Applications of supported liquid membranes and emulsion liquid membranes

Liquid membrane (LM)-based processes represent a promising alternative to traditional separation processes as they combine extraction and stripping into a single stage, thus having great potential for significantly reducing cost and ecological impact. Emulsion liquid membrane (ELM) and supported liquid membrane (SLM) are the most interesting LM-based processes in view of large-scale application. In the present article, some applications of these processes are described. To achieve the success of an ELM process on a large scale, an appropriate selection of the operating conditions, influencing both emulsion stability (e.g., type and concentration of surfactant, emulsification method) and the extraction/stripping process, is important. The optimized ELM process can be employed to efficiently remove organic (e.g., phenol, bisphenol A) and inorganic compounds (e.g., zinc, chromium, and cadmium) from wastewaters at industrial scale. SLM is today largely employed as a sample preconcentration technique for detecting analytes in liquid samples at trace levels in the field of biological and environmental analysis. The high process selectivity; the long-term stability; the use of the hollow fiber configuration, characterized by high membrane surface area; the optimal quality of treated water; and the green character make the SLM process feasible and effective in concentrating and recovering metallic ions from dilute industrial wastewaters. Thus, the two LM processes considered represent powerful, attractive, and technically feasible methods for selective separation and concentration of both organic and inorganic compounds from dilute aqueous solutions fulfilling sustainability criteria.