Separation of calcium chloride from waste acidic raffinate in HCl wet process for phosphoric acid manufacture: Simulated and experimental study

Phosphoric acid manufacture by HCl wet process is a phosphogypsum-free route, which is promising for replacing traditional H2SO4 wet process. However, large amount of CaCl2-containing acidic raffinate was dis-charged after solvent extraction of H3PO4. In this study, pure CaCl2.2H(2)O was recovered from the raffinate. The ionic forms and residual amount changes with the pH rise in the raffinate was first simulated by Visual MINTEQ software, and found the precipitation for the components was in the following sequential order of Si > F > P > Al > Cr > Pb asymptotic to Mg. Based on the calculation, one-step and multi-steps neutralization processes were designed for separation of impurities. Feed grade calcium hydrophosphate can be separated from the raffinate by multi-steps neutralization. A well-crystallized CaCl2.2H(2)O assaying 98.9 wt% was obtained after evaporative crystallization of the fluorine-depleted solution. Combined with our previous studies on the phosphate ore digestion and H3PO4 solvent extraction, a complete HCl wet process for H3PO4 manufacture was established.

Automated summary

This study achieved phosphoric acid manufacture by HCl wet process without phosphogypsum by recovering pure CaCl2.2H(2)O from acidic raffinate. The sequential order of precipitation for different components in the raffinate was determined through simulation and calculation. One-step and multi-steps neutralization processes were designed to separate impurities. Well-crystallized CaCl2.2H(2)O with high purity was obtained after evaporative crystallization.