Solidification/Stabilization of Lead Contaminated Soil Using Magnesia Phosphate cement and Ordinary Portland cement

Background and objectives: Solidification/stabilization is an effective technique for reducing the leachability of contaminants in soils. Magnesia phosphate cement and ordinary Portland cement can be used to remediate soils contaminated. In this study, the performance of the solidified/stabilized soil was compared for mixtures composed of magnesia phosphate and ordinary Portland cement. Materials & Methods: In this study, the experimental soil were contaminated with 500, 1000 and 5000 mg/kg of lead. Lead-contaminated soils were stabilized by mixing magnesia phosphate and Portland cement in proportions of 25% and 50% by weight. Cement and soil mortars were prepared with water-to-cement ratio 0.5 of distilled water. The performance was assessed using unconfined compressive strength (UCS), toxicity characteristic leaching procedure (TCLP), initial and final setting and X-ray powder diffraction (XRD). Results: The results showed that use of magnesia phosphate cement instead of Portland cement could significantly reduce the concentration of lead in TCLP leachate, the setting time and increase the buffer capacity and the formation of crystals in samples containing lead. In 28-day samples containing soil with 5000 mg Pb/kg, Pb concentration in TCLP leachate of samples stabilized with 50% and 25% cement had been determined as 0.41 mg/L and 1.15 mg/L for magnesia phosphate cement and 4.92 mg/L and 12.04 mg/L for Portland cement, respectively. However, using this type of cement instead of Portland cement reduces the compressive strength of 7 and 28 days. Conclusion: The substitution of Portland cement with magnesium phosphate cement for stabilization and solidification of contaminated soil revealed a significant decrease in leachability of heavy metals, setting time, maintenance and equipment cost.