Recycling of Tantalum from Waste Electrical and Electronic Equipment through Mechanical processing and Hydrometallurgical Separation of precious Metals

摘要

Tantalum is an important minor metal for the production of high performance capacitors. Approximately 60 % of the annual tantalum production is used in this application. Despite its price of 305 US $/kg (average price for 99.5 % Ta_2O_5, 2011 - 2015), there are no established recycling routes for tantalum from waste electrical and electronic equipment (WEEE). In conventional recycling processes, tantalum is usually lost in the slags of copper smelting because of its ignoble character. An economic recovery is not possible due to dilution. Reasons for this situation are the low or unknown tantalum contents in many waste streams, the small total mass of tantalum and a conflict of interest between precious metals and tantalum recycling. In this paper, the authors address these problems and present a mechanical processing route that produces marketable tantalum concentrates (approx. 30 % Ta content) from pre-sorted automotive control units at yields between 60 % and 70 %. 97 % of the WEEE may be fed into conventional recycling routes after the optimized comminution as tantalum is concentrated in the fraction of 2 to 6 mm. Further process steps are air classifying, eddy-current and magnetic separation. Additionally, results are presented for the hydrometallurgical recovery of precious metals from the tantalum concentrate to address the aforementioned conflict of interest.