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By and M. V Roper, H. N. Engelbrecht

Quality control interventions emanate from process upsets and trends that move product quality beyond the natural variation expected in a stable process. The ability to detect upset conditions and react in an effective manner protects both resource utilisation and compliance to specifications. Product quality control on coal processing plants traditionally relies on the reference (combined sampler and laboratory) system to measure product qualities. The introduction of online analyser (OA) technology, applied in different configurations, creates a second source of measurement information for control decision making. The case study was done on the primary sample stream of the final product stream at Exxaro’s GG7 and 8 plants, part of the Grootegeluk complex. It explores the OLA system’s ability to meet the OEM performance guarantee, perform equally to the reference system without analytical delay time, and assesses the effort to achieve this performance in a by-line analyser (BLA) configuration. In the paper, a conceptual comparison of the two measurement systems is done and the theoretical and practical comparison of measurement performance is discussed. Results demonstrate that the OA outperformed the OEM’s performance guarantee and achieved similar levels of performance to the reference system without the response delay. Keywords: Online analyser (OLA), by-line analyser (BLA), coal quality measurement, measurement performance

Jan 1, 2020

By W. C. Joughin

The science of soil mechanics is 100 years old, and rock mechanics is about 80 years old. While methods of analysis and design have been developed and have evolved over time, these are relatively young sciences. The rapid increases in computing power and new technologies have enabled more sophisticated modelling and monitoring. However, there are still many aspects of soil and rock mechanics that are not well understood. Geotechnical failures, which have major consequences, still occur. These consequences may include environmental damage, major production holdups and associated loss of revenue, damage to infrastructure, and loss of life. High-consequence events, which are rare, are more difficult to anticipate and to design for, because by their nature they involve extraordinary circumstances or conditions, often geological in nature. The risks are usually mitigated by conservative designs and monitoring. Detailed geotechnical investigations help us to understand the natural variability of soil and rock masses and identify unusual or unexpected conditions. Investigating and researching major geotechnical failures is essential to enable these unusual circumstances to be anticipated. In the past, severe unanticipated events may have been treated as natural events or ‘acts of God’. However, society now has much greater expectations and it is essential to have policies and procedures in place that enable appropriate management of these rare, high-consequence risks. A good example is the Global Industry Standard on Tailings Management (GISTM), which was introduced after the catastrophic dam collapse at Vale’s Corrego de Feijao mine in Brumadinho, Brazil. The address will explain the concepts of uncertainty and variability, and how they should be taken into account in geotechnical design. The challenges facing geotechnical engineers, mine owners, and managers will be discussed. referencing a number of real case studies.

Sep 6, 2023

By S. Tshikhudo

This paper outlines an investigation into the recovery of saleable fractions of coal from ?as-arising? South Export Plant effluent streams, using Baleen microscreening technology. South Export Plant, a subdivision of BHP Billiton Energy Coal SA (BECSA) Coal Processing, is a two-module plant treating 2000 t/h. The nominally -150 µm coal is untreated and is therefore passed from classifying cyclones to the thickeners for process water recovery. The thickened underflow is pumped into a series of slurry cells for further settling and recovery of supernatant water. The marginal quality, moisture content, and handlebility of this settled material renders it unsuitable for inclusion into saleable products and it is thus stockpiled and trucked to designated pits for disposal. Over the years, stockpiling and trucking has become an overly expensive exercise. In an effort to recover some of this cost, a task team was assigned to investigate less costly options to process slurry across BECSA plants. Various technologies such as froth flotation, sieve bends, and Reflux Classifier were considered, although the results were generally not beneficial ? this could be attributed to weathered/oxidized coal. A decision was made to pursue an alternative approach by testing the suitability of the new ?Baleen Filter?. The concept is to screen out the higher-grade fraction (+50 µm) as saleable product and reject the finer fractions to the slurry ponds. The Baleen Filter was found to effectively screen at an acceptable efficiency between 94% and 99.99%, with a very sharp cut-point (d50 and Ep). The actual yields from the screening results were better than the predicted yields in terms of both mass and energy as predicted from feedstock analysis.

