Background
Sulfide minerals such as pyrite (FeS2), galena (PbS), chalcopyrite (CuFeS2) and sphalerite (ZnS) in mine tailings oxidize in the presence of water and an oxidizing agent. The oxidizing agent is typically O2 or Fe3+ giving direct and indirect oxidation, respectively. The oxidation reactions produce a low pH runoff with high metal concentrations called Acid Mine Drainage (AMD). Capping solutions utilizing the capillary barrier effects (CCBE) is made of layers with distinct hydrological properties limiting the availability of oxygen.
This should prevent direct sulfide oxidation and AMD generation. However, old mine tailings where sulphide minerals have been oxidised leads to precipitation of abundant Fe3+-rich minerals. This is the case with the old mine tailings at Folldal and Doyon mines. The Fe3+ phases can make Fe3+ available for indirect oxidation after implementation of the CCBE cover. It is therefore uncertain if the CCBE concept is sufficient to prevent AMD generation of oxidized mine tailings.
Project aims
The aim of this MSc project is to investigate the geochemical system of AMD generation of direct and indirect sulphide oxidation. This is done by performing controlled laboratory experiments on unweathered and weathered mine tailings. Initial batch experiments on the Folldal mine tailings have been performed at NGI and the results are available for the student.
Further experiments should be performed on other materials (e.g. Doyon mine tailings) and optimized experiments. All input and output materials are described in detail for chemical and mineralogical composition, fluids are analysed for metal composition using ICP, and solid material for chemical and mineralogical composition using e.g., SEM-EDS, microprobe, XRD, XRF/ICP and optical thin section studies.
Results of the analysis provide the basis for developing a geochemical model of the system using PHREEQC or equivalent software. Additionally, the MSc will also include a literature search on the topic.
It is of special interest to investigate the role of Fe3+ for AMD generation after the CCBE cover has been established. The CCBE concept should be evaluated in light of indirect sulphide oxidation.
The end result should be a geochemical model describing the observed mineral reactions, pH and metal development in the reaction water.
Research questions
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How efficient is the CCBE concept on mine tailings where Fe3+ phases are available?
What will you learn
This MSc is suitable for a student who is interested in learning how to perform geochemical experiments, interpret chemical and mineralogical results, and implement them in a geochemical model. You will learn about environmental geology on a topic that is relevant all over the world.
Background of the candidate
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A background in chemistry, geochemistry, soil sciences or environmental sciences is preferred.
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Working language: Norwegian or English