Title of Invention

"A PROCESS FOR THE RECOVERY OF REFRACTORY GRADE MAGNESIUM FROM MARINE BITTERN THROUGH DESULPHATION ROUTE"

Abstract

The invention relates to a process for the recovery refractory grade magnesia from marine bittern. The increased demand for high purity magnesia as basic refractory has been prominent in all over the world since two decades. The present process is based on the formation of magnesium chloride during the process of desulphation by the addition of stoichiometric quantity of calcium chloride to bittern. As a result, sulfate ions are removed in the form of gypsum which was filtered out. The desulphated bittern is again treated with stoichiometric amount of ammonia and ammonium carbonate thus forming magnesium carbonate. The purity of MgO is 99.3 % and CaO/SiO2 ratio is also favourable. The process is not energy intensive and does not involve any boron removal steps. The high pure magnesia thus obtained in this process could be suitable for manufacturing high quality magnesite bricks for our consuming industries.

Full Text

The present invention relates to a process for the recovery of refractory grade magnesium from marine bittern through desulphation route This invention particularly relates to a process for the recovery of magnesium as magnesium carbonate from bittern, after removal of sulphate ions from bittern. Background of the invention In last few decades there is severe technological changes, which have occurred in iron and steel industry resulting in a change of refractory practice. The traditional open-hearth furnace and Bessemer converter have been replaced by the basic oxygen converter (BOF) and the electric arc furnace. This change has increased the demand for basic refractories, particularly, high purity magnesia. Magnesite ores have been usually upgraded by physical means, magnetic separation, heavy media separation or flotation. However, these techniques are having limitations, which often restrict in obtaining the desired quality product. The chemical leach route, although produces high-grade product can create significant corrosion problems by the use of strong acids. The direct decomposition of the leach liquor, viz. magnesium chloride is also energy intensive. Seawater magnesite is also a promising route to obtain the high-grade magnesia. Magnesium, which is present in seawater to the extent 1.3 g/1, is precipitated as magnesium hydroxide by the addition of lime or dolime. The processing route itself has the further disadvantage that large quantities of seawater must be handled and magnesium hydroxide is also difficult to filter. Moreover, boron contamination in trace also reduces the refractory properties significantly. Hence, a unique process that has not been covered so far has been developed to produce high purity magnesia from sea bittern, which is rich in magnesium salts. Reference may be made to various preparation methods of magnesium oxide, which is one of the most industrially useful compounds. These methods include preparation of Mg(0H)2 and MgCOs from brine & bittern of different densities. A few examples are given below. A process for preparation of Mg(0H)2 from residual natural brine during salt production comprising of two steps is described by Rabadzhieva et al . The first step includes desulphation using CaCl2 crystal or its solution and the second precipitation of Mg(0H)2 by adding milk of lime and dolomite milk [Rabadzhieva, D; Ivanova, K; Balarev, Kh; Trendafelov, D; Zh. Prikl. Khim., 1997, 70(3), 375-380]. Mg(0H)2 of 99% purity is prepared from waste bittern by adding commercial CaCl2 for desulphation followed by the addition of lime water [ Nabi, Safura N; Ali, Junab; Moliah, Shirajuddin; Bangladesh J. Sci. Ind. Res. 1993, 28(2), 33-7]. In another process CaSO4 is precipitated from cold 5% MgSO4 solution by CaCl2, and Mg(0H)2 is precipitated from the resulting MgCl2 solution. The precipitate is filtered immediately after precipitation and dried in sun before igniting [Kh.B. Medinskii and M.D. Trusov; J. Chem. Ind. (Moscow) 12, 697-9(1935)]. Seawater treated with CaCl2 gives easily filtered a- gypsum and the filtrate after concentration give NaCl. The liquor obtained after NaCl filtration further treatment with Ca(0H)2 separates out Mg(0H)2 [Jezek, Stanislav Belg. 732,243, 28 Oct 1969, Appl. 28 Apr 1969. 