Explanation

Roasting is the heating of a sulphide ore strongly in the presence of excess air to convert it into the oxide, for example 2PbS + 3O2 -> 2PbO + 2SO2, driving sulphur off as sulphur dioxide. Calcination instead heats carbonate or hydroxide ores in limited air to expel CO2 or water, while smelting is the subsequent high-temperature reduction of the oxide to the metal. Incineration is simply burning of waste. The sulphide-to-oxide conversion in air is roasting.