Removal of Pb, Zn, Cu, Cr and Ni in Iron Tailings by Leaching

In this paper, oxalic acid and EDTA-2Na were used as leaching agents to perform shock leaching tests on Pb, Zn, Cu, Cr and Ni in iron tailings. The effect of different leaching solution concentrations, liquid-solid ratios and shaking times on the removal effect of heavy metals were studied. The changes of heavy metal morphology after leaching were analyzed, and the correlation between leaching content and heavy metal morphology was discussed. The results showed that the removal rates of Pb, Cu, and Cr reached the highest when the oxalic acid concentration was 250, 100, and 200 mmol/L, respectively, and the removal rates were 19.9%, 43.9%, and 4.2%, respectively. The removal effect of Zn and Ni was best when the concentration of EDTA-2Na was 100 and 200 mmol/L, respectively, and the removal rates were 33.2% and 39.4%, respectively. During the oxalic acid leaching process, the removal rates of Cu and Pb gradually increased with the increase of shaking time, and the removal rates of Zn, Ni and Cr tended to be stable after 120 min. EDTA-2Na had little effect on the removal rate of heavy metals with the extension of the shaking time, and it basically stabilized when the shaking time was 60 min. When the liquid-solid ratio was 30:1, the removal effect of heavy metals was relatively good. The morphology of heavy metals after oxalic acid leaching was analyzed, and it was found that the leaching can not only effectively remove the easily migrated forms of heavy metals, but also caused the migration and transformation between heavy metal forms. Correlation analysis found that the correlation coefficients of heavy metal leaching content with exchangeable state and carbonate binding state were 0.930^* and 0.996^**, respectively. After leaching, the ratios of the exchangeable state and the carbonate-bound state of heavy metals in the iron tailings decreased, and the proportion of the residue state, the iron-manganese oxide-bound state and the organically bound state increased. This improved the stability of iron tailings in the environment, reduced the risk of iron tailings polluting the environment, and provided new ideas and theoretical basis for the harmless iron tailings.