Research

21 pages, 5002 KiB

Open AccessArticle

Residence Time Distribution Analysis of Drip-Irrigated Beds—The Effect of Material and Fluid Properties with Implications for Heap Leaching Practice

by Michael D. Odidi, Marijke A. Fagan-Endres and Susan T. L. Harrison

Minerals 2023, 13(2), 267; https://doi.org/10.3390/min13020267 - 14 Feb 2023

Cited by 1 | Viewed by 1944

Abstract

The quantitative effect of particle shape, porosity, wettability, particle size, and solution viscosity on the residence time distribution (RTD) profiles of non-reactive, steady-state, drip-irrigated ore beds characteristic of heap leaching systems is presented. Results were obtained using step-up tracer tests and allowed for [...] Read more.

The quantitative effect of particle shape, porosity, wettability, particle size, and solution viscosity on the residence time distribution (RTD) profiles of non-reactive, steady-state, drip-irrigated ore beds characteristic of heap leaching systems is presented. Results were obtained using step-up tracer tests and allowed for the analysis of preferential flow behaviour within the systems. The key findings were as follows. Increased particle sphericity enhanced channelling in beds of smaller particles, but not for larger particle sizes. Higher particle wettability caused greater liquid dispersion during both initial wetting studies and at steady-state fluid flux. Higher porosity levels and the inclusion of fines in mixed sized beds resulted in longer average solute residence times, higher liquid hold-up, longer solution and tracer breakthrough times, and increases in drain-down moisture percentages. Increasing the irrigation fluid’s viscosity, reflective of the increase in ionic concentrations in leach solutions, reduced both the solution and tracer breakthrough times and increased dispersion with signs of more discontinuous or isolated fluid volumes at steady-state. These results highlighted the importance of the inclusion of fines in agglomerated beds to improve uniform wetting especially those with low to moderate particle porosities (<2.5 m²/g specific surface area). The viscosity results suggest that there may be changes in preferential flow extent, due to variations in viscosity owing to the increasing sulphate concentration within the liquid phase in heaps and with time. Full article

(This article belongs to the Special Issue Recent Developments in Mineral Processing at University of Cape Town)

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16 pages, 1668 KiB

Open AccessArticle

Resource Intensity Trends in the South African Ferrochrome Industry from 2007 to 2020

by Reuben Dlamini and Harro von Blottnitz

Minerals 2023, 13(1), 44; https://doi.org/10.3390/min13010044 - 27 Dec 2022

Cited by 2 | Viewed by 1870

Abstract

Processing resource requirements in mineral extractive industries tend to increase over time as ore grades decrease, which consequently increases the environmental footprint of operations and products. This phenomenon may be alleviated by cleaner production interventions. South Africa is the largest global supplier of [...] Read more.

Processing resource requirements in mineral extractive industries tend to increase over time as ore grades decrease, which consequently increases the environmental footprint of operations and products. This phenomenon may be alleviated by cleaner production interventions. South Africa is the largest global supplier of chromium. This study investigates the impact of cleaner production process improvements on selected resource intensities of the South African ferrochrome industry. Sustainability data, available since the start of regular sustainability reporting in 2007, were used to compile resource intensity trends. This was followed by a review of industry capital projects relating to resource-use optimisation, interrogated in interviews with industry experts, to ascertain their effect on resource intensities. The emergence of a symbiotic relationship with the platinum-group metals industry was identified as a major development, with chromite ore intensity decreasing from 2.54 to 1.98 kg per kg ferrochrome. Electrical energy intensity was observed to decrease from 3.47 to 2.86 kWh per ton ferrochrome, mainly as a result of cleaner smelting technology, though cogeneration fired by furnace off-gases also contributed significantly. The introduction of cleaner production interventions in the South African ferrochrome industry was thus documented to have resulted in decreased resource use intensities. Full article

(This article belongs to the Special Issue Recent Developments in Mineral Processing at University of Cape Town)

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16 pages, 4766 KiB

Open AccessEditor’s ChoiceArticle

Crystal Engineering in Antisolvent Crystallization of Rare Earth Elements (REEs)

by Jonathan Sibanda, Jemitias Chivavava and Alison Emslie Lewis

Minerals 2022, 12(12), 1554; https://doi.org/10.3390/min12121554 - 01 Dec 2022

Cited by 3 | Viewed by 1993

Abstract

Antisolvent crystallization is a separation technology that separates the solute from the solvent by the addition of another solvent, in which the solute is sparingly soluble. High yields are achieved by using higher antisolvent-to-aqueous ratios, but this generates higher supersaturation, which causes excessive [...] Read more.

