Solidification/stabilization of lead-contaminated soils by phosphogypsum slag-based cementitious materials

In the present study, phosphogypsum slag-based cementitious material (PS) was designed, and the potential use for solidifying/stabilizing lead-contaminated soils was investigated. The physicochemical properties, performance, and mechanisms of its stabilization of lead in soil were studied by the methods of toxic leaching test, compressive strength, XRD, TGA, FTIR and XPS. The compressive strength of the PS solidified body was from 0.52 to 6.66 MPa when he concentration of lead ions in contaminated soil was set as 6000 mg/kg (0.6 %), 10,000 mg/kg (1.0 %) and 15,000 mg/kg (1.5 %) and the dosage of curing agent is 10 %, 20 % and 30 %., which is acceptable for backfill treatments or roadbed materials. Under the conditions, Pb leaching concentrations ranged from 40.98 to 355.21 μg·L-1, which was within the safety limit specified in Chinese standard (GB5085.3-2007). There is the potential for safe disposal and reuse of PS stabilized soil. TGA and XRD showed that the main components of PS-solidified soil were ettringite (AFt), calcium silicate hydrate (C-S-H), and lead phosphate. FTIR, XPS, and SEM-EDS analysis demonstrated the lead was successfully incorporated into AFt and C-S-H. Pb forms bonds with lead oxide and aluminum oxide tetrahedra and replaces part of the adsorbed Ca ions in AFt and C-S-H. In addition, the resulting phosphate precipitates were also encapsulated in the C-S-H phase, together with the stabilization of lead in the soil.