Removal of lead complexes by ferrous phosphate and iron phosphate: Unexpected favorable role of ferrous ions

Abstract

The high chemical stability of lead complexes in solution precludes most traditional removal methods. Achieving the efficient, cost-effective, and environmentally friendly removal of metal complexes from wastewater is a challenge. In this study, ferrous phosphate and iron phosphate were used to treat wastewater containing EDTA-Pb, and the differences in their removal processes were compared. Both materials enabled efficient removal of the EDTA-Pb complex from 50 mg Pb/L to <1 mg Pb/L, and the leaching of Fe was <50 mg/L. More attractively, the maximum adsorption capacity of ferrous phosphate significantly increased from 80.44 mg Pb/g to 436.68 mg Pb/g as the reaction environment changed from aerobic to anoxic. The concentration of Pb was reduced to the sub-ppm level by ferrous phosphate even when the initial concentration of EDTA-Pb was 300 mg/L. In-depth exploration of the removal mechanism of EDTA-Pb demonstrated that the synergistic effect of Fe2+ and Fe3+ contributed to the high removal efficiency of EDTA-Pb by ferrous phosphate. Moreover, ferrous phosphate was minimally affected by salinity and organics, but the iron phosphate performance was significantly suppressed. The potential application of ferrous phosphate was further explored by processing explosive wastewater containing lead complexes. The results showed that the residual Pb content was 0.94 mg/L (lower than the discharge standard of China) and the removal performance of iron phosphate was suppressed. The results demonstrate that ferrous phosphate is a promising material for the decontamination of EDTA-Pb-contaminated water.