Use of a Surfactant Liquid Membrane Contactor for Zinc Uptake from an Acid Aqueous Effluent

A procedure for uptake of zinc ions from an acid aqueous effluent using a surfactant liquid membrane contactor (SLM) was studied. The liquid membrane was prepared by dissolving the extractant, PC-88A (an alkylphosphonic compound), used as mobile carrier, and Span-80, a surfactant, in kerosene. The SLM allowed selective and efficient metal transport from the feed solution to the metal-receiving liquor in experiments carried out in a batch-type stirred contactor at 30°C. A screening factor-type experimental design and a response-surface optimization design were developed to determine the variables that influence zinc removal. An analysis of variance was carried out on the experimental data which made it possible to model mathematically the metal transport system by means of a regression equation. A maximum value of 99.32% was measured for the extent of zinc extraction under the experimental conditions used in this study. The optimal values of the main statistically significant variables were the following: 4.45% w/w of PC-88A concentration, a double emulsion-stirring speed of 250 rpm and a multiple emulsion-stirring time of 45 minutes, all values close to the minimum levels studied. The alkylphosphonic extractant molecule plays a fundamental role in the process as metal-carrier although it has a lower interfacial activity than the surfactant. The surfactant stabilizes the emulsion by reducing the interfacial tension and avoiding the coalescense of droplets. However, it is not recommended to use an excess of surfactant in the membrane because it would compete with the extractant molecules for the sorption of active sites on the interface, increasing the interfacial resistance and lowering the efficiency of the metal transport process. These results shows the feasibility of removal and/or recovery of metal ions from effluents or any dilute aqueous solutions using this contactor based on a surfactant liquid membrane.