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By J. van der Walt, W. Spiteri

Flyrock remains a significant threat to the health and safety of mine employees and integrity of infrastructure, as well as to the safety of the neighbouring communities and their property. This investigation was motivated by the general lack of fundamental research and mathematically quantifiable data in the literature regarding the relationship between blast design parameters and their impact on flyrock. The focus was to develop a concept that can be used to mathematically quantify the trajectory of flyrock resulting from a blast, which can be used for future research. The ultimate goal for this technique, once it has been fully developed, is to: ➤ Enable mining operations to generate a database with accurate historical flyrock measurements resulting from their blasting operations ➤ Allow research teams to conduct scientific investigations into flyrock and the impact of various blast design parameters ➤ Generate point-cloud data to visualize blasts and flyrock in a virtual reality environment for training and education purposes. This paper summarizes a conceptual technique and preliminary fieldwork that was carried out to determine the technique’s feasibility and motivate further development. The results show conclusively that a modified photogrammetric technique is capable of capturing flyrock data for further processing and analysis. The data acquisition procedure can, at this point, be used to meet the first aim of the project, namely to gather a field database of historical flyrock generation. Further development of the technique is ongoing and it is envisioned that the scientific-based technique will provide a method whereby future flyrock studies will be comparable and that assumptions will be limited.

Apr 5, 2023

By C. J. Badenhorst

The primary focus of management today is safety, or preventing negative, generally irreversible, events of acute duration. The outcomes of safety-related events are usually visible and can evoke strong emotions if the results are severe. Experts now see that occupational illness and disease also result in significant emotional and financial toll to workers, their families and communities, and to their employers. Effective health and safety management must include acknowledging the importance of occupational health hazards and the proportionate application of resources to address those issues. Improvement in workplace conditions and decrease or elimination of illness and disability are due to actions within the workplace and result from the implementation of risk prevention and control measures. However, success may only be visible months or years later and may require interventions that have to be maintained over prolonged periods. This demands continuous, co-ordinated effort to ensure sustainability of diverse occupational health programmes and the relevant management systems. Too often occupational health is not seen as being part of the general management of business, but rather the function of a medical practitioner somewhere off site in a clinic. Integration of occupational health management systems with other management systems within an organization is essential for its success.

Jan 1, 2004

By D. F. Malan, J. C. Esterhuyse

"Mining in the Carletonville area of the Witwatersrand Basin predates 1934. Owing to the depletion of higher grade ore, the current activities focus increasingly on the extraction of lower grade secondary reefs as well as remnant extraction. Of particular interest is multi-reef remnant extraction. Numerical modelling was conducted to investigate some rock engineering aspects of remnants being understoped on a secondary reef horizon. An analysis of the stress evolution in the middling between two reef horizons indicated that a zone of high major and low minor principal stress develops between the two reefs. This indicates a high risk of violent shear failure. Some pillars were nevertheless successfully understoped in the past and a study was conducted to better understand this phenomenon. An ’extended’ energy release rate concept introduced by Napier and Malan (2014) proved to be useful for investigating this problem. It was found that bedding planes and lithology appears to play a role in the stable dissipation of energy in multi-reef remnant geometries. The study indicated that the stope convergence and the various energy components are affected by the presence, position, and properties of a bedding plane. The energy solutions are complex and sometimes counterintuitive. Care should be exercised when modelling specific cases. The modelling was nevertheless valuable as it indicated that energy dissipated on weak layers may reduce the risk of violent failure in a multi-reef mining scenario. Additional work is required to investigate if crushing on the reef plane plays a prominent role when mining these remnants. IntroductionTo extend the lives of the Witwatersrand gold mines, work is being conducted to include a larger number of remnants and pillars in the reserve base of the mines. According to Jager and Ryder (1999), a remnant is an unmined block of ground surrounded by extensive mining. Remnants are typically left because of adverse or difficult mining conditions caused by geological structures, poor ground conditions, low grade, or rockburst damage (Durrheim, 1997). In contrast, pillars are typically the result of rock engineering designs to control energy release rates (ERR) and seismicity. During the early 1900s, remnants formed by the practice of scattered mining layouts had a significant effect on seismicity. Numerous task teams were appointed during this period. As the industry expanded, the severity of rockbursting increased and the research was formalized after the 1960s. Various recommendations were made and many of these are still used as best practice today (e.g. Jager and Ryder, 1999)."

