Differences among Ammonium Tungstate, Ammonium Paratungstate and Ammonium Metatungstate

The most distinctive difference between ammonium tungstate, ammonium paratungstate and ammonium metatungstate is their solubility in water.

bag of ammonium metatungstate sample photo

Ammonium tungstate is also called ammonium wolframate, its molecular formula is (NH4)6W7O24•6H2O. It is colorless trapezius crystal which is soluble in water and insoluble in alcohol. Under 100℃ it loses four molecular crystal water. Ammonium tungstate can be used as the raw material for ammonium phosphotungstate and other tungstate compound. It can also be applied in producing metallic tungsten and catalyst.

Ammonium paratungstate is a white crystalline salt of ammonium and tungsten, it is insoluble in water. Its shape is like sheet or needle. Ammonium paratungstate is used as a source for high-purity tungsten oxides, tungsten metal powders, carbides, or as a laboratory reagent. Also used in the manufacture ammonium metatungstate and other tungsten compounds as additives for the petrochemical industry.

Ammonium metatungstate is a tungsten chemical in the form of highly soluble hydrated crystals, solubility is 303.99/loogH:O when 20℃. It is white or slightly yellow crystals which has no harmful components and slightly acidic. Ammonium metatungstate is very versatile and can be used as catalysts, capacitors, nuclear shielding, flame retardants, corrosion inhibitors raw materials, but also excellent raw materials in the preparation of ultra fine tungsten powder, tungsten heavy alloy powder, phosphotungstic acid, arsenic acid, silicon tungstate.

Chinatugnten Online  Tel:86-592-512-9696 Fax:86-592-512-9797 Email:sales@chinatungsten.com

Difference Between Ammonium Paratungstate and Ammonium Metatungstate

The most apparent difference between ammonium paratungstate and ammonium metatungstate is APT insoluble in water, but AMT soluble in water.

ammonium metatungstate image

Ammonium paratungstate is a white crystalline salt of ammonium and tungsten, it is insoluble in water. Its shape is like sheet or needle. Ammonium paratungstate is used as a source for high-purity tungsten oxides, tungsten metal powders, carbides, or as a laboratory reagent. Also tungsten powder including tungsten trioxide, tungsten blue oxide. Also used in the manufacture ammonium metatungstate and other tungsten compounds as additives for the petrochemical industry.

Ammonium metatungstate is a tungsten chemical in the form of highly soluble hydrated crystals, solubility is 303.99/loogH:O when 20℃. It is white or slightly yellow crystals which has no harmful components and slightly acidic. Ammonium metatungstate is very versatile and can be used as catalysts, capacitors, nuclear shielding, flame retardants, corrosion inhibitors raw materials, but also excellent raw materials in the preparation of ultra fine tungsten powder, tungsten heavy alloy powder, phosphotungstic acid, arsenic acid, silicon tungstate. It can also be used as reagents for chemical analysis such as for chemical diagnosis; source material for the preparation of high purity tungsten trioxide used as a thin film substrate for certain semiconductor devices; high purity source material for research in tungsten chemistry; source material for DENOX catalysts industry; as a precursor to a variety of POM (polyoxometalates).

Chinatugnten Online  Tel:86-592-512-9696 Fax:86-592-512-9797 Email:sales@chinatungsten.com

Ammonium Paratungstate Preparing Ammonium Metatungstate

ammonium metatungstate powder picture

Ammonium metatungstate is an important tungsten-containing compound, mainly used as catalyst in petroleum cracking, organic synthesis, nitration, and so on. With the rapid development of petroleum refining, petrochemical engineering and other industries, the ammonium metatungstate usage is increasing very fast. In the prior art, ammonium paratungstate is used as a raw material, and a crystallization process is utilized for the preparation of ammonium metatungstate; this process is expensive, costly and energy-consuming, and the obtained product is unstable in quality, particularly the solubility is poor.

A process for preparing ammonium metatungstate using ammonium paratungstate as raw material comprising: (A) leaching wet ammonium paratungstate with nitric acid to obtain a dilute solution of ammonium metatungstate; (B) concentrating the dilute solution of ammonium metatungstate to be a concentrated solution of ammonium metatungstate; and (C) spray-drying the concentrated solution of ammonium metatungstate to obtain powder of ammonium metatungstate.

