(255d) Recycling of Heavy Metal Ions with Supported Liquid Membranes

Liquid membrane permeation with supported liquid membranes is considered an efficient membrane based separation technology. Membrane instabilities prevented this technology from industrial applications. To overcome the problem of membrane instability a new operation concept for supported liquid membrane permeation was developed. Continuous flux of extractant through the membrane perpendicular to the mass transfer direction was supposed to stabilize the liquid membrane and allow stable long term operation. The experiments were carried out with the EFCE test system for reactive extraction Zn2+|DEHPA|H+ with microporous polyethylene support layers for the membrane phase. In lab scale experiments this concept was successfully tested. Perpendicular solvent flux does not influence mass transfer negatively and it stabilizes the liquid membrane. Based on the successful stability tests of the basic lab size module in batch operation scale up of the mass transfer area by a factor of 70 was carried out. Scale up was validated by comparison of the diffusion coefficient. In a next step continuous operation of the raffinate phase and the strip phase was investigated. In long term experiments the supported liquid membrane did neither show loss of mass transfer rate after 30 days of continuous operation nor was any stability problem detected. Mass transfer, predicted from batch scale experiments, was confirmed in continuous operation. Mass transfer is controlled by diffusion through the membrane.