Roles of different mineral seeds in heavy metals removal/recovery from simulated and actual acid mine wastewater

Abstract Heavy metal being immobilised in the lattice of a mineral is beneficial for its removal, recovery and reuse from wastewater. It is therefore essential to determine how heavy metals can be transferred into minerals controllably. This work developed a potential way for transforming heavy metals (Cu 2+ , Pb 2+ , Ni 2+ , Zn 2+ and Cd 2+ ) in wastewater into solids with high efficiency by introducing crystal seeds. The results of this work demonstrate that the addition of hydrotalcite and paratacamite crystal seeds can enhance heavy metal removal, both in simulated and actual acid mine wastewater. The removal rate can be increased by 18–47% and 31.8% for each heavy metal and total heavy metals in the presence of each crystal seed, respectively. Additionally, the recovery products of heavy metals can be changed by crystal seeds. In the systems without crystal seeds, the recovery products are mixtures; but the pure phase can be achieved if crystal seeds are added. For instance, in the Cu 2+ –Al 3+ –Cl – system without crystal seeds, the products were mixtures of paratacamite and layered double hydroxides (LDHs). But the products could be altered easily by hydrotalcite or paratacamite seeds. Paratacamite seeds induced Cu 2+ to form paratacamite at pH 5.0, but a mixture of LDHs and paratacamite at pH 7.0. In contrast, hydrotalcite seeds induced Cu 2+ to form LDHs at both pH 5.0 and 7.0. From the perspective of enthalpies of formation, CuAl-LDH and paratacamite are potential products, but the former is generally more stable, and thus it becomes the dominant product of the reaction systems using crystal seeds. It is believed that the crystal seeds can accelerate the dynamic process of LDH formation. This work suggests a controllable way for heavy metals removal, recovery and reuse.