Chinatugnten Online  Tel:86-592-512-9696 Fax:86-592-512-9797 Email:sales@chinatungsten.com

Ammonium Paratungstate Preparing Metatungstate Solution

Metatungstate is one of many types of tungstate, the only compound which the structures have been identified as colorless crystals. It has high solubility in water, and can be derived from metatungstate. Since the metatungstate itself is extremely unstable and easily degradable, therefore, it has a large difficulty in preparation. In the traditional way, sodium tungstate often used to prepare metatungstate crystals, but the complex process, high production costs, low productivity, poor product quality and the environmental pollution and other defects make the way no to be better. Nowadays, harmonious environment, cost savings, simplified procedures are promoted, so its necessary to develop a process which has the simplified process, low cost and environmental pollution, and also conducive to industrial producing metatungstate.

Studies have pointed out that ammonium paratungstate (APT) can be used to prepare metatungstate solution. The steps as following:
1. APT powder heated to 270℃~350℃ for 30-60 minutes to dissociate, thus to generate ammonium metatungstate;
2. Add ammonium metatungstate powder into deionized water to leaching with stirring to get an emulsion;
3. Carry out filtration to remove insoluble, and the filtrate was placed in a water bath of 60~90℃ aging for 4~24 hours;
4. Filtered again, and exchanged by Cation Resin, then we get metatungstate solution.

As we can see from the above, the method APT used as raw material to prepare metatungstate solution has the advantages like: simplify process, easy to control, and low cost; In addition, since the reaction process doesn’t introduce any impurity element, so the purity and quality of metatungstate can be ensured; finally, the production process does not use ether and other volatile organic compounds, with minimal impact on the environment, so it is suitable for industrial mass production.

Chinatugnten Online  Tel:86-592-512-9696 Fax:86-592-512-9797 Email:sales@chinatungsten.com

Ammonium Paratungstate Preparing Ammonium Metatungstate--Electrodialysis Method

ammonium metatungstate

Ammonium metatungstate (AMT) is a tungsten compounds with high molecular weight and water-soluble, which is easily dissolved in water, the solubility of it can reach 100g/mL at room temperature. It can be prepared from the material of ammonium tungstate by the method of Bipolar Membrane Electrodialysis (BEMD).

Electrodialysis method uses the effect of electric field, makes water which is in the two sides of bipolar membrane dissociated into H⁺ and [OH]^- then directional moved to both sides of electrode, and entered into the liquid chamber (the salt chamber) and alkali chamber respectively. Electrodialysis method is widely used in the field of chemical, light, metallurgy, papermaking industry and so on.

The preparation process of AMT by the method of electrodialysis which is using ammonium tungstate or ammonium paratungstate as raw materials is performed as bellows:
1. Add ammonium paratungstate into anode chamber, when an electric current passes by, water dissociated into two forms--H⁺ and [OH]^- and directional moved to both sides of electrode under the action of strong electric field, and then respectively enter the liquid chamber (the salt chamber) and alkali chamber;
2. H⁺ ions enter the salt chamber to combine with WO₄^- and then will not go into alkali chamber ever again; ammonium ions move to cathode chamber through the exchange membrane, thus cause the concentration of ammonium metatungstate increased;
3. [OH]^- moves into alkali chamber through the anion exchange membrane to combine with ammonium ions which is continually moved in and no longer went into the anode chamber;
4. With the process of electrolysis carrying out, ammonium ions decreased and hydrogen ions increased continually in the salt chamber, thus cause the pH value of the solution in salt chamber decreased continuously;
5. Finally, ammonium metatungstate solution is released from the cathode chamber, and AMT generated.

Chinatugnten Online  Tel:86-592-512-9696 Fax:86-592-512-9797 Email:sales@chinatungsten.com

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.

Chinatugnten Online  Tel:86-592-512-9696 Fax:86-592-512-9797 Email:sales@chinatungsten.com