Removal of contaminants from soils using coupled electric-hydraulic gradient assisted by ion exchange medium

A novel in-situ process for soil decontamination using coupled electric-hydraulic gradient assisted by ion exchange medium ( CEHIXM) was proposed and verified by laboratory experiments. Two types of soil compositions were used in the experimental programs: (1) chemically noninteractive with metal contaminants and (2) chemically interactive with metal contaminants. Spent foundry sand was used to represent a chemically non-interactive solid phase. A blend of spent foundry sand and millpond sludge (90:10 w/w) was used to represent a chemically interactive solid phase. An instrument was specially designed and constructed to conduct the experiments for evaluation of the proposed process. The interaction of primarily four heavy metals Pb, Cd, Zn and Mn in the contaminated sources was investigated.; A theoretical model for the proposed process was formulated and solved using implicit numerical approximation. The model predictions of concentrations and soil pH profile and the rates of contaminant removal agreed well with experiments in cylindrical compacted chemically noninteractive and chemically interactive soil specimens of 10 cm long and 3.45 cm in diameter. Both the model simulation and the one-dimensional laboratory experiments demonstrated that high degrees of contaminant removal from the saturated sandy/silty soils could be achieved. Energy expenditures were shown to be 345 kWh/m3 of soil for chemically non-interactive solid phase and 480 kWh/ m3 of soil for chemically interactive solid phase when 50 volts of electric voltage was applied. As much as 93% of Pb, 97% of Cd, 98% of Zn and 94% of Mn were removed after 100 hours of the processing from chemically non-interactive solid phase. And 90% of Pb, 96% of Cd, 93% of Zn and 91% of Mn were removed after 200 hours of the processing from chemically interactive solid phase. Higher concentration of EDTA removed higher percentage of the heavy metals. High pH jumps and the accumulation of metals, along the length of the specimen near the pretreatment zone, were eliminated. The final pH of the pretreatment and the collection chambers water remained about 2.0 during all the experiments. As a result, the metals extracted from the solid medium remained in solution in the pretreatment chamber. The ion exchange resin used in this study was capable of capturing the canons. The optimum operating voltage was found to be 50 volts. Although additional modeling and laboratory experimentation are in order, the results of this dissertation demonstrate that the CEHIXM process may offer a new method for decontamination of coarse-grained polluted soils.