An Invention for APT/AMT Production-Examples

Ammonium tungstate, ammonium paratungstate, ammonium metatungstate or hydrated tungsten trioxide is produced by passing tungstate anions through an anion exchange membrane into an aqueous solution containing ammonium cations under the driving force of an electrical potential for a time sufficient to achieve a pH within the range in which the desired tungsten compound will form.

EXAMPLE I

An electrolytic cell is divided into positive and negative sides by placing an anion exchange membrane (111BZ6066 from Ionics Inc., Watertown, Massachusetts) between 2 platinum electrodes each having a surface area of about 6 square inches and suspended by means of a platinum wire in the cell. 450 Milliliters of a sodium tungstate solution containing 213 grams of WO3 per liter is placed on the negative side of the membrane. A solution of 400 milliliters of water with 10 milliliters of reagent grade (28% by weight) ammonium hydroxide is placed on the positive side of the membrane. A potential of about 12 volts is applied to the cell resulting in a current flow of about 1 ampere. After about 1 1/2 hours the current has increased to about two amperes, the pH has decreased from about 10 to about 9, and ammonium tungstate is formed. After about 6 hours the current has increased to about 3 amperes, the pH has decreased to about 8 and ammonium paratungstate crystals are formed. After about 12 hours, most of the ammonium paratungstate has dissolved, the pH has decreased to about 2.8, and ammonium metatungstate is formed. At this point the solution is removed from the positive side, evaporated down to form crystals, and the crystals identified by x-ray analysis as ammonium metatungstate.

 ammonium metatungstate

 

EXAMPLE II

The procedure of Example I is followed, except that 400 mls. of tungstate solution containing 317 grams of WO3 per liter is placed on the negative side of the membrane, a solution of 10 milliliters of 28% ammonium hydroxide in 400 milliliters of water is placed on the positive side, and a potential of about 10 volts is applied to the cell resulting in a current initially of about 0.5 amperes. After about 81/2 hours the current has increased to about 2.5 amperes, and ammonium paratungstate crystals have formed. After about 29 hours, the pH has decreased to about 1.5 and tungstic acid has formed. The solution is evaporated to dryness and analyzed. Results show that the product contains hydrated tungsten trioxide, and the following impurities in the total amount of less than 0.1 weight percent: aluminum, calcium, copper, iron, magnesium, molybdenum, silicon, tin, and sodium. With the exception of molybdenum, all listed impurities are present in amounts less than about 100 parts per million.

 

EXAMPLE III

The procedure of Example I is followed, except that a 400 ml solution of sodium tungstate containing about 79 grams WO3 /liter is placed on the negative side of the membrane, and 10 milliliters of 28% ammonium hydroxide in 400 milliliters of water is placed on the positive side. After about 24 hours the current had increased from 1.5 to 4.5 amperes and ammonium paratungstate crystals have formed.

 

EXAMPLE IV

The procedure of Example I is followed except that in order to increase the current flow through the cell a solution of 1:1 by volume of ammonium tungstate (280 grams WO3 per liter) and 28% ammonium hydroxide is placed on the positive side of the cell, and a solution of 280 grams per liter of WO3 (sodium tungstate) is placed on the negative side of the cell. After about 61/2 hours of cell operation, solution from the negative side is analyzed to show that 86.3% of the tungsten is removed. Essentially 100% of this tungsten is recovered in the form of ammonium paratungstate crystals from the positive side of the cell. These crystals as indicated by spectrographic analysis contain a total impurity content of less than 0.1 weight percent. Such impurities include the following: Al, Ca, Cu, Fe, Mn, Mo, Si. All the listed impurities each are less than 100 parts per million except molybdenum which was about 200 parts per million.

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