Effect of Chloride Ions on Electro-Coagulation to Treat Industrial Wastewater Containing Cu and Ni

Chien-Hung Huang,Mohanraj Kumar,Shan-Yi Shen,Cheng-Di Dong,Balasubramanian Dakshinamoorthy,Jih-Hsing Chang,Chiu-Wen Chen

doi:10.3390/su12187693

Abstract

A series of experiments with different NaCl concentrations added to the PCB (printed circuit board) wastewater were prepared to investigate the chloride effect on the formation of aluminum floc and removal efficiency of Cu and Ni. The effects of pH, current density, and different concentration of NaCl were studied and the results are discussed. Results imply that chloride ions are favored to avoid the passivation of the aluminum anode in the EC (electro-coagulation) system. Chloride ions used as the electrolyte can facilitate the release of Al3+, which results in the current efficiency of over 100% in the EC system. For the PCB factory’s wastewater, the EC system could remove Cu2+ and Ni2+ effectively (both Cu and Ni concentration of treated wastewater was less than 1.0 mg/L within three minutes). PCB wastewater’s pH value could maintain stably about 9.0 in the EC system when the initial pH value was around 2.5. The estimated electricity consumption for treating PCB wastewater by the EC process was about 0.894 kWh for each meter of cubic wastewater.

Highlights

The electro-coagulation (EC) technique has received considerable attention to remove heavy metals from the industrial wastewater for decades
In an EC system, the electro-dissolution of sacrificial anodes forms complexed species with hydroxide ions, which act as coagulant agents to separate pollutants from the wastewater
Several conclusions can be drawn: (1) Chloride ions are favored to avoid the passivation of the aluminum anode in the EC system

Summary

Introduction

The electro-coagulation (EC) technique has received considerable attention to remove heavy metals from the industrial wastewater for decades. In an EC system, the electro-dissolution of sacrificial anodes forms complexed species with hydroxide ions, which act as coagulant agents to separate pollutants from the wastewater. The extreme reactions of EC technology include (1) metallic ions generated by the sacrificial anode (Al or Fe is commonly used) in the reaction tank, (2) hydroxide ions generated by cathode to form floc, (3) the occurrence of coagulation precipitation (e.g., Al(OH)3) and (4) the metallic and organic pollutants which could be separated from the aqueous phase by such coagula [10,11]. To control all kinds of chemical reactions smoothly during electrochemical methods to process waste material, the electrical potential or current control is one of the essential operating parameters. A series of experiments with different concentrations of NaCl added to the wastewater (different initial pH values of sewage as well) were prepared to investigate the chloride effect on the formation of aluminum floc. The practical operational parameters of the EC process can be obtained for further application

Materials and Methods

The Effect of NaCl on Voltage and Consumed Electricity

The pH Variation of Wastewater during EC Operation

Findings

Conclusions