Improving the Accuracy of Geochemical Rock Modelling for Acid Rock Drainage Prevention in Coal Mine

Abstract.   The results of static tests are used to geochemically model the distribution of potentially acid and non-acid forming materials and plan mining excavation and overburden dumping to prevent or minimize the generation of acid rock drainage (ARD). The accuracy of the model depends very much on the amount and validity of the available pre-mine data and how the data is interpreted in both lateral and vertical directions. This results of such modelling was compared with subsequent overburden information provided by analysis of blast hole drill cuttings. We found that the model overestimated the amount of potentially acid forming material, but that it was still useful in ARD prevention.     

Design Criteria for Limestone Neutralization at a Nickel Mine

Abstract.   Design criteria were developed for the construction of a full-scale limestone neutralization plant to treat leachate from the waste rock of a nickel mine, using data from laboratory studies, pilot-scale studies, and operation of a full-scale limestone handling and dosing facility. We learned that: limestone powder can be slurried to a constant slurry density of 60 g/L; Fe (II) can be oxidised at low pH (2.5) at a rate of 16.1 g/(L/d) using geotextile as a medium; and that the integrated Fe (II)-oxidation and limestone neutralization process allows neutralization, Fe (II)-oxidation, and gypsum crystallization to take place at the same time, provided that the solids concentration is high (greater than 30 g/L). A full-scale plant with a capacity of 50 m³/h was designed and constructed. The plant consists of the following stages: biological Fe (II)-oxidation, a fluidised-bed limestone neutralization reactor, a complete-mix gypsum crystallization reactor, and a clarifier.     

Performance of Three Aquatic Plant Species in Bench-scale Acid Mine Drainage Wetland Test Cells

Abstract  We investigated pollutant removal from acid mine drainage (AMD) by three different aquatic plant species (Typha angustifolia, Desmostachya bipinnata, and Sacharum bengalense) in bench-scale wetland test cells of 1 m³. AMD was generated in the laboratory using chalcopyrite, galena, and sphalerite ore. A substrate containing 75% soil, 20% powdered goat manure, and 5% wood shavings was used in each cell. The performance of the system was evaluated for different water column heights (100, 150, and 200 mm) and for different retention periods (24, 48, 72, 96, and 168 hrs). The performance of the plant species was different for the various metals of AMD; therefore, multi-species plantings should be considered in constructed wetlands.     

Neutralizing Coal Mine Effluent with Limestone to Decrease Metals and Sulphate Concentrations

Abstract.   This paper describes pilot scale tests of a novel process for the neutralisation of acidic mine water. Leachate from a waste coal dump was neutralised with limestone, and iron, aluminium, and sulphate were removed. Specific aspects studied were: the process configuration; the rates of iron oxidation, limestone neutralisation, and gypsum crystallisation; the chemical composition of the effluents before and after treatment; the efficiency of limestone utilisation; and the sludge solids content. The acidity was decreased from 12,000 to 300 mg/L (as CaCO₃), sulphate from 15,000 to 2,600 mg/L, iron from 5,000 to 10 mg/L, aluminium from 100 to 5 mg/L, while the pH increased from 2.2 to 7.0. Reaction times of 2.0 and 4.5 h were required under continuous and batch operations respectively for the removal of 4 g/L Fe (II). The iron oxidation rate was found to be a function of the Fe (II), hydroxide, oxygen, and suspended solids (SS) concentrations. The optimum SS concentration for iron oxidation in a fluidised-bed reactor was 190 g/L. Up-flow velocity had no influence on the rate of iron oxidation in the range 5 to 45 m/h. Sludge with a high solids content of 55% (m/v) was produced. This is high compared to the typical 20% achieved with the high density sludge process using lime. It was determined that neutralisation costs could be reduced significantly with an integrated iron oxidation and limestone neutralisation process because limestone is less expensive than lime, and a high-solids-content sludge is produced. Full scale implementation followed this study.     

