Experiment Of Electrodynamic-(Fe) PRB Joint Remediation Of Cr(Ⅵ) Contaminated Soil

In this paper,Electrokinetic-Permeable Reactive Barrier Technology（EK-PRB）is used to remediate Cr（Ⅵ）contaminated soil.The reduction performance of PRB medium（common iron filings and nano-zero-valent iron）on soil Cr（Ⅵ）was studied through preliminary experiments.The composition ratio of iron in different valence states in ordinary iron filings and nano-zero-valent iron is different.The ordinary iron filings are mainly Fe²⁺and Fe³⁺oxides,while nano-zero-valent iron is mainly Fe⁰.This experiment explores iron with different valence states.The role in the reduction reaction,analysis of the reduction reaction mechanism.The remediation effect of electrodynamic（EK）single technology and EK-PRB combined technology were investigated,and the remediation effect of two PRB media of ordinary iron filings and nano-zero valent iron on Cr（Ⅵ）contaminated soil were compared and studied,and the effect of chromium in an external electric field was discussed The following migration laws,the reaction mechanism of chromium and PRB,and the five forms of chromium removal and transformation laws provide theoretical guidance for the practical application of EK-PRB technology in the remediation of chromium contaminated soil.The main research results of this article are as follows:（1）Pre-experimental results show that the ability of nano-zero-valent iron to reduce Cr（Ⅵ）is higher than that of ordinary iron filings.The highest reduction efficiency of nano-zero-valent iron is 94.42%,and the highest reduction efficiency of ordinary iron filings is 85.36%.As the dosage of reducing agent increases,the reduction efficiency of ordinary iron filings also increases.The reduction efficiency of nano-zero-valent iron reaches its peak at a molar ratio of 5;as the p H decreases,ordinary iron filings and nano-zero-valent iron The reduction efficiency of iron will increase;the initial moisture content of the soil has little effect on the reduction efficiency of Cr（Ⅵ）with the two reducing agents;compared with ordinary iron filings,nano-zero-valent iron has a longer validity period and is not easy to deactivate.（2）Compared with electrodynamic（EK）single technology repair,EK-nZⅥ combined repair has a 63%removal rate of chromium and a 48%removal rate of EK.The highest concentration of Cr（Ⅵ）after EK-nZⅥ restoration is 25.52mg/Kg（the concentration before restoration is 567.41mg/Kg,the removal rate of hexavalent chromium is 95.5%）,the highest concentration of Cr（Ⅵ）after EK restoration is 72.45mg/Kg（The removal rate is 89.65%）.The total chromium removal rate of the EK-nZⅥ joint repair experiment was 63%,which was slightly higher than the result of the EK-common iron filing joint repair experiment（59%）.After EK-nZⅥ restoration experiment,the highest concentration of total chromium was 305.12mg/Kg;after EK-common iron filings restoration experiment,the highest concentration of total chromium was 360.27mg/Kg.（3）In the original soil before restoration,chromium mainly exists in exchangeable state,accounting for about 80%.After the restoration experiment,the proportion of exchangeable state is maintained at 5%-8%;carbonate-bound chromium is affected by p H The content of the organic binding state and iron-manganese oxide binding state increased from 41%at the cathode end to 10% at the anode end,and the residual content was extremely low,and the concentration remained basically unchanged during the whole experiment.（4）Through Fourier infrared spectroscopy,XPS analysis and scanning electron microscopy analysis,it is found that Cr（OH）₃ precipitates are formed on the surface of nano-zero-valent iron.After the reaction,there are Cr（Ⅵ）and Cr（III）,Fe⁰ The reduction ability is stronger than Fe²⁺,and the physical adsorption of nano-zero-valent iron to chromium is higher than the reduction effect.