Evidences of Effective Treatment of Alkaline Mine Drainage with BaCO_3

摘要

An experimental lab scale reactor that treats alkaline mine drainage has been developed based on hydrogeochemical characteristics of most of the South African coal mines leachates, which generally have high concentrations of sulfates, TDS (total dissolve solid), salinity and heavy metals (mainly Fe~(3+) and Al~(3+)).The experiment development was based on the DAS system (disperse alkaline substrate). In this case, barium carbonate (BaCO_3) was used as alkaline reactive, fixed to a non-toxic inert matrix (wood chips). The experiment was carried out with 3 different proportions of wood:BaCO_3 (w/w); 1:2, 1:3 and 1:4 with a residence time of 24 hours. SO_4~(2-) and Ca~(2+) contained in AMD precipitate as BaSO_4 and CaCO_3, respectively, according to (1) thermodynamic modelling by PHREEQC, (2) geochemical and (3) mineralogical characterization. The pH increased up to 9-10, which allowed the removal of divalent metals. Reactors were maintained for 6 months and the results that were acquired from all of them demonstrated their reactivity, without saturation or clogging in any of the columns, towards the total removal of nitrates (100%), 93% of sulfates, 50% hardness (Ca~(2+), Mg~(2+) and Na~(2+)), as well as 68-93% of metal removal (Fe~(3+), Al~(3+), Cu~(2+), Zn~(2+) and Mn~(2+), in moderate concentrations). Therefore, parameters such as salinity, TDS and conductivity decreased throughout the experiment. Water volume treated was approx. 764 L during 26 weeks in the lab scale reactors and the physicochemical parameters of the water after treatment are within the allowable limits for drinking water, according to SANS 241 class 1 for Drinking Water (South African national standard, 2006; 2011).