Pekka Taskinen

A thermodynamic analysis of the binary alloy systems Cu-Cr, Cu-Nb and Cu-V

Abstract Thermodynamic properties and the phase diagrams of the binary alloys Cu-Cr, Cu-Nb and Cu-V have been critically assessed by the Lukas program using simultaneously thermodynamic and phase diagram measurements. Thermodynamic measurements were available on chromium-copper alloys only. Thus the thermodynamic properties of the binaries copper-niobium and copper-vanadium were estimated by using entirely the phase diagram data. The excess Gibbs energies were expressed by Legendre polynomials. Distribution equilibria for solutes in the zone-melting of copper were utilized for adjusting the solid-liquid equilibria of the copper-rich alloys. The complete Gibbs energy expressions for the alloy phases were presented allowing calculation of the phase diagrams and the thermodynamic mixing properties of the phases.

An assessment of the thermodynamic properties and phase diagram of the system Bi-Cu

Abstract The solution thermodynamics and phase equilibria of bismuth-copper alloys at 400–1500 K have been critically analysed. The liquid alloy as well as the copper terminal solution were treated as substitutional alloy phases. Their excess Gibbs energies were fitted by RedlichKister polynomials and the optimization of their model parameters was carried out by using the Lukas program. The activities in the liquid alloy deviate positively from Raoults law, the limiting activity coefficients at the infinite dilution according to the assessment being ln fo[Bi]Cu = 3019 T(K)−1.04 and ln fo[Bi]Cu = 2716 T(K)−1.33 . The integral enthalpy of mixing is exothermic and nearly symmetric with a maximum at xCu = 0.52 with ΔH = 6050 J mol−1. The integral excess entropy of the molten alloy vs. composition was found to be symmetric with the maximum at ΔSEx = 2.5 J (mol K)−1.

State of the art in nickel smelting: direct Outokumpu nickel technology

Abstract Experience of the direct Outokumpu nickel (DON) smelting process gained over the first ten years of operation is reviewed, including the significant environmental impacts. In 1995, production capacity at Harjavalta was increased from 17 000 to 52 000 t/year, by introducing DON technology, additional refinery capacity being based on hydrogen pressure reduction, producing nickel powder and briquettes. In the DON process, high grade nickel matte of low iron content is produced in the flash smelting furnace directly without subsequent converting. The metal values in the smelting slag are recovered in an electric furnace as an iron containing Ni matte. The mattes produced differ from conventional nickel mattes in many respects, and therefore focused R&D was required to adapt to their melting points, fluidities and settling properties. The low melting points of the high grade nickel mattes produced in the DON furnace, particularly those low in copper, have challenged furnace design, in particular in the hearth and its thermal engineering. Other key issues of DON technology are smelting of high magnesia concentrates, and the recovery of nickel and copper, as well as those of platinum group metals and cobalt. These factors can be affected by proper selection of process concept and operational conditions in the processing vessels. Selected results of thermodynamic modelling of DON and electric furnace mattes and high magnesia slags are reviewed, with reference to the mattes produced. The design principles of the flash furnace and electric furnace are also discussed.

MTDATA and the Prediction of Phase Equilibria in Oxide Systems: 30 Years of Industrial Collaboration

This paper gives an introduction to MTDATA, Phase Equilibrium Software from the National Physical Laboratory (NPL), and describes the latest advances in the development of a comprehensive database of thermodynamic parameters to underpin calculations of phase equilibria in large oxide, sulfide, and fluoride systems of industrial interest. The database, MTOX, has been developed over a period of thirty years based upon modeling work at NPL and funded by industrial partners in a project co-ordinated by Mineral Industry Research Organisation. Applications drawn from the fields of modern copper scrap smelting, high-temperature behavior of basic oxygen steelmaking slags, flash smelting of nickel, electric furnace smelting of ilmenite, and production of pure TiO2via a low-temperature molten salt route are discussed along with calculations to assess the impact of impurities on the uncertainty of fixed points used to realize the SI unit of temperature, the kelvin.

Novel process concept for the production of H 2 and H 2 SO 4 by SO 2 -depolarized electrolysis

Outotec open cycle (OOC) is a new low-energy process linking together production of hydrogen and sulfuric acid. While sulfuric acid is the world’s most widely produced chemical by mass at approximately 200 Mt/a, the OOC gives the potential for making 4 Mt/a of hydrogen gas as a by-product. H2SO4 manufacture requires a source of sulfur dioxide. 30% of world production of H2SO4 is from the SO2 by-product of pyrometallurgical processing of sulfur containing concentrates of metals such as copper, nickel and zinc. SO2 can also be made by direct combustion of sulfur. In OOC, a divided electrochemical cell is used for SO2-depolarized electrolysis of water. SO2 is fed to the anolyte and converted to H2SO4, while hydrogen gas is produced at the cathode. On the industrial scale, the equipment will be in the form of a membrane electrolyzer assembly or stack. A case is described where the OOC would be connected to a pyrometallurgical plant smelting 1 Mt/a of nickel and copper concentrate, producing 1 Mt/a of H2SO4 and 20 kt/a of hydrogen.