Jan 1, 2014

By N. Naudé, J. de Villiers, C. P. Bergmann

It is proposed that the physical and chemical composition of individual mineral particles are an appropriate basis from which to model the performance of minerals processing equipment. Such a particle-based approach enables modelling across disciplines such as comminution, classification and flotation and automatically generates the traditional mass and chemistry balances. The general approach followed is to generate full grade-recovery curves for a separator by sampling product and tailings at varying mass yields. AutoSEM characterisation of each sample provides particle data that is used to reconcile mineral deportment and liberation to the measured size and assay data. In this way, partition surfaces can be generated and modelled. In this paper, an empirical model for the performance of a gravity spiral concentrator treating fine chromite ore is proposed. The model is based on the combination of two partition surfaces and is able to accommodate both forward and reverse gravity concentration effects per size fraction. The results show that this approach is well suited to represent spiral performance for the cases evaluated. The effect of two feed particle size distributions on the performance of the Multotec SC21 and SC25 spirals is demonstrated. Simulations are run in an Excel environment, linked to Python-enabled routines for enhanced data management and calculation speed. Keywords: Spiral concentrator, gravity separation, particle-based modelling

Jan 1, 2020

By B. Larsen

The Søderberg electrode was invented about 95 years ago by the company Elektrokjemisk, later known as ELKEM. It is still the most commonly used electrode system in submerged-arc furnaces for ferroalloys, platinum smelting, and slag cleaning operations. The size of the furnaces and electrodes has increased over the years and electrode diameters up to 2000 mm are today in use. Such large electrodes can be challenging to manage, and large electrodes are also more demanding when it comes to the electrode paste used in the electrodes. Although electrode sizes and equipment around the electrodes have changed, the main principles of the Søderberg electrode processes are the same. To assists in proper understanding of the electrode processes and to optimize electrode management, Elkem has developed several mathematical tools covering various aspect of the process. Both temperatures and thermal stresses can be calculated during dynamic conditions. The paper demonstrates, with examples, how the tools are used in both education and as practical input to improved electrode performance.

Jan 1, 2012

By Mark Dangerfield

[Power-Point Presentation]

Jan 1, 2005

By А. V. Aksenov, S. G. Rybkin, А. Y. Senchenko

For gold plants in Russia, it is very complicated and costly to use cyanide leaching for efficient processing of gold refractory ores, where gold is closely associated with sulphide minerals and the significant amount of natural carbonaceous matter present. Oxidative roasting of gold refractory concentrates is a well-known method, making it possible to obtain a high recovery rate of precious metals to a target product. The use of oxidative roasting is limited in general by the expense of capturing and neutralising the harmful components of roasted gas, mainly sulphur (SO2, SO3) and arsenic (As2O3) oxides. This paper addresses testing and development of an optimised technology to process gold refractory gravity and flotation concentrates by means of oxidative roasting which stabilises arsenic as calcium arsenate. The process involves roasting of a gravity or flotation refractory ore concentrate in a mixture with lime and calcium chloride, with a supply of oxygen, and at 600-700°С. During the roasting a carbonaceous matter of the concentrate burns out and sulphide components transform into harmless calcium sulphate (CaSO4) and calcium arsenate (Ca3(AsO4)2), and iron passes into the form of hematite (Fe2O3). After disintegration, the roasting cinder is concentrated on a table to obtain a high-grade gravity concentrate and gravity tailings. The high-grade gravity concentrate is subject to smelting in a mixture with fluxing agents, which results in alloyed gold and slag. The gravity tailings are ground and reported to cyanide leaching. In the case of a flotation concentrate, the roast cinder is ground to minus 30 μm and subject to sorption cyanide leaching. High gold recovery (90-95%) of the target product and environmental safety are typical of the improved technology under consideration. Two national patents were granted for the methods developed to treat refractory concentrates bearing precious metals. Keywords: Gold concentrates, oxidative roasting, cinder, cyanide leaching, smelting, alloyed gold

Jan 1, 2020

By M. Bryson, G. Marap, M. Ntlhane, M. D. Hlahane

This study investigated flotation of phosphate from a low-medium grade 8-12% P2O5, 65-73% SiO2 sedimentary phosphate ore from Kropz Elandsfontein (herein referred to as Elandsfontein) in South Africa. Quantitative evaluation of minerals by scanning electron microscopy (QEMSCAN) was used to determine apatite grain size distribution, liberation and mineral association in the F2 horizon sample. The mineralogy indicated that apatite was liberated and for the Elandsfontein plant to operate at the design throughput, the flotation feed has to be milled to a coarse grind ranging between 300 μm and 425 μm. Reverse flotation process routes using varying reagent dosages, and flotation feed top sizes that could possibly yield a final product of 31% P2O5,10% SiO2 at a reasonable +70% P2O5 recovery were investigated. Based on the results, a split circuit of coarse (-300+212μm) flotation and fine (-212+20μm) flotation, was mostly preferred as compared to treating the whole ore. A final combined concentrate of 31% P2O5 and 10% SiO2 with P2O5 recovery of 84% could be produced from the reverse split circuit. The robustness of reverse flotation for both coarse and fine fractions was further investigated. Reverse flotation of the fines fraction was found to be robust and produced a final product of 31% P2O5. It was however more challenging to achieve the required product grade and recoveries on the coarser fraction (-425+212μm), suggesting that reverse circuit was not adequately robust at fractions coarser than 300μm. Keywords: Phosphate, sedimentary, reverse flotation, particle size

