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By Chad W. Brown

"A study of five commercially available solvent-extraction diluents in combination with three commercially available extractants under sub-Saharan African copper solvent-extraction conditions yielded intriguing results. A variety of physical and chemical property analyses showed that the diluents have some property differences, but overall the properties are similar and provide comparable solvent-extraction performance. Although each physical chemical property technique provides useful information, no individual test result suffices for prediction of diluent performance. Furthermore, a diluent should be evaluated within the conditions for which it is targeted to determine a true measure of performance. Overall, the diluents studied possess appropriate physicochemical properties for sub-Sahara Africa copper solvent-extraction conditions and can be utilized to achieve efficient, safe and reliable operations. INTRODUCTION Background Today, commercial SX diluents are available globally from a limited number of manufacturers. Production quality and consistency of these diluents have improved tremendously over the past 20 years. For example, diluent flash points have been increased incrementally to improve transport and handling while reducing fire hazards. In addition, properties have been successfully modified to minimize evaporative losses, ultimately reducing SX plant raw material costs. Diluent manufacturers have also focused on meeting performance requirements of SX plants, including eliminating components detrimental to SX operations, such as olefinic groups that can react with various species resulting in changing phase-disengagement properties over time, as well as ensuring that proper hydrocarbon components are present within diluent mixtures to maintain good reagent–metal complex solubility. These challenges have been met in the midst of ever-increasing stringent environmental regulations. Sub-Saharan Africa copper SX operations pose a unique set of conditions for diluents due to inherent ore compositions and the associated high reagent concentrations required for complete copper extraction. Chevron Phillips Chemical Company, LP has been manufacturing hydrocarbons and hydrocarbon-based diluents since the mid-80s, applying this experience to identify the physical properties considered crucial for proper performance in SX operations. This paper documents the findings of a study utilizing commercially available diluents in combination with extraction reagents commonly utilized in African SX operations to evaluate the relative performance of the diluents under sub-Saharan Africa copper SX conditions."

Jan 1, 2015

By R. Zivojinovic, S. Vujic, T. Tanaskovic

The problem of determining the optimum exploitation life of machinery, namely the optimum time for machinery and equipment replacement, represents a complex and highly responsible engineering task. Taking into consideration the situation prevailing at coal pit mines in Yugoslavia, the tasks of this class are very complex and difficult. To make a decision on replacement of capital equipment and machinery, such as bucket wheel excavators within the mentioned systems, understands a management task of utmost responsibility. It requires high professional and analytical knowledge as well as the reliable arguments, based on multidisciplinary professional approach. In this paper, the authors present their views on the problem of establishing the optimum exploitation life of bucket wheel excavators, offering an algorithm, based on dynamic programming, as a solution. Keywords: Bucket wheel excavators, exploitation life of machinery, optimization, operations research, theory of replacement, dynamic programming

Jan 1, 2003

By S. Sridhar, R. E. Aune, M. Hayashi

Thermophysical properties of silicate melts are strongly structure dependent. It is well known that the viscosities of slags increase with increasing the degree of polymerization of silicate anions. Even the thermodynamic properties of slags are dependent on the types of species and the population of the same in the melt. Thus, a link between the thermophysical and thermochemical properties of silicate melts is logically expected. The present paper elucidates the salient features of Darken?s excess stability approach to the Gibbs energies of solutions as applied to the viscosities of silicate melts. It is demonstrated, that the second derivatives of the viscosities of binary silicate melts with respect to composition indicate a maxima corresponding to the existence of stable compounds in these systems. The concept was successfully applied to the following systems: Al2O3-SiO2, CaO-SiO2, FeO-SiO2, MgO-SiO2and MnO-SiO2. In all the cases, the second derivative plots of viscosities with respect to composition showed peaks corresponding to the metasilicates. The second derivatives of the activation energies of viscous flow with respect to temperature has earlier been shown to reflect the formation of associates/embryos in the homogeneous silicate melts, indicating the readiness of the melt to separate a solid phase. Thermodynamic coupling of thermal diffusivities in the case of the system CaO-Al2O3-SiO2from the laser-flash measurements of these slags as a function of temperature are examined as part of the present study. Densities are estimated from integral molar enthalpies in the case of silicate systems and the results are presented. Keywords: silicate melts, viscosity; activation energy, thermal diffusivity; density

