a b s t r a c tThis work investigated various supercritical water oxidation (SCWO) systems, i.e. SCWO1 (only water), SCWO2 (water + H 2 O 2 ) and SCWO3 (water + H 2 O 2 /NaOH), for waste printed circuit boards (PCBs) detoxification and recycling. Response surface methodology (RSM) was applied to optimize the operating conditions of the optimal SCWO3 systems. The optimal reaction conditions for debromination were found to be the NaOH of 0.21 g, the H 2 O 2 volume of 9.04 mL, the time of 39.7 min, maximum debromination efficiency of 95.14%. Variance analysis indicated that the factors influencing debromination efficiency was in the sequence of NaOH > H 2 O 2 > time. Mechanism studies indicated that the dissociated ions from NaOH in supercritical water promoted the debromination of brominated epoxy resins (BERs) through an elimination reaction and nucleophilic substitution. HO 2 Å , produced by H 2 O 2 could induce the oxidation of phenol ring to open (intermediates of BERs), which were thoroughly degraded to form hydrocarbons, CO 2 , H 2 O and NaBr. In addition, the alkali-silica reaction between OH À and SiO 2 induced the phase transformation of glass fibers, which were simultaneously converted into anorthite and albite. Waste PCBs in H 2 O 2 /NaOH improved SCWO system were fully degraded into useful products and simultaneously transformed into functional materials. These findings are helpful for efficient recycling of waste PCBs.

In the present study, a green process for cuprous chloride synthesis from waste printed circuit boards (PCBs) was developed. High value-added cuprous chloride (98.7% purity) was obtained by treating metallic particles of waste PCBs with solution of cupric sulfate and sodium chloride. Typical noble metal (Pd) was dissolved by forming a stable chloride complex during the synthesis process as Cu2+ played the role of oxidant or concentrated in the residue. Under the optimum condition (VNaCl/mCuSO4 ratio = 6, [C/[Cu2+] mole ratio = 1.05, treatment time = 30 min, operation temperature = 60 °C), yield of cuprous chloride was 74.0% and approximately 98.5% of the copper could be recovered. It is believed that the process proposed is effective and practical for Cu recovery from waste PCBs.