A study of comminution efficiency in relation to controlled blasting in mining

Blasting parameters that were controlled in this study are burden and spacing distances and charge length. Modeling of rock fragmentation during blasting has been effected utilizing the finite element program, UTAH2PC. In the model burden distance was reduced by 25% from the normal hole configuration. Contour maps of safety factor as a function of distance from two bore holes are presented for both conditions. Size distributions of the surfaces of the blasted muckpiles are also presented and show that better fragmentation results when burden and spacing distances are reduced by 25%. Low-impact-energy single-particle fracture tests, single-particle roll mill crushing and ball mill grinding were conducted on 6 x 8 mesh fractions of the rock. Specific energy requirements for crushing rock that had been blasted with 25% reduction in burden and spacing distances or with 25% increase in charge length were reduced by approximately 40% and 20% in single-particle impact test and single-particle roll mill crushing, respectively. With ball mill grinding, when the product contained greater than 50 weight percent finer than 100 microns, significant reductions in specific energy used in grinding were also effected when the burden and spacing distances were reduced by 25% and the charge length was increased by 25%. Finally, the economic benefit that can be achieved by transferring part of the energy from crushing and grinding to blasting is discussed.