Efficient Extraction of Dichromate Anions Using TOPO in Multi-Dropped Liquid Membrane

This study presents the sequential extraction of dichromate (Cr 2 O 7 2− ) anions using a continuous multi-dropped liquid membrane (MDLM) system. Trioctylphosphine oxide (TOPO) dissolved in kerosene was employed as the mobile carrier in the organic phase. To determine the optimal operational conditions, both chemical variables (e.g., donor phase acid type, acceptor phase composition, and carrier concentration) and physical parameters (e.g., temperature, phase volume ratios, flow rate, and reactor frit porosity) were systematically investigated. Unlike earlier studies, this work uniquely emphasizes the critical influence of the reactor’s hydrodynamic and physical design on overall mass transfer efficiency. Kinetic evaluations confirmed that the dichromate transport strictly adheres to consecutive first-order irreversible reaction kinetics, enabling the precise calculation of fundamental kinetic parameters ( k 1 , k 2 , t max , \:Rₘᵐᵃˣ , \:Jdᵐᵃˣ , \:\:Jₐᵐᵃˣ ). Furthermore, the activation energy of the process was determined to be 14.60 kJ·mol − 1 (3.49 kcal·mol − 1 ), demonstrating that the extraction is fundamentally a diffusion-controlled mechanism. Under the optimized physicochemical conditions, the MDLM system achieved a maximum overall dichromate extraction efficiency of 96.31%.