Features of research of iron ore thermal decarbonization kinetics during roasting

Abstract

Prediction of availability of iron ore raw material for heat treatment, selection of powerand resource-efficient technological routes, operating procedures and their adaptation to periodically varying properties of iron ore raw material meet the lack of calculation techniques for thermal preparation and processing operations that rather completely take into account special features of this material. The data on thermal decarbonization kinetics, strictly required for quantitative calculations of chemical-metallurgical processes in the industrial roasting machines and ore smelting furnaces, are insufficiently substantiated and contradictory. Iron-bearing ores and minerals have complicated and heterogeneous polymineral composition. Source minerals, being subjected to heating, are characterized by physical-chemical transformations and mutual reactions; it leads to variations in composition and structure of materials, to appearance of heating effects and finalizes in accompanying by deep variations of thermal-physical parameters (TPP), such as heat capacity, temperature conductivity and heat conductivity. As soon as thermally activated chemical-metallurgical processes are determined by kinetic regularities and depend on heating conditions, TPP of iron ore raw material acquire complicated, temperature-temporal or temperature-concentrating type of relationships. Especial methodical difficulties are arising also during examination of calcination kinetics of bulk and pelletized iron ore raw material, because the results of investigations are influenced by the heat exchange processes in the samples. Lack of information about decarbonization kinetics of iron ore raw material as well as about the effect of chemical and mineralogical composition, material structure and heating rate on calcination process don’t allow to use the existing literature data on the results of thermal analytical researches of separate types of iron ore raw material and “clean” carbonate materials for description of calcination process of iron ore raw material [1–3]. Thereby, experimental investigation of the processes of carbonates dissociation with use of samples saving their initial material structure within the temperature range close to practical range is required for establishing the general regularities of calcination chemicalmetallurgical process [4, 5]. It can be found out e.g. in the area of high-temperature roasting of iron ore pellets in roasting conveyor-type machine or in sintered layer on the belt of a sintering machine [6, 7]. The first condition provides restriction on the minimal dimensions and shape of samples. Dimensions of samples should exceed substantially grain size of source minerals of typical dimension of structure of the examined material during all experiments [8, 9]. Shape of a sample should be chosen based on minimization of distorting influence of mechanical activation of surfacial inclusions, i.e. the relationship “sample surface / sample volume” should be minimal wherever possible [10, 11]. The second condition can be realized during conduction of experiments with high heating rates. The conducted analysis of exploration of the industrial roasting machines, operating at metallurgical and mining-concentrating works at present tine, displays that heating rate of material grains varies in real conditions in wide range and can reach 2000–2500 К⋅hour-1. Features of research of iron ore thermal decarbonization kinetics during roasting