Mechanism of Changes in Goaf Water Hydrogeochemistry: A Case Study of the Menkeqing Coal Mine

Abstract

Goaf water in mining areas is widely found in China’s coal mines. To clarify the hydrogeochemical characteristics of goaf water and the influence mechanism of water–rock interaction and further reveal microbial action on the formation of goaf water quality, the goaf water in the Menkeqing coal mine was taken as the object, and physical modeling was used to simulate the process of the real goaf changing from an oxygen-sufficient environment to an anoxic environment with the rise of groundwater level in this work. The experimental results showed that the water–rock interaction in the goaf was mainly the dissolution–precipitation of minerals in the rocks of the caving zone and fracture zone, cation exchange, and oxidation of pyrite in the coal layer. The primary sources of Na+ and K+ in the goaf water were the dissolution and reverse ion exchange of silicate minerals such as albite and potassium feldspar, while Ca2+ and Mg2+ mainly from the dissolution of minerals such as calcium feldspar, calcite, and chlorite. The oxidation of pyrite in coal was the main reason for the increase in SO42− concentration, the enhancement of reduction, and the decrease in pH and DO (dissolved oxygen) in the goaf water. Relative abundance of sulfate-reducing bacteria (SRB) in goaf (e.g., Desulfosporosinus, Desulfobacterium, etc.) increased gradually, inhibiting the increase in SO42− concentration in goaf water through the devulcanization of SRB. The inverse hydrogeochemical modeling was performed using PHREEQC for two stages of the simulation experiment: 0–30 days and 30–300 days. The simulation results show that the water–rock action in the formation of goaf water mainly occurred in the simulation experiment’s early stage (0–30 days), and the mineral dissolution is dominant throughout the experimental stage. The results of the study provide a theoretical reference for the prediction of highly mineralized water pollution in goaf and its prevention and control.

Water–Rock Interaction Processes in Groundwater and Flows in a Maar Lake in Central Mexico

“…(a) calcite precipitation (Equation ( 3)) [78] is a product of the dissolution of primary silicates, as biotite, amphibole and pyroxene, from rocks in the study area, which produces Ca 2+ in the solution, (b) the dolomite dissolution originated increases of Ca 2+ and Mg 2+ (Equation ( 4)) [79] and, consequently, calcite precipitation, as mentioned previously, (c) gypsum dissolution (Equation ( 5)) [80] and precipitation (Equation ( 6)) [81] could be related to Ca 2+ increase in the groundwater, from primary silicates and SO 4 2− from carbonate rocks, (d) plagioclase dissolution gives Ca 2+ and Na + to water (Equation ( 7)) [82], (e) albite dissolution causes kaolinite precipitation (Equation ( 8)) [83] is related to the increase of silica (Table 2), (f) albite dissolution provokes increases of HCO 3 − (Equation ( 9)) [84], which is linked to weak carbonic acid reacting with carbonate or silicate minerals to form HCO 3 − ions (Equation ( 10)) [85], (g) biotite dissolution produces increases of Mg 2+ and K + (Equation ( 11)) [86], and (h) amphibole dissolution causes increases of Mg 2+ and Ca 2+ (Equation ( 12)) [87,88].…”

“…The presence of Ca 2+ in water is thought to be from the weathering of carbonates (calcite, dolomite and gypsum) and silicate minerals (plagioclase) [36,80,82], in contrast to the Mg 2+ contents, which come from the weathering of silicate (biotite, amphibole) and carbonate (dolomite) minerals [44,45,85,89]. Furthermore, the Na + origin could be related to weathering of plagioclase, albite and amphibole [82][83][84]87], and weathering of andesite rocks may deliver Na + to water [44,45,90]. At the same time, the K + contents could be related to biotite weathering [44,45,86,89].…”

“…Moreover, the Cl − concentrations can be related to the weathering of hydrosilicate minerals (biotite, amphibole, and phyllosilicates) [45,[91][92][93]. Finally, the high values of HCO 3 − could be related to the weathering of carbonate (calcite and dolomite) and silicate (albite, amphibole and kaolinite) minerals [44,45,78,79,83,84].…”

Hydrochemical Characteristics and Water Quality of Shallow Groundwater in Desert Area of Kunyu City, Southern Margin of Tarim Basin, China

“…When CAI-1 and CAI-2 are all positive values, it suggests that there is a positive cation exchange, that is, Na + and K + in water exchange with Ca 2+ and Mg 2+ on the surface of mineral particles. Otherwise, if values are negative, the reverse cation exchange occurs, and the greater the absolute value, the stronger the cation alternation [42]. CAI-1 and CAI-2 are negative, with average values of −0.52 and −0.47, respectively.…”

Hydro-Chemical Characteristics, Genesis Analysis and Risk Assessment of Fuyuan Laochang Ore Concentration Area in Yunnan, China

“…The Ca 2+ /SO 4 2value of surface water is basically close to 1:1, which shows that Ca 2+ and SO 4 2in water basically originate from the dissolution of gypsum (CaSO 4 •2H 2 O), and the dissolution equation is shown in Equation (3). The ratio of pit mine water and some surface water samples is less than 1:1, and the SO 4 2content is too much, so there may be a cation exchange process (Equation ( 4)), which makes some Ca 2+ replaced by Na + [32].…”