The reducibility of the Greek nickeliferous laterites: a review

Abstract

This paper refers to a critical review of the Greek nickeliferous laterites roasting reduction studies for better understanding of the process thermodynamic and kinetic mechanisms, affecting decisively the smelting step in pyrometallurgical extraction of nickel from these ores. From this work, it is deduced that iron and nickel oxide reduction degree does not exceed 33 and 76% respectively, the reductive reactions being stopped within the first 20–30 min. Thus, part of ferric iron is transformed into ferrous iron (in the form of magnetite, wustite or fayalite) instead of metallic iron production. Also, no total conversion to metallic nickel takes place. Variation of roasting temperature (700–850°C), grain size of the ores and type of solid reductants, affect the reduction rates and the final reduction degrees obtained. Diffusion or mixed control mechanisms have been found to prevail during reduction. Low reduction degrees obtained are attributed to kinetic phenomena, such as the formation of fayalite (2FeO.SiO₂), which probably covers oxide grains and impedes reduction.