Antisolvent crystallization is a separation technology that separates the solute from the solvent by the addition of another solvent, in which the solute is sparingly soluble. High yields are achieved by using higher antisolvent-to-aqueous ratios, but this generates higher supersaturation, which causes excessive nucleation. This results in the production of smaller particles, which are difficult to handle in downstream processes. In this work, the effect of varying the organic (antisolvent)-to-aqueous (O/A) ratio and seed loading on the yield, particle size distribution, and morphology of neodymium sulphate product, during its recovery from an aqueous leach solution using antisolvent crystallization, was investigated. A batch crystallizer was used for the experiments, while ethanol was used as an antisolvent. Neodymium sulphate octahydrate [Nd₂(SO₄)₃.8H₂O] seeds were used to investigate the effect of seed loading. It was found that particle sizes increased as the O/A ratio increased. This was attributed to the agglomeration of smaller particles that formed at high supersaturation. An O/A ratio of 1.4 resulted in higher yields and particles with a plate-like morphology. The increase in yield was attributed to the increased interaction of ethanol molecules with the solvent, which reduced the solubility of neodymium sulphate. Increasing the seed loading resulted in smaller particle sizes with narrow particle size distribution and improved filtration performance. This was attributed to the promotion of crystal growth and suppression of agglomeration in the presence of seeds. Full article

(This article belongs to the Special Issue Recent Developments in Mineral Processing at University of Cape Town)

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11 pages, 1244 KiB

Open AccessArticle

Investigating the Influence of the Electrochemical Environment on the Flotation of Bornite and Chalcocite

by Tanaka P. Tafirenyika, Cyril T. O’Connor and Kirsten C. Corin

Minerals 2022, 12(12), 1527; https://doi.org/10.3390/min12121527 - 28 Nov 2022

Cited by 1 | Viewed by 1754

Abstract

Beneficiation of sulphide ores by flotation is ascribed to the natural electrochemical activity associated with sulphide minerals. Flotation is an electrochemical process comprising many interdependent conditions that are difficult to decouple in terms of controlling flotation performance. The extent of electrochemical activity is [...] Read more.

Beneficiation of sulphide ores by flotation is ascribed to the natural electrochemical activity associated with sulphide minerals. Flotation is an electrochemical process comprising many interdependent conditions that are difficult to decouple in terms of controlling flotation performance. The extent of electrochemical activity is mineral dependent and can be measured against a reference cell to differentiate between minerals. This difference in activity is known as the rest potential. The rest potential can be exploited to preferentially float one mineral over another as these properties result in different regions of flotation stability for different minerals. Bornite and chalcocite present an interesting study because when measured against the standard hydrogen electrode (SHE), there is a small difference in rest potential; bornite has a potential of 0.44 V and chalcocite a potential of 0.40 V. The key differentiating factor between the two minerals is the presence of iron in bornite (Cu₅FeS₄) and the lack thereof in chalcocite (Cu₂S). This study considers bornite and chalcocite microflotation, adsorption studies and zeta potential measurements, and three key factors were explored: pH, galvanic interactions and collector adsorption. The overall objective of the study is to understand the response of bornite and chalcocite to changes in pulp chemistry. Full article

(This article belongs to the Special Issue Recent Developments in Mineral Processing at University of Cape Town)

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11 pages, 789 KiB

Open AccessArticle

Valorization of South African Coal Wastes through Dense Medium Separation

by Juarez R. do Amaral Filho, Msimelelo Gcayiya, Athanasios Kotsiopoulos, Jennifer L. Broadhurst, David Power and Susan T. L. Harrison

Minerals 2022, 12(12), 1519; https://doi.org/10.3390/min12121519 - 28 Nov 2022

Cited by 1 | Viewed by 1932

Abstract

Sustainable management of coal waste is one of the major environmental concerns for coal mining, whether active or legacy, worldwide. Coal dump deposits demand a large physical area or footprint for disposal of solid waste, change the topography, and generate both pyritic dust [...] Read more.

