Passivation of lead and cerium in soil facilitated by biochar-supported phosphate-doped ferrihydrite: Mechanisms and microbial community evolution.

The massive exploitation and application of heavy metals and rare earth elements (REEs) lead to their exceeding the standard in soil. Herein, a new type of biochar supported phosphorus doped ferrihydrite (P-FH@BC) has been designed and enhance passivation of Pb and Ce in soil. SEM images of P-FH@BC showed P-FH nanoparticles adhered to the natural cavity and large pore diameter on the surface of biochar, which greatly avoided the agglomeration of nanoparticles. The residual state of lead or cerium increased 161.4% or 43.9% by adding 3% P-FH@BC after 90 days of incubation in 500 mg/kg lead or cerium simulated contaminated soil. The passivation of cerium by P-FH@BC is obviously inhibited with the coexistence of lead. The results of P-FH@BC magnetically separated from the soil characterization indicate that complexation, co-precipitation and the formation of secondary minerals mainly contribute to the high efficiency passivation ability of P-FH@BC for lead and cerium. By changing the addition of P-FH@BC, the soil pH can be adjusted and the soil organic matter and P contents can be improved. Moreover, P-FH@BC is an environmentally friendly material without ecotoxicity. And bacterial richness and diversity in soil were improved after passivation of Pb and Ce by adding P-FH@BC.