Characterization of Historical Tungsten Ore Tailings for Pre-selection of Feasible Reprocessing Methods; Yxsjöberg, Sweden (original) (raw)

2018, Luleå University of Technology

Historical tailings are secondary sources due to the presence of some amount of valuables minerals and metals. Metal content that has not been recovered earlier is now coming into the focus due to the improvements in technology; decreasing grades in primary deposits, increase of metal prices, and rising of environmental issues. In this thesis, historical tailings from the Yxsjöberg mine have been characterized by a number of methods including elemental analysis, XRD measurements, optical microscopy observations, quantitative liberation analysis and SEM-based analysis. Elemental analyses have been done in bulk and size fraction samples. XRD measurements were conducted on four main samples, optical microscopy on all samples and SEM-based measurements on two main samples. The results from characterization along with the information found in literature on the state of the tailings provided information about the society of minerals present in the tailings, grades of elements of concern and their corresponding distribution versus vertical profile and size fractions. Liberation condition of the scheelite phase and the accurate mineral chemistry of some important minerals were acquired. At the end of the characterization study, element-to-mineral conversion was used to quantify the presence of different minerals and their behavior in bulk and size fractions. By considering the current state of the tailings (based on characterization test works, literature study on the last improvements of the mineral processing technologies), feasible and promising reprocessing methods were selected for further investigation. This involved magnetic separation, enhanced gravity separation and flotation. Several separation tests using magnetic separators and the Knelson enhanced gravity separator were conducted in order to investigate the performance of the mentioned methods. The results showed that these methods are applicable to fulfill the corresponding separation tasks. Moreover, flotation method, which is nowadays used in processing of such mineral assemblages, has been recommended to test in future works. As a conclusion, a process flowsheet is proposed. As mentioned before, the main components of this process plant includes magnetic separation (low intensity) to reject iron contaminants, magnetite and pyrrhotite. The Knelson enhanced gravity method allows to recover scheelite particles within the size range between 150 to 300 μm. Conventional froth flotation method is suggested to be utilized for recovering fluorite, chalcopyrite, helvite, bismutite and scheelite within the size range between 75 and 150 μm in processing route and 10 to 75 μm in another. For particles below 10 μm, containing considerable amounts of liberated scheelite particles, newly developed flotation methods including column flotation and flocculation flotation are recommended, although tests and optimization remain to be done for final approval.