Removal of tin from tin coated steel by chlorination in air

Abstract

A high tin content in steel has detrimental effects during processing, fabrication and application of the steel. Removal of tin from the steel is therefore necessary if the scrap has to be recycled. The thermodynamics and kinetics of the removal of tin from steel scrap have been studied. Removal of tin has been demonstrated in air-chlorine gas mixtures (with a 10 : 1 volume ratio of dry air/chlorine) at relatively low temperatures of 403-473 K. Owing to its high vapour pressure, SnCl₄ is readily removed as a vapour from tin coated steel scrap. While tin is preferentially chlorinated, iron is not, but forms a protective layer of iron oxide on its surface. In a laboratory packed bed reactor operating at 403 K, the tin level of baled steel scrap has been shown to reduce from 0·25 to 0·039 wt-% in the presence of air-chlorine mixtures.