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Miettinen J.,Laboratory of Metallurgy | Gandova V.,Plovdiv University | Vassilev G.,Plovdiv University
Calphad: Computer Coupling of Phase Diagrams and Thermochemistry | Year: 2010

Thermodynamic description of the ternary CuPbZn system is presented. The adjustable parameters of the sub-systems, CuPb, CuZn and PbZn, are taken from earlier SGTE-based assessments and those of the ternary system are optimized in this work using the experimental zinc activity and phase equilibrium data. © 2010 Elsevier Ltd. All rights reserved. Source

Miettinen J.,Laboratory of Metallurgy | Docheva P.,University of Ruse | Vassilev G.,Plovdiv University
Calphad: Computer Coupling of Phase Diagrams and Thermochemistry | Year: 2010

A thermodynamic description of the ternary Cu-PbSn system at the Cu-Pb side is presented. The thermodynamic parameters of the sub-systems, Cu-Pb, CuSn and PbSn, are taken from earlier SGTE-based assessments and those of the ternary system are optimized in this study using ternary experimental lead activity and phase equilibrium data. The present ternary description is valid for tin contents up to 60 wt%. © 2010 Elsevier Ltd. All rights reserved. Source

Balomenos E.,Laboratory of Metallurgy | Panias D.,Laboratory of Metallurgy | Paspaliaris I.,Laboratory of Metallurgy | Friedrich B.,RWTH Aachen | And 7 more authors.
Proceedings - European Metallurgical Conference, EMC 2011 | Year: 2011

The Hall-Héroult process for the electrolytic reduction of alumina was developed at the end of the 19th century and is still currently the only industrial process for the production of aluminium. Today this process is ranked among the most energy and CO2 intensive industrial processes, consuming about 1 % of the globally produced electric energy and producing 2.5 % of the world's anthropogenetic GHG emissions. The direct carbothermic reduction of alumina has been proposed as an alternative process which can substantially improve the sustainability of primary aluminium production. Processes developed so far suffered from critical design issues, which resulted in low aluminium yields, primarily due to aluminium carbide and -oxycarbide formation and aluminium vaporization. Novel concepts currently being developed under the ENEXAL collaborative research project have the potential to overcome such problems by applying fundamental thermodynamic principles and innovative reactor designs. Thermochemical calculations predict that by carrying out the carbothermic reduction under vacuum, not only will the required reaction temperature be considerably lowered, but also the formation of gaseous Al should occur without the accompanying formation of Al2O, Al 4C3, and of Al-oxycarbides. Alternatively, liquid Al can be produced by a combination of high temperatures and high excess of carbon thereby again avoiding carbide and sub-oxide formation. The implementation of such carbothermic reduction processes in aluminium production could lead to energy savings of up to 21 %, GHG emissions reductions of up to 52 % and exergy efficiency increase of up to 10 percentile points. Additionally, the prospect of utilizing concentrated solar energy to provide process heat can render the primary aluminium production truly sustainable. This paper presents a thermodynamic study of the Al-C-O system, a short review on the alumina carbothermic processes developed so far and two novel carbothermic reductions concepts along with preliminary experimental results. Source

Kemper C.,RWTH Aachen | Friedrich B.,RWTH Aachen | Balomenos E.,Laboratory of Metallurgy | Panias D.,Laboratory of Metallurgy | Paspaliaris I.,Laboratory of Metallurgy
European Metallurgical Conference, EMC 2013 | Year: 2013

Many technological concepts for an alternative aluminium production process have been developed during the last century, because the still utilized Hall-Héroult process is one of the most energy and CO2 intensive industrial processes. However no basic approach was able to prevail in industrial scale. The most promising alternative process is still the carbothermic reduction of alumina, which has been investigated by several companies and researchers. The greatest challenges are the extensive aluminium volatilization occurring at high reaction temperatures, the complicated back-reaction and carbide formation mechanisms as well as critical reactor design issues. To lower the aluminium activity it is helpful to include a "carrier" metal like silicon into the reduction process. Co-reduction of the oxides reduces vaporization of both aluminium and silicon by forming an AlSi master alloy. A successful further development of such a carbothermic reduction process implicates a sustainable improvement in the primary aluminium production with significantly less energy consumption, reduced GHG emissions and lower investment costs. In previous investigations at IME, RWTH Aachen University, first experiments of creating an AlSi master alloy out of an oxide residue of Al-slag-treatment were conducted. The collaborative research project "ENEXAL" has resumed this idea, but with carbothermic reduction of technical pure raw materials. The present work presents the experimental validation in a small scale Lab-EAF (25 kW) of a previous performed theoretical thermodynamic study with Fact Sage 6.2 software. Different modes of operation, initial system compositions and reducing agents were considered as parameter for the investigation. To prove the quality of the AlSi-alloy chemical analysis were done as well as structure analysis. Over the course of the project an upscaling campaign in an existing 1MW pilot unit is scheduled. The full paper will be published soon after the conference in a scientific journal. Source

Boldyrev A.V.,Laboratory of Metallurgy | Balikov S.V.,Laboratory of Metallurgy | Bogorodskiy A.V.,Laboratory of Metallurgy | Emelyanov Yu.E.,Laboratory of Metallurgy
Tsvetnye Metally | Year: 2015

In recent years, gold mining industry has faced with significant changes in precious metals recovery from refractory ore or technogenic raw materials by direct cyanidation. These refractory ores include gold-pyrite and gold-arsenic ores and their concentrates, containing refractory gold. Their reserves make up a significant proportion, according to which, new prospective projects are constantly developed. This paper gives the results of POX of refractory gold-bearing concentrates using halide-ion as solvent for precious metals and activated carbon as adsorbent. It was found that gold did not recover to the solution when halide was added during POX. Silver was partially dissolved in the solution. When halogen-containing reagents and activated carbon were added during POX, gold was dissolved and loaded into the activated carbon. Sulfide oxidation degree was 99.3-99.6%. Gold recovery into granulated carbon was 94.7-94.8%, using chlorine-bearing solvents (NaCl, CaCl2 and carnalite); and 98-99% - using KI and KBr. This treatment process of refractory gold-bearing concentrates combines sulfide oxidation, dissolution and adsorption of precious metals. Metal recovery results obtained during this process can be compared with the recovery during POX-cyanidation. In this case, sodium cyanide is not used. This allows the reduction of capital and operational costs due to the absence of cyanidation, carbon-in-leach and detoxification of leaching tailing circuits. Source

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