Extraction of H3PO4 from low-grade phosphate rocks leachate of HCl-route by the mixture of TBP and IPE: Optimization, mass transfer and mechanism

Abstract

The mixed solvent of tributylphosphate and isopropyl ether was used to extract H3PO4 and separate Ca2+ and Cl− from low concentration wet process phosphoric acid prepared by low-grade collophane and 30 wt% hydrochloric acid solution. Then, the effects of extraction temperature, composition of solvent mixture, aqueous/organic phase ratio, extraction time and extraction stage were investigated, respectively. The result shows that the extraction process of H3PO4 is an exothermic process and the enthalpy changes (ΔH) is −12.50 kJ mol−1. The McCabe–Thiele diagram shows two counter-current stages achieves about 76.9 wt% H3PO4 extraction at 293 K. Based on the mass transfer theory of liquid–liquid extraction, extraction yields for all tested component were summarized as an exponential function of cross-flow extraction stages. Meanwhie, extraction mechanism studies show that the comlex of αH3PO4 βTBP was formed in extraction process and higher Ca2+ concentration was beneficial for H3PO4 extraction. Meanwhile, the effects of stripping temperature, aqueous/organic phase ratio and stripping time on the re-extraction performance of H3PO4, Ca2+ and Cl− were studied, respectively. The result of experiment will provide some theoretical support for the industrial application of HCl-route wet process phosphoric acid on low-grade phosphate rock and phosphate tailings.