Experimental Study On Remediation Of Copper-Lead Contaminated Soil By Waste Concrete PRB-electrokinetic Combined Method

Electrodynamic remediation technology is a kind of soil remediation technology favored by researchers at home and abroad in recent years.The technology has low cost and no secondary pollution.It is especially suitable for the removal of pollutants in low permeability clay.It can also be combined with other remediation technologies to repair the composite contaminated soil.In this paper,the copper and lead contaminated soil configured in the laboratory is taken as the research object,and the electrokinetic remediation technology and permeable reaction wall（PRB）are used to carry out the simulated remediation test.The main results are as follows:（1）In this paper,the safety of waste concrete as an adsorbent and its adsorption characteristics for heavy metals copper and lead in water were studied.Through heavy metal leaching test and static adsorption test,the effects of its safety,adsorption time,amount of adsorbent and initial concentration of heavy metals on the adsorption of heavy metals by waste concrete were investigated.The results show that with the decrease of the particle size of waste concrete,heavy metals are leached,but they are far less than the standard value,which will not cause secondary pollution.The adsorption of copper and lead by waste concrete conforms to the Langmuir isothermal adsorption model,and the fitted equilibrium adsorption amounts are40.75mg/g and 86.73mg/g respectively.The pseudo second-order kinetic model is more suitable to describe the adsorption process of copper and lead by waste concrete,indicating that chemical adsorption is the main factor controlling the adsorption rate.（2）In this paper,the traditional electrokinetic remediation technology was optimized by changing the remediation voltage and the concentration of citric acid in cathode electrolyte to improve the removal rate of heavy metals in soil.The results show that the removal rate increases with the increase of voltage,but it is not particularly obvious.When the repair voltage increases from 40 V to 50 V,the removal rate of copper increases by 5%,and the removal rate of lead increases by 5.66%,but the energy consumption only increases by 28.3%.When the repair voltage increases from 50 V to 60 V,the removal rates of both heavy metals increase by about 1%,while the energy consumption increases by 45.7%.Finally,50 V voltage is selected as the basic voltage for subsequent tests.Citric acid is used to control the pH of the cathode electrolyte,so that the soil near the cathode changes from alkaline to acidic,which is conducive to the removal of the two heavy metals.Through comparative analysis,it is determined that the removal effect is the best when the citric acid concentration is 0.2mol/l.（3）In this paper,waste concrete was used as PRB material,and 50 V and 0.2 mol/L citric acid were selected as the remediation conditions for combined EK-PRB remediation experiments,which were compared with electrokinetic remediation experiments alone.The experimental results showed that the removal rates of copper and lead were increased by 20.1% and 15%,respectively,compared with the electrokinetic remediation experiment alone.Moreover,the combined EK-PRB remediation was less current than that in the separate remediation,and the total energy consumption was saved by 3%.the addition of PRB materials could effectively improve the removal rate of both heavy metals in each soil area,reduce the enrichment of heavy metals in the soil,and also reduce the accumulation of heavy metals in the cathode electrolyte,so that the cathode electrolyte could be recycled.（4）In this paper,the practicality of waste concrete as a PRB material was analyzed by comparison through a combined remediation experiment using three materials that had been used as PRBs,activated carbon,zeolite,and steel slag,and waste concrete under the same remediation conditions.The experiments showed that the removal rates of both heavy metals were improved when the four PRB materials were used for combined electric-PRB remediation,with the steel slag and waste concrete as PRB materials improving the heavy metal removal rates between 15%and 23% when compared to the remediation alone,but the steel slag consumed 31.9% more energy than the concrete.Waste concrete as a resource reuse material is more cost effective compared to other materials and also saves resources and has better energy efficiency.