Dec 1, 2018

By H. Ramazi, A. Amini

"This article is devoted to the introduction of a new technique of electrical resistivity data processing called residual resistivity (RR). We define RR as measured resistivity minus background resistivity. To determine the background resistivity, the data acquired from electrical resistivity measurements along a given survey line is evaluated, and then an equation is fitted to the data corresponding to a chosen measurement station as a function of current electrode spacing (or array length). The RR technique was applied to several synthetic models to compare the conventional resistivity inversion of each model with its RR-based inversion. A case study was carried out in a karstic area in Zarrinabad, Lorestan Province, western Iran, to detect the location and geometry of probable cavities by conventional resistivity inversion and RR-based inversion. The results showed that the anomalous zones are better highlighted in the RR-based inversion images in comparison with the conventional inversion images. In some cases, anomalies detected by the RR-based images were hidden in the conventional method. IntroductionThe geoelectrical resistivity method has been widely used since the early 20th century, and plays an important role in several fields such as groundwater and subsurface mineral exploration, geotechnical and environmental investigations, and archeological studies (Bayrak and Senel, 2012; Candansayar and Basokur, 2001; Fehdi et al., 2011; Hee et al., 2010; Osella et al., 2003; Wilkinson et al., 2010). The goal of geoelectrical resistivity surveys is to determine the distribution of subsurface resistivity by measuring the current-potential difference on the ground surface (Aizebeokhai et al., 2010). In the electrical resistivity method, an electrical current is injected into the ground by two electrodes, called current electrodes (AB), and the potential difference is measured between another pair of electrodes, the potential electrodes (MN). Several methods of interpretation are available for application to electrical resistivity data, the simplest being the graphical interpretation of the apparent electrical resistivity pseudo-sections along each survey line. A second method, electrical resistivity inversion, has been developed to create relatively accurate two- and threedimensional computational resistivity models of subsurface sections (Loke and Barker, 1996; Niwas and Mehrotra, 1997; Nordiana et al., 2014; Oldenburg and Li, 1994; Papadopoulos et al., 2009; Yilmaz and Narman, 2014). In the inversion method, models of subsurface objectives are mathematically inverted to reach optimal solutions subject to prescribed objective functions, constrains, and convergence criteria. A common problem when using the electrical resistivity inversion method is that the inversion model of an electrical resistivity profile may be non-unique because different inhomogeneities in the investigation media can result in the same electrical response (Smith and Vozzof, 1984)."

Jan 1, 2016

By E. Arghavani, S. H. Amiri, S. Zare, F. Sepehri, M. Ramezanizadeh

Mineral processing plants include different stages like crushing, grinding, classification and concentration, all of which have partially affect the final product. To identify and solve the related problems of each stage, process audition should be carried out continuously to find the major solutions of improving product and decreasing the maintenance and operating costs. The Iranian Gohar-Zamin iron ore beneficiation plant consists of equipment such as gyratory and cone crushers, high pressure grinding rolls (HPGR), ball mill, dry and wet double-deck vibrating screens, hydrocyclones cluster, magnetic drum separators, thickener and horizontal vacuum belt filters. The defects of initial design as well as current non-standard operating conditions of equipment were monitored and detected and the opportunities for process optimisation were presented as follows: establishing the control loop of power draw for cone crushers, the modification of feeding chute in cone crushers to minimise the non-uniform wear of parts, removing segregation in the fresh feed bin and screen’s circulating load chute in order to provide the proper feed to HPGR, reducing wear rate on HPGR rolls surfaces, decreasing the amount of rejected materials in screen, equalising the solid content and particle size distribution (PSD) of feed in all magnetic drum separators and equalising the PSD of hydrocyclones overflow. This paper provides a guideline for the mineral processing industry to focus its efforts on process design to deliver the efficiency with minimum capital costs. Keywords: Process audition, gyratory crusher, cone crusher, HPGR, screening, hydrocyclones, magnetic drum separators

