Removal efficiency and binding mechanisms of copper and copper-EDTA complexes using polyethyleneimine

Copper is used extensively in semiconductor circuits as the multilayer metal. In addition to copper, waste streams often contain chelating agents like EDTA, which is widely used in the process to enhance solubility of copper, and it tends to form copper-chelated complexes. PEI--agarose adsorbents in a packed-bed column are capable of removing these anionic complexes, but the competitive binding between this chelating agent and PEI for copper is not well understood and needs to be explored. The current work focuses on investigating copper sorption by PEI-agarose adsorbent in the presence of EDTA. The pH of the column is fixed at 5.5 using 0.1 M acetate buffer. The ratio of chelator to copper ions is varied. Copper binding capacity and copper breakthrough curves are compared and contrasted to results without additional chelator present. An excess of EDTA leads to an increase in the fraction of free dissociated (anionic) ligand that competes for electrostatic attraction on protonated amine groups and therefore leads to a decrease in sorption capacity in the column. However, this waste treatment technique is still feasible for the semiconductor industry as large volumes of copper-contaminated solutions from actual waste can be concentrated 12-fold. When equimolar (copper to EDTA) or higher concentrations of EDTA are present, acetate can be utilized to recover the metal; for low ratios of copper to EDTA, metal recovery is achieved using hydrochloric acid.