—This research investigated the decomposition of mould resins in tantalum capacitors using sodium hydroxide (NaOH) for the recovery of tantalum. Specifically, NaOH was introduced into a reactor, and heated at the required temperature (350–650 °C) in an electric furnace under nitrogen flow. When the set temperature was attained, the tantalum condenser was introduced into the reactor, and heated at varying times for 5 min to 24 h. Following cooling to room temperature, the capacitor was recovered by filtration after treating with distilled water. The weight of the residue after filtration was determined to calculate the decomposition ratio. The elements in the filtrate were determined by atomic absorption spectroscopy and ion chromatography. The composition of the evolved gases was analyzed by gas chromatography. The decomposition ratios were comparable within the heating temperature range studied and reaction time of 24 h. A large amount of silica was eluted into the filtrate. At ≥600 °C, collapse of the tantalum components was observed, and the degree of elution of tantalum and chloride into the solution was high. At 530 °C, decomposition occurred rapidly and the decomposition ratio was almost constant after 5 min of reaction. An increase in the amounts of gas produced and halogens in the filtrate occurred within 20 min of reaction. Thus, recovery of the tantalum components from the capacitors was successful upon reaction with NaOH at 530 °C for 5 min owing to the effective decomposition and removal of the mould resin from the capacitor. Furthermore, most of the halogen gases generated from the decomposition of the mould resin could be trapped in NaOH, thereby inhibiting exhaustion of halogen gases. These results indicate that the recovery of tantalum from spent capacitors using NaOH is a feasible approach to recycle rare metals in electric equipments.
—Tantalum recovery, Decomposition of mould
resin, NaOH, Halogen gas.
Takaaki Wajima is with the Department of Urban Environment Systems,
Graduate School of Engineering, Chiba University, Japan (e-mail:
Cite: Takaaki Wajima, "Decomposition of Mould Resin in Spent Capacitors by NaOH for the Recovery of Tantalum," International Journal of Environmental Science and Development vol. 8, no. 4, pp. 285-289, 2017.