A PROCESS TO MANUFACTURE COMMERCIALLY ACCEPTABLE PHOSPHORIC ACID AND GYPSUM FROM ROCK PHOSPHATE

Abstract: The present invention provides a process for the manu­ facture of gypsum and phosphate from rock phosphate, the process comprises solubilising the phosphate and fluoride content of rock phosphate by treating it with fluosilicic acid (H₂SiF₆) optionally together with phosphoric acid in a reactor (3), treating the solution so obtained, optionally after filtra­ tion in unit (4), with sulphuric acid in a crystalliser (7) to precipitate gypsum and regenerate fluosilicic acid, filtering the slurry to remove gypsum, dividing the remaining liquor into two portions, the major portion (10) being recycled to treat further rock phosphate, the minor portion being treated to remove the phosphoric acid content thereof in unit (12). The removed phosphoric acid constitutes the product of the process and fluosilicic acid remaining in the minor portion is recycled to treat further rock phosphate.

Description: A process to manufacture commercially acceptable phosphoric acid and gypsum from-Rock Phosphate. This invention relates to a process to manufacture commercially acceptable phosphoric acid and gypsum from Rock Phosphate. The starting material to manufacture Phosphoric Acid is Rock Phosphate. The Rock Phosphate coming from different countries has varyiny(from- 20 to 30 per cent) proportions-of P205 content. Samples of Rock Phosphate which come from @orocco, Tunisia, Jordan, Senegal and United States of America have a higher percentage of P 205 than those which coma from: countrisa like India The Principal impurities are silica, iron and aluminium oxides designated as R2O3. (This is also called FERAL impurities). The existing process for the manufacture of Phosphoric Acid employ samples of Rock Phosphate richer in P 205 content. The existing processes comprise reacting finely ground Rock Phosphate powder with Sulphuric Acid giving Phosphoric Acid and Gypsum (Calcium Sulphate Dihydrate and/or hemi-hydrate) along with impurities consisting of silica and fluorine compounds. The product gypsum will require further purification. Some samples of Rock Phosphate are difficult to grind to a fine powder owing to hard silica impurities and they are not preferred for the practice of existing processes because the grinding. procedure becomes expensive. This invention provides a process for the manufacture of commercially acceptable Phosphoric Acid and Gypsum from any sample of Rock Phosphate (P-205 - rich or poor) without appreciable evolution of gaseous fluorine at the reaction stage. A striking feature of this process is the complete solubilisation of the P2O5 and fluorine contents of the sample of Rock Phosphate. The Fluorine content of the liquor could be utilised for the purpose of obtaining fluorine-based compounds. of great commercial value like SF5, AlF3 and Cryolite. This invention provides a process to manufacture froa 9ock Phosphate commercially acceptable Phosphoric Acid and gypsum comprising reacting coarser samples of Rock Phosphate with a mixture of Phosphoric Acid and rluosilicic Acid with a minute quantity of Sulphuric Acid at a- temperature from ambient to 100 C. until the Phosphate and Fluorine contents of the Rock Phosphate are substantially dis@olved, the resulting flurry being fed into a- crystalliser containing slurry fro previous batch. the slurry being reacted in the crystalliser with sulphuric acid, the reaction in the crystalliser being continued till gypsum crystal-foreation is complete, the crystalliser contents being filtered and the residu@ conteining s substantially gypsum crystals being, washed several times with @@ sach liquors and water, the filtrate and washings, containing a mixture of phosphoric acid and flucsilicic acid, being divided into two unequal portions, the @m@ll@r portion containing P2O5 "aquival@nt" to that contained in the Rock Phosphate at the beginning of the process, the @maller portion being concentrated to give phosphoric acid, the fluosilicic acid evolved during the concentration process being scrubbed and six ad with the larger portion, the last-mantion@d mixtur@ being racycl@d to a fr@@h quantity of Rock Phosphat@ to rep@at the process. In an embodiment of this invention, the aforesaid slurry produced by the reaction of Rock Phosphate with the mixture of Phosphoric Acid and Fluosilicic Acid with a minute quantity of Sulphuric Acid is filtered to remove the insoluble impurities and the filtrate and washings of the residue with leach liquor and water are fed into the crystalliser containing slurry from previous.batch. This embodiment gives purer gypsum crystals In another embodiment of this invention, the aforesaid slurry produced by the reaction of rock.phosphate with a mixture of phosphoric acid and fluosilicic acid with a minute quantity of sulphuric acid is filtered and the filtrate-- end washings of the- reaidue by leach liquor and water arc divided into two portions, the smaller portion containing P 205 "@quivalent" to that contained in- the rock-phosphate at the beginning of the process, thersmaller portion being concentrated, cooled and filtered, the' residue being wet calcium silicaflucride and the filtrate being the product phosphoric acid* the cake of the wet calcium silicofluoride along with the aforesaid larger portion being added into a crystalliser containing slurry from previous batch and sulphuric acid being added into the crystalliser, the reaction being continued till the gypsum crystalformation is complete, the gypsum crystals being filtered out leaving as filtrate a mixture of phosphoric acid and fluosilicic acid, which mixture is recycled to a fresh quantity of rock-phosphate to initiate the process. This embodiment gives purer gypsum crystals The foregoing three processes are applicable to all types of samples of rock phosphate, whatever their P 205 content, which is generally varying from 20 to 30 per cent. These processes give a quality of gypsum with respect to P 205 impurity that it can ba used, without further purification, in the manufacture of plasterboard or as an additive in the manufacture of cement. The processes claimed in claims 2 and 3 give gypsum containing less than 0.3 par cent P2O5 and such sample of gypsum is suitable as a whitner in the paper industry. A further advantage of these processes is the almost complete recovery of the fluorine content of the rock phosphate. This invention is now illustrated with reference to the accompanying three flow-she@ts by- the following six examples. The examples t and 2 read with flowsheet 1 illustrate the process claimed in claim 1 with rockphosphate samples respectively rich and poor in P2O5 content. Examples 3 and 4 read with flow sheet 2 likewise illustrate the process claimed in claim 2 with rock phosphate samples- respectively rich and poor and in P 205 content. Examples 5 and 4 read with flow sheet- 3 illustrate the process claimed in claim 3 with rock phosphate samples respectively rich and poor in P205 content These examples do not in any way limit the full ambit of the claims. EXAMPLE 1 : A sample (1) was taken of 20Q gma of low grade unbeneficiatad coarse rock phosphate of particle size of -@ to +25 mesh. On analysis the sample showed the following. composition : P2O5 : 33,00 % CaO 45.20 % 3.2 % SiO2 : 15.0Q % Fe2O3 + Al2O3 2.40 % CO2 1.00 % NaCl 0.1 % SO3 0.4 % The said sample was reacted in a well stirred reactor (3) with 2090 gms of acid mixture containing 20% W/W P2O5@ 11.91% W/@ H2SiF6, 0.5% W/W 0 H2 504 at 70 C. for a period of 2 hours. The slurry obtained, without filtration and 155 gms of 98.5% @/@ H2SO4 (2) were simultaneously fed into a well stirred crystalliser (4) containing slurry from previous batch, at 65 . for 3 hours After the reaction, the resulting slurry EMI5.1 was passed through the filter (5) and washed several times#to give 430 gms of wet gypsum cake along. with silica mud and. other insoluble impurities. The washed residue (6) was "Product" gypsum(Ca504 .2H 0) of e grade accept 2 able in the manufacture of cement. The aggregate filtrate weighing 2265 gms. comprised of acid mixture containing 21.28% W/W F2û5, and 11.3% W/W H2SiF6. This aggregate- filtrate- (2265 gms) was divided into two portions - one (8) weighing 301 gms and. the other (7) weighing 1964 gms, the smaller portion (8) weighing 301 gms was concentrated in the concentration unit (9) @to get 121 gms of "Product" Phosphoric Acid(11), containing 52% W/W P2O5 and 180 gms of liquor (1Q) containing 17.0s @/@ H25iF6 by scrubbing and recycling it. The recovery of H2SiF6 was 90S.. The 180 gms of liquor (10) was separately concentrated to get 136 gms liquor containing 21.41% W/W H2SiF6, of which 126 gms. were. added to the portion (7) containing 1964 gms )of the aforesaid filtrate to get 2090 gms of acid mixture (12) for being recycled to the reactor (3) for a-fresh sample of 200 gms of rock phosphate. The recovery of P2O5 from rock phosphate to "Product" phosphoric acid was 95% EXAMPLE 2 A A sample (1) was taken of 200 gms of low grede unbeneficiat@ coarse rock phosphate of particle size of 6 +25 mesh. On analysis the sample showed the following composition P205 : 20.04 % CaO : 26.65 % Fe2O3 + Al2O3 4.77 % F : 2.00 % SiO2 42.32 % LOI at 1000 C. 2.89 % The said sample was reacted in a well stirred reactor t3) with 1263 gms of acid mixture containing 20.0% W/W P2O5, 11.96% H2SiF6 and 0.5% W/W 0 H2004 at 70 C. for a period of two hours. The slurry obtained, without filtration and 92 gms of 96.5% W/W H2504 (2) were simultaneously fed into a well stirred crystalliser (4) containing slurry from previous batch, at 65 C. for 3 hours. After the reaction, the resulting slurry was passed EMI6.1 through the filter (5) and washed several times@to give 350 gms. of wet gypsum cake along with silica mud and other soluble impurities. The washed residue (6) was "Product" gypsum (CaSO4.2H2O) of a grade acceptable in the manufacture of cement. The aggregate filtrate weighing 1380 gms. comprised of acid mixture containing 21.09% 'i/W P205 and 11.26% 'wfw H25iF . This aggregate filtrate (13a0 gms) was divided into two portions: one (8) weighing 182 gms and the other (7) weighing 1198 gms. The smaller portion (8) weighing 182 gms. was concentrated in the concentration unit (9) to get 72 gms of "Product" phosphoric acid (11) containing 52% W/W P205 and 110 gms. of liquor containing 16.76% W/W H2SiF6 (10) by scrubbing and recycling it. The recovery of H25iFó was 90%. The 110 gms of liquor(10) was separately concentrated to get 70 gms. liquor containing 24.87% W/W H2SiF6, of which 65 gms. were added to the portion (7) containing 1198 gms of the aforesaid filtrate to get 1263 gins of acid mixture (12) for being recycled to the reactor (3) for a fresh sample of 200 gms of rock phosphate The recovery of P2O5 @ om rock phosphate to "Product" Phosphoric Acid was 93%. The following two examples illustrate the second embodiment of this invention The rock phosphate sample in example 3 has a higher percentage of P2O5 than the sample in example 4. The bracketed numeral references are to the accompanying sheet No.2. EXAMPLE 3 : A- sample (1) of 200 gms. of low grade unbeneficiated coarse rock phosphate from- Jhabua Hines in @adhy@ Pradesh of the particle size of -8 to +25 mesh- showed on analysis. the- following composition t P2O5 33.00 % CaU. : 45.20 % F F 3.2 % SiO2 15.00 % Fe2O3 + Al2O3 2.40 % CO2 1.00 % NaCl 0.1 % SO3 0.4 % The said sample was reacted in n well stirred reactor (3) with 2090 go of acid mixture containing 20.0% W/W P2O5, 11.91% W/W H2SiF6 and 0.5% W/W H2SO4 at 70 C. for a period of two hours. The result@ng slurry was passed through the filter (4) to-remove 130 gms. of wet insoluble impu- rities- (5) comprising quartz, mud, earthy matter and crude gypsum, The impurities werr washed. several times with l@ach liquors and water, and ths; filterco washings were added to the filtrate (6). The aggregate filtrate (6) weighing 2260 gms. contained in solution practically 98% phosphate and 95% of the fluorine content of the rock phosphate (1). Analysis of the filtrate gave 21.357% W/W P2O5, 11.354% W/W H2SiF6. The said 2260 gms. of filtrate (6) and 155 gma of 98.5% W/W H2SO4(2) were simultancou@ly fed into a well stirred crystalliser (7) containing slurry from previous batch at the temperature 65 C. for 3 hours. After the reaction, the resulting slurry wes passed through filter (8) and the residue (9) was washed with leach liquors and water and filtered several times. The washed residue (9) was 300 gins. of wet cake of product gypsum CaSO4 2H20) of a grade