Jan 1, 2020

By B. Amankwaa-Kyeremeh, W. Skinner, R. K. Asamoah, C. Greet

With the continuous increase in ore mineralogical complexity coupled with decreasing head grades, there is a need for mining industries to process large tonnages of material to meet global metal demands. Smarter, cheaper techniques are required to better map ore mineralogical variations proceeding to pre-concentration (flotation) stages for higher performance and metal recoveries. This paper is aimed at briefly reviewing previous studies on different selected ore mineralogy, with the focus on their pulp chemistry, to identify relationships which aid quicker flotation feed variation monitoring. Very little published work exists linking pulp chemistry parameters to flotation feed mineralogical variation. A successful application implies maximising grades at higher metal recoveries and reducing the cost of reagent for a better performing flotation circuit. Keywords: Mineralogical variation, flotation, pulp chemistry

Jan 1, 2020

By J. Petersen, A. E. Lewis, J. Chivavava

Rare earth elements (REEs) have special properties that prompted their extensive use in high-tech applications. The demand for REE has, therefore, increased over the past years, resulting in the supply risk of the materials. Extraction from non-conventional low-grade ores, like easy-to-mine ion adsorption clays (IACs), by hydrometallurgical methods is being explored to supplement the supply of REEs. The extraction of REEs from low tenor IAC leach solutions requires enrichment using cost-effective methods such as precipitation. Therefore, the aim of this study was to understand the recovery of REEs from IAC leach solutions using various reagents for precipitation. In the first part of the study, recoveries of REEs from IAC leach solutions through direct precipitation using H2C2O4 and NH4HCO3, as well as antisolvent crystallization using C2H5OH, were predicted via thermodynamic modelling using OLI Stream Analyzer. Verification experiments were then conducted through the use of an agitated reactor. Simulation results showed that high yields of REEs were possible using each of the reagents, but large quantities of C2H5OH were required. Experimental results confirmed the high yields predicted from simulations. Precipitation with H2C2O4 was found to selectively recover REEs while rejecting Al. However, utilization of NH4HCO3 and C2H5OH resulted in the co-precipitation of Al. Furthermore, the yield of Y from antisolvent crystallization was significantly lower than the theoretical value. The product recovered from antisolvent crystallization consisted of well faceted, large crystalline particles, which filtered faster than the fine, amorphous REE carbonates recovered using NH4HCO3. REE oxalates were crystalline, larger than the REE carbonates and, overall, showed the highest filtration rate.

Dec 11, 2024

By G. W. Donaldson

Theoretical and engineering aspects of slimes-dam construction by G. W. DONALDSON, M.Sc. (Eng.)(U.C.T.), D.I.C. (Visitor) Tile paper reviews the recommendations made in 1959-60 as a result of research into slimes-dam construction and finds that these recommendations are still valid. The requirements for pollution control, vegetating, in situ leaching, and future development of slimes dams as building areas are considered as they affect the engineering aspects of slimes-dam construction, and it is found that these requirements can be met without any major changes to current recommended slimes-dam construction practice.

Jan 12, 1973

By J. Petersen, K. Shaik

The traditional route utilised for the recovery of Platinum Group Minerals (PGMs) in South Africa involves the concentration of ore by flotation, followed by smelting to produce a PGM rich matte, which is then digested hydrometallurgically to solubilise base metals and Platinum Group Elements (PGE). HCl/Cl2 is conventionally used for PGE dissolution from concentrated material, which is an aggressive reagent associated with high maintenance costs as well as environmental concerns. Of interest is the leaching of PGMs directly from mineral ores, low grade concentrates and tailings in a cyanide-ferricyanide system as a more sustainable alternative. This system has shown favourable Pt recoveries among the Pt minerals, but with sperrylite (PtAs2) displaying highly refractory behaviour. The dissolution of sperrylite is investigated in a cyanide-ferricyanide system in the context of an electrochemical study involving OCP, chrono-amperometry and cyclic voltammetry. This approach allows the assessment of leaching characteristics as well as the investigation of surface passivation, which is believed to contribute to poor Pt recoveries. Some evidence is presented that such passivation is related to the formation of arsenide species on the mineral surface. Keywords: Sperrylite, PGMs, cyanide, ferricyanide, electrochemistry

