An Experimental Study on Cement-Solidified Cd-Contaminated Soils under Drying-Wetting Cycles

摘要

Many human activities can produce and release cadmium (Cd) to air, water, and soils. Soils are the major sink for Cd released into the environment. Unlike organic contaminants, which are oxidized to carbon (IV) oxide by microbial action, Cd does not undergo microbial or chemical degradation, and its total concentration in soils persists for a long time after introduction. The excessive presence of Cd in soil poses great risks and hazards to human health and is detrimental to the ecosystem. In the past 50 years, cement-based solidification/stabilization (S/S) of heavy metal-contaminated soil has received increasing research attention, and its application has expanded because of its advantages over many other existing methods such as relatively low cost, good long-term effectiveness and performance, ready commercial availability, general acceptance by the public, etc. However, considering the lasting effect and environmental impact of the S/S methocl, as well as the complicated surroundings of cement-solidified Cd-contaminated soils, further research is needed. In this study, a comprehensive series of tests such as low-temperature nitrogen gas adsorption/desorption, permeability, and Cd leaching were performed to investigate the performance of Cd-contaminated soils solidified with 2 %, 5 %, 8 %，and 10 % of cement during a various number of drying-wetting (D-W) cycles. The focus was put on the cracking occurrences and evolution with the number of D-W cycles, their influences on the pore/crack size and distribution, hydraulic conductivity, and final concentration of Cd leaching. Based upon the analyses of the test results, some conclusions are drawn and the optimum percentage of cement treatment was suggested for the soils under investigation.