Special Issue "Selected Papers from the International Committee for Study of Bauxite, Alumina & Aluminium 2016"

A special issue of Metals (ISSN 2075-4701).

Deadline for manuscript submissions: 31 October 2017

Special Issue Editor

Guest Editor
Prof. Dr. Houshang Alamdari

Aluminium Research Centre - REGAL, Université Laval, Quebec City, QC, G1V 0A6, Canada
Website | E-Mail
Interests: Solid Mechanics ; Numerical Methods; Finite Element Method and XFEM; Thermo-electro-mechanical Contact; Multi-physic Modelling ; Thermodynamic of irreversible processes applied to porous medium; thermo-mechanical behaviour of refractory materials; Hall-Héroult process

Special Issue Information

Dear Colleagues,

Aluminum, with 50 Mt in annual production, is as an essential material in modern engineering designs. Due to its remarkable properties, e.g., lightness, ease of forming, and recyclability, it is considered as the flag-bearer for green designs in transportation, architectural, and structural applications. The production process of this metal is, however, not free of environmental and technological challenges. Alumina is refined by the Bayer process, followed by aluminum electrolysis using the Hall-Héroult process, making this chain process as one of the most energy-intensive ones, with considerable residues and GHG footprint. The industry is, thus, continuously looking for a way to increase process efficiency and decrease its environmental impact. Having this objective in mind, major producers, as well as scientists, gather once a year during the ICSOBA event (http://www.icsoba.org/) in order to share their preoccupations, challenges, and possible solutions. This Special Issue is set to publish selected works presented at this event, in order to share recent progress and new achievements in this emerging field with broader scientific and industrial communities.

Dr. Houshang Alamdari
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All papers will be peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Metals is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1000 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • bauxite
  • alumina
  • aluminium smelting
  • red-mud
  • energy efficiency
  • carbon anode
  • electrolysis
  • cryolite
  • petroleum coke
  • coal-tar pitch

Published Papers (10 papers)

View options order results:
result details:
Displaying articles 1-10
Export citation of selected articles as:

Research

Open AccessArticle Investigation of the Frozen Bath Layer under Cold Anodes
Metals 2017, 7(9), 374; doi:10.3390/met7090374
Received: 6 July 2017 / Revised: 16 August 2017 / Accepted: 4 September 2017 / Published: 15 September 2017
PDF Full-text (4578 KB) | HTML Full-text | XML Full-text
Abstract
Hall-Héroult cell stability is highly affected by anode changing operations. Upon the insertion of a cold anode in the cell, a layer of molten cryolite freezes under the anode. The thickness, microstructure, and chemical composition of this layer vary as a function of
[...] Read more.
Hall-Héroult cell stability is highly affected by anode changing operations. Upon the insertion of a cold anode in the cell, a layer of molten cryolite freezes under the anode. The thickness, microstructure, and chemical composition of this layer vary as a function of time and its location in the cell. To better understand the evolution of the frozen layer, mandatory for the validation of numerical models, a measurement campaign was conducted on the anodes having a few hours of operation in the cell. The macrostructure of the selected frozen bath samples has been investigated using computed tomography while scanning electron microscope (SEM) has been used to qualify its microstructure. An energy-dispersive X-ray spectroscope (EDS) coupled to the SEM has revealed the chemical content. The results showed not only very different macrostructures between samples, but also significantly heterogeneous structure within the same sample. Nevertheless, for all samples, there is a clear distinction between the frozen cryolite and alumina/dusting phases, with the latter surrounding the cryolite matrix. Full article
Figures

Open AccessArticle Electrical Resistivity Measurement of Carbon Anodes Using the Van der Pauw Method
Metals 2017, 7(9), 369; doi:10.3390/met7090369
Received: 27 July 2017 / Revised: 7 September 2017 / Accepted: 8 September 2017 / Published: 13 September 2017
PDF Full-text (6961 KB) | HTML Full-text | XML Full-text
Abstract
The electrical resistivity of carbon anodes is an important parameter in the overall efficiency of the aluminum smelting process. The aim of this work is to explore the Van der Pauw (VdP) method as an alternative technique to the standard method, which is
[...] Read more.
The electrical resistivity of carbon anodes is an important parameter in the overall efficiency of the aluminum smelting process. The aim of this work is to explore the Van der Pauw (VdP) method as an alternative technique to the standard method, which is commonly used in the aluminum industry, in order to characterize the electrical resistivity of carbon anodes and to assess the accuracy of the method. For this purpose, a cylindrical core is extracted from the top of the anodes. The electrical resistivity of the core samples is measured according to the ISO 11713 standard method. This method consists of applying a 1 A current along the revolution axis of the sample, and then measuring the voltage drop on its side, along the same direction. Theoretically, this technique appears to be satisfying, but cracks in the sample that are generated either during the anode production or while coring the sample may induce high variations in the measured signal. The VdP method, as presented in 1958 by L.J. Van der Pauw, enables the electrical resistivity of any plain sample with an arbitrary shape and low thickness to be measured, even in the presence of cracks. In this work, measurements were performed using both the standard method and the Van der Pauw method, on both flawless and cracked samples. Results provided by the VdP method appeared to be more reliable and repeatable. Furthermore, numerical simulations using the finite element method (FEM) were performed in order to assess the effect of the presence of cracks and their thicknesses on the accuracy of the VdP method. Full article
Figures

