On the progression of leaching from large particles in heaps

Includes bibliographical references.Although heap leaching is by now a well-established technology choice in the mining industry, the process remains limited by low recoveries and long extraction times. It is becoming increasingly clear that the successful application of heap leaching technology will ultimately depend on having a comprehensive understanding of the underlying fundamental processes for optimisation to take place...The subject of this research was, therefore, to understand more clearly the diffusion reaction phenomena of reagents through large particles and to provide true and reliable physical parameters to formulate the relevant modelling approaches to large particle leaching. A combination of standard optical microscopy, SEM, QEMSCAN and X-ray CT techniques has been used for the characterization of crack networks and mineral dissemination in the ore particles, which are important characteristics that determine the diffusion of reagents into and out of particles and the reactions within

Heap leaching technology – current state, innovations and future directions: A review

Copyright © 2015 Taylor & Francis. This is an Accepted Manuscript of an article published by Taylor & Francis in Mineral Processing and Extractive Metallurgy Review on 20 November 2015, available online: http://www.tandfonline.com/10.1080/08827508.2015.1115990Heap leaching is a well-established extractive metallurgical technology enabling the economical processing of various kinds of low-grade ores, which could not otherwise be exploited. However, despite much progress since it was first applied in recent times, the process remains limited by low recoveries and long extraction times. It is becoming increasingly clear that the choice of heap leaching as a suitable technology to process a particular mineral resource, which is both environmentally sound and economically viable, very much depends on having a comprehensive understanding of the underlying fundamental mechanisms of the processes and how they interact with the particular mineralogy of the ore body under consideration. This paper provides an introduction to the theoretical background of various heap leach processes, offers a scientific and patent literature overview on technology developments in commercial heap leaching operations around the world, identifies factors that drive the selection of heap leaching as a processing technology, describes challenges to exploiting these innovations, and concludes with a discussion on the future of heap leaching.South Africa Research Chair Initiative (SARChI) - Chair in Mineral BeneficiationNational Research Foundation (NRF) of South Africa - Research Niche Area (RNA) gran

Laboratory Investigation of the Parameters of the Submerged Plates on the Turbidity Currents Characteristics

In dam reservoirs, the turbidity current is usually the cause of sediment transfer and deposition. Therefore, it is necessary to study this phenomenon. Here, experiments were made on the effects of the impermeable submerged plates on turbidity current head. In order to investigate the effects of the impermeable submerged plates, some parameters of the plates were changed, such as shape, angle of mounting of the plates with respect to the current axis, location and the dimensions of the plates. The results showed that the flow velocity of the turbidity current decreased by 25 to 27.1% with respect to the control state in case of different shapes of plates mounted. The analysis of the position of the plates showed that in different conditions, the flow velocity decreases 45.1% relative to the control state. Various mounting angles also resulted in 8.6 to 27.1% lower velocity relative to the control. Changing the width and height of the plates reduced the head velocity from 21.8 to 43.9% and 10 to 45.2%

Investigation and modelling of the progression of zinc leaching from large sphalerite ore particles

X-ray Computed Tomography (CT) was used to follow the progression of Zn leaching in a number of individual sphalerite ore particles, which were subjected to a long-term simulated heap bioleaching environment. The ore was prepared by two different modes of comminution – HPGR at 90 bar and cone crusher – and individual particles were selected from three different size fractions. Investigation of the reacted fraction of Zn vs distance from the centre of each particle indicated that leaching from large particles leads to near complete conversion near the surface, but only partial conversion in the zones that are closer to the centre of particles. The cores of the cone-crushed particles show hardly any conversion at all, especially in the larger particle sizes. Mathematical analysis shows that leaching from the large particle does not follow the shrinking core model. It is shown that the progression can rather be described by a combined reaction-diffusion process progressing through the network of cracks and pores closer to the particle surface. Extent and depth of this network are a function of particle size and comminution method. A simplified rate model is proposed that describes the extent of leaching as a function of time in terms of a set of parameters that can all be related to just particle size and crushing mode

Investigation of particles with high crack density produced by HPGR and its effect on the redistribution of the particle size fraction in heaps

