Efficient preparation of magnesium bicarbonate from magnesium sulfate solution and saponification-extraction for rare earth separation

Abstract

To realize the recycling of magnesium sulfate wastewater in the hydrometallurgy and separation process of Baotou mixed rare earth (RE) concentrate, the research on preparation of magnesium bicarbonate (Mg(HCO3)2) solution from magnesium sulfate solution by CO2 carbonation, extraction separation and transformation of RE sulfate solution by saponified HDEHP was investigated. The key influencing factors and carbonation mechanism in the preparation of Mg(HCO3)2, and the distribution of RE, calcium and magnesium elements in the saponification extraction were systematically studied. The results show that the conversion of Mg(HCO3)2 during carbonation is inhibited by calcium sulfate, but promoted by increasing the concentration of magnesium sulfate and decreasing the carbonation temperature. Under the optimized conditions, Mg(HCO3)2 solution with impurities (such as Fe, Al and Si) of less than 15 mg/L is prepared stably and efficiently, and the conversion rate of Mg(HCO3)2 is more than 95%. After multi-stage cascade extraction of RE sulfate solution, the RE extraction recovery is greater than 99.5%. Calcium sulfate crystals do not precipitate during the process, and the raffinate phase is magnesium sulfate solution that is used for the preparation of Mg(HCO3)2 solution.