Effect of soft fine particles on the kinetics and energetics of grinding hard coarse particles

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2016
Yılmaz, Selim
The main objective of this study is to investigate breakage parameters of a narrow size fraction of coarse particles of a hard mineral when ground in a mixture with fine particles of a soft mineral. For this purpose, quartz and calcite were selected as mixture components varying appreciably in hardness (quartz mohs scale:7 and calcite mohs scale:3) but having quite similar densities. Mixture feeds comprised of -1.18+0.85 mm quartz (hard and coarse) and -106 µm calcite (soft and fine) at various proportions were ground dry or wet in a laboratory batch ball mill for varying times. Besides, in order to delineate the effect caused by the hardness of the fine component in the mixture, a series of similar experiments were also performed with single-mineral mixtures of the coarse and fine size fractions of quartz. Breakage parameters were obtained from the results using the linear batch grinding kinetic model. In addition, using the energy split factor the fraction of specific energy consumed by the coarse quartz when ground in mixture with either calcite fines or quartz fines was compared with that consumed when the coarse quartz fraction was ground alone. The batch grinding kinetic experiments revealed that breakage distribution is normalizable for all coarse-to-fine ratios. Moreover, it was found that the cumulative breakage distribution function of the coarse quartz fraction remains also unchanged irrespective of whether the fine component in the mixture is fine quartz or fine calcite when ground under identical mill operation conditions. The breakage rate function of the coarse fraction increases as the ratio of the fine (either soft or hard) fraction in the mixture increases. This may be attributed to two reasons: one reason is that a part of the energy applied to particles that is not able to break the finer particles is transmitted to the coarser ones, and the other reason is that larger particles are nipped more easily by the grinding media, and hence exposed to greater number of breakage events. Test results also showed that the calcite fines are less effective than the quartz fines in increasing the breakage rate of the coarse quartz particles. This may be explained by the higher amount of energy absorbed by the soft calcite fines before fracture, and hence leaving less energy available for the breakage of the coarse quartz particles. The energy split factor also supports this finding in the sense that soft fine particles consume more specific energy compared to hard fine particles when ground with hard coarse particles.

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Citation Formats
S. Yılmaz, “Effect of soft fine particles on the kinetics and energetics of grinding hard coarse particles,” M.S. - Master of Science, Middle East Technical University, 2016.