Optimizing the Effluent Treatment at a Coal Mine by Process Modelling

Abstract:   The water network of a coal mine was audited and simulated by an interactive steady state model and the results were used to optimise the mines water management strategy. Simulation of the interactions showed that calcium carbonate powder could be used as an alternative to lime for neutralization of acid water at a reagent cost saving of 56%. Gypsum crystallization would reduce sulphate concentrations in the neutralization plant by 30% and in the coal processing plant by 60%. The capital cost for a neutralization/gypsum crystallization plant for separate treatment of coal discard leachate and less polluted streams would cost 3.0 million Rand (R), compared to R10.3 million for combined treatment. Only slightly less (8.9 t/d vs. 9.5 t/d) sulphate removal would be achieved during separate treatment. The over-saturation index (OSI) value can be controlled effectively by removing sulphate from the feed water for coal processing. Sulphate has to be lowered to 350 mg/L in a flow of 222 m³/h to obtain an OSI value less than 1. The capital cost of a 222 m³/h biological sulphate removal plant was estimated at R21.8 million (R4.1 million/(ML/d)); the running cost was estimated at R13.7 million/a (R4.10/m³). Pre-washing of the coal would reduce capital and running costs.     

Using Helicopter Electromagnetic Surveys to Identify Environmental Problems at Coal Mines

Abstract.  Helicopter-mounted electromagnetic (HEM) surveys have been used to delimit conductive mine pools and groundwater features at various areas in the eastern United States that contain abandoned surface and underground coal mines. HEM was used to delineate the source areas and flow paths for acidic, metal-containing groundwater. This will aid remediation efforts. A recent HEM survey of Kettle Creek Watershed, Clinton County, Pennsylvania, using a 6-frequency electromagnetic data acquisition system, is presented. The survey accurately located conductive pools within underground mines, acidgenerating mine spoil at surface mines, and areas of groundwater recharge and discharge.     

Underground Mine Water for Heating and Cooling using Geothermal Heat Pump Systems

Abstract  In many regions of the world, flooded mines are a potentially cost-effective option for heating and cooling using geothermal heat pump systems. For example, a single coal seam in Pennsylvania, West Virginia, and Ohio contains 5.1 x 10¹² L of water. The growing volume of water discharging from this one coal seam totals 380,000 L/min, which could theoretically heat and cool 20,000 homes. Using the water stored in the mines would conservatively extend this option to an order of magnitude more sites. Based on current energy prices, geothermal heat pump systems using mine water could reduce annual costs for heating by 67% and cooling by 50% over conventional methods (natural gas or heating oil and standard air conditioning).     

Mine Water Literature in ISI’s Science Citation Index Expanded™

Abstract.   Scientists in most countries are assessed by the number of papers published in journals that are cited in the Science Citation index. This article reviews the mine water related entries in the Science Citation Index Expanded and discusses the results. Mine water relevant literature is spread over more than 900 journals, with 13 of them accounting for 25% of all relevant papers. No journal focused on mine water relevant issues can be found in the Index.     

Effects of a Barite Mine on Ground Water Quality in Andhra Pradesh,India

Abstract.  An investigation was undertaken to determine the effects of a large barite mining operation on local ground water quality near Mangampeta,Andhra Pradesh, India.Water samples were collected from drinking water wells in the mining and adjacent regions. The drinking water in the mining region had sulphate concentrations that ranged from 211 to 589 mg/L, compared to sulphate concentrations of 25 mg/L or less in the non-mined areas. The natural existence of barite and the widespread mine waste dumps at Mangampeta are believed to be responsible for the higher levels of sulphate in the ground water.     

Radionuclide Contamination of Surface Waters, Sediments, and Soil Caused by Coal Mining Activities in the ruhr District (Germany)

Abstract.   The discharge of highly mineralised mine waters with enhanced ²²⁶Ra and ²²⁸Ra activity concentrations has affected creeks, rivers, sediments, soils, and plants along the Lippe River and its tributaries. ²²⁶Ra activity concentrations were elevated in all water samples receiving mine water, with activity concentrations gradually decreasing with increased distance from the colliery due to dilution and chemical precipitation of radium with barium. Increased concentrations of radium and radium decay products were also measured in sediments and flood-affected soils. The sediments show an enrichment of ²²⁶Ra up to a factor of 750, while the contaminated soils only reach a factor of 10. In aquatic plants, a 4-fold increase in ²²⁶Ra activity concentrations was measured downstream of the discharge points. The contamination of the river banks and adjacent floodplain with radium is responsible for enhanced gamma dose rates, which, along with the incorporation of soil by playing children, provide potential radiation exposure to the public.     

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.     