Acid Mine Drainage Flowing from Abandoned Gas Wells

Abstract  In northwestern Pennsylvania (USA), numerous abandoned natural gas wells are producing artesian flows of Fe-contaminated water. The origin of the polluted water has been generally assumed to be brines from the gas-producing sands. We sampled 20 artesian discharges where iron staining was conspicuous. The waters were not brines, but were more characteristic of acid mine drainage (AMD). The dominant cations were Fe, Ca, and Mg, while the dominant anion was sulfate. The study area has a long history of coal mining in the lower Allegheny formation; however, the coal beds are generally at higher elevations than the discharges. We propose that AMD formed in the coal mines is infiltrating into lower aquifers, moving outside the lateral limits of mining, and using abandoned gas wells as conduits to the surface. While flowing through the underlying sandstones, the AMD chemistry is modified by contact with siderite, the dominant carbonate mineral in this stratigraphy. This would suggest that current remediation strategies that emphasize plugging the pollution-producing gas wells may be ill-advised because the source of the polluted water is more shallow than currently assumed.     

A Bench-scale Assessment of a Combined Passive System to Reduce Concentrations of Metals and Sulphate in Acid Mine Drainage

Abstract  Passive treatment of acid mine drainage (AMD) requires a combined strategy to minimize the effect of climatic variability on the treatment performance of the system. A vertical-flow combined passive treatment system was developed and evaluated in a bench-scale laboratory test for a 290-day period. The combined system consisted of four components with specific treatment functions: an oxidation/precipitation basin for excess iron removal; a peat biofilter for heavy metal sorption and the establishment of anoxic conditions; a bioreactor for alkalinity generation and sulphate reduction; and an anoxic limestone drain for alkalinity addition. The benchscale system was dosed with moderate strength synthetic AMD at a surface loading of 95 L/m²/d, and operated under continuous flow conditions. Removal efficiencies were 99.7%, 99.9%, 99.9%, 98.6%, 98.2%, and 99.9% for Fe, Al, Zn, Mn, Ni, and Cu, respectively, while Cd remained more mobile with a removal efficiency of 66.5%. Sulphate concentrations were reduced from 3030 mg/L to 814.9 mg/L and the acidic drainage was neutralized to an effluent pH of 7.2 and an alkalinity of 1353.6 mg/L (as CaCO₃).     

The Use of Measured and Calculated Acidity Values to Improve the Quality of Mine Drainage Datasets

Abstract:  The net acidity of a water sample can be measured directly by titration with a standardized base solution or calculated from the measured concentrations of the acidic and basic components. For coal mine drainage, the acidic components are primarily accounted for by free protons and dissolved Fe²⁺, Fe³⁺, Al³⁺, and Mn²⁺. The base component is primarily accounted for by bicarbonate. A standard way to calculate the acidity for coal mine drainage is: Acid^calc = 50*(2*Fe²⁺/56 + 3*Fe³⁺/56 + 3*Al/27 + 2*Mn/55 + 1000*10^-pH)—alkalinity, where acidity and alkalinity are measured as mg/L CaCO₃ and the metals are mg/L. Because such methods of estimating acidity are derived by independent laboratory procedures, their comparison can provide a valuable QA/QC for AMD datasets. The relationship between measured and calculated acidities was evaluated for 14 datasets of samples collected from mine drainage discharges, polluted receiving streams, or passive treatment systems, containing a total of 1,484 sample analyses. The datasets were variable in nature, ranging from watersheds where most of the discharges contained alkalinity to ones where all of the discharges were acidic. Good relationships were found to exist between measured and calculated acidities. The average acidity measurement was 239 mg/L CaCO₃ and the average acidity calculation was 226 mg/L CaCO₃. Linear regressions were calculated for individual datasets and for the entire dataset. The linear regression for the entire dataset was: Acid^calc = 0.98 * Acid^meas – 8, r² = 0.98. The good correlation between calculated and measured acidity is the basis for an easy and inexpensive QA/QC for AMD data. Substantial variation between measured and calculated acidities can be used to infer sampling or analytical problems.     

