The Kinetics of Antimony Removal from Copper by Soda Injection

Sodium carbonate or soda was injected into 70 kg heats of copper under controlled atmosphere at various soda ash and carrier gas flow rates. Samples were taken during injection, and analyzed for antimony and oxygen. The soda utilizations were generally less than 25% of that injected. The fraction of antimony eliminated increased with oxygen content, reaching over 90%. There was no appreciable difference in reaction rate between light and dense soda, between nitrogen and air carrier gas or between soda and sodium bicarbonate. A theoretical analysis of the kinetics of the antimony removal with soda-rich slag indicates that the rate is controlled by antimony diffusion in the metal. The measured rates were indeed partially controlled by the antimony content in the copper, but also depended on the oxygen content. This latter observation may be attributed to the presence of a cuprous oxide phase containing soda which provides a rapid, parallel reaction path. The amount of this phase increases with oxygen content, thereby increasing the antimony removal rate. The implications of these findings for full-scale practice are discussed.