2018年3月27日星期二

Ammonium Paratungstate Waste Recycle

In production, for some reason, some Ammonium Paratungstate (APT) products are not qualified in terms of academic composition or physical properties.

ammonium paratungstate image

A small amount of ammonium paratungstate waste may be produced during the production process, which can be recycled. The method of recovering unqualified ammonium paratungstate is mainly by dissolving and filtering, and then recrystallization is carried out. Therefore the factory directly use ammonia as the solvent at high temperature to dissolve APT, but APT in ammonia water is solubility, lead to dilute solution concentration,the dissolution time is long. Thus, the modern industry began to gradually over the use of APT thermal decomposition into ammonium metatungstate for recycle.

The working mechanism of thermal decomposition is to control the appropriate temperature, calcined APT can be converted to ammonium metatungstate (AMT).

According to the high temperature decomposition performance of APT·H2O, when APT·4H2O is heated in air, it is dehydrated first at about 100 °C and then decomposed at 190 °C to 250 °C to dissolve the amorphous ammonium metatungstate formate. Some scholars have proved that the calcination temperature of the unqualified ammonium tungstate is better at 280 °C, and the leaching rate of the product at the concentration of 25% is the highest, up to 99.6%. So that the calcination treatment is carried out at an appropriate temperature in advance so that the unacceptable APT is better soluble in the NH3 solution and can create better recycle conditions for the unqualified ammonium paratungstate.

After calcination treatment of APT by pure water leaching, pH control in 3-4, after leaching filtration, evaporation and crystallization can be obtained ammonium metatungstate.

If you have any inquiry of APT, please feel free to contact us:
Tel.: +86 592 5129696      +86 592 5129595
Fax: +86 592 5129797

Yellow Tungsten Oxide

Yellow Tungsten Oxide (YTO) is a kind of tungsten trioxide, because the early purification of WO3 color is mostly yellow, so the early tungsten trioxide compounds are known as yellow tungsten oxide. 

Yellow tungsten oxide two different sizes of different particles, showing different color. When the yellow tungsten oxide crystal size is about 1.5um, it appears to be yellow. When the yellow tungsten crystal size is about 15um, it appears to be green. Although the appearance of different, the characteristics are similar.

yellow tungsten oxide image

Before 1970s, yellow tungsten oxide was widely used, and a large amount of tungsten oxide was used in the production of metal tungsten powder and tungsten carbide powder, and a large number of applications and production of tungsten alloy products, such as tungsten copper, tungsten nickel, tungsten nickel iron, tungsten silver, tungsten rhenium, thorium tungsten and so on. Another part is used in the manufacture of paints, coatings and catalysts for the petroleum industry.

There are many ways to prepare yellow tungsten oxide, the general method is the use of ammonium paratungstate (APT) calcination reduction, usually has four stages:

1. During the heating process, the material is dried and four crystal water is lost at 100 degrees centigrade.

2. Between 100 °C-220 °C, NH3 evaporated, and formed into amorphous ammonium metatungstate.

3. Between 220 °C - 450 °C, both NH3 and H2O are volatilized to form tungsten bronze.

4. When the temperature is above 450 °C, only WO3 remains in APT.

In the process of converting APT 4H2O to WO3, color changes are very prominent. When the material is calcined at 240 °C  shows white or gray, 270 °C from yellowish-white turn into yellow, with the decomposition degree yellow becomes darker, and starts to turn orange at 330 °C, and finally changed to brown, after cooling at room temperature changes into yellow.

The purity of APT determines the purity of yellow tungsten oxide. The crystal shape of APT has heredity to the crystalline form of yellow tungsten. The calcination temperature and the rate of thermal decomposition have obvious influence on the physicochemical properties of yellow tungsten.

Before the 1970s, domestic and foreign tungsten powder production mostly used tungsten trioxide as raw material. But after the 1970s, the industry developed a more stable nature, more easily doped blue tungsten oxide, yellow tungsten oxide finally retired after winning merit.

If you have any inquiry of tungsten oxide, please feel free to contact us:
Tel.: +86 592 5129696      +86 592 5129595
Fax: +86 592 5129797

Ammonium Metatungstate

Ammonium Metatungstate (AMT) is an important compound product in the process of tungsten smelting.

It can be prepared by thermal degradation of Ammonium Paratungstate (APT) and can also be prepared by ion exchange with ammonium tungstate solution.

ammonium metatungstate image

Ammonium tungstate water soluble white crystalline powder or slightly yellow, ammonium metatungstate dissolved in water, ammonium paratungstate slightly soluble in water, which is the difference between ammonium metatungstate and ammonium paratungstate.

Ammonium metatungstate is widely used as a raw material for the preparation of capacitors, nuclear shielding, flame retardants and corrosion inhibitors. It is also an excellent raw material for preparing superfine tungsten powder, high gravity alloy tungsten powder, phosphotungstic acid, arsenotungstic acid, silicotungstic acid.

In fact, what really makes ammonium metatungstate play an important role is in the field of petroleum processing. The field of petroleum processing, with the continuous development of the national economy, the strategic significance of oil has become increasingly prominent, and tungsten catalyst in some reactions with platinum-like catalytic activity, so that in the oil Industry has been widely used.

These years, preparation of ammonium metatungstate method has attracted much attention of many scholars,they have done a lots of research. The preparation of ammonium metatungstate also showed a hundred schools of thought contend, in addition to the traditional thermal degradation and ion exchange method, there are extraction, nanofiltration, electrodialysis, neutralization and so on.

