Insights into the simultaneous removal of Cr and Pb by a novel sewage sludge-derived biochar immobilized nanoscale zero valent iron: Coexistence effect and mechanism.

Cr and Pb are both highly toxic pollutants and commonly co-exist in some industrial effluents and contaminated waters. In this study, simultaneous removal of Cr and Pb by a novel sewage sludge-derived biochar immobilized nanoscale zero-valent iron (SSB-nZVI) was systematically investigated. It was well demonstrated that a porous structure was successfully formed on the SSB-nZVI when the starch was used as an additive. A synergistic effect on the adsorption and reduction over the SSB-nZVI was achieved, resulting in nearly 90 and 82% of Cr and Pb removal within 30 min, respectively. Cr was reduced prior to Pb. A low pH could accelerate the corrosion of nZVI as well as phosphate leaching. When Malachite green was added as a coexisting organic pollutant, its effective removal was found due to the formation of a Fenton-like system. The SSB-nZVI could be run consecutively three times with a relatively satisfactory performance. Most of Cr was converted into CrO and Cr(OH) on the SSB-nZVI surface, whereas most of Pb species existed as Pb(OH) (or PbO). A possible reaction mechanism on the SSB-nZVI involved the adsorption, reduction and precipitation of both Cr and Pb over the particles. Present study sheds light on the insight of the fate and transport of Cr and Pb in aquatic environment, as well provides helpful guide for the remediation of coexistence of pollutants in real applications.