Papers by Dimitrios Panias
The minerals, metals & materials series, 2024
Proceedings of the 3rd World Congress on Mechanical, Chemical, and Material Engineering, Jul 31, 2023
This paper investigates the recovery of gallium from the aluminate solution of Bayer process (Bay... more This paper investigates the recovery of gallium from the aluminate solution of Bayer process (Bayer liquors), using a synthetic chelating resin. Gallium is extensively used in modern electronics and strategic energy technologies [1, 2]. Today, almost 95% of the global gallium production is used in semiconductor applications, although new uses for the metal in high-tech alloys and energy technologies are constantly being discovered. The strategic importance of gallium in low-carbon technologies makes it critical to the global economy. For the Europe economy, it is considered a highly important raw material of high supply-risk and therefore, it is included in the EU list of Critical Raw Material (CRM), since 2011. The minerals of gallium are rare and of no significant economic importance to serve as primary sources of the element or its compounds. They are present usually in trace amounts in the aluminum, zinc and iron ores. Generally, gallium is produced as by-product of these ores processing or from other secondary resources, like as fly ash and electronic waste. It is estimated that about 90% of the primary gallium worldwide is produced from the aluminate solution obtained in Bayer process used for the production of alumina from bauxite [3]. The gallium content in Bayer liquor is low (about 200 ppm), making ion-exchange the most efficient method to be industrially applied for its recovery [4]. In this work, the recovery of gallium from the Bayer liquor was studied, using a commercial chelating resin based on the amidoxime functional group, the Puromet MTS9701 (Purolite Ltd., UK). The resin's capacity and selectivity and the kinetics of gallium recovery were experimentally investigated, while an attempt to understand the process mechanism and the factors affecting the process efficiency was also made. The process equilibrium was investigated according to Langmuir and Freudlich isotherms, while its kinetics was analyzed using the pseudo first-and second-order empirical models. Moreover, the regeneration process of resin was investigated with acidic and basic solutions and its performance in sequential cycles' operation was evaluated. According to the experimental results, the Freudlich isotherm and the pseudo second-order kinetic model were proved more accurate to describe the equilibrium and kinetics, respectively, of gallium loading on the chelating resin used. The ratio of resin to solution was the most important factor of process efficiency. Equilibrium was reached after 5 h, when more than 75% of gallium was selectively extracted from the Bayer liquor, using a resin to solution ratio equal to 50 g/L. The maximum extraction of gallium was about 80%, after 24 h. The used resin was proved to be highly selective for gallium, which was thought to be bound on the nitrogen atom of amidoxime group. The in-depth understanding of the binding mechanism between amidoxime and gallium could result in designing a more efficient process for the recovery of gallium from Bayer liquors.
Journal of Membrane Science, Oct 1, 2016
In this work, tubular γ-alumina ultrafiltration membranes have been modified with a sodium algina... more In this work, tubular γ-alumina ultrafiltration membranes have been modified with a sodium alginate/α-alumina suspension based on a modified polyol process in order to be used as forced flow membrane reactors. A C/Cu nanocomposite layer containing Cu nanoparticles of small and uniform size (ca. 14 nm) was deposited and stabilized on the external and internal surface of the membrane. The structural, morphological and gas permeance properties of the obtained catalytic membranes have been studied and their DeNO x performance has been evaluated in flow through mode of operation. NO catalytic abatement evaluation in flow through dead-end mode with 1% NO in N 2 fed from shell to lumen showed high efficiency even at low temperatures and reached 75% at 400°C. Steady state NO conversion efficiency reached about 30% at 400°C and heat treatment in He atmosphere at 440°C revealed the role of NO sorption onto the carbon dressing.
