Thermo-chemische Behandlung von Leiterplatten zur vermehrten Rückgewinnung von Tantal

Abstract

Technology metals like tantalum are an integral constituent in many key electronic technologies. The refractory metal is mainly used in the electrical and electronics industry in the form of tantalum capacitors. Due to their high specific capacity they are predestinated for the use in place critical applications. Up to this date, tantalum is not recovered from end-of-life electric and electronic devices.
In this work, the possibilities of a thermo-chemical treatment for the recovery of tantalum were examined. The work’s objective was to extract a fraction, which contains the entire tantalum at high concentration. At the same time the recovery of tantalum should not lead to the loss of other elements, particularly precious metals which have a high value.
In a first thermo-chemical treatment step at 650°C and under nitrogen atmosphere, the plastic fraction of printed circuit boards (PCB) was decomposed. At the same time the employed heat disintegrated the sintered anode bodies of the tantalum capacitors. By further treatment of the solid product by sieve classification, 56.0 % of the overall tantalum could be accumulated in the sieving fraction 0 - 0.063 mm which consisted of 24.1 Ma.-% tantalum. By grinding the solid product prior to sieve classification, 75.0 Ma.-% of the overall tantalum could be transferred into the fraction 0 - 0.063 mm. Because the grinding led to the comminution of all hard-brittle materials, the tantalum was diluted and its concentration was only 1.5 Ma.-%.
The results show that thermo-chemical treatment can contribute to the recycling of tantalum from end-of-life PCBs. With further treatment of the solid product, it seems possible to recover technology metals like tantalum economically and thereby contribute to ensure the resource base and to the protection of the environment.