Optimization Technology For The Electrokinetic Remediation Of Chromium Contaminated Soil By An Auxiliary Liquid Chamber Combined With Enhancing Agents

The chromium residue left by the chromium contaminated site is not effectively treated and improperly stacked,under the action of natural physicochemistry,its highly toxic and easily migratory Cr is released into the environmental medium,which pollutes a large area of soil and seriously threatens human health and ecological security.Electrokinetic remediation technique is effective in removing Cr from soils,especially the highly mobile Cr(VI).In the process of electrokinetic treatment of chromium residue contaminated soil,the opposite migration directions of Cr(III)and Cr(VI)and the difficulty of desorption and migration of Cr(III)from the soil result in an excessive accumulation of Cr in the middle of the soil chamber.In addition,the low moisture content in the middle of the soil chamber is not conducive to the migration of Cr.Therefore,in view of the above problems,the auxiliary liquid phase chamber was used to replace the soil in the Cr high accumulation zone near the cathode chamber,and compared with the control group(deionized water and nitric acid pretreatment)to explore the effect of the auxiliary liquid phase chamber setting on the electric remediation of chromium-contaminated soil,and on this basis,the combination of pretreatment reagent and auxiliary liquid phase chamber enhancer(nitrate-sodium nitrate,nitric acid-citric acid,Tween 80-GLDA,Tween 80-citric acid)was used to enhance the migration and removal of Cr and slow down the accumulation of Cr in the middle.The results showed that:(1)Compared with the control trials,the addition of auxiliary liquid chamber can adjust the moisture content and affect the advancement of the acid-base front of the soil chamber.In addition,the Cr migrating to the electrode chamber can be partially collected in the auxiliary liquid chamber,which shorten the migration path of Cr and enhanced the ability of the removal of Cr.(2)The pretreatment reagent combined with enhancer in auxiliary liquid chamber alleviated the middle accumulation of total Cr to a certain extent,with different mechanisms of action of the enhancers and different amounts of total Cr accumulation.When pretreated nitric acid and liquid chamber enhancer citric acid were used,the Cr(VI)removal rate was lower,but the total Cr removal was greatly improved at 44.66%.When Tween 80 was combined with enhancer GLDA in auxiliary liquid chamber,the surfactant Tween 80 promoted the migration of Cr(VI)and obtained the highest removal rate(83.98%).(3)The combined use of pretreatment reagents and enhancers in auxiliary liquid chamber showed certain differences in promoting the conversion of Cr from strongly bound Cr to weakly bound Cr.The auxiliary liquid chamber enhancer citric acid promoted the transformation of iron-manganese oxidation state and residual Cr state,while Tween 80 as a soil pretreatment reagent can convert part of the dissolved Cr into organic bound Cr.(4)The chromium concentration in different valence states in the liquid phase chamber and soil transport area varied significantly.The combination of nitric acid with the auxiliary liquid chamber enhancer citric acid facilitated the removal of Cr(III)from the S1 region but tended to cause partial adsorption of Cr(VI)on the surface of the soil particles.The addition of citric acid to the auxiliary liquid chamber promoted the resolution and migration of Cr(III)in the S3 region,and the relatively low p H was conducive to the reduction of Cr(VI)to Cr(III)by citric acid.The removal of Cr(VI)in the S5 region under the influence of the auxiliary liquid chamber enhancer GLDA was relatively high.(5)The pretreatment reagent combined with enhancer in auxiliary liquid chamber can improve the energy efficiency of the system,among which Tween 80 combined with auxiliary liquid chamber enhancer citric acid achieved the lowest energy consumption and the highest energy utilization efficiency.In this study,the auxiliary liquid phase chamber was used to replace the soil in the near-cathode Cr contaminated high accumulation zone.From the perspective of liquid chamber optimisation,the addition of an auxiliary liquid chamber enhancer and the combination of pretreatment reagents weakened the central accumulation of Cr and further enhanced the removal of Cr,providing some theoretical reference for the electrokinetic detoxification of Cr in field soils.