Remediation of Heavy Metal (Cu, Pb) Contaminated Fine Soil Using Stabilization with Limestone and Livestock Bone Powder

Abstract

Soil environments contaminated with heavy metals by typhoon flooding require immediate remediation. High-pressure soil washing using water could be a viable short-term solution for cleaning soil contaminated with heavy metals. Soil washing employing high-pressure generates heavy metal contaminated fine soil and wastewater. This contaminated fine soil cannot be reused without proper treatment because of the high levels of heavy metal contamination. Stabilization was used for immobilizing heavy metals (Cu, Pb) in the contaminated fine soil. The stabilizing agents used for immobilizing heavy metals (Cu, Pb) in the contaminated fine soil included two types of limestone (Ca-LS and Mg-LS) and livestock bone powder (LSBP). The Ca-LS, Mg-LS, and LSBP were applied to the contaminated fine soil at dosages in the range of 2 wt%10 wt%. Two different particle sizes (-#10 vs. -#20 mesh) and curing times (1 week vs. 4 weeks) were used to compare the effectiveness of the stabilization. Extractions using 0.1 N HCl were conducted to evaluate the stabilization effectiveness. Heavy metal leachability was significantly decreased with higher Ca-LS and LSBP dosages. The LSBP treatment was more effective than the Ca-LS and Mg-LS treatments and the Mg-LS showed the poorest performance. The highest degree of immobilization was attained using a 10 wt% LSBP (-#20 mesh), resulting in an approximate leachability reduction of 99% for Pb and 92% for Cu. The -#20 mesh material and 4 weeks of curing were more effective than the -#10 mesh material and 1 week of curing, respectively. The SEM-EDX results showed that metal precipitates and pyromorphite like phases could be responsible for effective heavy metal immobilization. This study suggests that Ca-LS and LSBP used at an optimum dosage can be effective stabilizing agents for immobilizing Cu and Pb in contaminated fine soils.