Jan 1, 2004

Leinster Nickel Operations, located in Western Australia, consists of an underground and three open pit mines in relatively adverse ground conditions. This paper reviews our ground control practices in the open pits, covering aspects of ground support, wall control and monitoring. These methods have been effective in allowing mining operations to continue beneath unstable slopes. In particular, the use of Ground probe?s slope stability radar has enabled the Harmony open pit to safely operate for months following indication of failure from traditional methods. This case study highlights the benefits of investing in appropriate slope stability monitoring systems.

Jan 1, 2006

By C. Kasatuka

Globalization creates investment opportunities for enterprises around the world. Attracting foreign investment has been a key challenge for economic growth in developing countries. Corruption, political instability, armed conflict, and other internal problems affect foreign direct investment (FDI) inflows negatively. A framework of criteria provides a basis for comparing non-commercial risk (NCR) among twenty-three mineral economies. Countries competing for foreign direct investment inflows are ranked from least to most risky. This study compares Inward FDI Performance Index (IND) with NCR ratings in developing countries and shows that risk is increasingly mitigated by means of appropriately structured insurance. Given the option for countries with similar mineral potential, investors will generally invest in the country that offers lower non-commercial risk. Keywords: foreign direct investment, non-commercial risk, developing countries.

Jan 1, 2006

Mining is an inherently risky business; from the technical, environmental, social, and economic uncertainties associated with advancing an exploration prospect to a viable project to the operating, market, and safety risks and uncertainties attached to a developed mine. Since we cannot totally escape the risk and uncertainty related to resource projects, as an industry we should improve our presentation of the upside and downside risks in the context of the project?s development path and maturity. More transparent, consistent, and balanced views of technical confidence will better inform both internal and external stakeholders about the expected risk in the project. International reporting codes set out the minimum standards, recommendations, and guidelines for public reporting of Exploration Results, Mineral Resources, and Mineral Reserves. However, the reporting code principles of transparency and materiality are largely subject to the interpretation of the competent person(s), which may introduce a degree of subjectivity in reporting, particularly the level of disclosure regarding supporting information. It is fundamental that Mineral Resources, Mineral Reserves, and study outcomes are reported so as to unambiguously present the level of inherent technical uncertainty (or confidence) in a project, while conveying a balanced view of the opportunities a project presents. Reporting needs to consider various stakeholders who may rely on this information, and present the data in the context of the changing risk profile associated with project development paths and project maturity. This paper discusses the interdependence of resource-to-reserve conversion, the consideration of various technical-economic study types, and the level of confidence conveyed to stakeholders relying on these technical reports and other company public announcements.

Jan 1, 2014

By A. Cichowicz

The objective of this work is to quantify the effect of the rock mass surrounding a stope or a tunnel on the seismic signal so that the rockburst damage on the excavation can be derived. It has been shown that the transfer function of rock mass surrounding an excavation can be modelled using a damped oscillator. The method of estimating the transfer function is extended in this paper. The parameters of a damped oscillator are estimated using inversion techniques and the transfer function is modelled as a time-varying system. The technique is tested on data acquired at three different sites in two deep gold mines. Employment of a modal model of the transfer function was suitable in two cases. Application of this technique is essential to track the time variation of the natural frequency during ground motion caused by a seismic event.

