Ultrafiltration of polymer-metal complexes for metal ion removal from wastewaters

A case-study using macromolecular metal complexes is described. Theresults of a process named Polymer Assisted Ultrafiltration (PAUF) for ion removalfrom various types of waters is reported. The water soluble polymers such aspolyetilenimine (PEI), polyacrylic acid (PAA), polyacrylic acid sodium salt (PAASS)and poly(dimethylamine–co–epichlorohydrin–co–ethylenediamine) (PDEHED) as chelatingagents, the Cu2þas model ion and five ultrafiltration membranes have beenused. The complexing agents were previously tested to establish the binding capacityand the best operating conditions for the process. Among the tested polymers the PEIappeared the most interesting one because its binding mechanism does not involve acounter ion release. It was tested in the simulation of wastewaters treatmentcontaining the Cu2þion chelated with citric acid; this is a problem of interest inthe recycling of water from soil washing operations. The polyethylenimine quantitativelybound the copper-citrate chelate at pH 5.5 and the three component complexwas separated by UF membranes producing a permeate with very low metalconcentration. The polymer regeneration was carried out with good results byoperating with the diafiltration method. The copper ion present in the diafiltrationpermeate in a form chelated with citric acid was recovered by oxidising the citrate in amembrane photoreactor. The positive results of the described case-study show thatMacromolecule-Metal Complexes play a key role for running effectively and selectivelythe PAUF process for removing metal ions from various type of waters.