The curing performances of lead-contaminated soil conditioned with modified phosphorus β-hemihydrate gypsum cemented materials

Abstract

A novel modified phosphorus β-hemihydrate gypsum (MPG) cementing material was developed to solidify lead-contaminated soil. The solidification effects of lead in the contaminated soil with MPG and Portland cement (PC) as curing agent were contrasted by the unconfined compressive strength (UCS), pH and leaching toxicity of solidified soil. The solidification mechanism of lead contaminated soil was analyzed by XRD, BET, SEM and EDS. The results demonstrated that when the addition of binder increased from 24 to 30%, the UCS of MPG solidified body became higher than that of PC solidified body by 14.7–18.8%. The pH of MPG solidified body was 9.81–10.69, which was 15.17–22.08% lower than that of PC solidified body. The lead leaching concentration of MPG solidified body decreased continuously with the curing time and became lower than the limit of hazardous waste content (5 mg L−1) stipulated in Chinese standards after 7-day curing. The results of microscopic analysis revealed that the main components of MPG solidified body were ettringite (AFt), reticulated gel of calcium silicate hydrated (C–S–H), lead phosphate ([Pb10(PO4)6(OH)2]) and lead sulfate (PbSO4) precipitation. The covering of C–S–H on soil particles and the ion exchange between lead and AFt contributed jointly to the stabilization of lead in the solidified soil. This is a valuable application exploitation study for the treatment of Pb contaminated soil and reutilization of waste phosphorus gypsum.