Jan 1, 2020

By A. Drumond, J. F. C. L. Costa, M. G. Lemos, A. L. Rodrigues, F. G. Niquini

The past decade has seen a renewed possibility of using machine learning algorithms to solve a large collection of problems in several fields. Data acquisition for mining operations has increased with the growth in sensor-based technologies, and therefore the amount of information available for mining applications has dramatically increased. Ore sorting equipment is available for separating ore from waste based on differences in physical properties detected by a real-time analyser. The separation efficiency depends on the contrast in these properties. In this study we investigate the application of machine learning models trained using data from the output of a dual-energy X-ray ore sorting apparatus at a gold mine. The particles were first hand-sorted into ore and gangue classes based on their mineralogical composition. Classification models were then used to help decide the balance between the number of true and false positives for ore in the concentrate, with a view to economic parameters, using their receiver operator characteristic (ROC) curves. The results showed AUC (area under the ROC curve) scores of up to 0.85 for the classification models and a maximum reward condition Fpr/Tpr around 0.5/0.9 for a simplified economic model.

Aug 8, 2024

By V. Borissenkob, L. D. Ropera, M. J. Danielc

Eccentric High Pressure Centrifugal Comminution (eHPCC) is a novel comminution device that provides a single step to achieve a desired target grind size. The mechanisms within the unit mirror particle breakage that is akin to high-pressure-grinding rolls (HPGR) and high-intensity-attrition with air classification. eHPCC receives lump and can produce a product P80 such that the progeny are at or less than natural grain size of the feed. The unit operates in either closed or open-circuit. The grinding zone is dry and free of steel grinding media. This paper presents evidence of eHPCC-2 capable of selective and preferential mineral liberation. A recent test campaign on a blend of underground quartzgold- vein ore was completed. The feed to eHPCC-2 trial was SAG mill trommel oversize (low-grade pebble rejects). eHPCC-2 operated open-circuit with air-fluidisation in the rotating-grinding-chamber, classifying particles based on terminal velocity of the air-swept product particles, displaying size and mineral composition classification taking place at the same time. There is an opportunity for future industrial research targeting eHPCC as an advanced integrated comminution and classification technology. Keywords: High pressure, high intensity, compression, attrition, comminution, classification

Jan 1, 2020

By Q. Fu, Q. Wang, L. G. Wen, M. X. Jia, J. J. Zhao, J. W. Zhou

The BGRIMM process mineralogy analyser (BPMA) is a new automated mineralogy software platform developed in China. This system consists of the BPMA software platform, controlling a combination of commercially available scanning electron microscopy (SEM) and energy dispersive Xray spectrometry (EDS). The BPMA software controls SEM and EDS through their application programming interfaces, to form an auto-SEM and EDS system that automatically acquires BSE images and X-ray spectra, respectively, and classifies minerals by spectrum-matching. After automated measurement and mineral identification, various quantitative process mineralogical data (e.g., mineral composition, mineral abundance, mineral liberation and intergrowth relationships, mineral associations, particle and grain sizes, particle density distributions, calculated assay, elemental deportments, mineral grade recovery and elemental grade recovery, etc.) would be calculated quickly, accurately and automatically. The BPMA could be used for ore characterisation as a new advanced automated mineralogy technology. Keywords: BSE image; X-ray spectrum; automated mineral identification; quantitative mineralogical investigation; automated mineralogy

Jan 1, 2020

By A. J. H. Newell, K. Doherty

A copper-gold project has required a number of trade-off studies underpinned by test work to settle on pragmatic flowsheets and throughputs to support a pre-feasibility study that provides a compelling financial case. The primary trade-off studies were based on the mine schedule, ore type feed-grade recovery relationships, likely concentrate grades and typical marketing terms as well as the estimated capital and operating costs for a range of throughputs and mining strategies. Secondary trade-off studies were conducted for specific circuits and additional processing options. Although the details of these studies are not presented, the technical options and subsequent flowsheets are discussed. While the flowsheets will be optimised during the feasibility study stage, the basis is now fixed for the four ore types that would be mined from the copper-gold orebody. The ore types, resulting from a strong weathering profile, exhibit a wide range of copper mineralisation and gold associations, as well as gangue types. They display a range of characteristics that necessitated a nuanced approach to flowsheet development. The primary separation techniques that have been employed include gravity, classification, flotation and leaching while a range of comminution methods have been selected to suit the properties of the ore types. While technical issues are important factors in terms of maximising the quality of separations, recoveries and revenues, attention to material handling, equipment characteristics, the mine schedule, and capital and operating costs are equally important considerations for settling upon a suitable and robust flowsheet. Keywords: Flowsheet, testwork, studies, saprolite gold, native copper, chalcocite, chalcopyrite

