Molybdenum processing techniques have been improvised constantly. Molybdenum or its alloys can be machined by all of the common machining methods. No extraordinary procedure or equipment required.
Molybdenum is a white platinum like metal with a melting point of 2,610 °C. It is very ductile and tough in its pure form. It has various characteristics such as high thermal conductivity, high resistance to corrosion, moderate hardness and a low expansion coefficient.
Molybdenum promotes toughness, high hardness, tensile strength and creep resistance when alloyed with other metals. The small amounts of molybdenum considerably possess the abrasion resistance and anti-corrosive properties. Molybdenum is therefore a fundamental, adding agent in the extraction process of steels.
A properly shaped molybdenum is as good as stainless steel under various machining mechanism . This metal can be machined with usual equipment. However, If the cutting tools are made of hard cast iron or cold-rolled steel, they may make the edges to break during machining molybdenum. The material is very abrasive, causing tools to wear out very quickly than normal steel or iron.
Below are the various processes of processing molybdenum:
Milling: In this process, ball or rod mill grinds and crush the mined ore to fine particles that are of 10-3 microns in diameter. The molybdenum is extracted from the gangue. The grinding mills reduce the rock’s size into a soccer ball or to the size of gravel. After that ball milling reduces the substance to the uniformity of face powder.
Flotation: The milled gangue powder is now mixed with a liquid and aeration is done in the flotation step. The less dense particles rise in the foam to be collected, while the gangue sinks to be discarded. This process separates the metals from the gangue and in the case of molybdenum/copper ores it separates the metals from molybdenite and copper sulphide. The resulting MoS2concentrate contains 92% MoS2. Advanced treatment is done by acid to dissolve impurities like lead or copper if required.
Roasting: It is done in air at temperature of 650°C which converts MoS2concentrate into MoO3 (roasted molybdenite) concentrate by the chemical reactions. Roasters basically are multi-level fireplace furnaces, in which molybdenite particles move from top to bottom against a current of hot gases blown from the bottom. The final roasted molybdenite concentrate contains at least of 57% molybdenum, and sulfur less than 0.1%.
Rhenium recovery: In this process some of the byproducts left are removed. The molybdenite concentrates contains small quantities of rhenium. Molybdenum roasters equipped to recover rhenium are one of the principal profitable sources of this exceptional metal.
Smelting Ferromolybdenum: In this step the oxide is mixed with iron oxide and reduced by aluminum in a thermite reaction. This produces ferromolybdenum chunk weighing some hundred kilograms. The product contains 75% molybdenum. After air cooling, the chunk is crushed to meet specified ferromolybdenum particle size range.
Upgrading Tech Oxide: This process is performed
Ø By sublimation to produce clean MoO3 (molybdic oxide). Ø By wet chemical processes to produce various types of clean molybdenum chemicals such as molybdates and molybdic oxides.
Production of Molybdenum metals: The metal is produced by hydrogen reduction of uncontaminated ammonium molybdate or molybdic oxide. The chemical reduction of pure ammonium dimolybdate or molybdenum trioxide to metal requires two stages because the conversion to metal releases heat that hinders the process.
Ø In the first stage reduction the reduction of MoO2 is performed at the temperature of 650ºC. Molybdenum dioxide is then reduced to molybdenum metal Ø In the next stage reduction is done using very high temperatures between 1,000 to 1,100°C.