é’½ Less resources, expensive, and secondary resource utilization have special significance. Tantalum Niobium secondary resources comprises two parts: tantalum and niobium smelting and processing waste generated in the process, another portion of tantalum and niobium and niobium products are scrapped components during use. At present, the recovery from secondary resources accounts for about 15% to 20% of the amount of raw materials.
Divided by the waste form, the waste mainly pure tantalum and niobium metal, an alloy and a compound of three. Pure metal scraps are generally recovered by chemical smelting, such as vacuum melting, electron beam melting, and hydrogenation milling. Various types of waste materials, such as compounds and alloys, have complex materials and various recycling processes have been developed. The following is a more representative wet process.
1. Cemented carbide is an alloy composed of tungsten carbide as the basic composite carbide (WC-TiC-TaC-NbC) and titanium and cobalt. It has complex composition and low bismuth content, and is generally only recovered as an enrichment.
(1) Zinc treatment
The process flow of this method is shown in Figure 1. The cemented carbide is first decomposed by liquid zinc at 800 ° C to break the bond between the carbide particles and the titanium metal cobalt . The decomposition product is then subjected to vacuum distillation to separate the zinc and recycled. The product after dezincification is finely ground and oxidized, then subjected to alkali treatment and water immersion, tungsten is introduced into the leaching solution in the form of NaWO 3 (from which ammonium paratungstate is prepared), and the tungsten slag is further leached with sulfuric acid to remove cobalt and titanium (further from the sulphuric acid solution) The cobalt and titanium are separated and recovered, and the leaching residue is a cerium enrichment.
Figure 1 Carbide scrap recycling
(2) Sodium nitrate melting and enrichment method
The cemented carbide scrap is first melted at 700-800 ° C with sodium nitrate to decompose and oxidize the cemented carbide. The main reaction is the same as that involved in 25.3.1. The obtained melt was first leached with water (thustained with tungsten), and the filtered slag was leached with hydrochloric acid (cobalt was recovered), and the ruthenium and osmium were finally concentrated in the hydrochloric acid leaching residue. The obtained concentrate contained Ta 2 O 5 30.4%, WO 3 1.26%, and TiO 2 38.6%.
Second, tantalum capacitor waste treatment
The recycling of waste tantalum capacitors is complicated. In particular, metal-clad liquid tantalum capacitors must first be removed by chemical methods (electrolysis, aqua regia, etc.) or mechanized methods, and then deoxidized by sodium reduction or carbon reduction. Electron beam melting is carried out to obtain a bismuth ingot. The resin-coated solid tantalum capacitor is first treated with sulfuric acid to remove the plastic casing; after the chip capacitor is pulverized, the wire is not picked by the magnetic separator, the plastic is separated by re-election, and the remaining anode block is leached with sodium hydroxide. Tin , silver is dissolved with nitric acid, manganese is leached with hydrochloric acid, deoxidized by sodium reduction, and then smelted by an electron beam furnace to obtain a bismuth ingot. The process diagram is shown in Figure 2.
Figure 2 Process diagram of solid capacitor recovery
Third, waste lithium niobate, lithium niobate single crystal recycling developed a variety of recycling methods
Fire main aluminothermic reduction, i.e., aluminum is used as the reducing agent, the reduction to the niobium powder of single crystal metallic iron or niobium or tantalum, and then the electron beam furnace smelting to obtain pure tantalum or niobium. The wet method mainly has an alkali treatment method, and the process flow is shown in FIG. The lithium ruthenium pentoxide single crystal is pulverized and melted at 700-800 ° C with sodium hydroxide, and the fusion reaction is:
2LiTaO 3 +10NaOH=2Na 2 TaO 5 +Li 2 O+5H 2 O
The melt is hydrolyzed to convert Na 2 TaO 5 to Na 2 O·Ta 2 O 5 hydrate:
6Na 5 TaO 5 +36H 2 O=4Na 2 O·3Ta 2 O 5 ·25H 2 O+22NaOH
The precipitate was treated with 6 mol/L hydrochloric acid to convert the hydrazine hydrate into Ta 2 O 5 ·xH 2 O, and lithium was formed into LiCl to separate from the hydrazine.
Figure 3 Schematic diagram of waste lithium niobate recovery process
4Na 2 O·3Ta 2 O 5 +8HCl+(x-7)H 2 O=3Ta 2 O 5 ·xH 2 O+8NaCl
Finally, Ta 2 O 5 with a purity of 98% was obtained. This method can simultaneously recover lithium hydroxide.
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