Conversion of waste cooking oil into value-added emulsion liquid membrane for enhanced extraction of lead: Performance evaluation and optimization

Abstract

This research study investigated the synthesis of environmentally benign green emulsion liquid membrane (GELM) employing waste cooking oil (WCO) as diluent. The emulsion was prepared using D2EHPA as the carrier, Span 80 as surfactant, and sulphuric acid as internal/stripping agent. The influence of nine operating variables namely, Span 80 concentration, D2EHPA concentration, shaking time, shaking speed, pH of the feed, treat ratio (TR), H₂SO₄ concentration, lead concentration in feed, and volume ratio of organic phase to aqueous phase (O/A) on the performance of lead extraction was studied. Plackett Burman design (PBD), was employed for the screening of variables. The Pareto analysis shows that six variables were the most significant variables at the confidence level of 95%. The selected variables were then screened applying Box-Behnken design (BBD). The optimum values of the variables were: D2EHPA concentration - 4.6 (v/v%), Span 80 concentration - 2.14 (v/v%), pH of the feed - 4.4, internal phase (H₂SO₄) concentration - 2 M, initial lead concentration - 173 ppm, phase ratio (O/A) - 1.3. At these optimum conditions, a maximum lead extraction of 97.39% was obtained. The mechanism for the extraction of lead was analyzed. Reuse and recycling of membrane phase show that the GELM can be recycled for 7 cycles without reduction in lead extraction efficiency. Kinetic analysis of lead extraction was performed using zero, first, and second-order model at optimum condition. The experimental data fitted well with first-order (R² - 0.9653). Thermodynamic studies indicated that the extraction procedure is endothermic, spontaneous in nature.

Keywords: Green emulsion liquid membrane; Kinetics; Lead; Thermodynamics; Waste cooking oil.