Avskiljning av uran från dricksvatten med reaktiva filter

Abstract: Water is our most important provision and its quality is above all dependent on the geological conditions in the area from where it is extracted. Due to geological properties there are certain areas with an elevated risk of high uranium levels in the ground water, which in turn constitutes a risk for human health. Consumption of water that contains a high concentration of uranium implies a health risk due to the chemical characteristics of uranium. Livsmedelsverket (The National Food Administration) and Socialstyrelsen (The National Board of Health and Welfare) therefore recommend that precautionary measures should be taken when the uranium concentration in ground water exceeds 15 micrograms per litre. In particular, drinking water collected from wells in areas with uranium-rich bedrock may have a harmfully high level of uranium. One of the wells of the Ärla water purification plant, located near Eskilstuna, Sweden, contains water that exceeds the guideline of 15 micrograms per litre. One interesting technique for removing uranium from drinking water is adsorption to reactive filter materials. Reactive filters represent a kind of low-cost technology that is intended to utilise a minimum of energy and chemicals. The filters may have specific physical and chemical properties that make them suitable for removing unwanted substances from the water. The aim of this thesis was to investigate the potential of two different reactive filters for uranium removal, i.e. iron-oxide-coated olivine (IOCO) and an anion exchange resin (Purolite). The study included batch experiments with artificial water, from the Ärla water purification plant, and water from a stream near the Stripa mine, both sites having uranium levels higher than 15 micrograms per litre. The results that were obtained by using iron oxide coated olivine filters were further analysed using the chemical equilibrium model Visual Minteq 2.52. The model used was then optimised for uranium removal. The study also included a column experiment with the two filter materials, using water from the Ärla water purification plant. The goal was to provide a more realistic picture of how efficient the filters really were concerning uranium removal. Results from the batch and column experiments showed that the iron oxide coated olivine filter efficiently removed uranium. The two filter columns showed different results, but both of them were able to reduce the uranium concentration to less than 11 micrograms per litre, i.e. significantly lower than the guideline mentioned above. The ion exchange did not work as planned as the filtering efficiency gradually declined during the latter part of the experiment. Presumably this was due more to technical problems than to chemical ones. It seems likely that channels may have formed in the filter material, causing a lower uranium removal efficiency. In conclusion, it can be established that iron oxide coated olivine is a potentially interesting filter material for the removal of uranium from drinking water, but further research and development is needed.