Sustainable management of coal waste is one of the major environmental concerns for coal mining, whether active or legacy, worldwide. Coal dump deposits demand a large physical area or footprint for disposal of solid waste, change the topography, and generate both pyritic dust and acid rock drainage (ARD) where pyritic coal waste is deposited. The beneficiation of dump deposits or, preferably, of coal waste prior to its dumping can reduce or even eliminate the liabilities related to coal waste management. In this work, dense medium separation studies of coal discards, using heavy liquids, resulted in three pooled fractions from typical South African coal waste discards from the Mpumalanga region for future use: (a) a fraction of low density with increased calorific value; (b) a fraction of intermediate density, rich in ash and acid neutralizing minerals and lower in sulfur; and (c) a fraction of high density, rich in sulfidic minerals including pyrite. The fractions were characterized using particle size analysis, sink-float studies, static tests to predict ARD potential, proximateand ultimate analysis, and gross calorific value. The results showed that approximately 70% of this discard coal is composed of a material of sufficient quality for energy generation in conventional power stations. A pyrite-rich concentrate made up 2% of the total discard mass; comprising more than 45% of the sulfidic mineral present in the feed and displaying no acid neutralizing capacity (ANC). The remaining discard fraction, with intermediate density, presented potential to be used for several ends including soil fabrication, co-disposal or as aggregate material in civil engineering; additional testing to ensure applicability for the selected re-purposing option should be chosen based on proposed use. Full article

(This article belongs to the Special Issue Recent Developments in Mineral Processing at University of Cape Town)

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11 pages, 4872 KiB

Open AccessArticle

The Electrochemical Response of Chalcopyrite and Galena to Degrading Water Quality

by Nolihle Ndamase, Margreth Tadie and Kirsten Claire Corin

Minerals 2022, 12(11), 1476; https://doi.org/10.3390/min12111476 - 21 Nov 2022

Viewed by 1374

Abstract

Water is used as a liquid medium as well as a means of transportation during mining operations. Flotation, in particular, is a water intensive process where water makes up about 80–85% of the pulp phase. Process water contains organic and inorganic species which [...] Read more.

Water is used as a liquid medium as well as a means of transportation during mining operations. Flotation, in particular, is a water intensive process where water makes up about 80–85% of the pulp phase. Process water contains organic and inorganic species which accumulate as they are recycled. To avoid the treatment costs of removing these contaminants, many mining operations allow the quality of their water to degrade over time. When this water is introduced into flotation circuits, the pulp chemistry is altered. Ionic species that accumulate in recycled process water have been shown by previous studies to be especially deleterious to flotation performance. Such ions include Ca²⁺, Cu²⁺, Mg²⁺, Pb²⁺, SO₄²⁻ and S₂O₃²⁻, amongst others. The flotation sub-process of collector adsorption which is responsible for inducing hydrophobicity on valuable mineral surfaces may be influenced by water chemistry. Accumulating ionic species have been shown to hinder collector adsorption which may reduce recovery of valuable minerals to the concentrate. Consequently, degrading water quality may threaten the economic viability of mining operations that make use of closed water circuits. Electrochemical techniques such as mineral rest potentials can be used to monitor the impact of changing water quality on collector–mineral interactions. Microflotation was used to determine whether mineral floatability was affected by changing water quality. This study therefore aimed to investigate whether electrochemical techniques such as rest potential measurements can be used to predict flotation performance under changing water quality. No definable relationship was found between the rest potential differences and the microflotation initial recoveries, however, rest potential measurements did identify the negative impact that thiosulphate ions may have on flotation processes. Full article

(This article belongs to the Special Issue Recent Developments in Mineral Processing at University of Cape Town)

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14 pages, 3414 KiB

Open AccessArticle

Solvent Extraction Studies of Copper from a Heap Leach Liquor Using Mextral 5640H

by Mostafa Hosseinzadeh, Jochen Petersen and Asghar Azizi

Minerals 2022, 12(10), 1322; https://doi.org/10.3390/min12101322 - 20 Oct 2022

Cited by 1 | Viewed by 3186

Abstract

In this study the extractive capability of Mextral 5640H was investigated for extraction of copper from a heap leach liquor. In this regard, the influence of parameters such as pH (0.2–2.8), extractant concentration in kerosene diluent (2.5%–10% v/v), temperature (25–70 [...] Read more.

