Acid mine drainage treatment by ash from wooden chip combustion: study of mine water composition in dependence on the ash dose and duration of mutual interaction

Abstract

The biomass ash (BA) from wooden chip combustion was used in the treatment of acid mine drainage (AMD) from open cast brown coal mining in the Czech Republic. The used AMD is characteristic of high contents of SO42- (1576 mg.l-1), Fe (20 mg.l-1), Al (15 mg.l-1), Mn (5 mg.l-1) and low pH (2.7), which need to be adjusted. The biomass ash samples were obtained through the combustion of wooden chips in an industrial boiler in Hodonín Power Plant, Czech Republic, and they predominantly contain SiO2 (45 wt.%), CaO (17 wt.%), Al2O3 (13 wt. %), MgO (6 wt.%), Fe2O3 (4 wt.%), K2O (3 wt.%), SO3 (3 wt.%), P2O5 (2 wt.%), unburnt materials and metals. The AMD treatment process included dosing of biomass ash (doses of 2.9 g, 6 g and 20 g of BA) to adjust the pH values to 8, 10, 12. The experiments observed the pH values and turbidity in selected time intervals within 7 days. Samples were analysed for metal contents, which had been abundant either in AMD or ash, or in AMD and ash simultaneously, in selected times of occurrence of the changes in pH and turbidity. After treatment by biomass ash (at the end of the experiment after dosing of 2.9 g, 6 g and 20 g of BA), the AMD was examined for the concentrations of Ca (449, 422 and 376 mg.l-1), Mg (135, 82 and 7 mg.l-1), K (14, 21 and 54 mg.l-1), Na (127, 123 and 172 mg.l-1), Fe (below the detection limit (bd) in all cases), Mn (1.4, 0.063 mg.l-1 and bd), Al (bd in all cases), As (0.005, 0.003 mg.l-1 and bd), Ba (0.08, 0.06 and 0.1mg.l-1), Sr (3, 3 and 4 mg.l-1), Zn (bd in all cases), Cr (bd in all cases), Cu (bd in all cases), Ni (0.06, bd and bd), Cd (bd in all cases), Co (0.04 mg.l-1, bd, bd) and Pb (bd in all cases). In all the cases, AMD treatment by the applied doses of biomass ash was effective. In addition, there was no harm caused to the environment since the technology didn't involve any release of hazardous elements from the used ash samples into the aqueous medium.