Process for producing high-purity magnesium oxide and lithium salt by using salt lake old brine

Abstract

The invention discloses a process for producing a high purity magnesium chloride, which is as follows: the crystal magnesium chloride separated from the salt lake old brine which is evaporated and concentrated or the residual liquid after the crystallization is processed by primary pyrolysis, counter moisture absorption and secondary pyrolysis. The invention also discloses a process for jointly producing the high purity magnesium chloride and the lithium salt, which is as follows: after the salt lake old brine is evaporated, concentrated and crystallized, the obtained residual liquid is processed by dehydration, primary pyrolysis, counter moisture absorption, secondary pyrolysis, gasification and calcination. The invention is widely adapted to the different salt lake brine, the extraction ratio of magnesium chloride and lithium salt is high. The invention is applied to magnesium chloride production alone, and is also applied to lithium salt joint production, thus the presently difficult technology problem of magnesium-lithium separation is completely resolved at home and abroad. The invention has the advantages of low requirement process, simple equipment, simple principle and easy mastery, short process for single product, low cost for comprehensive productions, .The invention is adapted to the production requirement of different size, and provides the new approach for comprehensive development of the salt lake in Chinese western region.

Description

technical field [0001] The invention belongs to the field of inorganic salt chemical industry, and in particular relates to a production process for preparing high-purity magnesium oxide and lithium salt by using old brine from salt lakes as raw materials. Background technique [0002] At present, the methods of producing magnesium oxide from brine at home and abroad mainly include: [0003] 1 brine-soda ash method; [0004] 2 brine-ammonium bicarbonate method; [0005] 3 brine-ammonia method; [0006] 4 brine-lime method; [0007] 5 Brine-spray pyrolysis method; (see "Magnesium Compound Production and Application", pp. 57-61, pp. 128-129), "Sea Lake Salt and Chemical Industry", Vol. 20, No. 2, pp. 26-29, Volume 20, Issue 3, Pages 37-38). [0008] There are many methods used at home and abroad to prepare lithium salt from brine, mainly including: [0009] 1. Brine-aluminate precipitation method; [0010] 2. Organic solvent extraction; [0011] 3. Ion sieve method (io...

AI Technical Summary

Problems solved by technology

[0018] 1. Before the brine enters the factory, a large amount of lime milk should be used to remove the sulfate radicals in the brine (for the brine containing sulfate radicals). In this process, the loss rate of lithium is generally about 30%. Not only that, Also add new impurities to the brine (Ca 2+ ions), affecting the final product quality

[0019] 2. Due to the change of time, the composition of the brine entering the factory changes greatly, especially the content of lithium, which changes in multiples or several times, resulting in the production process of the factory directly affecting the production capacity of the factory due to the change in the ratio of lithium and magnesium. cost out of control

[0020] 3. Magnesium chloride dihydrate is only calcined and pyrolyzed once. The content of the obtained crude magnesium oxide is about 57%, and the conversion rate of magnesium chloride is about 75%. No, other chemical methods are needed to produce lithium salts. In addition, when removing sulfate radicals, calcium enters brine, generates calcium oxide during calcination, and generates calcium hydroxide when adding water to wash, which has a direct impact on the quality of magnesium oxide.

[0021] 4. Due to the incomplete separation of magnesium and lithium in the front, there are still a large amount of magnesium ions in the liquid after the separation of solid magnesium oxide, so it is necessary to add soda ash (or other alkalis) to adjust the pH value of the liquid to 10.4-10.8. remove Ca 2+ , Mg 2+ ion, the resulting precipitate has no economic value, the most important thing is that it consumes soda ash and makes the loss rate of lithium about 30%

[0022] The above problems are the deficiencies of the existing traditional technology. In short, the lithium salt yield of the existing traditional technology is not high, generally around 30%, the ratio of lithium to magnesium is large, and the production cost is high.

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