Mineral Comminution Plant,Mineral Comminution Processing

The term comminution is used to describe a collection of physical processes that can be applied to a stream of ore to reduce the sizes of the particles in the stream. Many different types of processes are used, including breaking particles into smaller particles by crushers and grinding mills and separating particles into streams of different sizes by screens and classication devices.

The purpose of comminution is to transform raw ore into a more usable or more saleable product or to prepare it for further processing. A comminution circuit consists of a collection of processing units connected together (typically by conveyor belts). Comminution circuits may contain loops, typically re-cycling large particles through crushers until they reach the desired size. One or more streams of ore form the feed stream, entering the circuit typically from some preprocessing stage. One or more streams of transformed material exit the circuit as the product stream of the comminution process.

The following figure depicts the comminution circuit examined in this study . The feed stream is the result of a primary crushing stage, entering the circuit at a xed rate on a conveyor from the top left of the gure. The feed is passed over a scalping screen that allows particles less than the aperture of the screen (the undersize particles) to pass through. Oversize particles greater than the aperture of the screen (and due to the imperfect nature of a screen, some smaller particles) are directed to a secondary crusher. The crushed ore from the secondary crusher is then rejoined with the undersize ore stream before being passed to the product screen. The product screen lters particles less than a given size into a product stockpile, re-directing all oversize particles to a tertiary crusher. The tertiary crusher further crushes the ore, sending the output back to the product screen. The product stockpile is the output from the circuit.

comminution circuit

The type of crushers used in this circuit are cone crushers. A cone crusher has two parts: an inner rotating crushing surface revolving in an eccentric motion around the central axis of the crusher, and an outer xed crushing surface. Material is introduced into the crusher from above and is crushed as it ows downwards through the machine due to compression of the inner rotating crushing surface against the outer crushing surface. The gap between the inner rotating crushing surface and the outer xed crushing surface at the closest point in the cycle is called the closed-side setting (CSS) of the crusher . This setting can be reduced to obtain a narrower chamber and ner crushing, or increased to obtain a wider chamber and coarser crushing.

Cone crushers come in many variants, categorised by three attributes: size, cavity, and head. The size attribute species the size of the cone crusher by controlling the size of the housing to employ: possible values include HP160, HP220 and HP315. Bigger crushers tend to be better suited to coarser feeds and have greater capacities (the amount of ore that can pass through the crusher at any given time), but are more expensive. The cavity attribute allows a crusher to be ne-tuned as to the coarseness of its product. Different settings impose different restrictions on the minimum CSS and maximum feed size that the given crusher can handle. Finer values allow a ner CSS, but restrict the crusher' s ability to handle coarse feeds (as indicated by a smaller maximum feed size). The cavity attribute can be set to extra-ne, ne, medium, coarse, and extra-coarse. The head attribute also inuences the minimum CSS and maximum feed size that a crusher can handle, but compared to cavity , the effect is far more pronounced. T wo settings are possible: standard and short, where the latter corresponds to a much ner product than the former.

This comminution circuit contains four separate comminution components (the secondary crusher, the tertiary crusher, the scalping screen, and the product screen). While it is easy to pictorially represent and conceptually understand each component as one physical machine, in practice, due to the large amount of material processed by the circuit, each component is typically replaced by several physical machines all congured the same way and operating in parallel to one another . These parallel machines share the load of the component by splitting the incoming ore stream into several streams and re-directing each separate stream to one of the physical machines. For example, if the nal product is required to contain particles all less than some relatively small value (as is typically the case), the product screen and tertiary crusher must be con-gured for ne-level crushing. Since this will reduce the capacity of the tertiary crusher relative to that of the secondary crusher, several parallel crushers will be needed in the tertiary crushing stage to handle the relatively high volume of ore in the re-cycling ore stream.