Co-pyrolysis Biochar For Enhanced Electrokinetic Remediation Of Heavy Metals Contaminated Sediments

Due to industrial production,mining and other human activities,a large number of heavy metals enter the water environment and eventually gather in the sediment causing pollution problems.Heavy metal pollution in sediment has the characteristics of large stock,complex pollution types and easy to cause secondary pollution.Therefore,it is necessary to carry out research on remediation of heavy metals contaminated sediments.In this paper,electrokinetic-responsive permeation barrier(EK-PRB)remediation technology was adopted for artificially contaminated heavy metal(Pb and Cd)composite sediment,combing with the material characterization method and a heavy metal fugitive morphology simulation software.A multi-factor response model was built for modelling the removal efficiency and energy consumption,the effects of co-pyrolysis biochar filler performance,the type and concentration of the chemical agent,PRB quantity and location on heavy metal removal efficiency and energy consumption,respectively.The effects of co-pyrolysis biochar filler performance,auxiliary chemicals,PRB quantity and location on heavy metal removal efficiency,energy consumption and substrate properties were investigated.The main findings of this paper are as follows.(1)Low-density polyethylene(PE)-reed co-pyrolysis biochar(HBC)was successfully developed as reactive materials for EK-PRB remediation of heavy metal contaminated sediments.Through material characterization methods and adsorption performance investigation,the optimal pyrolysis conditions of the material were determined as follows: 1:1 mass ratio of reed and polyethylene was pyrolyzed at 500°C for 2 h.The material had a larger specific surface area and more functional groups.The equilibrium adsorption capacity of the co-pyrolysis materials was shown to be positively correlated with the adsorption rate and temperature by adsorption equilibrium studies.The adsorption capacity was best at p H 3-6,while the adsorption equilibrium capacity showed different degrees of decrease at p H > 6.Pb(II)was more susceptible to the influence of environmental p H than Cd(II).The adsorption process of Pb(Ⅱ)and Cd(Ⅱ)by co-pyrolysis materials was in accordance with the Langmuir model,and the adsorption process tended to be monolayer adsorption.The absorption characteristics of PE-HBC was explained well with the pseudo-second-order(PSO)and Langmuir models,which revealed that the absorption of Pb(II)and Cd(II)in water was monolayer chemisorption.(2)A novel combination of auxiliary agents(GLDA+CA+Na Cl)was developed to enhance electrokinetic remediation by discussing the effects of different component concentrations on heavy metal removal rates and energy consumption.0.2 mol/L of CA+GLDA and 0.05 mol/L of Na Cl mixed as leaching agent and electrolyte had optimal electrokinetic efficiency for electrokinetic remediation,and the removal rates of Cd(II)and Pb(Ⅱ)reached 65.6% and 68.0%,respectively.The response models of agent type,agent concentration and remediation time on heavy metal removal rate and energy consumption were constructed,and the maximum remediation efficiency and optimal remediation conditions for both heavy metals were optimized and predicted within the interval.Compared with the conventional citric acid remediation,the combined solution of auxiliary agents have better removal efficiency and less environmental hazards,which is a promising combination of auxiliary agents for electric remediation in sediment.(3)The effectiveness of the combined EK-PRB remediation technology and the effects of PRB location and quantity on the remediation efficiency of heavy metals were investigated.When a single PRB was placed in the middle of the substrate chamber based on the combined agent,the removal efficiency of Pb and Cd was improved by25.66% and 51.06%,respectively,compared with that of EK leaching remediation.When the number of PRBs was increased to two,which were placed in the middle of the substrate and near the cathode side,the best removal efficiencies of 56.8% and 57.4%were obtained for Pb and Cd from the substrate,respectively.It was demonstrated that EK-PRB based on the new co-pyrolysis material can achieve the remediation of heavy metal substrate composite pollution,and PRB can improve the adsorption efficiency of heavy metals by reducing the ion migration distance and controlling the pH of the surrounding environment.