Removal Of EDTA Complexed Cu(Ⅱ) By Attapulgite Supported Metal Oxide Based Catalyst System Combined With Alkali Precipitation

Heavy metal pollution does serious harm to the human body.Proteins and various enzymes in the human body would become inactive by reacting with heavy metals.Heavy metals such as lead,cadmium,and copper would cause serious pollution when they enter the water,soil,and atmosphere.For example,heavy metals would lead ecosystem endangure through the food chain as they were discharged along with waste water,accumulated in algae or sediment,and were absorbed by fish and shellfish.The removal of heavy metals in water treatment generally uses alkali precipitation.However,with the large number of applications of complexing agents in industrial production,a large amount of complexing agents are discharged into the sewage.The heavy metal ions could combine with the complexing agent and formed metal chelates which were easily soluble and chemically stable,caused great difficulties for removing heavy metals.The attapulgite is a kind of high-quality mineral with abundant reserves and low cost,which has the advantages of large specific surface area,strong thermal stability,and stable chemical properties,which makes it an applicable catalyst carrier.Thus in this study,attapulgite was used as a carrier to for synthesizing different catalyst.The Cu（II）-EDTA chelate was catalytically oxidized for breaking the coordination bond,and Cu（II）was discharged from complexation,followed by alkaline precipitation removal.The specific content mainly includes the following three parts:（1）The ATP-TiO₂ photocatalyst was successfully prepared by sol-gel method using attapulgite as the carrier and tetrabutyl titanate as the titanium source.The ATP-TiO₂ photocatalyst was characterized by XRD,EDS and XPS.The effect of initial concentration of complexed Cu（II）,initial pH,the amount of catalyst,and the calcination temperature of the catalyst on the removal rate of the complexed Cu（II）in UV/ATP-TiO₂ photocatalyst system were investigated to obtain the optimum.The results showed the optimum Cu（II）removal condition was that the initial Cu（II）concentration was 20 mg/L,the initial pH was 5,the catalyst calcination temperature was 510^oC and the amount of catalyst was 1 g/L,the complexed Cu（II）removal rate reached 98.54%after 3 hours’reaction.From the XPS analysis,it can be seen that after photocatalytic reaction,zero-valent copper exists on the surface of the catalyst,indicating that the divalent copper in the solution can be recovered as metallic copper to the surface of the catalyst.（2）Using attapulgite as a carrier,Fe₂O₃ was immobilized on the surface of attapulgite as a heterogeneous Fenton-like catalyst by the function of hexamethylenetetramine.ATP-Fe₂O₃ was characterized by XPS,XRD and FTIR.The comparation of different catalyst system was investigated include H₂O₂alone,ATP-Fe₂O₃ alone and combination of H₂O₂ and ATP-Fe₂O₃.In ATP-Fe₂O₃/H₂O₂ system,the effect of the initial pH,the concentration of hydrogen peroxide and the amount of ATP-Fe₂O₃ added to the removal of complexed Cu（II）were studied.Lastly,the application of cycled ATP-Fe₂O₃ to the removal of complexed Cu（II）was investigated.The results indicated that Cu（II）removal rate was 13.39%,7.07%and 40%when hydrogen peroxide,ATP-Fe₂O₃ and ATP/H₂O₂ was used,respectively,which were much less than removal efficiency by ATP-Fe₂O₃/H₂O₂.The optimal condition for the removal of complexed Cu（II）was that hydrogen peroxide concentration was 0.36 mol/L,ATP-Fe₂O₃ dosage was 16 g/L,initial pH was 3,and the initial complexed Cu（II）concentration was 40 mg/L,the complexed Cu（II）removal rate reached 98.99%after reacting for 1 h.The removal rate of complexed Cu（II）remained 90.58%after 5 times of ATP-Fe₂O₃ cycling.（3）Using attapulgite as carrier,Fe²⁺was reduced to Fe⁰ by NaBH₄ and loaded on attapulgite to synthesize ATP-Fe⁰ heterogeneous catalyst.The ATP-Fe⁰was characterized by FTIR and XRD.The comparation of different catalyst system was investigated include H₂O₂ alone,ATP-Fe⁰ alone and combination of H₂O₂ and ATP-Fe⁰.To obtaine the optimum condition of removing complexed Cu（II）,the effect of initial pH,H₂O₂ concentration,reaction time,reaction temperature and ATP-Fe⁰ dosage to the removal of complexed Cu（II）were investigated.At last,complexed Cu（II）removal by cycled ATP-Fe⁰ was studied.The results indicated that complexed Cu（II）removal rate was 20.6%and 13.05%when hydrogen peroxide,ATP-Fe⁰ was used alone,which were much less than the removal efficiency by ATP-Fe⁰/H₂O₂.The optimal condition for the removal of complexed Cu（II）with initial concentration 40 mg/L under room temperature was that the hydrogen peroxide dosage was 20 mmol/L,ATP-Fe⁰ was 2 g/L,initial pH was 5,reaction time was 45 min and the complexed Cu（II）removal rate reached 98.9%.The removal rate of complexed Cu（II）after the ATP-Fe⁰cycled for 5 times was 76.55%.The results indicated that ATP-TiO₂/UV、ATP-Fe₂O₃/H₂O₂ and ATP-Fe⁰/H₂O₂ system combined with alkali precipitation were highly efficient for removing of complexed Cu（II）which was existed as low concentration in polluted water.