Method for preparing high-purity magnesium chloride hexahydrate from waste brine

Abstract

The invention provides a method for removing trace impurities in magnesium chloride by using waste brine discharged in potassium chloride production as a raw material by an improved two-stage recrystallization technique. Each stage of the crystallization technique comprises the following steps: 1) free settling, 2) natural evaporation and crystallization, 3) size-grading selective recycling, 4) filtration, (5) saturated magnesium chloride solution washing and the like. By using the method, trace impurities, such as boron, sulfur, ferrum and the like, in magnesium chloride can be reduced to less than 5 ppm, and the purity of the product magnesium chloride hexahydrate is higher than 99.5%. The invention has the characteristics of low energy consumption and low cost, is simple to operate, and is applicable to refining magnesium metal, flame retardant, magnesium hydroxide or any other raw material by an electrolytic process.

Description

field of invention [0001] The invention belongs to the field of preparation of chemical and smelting raw materials, in particular to a method for preparing high-purity magnesium chloride hexahydrate by adopting a low-cost natural recrystallization process, and then used as high-purity anhydrous magnesium chloride required for the preparation of electrolytic magnesium or for producing other high-purity magnesium salt products raw materials. technical background [0002] my country's Qinghai Chaerhan Salt Lake is rich in magnesium resources, with a reserve of 4 billion tons, ranking second in the world and accounting for 1 / 3 of the world's total reserves. At present, Qinghai Chaerhan Salt Lake discharges a large amount of waste brine during the production of potash fertilizers. According to incomplete statistics, the annual total output of potassium chloride in the Chaerhan Salt Lake area is about 3.5-4 million tons, and the waste brine that needs to be discharged during the ...

AI Technical Summary

Problems solved by technology

For example, patented methods such as ZL97114157.6 and ZL93109924.2 only remove sulfate radicals in a targeted manner, and cannot guarantee that the sulfur content will drop below 10ppm, and the content of other impurities such as B and Fe is still high; the method proposed by CN1134917 is to heat the brine to nearly Boiling point, keep warm and filter, then evaporate and crystallize

Due to the high content of impurity ions in the solution, it is difficult to ensure that the S, Fe, and B ions are all reduced to below 10ppm in one recrystallization, and it needs to consume a lot of energy.

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