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By Atulya Verma, Samantha Espley, Nashel Kalaka

Numerical modelling simulations of proposed mining sequences are used to evaluate mining induced stress concentrations and their migration associated with the progress of mining. This analysis is a standard practice for most prospective mining projects at various levels of feasibility study. The studies are usually initiated at the beginning of the mining cycle, on a global scale, and are maintained and updated throughout the life of mine (LoM) to identify or address local issues and the required remedies as and when needed. Developments in numerical modeling techniques along with advancements in computing technology and data storage/management capacity have given rock engineers access to a huge volume of data that needs to be analyzed and assessed. The most common approach to numerically evaluate stress concentrations and migrations in underground mines is to select the points of interest in a given volume such as the back of an excavation or points within pillars around critical infrastructure, and plot the stresses or a derivative of stresses over time to represent life of mine concentrations and migrations of stresses. The problem with this approach is the sharp gradient of stresses close to excavation boundaries. Slight changes in the location of selected points can change the stress concentration and migration patterns substantially and all generalized statements about LoM risk can be challenged in one way or another. For global stresses, the most common current approach of data analysis is by viewing series of pictures representing stress contours. In this approach, it is easy to overlook some critical detail and/or be masked by personal preferences of contour/picture representation. To overcome the problem of representing and analyzing huge volume of stress simulation data, the authors, through their experience at different mining operations, developed a volume-based technique to reliably evaluate mining-induced stress concentrations and migrations. The volume-based approach is for risk-based assessments of adjacent regions in the rockmass, in and around planned stoping excavations. The volume of interest is the entire ore body that is planned to be mined, but it could be just a part of the ore body depending on the specific use case. The risk identifiers are the induced stresses as compared to the strength of the rockmass. Over the LoM, the risk identifiers are tracked versus the corresponding excavation ratio of the zone. This approach is very effective in identifying the stages of mining that are contributing the most to the mining induced stress risk and the results can be used for proactive planning and mitigations measures such as alternative mining sequences, or stope sizes, or extraction methods. The approach has also been very successful in application at mature mines, particularly in assessing the re-initiation of mining in zone that has been dormant for some time. The volume-based approach allows for an assessment of the current state of the rockmass and the identification of future risks when planning resumption of mining activities.

Jan 1, 2023

By Michelia Alba, Ronaldo S. Sampaio, Davi S. Braga, Mathieu Dubé

Climate change is pressuring industries and governments for decarbonization commitments, research, testing, and use of best practices to achieve the target of global warming below 1.5/2 °C. As it accounts for as much as 7% of all global CO2 emissions and 7% of energy consumption, the steel sector needs to address this issue with extended efforts. This paper provides information on the key potential of renewable biochar as an alternative fuel for pellet production. It also summarizes the successful application of biochar in a pioneering case study as the main fuel for a Grate-kiln pellet plant in Brazil, as well as the study of its use to replace coke and anthracite as an additive for iron ore pellets and other possible applications in the steel industry in COREM's precompetitive research & innovation program. The final discussion reveals the large quantity of biochar required by the Brazilian and Quebec scenarios for reducing CO2 emissions of iron ore pelletizing plants.

Jan 1, 2023

By Agbo Chima

Low-lying sections of open-pit mines accumulate water, especially during the rainy seasons, preventing access to resource-bearing areas. To sustain mining operations, the water must be lifted out of the flooded pits at a high flow rate using pumps. These pumps need to be mobile so that they can be removed during drill-and-blast operations. Most mobile pumps rely on diesel engines with high maintenance requirements. A special pump design was developed to address the unique needs of open-pit mining while making the dewatering process more sustainable. Using the target flow rate and head data, an efficient pump was designed, encased, and deployed in the open pit. A variable speed drive (VSD) was installed in a protective skid so that the pump could be tuned to match the preferred flow rate at any point during its operation. This system was tied to the national electrical grid instead of being powered by diesel pumps, which reduced the carbon intensity per kilowatt-hour. The high availability, low maintenance requirement, and greater reliability reduced the use of spare parts, the fuel consumption, and the logistics associated with operating the pump. This further reduced the carbon footprint of the dewatering process. This paper provides some of the two-year performance metrics for a deployment in West Africa. With a focus on availability, maintenance costs, average cost per volume lifted, and carbon footprint, this encased pump system is compared to the diesel-driven pumps that it aims to replace.

