Selectivity and competitive mechanism of cation exchange resin for Fe, Mg, and Al ions in phosphoric acid

The presence of iron, magnesium, and aluminum elements as the primary impurities in wet‐process phosphoric acid (WPA) adversely affects the industrial phosphoric acid and subsequent phosphorus chemical products. This study aims to investigate the selectivity and competition mechanism of Sinco‐430 cation exchange resin for Fe, Mg, and Al ions in phosphoric acid solution. By studying the effects of different process conditions on the removal efficiency, the suitable conditions for the static removal of metal ions from Fe‐Mg, Al‐Mg, and Fe‐Al binary systems were determined: solid–liquid mass ratio (S/L) of 0.3, phosphoric acid concentration of 27.61 wt.%, system temperature of 50°C, and rotational speeds of 200, 400, and 200 rpm, respectively. By calculating the selectivity coefficients of the resin for metal ions under different experimental conditions and mutual replacement experiments, the semi‐empirical formulas for the selectivity coefficients were derived and order of selectivity was determined as follows: Mg2+ > Fe2+ > Al3+. Visual MINTEQ 3.1 software and density functional theory (DFT) calculations demonstrated that at low pH, the main forms of Fe, Mg, and Al present in phosphoric acid were FeH2PO4+, Mg2+, and AlH2PO42+, respectively. This finding explained the differences in selectivity of the resin for Fe, Mg, and Al. The dynamic removal of metal ions from phosphoric acid was investigated. The order of metal ion selectivity of the resin by the dynamic method is the same as that of the static method, and the dynamic exchange behaviour was most consistent with the Yan model.