Simultaneous Copper and EDTA Ligands Recovery from Electroless Effluent with Metallic Copper and Formaldehyde

The traditional treatment of toxic and refractory copper(II)-ethylenediaminetetraacetic acid chelate (Cu(II)-EDTA) in electroless effluents often generates hazardous waste and secondary nitrogen-containing pollutants without maximizing the resource recovery. This study demonstrates a facile strategy to simultaneously recover Cu and EDTA ligands from Cu(II)-EDTA electroless effluent with commercially available metallic Cu and formaldehyde. In this strategy, metallic Cu is used to activate formaldehyde, a prevalent yet often overlooked cocontaminant in Cu(II)-EDTA effluents, to produce highly reductive hydrogen radical (^•H), which in situ decomplex Cu(II)-EDTA, reduces the central Cu(II) into metallic Cu, and release EDTA ligand. Impressively, this strategy can recover 99.9% of Cu from a real Cu(II)-EDTA effluent (∼2000 mg/L) as a high-purity Cu powder without further treatment, and 99.2% of EDTA from a real Cu(II)-EDTA effluent using a precipitation-acidification post-treatment procedure, earning a net profit of US $72.38 per ton. The proposed approach offers a "pollution-curing-pollution" solution to transform chelated metal waste into valuable resources.