Selective Fragmentation of Oolitic Iron Ores by Microwave Pretreatment
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Selective Fragmentation of Oolitic Iron Ores by Microwave Pretreatment Ernesto F. Campos-Toro, Shaoxian Song, Alejandro López-Valdivieso Instituto de Metalurgia, Universidad Autónoma de San Luis Potosí, Av. Sierra Leona 550, San Luis Potosí, C.P. 78210, Mexico. e-mail: [email protected] ABSTRACT There are plentiful of oolitic iron ore resources on the earth, which cannot be currently exploited because of great difficulties for beneficiating the ore. In this work, the selective fragmentation of a Chinese oolitic iron ore (which fragments ore particles along the interfaces of iron and gangue minerals) through microwave was studied in order to liberate the iron minerals at a coarse particle size and thus to effectively concentrate the iron minerals from the ore. The experimental results have shown that a large amount of fractures on the oolitic iron ore were formed along iron and gangue mineral interfaces after being treated by microwave radiation at an appropriate frequency and potential. Following a microwave treatment, the oolitic iron ore was ground by using a ball vertimill. It was indicated that the pretreatment increased the liberation of the iron and gangue minerals at the same particle size, about 10-20% and 10-30% respectively. INTRODUCTION It is an accepted fact that it is hard to liberate the iron minerals from oolitic iron ore because of the structure of hemispherical aggregates. With conventional grinding methods, it is necessary to carry out a very fine grinding (1-5 µm) to ensure that the iron mineral particles are free from their associations. Such fine particles are very difficult to be beneficiated with conventional processes of mineral concentration (flotation and magnetic separation) since the separation efficiency falls in the range of fine particles [1, 2]. Accordingly, there is a great significance to develop a new grinding process to realize the liberation of the iron minerals from oolitic iron ores at a larger particle size. Thermal treatments have been early studied to aid the fragmentation of ores. It has been found that microwave radiation has the potential to create intergranular fractures which increase liberation of minerals from ores with different dielectric properties or differential thermal heating [3]. Recent works [4, 5] have focused on the theoretical study of the effect of microwave application on minerals, in order to understand the mechanism by which the weakening of a theoretical mineral (usually pyrite/calcite) happens due to stresses exerted by thermal expansion of the mineral phases. However, few reports have been aimed at the direct application of this technique to complex ores. In this work, we attempted to explore the possibility of fragmenting oolitic iron ore along the phases of iron mineral/gangue minerals, which was termed as selective fragmentation. The objective of this work is to obtain more understandings of the fractures and selective fragmentation of iron minerals from ores by means of microwave treatment. EXPERIMENTAL
Materials The oolitic iron ore sample us
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