Tantalum resources are scarce and expensive, so the utilization of secondary resources is of special significance. Niobium-tantalum secondary resources include two parts: one is the waste generated during the smelting and processing of tantalum-niobium, and the other is the components of tantalum-niobium products that are scrapped during use. At present, tantalum recovered from secondary resources accounts for about 15% to 20% of the tantalum raw materials.

According to the form of waste, tantalum-niobium waste mainly includes three categories: pure metal, compound and alloy. Pure metal waste is generally recovered by vacuum melting, electron beam melting and hydrogenation powder making after chemical cleaning. There are many types of waste such as compounds and alloys, and the composition is complex. For this reason, various recycling processes have been developed.

Tantalum-containing cemented carbide is an alloy composed of composite carbides (WC-TiC-TaC-NbC) based on tungsten carbide and titanium and cobalt. It has a complex composition and a low tantalum-niobium content. It is generally only recovered as an enrichment.

1. Zinc treatment method

The sintered carbide is first decomposed with liquid zinc at 800°C to break the bond between the carbide particles and the metal titanium and cobalt. The decomposed product is then separated from zinc by vacuum distillation and recycled. The dezincified product is finely ground and oxidized, and then subjected to alkali treatment and water leaching. Tungsten enters the leaching solution in the form of NaWO3 (ammonium paratungstate is produced from it), and the detungsten slag is then leached with sulfuric acid to extract cobalt and titanium (and then further separated and recovered from the sulfuric acid solution). The leached slag is the tantalum-niobium enriched product.

2. Sodium nitrate melting enrichment method

The cemented carbide waste is first melted with sodium nitrate at 700-800°C to decompose and oxidize the cemented carbide carbide. The resulting melt is first leached with water to extract tungsten (and then tungsten is extracted), and the filtered slag is leached with hydrochloric acid to extract cobalt (and then recover cobalt), and tantalum and niobium are finally enriched in the hydrochloric acid leaching slag. The resulting enriched product contains Ta2O530.4%, WO31.26%, and TiO238.6%.

Tantalum capacitor waste treatment

The recycling of waste tantalum capacitors is relatively complicated, especially for metal-clad liquid tantalum capacitors, which must first be removed by chemical methods (electrolysis, aqua regia pickling) or mechanized methods, and then deoxidized by sodium reduction or carbon reduction, and then electron beam smelting to obtain tantalum ingots. Resin-clad solid tantalum capacitors are first treated with sulfuric acid to remove the plastic shell; for sheet capacitors, they are crushed and then magnetically separated to remove the wires, and the plastic is separated by gravity separation. The remaining anode blocks are leached with sodium hydroxide to remove tin, nitric acid to dissolve silver, and hydrochloric acid to leach manganese, deoxidized by sodium reduction, and then smelted in an electron beam furnace to obtain tantalum ingots.