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By J. O. Marsden

The copper industry is cyclical with the price determined by market forces (i.e. the balance between supply and demand for the metal.) The period of each cycle typically varies between 6 to 9 years. These cycles drive decision making for exploration, new project and mine development, mine closures, process improvement, research and development, and technological innovation. The gold industry is fundamentally different from copper in that supply and demand do not, alone, determine metal price and many other factors play a key role, including global and regional financial conditions, political stability, and the global future economic outlook. However, the gold price experiences trends and longer term cycles that similarly drive business decision making. This paper examines developments in the copper industry that have occurred over the past few price cycles (approximately 20 years) and explores how the lessons learned can be applied to gold extraction. A number of specific examples and opportunities are discussed in detail, including; technology development and innovation, cost control and business improvement, material characterization, comminution equipment, biological heap leaching, and concentrate pressure leaching.

Jan 1, 2009

By A. Esterhuizen

Since 2005 Two Rivers Platinum Mine has set out on an initiative to actively monitor and control ground conditions on a daily basis, by making use of borehole cameras and pro-actively amending the support and mining strategies based on day-to-day observations of the hangingwall conditions. Today the borehole camera observations form part of the Rock Engineering Department?s daily function, and the size and frequency of falls of ground and ensuing accident rates have been drastically reduced since implementation of the system. The Two Rivers Platinum fall-of-ground management system aims to support 100% of the possible fallout thickness, based on ongoing data gathering and interpretation, thereby ensuring safety and limiting support cost.

Jan 1, 2014

By J. Rajala

The Kupol mill facility processed a high grade free milling gold/silver ore containing 28.2 g/t Au, 324.8 g/t Ag and approximately 0.5% pyrite during 2008 operation. Gold predominantly occurs a selectrum in the ore and silver is predominantly present in the forms of acanthite, stephanite, pyrargyrite and proustite. Mill start-up was in mid-May 2008 and the mill reached the design throughput of 3 000 tpd in October. The ore was ground to approximately 70%?53 microns. A Knelson Concentrator recovered 9.8% gold and 0.5% silver. The gravity tails reported to a cyanidation circuit that has 14 hours pretreatment and 116 hours leaching. The slurry from cyanidation was then processed by counter current decantation (CCD) thickening to wash and separate the leach residue from the pregnant leach solution. Precious metals are recovered fromthe pregnant solution using the Merrill-Crowe process. The washed CCD leach residue slurry is treated with calcium hypochlorite to destroy cyanide and then sent to the tailings impoundment. Leaching is performed with a new technology called ?CELP? (CANMET Enhanced Leach Process). The Kupol mill overall gold and silver recoveries for 2008 were 95.4% and 85.6% respectively, which were 2.8% and 7.5% higher than targets. Gold and silver extractions in the leach circuit were 94.2% and 84.5% respectively. Leach profiles indicated that gold extraction reached a plateau in the 4th tank while minor silver dissolution occurred in the 5th tank. With the CCD circuit included, total gold and silver extractions increased to 95.4% and 86.6%, respectively. Optimization of the leaching strategy made it possible to reduce sodium cyanide concentration to as low as 410 ppm without compromising precious metals extractions. Silver was effectively leached from the refractory silver minerals because CELP produced more oxidized mineral surface relative to the conventional cyanidation leached mineral surfaces. The average cyanide consumption for 2008 was 1.3 kg/t. The new leaching technology proved to be very robust and performed efficiently even with changes in feed grade and ore mineralogy. Laboratory experiments produced results that were indicative of plant performance. The robustness of the technology and the laboratory test work contributed to the success of the Kupol mill start-up.

Jan 1, 2009

The depletion of favourably located and higher-grade mineral deposits, combined with more favourable metal prices and higher capital costs, has stimulated research into heap leaching of lower grade ores and wastes. This has resulted in renewed interest in heap leaching of uranium ores, and in the development of processes for the bacterial heap leaching of low-grade chalcopyrite ores and the acid heap leaching of nickel laterites. A complete programme of heap leach testwork typically involves a sequence of bottle roll tests and column tests, followed by piloting on test heaps. The initial testwork is aimed at determining the amenability of the ore to heap leaching, which depends on the characteristic of the ore with respect to porosity and permeability to leach liquor, acid consumption, metal recovery and percolation. Subsequent phases of the testwork focus on the development of the process design criteria for the treatment of the ore. Basic techno-economic models have also been developed as a tool for the initial estimation of heap leach viability. Mintek has also developed in-heap monitoring probes, coupled to an operator guidance system, in order to assist the operator in achieving optimal conditions for bacterial growth and heat preservation during pilot-plant operation.

