Process and plant for treating ore concentrate particles containing valuable metal

A process for treating ore concentrate particles containing valuable metal and having at least arsenic and sulfur containing components, which process comprises:

• roasting the concentrate particles in a first roasting step that creates first off-gas and operates with a low oxygen potential for dearsenifying the concentrate,
• treating the first off-gas leaving the first roasting step to separate calcine and a sulfide-rich first process gas component,
• roasting the calcine led from the first roasting step in a second roasting step that creates second off-gas and operates with an excess of oxygen, and
• treating the second off-gas leaving the second roasting step to separate calcine and a second process gas component,
• wherein the process further comprises
• forming a gas mixture of the first process gas component and the second process gas component, the gas mixture comprising oxygen-containing oxidizer gas, and
• post combustion of said gas mixture in a post combustion chamber, said post combustion operating to react said sulfide-rich first process gas component with said second process gas component, which acts as oxidizer gas, thereby decomposing any SO3 in the gas mixture, and
• exposing exit gas from said post combustion chamber to subsequent gas cooling and dust removal steps.