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• W2784963471 abstract "In any metallurgical plant, optimum comminution can be assured when a predictive process model is established. However, the current ore breakage characterisation practice, in addition to several other factors, is determined as one of the barriers for the development of predictive comminution models. In this project, a comprehensive review of the literature was conducted to investigate this issue. Hence, the current comminution models were discussed from the ore breakage characterisation perspective and drawbacks were identified and addressed. It was found that the existing practice does not represent the true properties of rock; what it reflects as ore hardness is a combination of ore properties and the effect of breakage environment, such as geometry, stressing velocity and etc. In other words, the characteristics of rocks and the breakage system are combined together in the outcome of a breakage test, which contradicts the original purpose of characterisation. This necessitated the understanding of the most fundamental element of breakage; the breakage of a single particle. Based on the literature, it was hypothesised that a single particle breakage test can be seen as a sequential process of several other sub-processes, referred to as primary breakage, classification, and selection. Each sub-process was determined to depend on either the properties of rock or the breakage environment or both. For instance, the “primary breakage function”, also known as the appearance function; the size distribution resulted from initial fragmentation of particles was related solely to the properties of materials. The “selection function”; referred to as the probability of particle selection was associated with the geometry of the comminution environment and other factors, such as stressing velocity. The classification function was linked to the geometry and the spatial distribution of fragments during breakage. Also, a model was developed for this process based on the three sub-processes. Each sub-process was then modelled individually. The characteristics of primary breakage were considered as the main component of the model that repeated itself in each sequence of breakage. Then, the effect of other selection and classification functions was incorporated into the model. The model was examined in its response to the three elements by conducting a sensitivity analysis that indicated promising results. Also, the model was validated for a single particle breakage characterisation approach known as drop weight testing mechanism for three types of materials, such as quartz, apatite, and silicate. In the case of quartz, the classification function was altered to reflect the brittle behaviour of quartz and the formation of wide spatial distribution which results from an extensive ejection of the fragments around the breakage environment. The results indicated a good agreement with the experiments. For the apatite particles, the selection functions were changed to reproduce the size distribution resulting from using three different geometries in the drop weight tester. In the case of silicate, a good agreement was found between the model and experiment. However, a substantial mismatch was found between the model and experiment at high energy levels and it increased as the applied energy increased. This error was related to the limitations of the model, i.e. the model does not account for the formation of a bed that occurs at high energy levels as well as the non-normalised breakage function. Also, an error propagation analysis was conducted to investigate how the error in each stage is propagated into the next levels. Later, the areas of improvement were identified. The concept of “a single breakage event as a process” was applied to study the effect of stressing velocity; a parameter that changes with the system of breakage (breakage mechanism). This means each sub-process such as primary breakage, classification and selection elements of the model were tested in their response to the stressing velocity. It was hypothesised that primary breakage characteristics such as primary breakage appearance function and associated fracture energy are not affected by the stressing velocity. An experimental procedure that involved two different mechanisms of breakage; compression and impact – the two mechanisms provide widely different stressing velocities - was developed for this purpose. The experiments were conducted on two different types of ore; magnetite and silicate. The results demonstrated that primary breakage characteristics such as appearance function and fracture energy were insensitive to the effect of stressing velocity, but sensitive to the properties of the rock. It was perceived that although the stressing velocity does not influence the primary breakage characteristics, it can possibly affect the selection and classification of the fragments in the breakage environment. Hence, the next hypothesis was set to examine this issue. Testing this hypothesis required that experimental procedure to be extended for compression and impact mechanisms beyond the first fracture characteristics. Hence, other experiments were conducted at higher levels of energy, allowing for progression of breakage post the initial fragmentation. The results indicated that applied strain rate can impact the classification of the fragments, resulting from the difference of the brittle behaviour of materials." @default.
• W2784963471 created "2018-02-02" @default.
• W2784963471 creator A5053893244 @default.
• W2784963471 date "2017-05-18" @default.
• W2784963471 modified "2023-09-28" @default.
• W2784963471 title "New approach for characterising a breakage event as a multi-stage process" @default.
• W2784963471 doi "https://doi.org/10.14264/uql.2017.537" @default.
• W2784963471 hasPublicationYear "2017" @default.
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