Geokemisk karakterisering av anrikningssand och gråberg från Kringelgruvan
Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
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 <4, which according Lottermoser (2003), is an indication that the material is acid producing.The acid base accounting also indicated that both the waste rock and tailings are acid producing. The test measures the capacity of acid production and acid neutralization without any consideration of the availability of acid producing and acid neutralizing minerals in the material. It would therefore be interesting to investigate the concentration of sulphur that is available for oxidation. Coating on the surface of the sulphides could prevent oxygen from reaching the sulphide and thereby prevent the weathering (Lapakko, 2002). To further study the weathering reaction in the mine waste in a long term aspect, a Humidity cell test on composite sample of oxidized tailings, unoxidized tailings and waste rock was conducted. The test show what elements are released during weathering, i.e. leaching of elements. The Humidity cell test should continue until the leachate has a constant discharge of metals and acidity. In this study, only the results of the first 17 week of the experiment were analyzed. The discharge of elements were relatively constant in the unoxidized tailings and in the waste rock, but not in the oxidized tailings. The results still give an indication on how the leaching of elements will change with time. The oxidized tailing will probably continue generating acidity and metal-rich leachate during time. The analysis of the Humidity cell test will continue for some additional weeks, but it is beyond the scope of this study.
Place, publisher, year, edition, pages
2012. , 74 p.
Life Earth Science
Bio- och geovetenskaper, sulfidhaltigt gruvavfall, geokemi, vittringsprocesser, surt lakvatten
IdentifiersURN: urn:nbn:se:ltu:diva-53324Local ID: a5bc0116-daae-4b91-a4bd-375bc2316997OAI: oai:DiVA.org:ltu-53324DiVA: diva2:1026698
Subject / course
Student thesis, at least 30 credits
Natural Resources Engineering, master's
Alakangas, LenaHolmström, Henning
Validerat; 20121025 (anonymous)2016-10-042016-10-04Bibliographically approved