Why can copper leaching produce less sulfur dioxide than smelting?

Copper leaching, also known as hydrometallurgy, produces less sulfur dioxide than traditional smelting because it is carried out at significantly lower temperatures.1

In contrast, smelting—a pyrometallurgical process—requires high-temperature roasting and converting of sulfide ores. During these stages, sulfur is oxidized to form sulfur dioxide gas as a byproduct. By avoiding these high-heat chemical reactions, leaching eliminates the generation of sulfur dioxide, though it necessitates the careful management of effluents and residues to ensure environmental safety.12