7pp]. In another process brine is neutralised to pH 6-7.5 by adding 5-30% alkali solution (NaOH), preheating to 35 -1250C, and adding stoichiometric amount of 10-40% CaCl2 for removal of SO42- ions. The gypsum is settled at 40-100 °C for >1.5hr,filtered and the liquor is bleached with bleaching agent (NaCl). The bleached supematent is evaporated under atmospheric pressure and cooling yields white colour MgCl2 [Wang, shizhong; Li, shi, sun, kesue; Faming Zhuamli shenqing Gongkai shuomingshu CN 1,099,008 (CI. C.OIF5/3O) 22 Febl995, Appl 93,109,924,19 Aug 1993 Spp]. Bittern of 27 °Be'after removal of SO42 ions using 18g CaCl2/l is treated with calcined dolomite (calcined at 1300-500 °C, for 2hrs) results in a recovery of 96% of Mg containing 2.6%CaO [Bakr, M.Y.; El-Abd, H.; Sprechsaal keram., Glas, Email, Silicate 1971,104(11), 494,496,498 ]. The desulphation of the brine of Sivash before and after the beginning of settling of NaCl can be carried out by Cl-Ca lye. Brine MgO suitable for refractories having of calcined dolomite at 700-800° in 2steps. First to precipitate SO/" as CaSO4.2H20 & second to precipitate Mg2+ as Mg(0H)2 [Shoichiro, Nagai; Yasushi, Fukumori and Yoshio, Togasaki; J, Ceram. Assoc. Japan 59, 456-61 (1951)]. In another example dolomite mixed with 3-5% limonite calcined at 9000C for 2hrs was mixed with diluted bittern of 32 °Be' to precipitate magnesium as Mg(0H)2 which contains 4-5% lime. Good magnesia clinker of The main drawbacks in all the above conventional processes are the non-formation of easily settled, washed and filtered magnesium hydroxide of desired purity. Generally, magnesium hydroxide is prepared from magnesium salt by the reaction with an alkali and other liming agents. While the chemical reaction involved is relatively simple, the practical application has been attained by overcoming insurmountable operating difficulties. Before lime treatment limestone is hard burned in two size ranges, 45-19 mm and 19-6 mm to reduce residual unbumed CaCO3 below 0.5%). The burned lime is slaked with decarbonated fresh water in a continuous slaker unit. Lime was considered as an undesirable impurity because of its tendency to form low melting compounds with the silicon, iron, aluminum and chromium oxide present in refractory material. In direct seawater process it is always necessary to remove dissolved bicarbonate ion from the seawater. Otherwise undesired lime contamination will be carried along with the magnesium hydroxide precipitate. Excess alkali was also used for the magnesium hydroxide precipitation to suppress the adsorption of boron which occurs in seawater and many inland brines. The limiting value of B2O3 content is 0.05 % to secure good hot strengths in magnesia refractories. The main objective of the present invention is to provide a process for the recovery of magnesium from marine bittern as magnesium chloride and further , conversion of magnesium present in the bittern to basic magnesium carbonate, which obviates the drawbacks as detailed above. Another objective of the present invention is to provide a novel process for the precipitation of magnesium from marine bittern as an easily settable and filterable form. In another objective of the present invention the carrier reagent, viz Ammonia used for precipitating the entire magnesium values present in the desulphated bittern can be recovered and recycled. In yet another objective of the invention the process does not involve external addition of dolomite. In yet another objective of the present invention is that process is not energy intensive and only involves addition of carrier reagents, stirring, filtration, dissolution, precipitation and drying. Novelty of the invention lies in the formation of magnesium carbonate by using ammonium hydroxide and ammonium carbonate in the process. Accordingly, the present invention provides a process for preparation of refractory grade magnesia from marine bittern through desulphation route which comprises: a) precipitation of gypsum through