Tungsten Processing and Refining

Chemical Refining Methods for Tungsten

When it comes to the processing of tungsten, a strategic metal with an array of industrial applications, chemical refining methods play a critical role. This process typically involves a series of chemical reactions that help in purifying the metal from its ore.

One of the primary methods employed in the chemical refining of tungsten is known as alkali roasting. This process involves roasting tungsten ores with alkalis like sodium carbonate (Na2CO3) or potassium carbonate (K2CO3). The reaction forms soluble tungstates, which are then extracted and purified further. It's important to note that the conditions for this reaction, such as temperature and roasting time, must be carefully controlled to ensure optimal yield.

Another crucial chemical refining method is acid digestion. Here, tungsten ores are treated with strong acids, such as hydrochloric acid (HCl) or sulfuric acid (H2SO4). The resulting tungsten compounds are soluble in water, allowing for their easy extraction and purification.

A variant of this method is pressure leaching, where the digestion process is carried out under high pressure and temperature. This not only increases the rate of reaction but also improves the overall efficiency of the extraction process.

In addition to these, hydrometallurgical processes involving the use of aqueous chemistry for the recovery of metals from ores, concentrates, and recycled or residual materials are also commonly used. These processes can offer significant advantages over pyrometallurgical processes, particularly in terms of environmental impact and resource efficiency.

Acid Leaching of Tungsten Concentrates

After initial processing, the tungsten ore often takes the form of a concentrate—a material enriched in tungsten compounds. Acid leaching is a prevalent method for further purification of these concentrates.

The acid leaching process involves the treatment of tungsten concentrates with strong acids. The choice of acid—sulfuric, hydrochloric, or nitric—depends on the specific nature of the concentrate and the desired outcome. The acid reacts with the tungsten compounds in the concentrate, forming soluble tungstates that can be easily separated from the insoluble residue.

It's worth noting that the efficiency of the acid leaching process depends heavily on factors such as acid concentration, leaching time, temperature, and particle size of the concentrate. For instance, higher temperatures and longer leaching times generally result in a higher extraction yield.

Furthermore, acid leaching is often followed by a series of washing and filtration steps to remove any remaining impurities. The resulting solution, rich in tungsten, is then ready for further purification and processing through methods such as solvent extraction and precipitation.

Solvent Extraction and Precipitation in Tungsten Refining

Once the tungsten has been leached into a solution, the next step in its purification is often solvent extraction. This process involves the separation of tungsten from other elements present in the solution using a suitable organic solvent.

In solvent extraction, the tungsten-bearing solution is mixed with the organic solvent. The tungsten ions react with the solvent, forming a complex that is soluble in the organic phase. This allows the tungsten to be selectively extracted from the solution.

Precipitation is typically achieved by adjusting the pH of the solution, causing the tungsten to precipitate out as a solid compound. The precipitated tungsten is then collected, washed, and dried, resulting in a high-purity product ready for further processing or use.

Physical Refining Techniques for Tungsten

Apart from chemical methods, physical refining techniques also play a significant role in tungsten processing. These techniques primarily involve changes in the physical state of the material without altering its chemical composition.

One of the most common physical refining techniques for tungsten is flotation. This process separates minerals based on differences in their surface properties. In the case of tungsten, the ore is ground into fine particles and mixed with water and flotation reagents. The tungsten particles become hydrophobic, attach to air bubbles, and float to the surface, where they can be collected.

Gravity separation is another physical refining technique used in tungsten processing. It exploits the differences in the specific gravity of different components in the ore. The heavier tungsten-rich particles settle at the bottom, while lighter waste materials float to the top.

Lastly, magnetic separation is also employed, especially when the tungsten ore is associated with magnetic minerals. The ore is passed through a magnetic field, which attracts the magnetic particles, effectively separating them from non-magnetic tungsten particles.

Hydrogen Reduction Process in Tungsten Refining

The hydrogen reduction process is an essential part of tungsten refining. It is a method used to reduce tungsten oxide (WO3) to metallic tungsten.

In this process, tungsten oxide is heated in a stream of hydrogen gas. The hydrogen reacts with the oxygen in the tungsten oxide, forming water and leaving behind pure tungsten. The reaction is typically carried out at high temperatures, ranging from 700 to 1000 degrees Celsius.

One of the key advantages of the hydrogen reduction process is that it produces highly pure tungsten. However, the process requires precise control of temperature and hydrogen flow rate to ensure complete reduction of the tungsten oxide.

Electrolytic Refining of Tungsten

Electrolytic refining is a widely used method for the purification of many metals, including tungsten. This process uses an electric current to drive a non-spontaneous chemical reaction.

In the electrolytic refining of tungsten, a tungsten anode and a thin sheet of pure tungsten as the cathode are immersed in an electrolytic solution containing tungsten ions. When an electric current is applied, tungsten ions from the anode dissolve into the solution and are deposited onto the cathode, forming pure tungsten.

The key advantage of electrolytic refining is its ability to produce very high purity tungsten. Furthermore, the process allows for the simultaneous recovery of valuable by-products from the anode sludge, making it an efficient and sustainable refining method.

How much is a pound of tungsten worth?

Tungsten, a rare and valuable metal, is known for its high melting and boiling points, making it an essential component in various industries such as metalworking, mining, and construction. The price of tungsten varies significantly due to several factors, including the cost of mining, refining, processing the ore, energy, labor, and market conditions.

As of 2023, the price of tungsten has been fluctuating between $852.90 and $20,250.00 per troy ounce. However, these prices are merely estimates and can change due to outstanding market conditions. To convert this to a per pound rate, we need to understand that one troy ounce is approximately 0.0685714 pounds. Therefore, the price range per pound of tungsten would be approximately $12,435.68 to $295,428.57.

However, it's important to note that the price of tungsten can also depend on its form. For instance, the price of tungsten carbide, a compound made from tungsten and carbon, is determined by factors such as purity, size, and shape. Tungsten in other forms like powder, plate, wire, and rod would each have a different price per kilo cost. This is a function of the raw material cost and the amount of work involved in producing the finished product.

In July 2023, industry sources indicated that the Tungsten APT (Ammonium ParaTungstate) Price CIF (Cost, Insurance, and Freight) Rotterdam was US$310-$331 per metric tonne unit (mtu). This price is specific to the form of tungsten known as Ammonium ParaTungstate, which is often sold and shipped for further processing into high purity tungsten powder.

The global tungsten market, valued at US$ 5.14 billion in 2022, is expected to reach US$ 8.81 billion by 2029, growing at a Compound Annual Growth Rate (CAGR) of 8%. This growth is likely to influence the price of tungsten in the future.

Moreover, the cost of tungsten can also be influenced by international trade dynamics. For instance, China and the US are dominant forces in global tungsten trade, showing a strong market gravitational effect. Any changes in their trade policies or domestic production can significantly impact the global tungsten prices.