Purification of industrial wet phosphoric acid solution by sulfide precipitation in batch and continuous modes: Performance analysis, kinetic modeling, and precipitate characterization

摘要

The purification of wet-process phosphoric acid has always been a challenge for both academic and industrial researchers. A treatment unit was developed to mitigate metallic impurities, such as cadmium, from industrial dilute wet phosphoric acid solution (25 P2O5) by NaHS precipitation in batch and continuous modes. The effects of operating parameters on the purification performance were evaluated: namely Sulfur/Cd2+ molar ratio, the presence of other metallic ions besides Cd2+, temperature, and hydraulic residence time. In the batch mode, equilibrium was attained in less than 20 min; augmenting Sulfur/Cd2+ molar ratio increased the CdS precipi-tation effectiveness up to 86, but temperature increment had an adverse effect. In the continuous mode, a hydraulic residence time of 40 min was necessary to reach the same yield as in the batch mode at 25 degrees C. Sul-fidation was found to eliminate simultaneously other metallic impurities (especially Cu and As) originally present in the wet-produced phosphoric acid. Finally, NaHS precipitation was able to reduce the concentration of cad-mium from 65.95 mg Cd/kg P2O5 to 11.15 mg Cd/kg P2O5 from untreated industrial WPA solution (25 P2O5) at 25 degrees C, which outperforms most of the published data based on alternative treatment processes.