Insights into leaching-response behavior of phosphorus, fluorine, and metal impurities during sulfuric acid leaching of phosphogypsum

Phosphogypsum (PG) utilization is restricted by the presence of residual phosphorus (P), fluorine (F), and metal impurities. In this study, sulfuric acid leaching was investigated as an industry-compatible method for PG treatment. The effects of acid concentration, liquid-to-solid (L/S) ratio, temperature, and time were systematically evaluated, and the responses of different impurity fractions were analyzed through correlation analysis, XRD, SEM–EDS, gypsum phase composition analysis, and whiteness measurement. Under the selected conditions of 40 wt% H 2 SO 4 , a L/S ratio of 4:1, 50 °C, and 2.5 h, the removal efficiencies of operationally defined total P, total F, water-soluble P, water-insoluble P, water-soluble F, and water-insoluble F reached 86%, 82%, 94%, 82%, 97%, and 70%, respectively, while the apparent mobilization efficiency of selected metal impurities reached up to 88%. The treated PG retained its gypsum phase, while the whiteness increased from 40.3% to 61.85%, residual soluble P (0.0133%) and F (0.0063%) contents in PG met the first-class standard for Chinese building materials. Correlation analysis revealed distinct leaching-response patterns among the P, F, and metal impurities. The metals were classified into four response groups, i.e., strong P-correlated response, P-correlated but condition-sensitive response, matrix-sensitive response, and condition-dependent response with possible secondary immobilization. Based on the observed impurity-removal patterns, an end-use-oriented graded purification framework was proposed for potential applications, subject to application-specific assessment. These findings demonstrate that sulfuric acid leaching is an effective strategy for resource utilization of PG and provides a basis for selecting sulfuric acid treatment intensity according to impurity-control requirements.