Abstract:

Acid mine drainage (AMD) is one of the major mining-related problems globally, owing to the oxidation of sulfide minerals, mainly pyrite and pyrrhotite. This research aims to reduce the reactivity of sulfides in mine waste rocks using silica, based on previous research.

A total of 1 kg of unoxidized pyritic waste rocks (11% S) were used in a column leaching experiment. The samples were crushed to >4 to <6 mm size fractions, split and homogenized and placed into four 500 mL columns. The cells were kept in a climatic chamber at controlled temperature and humidity. After 10 weeks of water leaching, three cells were treated with alkaline silicate-solution, as the source of dissolved silica. Prior to silica addition, one of the three cells was treated with hydrogen peroxide. The fourth cell was kept as a reference, with continued weekly water leaching.

The preliminary results are promising. Release of metals (i.e., Co, Mn, Zn) from the Si-treated cells was reduced compared to the reference, either due to different pH or silica coating on pyrite surfaces. SEM imaging and µ-XRF analysis on selected grains revealed the formation of a homogenous silica layer on the pyrite surface by secondary mineralization. The remaining solid will be subjected to water and acid extractions to investigate the stability and the geochemical partitioning of the layer.

More detailed results of the experiments, including leachate chemistry and qualitative SEM analyses of the waste rock, will be presented and the implications discussed.

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Dr. Hanna Kaasalainen