Sequence closed-loop recovery of fluoride, phosphate, and sulfate anions from phosphogypsum leachate via precipitation-electrodialysis-crystallization approaches

Abstract

Phosphogypsum (PG) is a large-scale industrial by-product generated during the production of phosphoric acid, typically being deposited in landfills worldwide. The leaching of fluoride (F−), phosphate (PO43−), and sulfate (SO42−) anions from PG into water bodies through rainfall results in significant environmental pollution. Herein, we propose a stepwise precipitation combined with electrodialysis and crystallization strategy for efficient recovery and valorization of multiple anions from PG leachate. Our method demonstrates effectiveness both theoretically and practically. Consequently, fluoride anions were precipitated as CaF2 and Ca5(PO4)3F at pH 4.7, with a recovery rate of 98.80 %; phosphate anions as MgNH4PO4·H2O at pH 8.5, with a recovery rate of 99.91 %; and sulfate anions through electrodialysis and crystallization with a recovery efficiency of 99.89 %, ensuring effluent met discharge standards. In addition, the concentrated sulfate-rich solution was employed for electrochemical production of persulfate, yielding ammonium persulfate salts after cooling crystallization. Our integrated approach for multiple anion recovery from PG leachate offers significant environmental and economic benefits, providing valuable insights and references for future research and practical production.