Recovery of copper and chelating agents from sludge extracting solutions

Removal of extraction solution containing chelated copper from printed circuit board industry sludge by cementation on powdered iron was studied. This work applied the recovery and extraction of ethylene diamine tetraacetate (EDTA) and diethylene triamine pentaacetate (DTPA) as remediation agents and metal precipitated from printed circuit board sludge extracting solutions. The recovery of copper by cementation process using powdered iron was dependent on the Fe:Cu molar ratio. Results of the experiments showed that recovery efficiencies were typical of those of a Fe:Cu molar ratio as high as 8:1 for each sludge sample. The differences of recovery efficiencies may be due to competition for active sites on the surface of the powdered iron. Copper deposits on the surface almost always occur in the form of the copper metal that are well distributed, with purified copper powder being observed in characterization with scanning electron microscopy (SEM) and X-ray powder diffraction (XRD). The recycled extract containing EDTA or DTPA was used to chelate supplementary fresh copper-containing sludge. Extraction efficiencies of copper by using Fe-precipitated EDTA or DTPA from previous cementation were higher than sequential application of the Fe-EDTA or Fe-DTPA solution. Similar copper extraction efficiencies using both pristine and reused extract containing chelants validates the enduring chelating capability of EDTA and DTPA and suggests further opportunities to employ recycled chelant to reduce its usage. This work confirmed the feasibility of copper removal from sludge chelated wastewater by cementation and subsequent recycling of chelant extraction.