Hydrometallurgy, 2020
A combination of smelting-reduction of bauxite and leaching treatment of the produced slag for al... more A combination of smelting-reduction of bauxite and leaching treatment of the produced slag for alumina recovery is known as the Pedersen process. The process is considered to be more sustainable for producing metallurgical-grade alumina than the Bayer process as it does not produce bauxite residue (red mud), which is one of the most abundant industrial byproducts in the world. In this work, the leachability of a ternary CaO-Al 2 O 3-SiO 2 slag produced from smelting-reduction of low-grade bauxite has been studied. The obtained calcium aluminate-slag consists of Ca 12 Al 14 O 33 and CaAl 2 O 4 phases with minor amounts of complex oxide phases. A leaching series have been carried out at different temperatures, Na 2 O (carbonate) :Na 2 O (caustic) concentration ratios. The composition of solids and leaching liquors were analyzed for measuring the recovery of the aluminum and silicon. The results show that the highest aluminum extraction extent in the current study is 46.7%, which is achieved at a temperature of 75°C, 1 atm, in 60 g/L Na 2 O (carbonate) solution, in 30 min of leaching time. A passive calcium-containing layer at the slag's surface acts as a mass transfer barrier for the reactants and products of the leaching reactions, making their diffusion the rate-limiting step. A high concentration of Na 2 O (caustic) may decrease the aluminum extraction of the slag as a result of insufficient carbonate anions in the system, where the dissolved aluminum reacts with the calcium cations and produce 3CaO•Al 2 O 3 •6H 2 O phase.
CRC Press eBooks, Apr 17, 2019
The Mytilineos Metallurgy Business Unit, former Aluminium of Greece (AoG), is one of the few vert... more The Mytilineos Metallurgy Business Unit, former Aluminium of Greece (AoG), is one of the few vertically integrated alumina and aluminium plants in the world, exploiting mainly Greek bauxite ores. Since 1991, AoG has been actively pursuing new and sustainable ways not only to safely store Bauxite Residue (BR) but also to valorise it as a secondary raw material resource. In this paper, the handling practice of filter-pressing the BR for dry disposal is presented, along with the major research results for BR valorisation produced the last decades in cooperation with NTUA, KU Leuven and other universities. Aspects of policy and legal framework, as well as process economics are also presented herein in light of formulating a pragmatic strategy for achieving a zero waste alumina production process.
Zenodo (CERN European Organization for Nuclear Research), Feb 3, 2023
Primary iron metallurgy is characterised by significant direct carbon dioxide emissions, due to t... more Primary iron metallurgy is characterised by significant direct carbon dioxide emissions, due to the carbothermic reduction of the iron ore. This paper deals with the electrification of primary iron production by developing a new and innovative process for the carbon-free production of metallic iron from bauxite residue which is a byproduct of the alumina industry. It is based on the electroreduction of iron oxides from bauxite residue suspensions in concentrated sodium hydroxide solutions, at low temperature and normal pressure. The iron oxide source used in the present study is bauxite residue provided by MYTILINEOS SA, Metallurgy Business Unit-Aluminium of Greece. The research study is a preliminary screening of bauxite residue as a potential raw material for iron production by performing experiments in a small-scale electrolysis cell. The first results presented here show that iron can be produced by the reduction of iron oxides in bauxite residue with high Faradaic efficiency (>70%). Although significant optimisation is needed, the novel process shows great promise.
Journal of Sustainable Metallurgy, Nov 28, 2016
A new concept for a holistic exploitation of the bauxite residue (BR) is presented, where a multi... more A new concept for a holistic exploitation of the bauxite residue (BR) is presented, where a multitude of niche and bulk application products are produced, leading to a near zero-waste, financially viable, and environmentally benign process. Based on the combination of recent research results, the ''Mud2Metal'' conceptual flow sheet was developed in order to produce added value products rationalizing BR sustainable valorization. The Mud2Metal flow sheet is analyzed technologically, environmentally, and economically, addressing the challenges and the effects of each processing step, for the case of the Greek BR. The Mud2Metal flow sheet is focused on the selective removal of rare earth elements, the subsequent production of pig iron for the iron and steel industry, and the valorization of the residual slag's engineered mineral matrix into a variety of building materials. Based on further technological innovation and flow sheet integration/optimization, the plant operation could become economically profitable for the alumina industry, environmentally benign, and socially acceptable; in one word: sustainable. Keywords Bauxite residue Á Red mud Á Zero-waste Á REE Á Scandium Á Slag valorization Á Iron
2015-Sustainable Industrial Processing Summit & Exhibition, Dec 15, 2015
Waste and Biomass Valorization, Apr 10, 2019
In this paper, the development of fire-resistant geopolymers for the passive fire protection of b... more In this paper, the development of fire-resistant geopolymers for the passive fire protection of buildings is investigated. The fire-resistant geopolymeric materials were based on the alkali activation of a metallurgical slag produced in primary copper industry with a highly alkaline solution of potassium hydroxide. In order to decrease the density of the developed geopolymers, their foaming or the addition of lightweight aggregates was also studied. The physical, mechanical and thermal properties of the developed materials were determined and their performance upon exposure to fire was tested according to the ISO-834 standard time-temperature curve, which is considered as appropriate for testing fire protection systems employed in buildings. During the whole test of the materials performance against fire, the temperature at the interface between concrete and geopolymer was recorded below 180 °C, as required by the ISO test followed, proving effectiveness for the developed materials to be used as a thermal barrier in buildings and constructions. After testing, the geopolymers kept their structural integrity, without presenting any significant macroscopic damage.
