Molybdenum is a metallic element which is most frequently used as an alloying addition in alloy and stainless steels. Its alloying versatility is unmatched because its addition enhances strength, hardenability, weldability, toughness, elevated temperature strength and corrosion resistance. Although molybdenum is primarily used in steels, its complex and unique properties have proved invaluable in a constantly expanding range of other alloy systems and chemicals. One of the unique features of molybdenum, as distinct from other heavy metals, is that laboratory tests have shown its compounds to be of low toxicity. corrupti quos dolores quas molestias excepturi sint occaecati laborum et dolorum fuga.
HISTORY
Molybdenum was not discovered until the latter part of the 18th century, and does not occur in the metallic form in nature. Despite this, its predominant mineral - molybdenite - was surely utilized in ancient times but would have been indistinguishable from other similar materials such as lead, galena and graphite. Collectively, these 
substances were known by the Greek word “molybdos”, which means lead-like. A 14th century Japanese sword has
been found to contain molybdenum. However, it was not until 1778 that the
Swedish scientist, Carl Wilhelm Scheele, was able positively to identify molybdenum. He decomposed molybdenite by heating it in air to yield a white oxide powder. Shortly thereafter, in 1782, Peter Jacob Hjelm reduced the oxide with carbon to obtain a dark metallic powder which he named “molybdenum”. By the end of the 1930’s, molybdenum was a widely accepted technical material. The conclusion of World War II in 1945
once again brought increased research investment to develop new civilian applications, and the post-war reconstruction of the world provided additional markets for structural steels, many of which already contained some molybdenum. The years from 1945 to the present have seen a dramatically expanding range of applications for molybdenum, its alloys and its compounds. Rising demand has been comfortably balanced by new sources of assured supply and by new processing technologies with superior recovery rates.
MINING & MILLING
The relatively low grade of most Mo ores necessitates the use of high volume low cost mining extraction techniques, most commonly:Massive open cast pits; or Underground block caving, wherein large blocks of ore are undercut
and allowed to collapse under their own weight.
Many molybdenum mines are amongst the most productive in the world, with the largest capable of moving over 50,000 tonnes of ore per day.
Mined ore is pulverized through a series of crushers and rotating ball and/or rod mills to fine particles that may be only microns (1/1000th mm) in diameter. This liberates the molybdenite from its host rock. A water slurry of the ore is then conditioned with reagents - including some fuel or diesel oil - which coats the
molybdenite particles, rendering them water-repellent. Separation by flotation takes place in aerated tanks. Molybdenite particles attach to rising air bubbles and concentrate in the surface froth which is swept into overflow troughs. Subsequent regrinding and reflotation stages increase the molybdenite content of the new concentrate stream, by steadily removing unwanted material. The final concentrate contains between 70-90% molybdenite. If required, an acidic leach may be employed to dissolve impurities such as
copper and lead.
ROASTING
The roasting process converts molybdenite concentrate into technical molybdenum oxide by the following chemical reactions: ->
These take place at 600-700 C in large multihearth furnaces or “roasters”. Sulphide concentrate is rabbled from the center to the periphery of one hearth where it drops to the hearth below and is rabbled back to the center. It reacts
continuously with a steady supply of forced air during the 10 hours it takes to 
complete the circuit across a dozen or more hearths. The resulting technical grade molybdenum oxide typically contains a minimum of 57% molybdenum, and less than 0.1% sulphur. Desulphurisation systems remove sulphur dioxide from the
effluent roaster gases. Some of the by-product molybdenite concentrates from copper mines contain
small quantities (<0.10%) of rhenium, a metallic element used in catalysts for the production of unleaded gasoline and in advanced superalloys for turbine blades of the latest jet engines. Molybdenum roasters equipped to recover rhenium are one of the principal commercial sources for this rare metal.
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