Ammonium metatungstate spray drying tower belongs to the spray equipments of ammonium metatungstate production, which is the most widely used of liquid forming process and drying industry. Spray-drying tower is suitable for preparing powder, granular solid product from liquid raw material with forms of suspoemulsions, solution, emulsion, and paste. Thus, when the finished product particle size distribution, residual moisture content, bulk density and particle shape are in line with the precision standard, the spray drying tower is supposed to be an ideal drying process.

 

Principle of ammonium metatungstate spray drying tower is that the air goes into the top dryer’ air distributor after filtered and heated, then the hot air will uniformly go into the drying room in the spiral. AMT feed solution through the high-speed centrifugal atomizer (rotary) at the top of the tower to be sprayed into the extremely fine mist liquid beads AMT, and dried AMT will come into being in a very short time when it in contacts with the stream of hot air. Then, ammonium metatungstate is exported continuously from the bottom of the spray drying tower and the cyclone, and the exhaust gases are vented by the fan.

 

Extended reading:

Spray drying tower is the equipment which can be used in drying biological pesticide, medicine and food microorganism, with the max evaporation rate of 10 kg/h, max gas drying rate of 150 kg/h; the main function of a spray drying tower is to dry the materials in solution state in it and then discharge in form of solid. There are 6 properties of a spray drying tower which show bellows:

1. The fast drying speed within seconds to finish;

2. Suitable for the heat-sensitive materials;

3. Widely apply in most of products with very huge difference;

4. The outlet product has excellent dispersion, fluidity and solubility;

5. Sample producing process and easy to operate and control;

6. The part which in contact with material is using stainless steel to protect raw material not to be polluted and extend the service life of the equipment.

The detection methods of ammonium metatungstate are graphite furnace atomic absorption spectrometry (GFAAS), flame atomic absorption spectrometry (FAAS), inductively coupled plasma emission spectrum (ICP-MS) and coprecipitation separation - hydride atomic fluorescence spectrometry (i.e. coprecipitation separation - HG - AFS method.

 

Graphite furnace atomic absorption spectrometry (GFAAS) is the method absorbing and analyzing atoms by atomization with current heating in an atomization device which produced by graphite and to form shapes of tubes, cups and others. Since all atoms of sample are getting involved in the atomization, and the atomic concentration diluted in the flame gas has been avoided, then the analytical sensitivity has been greatly improved. While, when that method applied in detecting trace metal element, its property is better than many of other methods, and will be used in analysis of small amount samples and detect analysis of solid sample.

 

Detection equipments of ammonium metatungstate are atomization device, flame atomic absorption spectrometer, and inductively coupled plasma mass spectrometer ect..

1. Atomization device is a device for sample atomization of atomic absorption spectrometry, which is used in both graphite furnace atomic absorption spectrometry (GFAAS) and flame atomic absorption spectrometry (FAAS). It converts the sample to a free atomic vapor (ground state atom) to absorb the characteristic radiation, and to calculate the element to be measured. There are many kinds of atomizers, and they can be divided into two categories of fire stuffing atomizer and electrothermal atomizer in common. The former includes pre-mixed and full consumption type; the latter includes graphite furnace, carbon wire atomizer, carbon rod atomizer, graphite increase exhaust, and graphite probes ect.;

2. Inductively coupled plasma mass spectrometer consists of plasma torch (composed of three concentric quartz tube), high frequency generator (to produce high frequency current), induction coil, gas supply system and atomization system and other parts;

3. Flame atomic absorption spectrometer is composed of light source, atomization system, spectroscopic system and detection system. The principle is that the instrument emits light with the characteristic spectral line of the element to be measured from the light source, then when the sample vapor passes through, the light will be absorbed by the under measure ground state atom, and finally measured by the weakened degree of radiation characteristic spectrum of light.

Ammonium metatungstate production equipment according to the different stages of production and different methods may be variety, such as pyrolysis method of AMT production, a reactor, rotary kiln, high-speed centrifugal spray drying equipment or spray atomization drying equipment may be used; In addition, other pyrolysis equipments include microwave oven, plate multiple hearth furnace and tubular multiple hearth furnace. The direct recovery AMT can be more than 95% when using tubular multiple hearth furnace.

