Abstract
The blending of different ore types is common practice to provide a consistent feed to a process either in terms of uniform assay or rock hardness. When several different deposits of varying grindabilities are blended prior to grinding, the hardness of the ore blend is usually estimated as the average of the component grindabilities. It is often suspected that this is not the real case. Investigations were therefore carried out to determine the variation of the Bond Work Index ( W i ) of an ore blend as a function of blend composition. Bond Work Index measurements were carried out on a sample of 100% pure hard rock ( W i = 14) and 100% soft rock ( W i = 6) and three blends of the two components. The work indices were measured by the Bond method and the Magdalinovic method. Both methods gave comparable results for the pure components but differed markedly for the blends. The work index, as measured by the Bond method, did not give a linear relationship with blend composition but was weighted towards the harder component. This would indicate that it is mainly the harder component which is comprising the circulating load. In the Magdalinovic method, no recycle streams are employed and the resultant work index measurement more closely follows a linear relationship with blend composition. As an aid to the understanding of the grinding mechanisms and interactions taking place in the mill, analysis of the breakage properties (breakage distribution function and breakage rate) of each pure component and the blends were also carried out. Qualitative analysis of the breakage properties suggests there is an interaction between the components of the blend which affects their individual breakage rates. From these results, breakage properties of the harder material appears to have a greater influence on the overall breakage properties and the Bond Work Index of the blend than the softer material. Attempts were made to use the measured breakage parameters and the batch grinding equation to simulate the Bond Work Index test and hence calculate the W i .
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