THE KINETICS OF SELENIUM REMOVAL FROM MOLTEN COPPER BY POWDER INJECTION

Chemical thermodynamic calculations show that selenium removal from co pper melts using sodium carbonate (soda ash) is only effective under r educing conditions. Reducing conditions can be generated by carbon, bu t even more effectively by calcium carbide which has not been used pre viously for such a purpose. To clarify the kinetics of these multiphas e, multicomponent reactions, various mixtures were either placed on to p of or injected into 70 kg heats of molten copper. The following reag ents were found to be effective in removing selenium: soda ash-graphit e mixtures, calcium carbide, and calcium carbide-soda ash mixtures, in increasing order of effectiveness. Experiments were also performed wi th synthetic blister copper containing oxygen, selenium, tellurium, bi smuth, nickel, silver, and lead. As expected from the thermodynamic an alysis, only the first three of these elements were removed. A mathema tical model was developed to describe the diffusion-controlled reactio n kinetics of selenium and oxygen removal at calcium carbide particle interfaces. Very good agreement between the model and experiments was achieved for the reaction paths of selenium and oxygen-when 35 pet of the particles were in contact with the melt. The utilization of powder varied over a wide range (0 to 10 pet), depending on the selenium and oxygen contents. The industrial implications of this work are discuss ed in terms of multielement removal, refractory erosion, temperature l oss, and reagent utilization.