Impacts of supporting electrolyte and aeration conditions on Fe mineral formation and heavy metal immobilization in Fe-electrocoagulation at acidic pH
In this study,a series of experiments on Fe-electrocoagulation were conducted to treat acidic heavy metal wastewaters.The effects of the type of supporting electrolyte and aeration on the performance of electrocoagulation and the species of Fe minerals were investigated.The results of the research showed that the acidic electrocoagulation process can be divided into two stages:Fe accumulation stage and Fe mineralization stage.The accumulation stage mainly involves the generation and enrichment of Fe(Ⅱ)/Fe(Ⅲ),while mineral formation and immobilization of heavy metals mainly occur in the latter stage.The use of NaNO3 as the supporting electrolyte resulted in the passivation of Fe anodes,leading to a low mineralization rate and heavy metal removal efficiency.Without aeration,Fe-electrocoagulation systems with NaCl,Na2SO4,and NaH2PO4 as supporting electrolytes generated magnetite,green rust,and vivianite,respectively.Under aeration conditions,iron hydroxide was formed in NaCl and Na2SO4 electrolyte systems,while iron phosphate was produced in the NaH2PO4 electrolyte system.Magnetite and green rust were found to have high adsorption efficiencies for the heavy metals Cd(Ⅱ),Cu(Ⅱ),and Ni(Ⅱ),with magnetite demonstrating a higher adsorption efficiency for Cd(Ⅱ)than green rust.Meanwhile,vivianite and iron phosphate effectively fixed Cu(Ⅱ)and Cd(Ⅱ),while Ni(Ⅱ)had poor adsorption on both minerals.The adsorption efficiencies of the four types of heavy metals for iron hydroxide were low.The results of leaching experiments showed that the adsorption stability of heavy metals on magnetite and green rust was better than that on vivianite,iron hydroxide,and iron phosphate.Overall,the findings of this study provide important evidence for the potential use of Fe-electrocoagulation as an effective method for treating acidic heavy metal wastewaters.
electrocoagulationsupporting electrolyteaerationiron mineralsheavy metal immobilization
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