Optimum fluxing, smelting and leaching practices have been determined for maximising the recovery of alumina and soda, but not iron, from a slag produced by oxidative smelting of bauxite residue at 1400uC. The rate and extent of dissolution of alumina and soda increased in a water leach as the CaO/SiO 2 ratio in the slag was increased from 0?1 to 2 by the addition of calcium carbonate to the dried bauxite residue. A water leach at 60uC, extracted 55% of the Al and 90% of the Na at 20 wt-% solids and 50 and 75% respectively, at 50 wt-% solids. Liquors containing y43 g L 21 Al and Na were obtained from leaches at 50 wt-% solids. By recycling this liquor in two further leaches on fresh slag at 50 wt-% solids, levels of 130 g L 21 Al and 125 g L 21 Na in solution were achieved. At these concentrations of alumina and soda, it is expected that the leach liquor should be suitable for recycling to the Bayer process. The dissolution of the alumina and soda from the slag was shown to be due to the leaching of a sodium aluminium silicate phase considered to be a member of the sodium aluminate-carnegieite solid solution series with a composition of (Na,Ca) 22x (Al,Fe 3z ) 22x Si x O 4 (0?2(x(0?5). Quantitative analyses in an environmental SEM and the leaching results indicated that the solubility of this phase increased with a decrease in the silicon content of the phase as a result of addition of calcium carbonate to increase the CaO/SiO 2 ratio and form larnite (Ca 2 SiO 4 ).
The aim of this study was to determine the behaviour of vanadium in molten slag and carbon saturated iron alloys using a metal-slag-gas equilibration technique under controlled CO atmosphere at temperatures between 1400 and 1500°C. The results obtained show (1) saturation of the metal with vanadium carbide when vanadium content of the metal was greater than 2.4 wt%; (2) Distribution ratio of vanadium between slag and metal to be less than 0.01; (3) the deduced activity coefficient of VO 1.5 decreases with increasing concentration of vanadium in slag.
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