Montmorillonite facilitated Pb(II) biomineralization by Chlorella sorokiniana FK in soil.

In this study, Chlorella sorokiniana FK, isolated from lead-zinc tailings, was employed for Pb(II) biomineralization with or without montmorillonite (MMT) addition in soil. Batch experiment results showed that montmorillonite facilitated Pb3(CO3)2(OH)2 formation on the surface of Chlorella-MMT composite, thus increasing algal cells' tolerance to Pb(II) poisoning. Surprisingly, Pb(II) adsorbed and biomineralized by Chlorella-MMT composite was 2.69 times and 3.76 times as much as that by Chlorella alone, respectively. The montmorillonite facilitated Chlorella-induced Pb biomineralization by promoting both photosynthesis and urea hydrolysis, mainly due to more hydroxyl functional groups generated during its binding with Chlorella and its high pH buffering capacity. Moreover, the SEM-EDS analysis indicated that the biomineral particles shifted from algal cell surface to montmorillonite surface in the composite during long-term Pb-detoxification. In-situ soil Pb(II) remediation experiments with Chlorella-MMT composites further showed that Pb was immobilized as carbonate form in the short term and as residue fraction in the long term. This study made the first attempt to explore the facilitating effects of montmorillonite on metal-carbonate precipitation mediated by microalgae and to develop a green, sustainable, and effective strategy for immobilization of heavy metal in soil by combining clay minerals and microalgae.