Effect Of Soil Charge On Effective Ionic Mobility In Soil

Heavy metal contamination of soil has been the one of the serious environmental problems with the rapid development of the industry. The main remediation techniques for heavy metal contaminated soil are chemical stabilization/solidification, chemical reduction, bioremediation, flushing, electrokinetic remediation(EKR) etc. Among this techniques, EKR as a novel efficient in situ soil remediation technology has attracted extensive attention around the world. Many factors including soil properties, the characteristic of pollutants, voltage gradient, adsorption/desorption, focusing phenomenon, working fluid, temperature and moisture content will affect the EKR time and efficiency. By numerical simulation, these factors could be all taken into account, which will thus optimize the EK process and provide reliable prediction for practical engineering.Recently several mathematical models have been developed to predict contaminant transfer in EK process. Some models presented good consistence with experiment results but limited to single contaminant, others can not fit the data of all ions when considering two or three ions. For present numerical simulation of EK, the mobility of ions in soil is estimated by ionic mobility at infinite dilution and soil mobility coefficient k, and the k-value which has no concern with the properties of ions and the interaction between soil particle surface charge and ions is usually estimated by tortuosity τ and porosity n. In this study, we choose two colored anions(Mn O4- and Cr O42-) to measure the ionic mobility in kaolin at three concentrations, studying factors affecting the effective mobility coefficient to revise the formula of effective ionic mobility in EK models.The experimental results demonstrate the factors influencing the effective mobility coefficient are geometrical property of soil, ion concentration and the interaction between soil particle surface charge and ions. The geometrical property of soil factor can be expressed by a function of soil porosity n and tortuosity τ, related to soil structure only. The effective mobility coefficient caused by ion concentration can be calculated by measuring the ion mobility in solution, the results show that ion concentration has effects on the effective mobility coefficient. The effective mobility coefficient caused by the interaction between the soil particle surface charge and ions can be calculated by measuring the ion mobility in kaolin(or adding cation exchange resin), the results show that the interaction between soil particle surface charge and ions has effects on the effective mobility coefficient, moreover the effective mobility coefficients for different ions in kaolin are different.In conclusion, we put on the revised calculation formula of the effective ionic mobility in EK model:zce×××=kknfuu￥),( tIn the numerical simulation of multiple ions in a soil medium, f(n, τ) is constant and kc can be measured for different ions, therefore by tuning parameter kz, simulation value could fit experiment results well.