Preparation Of Polypyrrole-melamine Foam Auxiliary Electrode And Its Electrokinetic Remediation Of Cr(Ⅵ)-contaminated Soil

Soil heavy metal pollution brings serious impact to human survival and development.How to efficiently remediate heavy metal Cr contaminated soil has become one of the research hotspots.Currently,reducing Cr(Ⅵ)to less toxic Cr(Ⅲ)and limiting its mobility is the main focus of research.Although this scheme can meet the soil use requirements,there is still a risk of re-oxidation and release of Cr(Ⅲ)from the soil.Therefore,it is significant to develop technologies for the effective separation and extraction of heavy metals from soil and their subsequent resource utilization.In this thesis,the prepared auxiliary electrodes were added to the traditional electrokinetic remediation(EKR)system to construct a novel EKR system,thus promoting the enrichment and removal of heavy metals from soil.In this study,polypyrrole/melamine foam(PPy-MF)auxiliary electrodes were prepared by in situ chemical polymerization.It is shown that the PPyMF auxiliary electrode combines the excellent electrochemical performance of conductive polymer polypyrrole(PPy)and the stable porous structure of melamine foam(MF).Firstly,PPy-MF was used as an adsorption material to adsorb Cr(Ⅵ)in solution,and the adsorption performance and influencing factors of PPy-MF for Cr(Ⅵ)were investigated.PPy-MF with the best adsorption performance was selected for EKR.Secondly,the PPy-MF auxiliary electrode was added to the traditional EKR system to investigate the effect of the PPy-MF auxiliary electrode on the current and electric field distribution in the system and to analyze the effect of soil pH and soil electrical conductivity(EC)on the migration and removal of Cr(Ⅵ)through the study of Cr(Ⅵ)removal performance.The operating mechanism of the PPy-MF auxiliary electrode to enhance EKR efficiency is clarified by the distribution characteristics of Cr in the system space.The results show that:(1)PPy-MF exhibited a maximum adsorption capacity of 140.2 mg/g when C(SDBS):C(CTAB)was 1:2 and pyrrole(Py)was dosed at 2 mL.The analysis shows that the PPy-MF auxiliary electrode has excellent charge/discharge capability(specific capacitance of 34.31 F/g)and low electrochemical impedance,which facilitates charge conduction,saves cost,and alleviates electrode polarization.(2)The PPy-MF auxiliary electrode coupled with the conventional EKR significantly improves the EC of the soil as well as the current strength of the EKR system and optimizes the distribution of the electric field.Because of the strong Lewis acid property of PPy,it can inhibit the development of an alkali front in the EKR process in addition to buffering the polarization of the catholyte’s pH.Acidic conditions are more conducive to the removal of heavy metals in soil.(3)The PPy-MF auxiliary electrode improved the average removal rate of total chromium from the soil of the EKR system,and the study showed that 34.5%,26.1%,and 25.2%were increased at 30 V,45 V,and 60 V,respectively,compared to the traditional EKR.In addition,the total chromium concentration in the anode solution was reduced substantially because PPyMF had good Cr(Ⅵ)adsorption and could reduce Cr(Ⅵ)to Cr(Ⅲ)immobilized on the auxiliary electrode.The EKR synergized with PPy-MF auxiliary electrode showed 83.3%,92.9%,and 94.5%Cr(Ⅵ)removal from the soil at 30 V,45 V,and 60 V,respectively,which were 11.5%,10.1%,and 9.9%higher than the traditional EKR at the same voltage gradient,and improved the overall Cr(Ⅵ)reduction rate of the soil.The use of PPy-MF auxiliary electrodes can achieve the effect of traditional EKR high voltage operation under low voltage supply conditions,saving electricity costs.(4)PPy-MF could improve the average removal rate of total Cr and Cr(Ⅵ)in soil of electrokinetic remediation system,indicating that PPy-MF auxiliary electrode promoted the electromigration of heavy metals in soil,which promoted a theoretical basis for improving the efficiency and applicability of electrokinetic remediation technology.PPy-MF as an adsorbent could significantly adsorb and reduce Cr(Ⅵ)in the soil,which not only played a fixed role in Cr(Ⅵ)in the soil but also reduced the possibility of secondary contamination.In addition,the increased reduction rate of overall soil Cr(Ⅵ)also reduced the ecological risk.This study provides a simple and effective auxiliary electrode for enhanced electrokinetic remediation of Cr(Ⅵ)-contaminated soil and provides a new reference for soil and sludge heavy metal remediation.