Materials and Manufacturing Processes, Dec 16, 2014
Today, the primary aluminum production is based on two processes: (a) the Bayer process and (b) t... more Today, the primary aluminum production is based on two processes: (a) the Bayer process and (b) the Hall–Heroult process. Both processes deal with several economic and environmental drawbacks. The production of aluminum is an energy intensive process, consuming 53–61 GJ/t of aluminum, while huge amount of red mud and gaseous emissions are inevitably produced through the whole process. The utilization of a new family of solvents called ionic liquids (ILs) in the primary aluminum production is the subject of this paper, which examines the possibility of dissolving metallurgical alumina, hydrated alumina, and bauxites in 1-ethyl-3-methyl-imidazolium hydrogen sulfate ([Emim]HSO4). The results show that hydrated alumina can be dissolved relatively easily at 210°C, forming a melt that contains 9% w/w of dissolved alumina, which is higher than the alumina content in Hall–Heroult melts. Bauxites can also be directly dissolved in this IL with iron presenting higher dissolution than aluminum, while silicon dissolution is negligible.
Journal of Materials Science, May 11, 2010
Polycondensation in alkali silicate solutions comprises a fundamental process of the geopolymeriz... more Polycondensation in alkali silicate solutions comprises a fundamental process of the geopolymerization technology. Previous works had shown that the hydrolytic stability of sodium silicate gels depends on the SiO2/Na2O ratio. Sodium silicate gels totally insoluble in water can be produced at SiO2/Na2O molar ratios higher than 4.4. This article aims at elucidating the effect of tetra-coordinated aluminum addition on the hydrolytic stability of sodium silicate gels. According to the results, the aluminum addition stabilizes the sodium silicate gels in an aqueous environment. A sodium silicate gel with SiO2/Na2O molar ratio 3.48, which is totally soluble in deionized water at ambient temperature, can be transformed to insoluble sodium hydroaluminosilicates with the addition of tetrahedral aluminum at Al/Si molar ratios higher than 0.08. In addition, this article studies the structure of prepared sodium hydroaluminosilicates and draws very useful conclusions for the geopolymerization technology.
Zenodo (CERN European Organization for Nuclear Research), Sep 28, 2020
Under the ULCOWIN and the SIDERWIN projects a novel process for carbon-free iron production has b... more Under the ULCOWIN and the SIDERWIN projects a novel process for carbon-free iron production has been developed. Iron ore is reduced to metallic iron through electrolysis in aqueous alkaline solutions. This research paper investigates the use of Bauxite Residue from the alumina industry, as an alternative raw material for iron production under the same technology. The process is investigated, in a high alkaline environment and under low temperature and ambient conditions. Several parameters, as well as their effect in the efficiency of the system, were examined at lab scale. Under the optimum combination of parameters studied iron production was achieved at current efficiencies exceeding 70%. Bauxite Residue has therefore the potential to be used as an alternative raw material in iron production through this novel sustainable process.
Minerals Engineering, 2009
This paper deals with the syn the sis of geo poly mers uti liz ing fer ro nick el slag as raw mat... more This paper deals with the syn the sis of geo poly mers uti liz ing fer ro nick el slag as raw mate rial. The uti lized slag is pro duced in the Greek plant LARCO dur ing the pyro met al lur gi cal treat ment of late rites for the pro duc tion of fer ro nick el, spe cifi cally at the step of the reduc tive smelt ing in elec tric arc fur naces. The per formed work includes the opti mi za tion of the slag-based geo poly mer ic sys tem through the study of the effect of the syn the sis param e ters on the mechan i cal prop er ties of the pro duced mate ri als. The structure of geo poly mers was deter mined with X-ray dif frac tom e try (XRD), Fou rier-trans form infra red (FTIR) spec tros copy and scan ning elec tron micros copy (SEM). The obtained results showed that the fer ro nick el slag is an excel lent raw mate rial for the pro duc tion of inor ganic poly mers using the geo po ly mer iza tion tech nol ogy. The mate ri als pro duced under the opti mum syn the sis con di tions were com pact and rigid and pre sented high com pres sive strength (118 MPa), as well as extremely low water absorp tion (0.7-0.8%).