Jan 1, 2023

By Maxim Martel, Karolan Tremblay

Westwood Mine has experienced several episodes of increased seismic activity. While current geotechnical characterizations such as RMR, GSI, and Q' index can identify the general rock quality and zones at risk of convergence, they fail in identifying zones at risk of seismic activity. Previous research at Westwood Mine has shown a correlation between seismicity and areas with strong rheology contrasts. To characterize this contrast, 300 UCS tests were analyzed with their associated geochemical data, and statistical analysis and regression were performed using IOGAS software to establish a relationship between resistance and geochemistry. UCS-generated data with XRF results were transferred to Leapfrog Geo to create a block model of intact rock strength. This block model dataset was used to perform a competency contrast block model, and back-analysis of specific seismic sectors at Westwood Mine were conducted to validate the model. The purpose is to develop an established geomechanical tool capable in identifying areas with greater seismic risk associated to a change in the rock strength characteristics. By identifying those areas, mitigation measures can be implemented to minimize impact of seismicity on the operation.

Jan 1, 2023

By Y. Makola, M. Kilumba, S. Mwaba, P. Ilunga, F. Banze, B. Nel, P. Kyoni, N. Mautsa, R. Nkomba, G. Ilu

Kamoto Copper Company is a copper cobalt mining company established in Lualaba Province of Democratic Republic of Congo under a Joint Venture between Glencore PLC and Gecamines (the state-owned mining company). Operations consist of underground and open pit mines, a concentrator producing sulfide concentrate and oxide ores milled slurry, and a hydrometallurgy plant producing copper cathode and cobalt hydroxides from concentrate and ores. The production capacity is 300 k/a of copper cathode and 35 kt/a of cobalt hydroxide. Since Q4 2020, the Luilu hydrometallurgy plant has experienced operational instabilities due to increase in proportion of dolomite in the ore mined and fed to the plant. This was diagnosed by the significant increase in calcium grade in ore and acid consumption, continuous foaming, and overflow of tanks with subsequent adverse impact on equipment availability due to corrosion caused by acidic spills, structure integrity, and safety concerns around the acidic slurry spills. Production was adversely impact due above equipment availability and often throughput restriction to mitigate the foaming and overflows. A high gangue-acid-consuming ore management programme was developed with the aim of mitigating these impacts. The programme included: (i) use of defoamer agent in leach to stop foaming and overflow, (ii) design of a mechanical solution to leach foaming and overflow, and (iii) froth flotation for copper and cobalt minerals separation from dolomite. Only option (i) is presented in this paper. Through laboratory testwork, pilot-plant testing, plant trial, and full plant implementation, Kamoto Copper successfully implemented a defoamer agent (Kemfoam X9980) dosing at leach, resulting in significant reduction in foaming and overflow of leach reactors and countercurrent decantation thickeners. The optimum defoamer dose rate obtained was 20 mg/L. Since then, the Luilu recovered its operational stability, the corrosion of critical equipment ceased, and availability improved as the acidic leach slurry spills ceased. The constraint on throughput due to leach foaming was addressed and the frequency of sliming events in the thickeners was significantly reduced as the foaming on the supernatant surface ceased, with subsequent significant reduction in interfacial crud in solvent extraction.

Jan 1, 2023

By W. Jilowa, C. Nguni, M. Simukoko, C. Nampungwe

The upsurge in cobalt price and demand is propelled by high demand from the electronics and electric vehicle industry. Konkola Copper Mines has cobalt occurring with copper in the ratio 1:10 in ore. The ore is treated in the concentrator and recovered at the smelter as an alloy (Cu 70%, Co 4%–7%, 15% Fe). Subsequent processing of the cobalt alloy is challenging, with very few plants able to treat it, leading to marketing challenges. Konkola Copper Mines sought to improve the cobalt alloy by producing a slag that is easier to handle and process in subsequent processes. Cobalt alloy (3.60% Co, 85.4% Cu) was re-melted in a copper bath four times the mass of the alloy. Silica and lime were added for phase separation and fire refining commenced. Following completion of fire refining and after holding the temperature at 1200°C, cobalt-rich slag was skimmed and blister copper was cast into anodes for electrorefining