Jan 1, 2020

By M. Ye. Scheglov, G. I. Voiloshnikov, S. M. Ryakhovsky, V. E. Dementyev, V. N. Alekseev, N. S. Voiloshnikova

Irgiredmet has substantial experience on RIP and RIL technology for gold recovery, having started development of ion exchange technology in 1964. Irgiredmet specialists were involved in the majority of RIL and RIP projects in the former Soviet Union and Russia, and took part in commissioning of practically all plants using ion exchange technology. Laboratory and pilot plant tests were conducted to develop process design criteria for designing 15 RIP plants of the former USSR using bifunctional macroporous anionite AM-2B or its analogs. This paper is devoted to the laboratory, pilot plant testing and introduction of RIP technology conducted in cooperation with GC Pertopavlovsk. Medium base resin PuroLite S992 (PuroGold) was used as adsorbent. Some adsorption regularities and the affinity of resin to metal cyanide complexes were studied. Laboratory batch and continuous pilot tests on resin-in-pulp process were held for oxidised ores from Pioneer, Albyn and Malomyr mines (Amur region, Russia) owned by the Petropavlovsk company. A simplified flowsheet for gold elution and resin regeneration was developed. Alkaline cyanide solution was used as gold eluent and gold was recovered from eluates by electrowinning. Process design criteria were developed on the basis of the testwork results, and the plants were designed and constructed by GC Petropavlovsk. The RIP plant at Pioneer was commissioned in May 2008, at Malomyr in August 2010, and at Albyn deposit in December 2011. These plants are currently in operation at design performance at throughputs from 3 to 6.5 Mt/year. The primary gold ores of Pioneer and Malomyr deposits are refractory to cyanidation; Irgiredmet also completed continuous testwork on RIP technology using medium-base resin for pressure oxidation (POX) residues derived from their flotation concentrates. In 2019 a hydrometallurgical plant for the treatment of refractory gold concentrate after POX was commissioned at Pokrovsky mine (Amur region). Keywords: Gold ores, cyanidation, RIP, RIL –processes, ion exchange resin, medium base resin, adsorption, elution, electrowinning

Jan 1, 2020

By P. M. Solozhenkin, O. I. Solozhenkin

Currently lead nitrate is used as the recommended activator in Au-Sb flotation. However, due to high levels of hazard, the application of lead nitrate constitutes a potential risk for human health and ecosystems. To mitigate the harmful impact of activators on the environment, further research on activation by alternative reagents has been launched to promote the efficiency of antimony ores. In the present study, adsorption of lead, copper and zinc cations has been investigated by nuclear quadrupole resonance (NQR), which has revealed copper and zinc cations penetration into the mineral lattice, although lead cations remain adsorbed on the mineral surface. However, the combination of zinc and copper cations leads to preferential volumetric adsorption of zinc in the mineral lattice and further surface adsorption of copper which positively affects the activation process. It has been established that activation of stibnite can be achieved effectively with the mixture of Cu2+:Zn2+=1:1 as much as with lead cations in antimony ore flotation. As a part of this work, the computational modelling has been used in prognosis of reagent activity evaluation (PRAE) for stibnite and aurostibite flotation by sulfhydryl collectors. The lower PRAE value the stronger the ability of a collector to form a stable complex with a mineral. PRAE has shown a strong negative trend to complex formation on the mineral surface of aurostibite and stibnite. Based on these studies, several collectors have been proposed for effective flotation. To verify the feasibility of proposed collectors tetramethyl (ethyl) thiuram disulfides (TMTD and TETD) have been used for flotation of stibnite, sphalerite, pyrite and arsenopyrite. Flotation performance has been improved significantly with TMTD that allows the avoidance of lead nitrate application and increases the recovery of antimony by 8,16%. Keywords: Stibnite, aurostibite, activation, lead, copper, flotation reagents

Jan 1, 2020

By S. Andika, O. A. Putri

Maintaining fleet productivity, which consists of balancing loader and truck performance, has always been a challenging task. An automatic dispatching system (ADS) is implemented to help monitoring fleet condition and assign trucks to a designated loader. Integrated data from real time Global Positioning System, Vehicle Health Monitoring System, and other production related data are acquired to support the ADS. However, the abnormal truck cycle has been the main culprit which resulted in unnecessary loader hanging time and trucks queuing time. Hanging and queuing time accounted for 2.34 and 2.07 minutes respectively per loading cycle or equal to 2,861 loose cubic metres per fleet per day production losses. Using integrated dispatching system data, the authors conducted research to study a truck’s hauling cycle that affects fleet productivity. The data is modelled to obtain the arrival rate pattern in a front loading area by adopting the queue theory algorithm. This paper aims to understand the potential pattern of a truck’s cycle abnormality and to resolve its occurrence.