Figure 1

Open AccessArticle Inspection of Prebaked Carbon Anodes Using Multi-Spectral Acousto-Ultrasonic Excitation
Metals 2017, 7(8), 305; doi:10.3390/met7080305
Received: 15 June 2017 / Revised: 2 August 2017 / Accepted: 5 August 2017 / Published: 8 August 2017
PDF Full-text (5262 KB) | HTML Full-text | XML Full-text
Abstract
Reduction cell operation in primary aluminum production is strongly influenced by the properties of baked anodes. Producing consistent anode quality is more challenging nowadays due to the increasing variability of raw materials. Taking timely corrective actions to attenuate the impact of raw material
[...] Read more.
Reduction cell operation in primary aluminum production is strongly influenced by the properties of baked anodes. Producing consistent anode quality is more challenging nowadays due to the increasing variability of raw materials. Taking timely corrective actions to attenuate the impact of raw material fluctuations on anode quality is also difficult based on the core sampling and characterization scheme currently used by most anode manufacturers, because it is applied on a very small proportion of the anode production (about 1%), and long-time delays are required for lab characterization. The objective of this work is to develop rapid and non-destructive methods for the inspection of baked anodes. Previous work has established that sequential excitation of smaller parts collected from an industrial sized anode using acousto-ultrasonic signals at different frequencies allowed detecting and discriminating anode defects (pores and cracks). This was validated qualitatively using X-ray computed tomography. This work improves the method by using frequency-modulated excitation and building quantitative relationships between the acousto-ultrasonic signals and defects extracted from tomography images using Wavelet Transforms and Partial Least Squares (PLS) regression. The new excitation approach was found to provide similar or better inspection performance compared with sequential excitation, while requiring a shorter cycle time. Full article
Figures

Figure 1

Open AccessFeature PaperArticle Discrete Element Method Investigation of Bulk Density and Electrical Resistivity of Calcined Coke Mixes
Metals 2017, 7(5), 154; doi:10.3390/met7050154
Received: 17 January 2017 / Revised: 21 April 2017 / Accepted: 24 April 2017 / Published: 26 April 2017
PDF Full-text (3040 KB) | HTML Full-text | XML Full-text
Abstract
Packing density and electrical resistivity of particles assemblies are important factors for a variety of applications of granular materials. In the present work, a three-dimensional imaging technique is coupled with the discrete element method (DEM) to model anode grade calcined coke particles. Three-dimensional
[...] Read more.
Packing density and electrical resistivity of particles assemblies are important factors for a variety of applications of granular materials. In the present work, a three-dimensional imaging technique is coupled with the discrete element method (DEM) to model anode grade calcined coke particles. Three-dimensional DEM models of samples with different size distribution of particles were studied to obtain the inter-particle contact information. As the content of fine particles increased, a higher inter-particle contact density and smaller average contact radius was observed in the samples. Confronting the DEM data and experimental measurements of electrical resistivity showed the simultaneous effects of packing density and contact density. Samples with higher contact density and smaller contact radius in general held high electrical resistivities. However, if increasing the contact density does not modify contacts between large particles, this will have a positive effect on packing density, so a lower electrical resistivity was obtained. Full article
Figures

Figure 1

Open AccessArticle A Non-Destructive Technique for the On-Line Quality Control of Green and Baked Anodes †
Metals 2017, 7(4), 128; doi:10.3390/met7040128
Received: 13 February 2017 / Revised: 27 March 2017 / Accepted: 1 April 2017 / Published: 6 April 2017
PDF Full-text (4973 KB) | HTML Full-text | XML Full-text
Abstract
Carbon anodes play an important role in the electrolytic production of aluminum. They have a significant economic and environmental impact. Carbon anodes are made of dry aggregates, composed of petroleum coke, recycled rejects, and butts, bound by coal tar pitch. Due to several
[...] Read more.
Carbon anodes play an important role in the electrolytic production of aluminum. They have a significant economic and environmental impact. Carbon anodes are made of dry aggregates, composed of petroleum coke, recycled rejects, and butts, bound by coal tar pitch. Due to several factors, defects (cracks/pores) appear in anodes during the fabrication process, affecting their quality. It is thus essential to control the quality of anodes before their use in the electrolysis cell. Current practice for the quality evaluation (visual inspection, core analysis) gives limited information. As an alternative to this practice, electrical resistivity measurements can be used. Electrical resistivity is one of the key indicators for anode quality and its homogeneity. A simple and non-destructive method has been developed for the specific electrical resistivity measurement of anodes (SERMA) for on-line control of anode quality. Various tests have been carried out at both lab scale and industrial scale. In this study, the electrical resistivity distributions in the lab-scale anodes were measured and compared with those of the tomography analysis. The method is able to detect defective anodes even before the baking process. Full article
Figures

