Separation of waste tantalum capacitors by supercritical methanol: Recovery of high-purity metal tantalum and producing of bisphenol/diphenyl chemicals

Abstract

With the rapid upgrading of electronic products, a large amount of waste tantalum capacitors (WTC) were generated. The recovery and purification of the WTC attracted widespread interest due to the high-value rare metal tantalum and resin materials. However, the recovery and purification of the WTC was difficult due to the heterogeneous complex composition including metal tantalum, nickel–iron, silver, and organic resins. High-temperature and the potential formation of the hazardous compounds such as dioxins are the main bottleneck of the traditional thermochemical treatment methods for the WTC. In this study, a novel and high-efficiency supercritical methanol (SCM) process was developed for the recovery and purification of tantalum and resins from the WTC based on the low hydrogen bonding numbers and dielectric constant of methanol. The tantalum could be recovered as pure metal tantalum, and the resins were converted into oil by the SCM process. The temperature, time, and solid-to-liquid ratio have significant effect on the conversion ratio of resins. Under the optimal SCM conditions (350 °C, 90 min, and 1:20 g/mL), 97.1% of the external resins of capacitor were converted into oil (99.5%) and gas (0.5%), and the high-purity metal tantalum could be fully recovered. GC–MS and FT-IR analysis showed that the products converted from the resins in the WTC mainly included high level of aromatic derivatives of bisphenol and diphenyl (88.02%), which could be used as fuel or chemical feedstock after proper upgrade. The SCM method is an environmentally friendly process for the recovery and purification of the WTC without any discharge of waste water and off-gas due to that the treatment medium methanol could be recycled. The conversion mechanism of resins in the WTC by the SCM process was proposed.