Performance of a Natural Wetland Treating Acid Mine Drainage in Arid Conditions

Abstract  A wetland naturally formed in the discharge from a copper mine tailing impoundment in Rajasthan, India. The wetland is abundantly vegetated. This study investigated changes that occurred in the seepage as it travelled 180 and 380 m (P₁ and P₂) through the wetland. The pH increased from 6.17 to 7.10 at P₁ and 7.34 at P₂ in the pre-monsoon season, 6.53 to 7.36 at P₁ and 7.77 at P₂ in the post-monsoon season, and from 6.20 to 6.63 at P₁ and 6.89 at P₂ in the winter. Contaminant removal at P₂ ranged from 40 to 95%.     

Waste from Biodiesel Manufacturing as an Inexpensive Carbon Source for Bioreactors Treating Acid Mine Drainage

Abstract.  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.     

A Computer-Aided System for Design of Drainage Facilities in Surface Mining

Abstract.   Drainage systems in large surface mines are designed to accomplish three basic objectives: keeping working conditions dry, stable and safe; lowering hydrostatic pressure and increasing the effective stress of soil to improve slope stability; and ensuring pit floor workability. This can be achieved with drainage facilities that include channels, water collection sumps, and pump stations. We report the development of a computer-aided system called Dewatering of Open Pit Mines (DEWOP), which can assist open pit mine designers to solve water-related problems. The system was developed in a Visual Basic object programming language, taking advantage of multi-user, open database connectivity, such as Microsoft Access, for storage and processing of information. In tests at coal and copper surface mines, it reduced drainage facilities costs by 8%.     

Injection of Fluidized Bed Combustion Ash into Mine Workings for Treatment of Acid Mine Drainage

Abstract  A demonstration project was conducted to investigate treating acid mine water by alkaline injection technology (AIT). A total of 379 t of alkaline coal combustion byproduct was injected into in an eastern Oklahoma drift coal mine. AIT increased the pH and alkalinity, and reduced acidity and metal loading. Although large improvements in water quality were only observed for 15 months before the effluent water chemistry appeared to approach pre-injection conditions, a review of the data four years after injection identified statistically significant changes in the mine discharge compared to pre-injection conditions. Decreases in acidity (23%), iron (18%), and aluminum (47%) were observed, while an increase in pH (0.35 units) was noted. Presumably, the mine environment reached quasi-equilibrium with the alkalinity introduced to the system.     

Long-term Performance of Passive Acid Mine Drainage Treatment Systems

Abstract.   State and federal reclamation programs, mining operators, and citizen-based watershed organizations have constructed hundreds of passive systems in the eastern U. S. over the past 20 years to provide reliable, low cost, low maintenance mine water treatment in remote locations. While performance has been reported for individual systems, there has not been a comprehensive evaluation of the performance of each treatment type for a wide variety of conditions. We evaluated 83 systems; five types in eight states. Each system was monitored for influent and effluent flow, ph, net acidity, and metal concentrations. Performance was normalized among types by calclating acid loading reductions and removals, and by converting construction cost, projected service life, and metric tonnes of acid load treated into cost per tonne of acid treated. Of the 83 systems, 82 reduced acid load. Average acid load reductions were 9.9 t/yr for open limestone channels (OLC), 10.1 t/yr for vertical flow wetland (VFW), 11.9 t/yr for anaerobic wetlands (AnW), 16.6 t/yr for limestone leach beds (LSB), and 22.2 t/yr for anoxic limestone drains (ALD). Average costs for acid removal varied from $83/t/yr for ALDs to $527 for AnWs. Average acid removals were 25 g/m²/day for AnWs, 62 g/m²/day for VFWs, 22 g/day/t for OLCs, 28 g/day/t for LSBs, and 56 g/day/t for ALDs. It appears that the majority of passive systems are effective but there was wide variation within each system type, so improved reliability and efficiency are needed. This report is an initial step in determining passive treatment system performance; additional work is needed to refine system designs and monitoring.     

