How to account for operating condition variability when predicting liner operating life with DEM – A case study

Wear prediction is important in the development and optimisation of liner design, and for helping to manage reline strategies. DEM is able to predict wear and profile evolution of liners over the life cycle for specific sets of conditions. However, real operation conditions often vary – usually in ways that are not known in advance, which limits the ability to use such model predictions in managing associated wear. In this study, we use a specific case of a tumbling mill to explore issues around the variability of wear caused by different operating conditions within the applicable range for the mill, and consider how these can be included in a modelling framework in order to assist with mill liner management.     

A GIS-based methodology for identifying sustainability conflict areas in mine design – a case study from a surface coal mine in the USA

Through proper design, coal mining operations can contribute to the social, economic and environmental aspects of sustainable development. The regulatory and permitting programmes for coal mining in the United States, which often focus on several largely environmental parameters, are barriers to holistic consideration of these three sustainability pillars. Some changes in the current US regulatory framework may be necessary to allow for systematic consideration of economic, environmental and social factors in order to achieve more sustainable development of mineral and energy resources. In the quest towards more sustainable mining activities, it has been suggested that mine design may be optimised in the context of sustainability using a systems engineering approach that simultaneously considers economic, environmental and social factors. The use of geographic information system (GIS) tools may aid in this approach by allowing for spatial analyses of various resources (e.g. mineral values, water resources, community infrastructure) and identification of potential areas of conflict between these factors. By GIS analysis of the on-the-ground issues related to sustainability, the key parameters to be considered in decision-making were identified. This type of analysis is crucial not only for regulatory compliance, but also to ensure that the operation has obtained the ‘social licence’ to mine. To demonstrate this approach, a case study was conducted on a mountaintop coal mining operation in central Appalachia. High-conflict areas were found to be primarily concentrated near streams and residential developments through the use of GIS. The case study suggests that use of this approach could have allowed for better communications and planning. The controversies surrounding permitting at the site, including litigation, could have also been avoided. Adoption of such a process could assist in the transition to a new regulatory framework that promotes and is based on sustainable development principles.     

Use of mesh adaptivity in simulation of flow in packed beds – A case study

Computational modelling of transport phenomena in packed beds is of interest in a wide range of engineering applications. We simulate flow in packed beds with similar conditions to heap leaching processes. The governing equations are the conservation of mass and Darcy’s law. The primary variables are pressure and saturation. To discretize the governing equation, a control volume finite element method is used. The numerical scheme is implemented in Fluidity, a general purpose flow simulator that is equipped with anisotropic mesh adaptivity techniques to control local solution errors and increase computational accuracy. We demonstrate the application of the developed method to solve for incompressible flow of air and liquid within packed beds of mono-dispersed non-porous particles and compare our results with experimental measurements by Ilankoon and Neethling (2012). To study the effect of heterogeneity on flow regime in packed beds, an experiment is conducted on a packed bed consisting of two regions with different particle sizes. The non-uniform packed bed is also simulated numerically and our comparison shows very good agreement. Mesh adaptivity resolves saturation fronts in two regions of the column with high-resolution meshes and reduces the discretization error. This study serves as a validation for our numerical approach for prediction of hydrodynamics of heap leaching processes at large scales.     

Genetic algorithms for the optimisation of the Schwartz–Smith two-factor model: a case study on a copper deposit

Mining companies typically seek ways to hedge risks affecting their production. One useful instrument to mitigate the financial risk is the futures contracts on commodity prices. Information from the transactions in futures markets is publicly available and can be analysed with the Schwartz–Smith two-factor model (SSTF). However, finding the parameters governing this model can be very challenging. This step is done using a deterministic optimisation approach called the Expectation–Maximisation algorithm (EM). The starting values of the model will have a significant effect on the convergence of the EM. To ensure the solution does not get stuck in a local maximum, the EM algorithm is performed multiple times with different starting values. This paper assesses the value of genetic algorithms (GA) to optimise the parameters of the SWTF model. Although they are slower than EM algorithms because they use random number generators to search for the optimal solution, GA optimise a population of solutions instead of working on only one solution at the time. Moreover, a constraint on the range parameter can be applied to ensure the parameter has a sound economic meaning. Once the SWTF parameters have been calibrated on the observation of futures contracts, the model can be used for the simulation of spot and futures prices. To demonstrate the performance of the proposed approach, a case study was conducted on a copper deposit. The simulations based on the SWTF model whose parameters are determined by GA are used. An active management strategy of the stockpile, dependent on discrepancies in commodity futures prices is tested. Results show that the active management strategy produces positive returns over the passive investment approach.     

