Assessment of the Stabilization of Cu-, Pb-, and Zn-Contaminated Fine Soil Using Cockle Shells, Scallop Shells, and Starfish

Abstract

Soil washing is a well-established remediation technology for treating soil contaminated with heavy metals. It involves the separation of contaminants from the soil using acidic washing agents. Nevertheless, the application of washing agents at high concentrations may lead to soil acidification and the destruction of the clay structure. To avert this problem, recently, a soil washing variant has been presented, which solely employs high-pressure water without any chemical solvents. However, the fine soil generated from soil washing at a high-pressure contains high levels of heavy metals and requires proper treatment. This study examines the use and applicability of natural aquaculture materials as stabilizing agents for treating heavy metals (Cu, Pb, and Zn) in fine soil generated by high-pressure soil washing. Three aquaculture materials were assessed, namely, cockle shells (CKS), scallop shells (SLS), and Asterias amurensis starfish (ASF). Each material was processed to yield three types of stabilizing agents: natural type (-#10 mesh), natural type (-#20 mesh), and calcined(C) type (-#10 mesh). Each stabilizing agent was added to the contaminated soil at a ratio of 0 to 10 wt%, and then, mixed with an appropriate amount of water. After wet curing for 28 days, the stabilization efficiency of Cu, Pb, and Zn was evaluated using 0.1 N HCl solution. The elution of heavy metals showed a decreasing trend with higher dosages of stabilizing agents. The calcined type (-#10) showed the highest stabilization efficiency, followed by the natural type (-#20) and natural type (-#10). In addition, a comparison of the efficiency of the different stabilizing agents showed that calcined ASF (CASF) had the highest stabilization efficiency, followed by calcined SLS (CSLS), calcined CKS (CCKS), natural ASF (NASF), natural SLS (NSLS), and natural CKS. Finally, analysis of samples exhibiting the highest stabilization efficiency by scanning electron microscopy–energy dispersive X-ray spectrometry (SEM–EDX) confirmed that the pozzolanic reaction contributed to the stabilization treatment. The results of this study demonstrate that heavy metal-contaminated fine soil, generated by high-pressure washing, can be remediated by stabilizing Cu, Pb, and Zn using waste aquaculture materials (CKS, SLS, and ASF), which are often illegally dumped into the sea or landfills and cause environmental damage.