From composition to performance: Evaluating the effect of emulsion liquid membrane components on lead removal from water.

This study aims to develop a chemically and operationally optimized emulsion liquid membrane (ELM) system for rapid and highly efficient Pb2+ removal from aqueous solutions while maintaining emulsion stability under reproducible operating conditions. Unlike previous ELM-based Pb2+ removal studies that mainly focused on individual membrane parameters, the present work systematically integrates membrane composition and operational hydrodynamic conditions to establish an optimized and reproducible ELM configuration. Lead (Pb2+), a highly toxic heavy metal commonly found in industrial wastewater, was selected as the target contaminant. The effects of solvent type, extractants, stripping agents, and surfactant concentration on lead removal efficiency were systematically evaluated. The optimized 22 mL membrane phase consisted of a mineral oil-toluene mixture (1:1) containing 3% sorbitan monooleate and 5% di-(2-ethylhexyl) phosphoric acid (v/v), while the 18 mL internal phase contained 1.2 mol L-1 sulfuric acid. The optimum emulsification speed and time were 10,000 rpm and 1 min, and the reactor stirring speed for mixing the 40 mL emulsion phase with a 250 mL external aqueous phase containing approximately 1000 mg L-1 Pb2+ was 300 rpm. Under these conditions, Pb2+ removal efficiencies exceeding 99% were achieved within 20 min, reducing final concentrations to below 1 mg L-1 while preserving emulsion stability and reproducibility. The findings provide critical insight into ELM design for industrial-scale heavy metal removal and highlight important considerations for scale-up applications.