Figure 1

Open AccessArticle Evolution of Anode Porosity under Air Oxidation: The Unveiling of the Active Pore Size
Metals 2017, 7(3), 101; doi:10.3390/met7030101
Received: 18 January 2017 / Revised: 14 March 2017 / Accepted: 15 March 2017 / Published: 18 March 2017
PDF Full-text (2409 KB) | HTML Full-text | XML Full-text
Abstract
The carbon anode, used in aluminum electrolysis (Hall–Héroult process), is over-consumed by air oxidation and carboxy-reaction (with CO2). Several anode features may affect this over-consumption, such as impurity content, graphitization level and anode porosity features (e.g., porosity volume fraction or pore
[...] Read more.
The carbon anode, used in aluminum electrolysis (Hall–Héroult process), is over-consumed by air oxidation and carboxy-reaction (with CO2). Several anode features may affect this over-consumption, such as impurity content, graphitization level and anode porosity features (e.g., porosity volume fraction or pore size distribution). The two first parameters are basically related to the quality of raw materials and coke calcination conditions. Anode porosity is, however, greatly affected by anode manufacturing conditions, and is possible to be modified, to some extent, by adjusting the anode recipe and the processing parameters. This work aims to investigate the effect of anode porosity on its air reactivity. Baked anode samples were prepared in laboratory scale and then crushed into powder form (−4760 + 4000 µm). The recipe for anode preparation was similar to a typical industrial recipe, except that in the lab scale no butt particles were used in the recipe. Anode particles were then gasified at six different conversion levels (0, 5, 15, 25, 35 and 50 wt %) under air at 525 °C. The porosity was characterized in several pore size ranges, measured by nitrogen adsorption and mercury intrusion (0.0014–0.020, 0.002–0.025, 0.025–0.100, 0.1–40.0 and superior at 40 µm). The volume variation of each pore range, as a function of carbon conversion, was assessed and used to determine the size of the most active pores for air oxidation. The most active pore size was found to be the pores inferior at 40 µm before 15 wt % of gasification and pores superior at 40 µm between 15 and 50 wt % of carbon conversion. Limitation of pore size range could be used as an additional guideline, along with other targets such as high homogeneity and density, to set the optimum anode manufacturing parameters. Full article
Figures

Figure 1

Open AccessArticle Impact of the Solidification Rate on the Chemical Composition of Frozen Cryolite Bath
Metals 2017, 7(3), 97; doi:10.3390/met7030097
Received: 15 December 2016 / Revised: 6 March 2017 / Accepted: 10 March 2017 / Published: 16 March 2017
PDF Full-text (2381 KB) | HTML Full-text | XML Full-text
Abstract
Solidification of cryolite (Na3AlF6)-based bath takes place at different rates along the sideledge, and around alumina rafts and new anodes. The solidification rate has a significant impact on the structure and the chemical composition that determine the thermal conductivity and thus the thickness
[...] Read more.
Solidification of cryolite (Na3AlF6)-based bath takes place at different rates along the sideledge, and around alumina rafts and new anodes. The solidification rate has a significant impact on the structure and the chemical composition that determine the thermal conductivity and thus the thickness of sideledge, or the duration of the existence of the temporary frozen bath layers in other cases. Unfortunately, samples that can be collected in industrial cells are formed under unknown, spatially and temporally varying conditions. For this reason, frozen bath samples were created under different heat flux conditions in a well-controlled laboratory environment using the so-called cold finger technique. The samples were analyzed by X-ray Diffractometer (XRD) and Scanning Electron Microscope (SEM) in Back Scattering (BS) mode in order to obtain spatial distribution of chemical composition. Results were correlated with structural analysis. XRD confirmed our earlier hypothesis of recrystallization of cryolite to chiolite under medium heat flux regime. Lower α-alumina, and higher γ-alumina content in the samples obtained with very high heating rate suggest that fast cooling reduces α–γ conversion. In accordance with the expectation, SEM-BS revealed significant variation of the Na/Al ratio in the transient sample. Full article
Figures

