BREAKAGE PROPERTIES OF ORE BLENDS

The blending of different ore types is common practice to provide a co nsistent feed to a process either in terms of uniform assay or rock ha rdness. When several different deposits of varying grindabilities are blended prior to grinding, the hardness of the ore blend is usually es timated as the average of the component grindabilities. It is often su spected 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 meas urements 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 Magdalinovi c 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 composi tion but was weighted towards the harder component. This would indicat e that it is mainly the harder component which is comprising the circu lating load. In the Magdalinovic method, no recycle streams are employ ed and the resultant work index measurement more closely follows a lin ear relationship with blend composition. As an aid to the understandin g of the grinding mechanism and interactions taking place in the mill, analysis of the breakage properties (breakage distribution function a nd breakage rate) of each pure component and the blends were also carr ied out. Qualitative analysis of the breakage properties suggests ther e is an interaction between the components of the blend which affects their individual breakage rates. From these results, breakage properti es of the harder material appears to have a greater influence on the o verall breakage properties and the Bond Work Index of the blend than t he softer material. Attempts were made to use the measured breakage pa rameters and the batch grinding equation to simulate the Bond Work Ind ex test and hence calculate the W-i.