Enhanced Cd(II) biomineralization induced by microalgae after cultivating modification in high-phosphorus culture.

In this study, high-phosphorus beared microalgae was prepared by cultivating modification in high-phosphorus culture, and used for the enhanced Cd(II) biomineralization in soil. Batch experiment results showed that Chlorella sorokiniana FK was modified successfully in highly phosphate culture. Both intracellular P (Poly-P, 29.7 mg/kg) and surface P (phosphoryl based functional groups, 3.7 mol/kg) were greatly enhanced, and the Cd(II) removal capacity surged to 45.98 mg/g at equilibrium in the Langmuir simulation. The EXAFS analysis indicated that Cd tended to form a more stable bidentate complex (RPO4)2Cd when bounding with phosphate groups on the surface of the high-phosphorus microalgae. Moreover, high-phosphorus beared microalgae not only had higher immobilization amount of Cd(II), but also promoted immobilized Cd from adsorbed state to mineralized state. After high-phosphate cultured, increased density of P-related groups provided more adsorption sites, while the decomposition of intracellular Poly-P released phosphate ions into cell surface microenvironment, which combined and promoted the formation of Cd3(PO4)2/Cd(H2PO4)2 on cell surface. Cd-contaminated soil remediation experiments applying high-surface-phosphate beared microalgae further showed that more Cd stabilized as a residue fraction within 49 days. This study proposes that the high-phosphate culture strategy is a good way to improve the immobilization of heavy metals in soil induced by microorganisms.

Chlorella sorokiniana FK-montmorillonite interaction enhanced remediation of heavy metals in tailings.

Non-ferrous metal mining activities are known to cause ecological irreversible damage in the tailings and surrounding areas as well as heavy metal (HM) contamination. The enhancement of Chlorella-montmorillonite interaction on the remediation of HM contaminated tailings was verified from the lab to the tailings in Daye City, Hubei Province, China. The results showed a positive correlation between the quantity of montmorillonite and the transformation of Pb and Cu into residual and carbonate-binding states, which resulted in a considerable decrease in the leaching ratio. The buildup of tailings fertility throughout this process benefited from montmorillonite's ability to buffer environmental changes and store water. This further offers a required environmental foundation for the rebuilding of microbial community and the growth of herbaceous plants. The structural equation model demonstrated that the interaction between Chlorella and montmorillonite directly affected the stability of HM, and that this interaction also had an impact on the accumulation of organic carbon, total nitrogen, and available phosphorus, which improved the immobilization of Pb, Cu, Cd, and Zn. This work made the first attempt to apply Chlorella-montmorillonite composite to in-situ tailings remediation, and proposed that the combination of inorganic clay minerals and organic microorganisms was an eco-friendly, long-lasting, and efficient method for immobilizing multiple-HMs in mining areas.