Autogenous grinding is a process of grinding ore in a rotating cylinder, using large pieces of the same ore. Autogenous mills operate mechanically like ball mills; however, the media used for grinding differs. Simply put, in autogenous grinding, the media is also the material that is being ground, whereas in other milling methods steel or porcelain balls are used as media.
The term autogenous grinding came about due to the concept of self-grinding of the ore. It is also referred to as "Run of Mine" or ROM grinding. A sturdy, rotating drum throws larger rocks of ore in a cascading motion, causing impact breakage of similar smaller rocks that need to be ground into finer particles.
Autogenous grinding is gaining in popularity, as the grinding media costs are much less, and this process does not produce as much slime or fines as traditional rod and ball mills.
Autogenous mills can handle both wet and dry operations. In some applications that require the grinding of minerals, such as talc, asbestos, and mica, dry semi-autogenous milling is the preferred choice. Grinding is easily enabled in autogenous mills by attrition. Also, autogenous mills have grate discharges, so as to retain the coarse grinding media in the mill while dispatching the fine particles.
The other benefits of using autogenous grinding include – reduction of metal wear, and elimination of secondary and tertiary crushing steps. Therefore, autogenous grinding offers more savings in capital and operational costs.