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Wet process of phosphoric acid purification by solvent extraction using tri-n-butyl phosphate and cyclohexanol mixtures

Li Xing (Sichuan University, Department of Chemical Engineering, Chengdu, China)
Li Jun (Sichuan University, Department of Chemical Engineering, Chengdu, China)
Jin Yang (Sichuan University, Department of Chemical Engineering, Chengdu, China)
Chen Ming (Sichuan University, Department of Chemical Engineering, Chengdu, China)
Feng Dongya (Sichuan University, Department of Chemical Engineering, Chengdu, China)
Guo Yunhai (Sichuan University, Department of Chemical Engineering, Chengdu, China)

Solvent extraction is an efficient, economical and widely-used technology for the purification of wet process phosphoric acid (WPA). This present work focused on the development of a solvent extraction system, TC, representing tri-n-butyl phosphate (TBP) and cyclohexanol mixtures. The equilibrium phase diagram of the system H3PO4−H2O−TC at 298.2 K and atmospheric pressure was obtained. The effects of extraction time, phosphoric acid concentration, extractant concentration, temperature and phase volume ratio on extraction efficiency were studied. The extracted complexes were estimated to be 1.8H3PO4 2TC. The extraction process of H3PO4 was exothermic and the enthalpy change, ΔH, was obtained. The solvent mixtures had a high efficiency for phosphoric acid purification via multi-stage counter-current extraction from the industrial WPA in a reciprocating plate extraction column with an H3PO4 extraction yield of 85.08 % at 313.2 K. The stability, extraction efficiency and recycling capability of TC for H3PO4 extraction were also estimated.

Keywords: mixing extractant, equilibrium phase diagram, extracting mechanism, reciprocating plate column