Studies of mineral liberation performance in sulphide comminution circuits
This paper describes studies of two relatively coarse-grained sulphide ore grinding circuits (one copper and one lead/zinc), carried out to quantify the behaviour of the liberated minerals. The work formed part of a larger study whose objective is the modelling of mineral liberation for comminution circuit simulation.
The circuits were sampled and mass balances calculated. The mineralogy of the solids in each process stream was quantitatively determined using QEM*SEM, from which mass flows of liberated mineral were calculated. Samples of circuit feed were also broken in a laboratory pendulum apparatus, and the degree of liberation measured using QEM*SEM.
The plant results confirmed the strong effects of classification on liberation performance, and the differences in the behaviour of different classifier types. The effects are usually negative, as the denser liberated values tend to concentrate in the classifier underflow product, resulting in large circulating loads of liberated mineral which are reground unnecessarily, whereas the liberated gangue is preferentially selected for the downstream separation step (flotation in the case considered here). The data also demonstrated that the net liberation in secondary grinding can be quite small, and that the extent of liberation in products from the coarse (primary) grinding stage can be substantial.
The evidence in one case suggested that the proportion of liberation in a particular size interval is independent of comminution history, and that the propensity of a mineral to be liberated can be assessed using single particle breakage tests and QEM*SEM analysis.
These observations imply the need to consider aspects such as coarse flotation early in the grinding process, positive sizing devices to close the grinding circuit (eg screens rather than hydraulic classifiers), and whether conventional multiple grinding stages are always justified in practice.
KeywordsBall Mill Size Interval Liberation Process Valuable Mineral Liberation Behaviour
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