Study On Removal Of Heavy Metal Ions Cu（Ⅱ） And Cr（Ⅵ） From Wastewater By Electrocoagulation Process

There are many industries such as metal smelting, electrolysis,electroplating and chemical industries discharging a large number ofwasterwater containing heavy ions into the environment every year. Thiskind of wastewater with very high toxicity, would damage human healththrough the food chain. So the effective measures must be taken to treatthe heavy metal wasterwater. Electrocoagulation is one of the commonlyused methods for hwavy metal wasterwater treatment, which was appliedfor the removal of Cu（Ⅱ） and Cr（Ⅵ） from wasterwater in this study.The influence of initial pH, reaction time, current intensity, NaCldosage, initial concentration of Cu（Ⅱ） and Cr（Ⅵ）, aeration and ionscoexistence on Cu（Ⅱ） and Cr（Ⅵ） removal was studied. The resultsshowed that, when initial Cu（Ⅱ） concentration was100mg/L, initial pHwas6, reaction time was20min, current intensity was4A, NaCl dosagewas0.2g/L, aeration rate was0.1m3/h, the Cu（Ⅱ） removal rate was ashigh as99.9%. Under the conditions that initial concentration of Cr（Ⅵ）was100mg/L, initial pH was6, reaction time was30min, current intensity was4A, NaCl dosage was0.2g/L, aeration rate was0.1m3/h, the Cr（Ⅵ）removal rate also reached99.9%.According to the results of preliminary experiments, the reaction time,current intensity and initial irons concentration were considered as maininfluencing factors and then the study on Cu（Ⅱ） and Cr（Ⅵ） removaland energy consumption was carried out by the multi-factors orthogonaltest method to determine the optimal conditions for Cu（Ⅱ） and Cr（Ⅵ）removal. The optimized operating conditions for Cu（Ⅱ） removal wasobtained with initial concentration of20mg/L, current intensity of3A andreaction time of30min, in which the removal rate was99.9%and energyconsumption was only0.2252kWh/mg. As to the ones for Cr（Ⅵ）removal, the conditions with initial concentration of40mg/L, currentintensity of4A and reaction time of30min were optimum, in which theremoval rate was99.9%and energy consumption was0.3003kWh/mg.In addition, electrocoagulation process was used to remove Cu（Ⅱ）and Cr（Ⅵ） from the real electroplating wastewater and it was revealedfrom that, the removal trend of Cu（Ⅱ） and Cr（Ⅵ） in electroplatingwastewater was basically the same as that in the synthetic water, thehighest removal rates were99.5%and99.7%, respectively, which all meetthe Emission standard of pollutants for electroplating(GB21900-2008).The mechanism of heavy metals removal in wastewater byelectrocoagulation was preliminary discussed based on the above experimental data.