Tantalum recovering processes from waste capacitors After the identification, disassembling and crushing steps, all considered as pre-treatments of the WTCs, the following step consists on the recovery of the Ta anodes and sintered body by the removal of the epoxy resin structure.
Capacitor’s productions represent around 34% of the total Ta applications and recycling the high content of Ta contained in the waste tantalum capacitors (WTCs) present in the waste printed circuit boards (WPCBs) of electric and electronic equipment is crucial and urgent and will definitively contribute to the long-term sustainability of Ta demand.
Despite the environmental risk that the crushing may entail (e.g., dust release to the atmosphere) and the loss of some Ta-concentrate, its application is advantageous for the subsequent Ta recovery processes and removal of undesired materials. 3. Tantalum recovering processes from waste capacitors
The CN103194604A patent proposed the treatment by CM with a simultaneous roasting by heating the residues at 700–800 °C for 4 to 6 h and bubbling with chlorine. Under these conditions, tantalum chloride [TaCl 5 (g)] was recovered with high purity (99.9%) after condensation by thermal reduction or vacuum carbon reduction method.
The Ta capacitors are usually divided in six categories based on their colour (orange or black) and size (small, medium and large) resultant from combining the two colours and the three sizes. Some of them may also have a small trademark with a plus sign. Fig. 3 shows a scheme of the most common Ta capacitor from PCBs and its material composition.
The first strategy developed by the authors was to perform an alkaline leaching (pH 11) using KOH (85 %, S/L ratio 7:1 at 160 °C for 35 min.) to dissolve Ta and other metals (Fe, Ag, Ni and Mn), as shown in Equation(4), followed by solvent extraction (1:1 Alquilat 336 dissolved in toluene).