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Since its development, the functional performance equation for ball milling (McIvor, 1988) has facilitated a new understanding of industrial circuit cause and effect relationships, leading to significant strides in operational performance. Success stories of this approach to plant circuit performance improvement are now too numerous to list. Finch and McIvor (circa 1986) also discovered that the functional performance mill grinding rate at the size of interest was the same cumulative grinding rate that is calculated from mill feed and discharge size distributions using a first-order rate equation. By calculating these cumulative grinding rates for all screen sizes, a complete ball mill model is generated (as used by Finch and Ramirez, 1981). Others in industry, Hinde and Kalala (2009), for example, have noted the same. Lacking the complexity needed to maintain their interest, most researchers have ignored this model, broadly opting instead for Epstein's (1948) characterization of grinding as a chemical reaction, combining selection rate and breakage size distribution functions. The much simpler ball mill model has previously been incorporated into a proprietary circuit modeling program (McIvor, 2005) and used for plant improvement work (for example, see McIvor and Finch, 2007, and McIvor, 2014). Now, by combining this business-friendly ball mill model with optimization criteria from functional performance analysis, a circuit modeling system (including the needed supplementary steps to assure successful plant implementation of circuit design changes) is at the disposal of every plant metallurgist, grinding equipment/ material provider and circuit designer.
The functional performance equation
The functional performance equation for closed ball milling circuits (Fig. 1) can be derived as follows (McIvor, 1988) - For any given particle reference size, calculate the production rate of new material of minus that size by the circuit by subtracting the amount (rate entering) in the circuit feed from the amount in the circuit product (cyclone overflow). This is the circuit production rate (CPR) at that size. This material is generated by the mill power applied to coarse material, i.e., larger than the reference size, therefore:
CPR (t/h) = mill power applied to coarse material (kW) x mill grinding rate of coarse material (t/kWh)
The circuit classification system efficiency (CSE) is the percentage of the mill solid material content that is coarser than the reference size. It also represents...