Mills circuit

Finishers. Magnetic finishing dmms are designed to produce the highest possible iron content in the concentrate. Typically, the feed size has been reduced to a nominal size of —74 fim (—200 mesh) or —44 fim (—325 mesh) in a ball mill circuit. The feed tank and feed arrangement of the finisher separator is usually of the semicountercurrent design. The objective is to disperse the feed particles in order to obtain maximum rejection of nonmagnetic particles. Both 762 and 914 mm dia dmms have been used in finisher appHcations. Dmm covers frequendy are not used in finisher constmction because of the material size. 

Several empirical formulas for classifier selectivity have been proposed. Such a formula is needed for computer simulation of mill circuits. The following formula has been found to fit data from several field installations for classifiers of many types, including vibrating screens (Vaillant, AIME Tech. Pap. 67B26, 1967). 

Rajamani and Herbst (loc. cit.) compared control of an experimental pilot-mill circuit using feedback and optimal control. Feedback control resulted in oscillatory behavior. Optimal control settled rapidly to the final value, although there was more noise in the results. A more complete model should give even better results. 

The hybrid circuit in Fig. 20-26 has proven most versatile, and can increase capacity of an existing ball-mill circuit by 30 to 100 percent. Recycling the rock as in the hybrid flow sheet reduces the need for coarse-b milhng. 

Tumbling-Mill Circuits Tumbling mills may be operated in normal closed circuit, as shown in Fig. 20-45 or 20-59, or in reverse arrangement in which the feed passes through the classifier before entering the mill (see secondaiy mill in Fig. 20-44 or 20-59). 

FIG. 20-56 Ball- and rod-mill circuit. Simplified flow sheet of the Cleveland-Chffs Iron Co. Republic mine iron-ore concentrator. To convert inches to centimeters, multiply hy 2.54 to convert feet to centimeters, multiply hy 30.5. (Johnson and Bjotne, Milling in the Americas, Gordon and Breach, New York, 1964.)... 

A wet-process plant maldug cement from shale and hmestoue has been described by Bergstrom [Roc/c Prod., 64—71 (June 1967)]. There are separate facilities for grinding each type of stone. The ball mill operates in closed circuit with a battery of Dutch State Mines screens. Material passing the screens is 85 percent minus 200 mesh. The entire process is extensively instrumented and controlled by computer. Automatic devices sample crushed rock, slurries, and finished product for chemical analysis by X-rav fluorescence. Mill circuit feed rates and water additions are governed by conventional controllers. 

However, the conclusions for aquatic ecosystem health confirmed the earlier concerns that large industrial emissions exist, such as those that occur when EDTA passes through municipal water treatment plants without being degraded. It was concluded that there is a need for specific measures to limit the risks. Concern was expressed particularly about potential emissions from detergent industries, paper mills, circuit board producers, and during recovery of EDTA-containing wastes. 

On possible instability of throughputs in complex milling circuits... 

The simplest technological systems with recycling flows are shown schematically in Fig. 1. In this, the scheme (a) corresponds to a closed milling circuit, and the scheme (b) to a network of classifiers, in which, the fine product of the first classifier has the repeated classification in the second apparatus. These basic elements can be a part of more complex circuits. First let us examine the closed circuit milling system. 

Fig. 1. Technological systems with recycling flows (a) closed milling circuit (b) network of classifiers. (3-absorber of particles).

Fig. 4. Areas of stable and unstable operation of the closed milling circuit...

V.P. Zhukov, V.E. Mizonov, et al., Mathematical modelling and structural optimisation of complex milling circuits, Theor. Found. Chem. Eng. 32 (1998) 288-293 (Russian). 

Estimate the heat loss HM from the mill circuit. The equation is Hu = (pm)(power input to mill), where pM is the fractional heat loss (20 percent, or 0.2). Thus,... 

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