Variance in heavy metal leachability of Pb-, Ni-, and Cr-contaminated soils through red brick sintering procedure

Abstract

The technology for remediating heavy metal–contaminated soil is considerably limited because heavy metals do not undergo decomposition. Off-site reuse has emerged as the main technique for treating heavy metal–contaminated soil. Soil is the primary material in red brick making; and in the sintering procedure, heavy metals could solidify and stabilize within bricks. In this study, lead-, nickel-, and chromium-contaminated soils were collected from multiple agricultural fields. The sintering process was performed using a kiln that was for making red bricks. The sintering temperature was approximately 1000 °C. Soil and brick samples, before and after sintering, were analyzed for metal extraction concentration and binding form distribution. After sintering, the concentrations of Pb, Ni, and Cr determined through X-ray fluorescence approximated the concentrations in the soil. However, in the bricks, the bioavailability concentration of Pb, Ni, and Cr is less than 1% of that in the soil; the toxicity characteristic leaching procedure (TCLP) leaching concentration of Pb in the bricks was only 4% of that in the soil, and the leaching concentrations of Ni and Cr were lower than the detectable concentration. For the aqua regia extraction method, in the bricks, the Pb, Ni, and Cr were extracted and the concentrations accounted for 4.6%, 8.8%, and 9.4% of the concentrations in the soil, respectively. After sintering, more than 95% of Ni and Cr in the bricks were in residual fractions. The sintering process has the ability to stabilize the heavy metals in the contaminated soil.