Study On Electric-PRB Remediation Of Chromium And Nickel Contaminated Soil

With the development of industrial society,the problem of heavy metal pollution becomes more and more serious.Among three pollutions including water pollution,soil pollution and air pollution,soil pollution is probably the most difficult problem to solve.Because soil pollution cann't be seen and after the disappearance of pollution source,the impact will continue for a long time.Heavy metal pollution is most serious in soil pollution.Therefore,the remediation of heavy metal contaminated soil is very necessary.Electrokinetic remediation is a technique to treat heavy metals contaminated soil by applying a low direct current(in order of mA/cm2 of the cross-sectional area)or a low potential gradient(in order of V/cm of the distance between the electrodes)to electrodes that are inserted into the ground.EK-PRB remediation is an economically feasible remediation technology to couple electrokinetic remediation with permeable reactive barrier.In this paper,EK-PRB combined technology was applied to remediate complex chromium and nickel contaminated soil.The effect of treat time,cathode-conditioning solution and the permeable reactive materials on the Cr,Ni removal efficiency has been explored.The main content and results are as follows:(1)Firstly,some physico-chemical properties and acid/base buffer capacity of the experimental soil has been measured.After studying the effect of four different treated time with 3d,4d,5d and 7d on the removal efficiency,it was found that with the increase of time,the removal efficiency of nickel and chromium increases,but no obvious difference can be seen from 5d and 7d treated time.Considering the economic benefit,the best treated time of electrokinetic remediation is 5d.Moreover,the influences on the chromium and nickel desorption rate of cathode liquid type and concentration were studied,and the orthogonal experiment indicated that the type of cathode liquid has a relatively high effect on the desorption rate of chromium and nickel.With the addition of citric acid(0.1 mol/L)used as cathode liquid,the removal rate of chromium increased from 42.69%to 61.76%,increasing by about 19.07%.Because of the strong buffering capacity of soil,the removal rate of nickel only increased from 14.66%to 16.29%after the addition of citric acid.(2)The permeable reactive material has been selected and the results indicated that 2-mercaptobenzothiazole modified titanate nanotube by the method ?(denoted as MBT-NTA-2)has a good adsorption capacity for Cr(?),and the optimal ratio of reagents of n(KI):n(CPTS):n(MBT)is 1.5:1:1.5.For the adsorption of Ni2+,sodium titanate nanotubes(denoted as NTA-Na)was the best material.The adsorption of Cr(?)and Ni2+ by two kinds of permeable reactive materials is in accord with Langmuir adsorption and pseudo two order kinetics model.(3)After the addition of 0.5 cm MBT-NTA-2 reaction wall near the anode,1 cm MBT-NTA-2 and NTA-Na reaction wall in the middle of soil room and 0.5 cm NTA-Na reaction wall near the cathode,the removal rate of Cr(?)and Ni2+ increased from 58.27%and 14.11%to 83.84%and 57.36%,increasing by 25.57%and 43.25%,respectively.