ELECTROCHEMICALLY MODULATED EQUILIBRIUM STAGE PROCESSES

A cyclical electrochemical process for the removal of solutes from one phase and their concentration in a second phase is analysed. Solutes are extracted by binding to a complexing agent present in the contacting phase and released to a receiving phase by converting the complexing agent electrochemically to a form with low affinity. The expression of the concentration in different streams is derived analytically and compared graphically. The graphical solution utilizes equilibrium relations for the reduced and oxidized form of the complexing agent with operating line equations. The analysis focuses on three different cases. The first one is where the feed is equilibrated with a fresh contacting phase at each stage. A high fraction of the solute can be removed in this case, but the solutes cannot be concentrated. In the second and third cases, the solute is concentrated in a receiving phase using one and two contacting phases, respectively. In these process, the fraction removed, the fraction concentrated in the receiving phase, and the number of cycles depend only on the magnitude of the distribution coefficients, which are modulated by the electrochemical reactions of the complexing agent. The analysis indicates that electrochemically modulated complexation stage processes will have distinct advantages over normal solvent extraction, if complexing agents with the appropriate properties can be identified or developed.