Jan 1, 2009

By F. Nakhaei, Z. Pourkarimi

Tailings produced from the iron ore industry present many challenges due to the high economic and environmental impacts involved with their disposal. However, the relative scarcity of high-grade iron ores has driven manufacturers to recover and recycle these valuable tailings (secondary sources). This study aimed at the purification of ultrafine tailings with high sulphur content from an iron ore concentrator via reverse flotation to produce pellet feed fines. A specially designed flotation column featured with a nano bubble generator and a conventional bubble generator were employed to assess the effects of nano bubbles on the desulfurisation performance of iron ore concentrate under different operating conditions. Results obtained from this study indicated that the sulphur content of iron concentrate could be reduced from 1.2% to 0.22% in the presence of nano bubbles. Also, the results showed that use of nano-micro bubbles increased sulphur recovery 20% more, in comparison to micro bubbles. Keywords: Column flotation, iron ore, tailings, slime, nano bubbles, desulphurisation

Jan 1, 2020

By M. Nicolle

The Tati Activox® Project will be the first full-scale implementation of the patented Activox® process (The Tati Activox® project was deferred in 2008. Please refer to the Norilsk Nickel press issue on the topic for more info). The process was developed by Norilsk Process Technology and has been tested on Tati mine sulphide concentrates in laboratory, pilot and demonstration plant scales and demonstrated its viability. There are inherent risks to the final scale-up of the process from the demo plant and one of them will be investigated in this paper. Compartment 1 is designed to leach approximately 77% of the total nickel leached. For this reason agitation requirements in the first compartment of the autoclave are reviewed. An attempt is made to minimize the process and mechanical risks associated in achieving oxygen mass transfer into the slurry solution. The agitator powers for oxygen mass transfer are calculated using empirical correlations and compared to demonstration plant testwork. The resulting gassed power per unit volume (P/V) is higher than most commercial autoclaves and raises uncertainty on the viability of using such high unit power inputs. Additionally, there is concern about the ability of the autoclave shell to withstand and support the higher loading of large agitators. An alternative solution to designing for the increased P/V is assessed in which the number of compartments within the autoclave is reduced from 5 to 4 by removing the compartment wall separating compartments 1 and 2. This results in an enlarged first compartment containing 3 agitators instead of 2. Therefore the compartment 1 oxygen demand is supplied through 3 agitators, which lowers the P/V per agitator. The reduction in the number of autoclave compartments raises the potential for short-circuiting the mean flow pattern by slurry particles. Short-circuiting and low velocity zones could result in a lower recovery of metal and localized hot spots, respectively. A computational fluid dynamic (CFD) analysis was conducted to quantify these concerns and also to evaluate further design considerations. The results indicate that the proposed design change to 4 compartments affects short-circuiting. The impact of increased short-circuiting on the overall autoclave recoveries is not quantified, however; it is expected to be negligible based on testwork done in the Tati Demonstration Plant and similar modifications made to another operating autoclave. The CFD analysis also suggests that there will be no low velocity zones within the compartment.

Jan 1, 2009

By M. B. C. Brandt

The near-surface wave attenuation factor k (kappa), which describes the attenuation of seismic waves with distance in the upper 1–3 km of the Earth, was determined for the Far West Rand gold mining area using seismic data recorded by station Parys (PRYS) of the South African National Seismograph Network. Twenty micro-events in the magnitude range 0.7 ? ML ? 1.8 for the period 1 July to 15 November 2015 were analysed. For the analysis a 10-second window for the S phase portion of the vertical component seismogram was selected. The result was an average k = 0.048 ± 0.014 s, which is much higher than for a stable continental region where k = 0.006 s. This is because the assumed Brune source model is inappropriate for describing mining-related events that often have moment tensors with a volumetric (implosive) component. The average k was calculated to be 0.098 ± 0.038 s for explosions of a similar magnitude. This higher value derived for mining-related k may be employed as a means of correcting the Brune source spectrum to calculate seismic moment as well as corner frequency for events in the mining areas of South Africa.

