Process optimization of magnesium removal from high-magnesium zinc sulfate solution by fluorination precipitation

Fluoride precipitation is considered one of the most effective techniques for magnesium removal in hydrometallurgy. However, this method has the problem of introducing a large amount of fluorine introduction and poor filtration performance of precipitates. Given this, the theoretical calculations of the fluoride precipitation were carried out. Then, the removal of magnesium from zinc sulfate solution by the fluoride precipitation method was investigated through the characterization of the solution composition precipitates, and the treatment of the precipitated liquid and precipitates. The results showed that the feeding modes and reaction temperature significantly affected the fluorine introduction and filtration performance of precipitates. Under the conditions of a fluorine-magnesium ratio of 0.75 (zinc fluoride dosage of 21.88 g), a temperature of 60 °C and a feeding time of 16 min, the removal rate of magnesium could reach 64.42%. In contrast, the fluorine concentration in the liquid after magnesium removal was only 0.22 g/L. Fluoride in the final liquid could be effectively removed using La(OH)₃, and its removal rate could reach more than 82%. After washing twice with pure water, the zinc in the washing products could be reduced from 17.12% to 0.67%, which can meet the technical specifications of industrial magnesium fluoride (YS/T 691—2009).