Mixed bacteria-loaded biochar for the immobilization of arsenic, lead, and cadmium in a polluted soil system: Effects and mechanisms

The present study explored the immobilization of mixed bacteria-loaded biochar on As, Pb, and Cd was explored. Physisorption and sodium alginate encapsulation were used to synthesize two kinds of mixed bacteria-loaded biochars, referred to as BCM and BCB. The observations of Scanning electron microscope, X-ray diffraction, and Fourier transform infrared spectroscopy distinctly demonstrated the colonization of mixed bacteria on biochar. Besides, the addition of BCM and BCB could increase soil pH with increasing incubation time. The residual fraction of heavy metals and soil dehydrogenase activities were also enhanced after 28 days of incubation. Pb was mainly immobilized by co-precipitation, which meant that Pb could be converted into a consistent crystalline form such as Pb5(PO4)3OH. The X-ray photoelectron spectroscopy and X-ray diffraction analyses of materials identified the formation of Ca2As2O7 and the presence of oxidation from trivalent arsenic to pentavalent arsenic. Cd was adsorbed by forming precipitations (CdCO3) and exchanging ions with the BCM and BCB. Synergistic reactions between anions and cations also contributed to the immobilization of heavy metals, such as the formation of PbAs2O6 and Cd3(AsO4)2. These results confirmed that mixed bacteria-loaded biochar was a feasible technology for the remediation of heavy metals contamination in site soils.