Separation of mercury from its aqueous solution through supported liquid membrane using environmentally benign diluent

This paper presents an experimental investigation on the facilitated transport of mercury through flat sheet supported liquid membrane (SLM) containing trioctylamine (TOA) as carrier and coconut oil, an environmentally benign solvent, as diluent. Co-transport mode of mercury transfer was studied using aqueous solution of NaOH as the strip phase. Various polymeric supports were tested in order to select the best SLM configuration. The SLM combination “PVDF–TOA–coconut oil” shows encouraging results and it was stable for a period of 98 h. The fundamental parameters, such as feed phase pH and concentration, strip phase concentration, carrier concentration, etc., affecting the transfer of mercury through the SLM were studied. It was observed that the extraction of mercury increases with increase in NaOH concentration in the strip phase, and becomes steady at a 0.3 M NaOH. The extraction process depends on feed phase pH and maximum extraction was achieved at a pH of 1. The carrier concentration had marginal effect on extraction as about 91% separation of mercury was achieved without any carrier in the SLM. Even at the most favourable operating condition (viz., 0.3 M NaOH, 4% TOA and pH 1), extraction of mercury was achieved up to 95%. Coconut oil showed better performance in the separation of mercury compared to other organic solvents such as dichloroethane and heptane.