In this study the extractive capability of Mextral 5640H was investigated for extraction of copper from a heap leach liquor. In this regard, the influence of parameters such as pH (0.2–2.8), extractant concentration in kerosene diluent (2.5%–10% v/v), temperature (25–70 °C), contact time (0–300 s), stirring speed (100–1200 rpm), phase ratio (O/A) (0.6–1.8) and Cu initial concentration (0.5–2 g/L) in the leach liquor were examined and optimized. The findings demonstrated that the Mextral 5640H extractant had a very high efficiency and selectivity in copper extraction from the leachate. 98.17% Cu, with less than 0.5% of Fe and Mn, were extracted at pH 1.6, 10% (v/v) Mextral 5640H concentration, ambient temperature (25 °C), 400 rpm stirring speed, 2 min contact time and an O/A phase ratio of 1:1. Under equilibrium conditions it was found that one mol of Cu is extracted by 7 mol of Mextral 5640H. Additionally, analysis using a McCabe–Thiele diagram suggests a two-stage extraction to reach the maximum extraction of copper (99.5%) from the leachate at operational condition using industrial mixer-settlers. Furthermore, a thermodynamic study was conducted, and the measured values of ΔH = 15.13 kJ/mol, ΔG = −6.95 kJ/mol and ΔS = 74.10 J/mol/K indicate an endothermic, spontaneous nature and high affinity of copper extraction. Full article

(This article belongs to the Special Issue Recent Developments in Mineral Processing at University of Cape Town)

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15 pages, 3837 KiB

Open AccessFeature PaperArticle

Mineralogical Factors Affecting the Dense Medium Separation of Nickel Sulfide Ores

by Keshree Pillay, Aubrey Njema Mainza, Deshenthree Chetty and Megan Becker

Minerals 2022, 12(10), 1311; https://doi.org/10.3390/min12101311 - 18 Oct 2022

Cited by 2 | Viewed by 2475

Abstract

Dense medium separation (DMS) is often used to reject a large portion of gangue material upfront to create cost and energy savings during processing. As lower-grade ores with complex mineralogy are being increasingly exploited, the properties of the gangue minerals begin to play [...] Read more.

Dense medium separation (DMS) is often used to reject a large portion of gangue material upfront to create cost and energy savings during processing. As lower-grade ores with complex mineralogy are being increasingly exploited, the properties of the gangue minerals begin to play a more important role in the upgrading of the ore. It is therefore important to understand these mineralogical factors to be able to select suitable processing routes for specific ore types. Two nickel sulfide deposits in southern Africa were chosen as case studies to understand differences in DMS efficiency when applied to different ores: Ore A and Ore B. Both ores showed nickel upgrades using DMS and the products were then characterized using QEMSCAN, with the aid of X-ray diffraction and electron probe microanalysis. Overall, particle density remains the main control on the separation, followed by sulfide texture, with massive and net-textured sulfides having larger grain sizes and therefore better liberation than disseminated sulfides. In addition to the concentration of sulfides, primary and secondary silicate minerals are separated by their density differences, which can affect the recovery of finely disseminated sulfides associated with them. Particle size is also important in DMS, with material near the cut-point density separating on size rather than density. The understanding of the mineralogical properties affecting DMS can aid in the prediction of the suitability of DMS for different ore types. Full article

(This article belongs to the Special Issue Recent Developments in Mineral Processing at University of Cape Town)

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20 pages, 6267 KiB

Open AccessArticle

A Study on the Applicability of Agitated Cyanide Leaching and Thiosulphate Leaching for Gold Extraction in Artisanal and Small-Scale Gold Mining

by Archippe Ngwey Manzila, Thandazile Moyo and Jochen Petersen

Minerals 2022, 12(10), 1291; https://doi.org/10.3390/min12101291 - 14 Oct 2022

Cited by 6 | Viewed by 2447

Abstract

Mercury amalgamation is the method of choice to recover gold in artisanal and small-scale gold mining (ASGM). However, despite the low cost and simplicity of this method, the use of mercury presents serious health and environmental risks, as well as low efficiency in [...] Read more.

Mercury amalgamation is the method of choice to recover gold in artisanal and small-scale gold mining (ASGM). However, despite the low cost and simplicity of this method, the use of mercury presents serious health and environmental risks, as well as low efficiency in gold extraction. This study investigates the application of cyanide and thiosulphate leaching as alternatives to mercury amalgamation. This investigation was undertaken by conducting leach experiments using cyanide at 1 g/L, 3 g/L, and 5 g/L, and ammonium thiosulphate at 0.1 M and 0.5 M, on three ore samples originating from an artisanal mining area in Zimbabwe. The operating conditions (T = 26 °C, solids loading: 30%, particle size: −300 + 150 µm) were selected to mimic as closely as possible the conditions of artisanal mining processes. It was found that cyanide leaching was the better performing technology compared to thiosulphate leaching, as it achieved gold extractions of 71.6%, 69.7%, and 67.8% for the three ore samples (Sample 1, Sample 2, and Sample 3, respectively), whereas thiosulphate leaching achieved gold extractions of 54.1%, 35.6%, and 38.0% for the three ores, respectively. Both methods outperformed mercury amalgamation, which typically achieves gold recoveries of 30%–50%. Studying the minerology of the ores, using XRF, XRD, QEMSCAN, SEM-EDS, and a diagnostic leach, revealed the presence of sulphide minerals hosting refractory gold which contributed to the low gold extractions observed. Besides achieving higher gold extraction, cyanide leaching proved to be a system that is easier to control compared to thiosulphate leaching, making it much more attractive to artisanal miners. Full article