Jan 1, 1999

By A. Nel

The gold mining industry in South Africa stands to benefit much from the implementation of the self-directed work team concept. Its introduction implies flatter hierarchical structures, empowerment of the workforce and increased participation. Research indicates that half of the initiatives to implement self-directed work teams, however, fail, and it is therefore imperative for companies to be aware of the factors impacting on the effectiveness of self-directed work teams in order to focus on these early in the implementation phase. The objective of the study was to qualitatively determine these factors. Semi-structured interviews based on the phenomenological method were carried out. The sample included members of, and individuals involved with, self-directed work teams (N= 26) from a large gold mining company in South Africa. Results show that most respondents rated the availability of resources to do their work as the most important factor affecting their effectiveness.

Jan 1, 2006

By S. Dalton

The use of coal for power generation is being questioned in many developed countries, as a result of ever-tightening environmental restrictions and concerns about the potential impact of CO2emissions on climate. Coal will continue to be the fuel of choice for new power plants for many developing countries with large percentages of the world?s population, because of its relatively low cost and broad availability. Even in many of the developed countries that are under pressure, coal will continue to fuel large percentages of power due to the installed base. Using coal efficiently and in an environmentally responsible manner will be a challenge for technology and politics in this new century, with the politics played out on the world stage. Coal use will vary in the next few decades, including short-term changes such as the use of more diverse coals and the increased use of efficient ultra-supercritical boilers to longer term ?refining? of coal to produce a range of energy and chemical outputs. This paper outlines EPRI?s Global Coal Initiative aimed at needed developments and demonstrations that support the long-term vision of environmentally sound and economical coal use for power generation, and discusses some of the forces that are driving this development effort.

Jan 1, 2001

By F. T. Cawood

The definition of mineral rents has historically been somewhat unclear, but a growing understanding of the source and composition of the revenues that comprise these rents mean that they can be more easily identified and quantified. Furthermore the way in which the flow of the rents from mineral developments are captured and then distributed has been a point of contention amongst the various stakeholders. Investors, the host government, the resource owners, environmental interests, indigenous groups and land owners are identified in this paper as the principal participants in mineral development and while each is entitled to a portion of the rent, the size of their portions will differ. A competitive rent-sharing model for southern African countries has been established and indicates how the range of stakeholders could be rewarded for their contribution. Acceptance of the sharing ratios amongst the recipients is a function of their understanding of the size of the rent and their position in the hierarchy of stakeholders. At first glance investors appear to receive the largest share of the rent, but they disburse some of the rent to hidden costs, which when all is said and done, means that investors and host governments retain approximately equal shares of the mineral rent. Both the investor and government are faced with the dilemma of how to equitably distribute the rents they have captured to minority stakeholders. Government captures corporate tax, mineral royalties and a wide range of subordinate taxes, but is required to construct policies that will ensure distributional equity among the various levels of government as well as among the provinces that comprise the country. Investors will have to ensure that a portion of the rents they capture are diverted to other stakeholders namely resource owners, environmental interests, indigenous peoples groups and the landowners. This paper identifies the major recipients of rent and provides some indication of equitable distribution ratios for mineral wealth among them?a first step in ensuring that mineral development is compatible with long-term sustainable development and in the best national interests.

Jan 1, 2002

By M. J. Nicol

Mr Vegter has analysed, in some depth, the approximations made in the treatment of the kinetic data presented in the original by ourselves (ref.1) and has come to the conclusion that ?under the experimental conditions used by Adams and Nicol (1986) the steady-state assumption was inaccurate?. We are acutely aware of the fact that the experimental method adopted does not permit the attainment of a true steady-state in the elution reactor. However, this does not eliminate the attainment of a pseudo steady-state by a suitable choice of the experimental parameters with the accompanying simplification of the analysis of the data with the aim of drawing the reader?s attention to the most important objective of the paper viz. the effect of various operating parameters on the rate of elution of gold.

