Title of Invention

"AN ECO-FRIENDLY PROCESS FOR MAKING EPSOM AND GYPSUM"

Abstract

An eco-friendly process for making epsom (MgSO4.7H2O) and gypsum (CaSO4.2H2O) is provided. Froth flotation beneficiation of low-grade rock phosphate containing 14 to 19 percent P2O5 generates considerable quantity of tailings that contain 5 to 6 percent of P2O5 and other constituents like CaO, MgO that are potentially useful for crops and plants. An eco-friendly process is developed for making good quality Epsom and Gypsum from these final carbonate tails (FCT). Leaching of FCT is done with dilute sulphuric acid and is followed by evaporation and crystallization. The final product obtained is in good yield and quality as compared to the parameters set by FCO. A mixture of magnesium ammonium phosphate and ammonium sulphate is obtained as by-product.

Full Text

Field of the invention The present invention relates to a process for making Epsom (MgSO4.7H2O) and Gypsum (CaSO4.2H20). More particularly, the present invention relates to an eco-friendly process for the production of epsom and gypsum, and utilization of gases released in the process. Background and prior art of the invention Reference may be made to WO/2001/085412, wherein for the production of high-purity gypsum, a calcium source is reacted with a mineral acid in a water phase to have the calcium source sufficiently dissolved as a calcium salt in the water phase, separating and removing undissolved residue from a resulting water phase, adding sulfuric acid to a water phase, which has been obtained by the removal of the undissolved residue, to crystallize gypsum, and separating the crystallized gypsum from the water phase. In this process, a low-purity calcium source is used. Reference may be made to US 6,475,313, wherein a process for making gypsum board is provided, the process comprising feeding a paper backing sheet and a fiberglass or plastic woven or non-woven scrim material in alignment to a board forming station, separating the paper and the scrim, feeding a high density calcium sulfate hemi-hydrate slurry into the trough formed between the paper and the scrim, and subsequently compressing the paper and the scrim into contact whereby the high density slurry is forced through the scrim, completely encapsulating the scrim in the high density slurry. As a result of this unique process, excellent bond is developed between the paper, the high-density gypsum layer and the foamed gypsum core. The gypsum board has improved through-penetration strength. Reference may be made to US 6,042,665, in which gypsum-based composite boards or shaped bodies can be manufactured from a mixture comprising calcium sulfate dihydrate and water, and optionally reinforcement materials or fillers, and conventional additives, by shaping the mixture to a raw form and hardening the raw form with water at a pressure exceeding the saturation pressure of calcium sulfate dihydrate. Reference may be made to US 4,966,739, in which the gypsum fiber boards are formed or molded from a mash containing calcium sulfate dihydrate and fibrous material. By heating and subsequently cooling the boards, the dihydrate is first converted into the hemi-hydrate and subsequently recrystallized again to the dihydrate. Known processes require day line setting times which are economically disadvantageous. According to the present invention these times are shortened by pulling or drawing water, an aqueous solution or a water containing mixture through the boards after the cooling step. Advantageously a setting accelerating agent can be dissolved in the water. By these features the setting time can be shortened to less than two hours. By addition of a binding agent, e.g. starch, to the fluid drawn through the boards the strength of the boards is increased. All of the patents cited above relate to processes for obtaining gypsum, which is suitable for board making purposes. None of the literature in prior art teaches any process for producing Epsom by using a waste mineral material as described in present invention, which was hitherto-fore creating environmental problems, but now is being utilized in making industrially useful products. Objects of the invention The main object of the present invention is to provide an eco-friendly process for making Epsom and Gypsum. Another object of the invention is to provide a process for making Epsom and Gypsum by utilizing final carbonate tails (FCT) of Jhamarkotra Rock Phosphate froth flotation beneficiation plant. A further object of the invention is to provide a process for making Epsom and Gypsum that does not produce any harmful by-products. Statement of the invention Accordingly, the present invention provides an eco-friendly process for making epsom and gypsum, the said process comprising the steps of leaching final carbonate tails of Jhamarkotra rock phosphate ore with sulphuric acid at around 60 to 80 degree C for about 3 to 4 hours to obtain slurry containing magnesium sulphate in solution and gypsum in solid form; filtering out slurry as obtained to separate out gypsum from solution; evaporating the solution and cooling to 10 to 30 degree C to obtain crystals of epsom; removing epsom by filtration from solution; neutralizing the remaining solution with ammonium hydroxide to obtain a mixture of magnesium ammonium phosphate and ammonium sulphate as by-products; scrubbing