acceptable in the manufacture of cement. The aggregate filtrate weighing, 2265 gins. comprised acid mixture containing 21.28% W/W P205 and 11.273% W/W H2SiF6. The aggregate filtrate(2265 gms) was divided into two portions : One (11) weighing 300 gins and the other (10) weighing 1965 gms The smaller portion (11) weighing 300 gms were concentrated in the concentration unit (12) to get 12t gms. of "Product" phosphoric acid (14) containing 52% W/W P2O5 and 179 gms. of liquor (13) containing 17.01% w/w H2SiF6 by scrubbing and rccycling it. The recovery of H2SiF6 was 90@ The 179 gms. of liquor (13) was separately concentrated to get 132 gms. of liquor containing 21.92% W/W H2SiF6 of which 125 gms. were added to the- portion (10) containing 1965 gins. of aforesaid filtrate to get 2090 gms. of acid mixture (15) for being recycled to the react r (3) for a fresh sample of 200 gms of rock phosphate The recovery of F205 from rock phosphate to "Product" phosphoric acid was 95%. EXAMPLE 4 A sample (1) of 200 gms. of low grade unbeneficiated coarse rock phosphate from Jhabua mines in Madhya Pradesh of particle size of -8 to +25 mesh showed on analysis the following composition P2O5 20.04 % CaO 26.65 % Fe2O3 + Al2O3 4.77 % F 2.00 % SiO2 : 42.32 % LOI at 1000 C 3.89 % The said sample was reacted in a well stirred reactor (3) with 1262 gms. of acid mixture containing 20.0% w/W P205, 11.96% W/W H2SiF6 and 0.5% W/W H2SO4 at 70 C. for a period of 2 hours. The resulting slurry was passed through the filter (4) to remove 170 gins. of wet insoluble impurities (5) comprising quart@, mu-d, earthy matter and crude gypsum. The impurities EMI9.1 EMI9.2 with leach liqu@rs and water and the residue (9) was washed/and filtered several times. The washed residue (9) was 180 gms. of wet cake of "Product" gypsum (CaSO4 2H2O) of a grade acceptable in the manufacture of cement. The aggregat@ filtrate weighing 1382 gma comprised of acid mixture containing 21.037% W/@ P205 and 11.234% 'w/W H25iF6. The aggregate filtrate (1382 gms) was divided into two portions - one (11) weighing 181 gms. and the other (10) weighing 1201 gms. The smeller portion (11) weighing 181 gms. was concentrated in the concentration unit (12) to get T2 gms of "Product" phosphoric acid (14), containing 52% W/W P2Q5, and 109 gms of liquor (13) containing 16.789% W/W H2SiF6 by scrubbing and recycling it. The recovery of H2SiF6 was 90%. The 109 gms of liquor (13) was separately concentrated. to get 67 gms- liquor containing 26.024% W/W H2;iF6 of which 62 gms were added to. the portion (10) containing 1201 gms of the aforesaid filtrate to get 123 gins of acid mixture(15) for being recycled to the reactor (3) for a fresh sample of 200 gms of rock phosphate. The recovery of P2O5 from rock phosphate to "Product" phosphoric acid was 93%. EXAMPLE 5 : 200 gms. of unbeneficiated coarse Rock Phosphate (1) with particle size a to +25 mesh from Jhabua mines of Madhye Pradesh (India) was selected which, in analysis, showed the following composition: P2O5 33 % CaO 45.20 % F 3.20 % SiO2 15 % Fe2O3 + Al2O3 2.40 % CO2 1.00 % NaCl 0.10 % SO3 0.40 % The Hock Phosphate sample was reacted with 2090 gins. of acid mixtur@ containing 20.0% P2O5 W/W, 11.91% H2SiF6 W/W and 0.5% H2SO4 W/W at 70 C. for a period of 2 hours in a well stirred reactor (3). The slurry was filtered in filter (4) to remove 130 gms. of wet insoluble impuriti@@ comprising quartz, mud, carthy matter and gypsum (5). The filtrate and washings weighing 2260 gins. contained practically 98% Phosphate and 95% Fluorine content of the Rock Phosphate, in solution Analysis of the filtrate gave P2O5 = 21.357 % W/W Fluorine expressed as = 11.354 % W/W H2SiF6 This moss of filtrate and washings wee divided into two streass S Stress (6) of 1860 gms. and @tream (7) of 400 gms. The stroam (7) was concentrated by vacuum evaporation (9) at 10 @@ of m@rcury pressure and 80 C. temperature. When the P2O5 reached a l@v@l of 45% W/W, crystalline calcium silico fluoride dihydrate, CaSiF6, 2 H2O was thrown out. The slurry was cool@d (11) to room temperature and filter@d. (12) It gave @5 gms. of wet crude cake (14) of crystalline calcium silico fluoride dihydrate and 140 gms. of product phosphoric