International journal of mine water

Water pressure due to groundwater presence has a great influence on the open pit slope stability and for that reason the risk of slope instability is dependent on water level in the slope. Factor of safety could be reduced from 1,3 to 1.0 if the water level increases. In all cases in open pit mining practice more than 40% of slope instability risks depend on groundwater conditions in the slope, To prevent slope failure, effective drainage system can be installed, and other factors can remain unchanged. The importance of controlling water surface in open pit slope is emphasized. In general, increasing the open pit slope angle and decreasing the failure risks, is directly proportional to effective drainage system.

Several large pits were left after alum shale was mined from 1942 to 1966 in the Kvarntorp area of Sweden. Of these, the pit lakes Pölen and Norrtorpssjön are the focus of this study. They have elevated levels of Na, K, Mg, Ca, Al, Mn, Fe, and sulphate, as well as trace elements, from weathering of the exposed shale. Both lakes had a stable pH below 4 until 1996 when the pH in Norrtorpssjön started to increase, exceeding 8 in 2010, due to inflow of leachates from alkaline waste dumped in an adjacent waste deposit, similar to a large scale anoxic limestone drain (ALD). Iron and Al concentrations decreased as the pH increased, indicating formation of particulate species which accumulate as sediments. The Co, Ni, and Zn concentrations also decreased, probably due to association with the solid phases, while Cu was less affected by the increase in pH, possibly due to formation of complexes with dissolved organic matter. Vanadium concentrations show limited solubility, while Mo concentrations increased at higher pH. Uranium concentrations decreased from above 80 μg/L to below 10 μg/L before rising to 30–35 μg/L due to the formation of soluble carbonate complexes at higher pH levels. The elevated levels of Li, Sr, and U indicate that weathering has continued despite the pH change. Both pit lakes are stratified, but no seasonal overturn has been observed. Long-term behaviour of this large-scale ALD and its implications are also discussed.

Alcohol-fed, semi-passive bioreactors have been used to support the growth of sulfate-reducing bacteria (SRB) for treatment of acid drainage from mine sites. An alcohol source not previously examined for use in these reactors is the glycerol-methanol waste remaining after the production of biodiesel fuel. In the laboratory, rock-filled columns were used to investigate biodiesel waste (BDW) as a carbon source for SRB. Columns were provided with water containing 900 mg/L sulfate, and fed reagent-grade glycerol or BDW in sufficient quantity to reduce 50% of the sulfate. Addition of 246 mg/L of reagent-grade glycerol resulted in 50% sulfate reduction and production of up to 59 mg/L of soluble sulfide, while the equivalent of 246 mg/L of glycerol provided as BDW resulted in 55% sulfate reduction and the production of up to 92 mg/L of soluble sulfide. During the initial stages of acclimation, propionic, acetic, formic, and lactic acids were observed. Acid concentrations were reduced over time in the effluent, and organic carbon in the BDW was nearly completely converted to carbon dioxide.

The vulnerability of the C2-1 and C3-1 coal seams to water inrush from overlying aquifers was evaluated for a portion of the Menkeqing coal mine. Geological and hydrogeological data were used to develop a conceptual model. Using the ‘three maps-two predictions’ method, an index model of water abundance (yield) of the overlying aquifers was constructed and overlain on a map that indicates potential fractured zone connections to the overlying aquifers. Superposition of the two zoning maps allowed development of a comprehensive inrush vulnerability map. Mine discharges were predicted under both natural and mining conditions using Visual Modflow, and appropriate prevention and control measures are proposed.

Steep terrain, intense rainfall, and seismic activity precluded use of conventional tailings storage facilities at the PT Freeport Indonesia (PTFI) copper–gold mine, in Papua, Indonesia. A controlled river tailings system was adopted as the only feasible way to manage the tailings. The tailings are transported to an engineered 230 km2 deposition area, which is bounded by levees on the east and west sides and is open on the south side to allow transport water and surges of rainfall to exit the area. We evaluated the performance of the ore-fed blending strategy for managing potential acid rock drainage formation of the tailings. Long-term leaching column tests and monitoring of deposited tailings provided insight on the reactivity, leaching behaviours, and neutralizing potential of the samples, and the ratio of acid neutralizing capacity (ANC): maximum potential acidity (MPA) that would ensure that the deposited tailings remain non-acid forming. We concluded that an ANC/MPA ratio >1.5 provides an adequate factor of safety to prevent acid generation and ensure long-term geochemical stability of the deposited tailings.

Results from bench-scale tests for thallium remediation in mining-impacted water are presented and removal mechanisms are discussed. The source water consisted of surface runoff mixed with groundwater from an inactive gold mine in central Montana. Bench scale columns were operated under continuous flow for 225 days to test for microbially-mediated thallium immobilization. Various compositions of straw and steer manure in a gravel matrix provided a source of organic nutrients and sulfate-reducing bacteria sufficient to initiate and maintain microbial sulfate reduction up to 270 mmol/m3d. Hydraulic residence times of 2.7 days produced an aqueous thallium effluent concentration below the analytical detection limit of 2.5 μg/L at 20°C in all the tested columns. These effluent levels were achieved for influent dissolved thallium concentrations varying from 450 to 790 μg/L. An increase in pH between influent (pH 6.9) and effluents (pH 7.5) was observed. Hydraulic conductivity remained relatively constant during the course of the experiments and varied for the different test columns between 0.2 and 10 cm/s. The highest k-values were observed in the horizontal flow column. In addition to the column tests, sterile serum-vial experiments were performed to confirm that thallium sulfide (Tl2S) formation and precipitation was the most likely mechanism for thallium removal. Data from the bench-scale experiments were utilized for the design of an on-site pilot-scale passive treatment system.

Large scale roof strata caving that occurs during coal extraction can irreversibly damage floor strata and result in riskier mining operations. Four research models incorporating floor water pressure were assessed for floor strata failure, using eight methods and two classification systems. A connection between floor strata failure and the coefficient of impact risk was developed. The derived equations represent a potentially effective method for providing a preliminary assessment of the risks associated with floor strata failure due to caving. A classification system of floor failure potential can be constructed to minimize risks during mining.

Multiple runoff connections for groundwater supply and water quality evolution mechanisms were disclosed using hydrochemistry, multivariate statistics, stable hydrogen and oxygen isotopes, and inverse hydrogeochemical modeling in a multi-layer groundwater system in a north China coal-mining district. Groundwater quality was mainly influenced by dissolution and weathering of carbonate, silicate, gypsum, halite, and fluorite, as well as cation exchange. Sulfate enrichment in the Carboniferous limestone aquifer may be due to pyrite oxidation, while gypsum dissolution and sewage contribute sulfate to the Quaternary alluvium. The Ordovician limestone groundwater is hydraulically connected to the other two aquifers. Incongruent dissolution of dolomite occurs when the Ordovician limestone water contacts the Carboniferous aquifer, while evaporation occurs when the Ordovician limestone water migrates upward through fractures to the Quaternary aquifer.