Jan 1, 2020

By J. P. Kirsch

This paper sets out to clearly identify all elements that make up an effective furnace feed system. These are outlined and the more common types of technology are listed. These technologies all play an important role in the final delivery of all feed materials to the furnace.

Jan 1, 2008

By C. G. Goncalves

The Gautrain rapid rail link project is currently Africa?s largest infrastructure project connecting South Africa?s major airport (OR Tambo), Johannesburg and Pretoria. Phase one is planned for completion in time for the 2010 FIFA Soccer World Cup and involves 80 km of track and 15 km of underground tunnels. The key shaft sinking blasting issues revolve around maximising advance and improving blasting cycles to meet the tight deadlines as well as environmental control which, in some cases takes place only 15m from the city infrastructure. To achieve success, DetNet South Africa supplied a range of electronic detonator systems to cater for the different blasting applications involved (tunnels, portals, shafts and viaduct foundations). One such product, QuickShot, was used for the first time in a major civil engineering project and has been used in most of the shaft sinking blasts to date. The QuickShot system combines pre-programmed electronic detonators with special on-bench components that enable the user to quickly and easily design the firing sequence solely by using the order of connections. This precludes the user from having to deal in absolute delay times. The connecting system enables benches to be hooked-up speedily by multiple users who have differing levels of experience. This paper provides details of how, after 33 months, the system has been embraced by the project by aiding in maximised advances, improved cycle times and meeting the required environmental constraints.

Jan 1, 2009

By C. Hartford, T. Holmes

Bulk-solids handling systems are often the most over-looked component and thereby weakest links in a processing plant’s value chain. Since their performance can dictate that of the entire operation, they actually deserve special attention. When designing a liquid handling plant, density and viscosity are well known and commonly used as design parameters. Bulk solids however, differ. While the design process is similar, the relevant parameters in handling bulk solids are instead friction, cohesive strength, compressibility, and permeability. These then vary depending on the mineralogy, particle size distribution and shape, moisture content, storage time-at-rest, temperature, and consolidation pressure. With so many variables, it becomes important to characterize each individual bulk solid across the full range of representative process conditions within the handling system, plant wide – or if you are not very lucky, suffer the consequences of poor material flow. Measuring flow properties and applying them correctly in bulk solid handling system design reduces project risk, saves significant capital, and drastically increases throughput, especially when done in the early stages of a project. Keywords: Flow Properties, Bulk Solids, Process Conditions, System Design

Jan 1, 2020

By M. Getz, G. Asbjörnsson, M. Evertsson, E. Clausen

The mining and minerals processing industry is gradually being digitalised to improve efficiency and reduce waste. One aspect of this transition is to ensure that relevant process-data in sufficient quality and quantity is given to the operator in the right format and at the right time to improve decision-making. Augmented reality (AR) can serve as a potential ICT-based support tool for human operators to achieve this goal. With AR, virtual information is combined with the real world in real-time. Therefore, AR technology has the potential to fulfil the need for improved data visualisation in Industry 4.0. This article is the result of a collaborative effort of Chalmers University of Technology and RWTH Aachen University to identify selected state-of-the-art applications of AR that are currently being applied in the mining and minerals industry or selected related industries. This paper aims to show opportunities for the application of AR in the mining and mineral processing industry with selected conceptual applications. This paper concludes with several requirements identified as necessary to implement the conceptual applications of AR in the mining and minerals industry. Keywords: Augmented reality, mining, mineral processing

