The bio-immobilization of Pb(II) induced by the Chlorella–montmorillonite composite in the Ca(II) environment

The clay–microbial consortium is ubiquitous in the soil near the mining area and plays an important role in the transport of heavy metals. In this study, Chlorella sorokiniana FK was separated from lead–zinc mine tailings. The montmorillonite–Chlorella sorokiniana FK system as a typical case was applied to study Pb(II) biomineralization in the presence of usually co-existent Ca(II) and further reduce the migration and transformation of Pb(II) in the Ca(II) environment. Chlorella sorokiniana FK showed good resistance to Pb(II), and the addition of montmorillonite provided a more stable pH environment, which is conducive to the stability of Pb(II)-bearing bio-minerals. Montmorillonite created a low-biotoxicity environment in the overall process, especially less Pb(II) bio-adsorption capacity of individual Chlorella to protect the process of mineralization effectively. Batch experiment results also demonstrated that montmorillonite as the formation site of bio-minerals results in dispersed minerals on the surface of Chlorella and Chlorella–MMT composite, which is beneficial to the survival of Chlorella. Moreover, Pb(II)-bearing phosphate minerals tended to form in the Ca(II) environment rather than without Ca(II). This study demonstrated the mechanism of Pb(II) immobilization induced by Chlorella in the Ca(II) environment, further presenting a green, sustainable, and effective strategy for Pb(II) bio-immobilization combining clay minerals and microorganisms.