The copper-lead phase diagram

Abstract The thermodynamic properties of solid and liquid copper-lead alloys at 25–1200°C have been critically analysed from the available literature sources. The excess Gibbs energies for the alloy phases have been optimised using least-squares methods by the Lukas program. The calculated phase diagram and a complete set of the excess Gibbs energy expressions are presented in addition to the limiting activity coefficients of the components at infinite dilution in the molten alloy.

Investigation of the Freeze-Lining Formed in an Industrial Copper Converting Calcium Ferrite Slag

Pyrometallurgical coppermaking processes are operated under intensive reaction conditions; high process temperatures and vigorous bath agitation is used to increase the kinetics of reactions and to achieve high smelter throughput. Slag freeze-lining reactor wall protection is a widely used technology in coppermaking processes, such as flash smelting and converting reactors. Freeze-linings mitigate and resist the effects of thermal and chemical attack by aggressive slags. In this laboratory-based study, a water-cooled probe “cold finger” technique has been used to investigate freeze-lining formation with calcium ferrite slags in equilibrium with metallic copper; the slag composition reflects that used in the industrial copper flash converting furnace of Rio Tinto—Kennecott Utah Copper. The effects of probe immersion times on the thickness and microstructures in the freeze-lining deposits have been investigated. A range of complex oxide solutions and copper-containing phases have been found in the deposits. The phase assemblages formed from the industrial calcium ferrite slag in the steady-state deposit are very complex and information on the phase equilibria of the multi-component systems with addition of minor elements may not be available. Subsolidus and subliquidus phase equilibria in the Cu-Ca-Fe-O system at metallic copper saturation along with interpolated temperature across the deposit, microstructural changes and compositional trends in the phases in the deposit have been used to understand the formation and characteristics of the phases in the steady-state freeze-lining. Also, it has been shown that under steady-state conditions a dense sealing layer consisting primarily of the spinel primary phase is formed at the deposit/liquid interface; however, the interface temperature is below the liquidus temperature. The findings of the study have potentially important implications for the operation of the converting furnace and the design of freeze linings in metallurgical systems.

Thermal behaviour of hydrous nickel–magnesium silicates when heating up to 750°C

Abstract The thermal decomposition sequence of hydrous nickel–magnesium silicates from Colombia and Brazil was studied under air/Ar atmosphere from room temperature up to 750°C by differential scanning calorimetry–thermogravimetry followed by X-ray diffraction and scanning electron microscopy analyses. Differential scanning calorimetry curves of the samples obtained showed three endothermic peaks at 100, 250 and 600°C due to the release of free water, the dissociation of goethite and the release of crystalline water respectively. To determine the mineral species and microtexture, the ores were studied by scanning electron microscopy. Scanning electron microscopy–energy dispersive spectroscopy analyses showed that the ores are rich in Mg and Mg–Fe silicates, Cr spinel, Mn oxide, goethite and silica and exhibit complex alteration texture. X-ray diffraction analyses of Colombia-2 and Mirabela (Brazil) after the experiments showed that the dehydroxylation produces an amorphous intermediate phase, which is supposed to be due to the exsolution of silica. However, Colombia-1 sample, which was confirmed to contain antigorite mineral, was observed to undergo dehydration and recrystallisation simultaneously.

Direct-to-blister smelting of copper concentrates: the slag fluxing chemistry

Abstract The fundamental feature of the flash smelting process is its capability to utilise the combustion energy of sulphidic raw materials, by conducting a carefully controlled roasting and subsequent smelting in a single furnace. Its furnace and equipment design is implemented so that the reaction enthalpy released in the suspension oxidation is fully used for melting the reactive and non-reactive particles of the feed mixture. Since the first industrial application in 1940s, flash smelting has been developed for other applications than copper matte smelting, including the oxygen enriched smelting, continuous converting to blister copper with low sulphur concentration, and direct-to-blister smelting. Along with actual evolution in the processing equipment, the basic metallurgy has been under careful evaluation and development. In spite of many favourable features of iron silicate slags, they become problematic in the direct-to-blister copper smelting environments, at oxygen partial pressures higher than in matte smelting. These conditions typically locate beyond thermodynamic stability range of the homogeneous, fully molten iron silicate slags, which are more or less fully degraded ‘internally’, precipitating their solid constituents, silica and/or magnetite.

Thermodynamic studies on arsenic-oxygen and selenium-oxygen interactions in molten copper

The effect of arsenic and selenium on the activity coefficient of oxygen in liquid copper at 1150° C was determined by electrochemical methods using oxygen concentration cells. Arsenic increases the activity coefficient of oxygen and selenium decreases it, the first-order interaction parameters being ϵAs0 = + 4.0 (±0.5), and ϵSe0 = −14.0 (±0.5). Temperature dependencies of the parameters were estimated by using earlier assessments in dilute copper-oxygen alloys.