Geokemisk karakterisering av anrikningssand och gråberg från Kringelgruvan

This thesis is the final part of the M.Sc. program in Natural Resources Engineering, at Luleå Technical University, and the project is conducted in collaboration with Golder Associates and Kringelgruvan AB.In this thesis, the sulphide bearing tailings of the Kringel graphite mine is investigated. In the current situation the Kringel mine is not in production, but as a result of increasing prices of graphite in combination with a high demand, Flinders Resources Ltd and Kringelgruvan AB are working to resume the graphite production at the site. To obtain permission to resume the graphite production, the old waste rock and tailings management must be redesigned and enhanced. This thesis include a geochemical characterization of the old mine waste in the Kringel graphite mine. The results will be included in the waste management plan. In the geochemical characterization waste rock, tailings and its leachate is investigated. The study includes site visits, sampling, laboratory work, and data interpretation. The study examines two excavated profiles in the tailings, which are examined by chemical analysis, pH, XRF, XRD, SEM, microscopy and particle analysis. The study also examines three composite samples consisting of; weathered tailings, unweathered tailings and waste rock. These composite samples are examined by humidity cell tests (for 17 weeks), chemical analysis and acid base accounting. Since both the waste rock and the tailings are deposited without any treatment the material is exposed to weathering. The aim with this study is to examine the weathering rates of waste rock and tailings, what weathering products will occur, if the material is producing acidity, and how the production of acidity will develop in short and long term. In the Kringel mine the dominating sulphide bearing mineral is pyrrhotite (FeS), and minor sulphide bearing minerals are pyrite (FeS2) and sphalerite (ZnS). The concentration of sulphur in the unweathered tailings is 3.88%, which converted to pyrrhotite corresponds to 10.6 wt%. The concentration of sulphur in the waste rock is 1.7%, which converted to pyrrhotite corresponds to 4.66 wt%.In field the tailings oxidation front has been estimated to 40cm. This corresponds to an oxidation rate of about 3.6 cm each year during field conditions. The amount of tailings exposed to oxidation each year is equivalent to about 6,288 tons of tailings. This represents approximately 51,028 kg of sulphur being oxidized each year.In the Kringel mine tailings pond the effective diffusion coefficient was calculated to 1.18 * 10-7 m2 /s. The effective diffusion coefficient was also determined by the PYROX computer software, which calculated the diffusion coefficient to 0.21*10-5 m2/s. Both diffusion coefficients are within the range of the diffusion coefficient in water (2.2*10-9 m2 /s) and in air (1.87*10-5 m2 /s) (Elberling, 1996). If the calculated effective diffusion coefficient (1.18 * 10-7 m2/s), is kept constant, the weathering front movement would continue downwards until it reaches the ground water table. The Kringelgruvan tailings pond is estimated to be approximately 5 m deep. It will thereby take approximately 1,712 years until the weathering front will reach the "bottom" of the tailings pond.The acid producing ability in the tailings is clearly demonstrated by the initial paste pH analysis. The test indicated pH