Effective lead passivation in soil by bone char/CMC-stabilized FeS composite loading with phosphate-solubilizing bacteria.

Bioremediation by phosphate-solubilizing bacteria (PSB) has attracted extensive attentions due to its economical and eco-friendly properties for lead (Pb) passivation in soil. Herein, bone char (BC) supported biochemical composite (CFB1-P) carrying advantages of BC, PSB, iron sulfide (FeS) and carboxymethyl cellulose (CMC) was designed and applied to Pb passivation. The composite at a mass ratio of BC:CMC:FeS = 1:1:1 possessed high passivation efficiency (65.47%), and has been demonstrated to offer appropriate habitat environment for PSB to defend against Pb(II) toxicity, thus enhancing the phosphate-solubilizing amount of PSB to 140.72 mg/L for passivating Pb(II). Batch experiments showed that the CFB1-P possessed excellent adsorption properties with maximal monolayer Pb(II) uptake of 452.99 mg/g during an extensive pH range of 2.0-6.0. Furthermore, by applying CFB1-P dosage of 3% into Pb-contaminated soil, the labile Pb fractions were reduced from 29.05% to 6.47% after simulated remediation of 10 days, and converted into steady fractions. The CFB1-P was demonstrated to achieve high Pb(II) passivation through combined functions of chemical precipitation, complexation, electrostatic attraction and biomineralization, accompanied by the formation of more stable crystal structures, for instance, Pb5(PO4)3OH, Pb3(PO4)2 and PbS. These results suggested CFB1-P as a potential alternative for efficient remediation of Pb-contaminated soil.