Forecasting time-to-failure of machine using hybrid Neuro-genetic algorithm – a case study in mining machinery

Forecasting of time-to-failure is an important aspect of a mining machine for the performance assessment, fault detection and schedule maintenance. The knowledge of failure time allows more defined arrangement of preventive maintenance. Traditional methods, including lifetime distribution models, fault tree analysis and Markov models, have a limitation of assuming a specific statistical distribution function to fit the failure time data. In this study, a hybrid data-driven method using neural network and genetic algorithm is proposed to forecast failure time. The forecasting model was developed using neural network algorithm and all the neural network parameters, i.e. input nodes, hidden nodes and the learning algorithms, are selected automatically using the genetic algorithm. The developed model was validated using the failure data of a mining machine. A case study was conducted investigating a load-haul-dump machine (LHD) in the mining industry. Failure historical data for the LHD machine were collected, and cumulative failure time was calculated for time-to-failure forecasting. Study results demonstrate that the developed model performs satisfactory in the prediction of next failure time. A comparative study reveals that the proposed method performs better than existing methods.     

New constitutive model for the study of creeping solids

In this paper, a incremental form of constitutive laws for creeping studies are proposed. The equations are based on the concept of creep hardening surface. Damage effects were introduced to the new constitutive relations to study solids creeping effects with pre-ex-isting damages. The present formula is easy to be adopted into other numerical procedures such as finite element methods.     

Understanding Gamsberg – A geometallurgical study of a large stratiform zinc deposit

The Gamsberg zinc deposit in the Northern Cape in South Africa has been the subject of a number of studies by Anglo American over the years. Two distinct ore types have been identified, namely pelitic and garnet-magnetite ore. The ore is characterised by relatively high manganese levels. Manganese reporting to the flotation concentrate is problematic for downstream refining.Anglo Research was asked by the exploration division of Anglo Base to study the relationship between the mineralogy and the floatability of the ore from reef intersections obtained from the eastern ore body. The two ore types were found to have different mineralogical characteristics resulting in different flotation responses both in terms of zinc and manganese recoveries and concentrate grades.The presence of the manganese sulphide, alabandite, was also established, and was found to be extremely detrimental to sphalerite flotation. The reasons for this were explained using the surface analysis facility at Anglo Research.     

Talvivaara mining company – From a project to a mine

The latest commercial application of bioleaching, and the first in Europe, is the Talvivaara Sotkamo Mine in North-Eastern Finland. The ore is low grade black schist, and contains pentlandite, pyrrhotite, chalcopyrite, sphalerite and pyrite as the main sulphide minerals. The ore and the possible utilization of the deposits have been extensively studied for over 20 years. Bioheapleaching technology was chosen for the extraction of nickel from the ore based on its favourable capital and operational costs and the good performance data obtained in a large on-site pilot trial. Mining was started in Sotkamo in April 2008 and building of the industrial scale bioheap in August 2008. The first shipment of nickel sulphide product was delivered to the customer in February 2009.The mining method at Talvivaara is open pit mining, after which the ore is crushed and screened, agglomerated and finally stacked on the primary heap pad. Air is supplied to the stacked ore with low pressure fans through aeration piping inside the heap. The heap is irrigated from the top with acidic leaching solution, and the solution is collected from the bottom of the heap. A 10% side flow is taken for metals recovery and the rest of the solution is recycled back to the irrigation of the heap. After approximately 13–14 months of bioleaching on the primary pad, anticipated recoveries are about 70% for nickel and 60% for zinc. The leached ore is then reclaimed and re-stacked onto the secondary heap pad. In secondary leaching the rest of nickel and zinc and part of cobalt and copper will be leached. The anticipated total recoveries after both primary and secondary leaching are 85% for nickel, 80% for zinc, and 50% for both copper and cobalt. In the metals recovery process, the metals are precipitated from the pregnant leaching solution using gaseous hydrogen sulphide. The resulting products are intermediates which are transported for further processing in refineries operated by the company’s customers.     

