Roasting of Molybdenum

The roasting process is converting molybdenite concentrate
into technical molibdic oxide by chemical reactions as follows:

2 MoS2 + 7 O2 = >2 MoO3 + 4 SO2

MoS2 + 6 MoO3 = >7 MoO2 + 2 SO2

7 MoO2 + O2 = > 2 MoO3

The described process takes place at a temperature of
600 - 700 °C in large multihearth furnaces, called

roasters .

Sulfide concentrate is rabbled from the centre the the periphery
of one hearth. It drops to the hearth below and is rabbled back
to the centre. It reacts continously with a steady supply of forced
air during around 10 hours which it takes to complete the circuit
across 12 or more hearths.

The resulting technical grade molibdic acid typically contains then
a minimum of 57 % molybdenum and less than 0,1 % sulphur.

The sulphur dioxide is removed from the effluent roaster gases
by using special desulphurisation systems.

Molybdenite concentrates coming from copper mines contain
small quantities of rhenium as a by-product (< 0,10 %).
Special equipped molybdenum roasters are one of the methods
to get the rare metal rhenium.

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