The application of comminution technology such as the High-pressure grinding rolls (HPGR), which is able to generate a high density of cracks in the ore particles, is favourable for leaching processes. Extraction of metallic values by the heap leach process, can take place on the particles with partial exposure of mineral grains, if it can provide sufficient surface front for chemical attack by leaching solution. The aim of this study was to assess the benefits of high crack density in the ore particles produced using the HPGR and how it could diminish due to inadequate percolation of the leaching agent. A zinc ore was comminuted using HPGR at three different pressure settings and with a cone crusher for the control experiment. Subsamples from the (+23/-25, +14/-16, +5.25/-6.75 mm) size fractions were characterized and packed into leach reactors. The reactors were stopped from time to time to investigate the progress of crack and micro-crack growth and its effect on metal extraction using the X-ray computed tomography (CT). The results are validated with those obtained using traditional techniques such as SEM and QEMSCAN. Investigation of the leach reactors residue indicated significant changes in the particle size distribution (PSD) of initial feed toward the fine size fraction. The residues from the reactors leaching the material prepared using the HPGR product contained more fine particles than the reactors, which were fed by cone crusher product. These differences were up to 10.3%

Emerging criticality: Unraveling shifting dynamics of the EU's critical raw materials and their implications on Canada and South Africa

Critical Raw Materials (or CRMs) are materials that are in high demand, difficult to replace and whose supply is prone to disruption. Various nations have defined CRM lists, although terminology, supporting data and assessment frameworks differ. The European Union (EU) has the longest published history of CRM lists with the first one published in 2011, followed by 3-year revisions. In this study, we analyze CRM designation trends over time by using the EU's five CRM lists to deduce the driving factors. Overall, the number of CRMs have increased by 1.67 new CRMs per year from 2011 to 2023, with the number of new CRMs yet to reach a plateau. Our analysis also reveals issues that could affect the value of the CRM lists including: (1) a hidden two-stage process with transparency issues; (2) static baselines with regards to criticality; (3) an overemphasis on ideology versus pragmatism; (4) a lack of differentiation between CRMs and strategic raw materials (SRMs); (5) a lack of foresight; and (6) a lack of consideration for extrinsic risks and system behaviour. Given these issues, we provide suggestions to improve the CRM assessment methodology and discuss the implications for the EU and the minerals industry. Subsequently, we extend our findings to Canada and South Africa, which are nations in the early stages of CRM framework creation. We find that Canada has more time to realize its CRM framework as compared to the EU, and that South Africa may be faced with a bifurcating reality of extra-national and national needs. Our findings also highlight serious geopolitical implications with the ensuing competition for resources likely resulting in the formation of economic blocs, clubs or cartels. Finally, improvements to the methodology resulting in more predictable outcomes would better incentivize the minerals industry to lower investment risk and ensure a smooth and pragmatic green energy transition

Quantifying the variability of a complex ore using geometallurgical domains

This comprehensive study focuses on the geometallurgical characterization of the complex Lappberget poly�metallic Zn-Pb-Ag-(Cu-Au) sulfide deposit at the Garpenberg mine, one of Sweden’s largest and most significant sources of zinc, lead, and silver. The research explores the intricate mineralogy and texture of the ore, investi�gating its impact on the variability of flotation performance for different ore types. QEMSCAN® analysis and element-to-mineral conversion (EMC) were employed to quantitatively characterize the ore in terms of mineral distribution and occurrence. The study revealed significant variability in Cu-Pb flotation compared to Zn flotation due to the targeted mineral varieties. While zinc primarily occurred in sphalerite grains, Cu-Pb flotation aimed to recover multiple Pb-, Cu-, Ag- and Au-bearing minerals that were finely grained and intricately intergrown with other sulfides. Grain size and the degree of liberation emerged as primary rate-limiting factors, especially in the Zn flotation circuit. Seven geometallurgical domains were defined based on the concentration efficiencies (i.e., selectivity and recovery) for sphalerite, galena, chalcopyrite, and Ag-bearing phases. The proposed geometallurgical characterization approach aims to transform geologically defined classes into geo�metallurgical domains by relating the deposit’s key mineralogical and textural characteristics to metallurgical performance

Modification of nano-clays with ionic liquids for the removal of Cd (II) ion from aqueous phase

