The winning of metals often requires fine grinding of very hard ore. The US Bureau of minesmeasured compressive strengths exceeding 100,000 PSI (700 MPa) in Minnesota taconites.Grinding down to 300 mesh (50 μ) is required for some fine-grained taconites. While other metalores may not be as strong, significant grinding costs are the rule rather than the exception. Oneauthor recently reported that a 7% drop in grinding costs would fully offset a doubling of thedrill and blast budget. Another author found that drill and blast costs were 13% of the costs ofproducing iron ore concentrate while fine crushing and grinding were over 60% of the cost ofproducing concentrate.This paper compares the cost of glass micro balloons (GMB) to grinding costs. In large diameterblasting, glass micro balloons are viewed as unnecessary and expensive. This is because theysignificantly drive up blasting costs plus critical diameter considerations do not come into play inlarge holes. However, energy expended late in the combustion process may not be conducive tothe development of microfractures necessary for efficient subsequent grinding. Reactionsoccurring at the C-J front may play a much larger role in the creation of microfractures thanthose occurring after the front had passed.Although it is a separate topic, granular aluminum has also been added to the model. AluminizedANFO has been effective product in taconite. However, several authors have cast doubt on theaddition of granular aluminum to emulsions.A simplistic model suggests that the cost of adding 1% GMB would be offset if grinding costsdropped by 1.2%. If 3% granular aluminum is also added, then powder costs would be offset ifgrinding costs dropped by 4.1%.
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