Chemistry of inorganic compounds – Treating mixture to obtain metal containing compound – Group vib metal
Patent
1998-12-31
2000-09-05
Griffin, Steven P.
Chemistry of inorganic compounds
Treating mixture to obtain metal containing compound
Group vib metal
423 55, 423 87, B01D 1100
Patent
active
061138681
DESCRIPTION:
BRIEF SUMMARY
FIELD AND BACKGROUND OF THE INVENTION
The present invention relates to a process for the preparation of pure alkali metal and/or ammonium tungstate solutions from alkaline tungstate solutions contaminated especially with silicon, phosphorus, arsenic, tin, antimony, vanadium, tantalum, niobium, titanium and molybdenum, wherein the solution is acidified and the precipitate, formed without the addition of precipitating agents or precipitating aids, is then filtered off.
The raw materials for the recovery of tungsten, especially its ores, always contain small amounts of molybdenum and arsenic. Although the products ammonium paratungstate and powdered tungsten metal arc currently required to have very low Mo and As contents. tungsten raw materials with higher molybdenum contents of more than 2 wt. %, based on tungsten, are increasingly entering the market.
The tungstate-containing solutions from the various digestion processes are contaminated with a number of different elements, depending on the raw material. Apart from molybdenum, the most frequently occurring impurities are phosphorus, arsenic, silicon, aluminium, vanadium, titanium, niobium and tantalum. Various precipitation processes are known for separating off these impurities typically, such processes involve, wherein, after the addition to a tungstate solution of precipitating agents such as magnesium chloride or sulfate or precipitating aids such as aluminium sulfate. The pH of the previously strongly alkaline tungstate solution is lowered to values of between 8 and 11. However, these precipitation processes cannot be carried out quantitatively, most of the arsenic, in particular, remaining in solution (Tungsten Symposium, San Francisco, June 1982, p. 77, Table 2).
Currently the most common process for the separation of molybdenum from tungstate solutions is precipitation as MoS.sub.3 from the previously purified tungstate solution (Gmelin, Tungsten, System no. 54, Supplement A1 (1979), pages 44 to 46). tungstate solution originating from the alkaline digestion is treated with NaHS at pH 8 to 10 and, after the formation of MoS.sub.4.sup.2-, is precipitated as MoS.sub.3 with H.sub.2 SO.sub.4 at a pH of 2 to 3. This precipitate normally includes approximately the same amount of tungsten as molybdenum and contains appreciable amounts of free sulfur and the arsenic.
Such a precipitation product can scarcely be used profitably and must therefore often be dumped as special waste. Furthermore the pH adjustment can only be effected with mineral acids, producing large amounts of neutral salt.
Mintek Report no. M 226 (25.11.1985) describes a process in which the MoS.sub.4.sup.2- is separated off with solid ion exchangers in the OH form. The disadvantages of this process are the low Mo absorption capacity of the ion exchangers, the lower degree of separation of the molybdenum from the tungsten, and the arsenic contained in the MOS.sub.3 precipitation product.
According to U.S. Pat. No. 4,288,413 the molybdenum is separated off as MoS.sub.4.sup.2- by extraction with quaternary ammonium compounds at pH values of between 7 and 9.
As arsenic is also extracted under these conditions, it can be separated from the tungsten but not from the molybdenum. Because the MoS.sub.4.sup.2- can only be stripped by means of oxidative additives like H.sub.2 O.sub.2 or NaOCI, no separation from the co-extracted tungsten takes place and the W losses are increased. The product is simply a mixture of sodium molybdate and sodium tungstate which is difficult to utilize further and which is also contaminated with arsenic.
One procedure for avoiding the As contamination is disclosed in German Patent DE-C 195 00 057, although nothing is said about contamination of the tungstate solutions by molybdenum.
The object of the present invention is to provide a process which makes it possible selectively to free tungstate solutions of impurities, but simultaneously to produce the minimum amount of waste, particularly special waste. It should be possible to obtain an economically usable molybdenum
REFERENCES:
patent: 3173754 (1965-03-01), Kurtak
patent: 3969484 (1976-07-01), Onozaki et al.
patent: 4115513 (1978-09-01), Kulkarni et al.
patent: 4279869 (1981-07-01), Coulson
patent: 4288413 (1981-09-01), MacInnis et al.
patent: 5676817 (1997-10-01), Gutknecht et al.
patent: 5891407 (1999-04-01), Gutknecht et al.
Gutknecht Wilfried
Mathy Wolfgang
Cohen Jerry
Griffin Steven P.
H. C. Starck GmbH & Co. KG
Rhee Michael
LandOfFree
Process for treating tungstate solutions to reduce molybdenum im does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Process for treating tungstate solutions to reduce molybdenum im, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Process for treating tungstate solutions to reduce molybdenum im will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2209029