Open circuit grinding consists of one or more grinding mills, either parallel or in series, that discharges a final ground product without classification equipment and no return of coarse discharge back to the mill. Some very simplistic examples of open circuit grinding are see below and are made of a Rod mill, Ball Mill or a Rod mill, ball mill combination. Not all ores can be ground in an open circuit type of arrangement. Some conditions which do favor open circuit grinding such as small
reduction ratios, reduction of particles to a coarse, natural grain size, recirculation of cleaner flotation middlings for regrinding and a non-critical size distribution of the final ground product. Some advantages of operating in the open circuit mode vs closed circuit are the minimum equipment requirements, high pulp density discharge and the simplicity of operation.
Closed circuit grinding consists of one or more mills discharging ground product to classifiers which in turn return the coarse product from the size separation back to the mill for further grinding. In this circuit, grinding efficiency is very dependent upon the size separation effected so care should be exercised in selecting the type and size of classifier used to close the system. This type of grinding is the most common circuit found in mineral processing facilities, mainly because a lot of ores and product requirements are not suitable for open circuit grinding. Some advantages presented by grinding in closed circuit are that this arrangement usually results in
higher mill capacity and lower power consumption per ton of product, it eliminates overgrinding by removing fines early and it avoids coarse material in the final ground product by returning this material to the mill. Although closed circuit grinding offers many choices for arrangement of the equipment as well as combinations of equipment, some of the more common circuits are rod mill/classifier, Ball mill/Classifier, Rod mill/Ball mill/Classifier and Rod mill/Classifier/Ball mill/Classifier.