonia mixture was passed into the contents of the reactor at a rate of 100 liters per minute till pH 7 reached. Air + ammonia passage was stopped. Simple air was passed at a rate of 150 liters per minute for two hours. All these operations were carried out at room temperature. The contents of the reactor were transferred to a settling tank and settled for four hours. The clear supernatent liquid was decanted and preserved for ammonia recovery. The residue was filtered and washed with demineralised water which was 0.1% with respect to hydroxylaniine hydrochloride, followed by deineralized wafer (ill free from chloride, dried at 100 t 10OC in and air oven followed by roasling al 800OC lo gel anhydionus iron (HI) oxide which analyses as per (he Table 8 with a yield of 1.75 Kg. The final anhydrous iron(Ifl) oxide (HPIO) may be powdered (o the required size. TABLE 8 (Table Removed) We claim: 1. An improved process for the preparation of high- pure iron oxide of ferrite grade which comprises : (i) treating the complex iron solution with air-ammonia mixture to effect coprecipitation of impurities with hydrated iron(III) oxide, (ii) filtering and pressing the residue to expel the mother liquor, (iii) treating the filtrate along with the recovered mother liquor with hydrated yellow iron(III) oxide, (iv) filtering and pressing the residue to expel the mother liquor, repeating the above treatment successively, as required, (v) treating the resultant filtrate with hydroxylamine hydrochloride, (vi) passing mixture of air and ammonia to precipitate iron oxide, (vii) filtering and washing the precipitate with demineralised water containing hydroxylamine hydrochloride, followed by drying, roasting and powdering of the roasted precipitate to obtain high-pure iron oxide. 2. An improved process as claimed in claim (1) where in the complex iron solution used is leach liquor from synthetic rutile industries. 3. An improved process as claimed in claims (1) and o (2) wherein the process is effected at 25 C. 4. An improved process for the preparation of high-pure iron oxide of ferrite grade substantially as herein described with reference to the examples.

Documents:

3351-DEL-1997-Abstract.pdf

3351-DEL-1997-Claims.pdf

3351-del-1997-complete specification (granted).pdf

3351-DEL-1997-Correspondence-Others.pdf

3351-DEL-1997-Correspondence-PO.pdf

3351-DEL-1997-Description (Complete).pdf

3351-DEL-1997-Form-1.pdf

3351-DEL-1997-Form-19.pdf

3351-DEL-1997-Form-2.pdf

3351-del-1997-petition-137.pdf

3351-del-1997-petition-138.pdf