Jan 1, 2020

By L. Makua, K. Langa, Ndlovu. S., C. Saguru

"Global demand for the three platinum group metals (PGMs) Pt, Pd, and Rh has been steadily growing due to their widespread use in emission control, industrial catalysis, and numerous other applications. The primary supply of PGMs is currently the mining industry. However, legislative, operational, and environmental challenges faced by many mining operations result in erratic supply patterns and deficits for these three metals. Naturally, recycling scrap material to recover Pt, Pd, and Rh has therefore aroused research interest in the scientific and engineering communities. Given that the majority of the global demand for these three metals is driven by emission control devices, autocatalytic converters are therefore a significant source of already processed and beneficiated PGMs for recycling.Although pyrometallurgical processes dominate the recycling industry, hydrometallurgical processes may offer certain advantages, chief among these being lower emissions and reduced energy consumption. In this investigation, scrap converter material was leached in acidic chloride media and the leach liquor subjected to solvent extraction and cloud point extraction (CPE) to recover the PGMs. The recoveries for Pt and Pd using Alamine 308® dissolved in kerosene with decanol as a modifier were 95% and 81%, respectively. The maximum recoveries using CPE after complexation with 2-mercaptobenzothiazole (2-MBT) in the presence of Triton X-100 and tin (II) chloride dihydrate as a reductant were 97% for Pd, 96% for Pt, and 91% for Rh. This demonstrates that CPE, although relatively new, may have some potential as a breakthrough PGM recovery technology. IntroductionPlatinum group metals (PGMs) have found a wide variety of applications in different industries due to their chemical, catalytic, and physical properties. PGMs are essential in automobile emission abatement, petroleum refining, and the pharmaceutical and electrical industries (Carabias-Martinez et al., 2000). However, the abundance of PGMs in the Earth’s crust is low and their primary sources are fast depleting (Crundwell et al., 2011).The high demand for PGMs, together with social, economic, environmental, and political aspects related to their production, has led to concerns about their future supply. This has resulted in renewed interest in recycling end-of-life material. PGM supply from recycling has doubled over the last decade, and currently contributes 22% to global supply (Johnson Matthey, 2016). This is in part due to the environmental, social, and operational challenges associated with mining of PGMs. For example, labour unrest, energy cuts, declining commodity prices, and declining ore grades have collectively made the mining landscape economically challenging (KPMG, 2015). On the other hand, the high content of PGMs in secondary sources makes their recovery from the increasing quantities of waste products important from a resource conservation viewpoint. Moreover, PGMs obtained through recycling have been demonstrated to have a 1% environmental cost from a life-cycle perspective, whereas PGMs obtained from mining contribute the remaining 99% of environmental cost (Bossi and Gediga, 2017). Sustainable resource recovery and the economic incentive of recycling have therefore been major drivers to justify investment in PGM recycling. The autocatalytic converter industry accounts for about 70% of the global consumption of these metals (Johnson Matthey, 2016) and therefore recycling spent converters has become a major source of Pt, Pd, and Rh (Figure 1)."

May 1, 2019

By L. Godfrey, Z. Nontso, F. Magweregwede, B. Maphalala, S. Khan

The aim of this paper was to establish if mineral resource scarcity is a driver for South Africa to transition to a circular economy. The project objectives were achieved by investigating economically viable, and critical or strategic minerals remaining in South Africa, as well as resource scarcity, as a driver for South Africa to transition to a circular economy. The study found that some minerals in South Africa, such as iron ore, lead, manganese, gold, and cobalt have less than 50 years of economically viable mining remaining. At least 18 minerals can be classified indicatively as critical or strategic: aggregates, bauxite, chromite, cobalt, copper, gold, graphite, iron, limestone, lithium, manganese, nickel, phosphorous, platinum group metals, rare earth elements, silver, titanium, and vanadium. The classification was based on the minerals’ economic importance, supply risk, and potential use in the development and manufacturing of emerging technologies. The findings suggest that the scarcity of mineral resources is a critical driver for the country to transition to a circular economy. Other identified drivers include socio-economic factors, climate change commitments, and business objectives. All minerals are non-renewable resources and at risk of depletion, therefore sustainable extraction and use are critical. Priority should be directed at investigating circular economy opportunities and substitutes for commodities at risk of being depleted within the next 50 years. There is an opportunity for South Africa to transition from a minerals export-based model to one that promotes local mineral beneficiation and manufacturing of end products.