Jan 1, 1997

By B. Samanta

This paper investigates the performance of the neural network technique in a placer deposit situated at the Nome district in Alaska. Initially a single neural network model was constructed to estimate the gold grade. However, at a later stage, an ensemble model consisting of multiple networks was also constructed via the Adaboost algorithm. The reason behind the use of the ensemble model of the Adaboost algorithm was to examine if the ensemble model provided superior performance to the single neural network. As indicated by other studies, Adaboost did not have a better performance than a single neural network in this specific application. This may be due to the high noise inherent in the gold data used in this project. Consequently R2 values of gold prediction are also poor for both the single and multiple networks.

Jan 1, 2005

Milling circuits are known to be difficult to control. In order to address these difficulties, it was decided to develop and test a model predictive controller (MPC) for a milling circuit. A milling simulator was written using Microsoft Visual C++ and used to design and test the MPC controller. Due to the large number of tuning parameters in a controller of this type, an optimizing algorithm was written that automatically tunes the controller. Good, robust control was obtained when the controller was tuned using this algorithm. Control was further improved by combining feedback and feed forward control and by using quadratic programming in the MPC algorithm. The movement of the manipulated variables was reduced by using a novel technique that allows the controlled variable to vary within a specified region around the set point. An optimiser controller was also successfully implemented to control the circuit at its maximum throughput.

Jan 1, 2000

Open cast mining has been practiced in South Africa since the late1970s under near ideal geotechnical conditions. In the past decade, with the exhaustion of the traditional South African coal fields, geotechnical conditions have deteriorated. In addition, the nature of the open cast coal mining industry is changing from the conventional strip mining of virgin coal seams to the extraction of underground coal pillars by buffer blasted highwalls. These industry changes have resulted in the need to re-examine the manner in which geotechnical engineering is applied to highwall design. This paper proposes a geotechnical design rationale for open cast highwalls. Furthermore, the rationale takes cognizance of the various geotechnical hazards associated with conventional strip mining and pillar extraction by buffer blasted highwalls. The need to use geotechnical domain models and blasting geotechnics, as proactive tools for rock fall reduction, are also discussed.

Jan 1, 2001

By F. -Z. Ji, A. G. Irons, M. Barati, K. Coley

In order to optimize carbon injection into oxidizing slags, in terms of carbon and iron yield, we must have a detailed understanding of the kinetics of the reactions involved. The current study measures the rate of carbon oxidation during injection at steelmaking temperature by means of injections of coal into EAF slags. The compositions of analysed outgoing gas were used to calculate gas flow rate and hence the gasification rate of carbon. A fundamental equation to predict residual carbon in slags was developed. The predictions using this model at moderate injection rates are in good agreement with experimental data. The reaction rate of EAF slag with carbon is under mixed control by the slag gas and the gas carbon reactions. The relative importance of each step depends mainly on the v-ratio of slags. A relative reactivity parameter ? has been defined and it is found to be important to carbon-slag reaction kinetics and slag foaming. Key words: carbon-slag reaction, kinetics, slag foaming.

Jan 1, 2004

By H. C. de Wet

The predevelopment and preparation of a total infrastructure in a deep level mining environment, prior to the shaft system being commissioned has major advantages. This paper intends to indicate these advantages and outline an understanding of the disadvantages. These benefits can be classified in three basic groups: the financial and timing advantages, a knowledge of the ore body and the development of required technology to meet the design parameters. The required technology in many aspects was still to be developed prior to successful application. Stemming from the technological evolution are some secondary advantages which will be described in each of the groups. Safety and health considerations and some practicalities made some of the new technology redundant prior to the actual application. In each case the actual achievements and the anticipated benefits will be indicated to allow the reader to distinguish clearly between planned and actual achieved advantages.

