Selective Leaching and Electrochemical Purification for the Recovery of Tantalum from Tantalum Capacitors

Tantalum (Ta) is a critical element that is used in many different electronic products. One of such products is epoxy-coated tantalum capacitors. They are composed of a tantalum metal anode, a tantalum oxide (Ta2 O5) dielectric and a manganese dioxide (MnO2) cathode. These capacitors are incredibly useful due to their capacitance per unit volume, frequency characteristics and stability. As the supply of tantalum that is economical to extract dwindles, it becomes important to develop a recycling technology for its recovery from tantalum capacitors. Our process uses pyrolysis, sequential leaching and electrochemical purification before the precipitation of a tantalum salt that feeds into the current tantalum production feedstock. First, the capacitors are pyrolyzed to remove the epoxy coating, where time and temperature were investigated. The resulting mass was milled to create a homogenous feedstock. In the leaching step, the manganese dioxide cathode is leached in hydrochloric acid (HCl) with hydrogen peroxide (H2 O2), and the silver (Ag), tantalum and tantalum oxide are leached in hydrofluoric acid (HF), again with hydrogen peroxide. Tantalum and silver do not leach into hydrochloric acid. The leaching rate was determined as a function of acid concentration and temperature. The hydrofluoric acid leachate is then electrochemically purified by the electrowinning of silver. The final tantalum-containing solution is treated with potassium fluoride (KF) to produce potassium heptafluorotantalate (K2 TaF7), the feedstock from which most current tantalum metal is produced through sodium (Na) reduction in molten salt. The total recovery rate and purity of the tantalum and silver are then confirmed with mass measurements as well as chemical analysis. This method provides an improvement over current methods due to its simplicity and reduction in the number and quantity of chemicals involved, only requiring 4 chemicals. It also demonstrates a new method for the separation of manganese from tantalum, a challenge in current recycling processes due to its similar properties to tantalum. Our process also produces an important byproduct in pure metallic silver.