Selective removal of magnesium from a lithium-concentrated anolyte by magnesium ammonium phosphate precipitation

Abstract

Abstract Magnesium was selectively removed from a lithium-concentrated anolyte (containing Li 3.5 g L −1 and Mg 14.4 g L −1 ) by MgNH 4 PO 4 precipitation method. Firstly, thermodynamic analysis of the systems Li + –Mg 2+ –PO 4 3− –H 2 O and Li + –Mg 2+ –PO 4 3− –NH 4 + –H 2 O were studied, and the optimal operating windows in which magnesium removal is the most probable were identified. Based on the theoretical considerations, Mg 3 (PO 4 ) 2 and MgNH 4 PO 4 precipitation methods were used to remove magnesium from our lithium-concentrated anolyte, and the results showed that MgNH 4 PO 4 precipitation method exhibits better performance than that of Mg 3 (PO 4 ) 2 on the complete removal of magnesium. Under the conditions of 1.0 times of theoretical amount dosage of (NH 4 ) 3 PO 4 and pH value 8.0, the concentration of magnesium was reduced to 11.1 mg L −1 , and the lithium concentration maintained 3.46 g L −1 , corresponding with the magnesium removal rate 99.92%, and the lithium recovery rate 98.91%. The obtained MgNH 4 PO 4(s) precipitate was a well-crystallized bulky particle, and it is in favour of filtration. Especially, it can be used as NP compound fertilizer, which is great beneficial for reducing the costs of magnesium removal.