| 1. |
- Beyglou, Ali, et al.
(författare)
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Target fragmentation for efficient loading and crushing : The Aitik case
- 2017
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Ingår i: Journal of the Southern African Institute of Mining and Metallurgy. - : Southern African Institute of Mining. - 2225-6253 .- 2411-9717. ; 117:11, s. 1053-1062
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Tidskriftsartikel (refereegranskat)abstract
- Blast-induced fragmentation has a significant influence on the operational efficiency of open pit mines, especially on loading and crushing, the two immediate tasks after blasting. This study presents an empirical method to determine the target fragmentation for efficient loading and crushing at the Aitik mine in Sweden. In the study, the loading efficiency of rope shovels was correlated to the energy consumption and throughput of a gyratory crusher. Two photographic techniques were utilized to assess the feed fragmentation, considering the lithological origin of the ore as an indicator of hardness. The results indicate ore hardness is most influential in mid-range fragmentation, with a marginal effect in coarser fragmentations. The influence of fragmentation is more pronounced in the coarse region, with a sudden reduction in efficiency for P80 values coarser than 800 mm. The results suggest tailoring the fragmentation to a P80 of 600-800 mm could lead to higher operational efficiency at Aitik.
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| 2. |
- Gustafson, Anna, et al.
(författare)
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Operator influence on the loading process at LKAB's Iron ore mines
- 2020
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Ingår i: Journal of the Southern African Institute of Mining and Metallurgy. - : The Southern African Institute of Mining and Metallurgy. - 2225-6253 .- 2411-9717. ; 120:3, s. 191-202
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Tidskriftsartikel (refereegranskat)abstract
- The loading process in sublevel caving mines entails loading material from the drawpoint using load haul dump machines that transport the material to orepasses or trucks, depending on the mine conditions. When each bucket is drawn from the drawpoint, a decision must be made as to whether loading should continue or be stopped and the next ring blasted. The decision to abandon the drawpoint is irrevocable, as it is followed by the blasting of the next ring. Abandonment of the drawpoint too early leads to ore losses and inefficient use of ore resources. Loading beyond the optimal point increases dilution as well as mining costs.The experience of the LHD operators is an important basis for manual drawpoint control. However, it has been difficult to establish which specific factors manual drawpoint control is based on. To try to shed more light on these factors we analysed the operators' experiences at LKAB's Kiirunavaara and Malmberget iron ore mines. The operators in the two mines completed a questionnaire on the current loading practices and the process of deciding to abandon 'normal' rings, opening rings, and rings with loading issues.It was found that in both case study mines, most decisions on the abandonment of drawpoints are made by the operators. The more experienced operators tend to make more decisions themselves rather than rely on support from the existing support functions.
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| 3. |
- Gustafson, Anna, et al.
(författare)
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Productivity of rock reinforcement : Methodology development
- 2016
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Ingår i: Journal of the Southern African Institute of Mining and Metallurgy. - : Academy of Science of South Africa. - 2225-6253 .- 2411-9717. ; 116:12, s. 1127-1134
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Tidskriftsartikel (refereegranskat)abstract
- The working environment for ground support installation in mines has improved during the last 20-30 years, with more mechanized equipment for installation of ground support elements such as bolts, cable bolts, and screens. Ground support installation productivity has, however, not followed the same development curve, remaining more or less constant. In some cases, for example the mechanized installation of bolts, productivity has even dropped. One reason for this is that modern mechanized bolt rigs are complex. In this paper we evaluate manual and mechanized ground support systems, propose a way to measure the productivity of bolt rigs, and make relevant comparisons between different mines and equipment. Some productivity measures for rock reinforcement are suggested, using productivity results from eight case study mines
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| 4. |
- Manzoor, Sohail, et al.
(författare)
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Predicting rock fragmentation based on drill monitoring: A case study from Malmberget mine, Sweden
- 2022
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Ingår i: Journal of the Southern African Institute of Mining and Metallurgy. - : The Southern African Institute of Minning and Metallurgy. - 2225-6253 .- 2411-9717. ; 122:3, s. 155-165
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Tidskriftsartikel (refereegranskat)abstract
- Fragmentation analysis is an essential part of the optimization process in any mining operation. The costs of loading, hauling, and crushing the rock are strongly influenced by the size distribution of the blasted rock. Several direct and indirect methods are used to analyse or predict fragmentation, but none is entirely applicable to fragmentation assessment in sublevel caving mines, mainly because of the limitations imposed by the underground environment and the lack of all the required data to adequately describe the rock mass. Over the past few years, measurement while drilling (MWD) data has emerged as a potential tool to provide more information about the in-situ rock mass. This research investigated if MWD can be used to predict rock fragmentation in sublevel caving. The MWD data obtained from a sublevel caving mine in northern Sweden were used to find the relationship between rock fragmentation and the nature of the rock mass. The loading operation of the mine was filmed for more than 12 months to capture images of loaded load-haul-dump (LHD) buckets. The blasted material in those buckets was classified into four categories based on the median particle size (X50). The results showed a strongercorrelation for fine and medium fragmented material with rock type (MWD data) than coarser material. The paper presents a model for prediction of fragmentation, which concludes that it is possible to use MWD data for fragmentation predict ion.