off the evolved gases with water spray to remove HF and compressing & cooling the remaining CO2 to obtain dry ice for industrial utility or absorbing in ammonia solution to get ammonium carbonate. Detailed description of the invention At the outset of the description that follows, it is to be understood that the ensuing description only illustrates a particular form of this invention. However, such a particular form is only exemplary embodiment and without intending to be understood as exemplary teaching of the invention and not to be taken restrictively. The raw material for the process of this invention is obtained from Rajasthan State Mines Minerals Ltd., Udaipur, which has captive rock phosphate mines at Jhamarkotra and the company also has a beneficiation plant. The plant has an installed capacity to process 3000 TPD (tonnes per day) of low-grade ore. During the process, two types of tailings are produced: Final Carbonate tails (FCT) and Bulk Circuit tails (BCT). The carbonate tail generated amounts to about 50 percent by weight of ore processed and contains 5 to 8 percent P2O5, 16 to 19 percent MgO and 32 to 35 percent CaO. At present mill tailings of nearly 1500 to 1800 tonnes per day are being dumped to tailing dams as wastes, which is creating environmental problems in disposal area. FCT contains good amount of dolomite, which can be used to produce useful products, which are having good industrial applications. The tailing is in the form of slurry and has a grain size of 74 microns. The dried tailing is the starting material for this process. The mineral appendages of Jhamarkotra rock phosphate beneficiation plant are the main waste material. Quantity of the waste called 'Final Carbonate Tails (FCT)' is about 55 to 60 percent of the rock processed. It contains mainly dolomite and 5 to 8 percent P2O5. A typical analysis of the dolomite tailings (waste) is given below at Table -1. Table -1 (Table Removed) Leaching of the FCT: The FCT is leached with adequate quantity (1:4) of 30 percent sulphuric acid at around 60 to 80 degree C temperature for about 3 to 4 hours in a tank reactor with an agitator. The following reactions take place during leaching; conversion rate is about 98 percent: CaCO3.MgCO3(s) + 2 H2SO4 (1) —-> CaSO4 (s) + MgSO4 (sol) + 2H2O (1) + 2CO2 (g) Ca10(PO4)6F2(s) + 10 H2SO4(1) + 20 H2O — > 6 H3PO4(1) + 10 CaSO4.2H2O (s) + 2HF (g) Filtration of the leach materials: The reactor product contains magnesium sulphate in solution and gypsum in solid form. The slurry is filtered to separate out gypsum from the solution. Drying of Gypsum: The gypsum is dried out at 100 degree C to remove free moisture in a rotary drier / solar tunnel dryer. Further drying at 120 degree C gives plaster of Paris and anhydrous calcium sulphate on further drying at 190 degree C. Evaporation and Crystallization of solution: The solution containing magnesium sulphate is evaporated, to about 40 percent concentration w/w having specific gravity of 1.35 g/cc, in an evaporator crystallizer and cooled to 20 to 30 degree C to get first crop of the crystals of MgSO4.7H2O. On further cooling the remaining solution to 10 to 15 degree C another crop was obtained. The Epsom crystals are separated from the liquor by centrifugal separator, purified and dried. Neutralization of the remaining mother liquor: The remaining mother liquor from the centrifuge is neutralized with ammonium hydroxide to pH of 8.0 to get a mixture of magnesium ammonium phosphate and ammonium sulphate as by product, which are crystallized after evaporation. Scrubbing of gases of reaction: The reaction gases from reactor tanks contain mainly CO2 and a little of HF gas. HF is removed by scrubbing the gas with water spray and the remaining CO2 gas is compressed to get liquid CO2, dry ice for industrial utility. The final products produced i.e. epsom is of Fertilizer Control Order (FCO) quality and Gypsum is of 94 to 96 grade. Recovery values of CaO, MgO are about 98 percent, and yield of MgSO4 with respect to that present in the leach solution is about + 70 percent. Gypsum obtained can be used for producing ammonium sulphate, plaster of Paris and other calcium products. In a preferred embodiment of the invention, the raw material final carbonate tails (FCT) used has a composition of P2O5 about 7.85 percent, CaO about 33.80 percent, MgO about 16.25 percent, SiO2 of about 1.80 percent, R2O3 of about 00.45 percent and LOI (loss on ignition) of about 36.50 percent by weight. In another embodiment of the present invention, the ratio of FCT to 30 percent sulphuric acid mixed for leaching is preferably from 1:3.5 to 1:4.5, more preferably about 1:4. In yet another embodiment of the invention, the gypsum obtained can be dried out to obtain plaster of paris and anhydrous calcium sulphate. In a further embodiment of the present invention, the drying temperature used for obtaining gypsum is in the range of 90 to 100 degree C. In yet another embodiment of the invention, the base used for neutralizing the mother liquor is ammonium hydroxide. In a further embodiment of the invention, the conversion rate of raw material to the final products is about 98 percent. Examples The following examples are for the purposes of illustration only and therefore should not be construed to limit the scope of the present invention: Example 1 Slurry was prepared by adding 800 grams of