Slags phase equilibria

Matte-slag-gas reactions in Cu-Fe-Ni sulphide ores. Sulphide ores are a major source of Cu, Ni and precious metals. A basic principle of the extraction processes is to blow air into the molten sulphide in order to oxidise (1) S, which forms a gas and (2) Fe, which forms predominantly FeO and then partitions to a slag phase which covers the matte. A key element in the recovery of the metals is the solidification of the matte which separates into a sulphur-rich matte and metal-rich liquid. This process may occur under non-equilibrium conditions with precious metals concentrating in the last metallic liquid. 

For slags exhibiting a transition in behavior, the transition temperature could usually be associated with a ternary eutectic temperature in the phase equilibrium diagram for the most closely related ternary system. 

As in the history of other ceramics, the great progress in refractories was partly due to developments in scientific understanding and the use of new characterization methods. Development of phase equilibrium diagrams and the use of X-ray diffraction and light microscopy increased the understanding of the action of slags and fluxes on refractories, and also of the effect of composition on the properties of the refractories. 

If significant slag forming components are present, such as in residue smelting, a separate slag phase will form in equilibrium with the matte. The NajO activity coefficient in slag is low compared... 

The iron-carbon solid alloy which results from the solidification of non blastfurnace metal is saturated with carbon at the metal-slag temperature of about 2000 K, which is subsequendy refined by the oxidation of carbon to produce steel containing less than 1 wt% carbon, die level depending on the application. The first solid phases to separate from liquid steel at the eutectic temperature, 1408 K, are the (f.c.c) y-phase Austenite together with cementite, Fe3C, which has an orthorhombic sttiicture, and not die dieniiodynamically stable carbon phase which is to be expected from die equilibrium diagram. Cementite is thermodynamically unstable with respect to decomposition to h on and carbon from room temperature up to 1130 K... 

Al, respectively, and (----) represent phase transitions in the silicon in equilibrium with the SiCF—CaO—A C slag. The numbers represent values in wt... 

In a steel refining process, molten steel eventually comes into equilibrium with slag and gas phases coexisting in the furnace. The furnace can be considered as a closed system. The species identified in each phase are given in the following ... 

Dining manufacturing of cement-based pipeline products, the silicates and alumi-nates present in the cement react with water to form products of hydration and, in time, these set to a hard mass. The various solid phases formed come into thermodynamic equilibrium with the interstitial water (pore water), which is rich in calcium, sodium, and potassium hydroxide phases. The presence of these hydroxides raises the pH of the pore water solution to about 13 or 13.5. Table 4.15 gives typical compositions of pore solution for two types of cement Portland and blast furnace slag cement. 

The equilibrium phases and phase eompositions in dependence of the refractory/slag ratio have been determined. For this purpose a variable has been introduced which is defined by the mass ratio of the refractory material to the total mass of refractory plus slag. = 0 represents the composition of the slag with no contact to the refractory material and = 100 represents the composition of the refractory material with no slag contact. 

Known reaction thermoc ramics and kinetics show the oxidizer distribution between alloy corrponents at the contact of liquid phases and the external diffusion process are conditioned by the sulphate concentrations in the surface layer of rretal melt and the equilibrium constants for interactions of metals with sulphate. In such cases the oxidation of liquid alloys enables the selective concentration of a target corrponent in one of the phases - slag or alloy. In particular, it has been found experimentally that in processing of iron-tin-arsenic rrelts by sodium and calcium sulphates the rate of oxidation of iron allowed the concentration up to 90% Sn and up to 90% As in alloy with the loss of not less than 60% Fe [3]. For short short... 

The equilibrium conditions for each reaction may be expressed in terms of the partial pressure ratios of CO to CO2 and are illustrated in Eigure 5.1. As a simplification this assumes solid-gas reactions with unit activity of the solid oxide reactants. If in the molten phase, such as PbO dissolved in slag, the activity will be much lower and the eqnihbrinm ratios for COiCOj will be correspondingly higher. For partial pressure ratios of one or above, covering the bulk of the reactions zones of the shaft. Figure 5.1 indicates that PbO reduction should proceed readily, ZnO can be reduced to zinc vapour above 800°C, and iron oxides will be reduced primarily to FeO. In Figure 5.1 the ZnO reduction equilibrium is shown for a zinc vapour partial pressure of 0.01 atmospheres or one per cent in the gas stream. Zinc partial pressure will vary widely however, this serves only to illustrate that zinc vapour will be present at partial pressures of this order. 

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