Jan 1, 2017

By D. F. Malan, J. A. L. Napier

A number of shallow coal or hard rock mines employ pillar mining systems as a strategy for roof failure control. In certain platinum mine layouts, pillars are designed to ‘crush’ in a stable manner as they become loaded in the panel back area. The correct sizing of pillars demands some knowledge of the pillar strength and the overall layout stress distribution. It is particularly important to understand the impact of the layout geometry on the effective regional ‘stiffness’ of the rock mass around each pillar. An important design strategy is to model relatively detailed layout configurations which include a precise representation of the local pillar layout geometry and to analyse multiple mining scenarios and extraction sequences to select optimal pillar sizes and barrier pillar spacing. Although computational solution techniques are now impressive in terms of run time efficiency, a major difficulty is often encountered in assigning suitable material properties to the pillars and in devising an effective material description of the layered rock strata overlying the mine excavations. This paper outlines an efficient numerical strategy that can be used to assess large-scale pillar layout performance while retaining the ability to modify individual pillar constitutive behaviour. The proposed method is applied to selected layouts to compare estimated average pillar stress values against values determined by detailed modelling and against observed behaviour.

May 3, 2023

High pressure grinding roll (HPGR) technology is used in an increasingly diverse range of applications, predominantly iron ore, gold and diamonds. KHD Humboldt Wedag HPGRs are applied world-wide, and consistently prove to be well designed and reliable operating units, with their performance meeting the pre-set standards. This publication summarizes some of the features and experiences for recent applications in treatment of copper ore, coarse iron ore, and gold ore. Summary data of roll surface wear life and operating data are given, together with operational observations. In addition, effects of feed segregation and truncated feed are discussed, as well as the implications of a product recycle flow sheet.

Jan 1, 2012

By C. Norden

The purpose of this article is to show how a representative overall equipment effectiveness (OEE) measurement can be calculated for an underground coal mining bord and pillar batch process. The calculation method, the typical losses (which include planned and unplanned availability losses, coal quality losses, and process rate losses) and the underlying logic are presented and discussed. It is argued that the current traditional underground bord and pillar mining process can currently provide a maximum theoretical OEE of only 49 per cent, while a realistic benchmark target should be in the order of 37 per cent, which relates to an average of 2400 t per shift or 1.2 Mt/a. In addition, it is argued that the current bord and pillar process is the current bottleneck to further improvement past the 2400 t per shift benchmark, and that fundamental process changes will be required to eliminate this bottleneck.

Jan 1, 2012

By T. Wallmach

Heavy mineral deposits are a source of the economic important element titanium, which is contained in minerals such as ilmenite, pseudorutile and rutile. In the Ranobe heavy minerals deposit these minerals occur not only as primary unaltered minerals but also display various degrees of alteration resulting in an increased titanium content of the deposit. The presence of the various FeTi-oxide minerals? textural relations is a reflection of geological processes and may ultimately be used to unravel the geological history of the deposit. These minerals have different chemical and physical properties that influence metallurgical tests and the quality of products produced from various mineral beneficiation streams. It is therefore of metallurgical importance that the minerals are well characterized, defined and monitored during preliminary beneficiation tests.

Jan 1, 2007

By Neal Harries

The monitoring of rock slopes is a common procedure in the management of hazards associated with slope instability. Slope stability radar has become widely accepted as the state-of-the-art method for management of hazards associated with unstable slopes in open pit mines. This is confirmed by the rapid adoption of the technology since inception in mid 2003, with over 70 GroundProbe slope stability radars now in use at open pit operations throughout the World. The use of a monitoring system such as slope radar to identify slope hazards is only part of the solution to minimise the consequences associated with slope instability. The presence of the hazard must also be effectively communicated to the mine personnel, so that the correct response to the hazard can be enacted, and the risk mitigated to an acceptable level. In some surface mines, due to the geotechnical characteristics of the rock mass, hazards can develop rapidly; with slopes progressing from stability to ultimate collapse in just hours. In these situations, it is vital that efficient systems are developed to evacuate the area of the pit affected. Such a system has been developed by GroundProbe in South Africa, with the vital driving force for the project being provided by the Anglo Platinum Mogalakwena mine operation based at Mokopane. The mine based development of the system was perceived as an essential aspect in the development of the successful system. From an early stage, the mine provided essential input on both hardware and software developments to allow the system to be rapidly integrated into the mining operation. This paper describes the pit evacuation alarm system that was developed and discussed the benefits obtained from a mine based development program.

