Natural Neutralization Of Acid Mine Water In Carbonate Deposits Of The Kizel Coal Basin
Fetisova, Natalia (1); Fetisov, Viacheslav (2); Bachurin, Boris (1); Imaikin, Aleksandr (2)
1: Mining Institute of the Ural Branch of the RAS; 2: Perm State University
The closure of mines of the Kizel coal basin (Perm kray, Russia) at the end of the last century and the cessation of groundwater pumping resulted in gradual level recovery of aquifer in fissured-karst Visean-Bashkirian (C1v3-C2b) carbonate rocks and formation a number of ascending springs. In some fields of the flooded coal basin in the zone of large faults, penetration of acid mine drainage (AMD) from flooded workings into overlying fissured-karst rocks takes place. The carbonate rocks contribute to acid neutralization and metal attenuation in the AMD. Scientific researches related to the study of hydrogeochemical processes occurring in the coal-overlying carbonate deposits and controlling acid neutralization of the mine drainage are almost absent for the Kisel coal basin.
Analyzing the available groundwater monitoring data, authors have suggested that some of the springs are the АMD that has been neutralized in different degree when flowing through the carbonate rocks. In order to understand the processes occurring in carbonate sediments and its effect on metal attenuationin the AMD, chemical composition data of the effluent from two ascending springs, which in previous studies (Imaikin AK, 2012; Imaikin AK, Imaikin KK, 2013) are called as discharges of groundwater extremely contaminated by mine water, were processed using methods of hydrochemical modeling. To assess the degree of possible dilution of the AMD by uncontaminated groundwater of the Visean-Bashkirian aquifer or, conversely, the degree of pollution of the groundwater by mine water, modeling of their mixing in various proportions was performed. At the next stage, modeling of interaction of mine water with calcite and dolomite was carried out. All simulations were performed using the PHREEQC with the WATEQ4F thermodynamic database. The data obtained as a result of the simulation were compared with the actual data of chemical composition of the spring waters.
Evaluation of the hydrogeochemical data and results of the modeling allows us to state that considered springs are discharges of the acid mine water which chemical composition is mainly controlled by dissolution of carbonate minerals, while their dilution by uncontaminated groundwater is insignificant. Fate of some dissolved metals after interaction of the mine water with carbonates, silicates and other minerals were evaluated on the basis of calculation of the springs water saturation index with respect to rock-forming and secondary minerals. Calculated saturation indexes of potential secondary minerals have allowed determination the main sinks of metals dissolved in AMD.