| Summary: | Current global estimates indicate that ca. 2400 million tonnes of iron is produced annually, most of which is used to make steel. Due to the associated costs, environmental challenges and energy consumption, steel is one of the world’s most intensively recycled materials. For example, about 98 % of structural steel is recycled in the USA. However, iron production is still increasing. Costs, prices and environmental demands have led to increased recycling, but also increased attention to the processes used to refine iron ores. This thesis focuses on the impact of variations in process waters on the refinement process at the Kiirunavaara mine, northern Sweden, and possible environmental implications.The water used to process iron ore is seldom considered in its full complexity, if at all. This could be problematic since it has been shown that ions in the water can affect key process steps, including dispersion, flotation, filtration and pelletization. To gain a better understanding of process water variations and their effect on refinement, process water at the Kiirunavaara plant was characterised by ultrafiltration, membrane filtration and ICP analyses, complemented with geochemical modelling. Leachings of the ore concentrate and Zeta potential measurements were performed to better understand process water influence on ore surfaces and different refinement steps effects on the ore surfaces in the refinement process. In addition, fine particles (< 5µm) were studied to obtain information about the unwanted fine particles in the ore concentrate. The findings indicate that Ca, S, Na and Cl are the dominant dissolved ions in the process water. The colloidal fractions of the major ions were < 3%. The main cause of variation in the major ions’ concentrations was probably dilution by rain and meltwater. The high concentrations of Ca and S probably originated from calcite buffering and sulphide oxidation in the drainage area, respectively, while the Na and Cl probably originated largely from fluid inclusions, and N ...
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