Journal of Materials Science, Jul 1, 2009
Geopolymerization is an innovative technology that can transform several solid aluminosilicate ma... more Geopolymerization is an innovative technology that can transform several solid aluminosilicate materials into useful products called geopolymers or inorganic polymers. Although the geopolymerization mechanism is not well understood, the most proposed mechanism includes four parallel stages: (a) dissolution of solid aluminosilicate materials in alkaline sodium silicate solution, (b) oligomerization of Si and/or Si–Al in aqueous phase, (c) polymerization of the oligomeric species, and (d) bonding of undissolved solid particles in the polymer. It is obvious that polymerization in sodium silicate solutions comprises a fundamental process in geopolymerization technology. Therefore, this article aims at studying experimentally the polymerization stage in synthetic pure sodium silicate solutions. The structure of sodium silicate gels as a function of the SiO2/Na2O molar ratio is examined and their hardness as well as hydrolytic stability are determined. In addition, the effect of aluminum incorporation in the hydrolytic stability of these gels is also examined. Finally, the structure of sodium silicate and aluminosilicate gels is correlated to the measured properties drawing very useful conclusions that could be applied on geopolymerization technology.
Johnson Matthey Technology Review, Jul 1, 2021
The primary iron metallurgy is characterized by significant direct CO2 emissions, due to the carb... more The primary iron metallurgy is characterized by significant direct CO2 emissions, due to the carbothermic reduction of the iron ore. This paper deals with the electrification of primary iron production by developing a new and innovative process for the carbon-free production of metallic iron from Bauxite Residue (BR) which is a by-product of the alumina industry. It is based on the electroreduction of iron oxides from BR suspensions in concentrated sodium hydroxide solutions, at low temperature and normal pressure. The iron oxide source, used in the present study is bauxite residue provided by Mytilineos S.A., Metallurgy Business Unit-Aluminium of Greece. The research study is a preliminary screening of BR as a potential raw material for iron production by performing experiments in a small-scale electrolysis cell. The first results presented here, show that iron can be produced by the reduction of iron oxides in the bauxite residue with high Faradaic efficiency (>70%). Although significant optimization is needed, the novel process shows great promise.
Proceedings of the 3rd World Congress on Mechanical, Chemical, and Material Engineering, Jun 1, 2017
The increase of aluminium demand globally, raises the interest of developing alternative technolo... more The increase of aluminium demand globally, raises the interest of developing alternative technologies to produce alumina from non-bauxitic sources, especially clays. This paper studies the extraction of aluminium from kaolin through leaching process, using aqueous solutions of acids and bases, as leaching agents. For this study, crude kaolin excavated in Milos Island, Greece, was used. Before leaching, crude kaolin was calcined; calcination achieves the dehydroxylation of kaolinite, which is the main mineralogical phase of kaolin and its transformation to metakaolin, an amorphous Al-Si phase from which aluminium is easily leached. Calcination of the crude kaolin used in this work was taken place at 850 o C for 2 h, given that these conditions revealed as optimum in the relevant experimental investigation. Leaching of aluminium from the calcined kaolin was performed with aqueous solutions of mineral acids (HCl, HNO 3 and H 2 SO 4), organic acids (C 2 H 2 O 4 , C 2 H 4 O 2 and C 6 H 8 O 7) and bases (NaOH, KOH and NH 4 OH). All leaching experiments were performed under constant conditions, regardless the leaching agent used. According to the experimental results, acids were proved more effective in aluminium extraction, than bases. However, aluminum extraction was accompanied by simultaneous extraction of Si which comprises an important impurity for the production of alumina from the pregnant liquor. Based on this consideration, oxalic acid was revealed as the most effective leaching agent, yielding more than 75% extraction of Al and less than 5% Si extraction.
Hydrometallurgy, May 1, 2009
... a pre-treatment prior to use of the concentrates is needed, in order to substantially decreas... more ... a pre-treatment prior to use of the concentrates is needed, in order to substantially decrease the silica ... (3). SiO 2 (s) + NaOH (aq) + H 2 ... Therefore, the dissolved silicon in the sodium hydroxide solution reprecipitates in the presence of dissolved aluminum during bauxite digestion ...