Natural vs. reclaimed forests – a case study of successional change,reclamation technique and phytodiversity

The present study accounts for the successional changes that took place in vegetation structure and composition over a time span of 25?years at reclaimed manganese mine site. Adjoining natural forest site was also studied for comparison of floral composition. The results corroborate the fact that as the age of succession increases, the reclaimed area gets invaded by higher successional species leading to an ecologically sound self-sustaining restructured system. This is an indication of the efficacy of the restoration programme. Plant species diversity of reclaimed site was 3.34, 2.81 and 2.12 for herbs, shrubs and trees, respectively, whereas in the adjoining natural forest site (Pench national park, reserved forest), it was 2.74, 1.88 and 2.13 for herbs, shrubs and trees, respectively. Phytodiversity assessments at both sites led to the conclusion that higher values of importance value index (IVI) were obtained for shrubs and herbs at the reclaimed site when compared to the adjoining natural forest site. However, higher values of tree diversity and IVI were associated with the natural forest site than the 25-year-old reclaimed site. This paper compares the composition of flora, species diversity and rapid succession of phytodiversity of a 25-year-old reclaimed site with nearby natural reserved forest site. Plant species richness of reclaimed site was 141, 38 and 18 for herbs, shrubs and trees, respectively, as compared to reserved forest site values of 55, 11 and 20 for herbs, shrubs and trees, respectively. Also, this paper evaluates the total and available nutrient, and microbial diversity in both the newly formed ecosystem and the adjacent natural forest site.     

How does the representation rate of features in a landscape affect visual preferences? A case study from a post-mining landscape

Previous studies of visual preferences for landscapes have been dominated by papers monitoring the presence of individual landscape features or their physical attributes. The objective of our study has been to evaluate how the representation rate of these features affects visual preferences for a landscape. We have studied a post-mining landscape that provides component physical features of a diverse and contrasting character. On the basis of an analysis of surface images, in combination with a questionnaire survey, our study has determined that the representation rate of most evaluated features affects the aesthetic value of the entire landscape scene. It has been established that certain groups of features in a post-mining landscape evoke various preferential tendencies among the public. The aesthetic value of a landscape decreased with increasing representation of surface quarries and urban structures, while increased representation of water and of rural structures resulted in an increasing aesthetic value. Woody vegetation and arable land were most preferred when they were represented non-dominantly, while mining infrastructure features were evaluated most negatively when they were non-dominant features of the landscape. Our findings thus point to the importance of the representation rate of features in the landscape as one of the key factors influencing the visual perception of the entire landscape scene.     

Promoting application—A driving force for sustainable development of rare earth industry

Rare earth industry is in another period of downturn in recent one year,which iS briefly reflected in weak demand,increasing inventories,suspended or reduced production by smelting and separation plants,production of functional material plants headed by rare earth permanent magnets under capacity,low price of rare earth minerals and rare earth raw materials,and difficult operation or operation at a loss in some plants.The harsh situation is mainly led by following reasons.Firstly, international economy remains weak and the growth rate of GDP in China slows down.Secondly,rare earth industry as a small business has been in the situation of oversupply and overproduction for years. Slight decrease in demand will have an instant impact on holistic rare earth industry.Thirdly,the negative impact of skyrocketing price rise in 2011     

Optimisation of air rate and froth depth in flotation using a CCRD factorial design – PGM case study

Air rate and froth depth are the most commonly adjusted levers in PGM flotation plants. The optimisation of these levers on each flotation cell has traditionally been done by varying either air rate at a fixed froth depth or vice versa. This approach does not consider the interaction relationship between air rate and froth depth and this effect on flotation performance.Factorial type experimental designs are best suited for investigating interaction effects between variables. This paper presents the use of a factorial type of experimental design being the (CCRD) Central Composite Rotatable Design for plant scale flotation optimisation of air and froth depth. The results obtained include three dimensional response surfaces and models of flotation response variables such as 4E PGM recovery and grade as a function of air rate and cell level. This paper illustrates the experimental methodology and discusses the results for normalised 4E PGM grade and recovery for a rougher cell treating a Platreef ore.These results indicate that interaction effects of air and froth depth are significant and are more pronounced at conditions of higher air and shallower froth depth. In addition, indices which are based on an optimisation objective such as grade multiplied by recovery and/or grade multiplied by recovery squared allows application of this technique as an optimisation tool. These indices can be used to determine an optimum operating range for air and level with the consideration of interaction effects.     

A fuzzy control system of the variable construction for the feedingcoal in the jigging process

This paper analyzes the detection means of the feeding coal in the jigging process,and puts forward a fuzzy control system of the variable construction in order to control the feeding coal. The fuzzy control system consists of three parts: bang-bang control, keep control and fuzzy control.     