The present study attempts to synthesize nano-modified clays of Na-bentonite (Bent) and montmorillonite (MT), using three imidazolium-based ionic liquids (ILs) including 3,3′-(hexyl)bis(3-methylimidazolium) bromide chloride ([H(mim)2[Br][Cl]), 1-hexyl-3-methylimidazolium chloride ([Hmim][Cl]) and 1-octyl-3-methylimidazolium chloride ([Omim][Cl]). X-ray diffraction (XRD), Fourier transformed infrared spectroscopy (FT-IR), carbon, hydrogen and nitrogen elemental analysis (CHN), scanning electron microscope (SEM) and specific surface area (SSA) (using N2-BET) techniques provided evidence of successful modification of the guest clays. Removal of Cd (II) from aqueous phase was investigated using the modified clays under different experimental conditions of reaction time, pH and adsorbent dosage. Detailed isotherms and kinetic studies showed that the modified clays have much higher Cd (II) adsorption capacity compared to those of the starting clay minerals. The maximum Cd (II) absorption capacities of 87.46 and 94.6 mg g−1 were observed in [H(mim)2]-MT and [H(mim)2]-Bent with d-values of 35.4 Å and 28.3 Å respectively. The [Omim]-clays had the highest adsorption affinities of Cd (II) in initial concentrations of Cd (II). This study shows that ILs could enhance the clay capacity and tendency for Cd (II) absorption with different trends based on the ILs structures. The modified clays using ILs are green and eco-friendly adsorbents and due to substantial increase in their capacity for the removal of heavy metals, they could have positive economic and environmental impacts

Eosinophilic Mucin Rhinosinusitis in Iranian Patients Undergoing Endoscopic Sinus Surgery

Introduction:  Eosinophilic mucin rhinosinusitis is a type of chronic rhinosinusitis (CRS). Diagnosis and treatment of this condition play a significant role in reducing the patients’ clinical symptoms. This type of rhinosinusitis has a higher relapse rate, compared to the other types. This disease is more resistant to treatment and more dependent on corticosteroid therapy, compared to the other types of rhinosinusitis. Regarding this, the present study was designed to evaluate the frequency of eosinophilic mucin rhinosinusitis in patients undergoing sinus surgery in a tertiary referral center and examine some clinical and laboratory characteristics regarding this type of rhinosinusitis.   Materials and Methods: This cross-sectional observational study was performed on patients over the age of 16 years, who were diagnosed with CRS in the otolaryngology clinic of a referral tertiary-level hospital, and were candidates for endoscopic sinus surgery. Based on the detection of eosinophilic mucin, the subjects were divided into two groups of eosinophilic mucin and non-eosinophilic mucin rhinosinusitis (controls). The groups were compared in terms of sino-nasal outcome test (SNOT-22) scores, Lund-Mackay staging scores, osteitis status, immunoglobulin E (IgE) level, and eosinophilia.   Results: In this study, 46 subjects participated, 29 (63%) cases of whom had eosinophilic mucin. The SNOT-22 score and serum IgE level were significantly higher in the eosinophilic mucin group, compared to those in the control group. Osteitis and Lund-Mackay scores were also higher in the eosinophilic mucin group than those in the control group; however, this difference was not statistically significant.    Conclusion: Patients with eosinophilic mucin rhinosinusitis showed a more severe clinical involvement. Seemingly, the Iranian patients have a lower and higher frequency of eosinophilic mucin rhinosinusitis, compared to the patients from the Western countries and East Asia, respectively

The current state and future directions of percolation leaching in the Chinese mining industry : challenges and opportunities

China is one of the most rapidly growing economies in the world and this growth is underpinned by growing demand for natural resources to meet base and precious metals and energy requirements. Even though China is currently the largest producer of several mined commodities, such as gold and the rare earth elements, meeting the future demands for metal consumption will require China to either develop new mining projects or increase material imports. In terms of nuclear energy requirements the country still depends on uranium imports. To meet this growth in Chinese demand, there has been a strong interest in technologies suited for mining and processing of low grade ore bodies. Percolation leaching methods have been very effective in extracting metals from low grade ores, which could not otherwise be economically extracted. Percolation leaching techniques, such as heap leaching, dump leaching, bio-leaching and in-situ leaching have been extensively employed in the Chinese mining industry in recent decades, primarily to extract gold, copper, rare earth elements and uranium. This paper discusses the application of various percolation leaching techniques in the Chinese mining industry and offers a scientific and extensive literature overview on technological developments in commercial percolation leaching operations in China. It also presents the current challenges of percolation leaching and recent technological and research developments and regulatory frameworks pertaining to the application of percolation leaching in China. The future directions of percolation leaching in the Chinese mining industry will also be presented to extract the low grade natural resources both economically and in an environmentally sustainable manner