10 – Gravity concentration

Publisher Summary This chapter presents the principle of gravity concentration, its methods, and types. Gravity concentration methods separate minerals of different specific gravity by their relative movement in response to gravity and one or more other forces, the latter is often the resistance to motion offered by a viscous fluid such as water or air. It is essential for effective separation that a marked density difference exists between the mineral and the gangue. Gravity methods of separation are used to treat a great variety of materials, ranging from heavy metal sulphides such as galena (sp. gr. 7.5) to coal (sp. gr. 1.3), at particle sizes in some cases below 50 μm. These methods were declined in importance in the first half of the twentieth century because of the development of the froth-flotation process that allows the selective treatment of low-grade complex ores. They remained, however, the main concentrating methods for iron and tungsten ores and are used extensively for treating tin ores, coal, and many industrial minerals. Many different machines have been designed and built in the past to effect separation of minerals by gravity. The chapter describes the various equipments used in modern mills.