Anaerobic Bioremediation of Acid Mine Drainage using Emulsified Soybean Oil

Abstract  Batch incubation and flow-through column experiments were conducted to evaluate the use of emulsified soybean oil for in situ treatment of acid mine drainage. Addition of soybean oil, soluble substrates, and a microbial inoculum to the batch incubations resulted in complete depletion of SO₄, 50% reduction in Fe, and an increase in pH to >6. A one time injection of emulsified soybean oil, lactate, yeast extract, and a microbial inoculum stimulated SO₄ and metal ion reduction for ≈300 days in laboratory columns packed with mine tailings receiving influent solutions with a pH≈3 and≈5. In all emulsion treated columns, SO₄ and Fe were reduced, pH increased to >6, and Al, Cu and Zn removal efficiency was 99% or greater. Cu, Fe, Mn and Zn were removed as metal sulfides and/or carbonates with removal efficiency decreasing with increasing metal sulfide solubility. The low pH and high heavy metals concentrations did not significantly inhibit biological activity. However, SO₄ removal with associated precipitation of metal sulfides may have been limited by the short hydraulic retention time (6-7 days) of the columns. There was a significant hydraulic conductivity loss in one of the four treated columns, indicating that hydraulic conductivity loss may be an issue under certain conditions.     

Small-Scale Chemical Changes Caused by In-stream Limestone Sand Additions to Streams

Abstract.  In-stream limestone sand addition (ILSA) has been employed as the final treatment for acid mine drainage discharges at Swamp Run in central West Virginia for six years. To determine the small-scale longitudinal variation in stream water and sediment chemistry and stream biota, we sampled one to three locations upstream of the ILSA site and six locations downstream. Addition of limestone sand significantly increased calcium and aluminum concentrations in sediment and increased the pH, calcium, and total suspended solids of the stream water. Increases in alkalinity were not significant. The number of benthic macroinvertebrate taxa was significantly reduced but there was no effect on periphyton biomass. Dissolved aluminum concentration in stream water was reduced, apparently by precipitation into the stream sediment.     

Evaluation of Hydrogeological Parameters Associated with Limestone Mining: A Case Study from Chandrapur,India

Abstract.  Hydrogeological study of the Manikgarh and Naokari limestone mining areas, located in the Chandrapur region of central India, indicate that the mining operations should not cause environmental problems. Conversion of hill mining to pit mining at the Manikgarh Limestone Mine should be feasible and safe. At the Naokari Limestone Mine, a partial diversion of a seasonal stream, the Bop Nala, has been proposed to simplify mining and maximize production; this can be done without significantly altering the natural drainage pattern of the area and is not expected to have any adverse effects on the hydrological regime of area.     

Microbial Growth and Action: Implications for Passive Bioremediation of Acid Mine Drainage

Abstract.  Due to the variable environmental nature of mine water, several species of bacteria are important in the generation of acid mine drainage (AMD) and in bioremediation treatment technology. Enzymatic metal transport and transformation allow bacteria to survive in high-metal environments and to oxidize, reduce, and exude metals. For example, the enzymes Cr (VI) reductase and cytochrome-c3 hydrogenase allow Pseudomonas sp. to reduce Cr (VI) to less toxic Cr (III). Much more toxic organomercuric compounds are transformed by Pseudomonas fluorescens and Escherichia coli, using the enzymes organomercurial lyase and mercuric reductase. The role of bacteria in the AMD environment is not yet fully understood and consequently researchers should pay attention in this field.     

Evaluation of Airborne Thermal Infrared Imagery for Locating Mine Drainage Sites in the Lower Youghiogheny River Basin,Pennsylvania, USA

Abstract.  Nighttime high-resolution airborne thermal infrared imagery (TIR) data were collected in the predawn hours during Feb 5-8 and March 11-12, 1999, from a helicopter platform for 72.4 km of the Youghiogheny River, from Connellsville to McKeesport, in southwestern Pennsylvania. The TIR data were used to identify sources of mine drainage from abandoned mines that discharge directly into the Youghiogheny River. Image-processing and geographic information systems (GIS) techniques were used to identify 70 sites within the study area as possible mine drainage sources. The combination of GIS datasets and the airborne TIR data provided a fast and accurate method to target the possible sources. After field reconnaissance, it was determined that 24 of the 70 sites were mine drainage. This paper summarizes: the procedures used to process the TIR data and extract potential mine-drainage sites; methods used for verification of the TIR data; a discussion of factors affecting the TIR data; and a brief summary of water quality.     