desulphation by adding stoichiometric amount of calcium chloride in the ratio of sulphate to calcium chloride 1:1.04, b) stirring the reactants in step a) at a temperature of 34-75°C for a period ranging 3-4 hour, c ) cooling the reactants in step b) to room temperature of 27-34°C and filtering to recover gypsum, d) treating the desulphated bittern derived as filtrate in step c) with ammonium hydroxide and ammonium carbonate to precipitate magnesium carbonate in the ratio of magnesium in bittern : ammonium hydroxide :ammonium carbonate of 1:12.6:4.83 at a temperature range of 40-70°C for a period of 3-4 hours, e) filtering the hot precipitated magnesium carbonate in step d) and washing it with hot distilled water several times to remove dissolved impurities, f) drying precipitated magnesium carbonate in step e) at a temperature of 110-1200C and calcinating the dried magnesium carbonate at 900-1000°C for a period of 1 -3 hours to obtain the desired product. In an embodiment of the present invention, the reactant ammonium hydroxide and ammonium carbonate are added while stirring and precipitation of magnesium carbonate is carried out preferably at a temperature of 40-70°C for a period of 3-4 hours. In an embodiment of the present invention, the recovery of magnesium as magnesium oxide from marine bittern is from 89 to 93 %. In yet another embodiment of the present invention, refractory grade magnesium recovered is 99-99.3 % pure. In yet another embodiment of the present invention during the formation of magnesium carbonate the ammonia used for the formation of magnesium carbonate is being generated and recycled. DETAILED DESCRIPTION OF THE INVENTION The present process has been developed with a view to produce a very high grade sintered magnesia and to avoid the disadvantages already experienced in the above mentioned processes. The salt industry in our country is generating a huge tonnage of waste bittern, which contains approximately 50.0 g/1 of magnesium. The concentration of magnesium increases with the increased concentration of bittern. The process is based on the removal of sulphate ions present in bittern by the addition of stoichiometric quantity of calcium chloride. The gypsum precipitated is separated out by filtration and the magnsium remains in the remnant bittern as magnesium chloride. The desulphated bittern is then treated with stoichiometric amount of ammonia and ammonium carbonate. The temperature is raised to 60-70 0C and the magnesium carbonate thus formed was filtered. The magnesium carbonate is washed thoroughly several times to remove other dissolved impurities. The magnesium carbonate is further dried and calcined. The purity of MgO is 99.3% and CaO/Si02 ratio is also favourable. There is no boron contamination and the bulk density is 3.35 gm/cc (sample fired at 1800 'C). The process is not energy intensive and does not involve any boron removal steps. The high pure magnesia thus obtained in this process could be suitable for manufacturing high quality magnesite bricks for our consuming industries. The process of this invention is illustrated by examples, which should not be construed to limit the scope of this invention. Example 1 Dalmia bittern 30 °Be'(Mg : 80.712 g/1, SO42-: 44.63 g/1) is used for the following experiments. To 250ml 30 °Be' bittern containing 20.178g Mg 8c 11.1575g SO42-fused solid CaCl2 of 11.6103 g is added with stirring noting the reaction temperature 34°C. The slurry is kept on a hot water bath to attain 75 °C reaction temperature and kept for 3h at this temperature. Then cooled to room temperature and filtered. The gypsum is washed with 30ml water and dried at 110 °C and weighed 13.8846g after drying. To the desulphated bittern 254.5ml of NH4OH (25%) is added with stirring. The temperature is 34 °C after addition of NH4OH. To the resulted slurry 97.366g solid (NH4)2C03 is added with stirring. The temperature was 39 °C after complete addition. The whole system is then kept on hot water bath till it attains 70 °C and kept for 3.Oh for complete precipitation of MgCOa. Filtered hot and washed further several times using 200ml warm water to make it free from other dissolved