Solidification/stabilization of nonvaluable residue from waste printed circuit board assembly

The process of copper recovery from waste printed circuit board assembly (PCBA) has remained a large fraction of solid waste called "Nonvaluable Residue (NVR)". This residue is considered to be a hazardous waste because Pb, Cu, and Sb exceed the regulatory levels. Solidification/Stabilization (S/S) treatment technique is selected to improve waste characteristics before disposal of in hazardous waste landfills. In this study, a cement-based solidification/stabilization was used to treat NVR. Unconfined compression strength test (UCS) and toxicity characteristic leaching procedure (TCLP) were mainly used for physical and chemical characterization of the solidified/stabilized products. After curing for 28 days, the compressive strength and heavy metal leachability (Pb, Cu, Sb) were tested. The results showed that the compressive strength of blank sample was 20.75 MPa while compressive strengths of the solidified/stabilized NVR products were 7.36, 4.17 and 1.35 MPa for 20%, 30% and 40 wt% of NVR, respectively. All experimental mixture ratios satisfied the UCS requirements (0.35 MPa). In addition, the concentrations of Pb, Cu, and Sb in the TCLP leachate of all solidified/stabilized NVR products were lower than the limit value and the original waste. This study indicated that cement-based S/S treatment process was able to improve heavy metal immobilization and subsequently minimize potential environmental impacts in landfill disposal.