Mechanical Study Of Rapid Reductive Removal Of Complexed Cu(Ⅱ) And Copper Recovery By Anoxic Iron Electrocoagulation

In recent years,the treatment of complexed heavy metal wastewater has become a hot and difficult problem.At present,the most commonly used method is to add iron salt for the replacement decomplexation,but this technology not only increases the labor cost,but also needs to add alkali to precipitate heavy metal ions later.Electrocoagulation technology has been proved to be a green and effective process for treating different types of wastewater containing heavy metals.It can control the casting acceleration rate of Fe（Ⅱ）and adjust the p H of the solution by adjusting the current intensity.In this study,based on the reductive displacement by Fe（Ⅱ）ions,we proposed a new process of anoxic iron electrocoagulation controlled by current regulation.Based on this process,the main research contents and conclusions of this paper are as follows:（1）With Cu（Ⅱ）-EDTA as the targeted pollutants,the factors（current intensity,initial p H,coexisting ion concentration,ligand concentration,etc.）affecting the removal of complexed Cu（Ⅱ）by anoxic iron electrocoagulation were studied.It is found that Cu（Ⅱ）-EDTA was the most economic removed at the current intensity of 200 m A.At different initial p H（2-7）,the removal rate of Cu（Ⅱ）-EDTA is above 90%.Ca²⁺and Mg²⁺has little effect on Cu（Ⅱ）-EDTA removal,but HPO₄^2-has a significant impact on the removal of Cu（Ⅱ）-EDTA by binding Fe（Ⅱ）.Replacing the complexed agent EDTA with other organic ligands（NTA,citric acid,tartaric acid,etc.）,the removal rate of complexed copper can reach more than 88%after 30 min of electrolytic.（2）By determining the distribution of copper under different initial p H conditions,the removal mechanism of bivalent copper ions in the complexed state is different under the initial p H<3 and≥3.At an initial p H<3,the dissolved Fe²⁺reduces most of the Cu（Ⅱ）-EDTA to Cu（I）-EDTA.At the initial p H≥3,Cu（Ⅱ）-EDTA is mainly reduced by Fe²⁺to Cu（I）-EDTA,and then replaced to be free Cu（I）,at last precipitated in the form of Cu₂O.The solid samples generated by iron electrocoagulation were tested by XPS,SEM,XRD,FTIR and XAS,which further confirmed that the Cu（I）ions in solution were mainly precipitated in the form of Cu₂O on sulfate green rust and magnetite at the initial p H 3.（3）The efficiency and mechanism of of Cu recovery by aeration and H₂O₂addition were compared.The results showed that with the addition of oxygen or H₂O₂,Fe（Ⅱ）oxidizes to Fe（ⅡI）.As Fe（ⅡI）consumes the OH^-of the solution,the Cu₂O in the precipitate was dissolved.Thus,the concentration of Cu ions in the solution is rising,and exists in the solution in the form of ions,instead of complexed Cu.49%of copper was recovered by aeration for 60 min,but 61%of copper was recovered by adding 0.3ml of hydrogen peroxide.