Measurement of impact breakage properties of ore particles using a series of devices

Single particle impact breakage experiments provide essential data to aid in the fundamental understanding of rock fracture in comminution. Such experiments, conducted using devices such as the drop weight tester, split Hopkinson bars and more recently the rotary breakage tester, have been successfully used to characterize ore breakage properties in relation to measured fracture energies. Current theoretical understanding of impact breakage is that there are three important energy regimes to the process. Below a certain energy value, Eo, breakage will never occur for an infinite number of impacts. Second is an intermediate energy zone for which breakage occurs after a number of consecutive impacts and after a critical energy value, Ecrit, is a regime where breakage typically occurs for a single impact. This work was therefore undertaken in order to identify the energy values described for impact breakage of a chosen homogenous ore and a conventional mining gold ore. Drop weight tests on gold ore were used to calculate A and b hardness parameters using both the standard JK breakage model and the modified Shi-Kojovic model. The A x b values with the modified model gave consistently higher values than the standard model, typically increasing by 2-5%. Split Hopkinson pressure bars were used to establish the ultimate compressive stress of blue stone through single impact breakage tests and the fraction of impact energy utilized to cause particle fracture. From these tests it was noted that less than 50% of available impact energy was utilized to cause fracture, with cylindrical specimens absorbing the highest fraction of 43%. The rotary breakage tester was used to conduct incremental breakage experiments with blue stone and gold ore. The probability to breakage at the impact energies tested was found to remain relatively consistent over consecutive impacts. This showed that a model could be fitted between the cumulative probability to breakage and the number of impacts at these energy levels. The values of Eo for blue stone and gold ore were calculated to be 0.0464 and 0.00366 respectively. Ecrit for 90% probability to first impact breakage for these two ores was 0.344 and 0.281 respectively. It was found that incremental breakage was much more inefficient than single impact breakage. From tests with both split Hopkinson pressure bars and the rotary breakage tester, breakage degrees for single impacts increased rapidly with increase in breakage energy whilst the breakage degrees obtained from incremental breakage tests for similar amounts of energy expended remained low.

Grantor dc:publisher.institution

Department of Chemical Engineering

Year dc:date.issued

2007

Author dc:creator

• Bbosa, Lawrence Sidney

Advisor dc:contributor.advisor

• Mainza, Aubrey

Language dc:language.iso

eng

Handle dc:identifier.uri

http://hdl.handle.net/11427/5346

OAI identifier oai:identifier

oai:open.uct.ac.za:11427/5346