Mechanisms of mercury ions separation by non-toxic organic liquid membrane via DFT, thermodynamics, kinetics and mass transfer model

Abstract

This work focuses on the separation of mercury ions from synthetic produced wastewater via hollow fiber supported liquid membrane (HFSLM). Standard sunflower oil is used as a non-toxic extractant and solvent for mercury ions separation from wastewater. Under optimal conditions: 20 ppm NaCl in wastewater, 0.1 M thiourea in 0.5 M HCl as stripping solution, flow rates of feed and stripping solutions of 100 mL/min, and temperature 323 K, percentages of extraction and stripping reach 98% and 81%, respectively. The mechanisms of extraction and stripping reactions were investigated via the density functional theory (DFT). For the extraction, a linoleic acid extracted HgCl2 and formed halogen bond. For the stripping, two protonated thiourea stripped HgCl2 and formed covalent and halogen bonds. According to the thermodynamics study, extraction reaction is found to be endothermic (ΔHEx0 = 1,001.00 J/mol), irreversible (ΔSEx0 = 3.45 J/mol K), and spontaneous, (ΔGEx@323K0 = −112.65 J/mol). Finally, the mathematical model including conservation, convection, diffusion, reaction, and accumulation was developed. The differences of mercury ions concentration in feed and stripping phases from the experiments and the predicted data from the mathematical model were 5% and 2%, respectively indicating that the model is acceptable.