Jan 1, 2008

By N. B. Devi

The extraction of Cu(II) from HCl media using Cyanex 923 in kerosene was investigated. The effect of shaking time, aqueous phase acid concentration, extractant concentration, chloride ion concentration, various metal ions (Mn2+, Mg2+, Fe2+, and Ni2+), and temperature on the extraction were studied. Using 0.1 M Cyanex 923 the extraction of Cu(II) was 6.7 per cent from 3 M HCl, which increased up to 78.5 per cent with 6.5 M HCl and then decreased due to acid extraction by the extractant. The maximum extraction (97.5 per cent) was obtained with 1 M Cyanex 923 from 5 M HCl solution. A mathematical model has been developed to describe solvent extraction equllibria over wide ranges of concentration of extractant, acid, and chloride ions. The composition of the extracted species has been predicted on the basis of slope analysis results and extraction equilibrium modelling. The negative values of enthalpy change and entropy change confirm the exothermic formation of the extracted complex.

Jan 1, 2012

By M. Verri

The paper describes the design options available for the simultaneous production of liquid sulphur dioxide, via cryogenic condensation, and sulphuric acid in a sulphur-burning sulphuric acid plant. The impact of the operating conditions of the cryogenic condensation on plant capital and operating costs are discussed, with the main focus on the optimization of the most important economic and operative drivers of the non-ferrous mining industry, such as energy efficiency, reliability, and availability. A case history relevant to an integrated sulphurburning plant producing liquid sulphur dioxide and sulphuric acid, recently started up in the Democratic Republic of Congo, is described. Keywords sulphur burning, sulphuric acid, liquid SO2, cryogenic SO2 condensation, liquid sulphur dioxide, sulphur dioxide.

Aug 1, 2013

By J. N. Van der Merwe

"The probability of survival of coal pillars is a more rational indicator of stability than the safety factor. Over time, pillars undergo reduction in size by progressive scaling of the sidewalls. The probability of survival is therefore not constant but reduces over time. The rate of scaling can be quantified, and the reduction of the probability of survival as a function of time can therefore also be quantified. The paper describes the link between the factor of safety, probability of survival, and reduction of the probability of survival. Using the safety factor, probability of survival, and the time at which the probability of survival will reduce to 50% is proposed as a more rational method of evaluating pillar stability than the safety factor alone.IntroductionCoal pillar strength has long been the subject of research in South Africa and several other coal-producing countries. However, it began receiving serious attention only after the Coalbrook disaster in 1960. The most important outcomes of the initial investigations were the groundbreaking research by Salamon and Munro (1967) that resulted in the well-known power formula for pillar strength, and the work by Bieniawski (1969) that resulted in a linear formula for strength. The former approach was based on empirical back-analysis of failed and stable pillar cases, and the latter on in situ strength tests on large specimens.The Salamon and Munro (1967) formula has been widely used in South Africa and even adapted for application to hard rock pillars by researchers such as Hedley and Grant (1972).At the time of the initial work by Salamon and Munro, there were only 27 failed pillar cases suitable for analysis. It was not possible at the time to determine site- or seam-specific strength, and the result was a general formula for use in all seams in all mining districts. Since that time pillars have continued to fail and the database continued to grow – as of 2013, there were 85 cases in the database. Using the additional data, there have been a number of re-evaluations of the strength formula and it has also become possible to differentiate between the different mining seams and areas."