A comparison of methods for measuring the induction time for bubble–particle attachment

Froth flotation is an exceedingly complex physicochemical process. The convenience of distilling much of the complexity of the particle–bubble interactions into a single parameter has led to the continuing popularity of the classical ‘induction time’ to quantify the threshold for particle–bubble attachment to occur. Despite this popularity and the simplicity of the concept, there is no single universal method of evaluating the induction period.In this paper, we begin with a critical review of the available techniques for estimating the induction period. These are: back-calculation from experimental (micro)flotation tests; pushing a particle toward a stationary bubble (or vice versa) using an atomic force microscope (AFM); pushing a bubble toward a stationary bed of particles in the ‘Induction Timer’; pushing a bubble toward a stationary solid surface using the ‘integrated thin film drainage apparatus’ (ITFDA); and dropping particles onto a submerged stationary bubble using the ‘Milli-Timer’ device. Each one of these methods has advantages and disadvantages, and the best choice depends on the application.In the experimental section, we present quantitative comparison of the induction periods estimated using two different techniques, namely the Induction Timer and the Milli-Timer. The same particles were tested in each device, under the same conditions. It was found that by tuning the operation of the particle pick-up device, similar estimates of induction period could be obtained to the estimates made by direct observation with the Milli-Timer. In the former device a bubble is driven toward a particle bed at a controlled rate, whereas in the latter a particle’s motion is governed by the hydrodynamics. The potential to match these presents an intriguing prospect for better understanding the bubble–particle interaction, and the possibility to ‘calibrate’ the simpler Induction Timer against direct observations.     

Contemporary advanced control techniques for flotation plants with mechanical flotation cells – A review

Successful control of flotation plants in modern conditions represents a challenging and complex task that has yet to be accomplished. There have been multiple attempts, however, to find an appropriate control technique that would completely cover the dynamic, complex and poorly-defined flotation system. This paper presents a literature review of current theoretical and applied researches in the field of control of flotation plants with mechanical flotation cells. Significant aspects of the stratification of control levels are described in the paper, with emphasis on advanced techniques that include predictive and intelligent control methods.Traditional PID controllers are found not suitable for the comprehensive control of dynamic flotation systems, except, in part, for the lower hierarchy levels. In the area of advanced control, model predictive methods can improve flotation process performances, but as a rule, in a short period of time. Intelligent methods are playing a significant role in flotation process control, increasing its flexibility, although none of the available variations completely satisfy all the process control aspects.Bearing in mind the results achieved so far, further improvements are expected in the areas of overall control strategy, individual control components and repositioning of advanced control methods.     

Separation of uranium and thorium from rare earths for rare earth production – A review

Rare earths play critical roles in the applications of advanced materials. Recently, the recovery of rare earths from a variety of resources has gained much interest. Radioactive elements of uranium and thorium are usually associated with rare earth deposits. The separation of uranium and thorium from rare earths is often a big concern in rare earth industry in order to reasonably manage the radioactive nuclides. This paper reviews the technologies used for separating uranium and thorium from rare earths in rare earth production, particularly in China. Some potentially applicable methods, such as precipitation and solvent extraction for the separation of uranium and thorium from rare earths in different media were also reviewed.     

Historical use and future development of chemicals for solid–liquid separation in the mineral processing industry

From their ancient beginnings to the present day, coagulants and flocculants, used to enhance solid–liquid separation by particle aggregation, are described; particular reference is given to developments in the mineral processing industry. The impact of polyacrylamide-based flocculants on technical effectiveness, disposal possibilities and environmental control, over the last 40 years, has had a profound effect on the efficiency and design of solid–liquid separation equipment. Recent developments, in terms of molecular architecture, offer new horizons for the future at a time when requirements for separating solid particles from liquid are becoming more demanding in the minerals industry.     

Biochemical and genomic facets on the dissimilatory reduction of radionuclides by microorganisms – A review

Development of environmentally sustainable technologies for remediation of radionuclides is paramount because of their long-term persistence in different ecological niches and acute toxic and teratogenic effects on human, terrestrial and aquatic life. The radionuclides U (VI), Tc (VII), Pu (VI) and Np (V) are enzymatically reduced to environmentally benign U (IV), Tc (IV), Pu (IV) and Np (IV), respectively by anaerobic microorganisms for production of energy and/or as a process of detoxification for their survival. These anaerobic microorganisms produce the oxidoreductase class of enzymes for the metabolism of radionuclides. These microorganisms have potential applications for the in situ environmentally friendly mitigation of radionuclides in subsurface environments. Appropriate knowledge on the biochemical and genetic pathways of radionuclides reduction by microorganisms will not only provide information on the fate and dynamics of these compounds in subsurface geological environments but also help to implement best management practice(s) for immobilization of these toxic compounds in waste effluents generated by the mining and nuclear industries. This review describes the phylogenetic diversity of radionuclides-reducing microorganisms present in the environment, various enzymatic systems associated with the reduction of radionuclides, and identification of genes involved in regulation of different enzymatic redox reactions.