Abstract
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 discharged after solvent extraction of H3PO4. In this study, pure CaCl2·2H2O 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≈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 CaCl2·2H2O 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.
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