Removal of Al and Mg ions in wet-process phosphoric acid via the formation of aluminofluoride complexes.

With the decrease in the phosphate rock grade, the minor element ratios (MER) [(FeO wt% + AlO wt% + MgO wt%)/PO wt%] of wet-process phosphoric acid (WPA) exhibits a linear upward trend. This can lead to a huge challenge for the high-quality production of feed calcium phosphate salt (FCPS). In the present study, we proposed a novel and economical strategy to precipitate Al and Mg via the formation of aluminofluoride complexes (NaMgAlF·HO) with the anhydrous sodium sulfate (NaSO) and hydrofluoric acid (HF) as precipitation agents. Because of the low solubility of the complexes in WPA, the removal efficiencies of Al and Mg ions could reach 99.5% and 64.8%, respectively. The maximum mass loss of PO was less than 0.5%. The precipitates could be separated and converted into the HF and NaSO for reuse, thus further decreasing the cost of WPA purification.