|dc.description.abstract||Electroplating process is comprised of pre-treatment, electroplating, and post-treatment. In pre-treatment, the metallic material to electroplate is placed at the anode and absorbed onto the material to be electroplated at the cathode via electro-deposition, with the plating solution as the medium. Though, the plating solution varies with the electroplating metal and composition, however, inevitably, it always exhibits the properties of high heavy metal content, low pH, high COD, etc..
The objective of the present study was the investigation of a recycling method for “Stannous sulfate wastewater” from acidic tin electroplating. The addition of Coagulant and standing time as well as electrolysis was investigated experimentally. The feasibility of recycling the upper deposition solution and the heavy metal absorbed at the cathode during electrolysis were assessed to increase the cost effectiveness, reduce the operation costs of the waste water plant and reduce environmental pollution to meet the water effluent standard.
Experiments showed the optimum concentration of coagulant A added to the waste water containing stannous sulfate was 3-5% and the optimal deposition time was 240 minutes. Using coagulant B, the optimal coagulant ratio was found to be 5~10% and the optimal deposition time remained 240 minutes. To remove the stannic compound from the wastewater by electrolysis, an uninterrupted electric current of 7A for 4 hours was found to be optimal from the cost and time point of view.
Based on the calculations for the 9040kg of stannous sulfate tin electroplating solution purchased annually, the costs for stannous sulfate in March 2015 was NTD891/kg, for its replacement was NTD8,054,640, and for reducing COD concentration in stannous sulfate wastewater to 582 mg/L and pH 6.5 to meet the controlled value of the industrial zone was NTD804,800. Therefore, the total cost for stannous sulfate treatment was NTD8,859,440. The tin metal absorbed at the cathode following electrolysis at 7A for 6 hours afforded the profit of NTD115,703, with the cost of electricity for electrolysis included. As a result, it was suggested that the recycling of stannous sulfate wastewater by electrolysis could effectively ease he cost for the company, as compared to the current stannous sulfate wastewater treatment.
Keywords: electroplating process, COD, electrolysis, coagulant, stannous sulfate, tin metal.