Treatment Of The Wastewater Containing Cadmium By Electrodeposition And Coagulation Method

Cadmium is a kind of heavy metal which is carcinogenic. It’s very threatening thatcadmium is absorbed by drink water or food chain. Hence Removing of cadmium is verysignificant. In this study, the wastewater containing cadmium was treated by electrodepositionand coagulation method. As the recovery of cadmium metal, the concentrations of cadmium intreated water reached0.1mg/L of the prescribed discharge standards in "integrated wastewaterdischarge standard "(GB8978-1996).Recovery of cadmium in water was investigated by an electrochemical deposition approachin a multi-anodes and multi-cathodes cell in this study. Ti plate and stainless steel were comparedto select the suitable cathode for cadmium recovery. The effects of initial concentration (400mg/L,600mg/L and1000mg/L), initial pH (1.5,3.5,5.5and7.5), current density (1.49mA/cm2,2.97mA/cm2,4.46mA/cm2and5.95mA/cm2), supporting electrolytes (NaCl, NaNO3, andNa2SO4), humic acid, and complexing agents (EDTA, sodium citrate, and aqua ammonia) on therecovery of cadmium were examined. The reduction peak of cadmium on Ti plate was-0.64V to-0.78V vs. SCE (saturated calomel electrode). The pseudo-first-order kinetic constants and thecurrent efficiency increased with the increase of initial concentration. The acdic media improvedthe recovery efficiency. When the current density increased from1.49mA/cm2to4.46mA/cm2,the recovery ratio were96.98%and99.34%after electrochemical deposition of120min. Whilefurther increase current density, little increase of recovery ratio was observed. The presence ofsodium nitrate decreased the recovery efficiency due to the competition reaction between nitrateand cadmium reduction on the cathode. HA with the concentration of200mg/L reduced thecadmium recovery at the first60min of electrochemical deposition, while it didn’t impact on the recovery at the second60min. Presence of aqua ammonia increased the deposition rate. X-raydiffraction (XRD) and scan electron microscopy with energy dispersive X-Ray spectroscopy(SEM-EDS) analysis demonstrated that the depositions were composed of cadmium andcadmium hydroxide.In the process of coagulation, we studied the effect of different pH value （5.0、6.0、7.0、8.0、9、0）, the flocculant for the form of Al and dosage of flocculant on cadmium removal. Theexperimental results show that the initial pH value of9, cadmium removal effect is better. Theflocculant for the form of Al with high polymer effected better. With polyaluminium chloride(PAC) dosing quantity increasing which the basicity was66.67%, cadmium removal efficiencyincreased significantly. XRD demonstrated that floc was compose of cadmium carbonate andcadmium hydroxide.