Co-disposal of lignite fly ash and coal mine waste rock for neutralisation of AMD
(English)Manuscript (preprint) (Other academic)
The WRs from a lignite producing coal field and FA produced from a power plant incinerating lignite from this field have been investigated in this study with objectives including the effect of WR particle size, co-disposal of FA (cover and mixture) and WRs on AMD and leachate quality and potential for secondary mineralisation using PHREEQC. The effect of particle size has been clearly observed where smaller particle sizes (2mm) produced low pH (~2) leachates with elevated concentrations of the sulphide related elements (such as Fe, SO42-, Al, Zn, Co, Cr, Cu, Mn and Ni) compared to 5mm (pH~3) and 10mm (pH~3.7) particles, indicating that sulphide oxidation has been pronounced in smaller particles. Co-disposal of FA as mixture readily provides acid buffering minerals, resulting in better pH (~3–6) and leachate quality from the beginning, except initial flush-out on the first rinse. However, acidity produced by secondary mineralisation contributes towards the acidification of the system, causing stabilisation of pH at around 4.5−5. In contrast, the pH of the leachates from the FA cover scenario gradually increases from strongly acidic (pH~2) to mildly acidic (WR1: pH~5 and WR2: pH~4) and circumneutral (WR3: pH~7) along with decrease in EC and elemental leaching. Gradually increasing pH can be attributed to the cover effect, which reduces oxygen ingress, thus sulphide oxidation, causing pH to elevate. Since pH~4–5 is sufficient for the secondary Fe- and Al-mineral precipitation, the FA cover performs very well to achieve that until the conclusion of the column leaching experiment. However, due to slower reactivity of the system, leaching in the beginning cannot restricted. The co-disposal of FA as cover and/or mixture possess potential for neutralisation of AMD and improving leachate quality significantly. However, both systems need to be up-scaled and investigated for AMD neutralisation, leachate quality, kinetic modelling and geotechnical properties.
Coal mine waste rock, acid mine drainage (AMD), fly ash, co-disposal, dry cover, mixing
Environmental Management Mineral and Mine Engineering Environmental Sciences Geochemistry
Research subject Applied Geochemistry
IdentifiersURN: urn:nbn:se:ltu:diva-60260OAI: oai:DiVA.org:ltu-60260DiVA: diva2:1045543