Molybdenum does not occur in a pure state in nature and must be extracted and refined. The process of making molybdenum involves several stages, from mining the ore to refining the metal. Below, we will explore the process of making molybdenum, including its extraction methods and processing techniques.
1. Molybdenum Mining
Molybdenum is primarily derived from molybdenite (MoS₂), but can also be found in other minerals such as pyrocatechite (PbMoO₄) and calcomolybdenite (CaMoO₄). Most molybdenum is extracted as a byproduct of copper mining, with molybdenite often found in copper ores.
Molybdenite: Molybdenite is the primary ore used to extract molybdenum and is often found in porphyry copper deposits. After mining, the ore is sent to processing plants for further extraction.
Other Ores: Molybdenum can also be extracted from secondary ores such as wolfenite and molten lead, but these ores are much less common than molybdenite.
2. Crushing and grinding of the ore
After the molybdenum ore is mined, it is crushed and ground to break the material into smaller fragments. This process increases the surface area of the ore, allowing for more efficient extraction of the molybdenum in subsequent processing stages.
Crushing: Large pieces of ore are first reduced to a smaller, more manageable size.
Grinding: The crushed ore is then ground into a fine powder to facilitate the extraction process.
3. Froth flotation process
Molybdenum is typically extracted from molybdenite using a process called froth flotation, which is often used to separate valuable minerals from unwanted materials, also known as gangue. This method relies on differences in the hydrophobic (water-repelling) properties of minerals in the ore.
Flotation chemicals: The ground ore is mixed with water, and chemicals called frothers and collectors are added. Frothing agents create bubbles, while collectors attach to the surface of the molybdenum-bearing particles, causing them to cling to the bubbles.
Separation: The molybdenum-bearing particles rise to the surface, forming a froth layer that is then skimmed off. The remaining gangue material remains in the flotation tank, and the molybdenum concentrate is collected.
4. Roasting
The molybdenum concentrate obtained from flotation contains molybdenite (MoS₂), which is not in pure metallic form. To separate the molybdenum from the sulfur and other impurities, the concentrate goes through a roasting process.
High Temperature: The molybdenum concentrate is heated in a furnace to temperatures of about 500-700°C (932-1,292°F), causing the sulfur to react with oxygen and form sulfur dioxide (SO₂).
Oxidation: During roasting, the molybdenum disulfide (MoS₂) is oxidized and converted to molybdenum oxide (MoO₃). The sulfur dioxide gas is typically collected and can be further processed to produce sulfuric acid, which is a byproduct of the process.
5. Reduction to Molybdenum Metal
Once molybdenum oxide (MoO₃) is produced, it can be reduced to pure molybdenum metal using a high temperature process called reduction. There are several ways to reduce molybdenum oxide, but the most common method is to use hydrogen. In some cases, molybdenum oxide can also be reduced using carbon (in the form of coke), a process called carbothermal reduction. However, this method produces molybdenum carbide (Mo₂C) as an intermediate, which must then be further processed to obtain pure molybdenum.
6. Purification and Refining
After reduction, molybdenum metal is usually impure and may contain trace impurities. To achieve the high purity required for many applications, molybdenum is refined using several methods:
Electrolytic Refining: This process uses electrolysis to purify molybdenum. Impure molybdenum metal is made into an anode in an electrolytic cell to form a high-purity molybdenum cathode.
Vacuum Arc Remelting (VAR): In this process, molten molybdenum is subjected to a high-energy arc under vacuum to remove residual impurities.
7. Refined molybdenum is typically processed into a variety of forms, including the following:
Molybdenum Powder: Purified molybdenum is usually made into a fine powder that can be used to produce molybdenum alloys or for additive manufacturing (3D printing).
Molybdenum Bars and Rods: Molybdenum metal can be made into bars, rods, or sheets for a variety of industrial applications, including high-temperature environments such as jet engines, nuclear reactors, and industrial furnaces.
Molybdenum Alloys: Molybdenum is often combined with other metals (such as iron, nickel, chromium) to make strong, heat-resistant alloys used in industries such as aerospace, electronics, and manufacturing.
After being refined and purified, molybdenum can be made into a variety of shapes and alloys and is essential in industries such as aerospace, energy, and electronics.