acid (13) containing 45% P205 W/W in the filtrate A total quantity of 175 g.e, of water (10) was distilled oft in the above process, The recovery of P2O5 from Rock Phosphate to product acid was about 95%. The 85 gins. cake (14) of wet crude, crystalline, calcium silicofluoride dihydrate, CaSiF6#2H2O, was then added into a well stirred crystalliser (8) along with the major stream (6), containing 1860 g.e. of the aforesaid filtrate from the earlier stage (4) and was reactad with 155 get of 98.5% W/W H2SO4 (2) which was simultancou@ly added to the same crystalliser (8) at 65 C. temperature, during a cour@e of 3 hours. On filtration and washing (15), this reaction gave 300 gms. of wet gypsum cake, CaSO4#2H2O(16). This gypsum was dazzling white in colour and contained a maximum of 0.3% P2O5 and 0.25 F impurities on dry basis. This is of a quality as desired for it@ use in cement manufacture. This stap also resulted in a filtrate comprising 2000 gms. of acid containing 20.9% W/W P2O5 and 12.54% W/W H2SiF6. This filtrate after suitable dilution with 90 ml wash water resulted in 2090 gms. of racycl@ acid containing 20% W/W P2O5 and 12.0% W/W H2SiF6. The said mixture was recycl@d (17) to the r@actor (3) for a fr@sh lot of 200 gms. of Rock Phosphate. EXAMPLE 6 : In this example, the Ruck Phosphate selected has a lower p@rcentage of P2O5 and @ higher perc@ntage of silic@ than in the example 1. 200 gms. of low grade unb@n@ficiated coarse Rock Phosphate (1) from @habu@ mines of Madhy@ Pr@d@@h (Indi@) with particl@ @iz@ -8 to +25 @@sh and containing high silice impuriti@@ and low P2O5 and other constituent@ @@ specified in the analysis given b@low : :- P2O5 20.04 % CaO 26.65 % Fe2O3 + Al2O3 4.77 % F 2.00 % SiO2 42.32 % LOI at 1000 C. 2.89 % was reacted with 1263 gms. of recycled acid mixture containing 20% W/W P205, 11.96% W/W H2SiF6m and 0.5% W/W 0 H 2S04 at 70 C. for a period of 2 hours in a well stirred reactor (3). The slurry was filtered in filter (4), to remove 170 gms. of wet insoluble impurities comprising quartz, mud, earthy matter and gypsum (5). The filtrate and washings weighing 1393 gms contained practically 96% phosphate and 90% fluo-, rine content of the Rock Phosphate in solution. The analysis of the- filtrate gave P205 : 20.90 % W/W Fluorine expressed as H,SiF 11.17 % W/W This mass of filtrate and washings was divided into two streams : Stream (6) containing 1153 gms.. and stream (7) containing 240 gms. The stream (7) was then subjected to concentration by vacuum evaporation (9) at 10 mm of mercury pressure and 80 C. temperature. When the concentration of P 205 reached a level of 45% W/W, crystalline calcium silicofluoride dihydrate CaSiF6.2H20, was thrown out. The slurry was cooled (11) to room temperature and filtered (12) off to give 50 gms. of wet crude cake (14) of crystalline calcium silicofluoride dihydrate and 83 gms. of Phosphoric Acid (13) containing 45 per cent P205 W/W in the filtrate as the product sought by this invention. A total quantity of 107 gms. of water (10) was distilled off in the above process. The recovery of P 205 from Rock Phosphate to product phosphoric acid was about 93% The 50 gms. cake (14) of wet crude crystalline calcium silicofluoride dihydrate, CaSiF6, 2H20, was then added into a well stirred crystalliser (8) along with the major stream (6) containing 1153 gms. of the aforesaid filtrate from the earlier stage and was reacted with 94 gms. of 98.5% W/4/H2S04 (2) which was simultaneously added to the same crystalliser at 650C temperature during a course of 3 hours. On filtration and washing (15) this reaction gave 180 gms. of wet gypsum cake, CaSO4.2H2O (16). This gypsum was dazzling white in colour and contained a maximum of 0.3% P205 and 0.2% F as impurities on dry basis. Such gypsum is of a quality as desired for its use in cement manufacture This last step alsa resulted in a filtrate comprising 1238 gms. of acid containing 20.425% P2O5 and 12.207% W/W H2SiF6. The said filtrate after suitable dilution with 25 ml. of wash water resulted in 1263 gms. of acid mixture containing 20.0% W/W P2O5 and 11.96% W/W H2SiF6. The said mixture was recycled to the reactor (3) for a fresh lot of 200 gms. of Rock Phosphate.

