How low must sulfur content be for roasted molybdenum calcine to be finished?

In the process of roasting molybdenite concentrate to produce technical molybdic oxide, the conversion of molybdenum disulfide (MoS₂) into molybdenum trioxide (MoO₃) is considered finished when the sulfur content of the calcines falls below 0.1 percent. This roasting process is typically conducted in multiple-hearth furnaces, where temperature control is critical to prevent the sublimation of MoO₃.1