Jan 1, 2023

By J. Petersen, T. Moyo, J. Dinga

The leaching of chalcopyrite in ferric sulfate media is notorious for its slow and inhibited kinetics. Different methods have been proposed to improve the kinetics, including the use of organic compounds as additives to the leaching media. In this study, the enhancing effect of methanol, ethanol, 1-propanol, and 2-propanol on the leaching of chalcopyrite in aerated acid ferric sulfate solutions using different reactor systems was investigated. The results revealed a clear improvement of copper dissolution by methanol and 1-propanol relative to tests with no additives under similar conditions. Operating a continuous-flow mini-column reactor yields surprisingly good results, potentially related to the maintaining of a consistent leaching micro-environment on the mineral surface. Scanning electron microscopy studies showed that the alcohols result in the removal of surface deposits formed during the anodic dissolution, potentially thus facilitating improved cathodic reduction of the ferric ion to drive the anodic dissolution.

Jan 1, 2023

By B. Mbuya, A. F. Mulaba-Bafubianda, J. M. Mvita

The paper explains the main effects of input leaching parameters, such as addition of a reducing agent, acidity, agitation, temperature, and leaching system potential, in relation to observed and predicted yields of sought-after cobalt. An artificial neural network coupled with graphical probability networks was developed wherein the abovementioned input parameters were used to predict the percentage of dissolved cobalt. Furthermore, similarities and differences between the Bayesian and neural network approaches in terms of their key outcomes are compared with respect to study of the dissolution of cobalt in sulfuric acid. Key results indicate that there is a need to use neural network results to predict conditions for dissolution of cobalt, while using Bayesian network to explain inferences about conditions of the input parameters, thereby achieving realistic predictions.

Jan 1, 2023

By C. Dorfling, M. Tadie, S. Grobbelaar

The physicochemical properties of the complex electrolytes used in direct copper electrowinning are an important consideration for the development of a high-fidelity model of the process. Direct electrowinning electrolytes typically contain a high background of metallic impurities. The effect of metallic ions on the properties and accompanying change in the limiting-current density for copper reduction have been the subject of several studies. Although various empirical correlations have been published for describing the physicochemical properties of electrowinning electrolytes, the correlations are only applicable to a limited range of conditions and cannot be extrapolated without further validation. Consequently, in this paper we validated existing physicochemical property correlations for the full range of operating conditions applicable to direct copper electrowinning and developed a new correlation for predicting the associated limitingcurrent density for copper deposition. Following, we evaluated the benefit of using the validated correlations as a component of a dynamic electrowinning model.

Jan 1, 2023

By M. Mbonami, R. Pretorius, J. Miller, P. Kyony, B. Nel, N. Mautsa

Challenges due to the formation of stable froth in acid leach systems is common at many copper and Ccbalt producers. Stable froth affects downstream process, critical equipment, and operational parameters. In severe cases the froth present safety and environmental risks and increased operational costs. Solids reports in the pregnant leach solution, accumulates, and clogs launders resulting in a potential costly safety and environmental risk. Solvent extraction is operationally affected by crud formation, organic solvent and extractant losses, reduced mass transfer due to the solids carried downstream. This article reviews the generally inadequate mechanical and hydraulic solutions of froth elimination employed over the years. The recent introduction of a chemically based solution able to eliminate froth problems that can potentially turn around the situation for those who adopt the technology.

Jan 1, 2023

By R. B. Khumalo, F. K. Mulenga

Sampling in a continuous flotation plant is always a challenge as these plants are meant for production and not research work. The continuous flotation operation used in this work produced three sets of data: the first was based on overall plant performance, done by sampling the feed, concentrate, and tails; the second was based on the roughers row cell-by-cell; the third set of results came from the cleaners/recleaners row cell-by-cell. The highest recovery results in all sets of data obtained lie in the particle size ranges of 40 μm and 100 μm, which is in agreement with results by other researchers in the same field. King’s theoretical (model) recovery proved to be able to fit the experimental data but there is still room for improvement as the sum of squared error ranged between 400– 1200. Data obtained in continuous flotation operation could be used with batch flotation test-work to characterize scale-up of flotation cells.

