Study On In-situ Leaching Technology Of Chromium-contaminated Soil And Demonstration Project

In our country, groundwater, surface water and soil were severely polluted bychromium residue, and ecological environment and human health were also threatenedimmensely. Remediation chromium contaminated site was one of the desiderated caseof our country because the high contamination concentration and the easily diffusion.Soil flushing can thoroughly remove contaminants from contaminated soils with lowcost, and it’s easily to control the remedial process, so it is commonly used in theremediation of contaminated soils which were buried deeply and polluted seriously incontaminated site. But there were few researches study on in-situ leaching ofchromium contaminated soil.This article studyed the simulation experiment anddemonstration project of in-situ leaching technology on chromium contaminated soil.The study provided theoretical basis and guidance for the practice of the in-situleaching technology.Based on the feature of chromium contaminated soil, column simulator was usedto simulate soil flushing. And outlet concentration, volume and soil concentration wasmonitored for a long term. The mathematical model (analyzed by COMSOL software)was used to forecast the transformation of the water and hexavalent chrome in the soiland groundwater, and discuss the influence factor of soil flushing. Demonstrationproject was successfully run in a chemical plant in Qinghai. The impact ofgroundwater flow caused during the course of pumping in the situation of differentpump flow, different pump depth and different site of pump well were studyed.The results of the study indicated that:(1) The desorption balance curve can be used in simulation of in-situtreatment.The concentration in the top of hexavalent chrome can fall into limitedconcentration. The concentration in the feet of hexavalent chrome is balanced with theconcentration of the liquid.(2) Simulation results showed that the concentration of outlet water is big whenleaching begains, then it falls fast, the volume of outlet water remained at around200mL·d; the concentration of Cr VI falls mainly in the early50days, the dissolutionvalue accounted for90.85%of total dissolution value; the minimum concentration value of soil is186mg·kg-1approached to its adsorption limit176.7mg·kg-1; whenadding ferrous sulfate as reagent into the soil, after12days’ running, the permeabilityquotient of soil decrease to70mL·d, and the concentration of hexavalent chrome inliquid is nearly zero after12days, the concentration of soil is lower than withoutferrous sulfate.(3) COMSOL simulation can be used to forecast the law of soluble pollutantsmoving in the groundwater flow in different conditions, to predict pollution halo,pollutants distribution, and this method is universally applicable to all groundwaterpollution problems.(4) Pumping test results showed that pump with pumpage of15m3·h-1cancontrol the underground water flow of this area; The impact of underground water flowfield control is small caused by pump depth. The pump wells of1#and3#wereoperated at the same time in order to ensure the effect of flow field control. In-situleaching project ran based on that, the concentration of Cr VI in soil falled obviouslyafter60days’running.