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| 5. |
- Mwandawande, I., et al.
(författare)
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Investigation of flow regime transition in a column flotation cell using CFD
- 2019
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Ingår i: Journal of the Southern African Institute of Mining and Metallurgy. - : Academy of Science of South Africa. - 2225-6253 .- 2411-9717. ; 119:2, s. 173-186
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Tidskriftsartikel (refereegranskat)abstract
- Flotation columns are normally operated at optimal superficial gas velocities to maintain bubbly flow conditions. However, with increasing superficial gas velocity, loss of bubbly flow may occur with adverse effects on column performance. It is therefore important to identify the maximum superficial gas velocity above which loss of bubbly flow occurs. The maximum superficial gas velocity is usually obtained from a gas holdup versus superficial gas velocity plot in which the linear portion of the graph represents bubbly flow while deviation from the linear relationship indicates a change from the bubbly flow to the churn-turbulent regime. However, this method is difficult to use when the transition from bubbly flow to churn-turbulent flow is gradual, as happens in the presence of frothers. We present two alternative methods in which the flow regime in the column is distinguished by means of radial gas holdup profiles and gas holdup versus time graphs obtained from CFD simulations. Bubbly flow was characterized by saddle-shaped profiles with three distinct peaks, or saddle-shaped profiles with two near-wall peaks and a central minimum, or flat profiles with intermediate features between saddle and parabolic gas holdup profiles. The transition regime was gradual and characterized by flat to parabolic gas holdup profiles that become steeper with increasing superficial gas velocity. The churn-turbulent flow was distinguished by steep parabolic radial gas holdup profiles. Gas holdup versus time graphs were also used to define flow regimes with a constant gas holdup indicating bubbly flow, while wide gas holdup variations indicate churn-turbulent flow.
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| 6. |
- Mwandawande, I, et al.
(författare)
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Investigation of the mixing characteristics of industrial flotation columns using computational fluid dynamics
- 2022
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Ingår i: Journal of the Southern African Institute of Mining and Metallurgy. - : Academy of Science of South Africa. - 2225-6253 .- 2411-9717. ; 122:5, s. 245-257
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Tidskriftsartikel (refereegranskat)abstract
- The mixing characteristics of industrial flotation columns were investigated using computational fluid dynamics (CFD). Particular emphasis was placed on the clarification of the relationship between the liquid and solids mixing parameters such as the mean residence time and axial dispersion coefficients. The effects of particle size and bubble size on liquid dispersion in the column were also studied. An Eulerian-Eulerian method was applied to simulate the multiphase flow, while additional scalar transport equations were introduced to predict the liquid residence time distribution (RTD) and particle age distribution inside the column. The results obtained show that particle residence time decreases with increasing particle size. The residence time of the coarser particles (112.5 ??m) was found to be at least 60% of the liquid residence time, while the finer particles (19 ??m) had a residence time similar to the liquid. The results also show that an increase in the particle size of the solids results in a decrease in the liquid vessel dispersion number, while a decrease in the bubble size increases liquid axial mixing. Finally, the simulated axial velocity profiles confirm the similarity between the liquid and solids axial dispersion coefficients in column flotation.
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| 7. |
- Mwandawande, I, et al.
(författare)
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Prediction of gas holdup in a column flotation cell using computational fluid dynamics (CFD)
- 2019
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Ingår i: Journal of the Southern African Institute of Mining and Metallurgy. - : Academy of Science of South Africa. - 2225-6253 .- 2411-9717. ; 119:1, s. 81-95
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Tidskriftsartikel (refereegranskat)abstract
- Computational fluid dynamics (CFD) was applied to predict the average gas holdup and the axial gas holdup variation in a 13.5 m high cylindrical column 0.91 m diameter. The column was operating in batch mode. A Eulerian-Eulerian multiphase approach with appropriate interphase momentum exchange terms was applied to simulate the gas-liquid flow inside the column. Turbulence in the continuous phase was modelled using the k-epsilon realizable turbulence model. The predicted average gas holdup values were in good agreement with experimental data. The axial gas holdup prediction was generally good for the middle and top parts of the column, but was over-predicted for the bottom part of the column. Bubble velocity profiles were observed in which the axial velocity of the air bubbles decreased with height in the column. This may be related to the upward increase in gas holdup in the column. Simulations were also conducted to compare the gas holdup predicted with the universal, the Schiller-Naumann, and the Morsi-Alexander drag models. The gas holdup predictions for the three drag models were not significantly different.
