Tungsten metallurgy is generally divided into four steps (of course, these four steps also apply to the metallurgy of other rare metals, such as molybdenum, titanium, and rare earth) :
1. Mineral decomposition tungsten ores are industrially used in two types, scheelite (CaWO4) and wolframite ([Fe, Mn]WO4). Generally speaking, high pressure soda leaching is used for scheelite, and caustic soda leaching is used for wolframite. For black and white tungsten mixed ore, the use of soda or caustic soda depends on the specific impurity content and mineral taste, because of the high quality black tungsten has been very few, so the combination of black and white tungsten in the industry is the mainstream. Still have a bit more special is for super scheelite, or an artificial scheelite relatively few (iron), using acid decomposition, the biggest benefit of acid decomposition is under acid condition, can join ferrosilicon to remove a small amount of molybdenum (tungsten molybdenum separation has been the difficulty of tungsten metallurgy if you need to recycle molybdenum, can be in the process of purification were to join the sulfur sodium hydride, But the conditions also need to be acidic).
2. Purified material The purified material used to prepare tungsten is ammonium paratungstate (APT), a salt of tungsten with very little water solubility, which has been directly traded on the market. The preparation of APT from crude sodium tungstate solution obtained by mineral decomposition usually involves classical chemical methods, extraction and ion exchange (there are many new processes that are not introduced). The chemical process is divided into three steps: silicon removal by medium method, phosphorus and arsenic removal by magnesium phosphate salt method, and molybdenum removal by sodium thiocyanate. Alkaline extraction: The representative of alkaline extraction is Chenzhou diamond tungsten. It can deal with higher concentration of liquid, but can only transform can not remove the impurity ion exchange: the example of exchange is the legend of the column, but this column in the industry is much larger than the laboratory, but the principle is not all bad. Its representative is Xiamen tungsten. It can remove impurities, also can transform (depth molybdenum removal is still not as good as chemical method). The only drawback is that it can only treat dilute solution, and too much waste water (which can understand the advantages of Xiamen tungsten) these three methods are not exclusive, often used together, or use two of them to remove impurities and transformation. APT can be obtained by evaporation crystallization of the feed liquid after impurity removal and transformation. In the process of evaporative crystallization, the purity can be further improved by some means such as controlling the crystallization rate. At this point, APT is produced and can be traded in the market.
3. Metal production with APT
Tungsten is chemically stable and does not react with hydrochloric acid or sulfuric acid, even when heated, and will not be dissolved in aqua regia.
Tungsten extreme high temperature resistance, known as nature's most difficult melting metal, melting point as high as 3410℃;
Tungsten is one of the hardest metals in the world and can only be pressed when heated to very high temperatures.