(This article belongs to the Special Issue Recent Developments in Mineral Processing at University of Cape Town)

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19 pages, 4503 KiB

Open AccessArticle

Effect of Heat Transfer Driving Force and Ice Seed Loading on the Production of Ice and Salt from a Dilute Brine Treated Using Eutectic Freeze Crystallization

by Anotidaishe Spencer, Jemitias Chivavava and Alison Emslie Lewis

Minerals 2022, 12(9), 1094; https://doi.org/10.3390/min12091094 - 29 Aug 2022

Cited by 1 | Viewed by 1616

Abstract

Eutectic Freeze Crystallization (EFC) is a separation technology that separates solute from solvent by cooling the brine to a temperature below its eutectic point, such that ice and salt simultaneously crystallize out of the solution. Achieving consistent production of ice and salt at [...] Read more.

Eutectic Freeze Crystallization (EFC) is a separation technology that separates solute from solvent by cooling the brine to a temperature below its eutectic point, such that ice and salt simultaneously crystallize out of the solution. Achieving consistent production of ice and salt at high production rates has been a challenge for EFC. This is due to heat transfer limitations, which are more severe when EFC is applied to dilute brines. This work investigated the effect of the heat transfer driving force, ΔT_LMTD, and ice seed loading (SL) on the production of ice and salt from a dilute brine. A 1.45 L stirred crystallizer was used for the experiments at varying coolant temperatures to investigate the effect of ΔT_LMTD, and at varying seed masses to investigate the effect of seed loading. It was found that, as the ΔT_LMTD increased, the yield of ice and salt increased. This was attributed to the increase in the heat transfer rate as ΔT_LMTD and heat transfer rate are directly related. The ice yield was divided between ice in suspension and ice formed on the wall (scale layer), with a majority of the total ice yield being scale ice. Increasing the seed loading (SL) increased the yield of ice in suspension and decreased the yield of scale ice. The seeds allowed for increased surface area for crystallization in the bulk. This allowed for most of the supersaturation to be consumed in the bulk, leaving little supersaturation for crystallization at the wall. This reduced the propensity for scale formation. The reduction in the scale layer increased the heat transfer rate between the bulk and the coolant, allowing for more ice to be formed in suspension. Full article

(This article belongs to the Special Issue Recent Developments in Mineral Processing at University of Cape Town)

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15 pages, 3137 KiB

Open AccessFeature PaperArticle

A Methodology to Determine the Potential for Particulate Ore Sorting Based on Intrinsic Particle Properties

by Michael Duncan and David Deglon

Minerals 2022, 12(5), 630; https://doi.org/10.3390/min12050630 - 16 May 2022

Viewed by 1951

Abstract

Sensor-based particulate ore sorting is a pre-concentration technique that sorts particles based on measurable physical properties, resulting in reduced energy consumption by removing waste prior to grinding. This study presents an integrated methodology to determine the potential for ore sorting based on intrinsic [...] Read more.

Sensor-based particulate ore sorting is a pre-concentration technique that sorts particles based on measurable physical properties, resulting in reduced energy consumption by removing waste prior to grinding. This study presents an integrated methodology to determine the potential for ore sorting based on intrinsic particle properties. The methodology first considers the intrinsic sortability based on perfect separation. Only intrinsically sortable ore is further assessed by determining the sensor-based sortability. The methodology is demonstrated using a case study based on a typical copper porphyry comminution circuit. The sorting duty identified for the case study was the removal of low-grade waste material from the pebble crusher stream at a suitable Cu cut-off grade. It was found that the ore had the potential to be sorted based on the intrinsic and ideal laboratory sensor sortability results but showed no potential to be sorted using industrial-scale sensors. The ideal laboratory XRF sensor results showed that around 40% of mass could be rejected as waste at copper recoveries above 80%. An economic analysis of the sortability tests showed that, at optimum separation conditions, the intrinsic, ideal sensor and industrial sensor sortability would result in an additional annual profit of ~$30 million, $21 million and $−7 million (loss), respectively. Full article

(This article belongs to the Special Issue Recent Developments in Mineral Processing at University of Cape Town)

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