Open Collections

Improvements in comminution efficiency through high velocity impact

University of British Columbia

In order to conduct efficient physical separation of a valuable mineral from an ore, the mineral in question must be liberated (broken into finer particles). Comminution, the physical process of rock breakage, accounts for a large portion (50 to 70%) of energy costs in the mining industry. Conventional comminution uses compressive forces to initiate and propagate cracks throughout the rock mass, yet it actually breaks under tension. Converting compressive forces into tensile ones is only 1 to 2 percent efficient. Blasting rock, in contrast, shows energy efficiencies of the order of 10 to 20%. This difference exists because a larger amount of forces are applied directly in tension and because the velocity of impact (and the rate of energy input ) is orders of magnitude higher (10,000 m/s versus 10 m/s). This thesis reports on studies that build on previous work that showed high strain rates achieved through high speed impact can enhance the energy efficiency of comminution. The work examines the effects of high energy input and impact speed as separate, but interconnected, phenomena to explain from where the efficiency improvement derives. The project also takes a preliminary look at rock-on-rock breakage. Magnetite samples of varying sample weights and size distributions were impacted by a projectile at various speeds. Different materials and weights of projectile were studied. Before and after each experiment, the specific surface area of the sample was measured and the energy recovered as new surface energy was calculated. The results indicate that energy efficiency increases to about 5% (over 3 times that observed in conventional comminution) as impact speed reaches the range of 200 to 300 ms⁻¹. Above this velocity, the efficiency begins to fall off although significant comminution at higher than normal efficiency is still attained. The efficiency improvement results from both increased input energy and impact speed. Suggestions are given as to how this energy improvement could be scaled-up into a Barmac crusher. Recommendations are given for a new target chamber in the UBC CERM3 high-velocity facility in which the peak efficiency point at maximum compression might be eliminated in future testwork.

Text

2012-04-23

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/42175

Mining Engineering

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/4.0/