Immobilization Of Lead And Arsenic By Biochars

Heavy metal contamination in soil is not optimistic in our country. Lead and arsenic are normal pollutants which could remain in environment for a long time. Moreover, they are highly toxic. In this constitution, remediation technology for lead and arsenic in soils have been research hotspot for a long time. While biochar is considered to be a green, cost and effective amendment for soil remediation. The present study employed sorbents of common biomass origin (poultry manure, swine manure, corn straw) that pyrolysised for heavy metal (Pb and As) immobilization in water and soil, while Fe-load biochar derived from corn straw was also prepared. The purpose was to explore the effects of biochar after it was applied to mine contaminated soil, as well as to provide theoretical support for the remediation of heavy metal contaminated soil and risk assessment, improving soil quality and protecting human health.The method of batchexperiments, SRXRF, XRD, et al were used to study the mechanism of lead adsorption on swine manure and its biochar as well as poultry manure biochar. The result suggested precipitation was the primary mechanism for Pb adsorption on swine manure and its biochar where ash content played an important role. Our results suggested the precipitation as Pbs(PO4)3Cl and Pb-carbonate such as Pb3(CO3)2(OH)2, Pb4(S04)(C03)2(OH)2should be a significant mechanism for Pb immobilization by swine manure and its biochars. The high-temperature biochar was beneficial for the formation of Pb-carbonate with good crystalline.However, Pb adsorption and precipitation were found on poultry and its biochars for the ash content was low. Swine manure had higher organic complexation or ion exchange capacity at low pyrolysis temperature (300℃), and the precipitation were mainly Pb-carbonate and Pb-phosphate. Pb-carbonateand lattice Pb-phosphatewere generated on poultry manure biochar pyrolysised at 500 ℃. the result also showed that the release kinetics of solube P controlled the formation of Pb-phosphate.Batch experiments were conducted to study the adsorption behavior of arsenate onto the iron loaded or biochar derived from corn straws (CS-Fe600). The material has high adsorption capacity (14766mg/kg) on the As compared with biochar derived from corn. Moreover, the its maximum buffer capacity was 1056 fold to corn straw biochar. Kinetics study showed that the overall adsorption rate of arsenate was illustrated by the pseudo-second-order kinetic model.Overall, the mechanism for Pb immobilization by CS-Fe should be electrostatic interactions.The immobilization of Pb and As with 10% of biochar derived from poultry manure at 500℃(PMO500) incorporated in mine soil was investigated. The result showed that PMO500 had significant effect on immobilization of Pb while would increase the leaching and bioaccessibility of arsenic.