Application of Supercritical Water To Decompose Brominated Epoxy Resin and Environmental Friendly Recovery of Metals from Waste Memory Module

Abstract

Waste Memory Modules (WMMs), a particular kind of waste printed circuit board (WPCB), contain a high amount of brominated epoxy resin (BER), which may bring a series of environmental and health problems. On the other hand, metals like gold and copper are very valuable and are important to recover from WMMs. In the present study, an effective and environmental friendly method using supercritical water (SCW) to decompose BER and recover metals from WMMs was developed instead of hydrometallurgy or pyrometallurgy simultaneously. Experiments were conducted under external-catalyst-free conditions with temperatures ranging from 350 to 550 °C, pressures from 25 to 40 MPa, and reaction times from 120 to 360 min in a semibatch-type reactor. The results showed that BER could be quickly and efficiently decomposed under SCW condition, and the mechanism was possibly free radical reaction. After the SCW treatments, the glass fibers and metal foils in the solid residue could be easily liberated and recovered, respectively. The metal recovery rate reached 99.80%. The optimal parameters were determined as 495 °C, 33 MPa, and 305 min on the basis of response surface methodology (RSM). This study provides an efficient and environmental friendly approach for WMMs recycling compared with electrolysis, pyrometallurgy, and hydrometallurgy.

Advanced degradation of brominated epoxy resin and simultaneous transformation of glass fiber from waste printed circuit boards by improved supercritical water oxidation processes

“…2 shows that the oil-phase products of the SCWO1 systems were mainly phenols. This result was consistent with previous studies (Li and Xu, 2015;Xing and Zhang, 2013;Yin et al, 2011). Moreover, the sole addition of NaOH could increase the debromination efficiency in the SCWO systems, but the degradation products of BERs are still phenol and HBr (Table 1).…”

“…The solvent water then undergoes homolytic cleavage to form very active HO Å (H 2 O M H Å + HO Å ), which can attack the weak CH 2 AOAbenzene ring on the BERs, breaking down the polymers into small molecules. The weak bonds in the small molecules induce further free radical reactions ultimately resulting in bromophenols (① ② ③) (Li and Xu, 2015). Any Na + which dissociates from NaOH in SCWO3 system is positively-charged and can react with Br in bromophenols leading to the formation of NaBr, while OH À mainly undergoes nucleophilic substitution with Br-containing organic substances thereby eliminating Br (Lin and Wang, 1999).…”

Innovative leaching of cobalt and lithium from spent lithium-ion batteries and simultaneous dechlorination of polyvinyl chloride in subcritical water

“…and are used as green solvents to decompose hazardous organic polymers. In SCF, hazardous organic polymers can be decomposed into small molecules, leading to environmental protection [23,24]. SCF is becoming an increasingly popular technique for the disposal of waste electronic equipment, however there is little research on its ability to recover metals from spent LIBs.…”

Direct extraction of palladium and silver from waste printed circuit boards powder by supercritical fluids oxidation-extraction process

“…These results revealed that base metals in raw waste PCBs could be oxidized by treatment with supercritical water to form metal compounds soluble with diluted hydrochloric acid [22,30]. Moreover, organics (brominated epoxy resin-CH n O m Br) of large molecules in raw waste PCBs could be effectively decomposed into phenol (C 6 H 5 OH) and HBr in supercritical water, effectively achieving precious metal enrichment [25][26][27]. Therefore, the main composition element of the PMC was C, Si and O. Pd and Ag in raw waste PCBs were successfully enriched in PMC after treatment.…”

“…Hazardous organic polymers of waste PCBs can be decomposed into compound of small molecular weight so as to achieve the goal of environmental protection. However, most of those studies focused on the degradation characteristic of organic polymers [25][26][27]. Very few researches have been carried out on the enrichment characteristics of precious metals under supercritical conditions.…”