Mar 5, 2025

By A. K. Raji, E. F. Orumwense, M. O. Ojumu

This research paper introduces a novel passive method for ocean mining using an electricpowered robotic subsea dredging crawler designed to operate in various subsea conditions, including unstructured and rough terrain. The electric-powered robotic subsea dredging crawler is equipped with two driving tracks and features a complex assembly of tank tread chain link, tank tread idler wheels, tank tread sprockets, bronze bushings, motor hub, motor mount, and a 12-volt direct current motor. To evaluate the performance of the electric-powered robotic subsea dredging crawler, it was compared with existing ocean hydraulic exploration crawlers, such as MK3 ROST, in terms of drive performance on an inclined ramp with five angles of inclination (0°, 15°, 20°, 25°, 30°). The experiment aimed to determine the maximum velocity, torque, and efficiency of the crawler at different angles of inclination. The collected data were analysed and plotted using Python, and the effect of the electric-powered robotic subsea dredging crawler’s weight on its driving performance was also considered. The results of this study demonstrate a quadratic relationship between driving performance and inclination angle, which can be used to optimise the electric-powered robotic subsea dredging crawler’s performance for future ocean mining robot drive applications.

Oct 2, 2025

By G. Segaetsho

"Conventional blasting rules of thumb used to develop blast designs are based on parametric ratios, with insufficient consideration of the rock mass factors that influence the achievability of final wall designs. At a hard-rock mine in Botswana, catchment berm designs were frequently unachievable, which exposed the mining operation to safety hazards such as local wallrock failure from damaged crests, frozen toes, and rolling rockfalls from higher mining levels. Increased standoff distances from the highwall reduced the manoeuvring area on the pit floor and the extraction factor that was safely achievable. Application of rock mass classification and the Blastability Index (BI) as a means to improve wall control was investigated. Zones were defined according to rock types forming the western highwall rock mass, and distinguishing rock mass classification factors were used to establish the suitable wall control designs. The approach combined rock mass classification methodologies such as the Geological Strength Index and the Rock Mass Rating, and related them to the BI and discontinuities of the rock mass to produce a design input tool that can be used to develop objective wall control designs. The designs driven by the tool inherently take into account the rock mass characteristic factors at the centre of the rock mass classification methods mentioned above, and significantly reduce the dependence on rules of thumb. It was found that this approach produces designs with explosive energy measures that are consistent with the required rock-breaking effort and the behaviour of discontinuities, while preserving perimeter walls.IntroductionBlasting is the first step in the comminution process. Various coordinated inputs contribute to its success, and in turn to the efficient execution of processes that lie downstream from the blasting step. Primary to meeting production and operational objectives of a mine, as well as the protection of human life and the mineral resource, is the achievement of highwall design specifications and competence. To this end, this study investigated the use of existing tools and knowledge for the achievement of highwall control goals at a hard-rock mine in Botswana."

Jan 1, 2018

By J. Hadjigeorgiou, G. Knox

Since their introduction in 2010, paddled energy-absorbing rockbolts have been widely used in seismically active hard rock mines. This paper provides new data and reviews previous work to quantify the performance of paddled energy-absorbing rockbolts under controlled laboratory conditions. Of significance is the realization that the typical split location in impact tests, at the centre between two paddle anchor points can at best provide an upper limit value. This inherent variability in performance under different testing configurations should be acknowledged and taken into consideration in the design of ground support in seismic conditions. This paper discusses the reduction in capacity of paddled rockbolts as a function of loading angle from a maximum value during axial tests (0° loading angle) to the lowest value during pure shear (loading angle of 90°). A significant reduction in displacement capacity is observed as the loading angle changes between axial (0°) and 40°. Beyond a 40° loading angle up to shear (90°) loading the reduction in displacement capacity is less significant. Due to the variances in the capacity observed through the variance of the testing configuration: loading mechanism, direction of loading, location / presence of a discontinuity, it must be recognized that results from laboratory-based testing are not independent of the testing configuration. This should be acknowledged when extrapolating anticipated performance in the field.

