Evaluation of ilmenite as a possible medium in a dry dense medium fluidised bed

Abstract

Dry beneficiation of coal as alternative to water-based methods is in high demand, especially in arid geological environments. Benefits of this dry process include that it eliminates the need for water use, while high separation precision and quick return on investment are also possible. One of these dry beneficiation methods proposed and developed in China is the dry dense medium fluidized bed of coal. Published work on this method of separation has mainly focused on using magnetite as a medium, but the recovery and reuse of the magnetite were found to be problematic. This study will extend the possibilities of this method by investigating the use of ilmenite (FeTiO3) as an alternative medium for the dry dense medium fluidization process. Ilmenite is considered due to its clean surface properties, hydrophobicity, and sphericity. It is expected that the ilmenite will not attract contaminants to its surface and will not be lost to the coal due to attachment. The initial investigation considered two types of mediums: a reference medium, which consists of ilmenite and sand; and a medium that resembles the medium used in the current dry dense medium fluidization process, consisting of ilmenite and fine coal. The experiment was conducted on coal sized between – 50+13,2 mm in a laboratory-scale cylindrical fluidized bed, and density tracers were used to determine the écart probable moyen (EPM). The results revealed that a uniform and stable fluidized bed can be achieved in both scenarios. At optimal conditions, the bed medium mixtures consisting of ilmenite with sand had a separation EPM of 0,045, and a cut density of 1800 kg/m3. As a result, the sand could not be used to separate coal as lower cut densities are required by the coal industry. The blend of 60% fine coal and 40% ilmenite as medium at an observed bed split of 1580 kg/m3 was used as the optimum condition with a separation efficiency (EPM) of 0,05. The yield of feed to the plant coal sample (AFE) and run of mine coal sample (ROM) were 61,44% and 71,27% respectively at the optimal condition of a binary medium of fine coal with ilmenite. It was found that the ilmenite does not attach to the surface of dry coal, resulting in the highest recovery of 99,79% when the ilmenite is only used once. The recovery of ilmenite slightly decreased with increase the surface moisture content of coal. The biggest losses of ilmenite on coal were 24,25 kg/t at an external moisture of 4%, which translated into $3,88. However, the experiments did not make use of the high-frequency screen, which will result in better recoveries. At the end of this study the conclusion can be made that ilmenite can be considered as a viable alternative medium in a dry dense medium fluidized bed process, due to its material properties.