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

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, respec-tively. The result shows that the extraction process of H3PO4 is an exothermic process and the enthalpy changes (DH) 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 aH3PO4 bTBP 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.(c) 2022 Elsevier B.V. All rights reserved.

Automated summary

In this study, a mixed solvent of tributylphosphate and isopropyl ether was used to extract H3PO4 and separate Ca2+ and Cl- from low concentration wet process phosphoric acid. The extraction process of H3PO4 was found to be exothermic with an enthalpy change of -12.50 kJ mol-1. The effects of extraction temperature, solvent composition, aqueous/organic phase ratio, extraction time, and extraction stage were investigated.