Claims: CLAIMS 1. A process to manufacture from rock phosphate commercially acceptable phospnoric acid end gypsum comprising reacting coarser samples of rock phosphate with a mixture of phosphoric acid and fluosilicic acid with a minute quantity af sulphuric acid at a temperature from ambient to 100 C. until the phosphate and fluorine contanta in the rock phosphate are substan- telly dissolved, the resulting slurry being fed into a crystallisar containing slurry fro previous hatch, the slurry being reacted in the crystals liser with sulphuric acid, the reaction in the crystalliser being continued till gypsu-crystal formation ia complete, the crystalliser contents being filtered and the residue containing substantially gypsum crystals being washed several times, the filtrate and washings containing a mixtures of phosphoric acid@fluosilicic acid, being divided into two unequal portions* the smaller portion containing P205 esquivalent" to that contained in ths rock phosphate at the beginning of the process, the smaller portion being concentrated to give phosphoric acid, the fluosilicic acid evolved during the concentration process being scrubbed and mixea with the larger portion, the last mentioned mixture being recycled to a fresh quantity of rock phosphate to repeat the process 2. A process to manufacture from rock phosphate commercially acceptable phosphoric acid and gypsum as claimed in Claim 1 wherein the slurry produced by the reaction of rock phosphate with the mixture of phosphoric acid and fluosilicic acid containing a minute quantity of sulphuric acid is filtered to removed insoluble impurities and the filtrate and washings of the resioue are fed into the crystalliser containing slurry from previous batch. 3. A process to manufacture from rock phosphate commercially acceptable phosphoric acid and gypsum as claimed in claim 2, wherein the filtrate and washings of the residue are divided into two portions, the smaller II portion containing P 205 equivalent to that containd in the rock phosphate at the beginning of the process, the smaller portion being concentrated and cooled and filtered, the residue being wet calcium silicofluoride end the filtrate being product phosphoric acid,. the cake of wet calcium ailicofluoride being added to- the aforesaid larger portion in a crystalliser containing slJrry from previous batch and sulphuric acid being added into withe crystalliser, the reaction in the crystalliser being contint:cd till the gypsum crystal formation is complete,. the gypsum crystals being filtered and washed, the filtrate being recycled to a fresh quantity af rock phosphate to repeat the process. 4. k. process for the manufacture of gypsum and phosphoric acid 5from rock phosphate, which process comprises treating rock phosphate with fluosilicic acid optionally together with phosphoric acid to solubilise the phosphate content thereof, regenerating fluosilicic acid and precipitating gypsum by treating at least part of the product so obtained with sulphuric diacid, separating out the gypsum, separating out product phosphoric acid and re-cycling the regenerated fluosilicic acid to treat further rock phosphate. 5. A process as claimed in claim 4, wherein at least part of the solution obtained from the solubilisation step is concentrated Suntil calcium silicofluoride precipitates. 6. A process as claimed in claim 5, wherein only a portion of the solution obtained from the solubilisation step is concentrated to precipitate calcium silicofluoride, the mother liquor remaining after precipitation constituting the product phpsphoric acid and the precipitated calcium silicofluoride being passed to the sulphuric acid treatment step. 7 A process as claimed in claim 4r wherein substantially the whole of the solution obtained from the dissolution step is treated with sulphuric acid and the gypsum precipitated thereby- is- separated from the slurry so obtained 8 A process as claimed in claim 7, wherein the product phosphoric acid is derived by scrubbing at least a portion of the liquor remaining after the sulphuric acid treatment step. 9. A process as claimed in any one of claims 4 to 8, wherein the product of the solubilisation step is filtered to remove undissolved impurities prior to fle sulphuric acid treatment 10, Phosphoric acid and/or gypsum obtained from a process as claimed in any one of claims 1 to 9.

Inventors: PUROHIT, GURURAJ YALGURDRAJ, VAIDYA, MANOHAR, VYAS, RADHESHYAM, VAIDYA, MANOHAR 4 TAKSHASHEELA CO-OP HOUS. SOC.
Applicants: DHARAMSI MORARJI CHEM CO LTD
Application year: 1983
Main classification: C01B25
IPC codes: C01F11, C01B25