Experimental study on the mechanism and thermodynamics of extraction of Fe3+ from phosphoric acid solution

Abstract

The new extractant (P12) was used to remove Fe3+ from the simulated liquid of wet process phosphoric acid in this work. The solubility of P12 in white oil under the action of P204(Di-(2-ethylhexyl) phosphate) and n-octanol is discussed in detail. Then, the effects of reaction temperature, reaction time, the volume ratio of extraction phase and aqueous phase (O: A), pH of the phosphoric acid solution(simulated solution) and various anions on the extraction process were discussed. The extraction efficiency increases with the increase of extractant P12, the decrease of pH and the increase of O: A. Under the condition of pH=0.2, O: A= 1:1, the extraction efficiency of P12=5 %, 7 % and 9 % can be up to 70.86 %, 81.84 % and 90.93 % respectively. The extraction mechanism and extract composition were determined by slope method, FTIR and SEM. The ΔH< 0, ΔG< 0, ΔS < 0 in the extraction process proves that the extraction process was a spontaneous and exothermic process. The extraction mechanism proves that the extraction process involves both cation exchange and complexation of extractant. The composition of the extract may be [Fe(H2PO4)2.4A0.6(HA)0.84(H2O)](o), [Fe(H2PO4)2.2A0.8(HA)1.12(H2O)](o). And stripping efficiency of 5.5 M HCl can reach 100 % at A: O=4:1, ΔH=38.9357 kJ/mol in stripping process prove that it is endothermic.