Jan 1, 2016

By L. S. Linda, P. G. H Pistorius

Ferritic stainless steel is utilized to fabricate automotive exhaust systems using a ferritic weld metal. Ductility of the weld metal is higher if its microstructure contains a significant proportion of equiaxed grains. The formation of equiaxed (rather than columnar) grains is favoured by a higher titanium weld metal content. In this study, the Ti content of ferritic stainless steel weld metal was changed by using Tifree (Type 436) and Ti-containing (441) ferritic stainless steel as base metals. The metal-cored welding consumable contained 0.4% Ti. Gas–tungsten arc welding and gas–metal arc welding processes were compared. The weld metal Ti content ranged from zero to 0.5% Ti, as determined from scanning electron microscopy supplemented by inductively coupled plasma optical emission spectroscopy. Cross-sections of the weld beads were subjected to point counting (to estimate the fraction of equiaxed grains) and image analysis (to estimate the average grain size). Point counting proved to be more reliable. The fraction of equiaxed grains was sensitive to the Ti content, but not to the welding process. Below 0.4% Ti, the fraction of equiaxed grains gradually increased with an increase in the weld metal Ti content; above 0.4% Ti, the fraction of equiaxed grains rapidly increased with increasing Ti content. The transition in behaviour at 0.4% Ti corresponded to a Ti content at which Ti-rich precipitates became stable at the estimated liquidus temperature of the weld metal.

Jul 2, 2022

By Anders Erlandsson

"The crude ores from the LKAB mines are sorted and refined into a number of products. As there are a number of different plants the flow of material is often complex.in connection with studies of a proposed extensive investment program it was necessary to get a good measure of the changes which would be caused in the total profit by the different possible investments. A linear programming model was set up to accomplish this, and to cover the consequential effects on the production system. The objective function of the model maximized the total profit, taking into account restrictions in materials balances, blending conditions, production capacities and market. The changes in total profit resulting from the different investment alternatives, together with investment and fixed costs, were used in a series of investment analyses. The application has proved to be very successful and the results come very near to what was expected."

Jan 1, 2014

By D. F. Malan, L. Scheepers

Seismic risk in the deep gold mines of South Africa has been studied for many decades. A clear understanding of the effect of geotechnical conditions on the seismic hazard nevertheless remains elusive. Certain reef types seem to be associated with a higher risk of rockbursts. The stability and deformation behaviour of excavations on the different reef horizons are affected by the rock types and the varying strength properties. The seismic response to mining is therefore also expected to differ according to the geotechnical conditions. As a case study of this behaviour, the seismicity at Mponeng mine was investigated. On the VCR (Ventersdorp Contact Reef) horizon, two areas can be delineated. On the eastern side of the mine, the footwall is shale, and on the western side it is a strong brittle quartzite. More large-magnitude events occur in the area with the shale footwall than the area with the quartzite footwall. Moment tensor analyses indicated that the majority of the large-magnitude events are not related to geological structures, but are face-related, implying that shear failure of intact rock is occurring ahead of the mining front. Preliminary modelling indicated that the closure volume for the shale footwall may be higher than that for the quartzite footwall, providing a possible explanation for the observed difference in seismic response.

Mar 2, 2022

By L. G. Austin

The paper summarizes the current state of development of simulation models for SAG and FAG mills, and gives the results of recent investigations of the physical processes occurring in autogenous grinding. The breakage process is treated as the sum of three regions of breakage actions: normal breakage caused by nipping of particles between media (steel balls or pebbles); abnormal breakage caused by media when the particle or lump is too big in relation to the media to be readily nipped; and self-breakage resulting from the chip¬ping fracture and abrasion of the tumbling action of rock lumps. Each region of breakage action has associated specific rates of breakage and primary progeny fragment distributions. A simplified form of the model was used to predict the performance of an 8 m diameter SAG mill with L/D = 0.5 grinding a copper ore, and predicted maximum capacity and minimum kWh/ton at about 6% ball load at 25% total filling. Two FAG mills of L/D = 2 were necessary to give the same capacity, and the simulations indicated a lower kWh/ton for these mills. For this ore, both systems were technically feasible.

Jan 1, 1987

By J. Björkvall, L. Bååth, D. Malmberg, J. Malm

Microwave technology has for decades been a tool for astronomers to map and understand the complexities of the universe its composition and extent. It is also used on a laboratory scale by spectroscopists to examine properties of atomic and molecular compounds. In this novel work we will introduce microwave technology to be used for the investigation of liquid slag structures. The preliminary results indicate that the alteration of the slag composition could be correlated to the measured microwave refractive index. Investigations have been performed in the Al2O3-CaO-SiO2slag system. Keywords: Microwave technology, slag, structure, liquid, Al2O3-CaO-SiO2

Jan 1, 2004