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+, Mg2+ and Al3+) 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 Al3+, Mg2+ and F- can be higher than 90 % in the form of NaAlMgF6 and Na3AlF6 precipitations as the n(Na+): n(Al3+): n(Mg2+): n(F-) = 5: 1.5: 1: 6 in pure systems. DFT calculations further confirm that the NaMgAlF6 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+, Al3+, Mg2+ and F- are co -precipitated in the form of NaAlMgF6, 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.