Research On The Treatment Process Of Cadmium Electroplating Wastewater

Cadmium has excellent physical and chemical properties and plays a special role in electroplating.According to the complexing agent system,cadmium plating can be divided into cyanide cadmium plating and cyanide-free cadmium plating.Cyanide cadmium plating has been phased out due to the use of highly toxic cyanide,and now most enterprises adopt cyanide-free cadmium plating process.At present,ammonia-carboxylic complex electroplating cadmium is widely used.Because of the additionofcomplexingagentssuchasammoniatriaceticacidand ethylenediaminetetraacetic acid,the difficulty in treating cadmium wastewater is increased.Now,the implementation of the"Electroplating Pollutant Emission Standard"GB 21900-2008"Table 2"stipulates that the total cadmium emission limit in the discharged wastewater is 0.05mg/L.It is difficult to achieve stable discharge standards by the traditional precipitation method.Therefore,it is of great practical significance to study the treatment of complex electroplating cadmium wastewater.The experimental water used in this paper is 15mg/L NH₄Cl-Cd,NTA-Cd,EDTA-Cdsimulatedwastewaterandactualammonia-carboxyliccomplex electroplating cadmium wastewater.Through theoretical calculation and experimental verification,it is proved that the presence of complexing agent has a great influence on the removal of cadmium ions.The effects of Fenton oxidation flocculation,photocatalyticoxidation-reductionoftitaniumdioxide,potassiumferrate oxidation-flocculation,ferriteatroomtemperature,TMT-15precipitation,Lason-915C precipitation and Fenton pre-breaking-chelating precipitation combined processes on the removal of cadmium ions were studied.The flocculation effects of polyaluminium chloride,aluminium sulfate,polyferric sulfate and polyaluminium sulfate were compared.The experiment determined that Fenton reagent had the best effect of oxidative breaking.PAC and PAM assisted Lason-915C had the best effect on the precipitation of cadmium ion.The best treatment process of complex cadmium wastewater was the combination process of Fenton pre-breaking and chelating precipitation.NH₄Cl-Cd simulated wastewater could meet the emission concentration limit after being treated by Fenton oxidation flocculation or potassium ferrite oxidation flocculation.The residual cadmium concentration of NTA-Cd,EDTA-Cd simulated wastewater and factory actual wastewater treated by Fenton pre-breaking complexation-chelating precipitation process were 0.033 mg/L,0.035 mg/L and 0.036 mg/L,respectively,which met the emission concentration limit requirements.