| This research is the first systematic study of the interaction between smelter slag and aqueous sulphur dioxide (SO2(aq)). In Canada alone, over 2 million tonnes of smelter slags containing Co, Ni, and Cu are produced and stockpiled each year. Smelters also produce SO2, an air pollutant. The objectives of this research were to understand the characteristics of slag, the reaction of slag with SO2(aq), and to develop a novel method for extracting Co, Ni and Cu from slag using SO2(aq).; The properties of slags from different smelters were studied, with emphasis on the form of Co, Ni, Cu and Fe. Leaching experiments were carried out in a batch reactor. The parameters investigated included concentration of SO 2(aq), stirring speed, particle size, temperature, pH and O2 percentage.; The form of Co and Fe was primarily oxide (>90%), however, significant portions of Ni and Cu (30%–90%) in the slags were in the sulphide form. SO2(aq) alone, was effective in leaching Co and Fe from the slag. Ni extraction was lower due to its significant presence in the sulphide form. Cu was precipitated as Chevreul's salt. In the presence of O2, improved Cu and Ni extractions were obtained as the sulphide phases were attacked by Fe3+ generated in the system.; Thermodynamic modeling indicated that Fe precipitates as an Fe(II)-sulphite in the slag-SO2(aq) system. Fe(II)-SO32− and Fe(II)-HSO3− complexes were observed to control the solubility of the slag in SO2(aq). Experimental work on slag dissolution was found to correlate reasonably well with the thermodynamic modeling.; A new model was developed to quantify the acid and ligand effects of SO2(aq) dissolution of slag. The model was used to fit the leaching curves and good agreement was obtained. A new observation was made on the effect of particle size distribution on the modeling of fluid-solid reactions. It was discovered that for covariance (CV) values between 0.7 and 1.2, a chemical reaction controlled system erroneously follows the inert/ash layer diffusion equation if the particle size distribution is ignored in the shrinking core model. The slag-SO2(aq) system was chemical reaction controlled with activation energy of about 60 kJ/mol. |
