Unit model parameters

Ball Mill

Choose model GMIL.

residence time = 4 minutes

Selection function: Taconite

Liberation model: Ljubljana model

Note: This model has a set of pre-determined Selection and Breakage functions. It is necessary to tell Modsim that the Ljubljana model is to be used. This is because the Beta function model cannot be pre-calculated in the same fashion as the Ljubljana model, and it depends on the Breakage function parameters specified in the mill model. This is so because the Beta function model allows for preferential breakage, and the solution is constrained by the traditional breakage function and the principle of conservation of phase. If you are interested in phenomena such as differential breakage, preferential breakage, selective breakage, and the Andrews-Mika itself, read this technical paper on Mineral Liberation and the Batch Comminution Equation.

Here the particle size distribution in the mill product is calculated using the traditional PBM approach. The selection function is used to determine the probability a particle of a given size breaks (independent of its composition) and the breakage function is used to calculate the probability that a progeny reports to a given size below that of the parent particle size. The Andrews-Mika is used to determine the probability that the progeny reports to any one of the twelve grade classes that have been defined, and this of course depends on the parent composition, and how much smaller than the parent the progeny is. Here is a description of an Andrews-Mika diagram and this should help you understand the role of this important function when liberation is involved. The conception of the Ljubljana model has been published in ths technical paper on Calculation of the Liberation Spectrum in Products Produced in Continuous Milling Circuits.

 

Wet Drum Magnetic Separator

Choose model WDM2

Sharpness index = 0.9

Grade for 50% recovery = 0.1

Small size limit of short circuit = 0.466

Bypass coefficient = 56

Water Split to tail stream = 0.78

The magnetic separator is largely dependent on grade, and grade is indeed the operating variable in this separation model. Particles with as little as 10% Magnetite have a 50% probability of being recovered in the magnetics stream. Low grade particles cannot be economically ground and these are removed from the circuit.

Hydrocyclone

Choose model CYCA

Short circuit to underflow = 0.1

Sharpness index = 0.6

Cut size = 120 microns

Classification function = Logistic

Allow D50 to vary with density and specify the parameter for D50 x density as 0.8

This is a simple model for the Hydrocyclone. In the plant, it was observed that particles with high Magnetite content tend to concentrate in the Underflow. This is because D50 is smaller for havier particles, as previuosly discussed in the course.