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

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. The optimal conditions for extraction were investigated. The results showed that the extraction of H3PO4 was an exothermic process with an enthalpy change of -12.50 kJ mol-1. The McCabe-Thiele diagram indicated that about 76.9 wt% H3PO4 extraction could be achieved at 293 K with two counter-current stages. The extraction mechanism involved the formation of aH3PO4 bTBP complex, and higher Ca2+ concentration promoted the extraction of H3PO4. The study also examined the re-extraction performance of H3PO4, Ca2+, and Cl- under different conditions. The experimental results provide theoretical support for the industrial application of HCl-route wet process phosphoric acid.