water to 1000 g of carbonate tails using a stirrer. To this pulp, 2900 grams of 30 percent sulphuric acid was added slowly in a time period of '/a hour with good agitation with motorized agitator, later 320 grams of 98 percent sulphuric acid was added slowly in a time period of '/a hour with continued agitation and addition of 1000 grams of water. Agitation was continued for total 3 hours from the start. During this reaction, hot CO2 gas evolved violently. A temperature of 60 degree C was maintained which helped in good release of CO2 and to get higher concentration of MgSO4 solution, as solubility of MgSO4 increases with increase in temperature. Hot conditions also helped in reducing solubility of CaSO4, which decreases with increase in temperature. Some water also got evaporated with CO2. After reaction, total pulp was filtered and filtrate (solution of MgSO4) was collected for evaporation concentration and crystallization. The precipitate CaSO4.2H2O has good amount of absorbed MgSO4, which was washed with copious amount of water, so that only traces are left in the gypsum cake. About 1100 g of gypsum dihydrate was obtained after drying at 100 degree C; further drying to 190 degree C gave about 850 g of CaSO4 anhydride. Example 2 About 16 to 20 percent of magnesium sulphate solution was obtained after filtration of the gypsum cake and wash liquor contained 3 percent MgSO4. By evaporation, about 40 percent w/w concentration solution of specific gravity 1.35 was obtained from these solutions. The concentrated solution was cooled to 25 degree C to get first crop of crystals of epsom salt. Then it was cooled further to produce another crop at 10 degree C. Thus the yield of epsom salt was obtained up to an extent of 70 percent. The remaining liquor contained P2O5 leached from the tails and left out sulphuric acid and 225 g of MgSO4.7H2O. A comparative analysis of quality of Epsom produced by the process of this invention to the quality specified by Fertilizer Control Order (FCO) is as: 5. No. Details FCO Specifications Epsom produced in the lab 1. [ Form Free flowing crystals Free flowing crystals (Table Removed) Advantages of the process: 1. These industrial products are produced from a waste material that is creating environmental problems. 2. By-products ammonium magnesium phosphate, ammonium carbonate are fertilizers and fluorosilicic acid is an industrial material. We claim: 1. An eco-friendly process for making epsom and gypsum, the said process comprising the steps of: a)leaching final carbonate tails of Jhamarkotra rock phosphate ore with 30 percent sulphuric acid at around 60 to 80 degree C for about 3 to 4 hours to obtain slurry containing magnesium sulphate in solution and gypsum in solid form; b)filtering out slurry as obtained in step (a) to separate out gypsum from solution; c)evaporating the solution as obtained in step (a) and cooling to 10 to 30 degree C to obtain crystals of epsom; d)removing epsom by filtration from solution and washing with hot water of step (c); e)neutralizing the remaining solution of step (d) with ammonia solution to obtain a mixture of magnesium ammonium phosphate and ammonium sulphate as by-product; f)scrubbing off reaction gases with water spray to remove HF and compressing remaining CO2 to obtain dry ice for industrial utility. 2. An eco-friendly process for making epsom and gypsum as claimed in claim 1, wherein the raw material final carbonate tails used has a composition of P2O5 about 7.85 percent, CaO about 33.80 percent, MgO about 16.25 percent, SiO2 of about 1.80 percent, R2O3 of about 00.45 percent and loss on ignition of about 36.50 percent by weight, where R stands for aluminum and/or iron. 3. An eco-friendly process for making epsom and gypsum as claimed in claim 1, wherein the ratio of final carbonate tails to 30 percent sulphuric acid mixed for leaching is from 1:3.5 to 1:4.5. 4. An eco-friendly process for making epsom and gypsum as claimed in claim 1, wherein the gypsum obtained in step (b) is dried out to obtain plaster of paris and anhydrous calcium sulphate. 5. An eco-friendly process for making epsom and gypsum as claimed in claim 1, wherein the drying temperature used for obtaining gypsum is in the range of 90 to 100 degree C. 6. An eco-friendly process for making epsom and gypsum as claimed in claim 1, wherein the base used for neutralizing the mother liquor is ammonium hydroxide. 7. An eco-friendly process for making epsom and gypsum as claimed in claim 1, wherein the conversion rate of raw material to the final products is about 98 percent. 8. An eco-friendly process for making epsom and gypsum substantially as hereinbefore described with reference to the examples.

Documents:

1351-del-2007-Abstract-(11-09-2014).pdf

1351-del-2007-abstract.pdf

1351-del-2007-Claims-(11-09-2014).pdf

1351-del-2007-claims.pdf

1351-del-2007-Correspondence Others-(11-09-2014).pdf

1351-del-2007-Correspondence Others-(17-10-2014).pdf

1351-del-2007-Correspondence Others-(20-06-2014).pdf

1351-DEL-2007-Correspondence-Others(02-09-2009).pdf

1351-del-2007-correspondence-others.pdf

1351-del-2007-Description (Complete)-(11-09-2014).pdf

1351-del-2007-description (complete).pdf

1351-del-2007-form-1.pdf

1351-DEL-2007-Form-18.pdf

1351-del-2007-Form-2-(11-09-2014).pdf

1351-del-2007-form-2.pdf

1351-del-2007-form-26.pdf

1351-del-2007-form-3.pdf

1351-del-2007-form-5.pdf