Grinding circuits

The three basic types of size reduction circuits used to produce a fine product ate shown in Eigure 1. The final stages of the grinding circuit are typically operated in closed circuit, at comparatively high circulating loads, so that the material has tittle chance of being broken a second time before it is removed from the circuit by a classifier. Rod mills are operated normally in an open circuit. 

A. J. Lynch, ed.. Mineral Crushing and Grinding Circuits, Elsevier, Amsterdam, the Nethedands, 1977. 

Typically, ore bodies are relatively low in iron content. Iron minerals are finely divided in a gangue matrix. Wet grinding is usually required to Hberate the iron minerals, although some beach sands may have Hberated iron mineral values. Wet dmm separators are limited to the treatment of material <10 mm. The magnetic dmm separators appHed are usually related to the grinding circuit required to Hberate the iron mineral, and are typically designated by appHcation as cobbers, roughers, or finishers. 

Flotation. The slurry of ground ore leaving the grinding circuit may be separated from part of the water in thickeners or may go directly to the flotation cells. The latter are rectangular tanks into which air is injected or drawn via impellers. Flotation is based on producing a water-repellent chemical film on the exposed sulfide minerals in the ground ore. The sulfide minerals collect on the surface of the air bubbles and rise to the top of the flotation cell, where they can be removed from the froth. The froth overflows the cells in collector troughs called launders. 

In rnanv instances, superior Rotation results are obtained bv conditioning the ore with the reagents before the Rotation step, ()ilv-type collectors are sometimes added to the grinding circuit to ensure dis-... 

Herbst et al. [International J. Mineral Proce.ssing, 22, 273-296 (1988)] describe the software modules in an optimum controller for a grinding circuit. The process model can be an empirical model as some authors have used. A phenomenological model can give more accurate predictions, and can be extrapolated, for example from pilot-to full-scale apphcation, if scale-up rules are known. Normally the model is a variant of the popiilation balance equations given in the previous section. 

Pin MiUs In contrast to peripheral hammers of the rigid or swing types, there is a class of high-speed mills having pin breakers in the grinding circuit. These may oe on a rotor with stator pins between circular rows of pins on the rotor disk, or they may be on rotors operating in opposite directions, thereby securing an increased differential of speed. See also the Mikro-ACM pulverizer described later. 

Mular, A.L. and W. R. Bull, W.R. (Editors), Mineral Processes Their Analysis, Optimization and Control, Queens University, Ontario (1969) Mular, A. L. and N. A. lull, N.A., The Selection of Cyclone Classifiers, Pu ps and Pump Boxes for Grinding Circuits, Mineral Processing Plant Design , AIME, New York (1978)... 

The particle size distribution of the product is one of the most important product characteristics of grinding circuits. Instead of the complete distribution, however, we are limited mostly to determining a few characteristic parameters of the product size such as the mean particle size and the variance,... 

Based on these considerations, the purpose of optimisation is to determine the values of the design variables d of the grinding circuit to produce such particulate product that the objective function be minimal. 

D. Espig, V. Reinsch, Computer aided grinding circuit optimization utilizing a new mill efficiency curve, Int. J. Miner. Process. 44 15 (1996) 249-259. 

R. Lestage, A. Pomerleau, D. Hodouin, Constrained real-time optimization of a grinding circuit using steady-state linear programming supervisory control, Powder Technol. 124 (2002) 254-263. 

Lynch—Mineral Crushing and Grinding Circuits, Elsevier. 

In this figure one sees all the steps that go into making ceramics, starting with grinding the ceramic powders to develop a very fine particle-size distribution (the grinding circuits contain classification and recycle loops). This is... 

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