Pyrometallurgy Innovation Centre (PYROSEARCH)

  • Effects of Al2O3, CaO and Cr2O3 on liquidus temperatures of Fe-Mg-Si-O slags

    Ilyushechkin, A.; Hayes, P. C.; Jak, E. (2015). Experimental studies have been carried out to determine phase equilibria in the Fe-Mg-Si-Al- Ca-Cr-O system in air and in reducing atmospheres. The univariant lines between spinel and tridymite primary phase fields, and between the pyroxene and tridymite primary phase fields in the Fe-Mg-Si-O system with and without CaO, Al2O3 and Cr2O3 addition have been determined. The measurements demonstrate clearly that the presence of Al2O3 and CaO in the system lowers the liquidus in the silica primary phase field. The study also confirms that lowering the oxygen potential in the system lowers the liquidus temperatures for Fe-Mg-Si-Al-Cr-Ca-O slags.

  • Phase equilibria studies of the "MnO"-Al2O3- SiO2 system in equilibrium with metallic alloy. Part 1: Development of the technique and determination of liquidus isotherms between 1423 K and 1523 K

    Haccuria, Elien; Hayes, Peter C.; Jak, Evgueni (2014). Phase equilibria in the "MnO"-AlO-SiO pseudo-ternary system in equilibrium with metallic alloy have been experimentally investigated in the temperature range from 1423 K to 1523 K. This study is a part of a broader research program on the phase equilibria in the AlO-CaO-LiO- "MnO"-SiO system, which is of importance to the slags used in a novel pyrometallurgical process for recycling of electric car batteries. The experimental procedures involve equilibration of high purity powder mixtures at high temperatures, rapid quenching, and accurate measurement of phase compositions using electron probe X-ray microanalysis, which allow the slag liquidus temperatures to be determined. This paper is part 1 of a series of two papers and focuses on the improvement of the experimental methodology. A number of elementary reactions taking place in the samples have been identified, including the formation of a tridymite ring around the alloy particles, manganese oxidation and manganese vaporization. This enabled relevant modifications to the experimental methodology to be introduced. The liquidus at 1423 K, 1473 K and 1523 K in the high silica area and the solid solubility data in the tridymite and rhodonite phases have been reported.

  • Further experimental investigation of freeze-lining/bath interface at steady-state conditions

    Fallah-Mehrjardi, Ata; Hayes, Peter; Jak, Evgueni (2014). In design of the freeze-lining deposits in high-temperature reaction systems, it has been widely assumed that the interface temperature between the deposit and bath at steady-state conditions, that is, when the deposit interface velocity is zero, is the liquidus of the bulk bath material. Current work provides conclusive evidence that the interface temperature can be lower than that of the bulk liquidus. The observations are consistent with a mechanism involving the nucleation and growth of solids on detached crystals in a subliquidus layer as this fluid material moves toward the stagnant deposit interface and the dissolution of these detached crystals as they are transported away from the interface by turbulent eddies. The temperature and position of the stable deposit/liquid interface are determined by the balance between the extent of crystallization on the detached crystals and mass transfer across the subliquidus layer from the bulk bath. A conceptual framework is developed to analyze the factors influencing the steady-state deposit/interface temperature and deposit thickness in chemical systems operating in a positive temperature gradient. The framework can be used to explain the experimental observations in a diverse range of chemical systems and conditions, including high-temperature melts and aqueous solutions, and to explain why the interface temperature under these conditions can be between Tliquidus and Tsolidus.

  • Understanding slag freeze linings

    Fallah-Mehrjardi, Ata; Hayes, Peter C.; Jak, Evgueni (2014). Slag freeze linings, the formation of protective deposit layers on the inner walls of furnaces and reactors, are increasingly used in industrial pyrometallurgical processes to ensure that furnace integrity is maintained in these aggressive, high-temperature environments. Most previous studies of freeze-linings have analyzed the formation of slag deposits based solely on heat transfer considerations. These thermal models have assumed that the interface between the stationary frozen layer and the agitated molten bath at steady-state deposit thickness consists of the primary phase, which stays in contact with the bulk liquid at the liquidus temperature. Recent experimental studies, however, have clearly demonstrated that the temperature of the deposit/liquid bath interface can be lower than the liquidus temperature of the bulk liquid. A conceptual framework has been proposed to explain the observations and the factors influencing the microstructure and the temperature of the interface at steady-state conditions. The observations are consistent with a dynamic steady state that is a balance between (I) the rate of nucleation and growth of solids on detached crystals in a subliquidus layer as this fluid material moves toward the stagnant deposit interface and (II) the dissolution of these detached crystals as they are transported away from the interface by turbulent eddies. It is argued that the assumption that the interface temperature is the liquidus of the bulk material represents only a limiting condition, and that the interface temperature can be between T and T depending on the process conditions and bath chemistry. These findings have implications for the modeling approach and boundary conditions required to accurately describe these systems. They also indicate the opportunity to integrate considerations of heat and mass flows with the selection of melt chemistries in the design of future high temperature industrial reactors.

  • Investigation of freeze-linings in aluminum production cells

    Fallah-Mehrjardi, Ata; Hayes, Peter C.; Jak, Evgueni (2014). The molten cryolite bath creates chemically a very aggressive environment in the Hall-Héroult cell, and thus, the formation of a protective solid layer (freeze-lining) on the cell wall is essential for the operation of the present cell designs. To provide further information on the formation of the freeze-lining deposit in this system, laboratory-based studies were undertaken using an air-cooled probe technique The effects of process conditions, i.e., time, bath agitation, and superheat on the microstructures, morphologies of the phases, and the phase assemblages adjacent to the deposit/bath interface were investigated. A detailed microstructural analysis of the steady-state deposits shows that a dense sealing primary-phase layer of cryolite solid solution was formed at the interface of the bath deposit for the process conditions examined. The formation of sealing primary-phase layer at the bath/deposit interface explicitly indicates that the deposit/liquid bath interface temperature is equal to that of the liquidus of the bulk bath. The experimentally investigated liquidus temperature and subliquidus equilibria differ significantly from those previously reported.

  • A synergistic hydro- and pyro-metallurgical process for low-energy copper production

    Hawker, William; Vaughan, James; Hayes, Peter; Jak, Evgueni; Keating, Tony; Hourn, Mike (2014).

  • Copper processing

    Hawker, William; Vaughan, James; Hayes, Peter; Jak, Evgueni (2014).

  • Investigation of the freeze-lining formed in an industrial copper converting calcium ferrite slag

    Fallah-Mehrjardi, Ata; Jansson, Jani; Taskinen, Pekka; Hayes, Peter C.; Jak, Evgueni (2014).

  • Investigation of freeze-linings in a nonferrous industrial slag

    Fallah-Mehrjardi, Ata; Hayes, Peter C.; Vervynckt, Stephanie; Jak, Evgueni (2014).

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