Effective supported liquid membranes for facilitated extraction phenomenon of cadmium (ii) ions from acidic environments: Parameters and mechanism

We have developed three new supported liquid membranes (SLMs), for removal of Cd(II) from acidic environments. For the preparation of adopted membranes, we used a plate paper of the polymer PVDF, as porous support with thickness of 100 μm and pore diameter of 0.45 μm, and respectively, amphiphilic molecules of methyl cholate (MC), Trioctylphosphine oxide (TOPO) or tri‐n‐octylamine (TOA) as extractive agents, each dissolved in the organic phase toluene. We have developed a kinetic model to calculate the macroscopic parameters, permeability (P) and initial flux (J0) on the adopted membrane, and a thermodynamic model to determine the microscopic parameters, association constants (Kass) and apparent diffusion coefficients (D*), specific to the association of the substrate with the extractive agent, and diffusion of formed complex (TS) through the membrane organic phase. The proposed models verify the experimental results. We observed the influence of the agent nature, its concentration and the substrate concentration, on the parameters for the facilitated extraction of these ions through each of the developed membranes. On the other hand, these results show that the migration of Cd(II) through the membrane, is not a simple diffusion movement, but this migration is done according to the substrate successive jumps from one site to the other of extractive agent. In order to understand this mechanism and explain the obtained results, we have studied temperature factor influence, and we have calculated the activation parameters (Ea, ΔH≠, Δ S≠) related to the transition state for the association reaction of substrate with MC and TOA agents.