How does molybdenite become technical molybdic oxide?

To produce technical molybdic oxide, molybdenite concentrate (molybdenum disulfide, ${\text{MoS}}_2$) is converted through a roasting process, typically conducted in Nichols-Herreshoff-type multiple-hearth furnaces.1

The process involves the following steps:

• Feeding and Preheating: The concentrate is fed into the top of the furnace against a current of heated air and gases blown from the bottom.1
• Roasting: In the first hearth, the material is preheated, causing flotation reagents to ignite and initiating the transformation of ${\text{MoS}}_2$ into molybdenum trioxide (${\text{MoO}}_3$).1
• Exothermic Control: This reaction is exothermic and continues through subsequent hearths. Operators control the temperature by adjusting oxygen levels and using water sprays to ensure it does not exceed 650 °C (1,200 °F), preventing the sublimation of ${\text{MoO}}_3$.1
• Completion: The process concludes when the sulfur content of the resulting calcines falls below 0.1 percent, yielding a product that is 85–90 percent ${\text{MoO}}_3$.1

This technical molybdic oxide is then used primarily in the production of alloy steels and other foundry products.23