Efficiency of Bauxsol™ in Permeable Reactive Barriers to Treat Acid Rock Drainage

Abstract  Permeable reactive barriers (PRBs) and flow-through reaction cells are fairly new passive treatment alternatives to conventional lime treatment of acidic rock drainage (ARD). They are ideal for the treatment of flowing ARD and are particularly useful when contaminants are likely to persist for several years. This paper describes column tests performed to simulate a PRB constructed using Bauxsol™, a chemically and physically treated bauxite refinery residue, as a reactive material. This experimentation shows promising results for the Bauxsol™ PRB method in neutralizing pH and removing metals from acidic mine effluents.     

Evaluation of Airborne Thermal Infrared Imagery for Locating Mine Drainage Sites in the Lower Kettle Creek and Cooks Run Basins,Pennsylvania, USA

Abstract.  High-resolution airborne thermal infrared (TIR) imagery data were collected over 90.6 km² (35 mi²) of remote and rugged terrain in the Kettle Creek and Cooks Run Basins, tributaries of the West Branch of the Susquehanna River in north-central Pennsylvania. The purpose of this investigation was to evaluate the effectiveness of TIR for identifying sources of acid mine drainage (AMD) associated with abandoned coal mines. Coal mining from the late 1800s resulted in many AMD sources from abandoned mines in the area. However, very little detailed mine information was available, particularly on the source locations of AMD sites. Potential AMD sources were extracted from airborne TIR data employing custom image processing algorithms and GIS data analysis. Based on field reconnaissance of 103 TIR anomalies, 53 sites (51%) were classified as AMD. The AMD sources had low pH (<4) and elevated concentrations of iron and aluminum. Of the 53 sites, approximately 26 sites could be correlated with sites previously documented as AMD. The other 27 mine discharges identified in the TIR data were previously undocumented. This paper presents a summary of the procedures used to process the TIR data and extract potential mine drainage sites, methods used for field reconnaissance and verification of TIR data, and a brief summary of water-quality data.     

Numerical Modelling of Flow and Capillary Barrier Effects in Unsaturated Waste Rock Piles

Abstract  Flow systems in unsaturated waste rock piles were simulated using a two-dimensional numerical model (HYDRUS). The conceptual models are based on homogeneous (unstructured) waste piles, and on structured piles that include either horizontal or inclined fine-grained layers within a coarser host material, forming a capillary barrier system. The approach considers fully transient conditions and uses observed climatic data from a mine site in northern Quebec, Canada. All physical properties of the porous media, including the water retention curves, were obtained from measured data. Different geometric configurations were tested to determine their effect on moisture distribution and water flow, which ultimately control the potential for acid rock drainage (ARD). The simulations begin with a relatively dry initial condition under hydrostatic equilibrium. After an initial transient period, the simulated internal moisture distribution became periodic with a regular pattern of seasonal fluctuations. The simulations suggest that flow can be controlled in such systems using inclined fine-grained layers that retain and divert moisture due to capillary barrier effects. With horizontal layers, the local flow regimes become unstable, causing vertical preferential flow zones to develop below the barriers wherever the local water pressure first exceeds the entry pressure of the underlying coarser material. In this scenario, ARD production can remain high since a large fraction of the internal pile is being flushed. A shallow downward slope in the layers forces drainage toward the outer boundary and maintains lower saturation in the centre of the pile, thus potentially reducing the amount and mobility of ARD. NSERC Polytechnique/UQAT Industrial Chair: Env and Mine Waste Mgmt