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| 8. |
- Naghavi, H., et al.
(författare)
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The effects of froth depth and impeller speed on gas dispersion properties and metallurgical performance of an industrial self-aerated flotation machine
- 2019
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Ingår i: Journal of the Southern African Institute of Mining and Metallurgy. - : Academy of Science of South Africa. - 2225-6253 .- 2411-9717. ; 119:7, s. 661-669
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Tidskriftsartikel (refereegranskat)abstract
- In self-aerated flotation machines, the gas rate depends on operational variables (e.g. froth depth and impeller speed), pulp properties (e.g. solid content and viscosity), and reagent addition (e.g. type and concentration of frother). The gas rate has a strong correlation with the flotation performance by influencing the gas dispersion properties and froth retention time. A factorial experimental design was used to study how the gas dispersion properties, the froth retention time, and the flotation performance respond to changes in froth depth and impeller speed (as the most common operational variables). An in-depth understanding of the effects of impeller speed and froth depth on the gas dispersion properties, especially the bubble surface area flux and froth retention time, is necessary to improve operating strategies for self-aerated flotation machines. All experiments were carried out in a 50 m(3) self-aerated flotation cell in an iron ore processing plant. The results showed that the froth depth affected the metallurgical performance mostly via changing the froth retention time. The impeller speed had two important impacts on the metallurgical performance via varying both the froth retention time and the bubble surface area flux in the froth and pulp zones, respectively. The interaction effects of the froth depth and impeller speed were also established. This allowed us to develop a strategy for operating self-aerated flotation machines based on varying the froth depth and impeller speed with regard to the cell duty.
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| 9. |
- Salama, Abubakary, et al.
(författare)
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Financial analysis of the impact of increasing mining rate in underground mining, using simulation and mixed integer programming
- 2017
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Ingår i: Journal of the Southern African Institute of Mining and Metallurgy. - : Southern African Institute of Mining. - 2225-6253 .- 2411-9717. ; 117:4, s. 365-372
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Tidskriftsartikel (refereegranskat)abstract
- This paper challenges the traditional notion that mine planners need to plan production so as to incur the lowest mining cost. For a given mine configuration, a mine that increases its mining rate will incur increased mining costs. In an environment in which operations are fixated on cost reduction, a proposal that increases costs will not be readily accepted. Such a proposal requires financial justification-the increase in costs might be recuperated by the additional production. This paper evaluates the net present value (NPV) across a range of copper prices for two underground orebodies located at different depths, using a production rate of 300 kt per quarter and a scenario that introduces additional equipment and costs for 450 kt per quarter. The evaluation was based on the changes of NPV for the orebody located at a shallow depth compared with the orebody at a greater depth. Discrete event simulation combined with mixed integer programming was used for analysis. Unlike traditional sensitivity analysis, this study re-optimizes the mine plan for each commodity price at each production rate. The results show that, for the low mining rate at the final copper price, an NPV of A$ 1530.64 million is achieved, whereas an NPV of A$ 1537.59 million is achieved at a higher mining rate. Even though pushing mining rates beyond traditional limits may increase mining costs, this option may be beneficial at certain commodity prices, particularly when prices are elevated.
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| 10. |
- Shekhar, Gurmeet, et al.
(författare)
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Draw control strategies in sublevel caving mines : A baseline mapping of LKAB's Malmberget and Kiirunavaara mines
- 2018
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Ingår i: Journal of the Southern African Institute of Mining and Metallurgy. - : The Southern African Institute of Mining and Metallurgy. - 2225-6253 .- 2411-9717. ; 118:7, s. 723-733
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Tidskriftsartikel (refereegranskat)abstract
- The Malmberget and Kiirunavaara mines are the two largest underground iron ore operations in the world. Luossavaara-Kiirunavaara AB (LKAB) uses sublevel caving (SLC) to operate the mines while maintaining a high level of productivity and safety. The paper enumerates the loading criteria and loading constraints at the mines and outlines details of mine design, layout, and geology affecting the draw control. A study of the various draw control strategies used in sublevel caving operations globally has also been done to establish the present state-of-the-art. An analysis of the draw control and loading operations at the Malmberget and Kiirunavaara mines is summarized using information collected through interviews, internal documents, meetings, and manuals. An optimized draw control strategy is vital for improving ore recovery and reducing dilution in SLC. Based on the literature review and baseline mapping study, a set of guidelines for designing a new draw control strategy is presented. The draw control strategy at Malmberget and Kiirunavaara is guided by a bucket-weightbased drawpoint monitoring system that is part of the overall framework. Both mines employ a draw control strategy that considers the production requirements and mining constraints while regulating the loading process through an empirical method based on bucket weights and grades. However, in the present scenario of fluctuating metal prices and increasing operational costs a new draw control strategy is needed which is probabilistic in nature and can handle the uncertainties associated with caving operations.
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