Permeation of complexed metal ions through a hydrophobic membrane

Selective concentration of a heavy metal complex with acetylacetone (acac) through a hydrophobic polystyrene membrane was carried out under a pressure gradient. A chelate forming heavy metal was selectively concentrated about 2 fold by this method. When using a coating membrane with a high water flux, the permeabilities increased with increasing complex fraction in the aqueous solution, while using a membrane with a low water flux, a bulky complex was not highly concentrated because of steric hindrance. The complex partitioned on the membrane surface was transported and concentrated under a pressure gradient and a linear relationship was found to exist between permeabilities and partition coefficients. It will be possible to concentrate hydrophobic organic solutes by this method, for acac was concentrated when the Cu—acac complex was formed. As the permeabilities increased with decreasing pressure and membrane compaction was strong for a coating membrane, it seems effective to permeate at a low pressure.