Extraction of Silver Ions from Aqueous Solutions by Emulsion Liquid Membrane

Abstract

A comprehensive study pertaining to the emulsion liquid membrane (ELM) extraction process to enrich dilute aqueous solutions of silver salt is presented. The study has highlighted the importance and influence of membrane composition for maximizing the extraction of Ag+ ions. The liquid membrane was made up of Cyanex-302 as an extractant and the industrial solvent mainly consists of paraffinic and naphthenic hydrocarbons (C10-C14) as a diluent, Montane®-80 (sorbitan monooleate) as the surfactant and nitric acid solution as the stripping solution. The selection of the extractant (Cyanex-302) and the stripper (HNO3) was based on conventional liquid–liquid extraction studies. The role of pH as an important parameter in the LEM process for extraction of Ag+ was studied. Extraction of Ag+ increased with an increase in strip phase and carrier concentration. The fundamental parameters (emulsion stability, pH of the feed aqueous solution, agitation speed, surfactant concentration, strip phase concentration, carrier concentration, surfactant concentrations and treatment ratio) affecting the separation of Ag+ through the ELM were investigated to select the best combination of process parameters. The maximum extraction of Ag+ (about 99%) was achieved at a Montane®-80 concentration of 5% (v/v), strip phase concentration of 0.4M nitric acid and a phase ratio of 1:1.