Tungsten powder production from scheelite concentrates

Abstract

In this study. it is aimed to treat scheelite concentrates obtained from Uludag, Bursa (Turkiye), and containing approximately 50% W, by chelate-added acidic leaching and followed by the precipitating of tungsten salt, producing the pure tungsten oxide, and finally obtaining the submicron size pure tungsten metal powder by the reduction of this oxide in a horizontal tube furnace by hydrogen. A comparison of the precipitating reagents and optimization of the precipitation parameters is also conducted along with a search for the possible existence of an environment-friendly process with no waste streams and requiring no neutralization. The optimum leaching conditions were found to be: 2 h leaching period, 80degreesC, 2M HCl, and W/PO43- mol ratio of 7. Moreover, it has been found that tungsten existed in the solution could be precipitated with a high efficiency in the form of a complex salt; (NH4)(x)(.)P(y)O(z)(.)rWO(3)(.)tH(2)O, by the addition of an alkaline reagent. Aforementioned salt has a submicron size and can be transformed into an ultra pure tungsten oxide by simple thermal decomposition (> 600degreesC, 0.5 h). The pure tungsten oxide obtained is also a nano-sized material. Then WO3 can be processed by a two-step reduction with hydrogen under controlled conditions in 4 h to yield a pure tungsten powder, a product highly preferred in powder metallurgy applications. Metallic tungsten powder obtained has a purity of 99.7% W and specific surface area of 2.428 m(2)/g.