Mechanism Research Of Oxidation/Reduction And Fixation Of Water Pollutants Based On Iron-air Primary Battery Reaction

Chromium and arsenic are widely distributed in many natural aquatic environments and avariety of relevant industrial effluents.Due to their hypertoxicity,carcinogenicity and stong mobility,Chromium and arsenic are stipulated as priority pollutants.Hence disposal of waste containing Cr/As pollutants becomes a wellrecognized environmental issue of the modern world and till now,many traditional and advanced approaches have been applied for the remediation of Cr(Ⅵ)/p-ASAcontaminated effluents or sites.In spite of this,these approaches still need to be upgraded for more cost-effective and environmental compatibility.In addition,further studies are still required to inspect the reaction mechanisms of many remediation technologies.In view of this,we developed an IAFC system consisting of an iron anode and an activated carbon-PTFE based air-cathode,and evaluated its performance for Cr(Ⅵ)removal and power generation.In this reaction system,cathodic reaction-assisted Fe(Ⅱ)reduction contributed to the reductive removal of Cr(Ⅵ).It was found that the decrease of solution p H from 6.0 to 3.0 could promote the removal of Cr(Ⅵ)due to the enhanced yield of Fe(Ⅱ)ions and cathodic reduction,accompanying the increased power generation from 1040 m W m-2 to 2880 m W m-2.Besides,the Cr(Ⅵ)removal and power generation could be also promoted by elevating Na2SO4 concentration from 0.01 M to 0.1 M.In the IAFC process,the removal of Cr(Ⅵ)mainly proceeded via the homogeneous reduction with dissolved Fe(Ⅱ)ions,heterogeneous reduction with the adsorbed or structural Fe(Ⅱ)at the precipitant and heterogeneously cathodic reduction.Subsequently,electrostatic adsorption and/or co-precipitation of Cr(Ⅲ)with Fe(Ⅲ)(oxy)hydroxide solids promoted the removal of Cr from solution in the IAFC system.In the IAFC system,the presence of phosphate and Si O32-has negligible effect on Fe(total)concentration and Cr(Ⅵ)removal,and this indicates that the IAFC system can effectively achieve the appreciable removal of Cr(Ⅵ)in some complex wastewater.Besides,an IAFC system consisting of an iron anode and a carbon black/PTFE air cathode has the synergistic effect of electric Fenton and electrocoagulation,and is a promising alternative for wastewater treatment.In this study,the performance of the IAFC process for p-arsanilic acid(p-ASA)removal and electric power generation were evaluated at initial p H of 3.0-6.0.The optimum p H for p-ASA removal was found to be 4.0 and approximately 95% of p-ASA could be removed within 15 min because of the stronger electrostatic attraction between p-ASA-and positively charged iron precipitant.In this case,adsorption on the iron precipitant and Fenton oxidation contributed almost equally to the removal of p-ASA with the concentration of residual inorganic arsenic below 10 μg L-1 in solution.Notably,the kinetics study revealed that the IAFC process had superior p-ASA removal efficiency as compared to electro-Fenton or electrocoagulation alone.Besides,as compared with chloride and nitrate ions,the presence of phosphate ions could deteriorate the removal of arsenic species to much more extent via competing with arsenic species for the adsorptive sites on the surface of iron precipitant.In summary,this paper constructs an iron-air fuel cell reaction system,which utilizes its oxidation/reduction ability and flocculation effect to achieve the treatment of typical water pollutant Cr(Ⅵ)/p-ASA.The system can also output electric energy while treating pollutants,which solves the limitations of traditional electric flocculation technology,such as large energy consumption and single use.The constructed IAFC system can be used in remote areas and in an environment where electricity is difficult to supply,and has certain reference value.