Colloids and Surfaces A: Physicochemical and Engineering Aspects, Jul 1, 2007
In this paper the effect of the water, sodium hydroxide and sodium silicate contents in the synth... more In this paper the effect of the water, sodium hydroxide and sodium silicate contents in the synthesis of fly ash-based geopolymers on their compressive strength is investigated. X-ray diffractograms of geopolymers indicated the existence of the major crystalline phases of fly ash, as well as the formation of a new amorphous phase in the geopolymeric matrices. Fourier-transform infrared (FTIR) spectroscopy analysis revealed essential fly ash phase transformations within geopolymers that affected their mechanical strength. Compressive strength of the produced geopolymers is correlated with the role that the investigated parameters play in the geopolymerization process. The compressive strength is increased with the decrease of water content, as well as with the increase of sodium silicate in the synthesis of geopolymers. Concerning the sodium hydroxide content in the geopolymers synthesis compressive strength is observed to being optimized for a sodium hydroxide concentration in the aqueous phase equal to 6.6 M. In general, a compromise among the investigated parameters might lead to geopolymeric materials with a compressive strength higher than 40 MPa.
Bhm Berg- Und Hüttenmännische Monatshefte, Jun 19, 2017
Rare Earth Elements (REE) are essential in the day to day life both in developed and developing c... more Rare Earth Elements (REE) are essential in the day to day life both in developed and developing countries worldwide. Due to their catalytic, magnetic, electrical, chemical, heat resistance, and optical properties, they are used in a wide range of high-tech, high value-added, and fast-growing sectors. The current state-of-the-art processes for REE extraction follows complicated, energy and resource intensive technologies, including a beneficiation stage for the production of a RE-rich concentrate, leaching/purification/separation into individual high purity RE solutions, precipitation as individual RE compounds, and finally production of RE metals or alloys through metallothermic reduction or fused-salt electrowinning. Currently, China is the main REE market player, dominating production, demand, and exports. Novel, cost-effective, and resource-efficient REE extraction processes are currently under development tailored specifically for European REE primary and secondary deposits and for European health, safety, and environmental standards, under the EURARE project. This paper analyses the currently used processing technologies for REE production, identifies problems and technical challenges associated with them, and examines the prospects of establishing novel technologies for an efficient and economically viable REE production from European REE deposits. The results are presented on a promising new technology for extracting REE from secondary resources using ionic liquids. REE extraction yield of 60–80% with respective Fe extraction less than 3% has been already achieved.ZusammenfassungSeltene Erden (SE) sind im täglichen Leben sowohl in den Industrieländern als auch in den Entwicklungsländern weltweit wichtig. Aufgrund ihrer katalytischen, magnetischen, elektrischen, chemischen, hitzebeständigen und optischen Eigenschaften werden sie in einer breiten Palette von Hightech‑, Hochwert- und schnell wachsenden Sektoren eingesetzt. Die neuesten Prozesse für die SE-Extraktion folgen komplizierten, energie- und ressourcenintensiven Technologien, einschließlich einer Veredelungssstufe für die Produktion eines SE-reichen Konzentrats, Auslaugung/Reinigung/Trennung in einzelne hochreine SE-Lösungen, Niederschlag als einzelne SE-Verbindungen und schließlich die Produktion von SE-Metallen oder Legierungen durch metallotherme Reduktion oder Salzschmelzflusselektrolyse. Derzeit ist China der wichtigste Akteur am SE-Markt, der die Produktion, die Nachfrage und den Export dominiert. Neue, kostengünstige und ressourceneffiziente SE-Extraktionsprozesse werden derzeit im Rahmen des EURARE-Projekts speziell für die europäischen SE-Primär- und Sekundärlagerstätten und für europäische Gesundheits‑, Sicherheits- und Umweltstandards entwickelt. Dieser Beitrag analysiert die aktuell eingesetzten Verarbeitungstechnologien für die SE-Produktion, identifiziert Probleme und technische Herausforderungen, die mit ihnen verbunden sind, und untersucht die Perspektiven, um neue Technologien für eine effiziente und wirtschaftlich lebensfähige SE-Produktion aus europäischen SE-Deponien zu etablieren. Die Ergebnisse einer vielversprechenden neuen Technologie zur Extraktion von SE aus sekundären Ressourcen mit ionischen Flüssigkeiten werden präsentiert. Eine REE-Extraktionsausbeute von 60–80 % bei einer entsprechenden Fe-Extraktion von weniger als 3 % wurde bereits erreicht.
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Papers by Dimitrios Panias