LAUSR

Ordinary Portland cement (OPC) and lime are commonly used to treat soils contaminated by heavy metals, such as cadmium (Cd) and manganese (Mn). However, the production of these two binders is not sustainable, consuming high energy and emitting high carbon dioxide (CO2). In this contest, this study proposed a novel and sustainable method of carbonating magnesia (MgO) for treatment of Cd- and Mn-contaminated soils, which can sequester CO2 and immobilize Cd and Mn in the soils. To validate the method, a range of experiments were performed. First, MgO and CO2 were used to treat contaminated soils. Then, the properties of the treated soils were evaluated by unconfined compressive strength test, one stage batch leaching test, X-ray diffraction test, and thermogravimetric analysis. It was found that the carbonation process of MgO-treated soils was decelerated by Mn, but not significantly decelerated by Cd. After carbonation, multiple magnesium carbonates were formed in both contaminated soils, and CdCO3 was formed in the Cd-contaminated soil, while MnCO3 was not confidently determined in the Mn-contaminated soil. Both Cd and Mn negatively affected the strength of carbonated MgO-treated soils; nevertheless, if the concentration of Cd or Mn was not more than 8000 mg/kg, 5% MgO-treated soils after carbonation could meet the strength requirement of higher than 1000 kPa. The treatment decreased the Cd leachability to be below the limit for non-hazardous wastes. The leached concentration of Mn was decreased to be lower than the limit of drinking water.