BACKGROUNDIn china, the grade of phosphate ores has decreased sharply in recent years. Existing solvents are inefficient for the extraction of wet-process phosphoric acid produced by low-grade phosphate ores. Organic solvent dibutyl sulfoxide was developed to improve the extraction capacity of wet-process phosphoric acid, especially at low-acid concentration. RESULTSThe effects of extraction time, temperature, phosphoric acid concentration and impurities concentration on the extraction were investigated. The extraction process is exothermic and the enthalpy change is -5.86 kJ mol(-1). Dibutyl sulfoxide is relatively selective for Mg2+ and Al3+ while the selectivities of Fe3+, F- and SO42- are moderate. The liquid-liquid equilibrium of water-dibutyl sulfoxide-phosphoric acid system was determined at 298.15 K. The stability of dibutyl sulfoxide and the process flows of extraction, scrubbing and stripping were investigated. The extraction mechanism of dibutyl sulfoxide for phosphoric acid was proposed and the extracted complex H(3)PO(4)0.3DBSO was obtained. CONCLUSIONDibutyl sulfoxide is demonstrated to be a powerful solvent for the extraction of wet-process phosphoric acid even at low concentrations. Dibutyl sulfoxide can be a potential supplemental organic solvent for the extraction of wet-process phosphoric acid produced by low-grade phosphate ores. (c) 2017 Society of Chemical Industry