Figure 1

Open AccessArticle Effects of Charcoal Addition on the Properties of Carbon Anodes
Metals 2017, 7(3), 98; doi:10.3390/met7030098
Received: 26 January 2017 / Revised: 10 March 2017 / Accepted: 13 March 2017 / Published: 16 March 2017
PDF Full-text (1960 KB) | HTML Full-text | XML Full-text
Abstract
Wood charcoal is an attractive alternative to petroleum coke in production of carbon anodes for the aluminum smelting process. Calcined petroleum coke is the major component in the anode recipe and its consumption results in a direct greenhouse gas (GHG) footprint for the
[...] Read more.
Wood charcoal is an attractive alternative to petroleum coke in production of carbon anodes for the aluminum smelting process. Calcined petroleum coke is the major component in the anode recipe and its consumption results in a direct greenhouse gas (GHG) footprint for the industry. Charcoal, on the other hand, is considered as a green and abundant source of sulfur-free carbon. However, its amorphous carbon structure and high contents of alkali and alkaline earth metals (e.g., Na and Ca) make charcoal highly reactive to air and CO2. Acid washing and heat treatment were employed in order to reduce the reactivity of charcoal. The pre-treated charcoal was used to substitute up to 10% of coke in the anode recipe in an attempt to investigate the effect of this substitution on final anode properties. The results showed deterioration in the anode properties by increasing the charcoal content. However, by adjusting the anode recipe, this negative effect can be considerably mitigated. Increasing the pitch content was found to be helpful to improve the physical properties of the anodes containing charcoal. Full article
Figures

Figure 1

Open AccessArticle Application of Boron Oxide as a Protective Surface Treatment to Decrease the Air Reactivity of Carbon Anodes
Metals 2017, 7(3), 79; doi:10.3390/met7030079
Received: 18 January 2017 / Revised: 13 February 2017 / Accepted: 28 February 2017 / Published: 3 March 2017
Cited by 1 | PDF Full-text (4306 KB) | HTML Full-text | XML Full-text
Abstract
The oxidation of a carbon anode with air and CO2 occurs during the electrolysis of alumina in Hall-Héroult cells, resulting in a significant overconsumption of carbon and dusting. Boron is well known to decrease the rate of this reaction for graphite. In
[...] Read more.
The oxidation of a carbon anode with air and CO2 occurs during the electrolysis of alumina in Hall-Héroult cells, resulting in a significant overconsumption of carbon and dusting. Boron is well known to decrease the rate of this reaction for graphite. In this work, the application of boron oxide has been investigated to evaluate its inhibition effect on the air oxidation reaction, and to provide an effective protection for anodes. Different methods of impregnation coating have been explored. Impregnated anode samples were gasified under air at 525 °C according to the standard measurement methods. X-ray tomography was used to obtain the microstructural information of the samples before and after air-burning tests. The impregnated samples showed a very low oxidation reaction rate and dust generation. Full article
Figures

Figure 1

Open AccessArticle The Effect of Varying Mixing Temperatures and Baking Level on the Quality of Pilot Scale Anodes—A Factorial Design Analysis
Metals 2017, 7(3), 74; doi:10.3390/met7030074
Received: 20 December 2016 / Revised: 7 February 2017 / Accepted: 13 February 2017 / Published: 25 February 2017
PDF Full-text (2731 KB) | HTML Full-text | XML Full-text
Abstract
Identifying optimum anode baking level and mixing temperature are important when producing high quality anodes. The effect of varying mixing temperature and baking level were investigated in terms of the resulting apparent anode density, specific electrical resistivity (SER), air permeability, coefficient of thermal
[...] Read more.
Identifying optimum anode baking level and mixing temperature are important when producing high quality anodes. The effect of varying mixing temperature and baking level were investigated in terms of the resulting apparent anode density, specific electrical resistivity (SER), air permeability, coefficient of thermal expansion (CTE), air reactivity, and CO2 reactivity. Six pilot-scale anodes were prepared at Hydro Aluminium using a single source petroleum coke and <2 mm coke fractions. A coal tar pitch was used with Mettler softening point of 119.1 °C. The aggregate was mixed at 150 °C or 210 °C and baked to a low, medium, or high baking level. A 22 full-factorial design analysis was performed to determine the response of the analyzed properties to the applied mixing and baking temperature. Apparent density, SER, and air permeability were found to be highly dependent on mixing temperature. Apparent density and SER were also slightly affected by baking level. CTE was found to be independent of both baking level and mixing temperature. Air reactivity was found to be mainly dependent on baking level, while CO2 reactivity was dependent on both mixing temperature and baking level. Full article
Figures

Figure 1

Journal Contact

MDPI AG
Metals Editorial Office
St. Alban-Anlage 66, 4052 Basel, Switzerland
E-Mail: 
Tel. +41 61 683 77 34
Fax: +41 61 302 89 18
Editorial Board
Contact Details Submit to Special Issue Edit a special issue Review for Metals
logo
loading...
Back to Top