 

At present, the pyrolysis equipment for producing ammonium metatungstate is mainly rotary calciner, which is a rotary kiln. A rotary kiln is a pyroprocessing device used to raise materials to a high temperature (calcination) in a continuous process. The kiln is a cylindrical vessel, inclined slightly to the horizontal, which is rotated slowly about its axis. The material to be processed is fed into the upper end of the cylinder. As the kiln rotates, material gradually moves down towards the lower end, and may undergo a certain amount of stirring and mixing. Hot gases pass along the kiln, sometimes in the same direction as the process material (co-current), but usually in the opposite direction (counter-current). The hot gases may be generated in an external furnace, or may be generated by a flame inside the kiln. Such a flame is projected from a burner-pipe (or "firing pipe") which acts like a large bunsen burner. The fuel for this may be gas, oil, pulverized petroleum coke or pulverized coal. 

Ammonium metatungstate produced by ion exchange method will probably use ion exchange resin, crystallizer, or spray dryer and other production equipments. Alkali decomposition furnace is mainly used for decomposing tungsten ore during the preparation of AMT to dissolve tungsten into a solution. A plate and frame filter press is the most fundamental design, and many now refer it as a "membrane filter plate". This type of filter press consists of many plates and frames assembled alternately with the supports of a pair of rails. It is used for the impurity removal process of sodium tungstate for preparing high purity sodium in the APT preparation.

Ion exchange colum is used for removal of S, Mo, P, As, Ca, Cu and Sn and other impurities. Co-current deionization refers to the original downflow process where both input water and regeneration chemicals enter at the top of an ion exchange column and exit at the bottom. Co-current operating costs are comparatively higher than counter-current deionization because of the additional usage of regenerants. Because regenerant chemicals are dilute when they encounter the bottom or finishing resins in an ion exchange column, the product quality is lower than a similarly sized counter-flow column. Spray drying is a method of producing a dry powder from a liquid or slurry by rapidly drying with a hot gas. This is the preferred method of drying of many thermally-sensitive materials such as foods and pharmaceuticals.

The surface decarburized WC-Co gradient cemented carbide based on impregnation liquid of ammonium metatungstate solution (AMT) can greatly enhance the comprehensive performance of cemented carbide; and with the simple process, easy to operate, it is suitable for industrial production. The preparation steps are as follows: 

1. Put the conventional WC-Co carbide under vacuum conditions at 100~500°C for dewaxing, then to carry out presintering in 800~900°C to obtain presintering billet with a certain strength and porosity; 

2. After them, the sample is dipped into ammonium metatungstate solution to form concentration gradient of AMT with a certain depth and distribution from the surface layer to the inner; 

3. Then, after the sample is dried, put it in vacuum furnace for sintering along with slow heating in low temperature stage, to make the ammonium metatungstate decomposed, which the broken down products (tungsten oxide) will react with surface substance of WC, Co, then we can get surface decarburized WC-Co gradient cemented carbide. 

 

Cemented carbide is a kind of metal ceramic tool material which prepared by powder metallurgy method by taking refractory metal compounds (such as WC, TiC, TaC, NbC, etc.) as the matrix, and transition of metals (like Co, Fe and Ni) as bonding phase. Due to its high strength, hardness and elastic modulus, wear resistance, corrosion resistance, low thermal expansion coefficient and stable chemical properties, etc, it in has important application in metal cutting, wood processing, oil drilling in mines, composite materials processing and other respects. Conventional class of WC-Co carbide is uniformly consisted with two phases of WC and binding phase, however it exists contrary relationship between the hardness, wear resistance and strong toughness. The WC - Co gradient cemented carbide structure with high wear-resistance and hardness surface, toughness core part was developed in the 1980s, while the appearance of surface decarburized WC-Co gradient cemented carbide makes it easier to control surface eta phase formation depth, and thereby to prepare the superior performance of WC-Co carbide.