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.