The generation of obsolete scrap in Japan is increasing and expected to account for more than 40% of total steel production by the year 2010. To make effective use of all of this steel scrap generated, the deterioration of hot workability of steel products may arise as a problem caused by copper and tin accumulations. This paper selects and summarizes the results of research on the removal of residual copper and tin from steel scrap from among the research activities of two groups formed concerning the utilization of steel scrap - Committee for Removing Residual Elements from Steel Scrap of the Iron and Steel Institute of Japan (ISIJ) and Scrap Recycling Technology Research Project of the Japan Research and Development Center for Metals (JRCM).
(1) If Japan is to use all of the steel scrap generated as feed material for steel production in 2010, the average removal ratio will have to be improved to about 55% for copper and 30% for tin.
(2) When copper is present mixed with steel, mechanical separation following shredding (including cryogenic processing) is the most practical method for removing copper from steel scrap Separation of liquid copper from solid steel by adjusting the atmosphere conditions in the steel scrap preheating step, selective melting of copper in an aluminum bath, and selective dissolution of copper by a wet process with ammonia, for example, also have potential for practical application. Removal of copper by vaporization under vacuum promoted by the vigorous CO bubble formation was studied as the method for separating copper dissolved in steel. A combination of these methods is expected to achieve the target copper removal ratio of 55%.
(3) Unlike copper, tin is low in content and less advantageous to be recovered. The addition of another step for the sole purpose of removing tin from steel scrap is not economically justified. The method of separating the tin coating as oxide film in the steel scrap preheating step and the method of vaporizing tin as stannous sulfide (SnS) in the steel scrap melting step were investigated. Each method was confirmed to be capable of removing tin from steel scrap by about 40%.
(4) A total process was proposed that is composed of steel scrap preheating, melting and dust treatment and removing these residual elements from steel scrap. The total process is planned for evaluating each technology as a combined system.