BINARY METAL-ION SORPTION DURING PERMEATION THROUGH CHELATING POROUS MEMBRANES

An iminodiacetate (IDA) group as a chelate-forming group was introduce d uniformly throughout a porous polyethylene membrane of a hollow-fibe r form. The binary metal ions (Co2+ and Cu2+) were transported to the IDA group by convection by permeating the aqueous solution outwards at a residence time of 1.7 s through the chelating porous membrane whose thickness was 0.85 mm. The time course of the concentration profile o f the metals sorbed across the membrane during permeation was determin ed along with the determination of the breakthrough curves. At an init ial stage, both metal ions were quantitatively sorbed onto the membran e, where the copper ion occupied the inner part and the cobalt ion occ upied the outer part, and while the effluent volume increased, the Cu ion with a high affinity for the IDA group displaced the initially sor bed Co, and finally, occupied almost all of the IDA groups. Negligible diffusional mass-transfer resistance of Co and Cu ions to the IDA gro up and instantaneous displacement of the sorbed Co with Cu ion were de monstrated in the permeation mode.