Comminution and Classification Circuits

These equations with the operating parameters give the performance characteristics of a specific hydrocyclone design. A similar series of equations can also be used to describe the performance of gas cyclones of different, geometrically similar design. Gas and liquid cyclones are also often used for size classification in grinding circuits. 

FIGURE 4M (a) Left Measured and predicted tangential velocities in a 75-nun hydro-( lone right measured and predicted axial velocities in a 75-nun hydrocydone. (b) Predicted fluid streamlines and particle tirgectories in a 75-nim hydrocyclone. 

FIGURE 4.18 (Continued) (c) Predicted particle volume fraction for 35% weight CaCOs powder in a 75-mm hydrocyclone, (d) Experimental and predicted size selectivity curves for 35% weight CaCOg powder in a 75-mm hydrocyclone (the interactions correspond to viscosity corrections made for the particle volume fraction distribuiuBi within the hydrocyclone). From Rcgamani and Mifai [48]. 

FIGURE 4J.9 Schematic of (a) postclassification closed dicuit grinding and (b) preclas-sification closed circuit grinding. 

FIGURE 4SO Size selectivity function for sieves and classifiers. 

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Several classification functions, C(L), are given in Figure 4.20. Here, the fraction of particles by mass reporting to the recycle stream is given as a function of particle size, L, for a screen and a cyclone. Several authors have used empirical classification functions instead of dassifier performance curves with reasonable results for the overall comminution-classification circuit control. The steady state (i.e., dmidt = 0) macroscopic population balance on a discrete mass basis over the grind-... 

To use natural minerals it is necessary to grind them down to a desired particle size distribution. Grinding can be performed with the minerals dry or slurried in liquid. In most laboratories, this process is performed in a batch jar mill while on an industrial scale, continuous comminution equipment is used in conjunction with size classification equipment to recycle the coarse material. Figure 4.1 shows a typical comminution circuit with classification and recycle steps, as well as separation of the mineral from the conve3ring fluid. 

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