Mineral processing can involve four general types of unit operation: comminution – particle size reduction sizing – separation of particle sizes by screening or classification concentration by taking advantage of physical and surface chemical properties and dewatering Mineral processing can involve four general types of unit operation: comminution – particle size reduction sizing – separation of particle sizes by screening or classification concentration by taking advantage of physical and surface chemical properties and dewatering – solid/liquid separation. In all of these processes, the most important considerations are the economics of the processes and this is dictated by the grade and recovery of the final product. To do this, the mineralogy of the ore needs to be considered as this dictates the amount of liberation required and the processes that can occur. The smaller the particles processes, the greater the theoretical grade and recovery of the final product, but this however is difficult to do with fine particles as they prevent certain concentration processes from occurring. Comminution is particle size reduction of materials. Comminution may be carried out on either dry materials or slurries. Crushing and grinding are the two primary comminution processes. Crushing is normally carried out on "run-of-mine" ore, while grinding normally carried out after crushing may be conducted on dry or slurried material. In comminution, the size reduction of particles is done by three types of forces: compression, impact and attrition. Compression and impact forces are extensively used in crushing operations while attrition is the dominant force in grinding. The primarily used equipment in crushing are jaw crushers, gyratory crushers and cone crushers whereas rod mills and ball mills, usually closed circuited with a classifier unit, are generally employed for grinding purposes in a mineral processing plant. Crushing is a dry process whereas grinding is generally performed wet and hence is more energy intensive. Sizing is the general term for separation of particles according to their size.