If you have any inquiry of ammonium metatungstate, please feel free to contact us:
Tel.: +86 592 5129696      +86 592 5129595
Fax: +86 592 5129797

Ammonium Metatungstate Preparation -- Ion Exchange Method

Ion Exchange method is the process of preparing ammonium metatungstate. It is made from ammonium wolframate solution or ammonium paratungstate. 

This method is also one of the main methods for preparing ammonium metatungstate (AMT) at present.

ammonium metatungstate preparing image

The main mechanism of ion exchange method is that use NH4+ in H+ solution of strong acid or weak acid type H+ cation resin to process ion exchange. Under the condition of pH 3.5, H+ enters solution , cook for 5 hours at 98 °C. Converting ammonium tungstate into stable ammonium metatungstate solution. Then after evaporation and concentration, ammonium tungstate was converted to stable ammonium metatungstate solution. Again after evaporation and concentration, AMT crystals were prepared by freeze crystallization or spray drying. The resin saturated by NH4+ is recycled after treatment with hydrochloric acid solution. 

ammonium metatungstate preparing image

Because of the simple process and convenient control, the ion exchange method can avoid the formation of APT. It does not bring new pollutants into the process, it has gained popularity because of process continuity. The main drawback is that a small amount of colloidal tungstic acid may be produced during the ammonium removal process and plug the resin layer and resin pores. In addition, the tungsten liquid entrained by the resin must be removed.

The resin should be regenerated by acid, which will increase the operation step and bring troubles to the production. Of course, there is no denying that the production of AMT by ion exchange method has the potential for development.

Recently, some scholars have proposed a new method of making high-purity ammonium  metatungstate (AMT). The method adopts cation interchange under the low pH condition. A mixture of ammonium paratungstate and water is exchanged with a cationic material to obtain a high-purity ammonium metatungstate product.

If you have any inquiry of ammonium metatungstate, please feel free to contact us:
Tel.: +86 592 5129696      +86 592 5129595
Fax: +86 592 5129797

Ammonium Metatungstate Preparation -- Nanofiltration Method

Ammonium Metatungstate (AMT) is an important compound product in tungsten smelting process.It is widely used in areas. 

The common methods of preparing ammonium metatungstate include thermal degradation and ion exchange, extraction, nanofiltration, electrodialysis and neutralization.

nanofiltration method image

Nanofiltration membrane is a new type of pressure driven separation membrane developed since 1980s. Nanofiltration method is a membrane separation technique, which is independent from reverse osmosis membrane technology.

Filter membrane is the main focus of nanofiltration. The separation performance of nanofiltration membrane is between reverse osmosis and ultrafiltration membrane. It has a good removal effect on low molecular weight substances, high valence ions, low valence cations and anions. Therefore, some scholars used the nanofiltration method to prepare ammonium metatungstate (AMT) from the original solution of ammonium paratungstate (APT) crystallization.

The separation of chloride ions from the crystallization mother liquor by nanofiltration can overcome the shortcoming of the difficulty in removing the chloride ions in the crystallization liquor of the APT process by ion exchange. At the same time the use of nanofiltration membrane acid anion NO3-, but also the main material of the tungsten does not wear, to achieve the purpose of producing pure AMT crystal.

It is important to note that when APT crystallization liquor is dealt by nanofiltration method, the appropriate hydrochloric acid is added to neutralize and adjust the acid, and then the impurity is removed by nanofiltration. The quality of the obtained AMT is better.After the industrial proof, our country's nanofiltration membrane production technology has made great progress. Nanofiltration method has no pollution, high impurity removal efficiency, and has been able to control costs, and has the potential for popularization. 

If you have any inquiry of ammonium metatungstate, please feel free to contact us:
Tel.: +86 592 5129696      +86 592 5129595
Fax: +86 592 5129797

Ammonium Metatungstate Preparation -- Extraction Method

The extraction method is a preparation process that use ammonium tungstate with ammonium tungstate solution as raw material. 

This method is also one of the processes for preparing Ammonium Metatungstate (AMT) at presnt. The extraction principle of ammonium metatungstate (AMT) extraction method is similar to that of ammonium tungstate extraction method, which needs to experience four stages including extraction, water washing and stripping. The whole extraction process is carried out in a box-type mixer-settlers, the difference is that in the reverse extraction operation, the concentration and dosage of the extractant are different.

ammonium metatungstate extraction preparing image

In the process of production, using ammonium tungstate solution as raw material, ammonium metatungstate was extracted by solvent extraction, extraction of NH4+ ion from ammonium metatungstate solution by a cationic extractant, then, the solution of pH in the condition of 3~4, ammonium metatungstate solution was obtained by reverse extraction. This is a simple and economical method. Ammonium metatungstate solution obtained by solvent extraction, ammonium nitrate was prepared by concentrated crystallization or spray drying.

ammonium metatungstate preparing image

Some scholars used EPA-88-1 extractant to prepare ammonium tungstate from ammonium metatungstate solution.The most important feature of this method is that two product of ammonium tungstate and ammonium metatungstate can be obtained simultaneously by changing the pH value of different raffinate. The production cost is correspondingly reduced, the cycle is shortened, and the energy consumption is low, and the utility model is especially suitable for the technical transformation project of the existing ammonium tungstate factory.

Ammonium metatungstate has the same advantages as ion exchange method. It is simple, continuous and low cost. But the biggest weakness of the extraction method is that the solid substance is easy to cause emulsification during the extraction process. The whole process is easy to fail in some simple situations, and that's why it hasn't been as popular as ion exchange.


If you have any inquiry of ammonium metatungstate, please feel free to contact us:
Tel.: +86 592 5129696      +86 592 5129595
Fax: +86 592 5129797