Efficient resource treatment of hexavalent chromium wastewater based on lead carbonate (cerussite)-induced precipitation separation

Recycling treatment of wastewater containing hexavalent chromium [Cr (VI)] has always been an important environmental issue. In this paper, taking advantage of the natural affinity of CrO 4 2 − and lead ions, lead carbonate was selected as a precipitant to recover Cr (VI) in the form of chrome yellow (PbCrO 4 ). Firstly, the variation of Cr (VI) and lead species in K + -CrO 4 2 − -Pb 2+ -CO 3 2 − solution system with pH and PbCO 3 dosage was calculated by Visual MINTEQ. The results show that the treatment effect is better under acidic conditions. Then, the effects of parameters on the removal rate of Cr, including the initial pH of solution, reaction time, reaction temperature, and the dosage of lead carbonate, were studied by batch experiments. Results show that the initial pH of solution, reaction time, and the dosage of lead carbonate have great influence, whereas reaction temperature has slight influence. And the concentration of Cr (VI) could be reduced from 100 mg/L to 0.043 mg/L at an initial pH of 3, a reaction time of 45 min, and the dosage of lead carbonate as n(PbCO 3 )/n(K 2 CrO 4 ) = 2. The precipitates are analyzed by XRD , SEM , and EDS，and the results are consistent with the predictions of Visual MINTEQ, that is, the newly produced substance is only PbCrO 4 . The reaction mechanism of Cr (VI) on the surface of lead carbonate was studied by the adsorption kinetic model, and the results showed that the reaction was more fit with the pseudo-second-order kinetic model . Density functional theory (DFT) calculations show that CrO 4 2 − could effectively react with lead atoms with unsaturated coordination bonds on the surface of lead carbonate and free lead ions leached from the surface of lead carbonate to form lead chromate . Under acidic conditions, the removal of Cr (VI) by PbCO 3 may involve two main mechanisms: the mineralization and precipitation of lead and chromate ions dissolved from the surface of cerussite and the chemical adsorption of chromate ions on the surface of cerussite. This study provides a new and efficient strategy for the resource treatment of Cr (VI)-containing wastewater.