Oct 9, 2024

By R. J. Davidson, M. V. Nkosi, V. Veronsee

When activated carbon is used for the recovery of gold and silver from Witwatersrand gold-plant solutions, severe fouling of the carbon by calcium carbonate is experienced. Also, difficulty is encountered in the retention of the adsorbed silver on the carbon because it is displaced by gold. The acidification of plant pregnant solutions before they are contacted with carbon was therefore investigated as a means of overcoming these shortcomings. The results from batch laboratory experiments on the effect of pH on gold adsorption from plant solutions and from synthetic solutions of high ionic strength indicated reaction rate optima in the region of pH 5 and below pH I. The effect of pH on the equilibrium capacity constant for gold adsorption onto activated carbon was also studied, using both a plant solution and a synthetic solution of high ionic strength. In the case of the plant solution, the results suggested only a marginal change in carbon capacity for gold in the pH range 12 to 6, with significant increases in capacity at lower pH values. In the case of the synthetic solution of high ionic strength, the capacity constant was found to increase steadily as the pH was lowered from 12 to I. It was also found that the gold adsorption capacity of the carbon was significantly better for the synthetic solution. No precipitation of gold from the pregnant solution (gold content approximately 6 g/t) was noted as the pH was decreased to values as low as ,. However, about 25 per cent of the 0,6 g/t silver content was found to have precipitated when a pH value of 3,0 was attained. Further substantial precipitation of silver took place as the pH was lowered further. The investigation was extended by the passing of suitably acidified gold-plant solutions through one or more columns containing activated carbon. Preliminary results showed that the particle size of the carbon had a significant effect on the rate of gold adsorption. No displacement of adsorbed silver by gold was observed to take place at an influent pH of 5. In a typical continuous 'merry-go-round' operation involving three columns in which gold was eluted from the lead column every 48 hours, effluent values averaging 0,001 g/t gold could be consistently achieved under simulated plant-operating conditions. The results were obtained at relatively high velocities of influent solution, resulting in very little hold-up of gold in the carbon-recovery circuit. More than 99,9 per cent of the gold and more than 99,8 per cent of the silver was recovered in the adsorption circuit, while the elution data indicated an average elution recovery of 99,8 per cent of the adsorbed gold and 98,2 per cent of the adsorbed silver. Elution of the carbon was carried out at 91 QC. This involved pretreatment of the carbon with a sodium cyanide solution, followed by elution with deionized water. At a loading flowrate of 66 bed volumes per hour, the indicated take-up of metals on the carbon in the lead column was as follows; 53 k g/t gold, 6 k g/t silver, 57 k g/t copper, 14 k g/t nickel, and I k g/t zinc. Only a trace of cobalt was adsorbed. At an elution rate of 1,7 bed volumes per hour, the lead column was found to be completely stripped in under 5 hours, with concentrations of gold in the eluate reaching 6 to 7 g/l. Besides the excellent adsorption and elution results obtained when acidified pregnant solution was used, no fouling of the carbon was indicated, and the pressure drop across the three columns was considered to be well within practical limits. When compared with conventional zinc precipitation, the carbon process would appear to have considerable economic merit, with strong indications that significant savings would be possible both in capital and operating costs. Further pilot-plant experiments, preferably on a gold plant, would be required before a meaningful cost comparison could be made with the existing process.

Jan 1, 1979

By D. Odendaal, S. Bharat, R. D. Cromarty

The aim of this investigation was to determine the effect of high-temperature heat treatment on the electrical resistivity of charcoal. Samples of two different wood types (eucalyptus and black wattle) were pyrolised in a retort at a temperature of 700°C and the resulting charcoals heat-treated in an induction furnace at temperatures from 800°C to 1800°C and residence times from 60 to 120 minutes. After cooling, the resistivities of the samples were measured at room temperature using the four-point probe technique. It was found that as the heat treatment temperature increased the electrical resistivity of the charcoal decreased, approaching an asymptotic value at higher temperatures. Longer residence times decreased the resistivity, but this effect was not pronounced.

Oct 3, 2023