Leakage and swell in emulsion liquid membranes: experimental studies and corrected computational methods

Abstract

Emulsion liquid membrane (ELM) systems are water-in-oil emulsions dispersed in water, which, with appropriate chemistry, can efficiently extract and concentrate metals (e.g., cadmium, chromium, copper, cobalt, nickel, lead, zinc, mercury, gold and silver), weak acids and bases (e.g., phenolics and amines), inorganic species and pharmaceuticals (e.g., acetaminophen and amino acids) from the external water phase. Since their invention in 1968, ELM systems have been studied extensively. Most studies in the literature have investigated the extraction performance of ELM systems. This dissertation reports experimental investigations of several formulation and operating parameters on leakage and swell of the internal water droplets, which reduce extraction efficiency and concentration of extracted substances. Leakage and swell were measured in both batch and continuous stirred tank reactor (CSTR) systems for the same formulation and operating conditions. The batch and CSTR results are compared to test, for the first time, whether leakage and swell in the CSTR system can be predicted from measurements in the batch system, which is easier to study. Several other researchers have used pH change in the external water phase to quantify leakage of internal droplets containing acid or base. Often the equations they used to calculate leakage contain unstated simplifying assumptions that can produce significant error for some experimental conditions, including those observed in several of these studies. In this dissertation general equations are developed and compared with simplified equations reported in the ELM literature over more than 30 years to identify the underlying assumptions and the magnitude of the potential error. A detailed analysis of one previously reported ELM leakage study based on pH measurements was performed. The original leakage results are corrected, which led to revised conclusions about the effects of formulation and operating conditions on leakage.