Simultaneous removal of Al3+, Mg2+ and F- from wet-process phosphoric acid achieved by a co-precipitation strategy

Fluorine (F) is a high-value resource that has been overlooked in the production of wet-process phosphoric acid (WPA) due to its high susceptibility to complexation with metal cationic impurities, hindering F efficient recovery and subsequent phosphoric acid purification. In this paper, a co-precipitation strategy is proposed for recovering F from the WPA. Varieties of combinations between metal cation (Na + , Mg 2+ and Al 3+ ) and F - with different molar ratios in aqueous and phosphoric acid systems are designed to explore the co-precipitated regulation. Results show that the simultaneously removal efficiencies of Al 3+ , Mg 2+ and F - can be higher than 90 % in the form of NaAlMgF 6 and Na 3 AlF 6 precipitations as the n(Na + ): n(Al 3+ ): n(Mg 2+ ): n(F - ) = 5: 1.5: 1: 6 in pure systems. DFT calculations further confirm that the NaMgAlF 6 precipitation is the most stable structure identified by using XRD Rietveld refinement. Based on this fact, extra Na + and F - are added into the industrial WPA, so that the Na + , Al 3+ , Mg 2+ and F - are co-precipitated in the form of NaAlMgF 6 , and the ultimate removal efficiencies can exceed 90 % under the optimal conditions. Besides, low-cost cycling recovery of Na + and F - are also investigated. These findings are promising for the efficient utilization of F resources from phosphate rock and other ores, which is of great economic and environmental significance.