The Treatment Of Electroplating Effluent With Low Content Of Complex Copper And Complex Nickel

The large quantities of complex agents—citric acid in electroplating process make the metal copper and nickel hard to precipitate. In this paper, the methods PAC adsorption and ferric sulphate coagulation/sedimentation, which were applied to treat the electroplating wastewater contained Cu2+ and Ni2+ with low concentration, were studied.Activated carbon (AC) is an excellent adsorbent for its large specific surface area and stable chemical properties. Generally, AC absorb non-polar molecules by physical adsorption, however it can still absorb some substances by chemical adsorption as it contains lots of functional groups on its surface. In this paper, the performance of PAC on Cu2+ and Ni2+ adsorption was studied by the method of static adsorption test. To find optimum condition of adsorption, the effects of the concentration of complex agents, the dosage of PAC, pH of the solution and temperature on performance of PAC on metal adsorption were also tested. The result shows that:at the PAC dosage of 10 g/L, pH of 3.0, adsorption time of 60 min, the concentration of Cu2+ decreased from 50 mg/L to 3.4 mg/L, and the removal rate was higher than 93%; at the PAC dosage of 10 g/L, pH of 11.0, adsorption time of 60 min, the concentration of Ni2+ decreased from 20 mg/L to 5.45 mg/L, the removal rate is higher than 70%.Modified by HNO3 or KMnO4, the acidic functional groups on the surface of PAC increased, this enhanced the capacity of PAC on Cu2+ and Ni2+ adsorption. The PAC modified with HNO3(1+1) exhibited an excellent performance on Cu2+ adsorption. The removal rate of Cu2+ is as high as 97.4%. The removal rate of Ni2+ of PAC which was modified with KMnO4 (0.12 mol/L) was 97.6%, that was 25.3% higher than that of unmodified PAC.After regeneration by HCl and NaOH, copper desorption rate of saturated PAC was higher than 89.9%, nickel desorption rate of saturated PAC was higher than 91%. After 5 times of regeneration, the adsorption capacity of PAC on copper and nickel remained unchanged. Thus PAC can be recycled by several times.The method of ferric sulphate coagulation/sedimentation was applied to treat the electroplating wastewater. The dosage of ferric sulphate, pH and other factors were confirmed. At the ferric sulphate dosage of 2.0 g/L, pH of 12.0, the removal rate of Cu2+ and Ni2+ is higher than 99%, when the initial concentration of Cu2+ and Ni2+ were 50mg/L and 20mg/L. Treated by this method, the concentration of Cu2+ and Ni2+ in the effluent are conform to the state standards.The methods of PAC adsorption and ferric sulphate coagulation/sedimentation can gather heavy metal effectively; this may realize the treatment and reuse of complex copper and nickel with low concentration in electroplating effluent.