Heavy metals leaching in bricks made from lead and zinc mine tailings with varied chemical components

- Impacts of SiO2:Al2O3 and Fe2O3:CaO:MgO on metals leaching were examined.
- Leaching of Zn, Pb are highly depended on the chemical compositions in bricks.
- Presence of PbAl2Si2O8 could facilitate the immobilization of Pb2+ in bricks.
- Higher CZn could be attributed to the formation of Zn2SiO4 in bricks.
- Concentrations of Cd, Cu, Pb, Zn in leachate are all below the standard.

The stabilization/solidification approach has received considerable attentions for the disposal of hazardous metal-bearing mine tailings. A poor understanding of the immobilization mechanism of heavy metals in final products always restricts its practical applications. We reported that, the stabilization of toxic heavy metals (Zn, Pb, Cd and Cu) in bricks made from the lead and zinc mine tailings (LZMT) was highly dependent on the relative contents of SiO2, Al2O3, Fe2O3, CaO and MgO in LZMT. As the (SiO2 + Al2O3)/(Fe2O3 + CaO + MgO) ratios (SA/FCM ratios) increased, the CPb, CCd, or CCu in leachates slightly decreased first and then increased. Much differently, CZn firstly increased and then decreased, having highest CZn (3.92 mg/L at 30th day) at the SA/FCM ratios of 0.80. Compared with CZn and CPb, a much small CCd and CCu can be found. Notably, the CZn and CPb are also impacted by the change of SiO2:Al2O3 ratios (and Fe2O3:CaO:MgO ratios as well). The CPb decreased as the SiO2:Al2O3 ratios increased from 1:0.046 to 1:1.354, while the CZn reached a highest value at SiO2:Al2O3 ratio of 1:0.084. The XRD analysis suggests that, the Al and Si can interact with Pb to form PbAl2Si2O8, which facilitates the immobilization of Pb2+. Excessive amount of SiO2 and Al2O3 bring the difficulties to forming stabile skeletons, resulting in the leaching of Pb readily. As for Zn, higher CZn is generally owing to the occurrence of acid-soluble Zn2SiO4 in bricks. The stabilization of Zn was achieved once Al3+ was introduced as host to be substituted by Zn2+ in the aluminate or aluminosilicate matrix. The findings could enrich the mechanistic understanding and pathway of heavy metals immobilization in eco-environmental products from LZMT.

126