Emulsion liquid membrane extraction of palladium from simulated electroplating wastewater

Abstract

Recently, electroplating wastewater has become a major concern in terms of environmental problem due to toxicity of hazardous metals. However, the monetary value of precious metals, such as gold and palladium, has become a great concern too nowadays. Due to its special electric conductivity and very limited availability, several methods have been tested to identify the potential methods with high selectivity on precious metal recovery from electroplating wastewater. This study was carried out to recover the targeted metal ion, which is palladium, using emulsion liquid membrane (ELM) process. The research involved four major parts, which were liquid membrane component selection, stability study, extraction and recovery, and palladium extraction in matrices solution. Meanwhile, the ELM system comprised of three liquid phases, which were feed phase, liquid membrane organic phase, and receiving phase. The phases of liquid membrane and receiving were emulsified and dispersed into the feed phase to be treated. The important parameters affecting the membrane stability and the recovery of palladium including emulsifying and extraction time, homogenizer and agitation speed, concentrations of surfactant, carrier and stripping agents, pH of feed phase, and treat ratio were investigated. All experiments were carried out using bath extraction process and the recovery part employed a high voltage demulsifier. The results show that the most stable emulsion with 8% of swelling was achieved at 2% (w/v) of span 80, 3 minutes of emulsifying time, 12000 rpm of homogenizer speed, and 200 rpm of agitation speed. The optimum conditions obtained for the extraction and the recovery processes were at 0.2 M of Cyanex 302, 1.0M thiourea in 1.0M H2SO4 of stripping agent, 1:3 treat ratio, pH 3 of feed phase, and 5 minutes of extraction time. At these optimum conditions, the maximum extraction and recovery of the palladium was 97% and 40%, respectively. Therefore, the ELM process has shown great potential in extracting palladium from aqueous solution and industrial application.