Study On The Process And Mechanism Of Electrolytic Cycle Persulfate Oxidation Method In The Remediation Of Typical Organic Pollution Soil

The problem of organic soil pollution not only poses a serious threat to the surrounding environment and the health of the inhabitants,but also seriously hinders the reuse of urban land resources.Persulfate advanced oxidation processes（PS-AOPs）has the advantage of strong oxidation capacity and wide applicability in the field of organic contaminated soil remediation.However,because persulfate is converted to sulfate after it acts as an oxidant,this process is irreversible in the absence of other functions,making the reagent has a one-time consumability and high demand,which results in huge consumption of persulfate and high remediation costs.In addition,a large amount of sulfate remains and accumulates in the soil after remediation,causing great harm to the environment,ecology and human health,seriously restricting the application of this technology.In this regard,according to the principle that persulfate can be reduced after remediation and oxidized by electrochemical reactions,this project proposes to regenerate the repair agent on site after recycling,thus the cyclic utilization of persulfate is expected to be realized.In pursuit of high regeneration rate and high oxidation activity of remediation agent,an integration system of ammonium sulfate electrochemical regeneration,electrical/carbon synergy activation and organic contaminated soil remediation was proposed in this study.Using carbon fiber as porous electrode materials,ammonium sulfate was prepared by electrochemical synthesis on the electrode interface through penetrating through porous anode under the action of driving;then the generated ammonium persulfate was co-activated by electrical/carbon when penetrating through porous cathode;the activated agent was injected into the soil for organic pollutants degradation by multi-path;the agent after remediation was withdrew and reinjected into the electrochemical reaction reactor after pre-treatment.The research results will facilitate to provide theoretical basis and practical foundation for reducing the application cost and ecological risk of PS-AOPs in remediation of organic contaminated soil.The main research results are as follows:（1）Mechanisms of electrochemical generation of ammonium persulphate at electrodes.During the electrochemical synthesis of ammonium persulphate,enhanced convective mass transfer within porous electrodes can significantly enhance the mass transfer and electrochemical reactivity of the solution,thereby improving the efficiency of ammonium persulphate synthesis.The results indicate that electron transfer becomes the rate-determining step in the electrochemical synthesis of ammonium persulphate.With the optimal parameter（voltage of 8 V,flow velocity of 10 m L/min,ammonium sulfate concentration of 3 M）,the generated concentration of ammonium persulfate was as high as 1.35 M and the current efficiency was 91.26%.（2）The synergistic effect of electro/carbon activated ammonium persulphate generates free radical pathways and non-free radical pathways for the multi-path remediation of organically contaminated soils.The results showed that electrical/carbon could effectively activate ammonium persulfate,and simulation experiments and dynamic analysis indicated that the production of active substances promoted by electron transmission was the key to improve the activation efficiency.Thus,92.15%of naphthalene in the contaminated soil was removed by the non-radical pathway（active substance PS^*with transition state structure and active substance of O₂·^-and ¹O₂）and the free radical pathway（SO₄·^-,·OH）.（3）The electrolytic cycle system for remediation of organic contaminated soil was constructed,and the performance of this system was explored.The results show that a great remediation efficiency was maintained after 5 cycles,and the stability of the circulating system was proved because the electrode could still maintain a large surface area,effective functional groups,and electronic transmission capacity.The regeneration of sulfate solution could achieve,no competing mechanism existed between regeneration of persulfate and degradation of soluble organic impurities,because the impurities could be removed timely through adsorption-direct oxidation-indirect oxidation（·OH and O₂·^-）processes.In addition,the circular system showed excellent remediation performance under remediating soil with different particle size,acid-base environment,multiple pollutants and ions,exhibiting extensive applicability.