Separation of H3PO4 from HCl-wet-processing phosphate rocks leach liquor by TBP: Extraction equilibria and mechanism study

Tri-n-butyl phosphate (TBP) with various combinations of extractants was used to extract H3PO4 from a phosphate leach liquor. The results showed that 80 vol% TBP diluted in kerosene was suitable for extraction yielding. The effects of operational parameters and composition on the extraction behavior were investigated by an orthogonal experiment (L-16(4(5))) and relevant analysis. Aiming to yield the concentrated acid extract, the theoretical stages and minimum dosage of extractant was simulated by plotting McCabe-Thiele diagram. A four-stage countercurrent extraction was carried out through a series of cascade experiments, indicating that over 83% H3PO4 and 10% CaCl2 in the actual iron-removed acid were extracted into organic phase. Furthermore, the extraction mechanism between H3PO4 and TBP at the presence of CaCl2 has been discussed. The assumption that the H3PO4 is extracted by TBP as a neutral extraction complex in a form of pH(3)PO(4)center dot qTBP was characterized by FTIR, H-1 NMR and P-31 NMR analysis. The extraction equilibrium of H3PO4 in the H3PO4-CaCl2-H2O-TBP system showed an extraction of 0.66 mol and 0.74 mol H3PO4 against each mole of TBP could be loaded from the synthetic acid containing 1.0 mol/L and 2.5 mol/L CaCl2, respectively. The results are contributive to design a new and efficient extraction process to separate H3PO4 from the phosphate leach liquor of HCl route.