Jan 1, 2023

By R. Weideman, K. du Preez

Biological sulfate reduction has become a successful treatment alternative for acid mine drainage and Mintek is developing biological processes for treatment of highsulfate mine waters. Treatment of these high-sulfate waters is achieved by sulfatereducing bacteria that reduce sulfate to produce sulfide as a product, in the form of H2S and HS− at neutral pH. This introduces the opportunity to apply treated effluents from biological treatment processes for the recovery of metals, such as copper, from metallurgical waste streams. This study models the kinetics of copper sulfide precipitation from a complex bioleach liquor. The results indicated a rapid rate of reaction and the formation of covellite, suggesting the potential to use biogenic sulfide to recover copper as a metal sulfide product.

Jan 1, 2023

By M. Wrobel, J. Hammerschmidt, M. Runkel

Fluid-bed technology is a key pyrometallurgical step for processing a vast number of ores and concentrates. Over the past 50 years, considerable research and development efforts have been made by Metso Outotec to expand the application window of this technology. This paper illustrates different processing routes where fluid-bed technology plays an important role in the production of the copper. The fluid-bed processes utilized are partial, sulfate-producing, and dead roasting. The focus of this paper considers the advantages of the dead-roasting process. This “zero waste” process can provide copper oxides, steam, electrical power, and sulfuric acid for new and existing solvent extraction–electrowinning plants. In a case where an operation is running out of oxidic ores and concentrates, fluid-bed roasting can be applied to close this gap and provide the required copper oxides in a sustainable way.

Jan 1, 2023

By L. Thomas, D. Muteba, L. I. Nsenga, B. Mbao, G. Longo Banza

Owing to the high ore grades in the African Copperbelt and variable acid consumption, agitated leaching is common practice and is used more widely in Africa than in other regions. Two common challenges for agitated leach–solvent extraction circuits are higher presence of colloidal silica in the pregnant leach solution and elevated levels of total suspended solids. Both can negatively affect the physical and metallurgical performance of the solvent-extraction circuit, and lead to higher processing costs or reduced copper production. Operating in organic continuity is preferred to address such challenges, but is not always possible: additional treatment options may be advantageous. For this reason, Solvay recently introduced ACORGA® CR60LT, a new chemical additive to address these concerns. Continuous addition to the pregnant leach solution improves physical performance without negatively affecting Cu transfer or cathode quality. Results and benefits from commercial utilization of ACORGA® CR60LT at different operations in the Copperbelt are reviewed

Jan 1, 2023

By Z. Ruetz

Portable X-ray fluorescence (pXRF) analysis has been widely adopted in the geochemical and environmental field as a cost-saving alternative to standard analyses. This paper outlines the efficacy of a method for indirectly quantifying organic copper content in solvent extraction circuits via stripping of the chelated metal with concentrated sulfuric acid in a single contact and subsequent pXRF aqueous analysis. pXRF analysis is common within the mining industry but presents unique challenges with liquid analysis, the most prevalent of which are briefly discussed. This method was developed specifically for mining operations with regional constraints and limited resources. Providing an in-field alternative to flame atomic absorption spectrophotometry and inductively coupled plasma optical emission spectroscopy, this entirely mobile XRF analysis method produces consistent and accurate results within minutes and at a fraction of the cost.

Jan 1, 2023

By H. Laitala, M. Lampi

Metso Outotec has developed a wide range of solvent-extraction technologies over decades and has introduced Metso Outotec VSF®X solvent-extraction plant. Standardized and modularized, Metso Outotec VSFX Plant provides a novel way to design, manufacture, transport, install, operate, and maintain solvent-extraction plants far better than in the past with highly sustainable and safe methods. For the customer, this means fast-track projects with savings in means of time, costs, quality, and operation. Sicomines and Metso Outotec have together implemented and commissioned a modern and efficient copper solvent-extraction plant. Plant commissioning and ramp up of the plant were fast and the plant is now operating efficiently. This paper presents Sicomines’ VSFX copper solvent-extraction project and gives a sight into operating figures for the plant.

