International Journal o[ Mineral Processing, 22 (1988) 251-259 251 Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands Rheological Effects in Grinding Circuits S.K. KAWATRA and T.C. EISELE Metallurgical Engineering, Michigan Technological University, Houghton, M149931 (U.S.A.) ( Received January 10, 1986; accepted after revision August 14, 1987) ABSTRACT Kawatra, S.K. and Eisele, T.C., 1988. Rheological effects in grinding circuits. Int. J. Miner. Pro- cess., 22: 251-259. The grinding efficiency of circuits using tumbling media mills in closed circuit with hydrocy- clone classifiers may be improved by control of the mill slurry rheology. The theology affects both the rate of fine material production by the grinding mill, and the separation performance of the hydrocyclone. In addition, the manner in which theology changes are produced will affect hydro- cyclone performance. This parameter is neglected in process control situations due to the difficulty of making rheological measurements of dense slurries on-line. In recent years, a number of new viscometers has been developed which may be useful for this purpose. INTRODUCTION The single most energy-intensive unit operation in mineral processing is comminution. Size reduction consumes approximately 25% of the total energy used in mineral concentrators, while typically less than 5% of this energy is consumed in the production of new mineral surface (NMAB, 1981 ). There is thus much room for improvement in grinding operations, and even a slight increase in efficiency will produce substantial energy savings. Such improve- ment is most readily obtainable by optimization and control of mill-operating conditions. Extensive research on the performance of tumbling-media mills has allowed the formulation of a number of excellent simulation programs and on-line con- trol strategies (Herbst and Rajamani, 1979). However, due to the unavaila- bility of suitable viscometers for mineral slurries, the control of mill rheology has been neglected, even though a number of investigators (Austin et al., 1984; El-Shall and Somasundaran, 1984) have determined that rheology has a large effect on the efficiency of both grinding mills and hydrocyclones. In general, it is not feasible to assume that rheology may be predicted from the value of other parameters, such as percent solids, as shifts in ore character, particle size, and temperature will also alter slurry rheology. The effect of tem- perature is particularly significant in areas with large seasonal temperature 0301-7516/88/$03.50 @) 1988 Elsevier Science Publishers B.V.