impurities. The MgCO3 obtained is dried at 110 °C and then calcined at 1000 °C for 2hrs to recover pure MgO. The recovery of magnesium as magnesium oxide is 91.00 % with respect to magnesium present in bittern. The purity MgO is 98.94% Example 2 To 1000ml of 30 0Be' bittern containing 80.712g Mg & 44.63g SO42-fused solid CaCl2 of 46.44g is added with stirring noting the reaction temperature 34 0C. The slurry is kept on a hot water bath to attain 75 °C reaction temperature and kept for 3hrs at this temperature. Then cooled to room temperature and filtered. The gypsum is washed with 100ml water and dried at 110 °C and weighed 57g after drying. To the desulphated bittern 1018ml of NH4OH (25%) is added with stirring. The temperature is 34 °C after addition of NH4OH. To the resulted slurry 389.5g solid (NH4)2C03 is added with stirring. The temperature was 40 °C after complete addition. The whole system is then kept on hot water bath till it attains 70 0C and kept for 3.0hrs for complete precipitation of MgCOs. Filtered hot and washed fiirther several times using 800ml warm water to make it free from other dissolved impurities. The MgCOs obtained is dried at 110 °C and then calcined at 1000 0C for 2hrs to recover pure MgO. The recovery of magnesium as Magnesium oxide is 93.00 % with respect to magnesium present in bittern. The purity of MgO is 99.30%. The main process advantages of the present invention are: 1) Bittern is desulphated by using Calcium chloride as carrier reagent. 2) Desulphated bittern, which is rich in Magnesium chloride, is converted to Magnesium Carbonate using Ammonia and Ammonium carbonate, which on calcination at 1000 0C yields magnesium oxide. 3) The purity of MgO is found to be more than 99%. 4) The magnesium oxide is free from Boron. No specific boron removal step is required. 5) The carrier reagent, viz. Ammonia used for precipitating the entire magnesium values present in the desulphated bittern can be recovered and recycled. 6) The process does not involve external addition of dolomite. 7) The process involved is not energy intensive and only involves addition of carrier reagents, stirring, filtration, dissolution, precipitation and drying. We Claim: 1. A process for the recovery of refractory grade magnesium from marine bittern through desulphation route which comprises: a) precipitation of gypsum through desulphation by adding stoichiometric amount of calcium chloride in the ratio of sulphate to calcium chloride 1:1.04, b) stirring the reactants in step a) at a temperature of 34-75°C for a period ranging 3-4 hour, c ) cooling the reactants in step b) to room temperature of 27-34°C and filtering to recover gypsum, d) treating the desulphated bittern derived as filtrate in step c) with ammonium hydroxide and ammonium carbonate to precipitate magnesium carbonate in the ratio of magnesium in bittern : ammonium hydroxide :ammonium carbonate of 1:12.6:4.83 at a temperature range of 40-70°C for a period of 3-4 hours, e) filtering the hot precipitated magnesium carbonate in step d) and washing it with hot distilled water several times to remove dissolved impurities, f) drying precipitated magnesium carbonate in step e) at a temperature of 110-120°C and calcinating the dried magnesium carbonate at 900-1000°C for a period of 1-3 hours to obtain the desired product. 2. A process as claimed in Claim 1, wherein the recovery of magnesium is 89 to 93% and 99-99.3 % pure. 3. A process for the recovery of refractory grade magnesium from marine bittern through desulphation route substantially as herein described with reference to the examples.

Documents:

473-DEL-2004-Abstract (23-10-2009).pdf

473-del-2004-abstract.pdf

473-DEL-2004-Claims (23-10-2009).pdf

473-del-2004-claims.pdf

473-DEL-2004-Correspondence-Others (23-10-2009).pdf

473-del-2004-correspondence-others.pdf

473-del-2004-correspondence-po.pdf

473-DEL-2004-Description (Complete) (23-10-2009).pdf

473-del-2004-description (complete).pdf

473-DEL-2004-Form-1 (23-10-2009).pdf

473-del-2004-form-18.pdf

473-DEL-2004-Form-2 (23-10-2009).pdf

473-del-2004-form-2.pdf

473-DEL-2004-Form-3 (23-10-2009).pdf

473-del-2004-form-3.pdf

473-del-2004-form-5.pdf