The present invention relates to improvements in a process for the recovery of tungsten and more particularly in improvements in a process employing acidic hydrogen peroxide to recover tungsten from scrap tungsten alloys.

 

Tungsten is a valuable and useful metal in for example electric light filaments and in drill bits, but high grade ores containing it are comparatively scarce so that there is continuing interest in its recovery from scrap materials. One source of scrap comprises tungsten alloys such as tungsten carbide pieces, each of which on average weigh several grams and are typically several mm such as at least 5 mm in size, many are 1 or 2 cm in size and some are even up to 10 cm in size. The tungsten carbide is often cemented with other metals such as cobalt, and can contain minor fractions of other metals such as titanium and tantalum typically often present as the respective carbides. The pieces can also be coated with a thin layer of, for example aluminium nitride or niobium or titanium or tantalum compounds. Both pyrometallurgical and hydrometallurgical methods have been suggested for recovering tungsten from scrap pieces, but the former methods currently suffer from the increased cost of energy in recent years, and the aforementioned coatings can interfere with tungsten recovery disproportionately. Other tungsten alloys that can be treated according to the present invention in piece form can contain significant proportions of copper, nickel and cobalt and minor amounts of group IVB and VB metals including titanium, tantalum, niobium and zirconium. A characteristic of tungsten alloy scrap pieces is that virtually none of the metal can be leached out using a mineral acid solution free from added oxidant.

 

Disintegration of drill-type tungsten/cobalt alloy scrap using a hydrochloric acid solution of hydrogen peroxide has already been suggested by Toyo Soda in Japanese patent application publication No. 1977-13408 which resulted in the leaching of the cobalt into solution and the disintegration of the resultant mass into a tungsten-containing powder. However, the problem still remains of recovering tungsten from the powder so that this disclosure represents only a partial solution to the problem of tungsten recovery.

 

In one other patent, Shwayder in U.S. Pat. No. 3,438,730, has advocated the use of phosphoric acid solution to disintegrate carbide masses, and once again he is producing a powder of tungsten carbide rather than extracting the tungsten into solution. In one comparison, he uses a mixture of hydrochloric acid and hydrogen peroxide, with at best 13.5% wt recovery. Even if that statement implied recovery into solution, which from the context is doubtful, it does not form the basis for a viable process for extracting tungsten from its scrap.

 

 

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