Copper recovery via polyelectrolyte enhanced ultrafiltration followed by dithionite based chemical reduction: Effects of solution pH and polyelectrolyte type

A chemical reduction process was proposed to recover copper from the retentate of polyelectrolyte enhanced ultrafiltration (PEUF). Three polyelectrolytes (PSS, PAA, and PEI) containing various functional groups and molecular weights were studied to explore their effects on the copper removal in PEUF and on the copper recovery by chemical reduction under various pH conditions. With PSS which contains sulfonic group, copper was removed reasonably well (ca. 75%) by PEUF even under acidic pH value of 3. With PAA which contains carboxylic group, copper removal was a bit low (∼60%) under pH 3.0 but increased substantially at pH 4.0. A branched PEI having amine group achieved the highest Cu removal of 94% at pH 3. The copper removal efficiency decreased slightly with increasing pH due to the high permeation of PEI through membrane. Chemical reduction achieved the complete copper recovery for solution containing PSS. The copper recovery efficiencies were more than 95% for PAA solution with pH values ranging from 3 to 9 at reaction time of one hour. For PEI, the recovery efficiencies ranged from 20 to 96% and were pH dependent. Aggregated and settled readily copper particles were produced by chemical reduction in PSS solution. XRD analysis identified cuprous oxide in all of the samples. Dependent of pH and polyelectrolytes, additional peaks matching those of elemental copper were identified. TGA analysis showed that solids produced from PSS and PAA systems contained no polyelectrolytes while solid collected from PEI system contained 32% of polyelectrolyte.