In Situ Treatment Of Soil Contaminated With Chromium

In our country, groundwater, surface water and soil were severely polluted by chromium residue, and ecological environment and human health were also threatened immensely. Remediation chromium contaminated site was one of the desiderated case of our country because the high contamination concentration and the easily diffusion. Soil flushing can thoroughly remove contaminants from contaminated soils with low cost, and it's easily to control the remedial process, so it is commonly used in the remediation of contaminated soils in foreign countries.For metals, soil flushing would be most effective in removing water-soluable species, such as hexavalent chrome. Soil flushing is most applicable to the multiple pore, easy penetration soil. Research showed that, permeability coefficient of the soil is more than 10-3cm/s, which can be recommended to use soil flushing to repair them. Soil flushing with water alone can be applied to the concentrated or dilute portions of the groundwater plume, depending on how easily the metals contamination can be mobilized. Qinghai Haibei chemical plant face a serious pollution, the chrome content of the soil was very large, suitable for diposed by in-situ flushing technology. And the leaching reagents or solidification/stabilization agents was also considered. The continuous semi-spread type and intermittent semi-spread type of leaching were selected. Based on the needs of depth of the site, three kinds of leaching mode was studied, and the mathematical model (analyzed by COMSOL software) was used to forecast the transformation of the water and hexavalent chrome in the soil and groundwater.The results of the study indicated that:(1). Cr of the soil exists mainly in acid extractable species. In partial alkaline conditions, it had little impact on the form and valence of chrome to change pH.(2). In partial alkaline condition, water is more suitable for eluent. For Qinghai chemical plants, ferrous sulfate and glucose is suitable for solidification/stabilization agent. Ferrous sulfate can reduce hexavalent chromium effectively; however, from the environmental perspective, glucose was more suitable for a solidification/stabilization agent.(3). For in-situ leaching, continuous semi-spread type can save time effectively; Intermittent semi-spread type can effectively conserve water. Meanwhile, combine continuous leaching with semi-spread leaching can remove the hexavalent chromium fully.(4). The migration of hexavalent chromium was controlled mainly by the convection and dispersion of the water. Initial pressure head is the most sensitive parameter in the solute transport model, which need to be strictly controlled.(5). COMSOL simulation can be used to forecast the law of soluble pollutants moving in the groundwater flow in different conditions, to predict pollution halo, pollutants distribution, and this method is universally applicable to all groundwater pollution problems.