Jan 1, 1997

By R. Altindag

Engineers and researchers need to estimate the mechanical properties of rocks from P-wave velocity. In previous studies, the researchers have investigated either the limited values or all the data belonging to sedimentary, igneous, and metamorphic rocks together in the same statistical analysis. In this study, the raw data pertaining to only sedimentary rocks was taken from previous studies and evaluated. For this purpose, a total of 97 samples of sedimentary rock types were subjected to statistical analysis. First, the relationships between P-wave velocity and physical-mechanical properties were investigated by simple regression analysis. All the data were then subjected to multi-regression analysis. Some empirical equations with high correlation coefficients were derived for rock engineers. The equations obtained from the analyses are compared with previous equations found in literature.

Jan 1, 2012

By R. J. Kendall

As we enter the new millennium, the South African mining industry has to ensure that it becomes more competitive if it is to survive in the ever more demanding global environment. Traditionally, mechanization in narrow stopes has been limited to the use of scraper winches, and numerous mechanization attempts have been restricted to pilot projects operated on an extremely limited scale (with varying degrees of success). The benefits of hydropower are well documented, and Northam Platinum has shown these benefits to be achievable on a mine-wide basis. However, the equipment originally developed for hydropower systems has followed the traditional labour-intensive approach commonly used in deep level narrow stoping operations. The problems experienced with the hydropower system are discussed and the rationale for developing alternate technologies is explored. The hydropower system has shown to be a versatile powering medium which can be harnessed for a diversity of uses. It (hydropower) enables the mining engineer to change traditional paradigms and to design an entirely new approach for optimizing the mining operation based on explosive techniques. The system developed for Northam consists of the following: ?Purpose-built stope drill rig operated off the hydropower system with special features to ensure accurate drilling patterns throughout the length of the blast hole ?Purpose-built high rate cleaning system for rapid transfer of fractured ore to the stope orepass ?Redesigned stope layout to facilitate in-stope water control and to recover fines from the run-off water ?Purpose-built drill rig for rapid establishment of reef raises and advanced strike gullies ?Purpose-built drill rig for flat end development. On both types of development end rig, emphasis is placed on ensuring accurate drilling patterns throughout the length of the hole to maximize linear advance per blast. The paper discusses the implementation of the Northam system on a large scale as well as current initiatives to further improve on the efficiencies of mining operations. It concludes by emphasizing that mechanized hydropowered stope technologies are in their infancy and thus offer unlimited scope in progressing beyond today?s paradigms to present as yet unthought of solutions for optimizing deep level ore extraction.

Jan 1, 2000

By R. G. B. Pickering

Over the last few years Lonmin Platinum and Sandvik have embarked on a unique partnership of collaboration through a systematic approach to developing equipment to mechanize and automate narrow reef platinum mining. After the initial design and manufacture of the equipment the key aspect is the integrating equipment, people and method into a mining system. Another key aspect of mechanization is the optimization of equipment utilization, and this philosophy has ensured continual evolvement of mining methods. This paper describes the trials and development that have resulted in the mining method described as Lonmin mechanized breast.

Jan 1, 2007

By L. Bircumshaw

Paper written on project work carried out in partial fulfilment of BSc (Eng) (Chemical) degree This paper details the formulation of a mathematical model for the simulation of a primary bioleach reactor, with specific reference to the leaching of pyrite. The model is based on the direct reaction mechanism, where the leaching of pyrite is said to occur via a two-step process. The process involves the formation of ferrous?iron through the chemical leaching of pyrite and subsequent bacterial oxidation of ferrous-iron back into ferric-iron. At steady state the rate of chemical leaching and bacterial oxidation are linked by the ratio of ferrous-iron to ferric-iron in solution. The extent of conversion of pyrite in the reactor system is described using the segregated flow model, with the exit age distribution of the solid phase being described by the Tanks-in-Series model. The final phase in model formulation involves the inclusion of steady state material balances on the bacteria and fluid phase components. The model is compared to pilot plant data and laboratory data for two different types of pyrite concentrates, with simulation results showing that the model is in good agreement with the data. Author key words: Bioleaching; pyrite; primary reactor; modeling; segregated-flow model; tanks-in series model.

Jan 1, 2006