Jan 1, 2023

By N. C. J. Dempers, J. A. L. Parker, R. A. Wildenboer

More than half of global cobalt reserves are located in the Southern African Copperbelt, stretching over the northern tip of Zambia and southern area of the Democratic Republic of Congo. In these areas, cobalt is not typically produced as a primary product but as a byproduct of copper production. Ores from this region often contain uranium, which is readily leached under typical copper leach conditions and enters the process. Uranium does not pose a challenge to copper production, but it becomes a significant problem when it follows cobalt to the cobalt precipitation process and results in unacceptably high levels of U in the final Co product. This paper evaluates the existing process technologies that can be used to remove uranium from cobalt-bearing process streams, including phosphate precipitation and ion exchange. Advantages and disadvantages of the uranium removal processes are discussed, and important design considerations are highlighted.

Jan 1, 2023

By C. Gatschlhofer, A. Krammer, H. Raupenstrauch, T. Hochsteiner, A. Holzer, L. Wiszniewski

The rising demand for lithium-ion batteries, coupled with international climate targets, emphasises the need for circular economy and zero-waste recycling approaches. However, so far, no industrial-scaled solutions are available that fulfil global recovery targets. Therefore, a novel pyrometallurgical reactor was developed at the Chair of Thermal Processing Technology at Montanuniversitaet Leoben to avoid lithium slagging and recover volatile elements via the gas phase. Nevertheless, previous results show that several impact factors, including interfering elements or pre-treatment steps, strongly limit the recycling efficiency of black mass. To simulate the black mass and provide feedback on possible influences of pre-treatment steps, cathode material from production with additives of interfering elements was analysed regarding melting behaviour. The results show that formation of a further processable alloy was increased by almost 50% when pretreatment steps were excluded, indicating pre-treatment steps as a major influence to be considered within this specific recycling route.

Jan 1, 2023

By M. Smit, N. C. J. Dempers, S. Lunkov, C. Saguru, J. Nel

A common method for the recovery of copper is by heap leaching, solvent extraction, and electrowinning. During solvent extraction, the solution is continuously recycled, and it is necessary to remove impurities that build up in the raffinate. For the process investigated in this study, the main impurities include Fe, Co, As, and Zn. Recovery of these impurities can provide economic benefits while adhering to legal and environmental constraints. Such impurities are often removed by precipitation utilizing a neutralizing agent, such as limestone or lime, but it is also possible to remove the impurities by sulfide precipitation. Sodium hydrosulfide (NaHS) is used to selectively precipitate copper, arsenic, and zinc from a solvent-extraction raffinate stream. The resulting sulfide precipitate is bagged and sent to a roaster for further treatment. The design of the sulfide precipitation was investigated to optimize the processing conditions (including temperature, pressure, and residence time), the materials of construction, and the toxicity and explosive nature of the hydrogen sulfide gas produced

Jan 1, 2023

By S. Ling, T. Liu, Y. Shang

A new copper-molybdenum flotation technology developed for a certain coppermolybdenum ore is introduced. We achieved copper-molybdenum bulk flotation in lowalkali conditions. Locked-circuit test results showed that the bulk concentrate contained 21.05% Cu and 1.10% Mo, with copper recovery of 87.37% and molybdenum recovery of 77.07%. For the copper–molybdenum separation process of the bulk concentrate, we use a new depressant, BK511, to replace the traditional sodium hydrosulfide. We achieved copper–molybdenum separation through one rougher, nine cleaner, and two scavenger processes. The results of locked-circuit tests showed that the molybdenum concentrate contained 46.19% Mo and 0.75% Cu, with molybdenum recovery of 93.80%; the copper concentrate contained 21.50% Cu and 0.069% Mo, with copper recovery of 99.92%. This new technology overcomes disadvantages of using large amounts of lime, sodium hydrosulfide, and other reagents in traditional copper–molybdenum flotation.

Jan 1, 2023