Stabilization of compound lead and arsenic contaminated soils by using two iron-based materials: Long-term efficacy

Long time scale tests are a key step in verifying the effectiveness and practicability of remediation materials in treating soil contaminated by heavy metal(oids)s (HMs). In this study, two materials, compound calcium oxide and ferrous sulfate (inorganic-inorganic combined material, denoted as IIM), and goethite nanoparticles modified biochar (organic-inorganic combined material, denoted as OIM), were tested for stabilization of arsenic (As) and lead (Pb) co-contaminated soil. Monitoring occurred at several fixed intervals up to 180 days, which includes leaching toxicity assessment, microstructure, and mechanical strength testing. The results indicate that IIM exhibited superior remediation effect within the initial 7 days but was less effective than OIM from 30 to 180 days. After 180 days, stabilization rates of IIM and OIM were 65.53% and 93.58% for As, and 99.27% and 99.71% for Pb, respectively. The cohesion of IIM-treated soils increased by 24.80% to improve the shear strength, while OIM-treated soil mainly rose the internal friction angle by 14.94%. This can be attributed to fact that IIM has a mean weight diameter (MWD) of 0.69 mm with better stability and a richer macropore structure, while OIM aggregates are slightly less stable at 0.64 mm of MWD, with mesoporous content at 49.79%. These findings provide valuable data and guidance on the long-term efficacy of remediation materials in HMs contaminated soils.