中国有色冶金

The third generation sulfuric acid rare earth separation process uses a lot of magnesium ions, which produces a lot of transformed magnesium sulfate wastewater. The wastewater contains SO^2-₄, saturated calcium sulfate, Mg²⁺, oil and suspended solids, and the water quality is unstable, so it is difficult to treat. Traditional lime neutralization method and traditional evaporation concentration method have some problems, such as high treatment cost and low efficiency, which lead to the treatment of rare earth magnesium sulfate wastewater has been in a blank state. This paper proposes a green process route of “calcium hydroxide neutralization-reuse of rare earth leaching”, and conducts research from three aspects: neutralization and impurity removal of magnesium sulfate wastewater, rare earth recovery rate in the neutralization liquid leaching process of sulfate rare earth, and moisture content of tailings. The following main conclusions are obtained. The process of neutralizing magnesium sulfate wastewater by calcium hydroxide is mainly affected by the pH value of the solution， when the wastewater pH is 9.5, the content of SO^2-₄ is 80.5g/L, the content of Mg²⁺ decreases to 14.7g/L, and the addition of calcium hydroxide is the smallest. The pH value of neutralization solution has a great influence on the water content of leaching tailings. When the pH value is large, the water content is low and the cake forming degree is good, when pH=9.5, the leaching rate of rare earth did not decrease obviously, and the water content of rare earth tailings reached 42.3% (the water content required for production was less than 43.0%), which reached the standard of entering the tailings pond. Conventional stirring is adopted in this process, because when the concentration of sulfate radical is more than 85.0g/L, the soluble complex formed by Ce⁴⁺, SO^2-₄ and Mg²⁺ is destroyed by high-shear stirring, so that tetravalent cerium and magnesium sulfate wastewater form flocs to precipitate, blocking the water flow channel of filter cake and affecting solid-liquid separation.Using this method to neutralize magnesium sulfate wastewater and then reuse it in rare earth calcine leaching process, rare earth leaching is not affected, and magnesium sulfate wastewater can be recycled.