Fine grinding refers to the comminution process in which ore particles are reduced in size to very fine particle sizes, typically below 75 microns (200 mesh) and in some applications below 20 microns, to achieve the degree of mineral liberation necessary for effective downstream separation and recovery. Fine grinding is a critical and energy-intensive stage in the processing of many ore types encountered in bauxite, gold, iron ore, and diamond mining operations where the valuable mineral is finely interlocked with the host gangue at a microscopic scale.
In gold mining, fine grinding is employed in the processing of refractory gold ores where gold is locked within sulfide mineral matrices, particularly pyrite and arsenopyrite. Ultra-fine grinding, typically to particle sizes of 10 to 20 microns, is used to expose the gold to subsequent oxidation and cyanide leaching. Technologies used include high intensity horizontal stirred mills such as the Isamill and Vertimill, which achieve very fine product sizes more energy-efficiently than conventional ball milling.
In iron ore processing, fine grinding is applied to magnetite concentrates produced by magnetic separation to achieve the particle fineness required for pellet feed, where specific surface area targets of 1,500 to 2,000 cm²/g or higher are typically specified by pellet producers. Ball mills and more recently, high-pressure grinding rolls (HPGR) in combination with ball mills, are used for iron ore fine grinding. In bauxite and alumina processing, fine grinding of aluminum hydroxide seed crystals influences the particle size distribution of the final alumina product.
The energy consumption of fine grinding circuits represents a significant proportion of total plant operating costs, making the selection of the most energy-efficient grinding technology and the optimization of grinding media size, mill filling, and circuit classification a major focus of plant engineering and operational improvement efforts.