Sep 1, 2021

By N. Hamlef

In this study, the effects of heat treatment on phase formation and surface morphology of the Cr-Pt coated system are investigated using X-ray diffraction and electron microscopy techniques. The CrPt andCr4Pt (Cr3Pt - A15 type) phases were formed after heat treatment of the coated samples. Heat treating at 1000°C renders a distinct island coating morphology that is non-continuous in nature. A diffusional model is proposed for this coated system with regards to the surface morphology formation after heat treatment.

Jan 1, 2014

By T. Wajima

Recovery of precious metals from hydrochloric solution using sulfur-impregnated carbonaceous adsorbent was examined. Sulfur-impregnated adsorbent with adsorption abilities of precious metals can be prepared from activated carbon using pyrolysis at 600 oC under 10 % H2S gas flow, and the adsorbed Au and Pd were precipitated as metal phase on the surface of the adsorbent. The adsorbents after precious metals adsorption were burned at 700 oC to obtain the residue mainly containing precious metals. The adsorbent was found to be highly efficient and selective for the uptake of precious metals, especially Au, in the presence of excess base metal ions from simulated spent automotive catalyst eluted solution using a column pack test. Keywords: Gold, platinum, palladium, reduction precipitation

Jan 1, 2020

By K. Cole, D. Mesa, P. R. Brito-Parada, M. R. van Heerden

Turbulence in stirred tank flotation vessels determines the bulk transport of particles and has an important role in particle-bubble collisions necessary for attachment. Positron emission particle tracking (PEPT) produces quantitative measurements of the kinematic motion of different particle classes inside flotation vessels. This paper presents flow profiles of the vessel, residence time distributions, flow profiles through the mesh and macroturbulent kinetic energy distributions as experienced by valuable (hydrophobic) mineral particles in a laboratory scale flotation vessel. The results highlight the impact of the rotor-stator design and a retrofit mesh modification at the upper part of the vessel which improve recovery by decreasing turbulence in the quiescent zone and at the interface. Keywords: Flotation machines, turbulence, PEPT

Jan 1, 2020

By E. K. Mutinda, D. K. Maina, R. M. Kasomo, B. O. Alunda

Assessment of blast fragment size distribution is critical in mining operations because it is the initial step towards mineral extraction. Different empirical models and techniques are available for predicting and investigating the consequences of blasting, one of which is the Kuznetsov Cunningham-Ouchterlony (KCO) model. In this paper we summarize the advances in the empirical models from inception until now, and explore the improvements that have been made so far with particular emphasis is on the most recent KCO model. Utilization of the model and the errors that arise between expected and the actual outcomes are analysed. The results indicate that the KCO model remains useful for predicting the blast fragmentation at limestone mine sites, despite the availability of other advanced prediction models. It is also a valuable instrument for pre-surveying the impact of varying certain parameters of a blast plan.

Mar 1, 2021

By R. L. Setsepu, S. O. Bada, J. Abdulsalam

The utilization of biomass as a solid fuel for co-firing has received great attention from boiler manufacturers as a clean coal technology (CCT) option. This research aimed to produce biocoal pellets, as a clean energy fuel, using hydrochar from trees planted to rehabilitate acid mine drainage (AMD) water and fine coal discards. The hydrochar was synthesized by hydrothermal carbonization of Searsia lancea harvested from AMD-contaminated land at a temperature of 280°C and a residence time of 90 minutes. It was blended with discard coal (–1 mm) at ratios of 25% and 50% hydrochar to produce different forms of solid pelletized biocoal (BC). The physicochemical and mechanical properties of each of the biocoal pellet blends were determined. The 100% hydrochar had the highest calorific value of 29.99 MJ/kg, while the raw discard coal had a calorific value of 16.73 MJ/kg. The ash content decreased from 42% in the discard coal to 25% in the blend of 50% coal and 50% hydrochar biocoal pellets. Biocoal pellets comprising 25% hydrochar and 75% discard coal (BC25 HC/75 COAL) displayed the best mechanical properties (compressive strength 3.06 MPa) of all the fuels, but the physicochemical properties were inferior to the BC50 HC/50 COAL pellets. This research has demonstrated that hydrochar synthesized from a tree species planted for hydraulic control of AMD has the capability to act as a binder for improving the mechanical properties and energy characteristics of fine discard coal.

Dec 1, 2021