Using a Water Balance to Determine the Source of Water in the Flooding Underground Mine Workings of Butte

Abstract.  Nearly 10,000 miles (16,000 km) of underground mine workings began flooding on April 22, 1982 when the large pumps used to dewater the mines of Butte, Montana were shut off. In the first few months, water levels in the workings rose hundreds of meters. Flooding continues to this day at a slower rate, nearly 25 years later. An early evaluation of the water chemistry in the flooding mines suggested that the initially poor water quality was the result of flushing of a reservoir of stored acidity and metals. However, a detailed water balance for the Berkeley pit, underground workings, and associated mining features suggests an alternative explanation. During the early period of mine flooding, acidic surface water from the deactivated heap leach operations and nearby acid rock drainage were routed into the empty Berkeley Pit, and thence drained downward and outward into the underground mine workings, causing widespread degradation of water quality in the underlying workings. After 21 months, the hydraulic gradients in the system reversed, causing a change in the direction of ground water flow and a gradual improvement in water quality of the mine shafts.     

Geochemical Evolution of a Surface Mine Lake with Alkaline Ash Addition: Field Observations vs. Laboratory Predictions

Abstract.  In the Eastern Middle Anthracite field of Pennsylvania, a formerly acidic (pH = 3.6) surface mine lake (initially approximately 45,000m³ in volume) is being reclaimed using fluidized bed combustor (FBC) ash. The pH of the water in the pit dramatically increased when the alkaline ash was added. The pH of the water is now well buffered, and has not dropped below a value of 11.0 since March 2000. Analysis of data from samples collected over the past six years indicate that the lakes alkalinity is controlled by carbonate, silicate, and hydroxide reactions. The relative importance of these factors varies with ash input, and can be determined in a predictable fashion. Laboratory tests determined that the mass of CaO was more significant than the particle surface area on the pH of the solution. Using only alkaline material, the transition between caustic and carbonate alkalinity was apparent, though this did not account for interaction with silicate minerals, which should be considered when using alkaline ash for reclamation. Field data indicate that with time, the pH will again decrease but will be buffered by calcite present on both the upper walls of the mine pool and within pores of the FBC ash. Less than 1% of the ash is currently used to increase the pH and alkalinity, so a large reserve exists for long term buffering capacity.     

Environmental Risks Associated with Beneficial End Uses of Mine Lakes in Southwestern Australia

Abstract  Lakes develop when pits from open cut mines are left to fill with groundwater. In recent years, mining companies, mining communities, and regulatory agencies have begun to consider potential beneficial end uses for mine lakes. Beneficial end uses are unlikely to be without environmental impacts, however, and a proper consideration of the total benefit to the community should consider them. This paper briefly reviews potential beneficial end uses and possible environmental impacts that might arise with them for mine lakes in the Collie Basin, a coal mining region in Western Australia. We identified eight distinct, but not necessarily incompatible, end uses from a search of the literature on mine lakes throughout the world: recreation and tourism, wildlife conservation, aquaculture, irrigation, livestock water, potable water, industrial water, and chemical extraction. Recreation, conservation, and possibly aquaculture use the mine lake directly, whereas the other end uses utilise extracted water. All end uses have the potential to have environmental effects, with the most common being an actual or perceived impact on human health and safety. A semi-quantitative risk assessment, using published literature sources, identified wildlife conservation as the end use with the least environmental risk, and irrigation as the end use with the greatest environmental risk. Such risks need to be balanced against economic and social benefits. There is an urgent need for a regulatory framework to address mine lake options.     

Use of Pb, <Superscript>18</Superscript>O,and <Superscript>2</Superscript>H Isotopes in Mining-related Environmental Studies

Abstract.   An isotopic and geochemical study of surface water and groundwater was undertaken at the Sullivan Mine, a sediment-hosted Pb-Zn massive sulphide deposit with a well-defined homogeneous Pb isotopic composition. The Pb isotopic composition of surface water and groundwater samples from near the mine site define a mixing line between Sullivan Pb and at least one other end member. The ¹⁸O and D isotopic results fall along an evaporation line that shows mixing between water from evaporative sources with water from meteoric sources.     

Geochemistry of Perched Water in an Abandoned Underground Mine, Butte, Montana

Abstract.  The Lexington tunnel is the last accessible underground mine working in the Butte, Montana mining district. Used as recently as 1993, the tunnel and adjacent workings have been abandoned for over 10 years. Although the Lexington tunnel is over 200 m above the regional water table, perched water is present over much of its extent. Mine water near the portal is moderately acidic (pH 4 to 5), with extremely high concentrations of metals, including Cu (up to 1000 mg/L) and Zn (up to 1400 mg/L). In the middle reaches of the tunnel, the quality of the water is much better, with near-neutral pH, high bicarbonate alkalinity, and lower concentrations of heavy metals. The low acidity and metal content is attributed to a lack of pyrite and other sulfides in this portion of the mine, as well as the presence of carbonate minerals, such as rhodochrosite (MnCO₃), in exposed veins. Sulfide minerals are more widespread further back in the tunnel, and are now oxidizing rapidly, leading to pockets of severe acid drainage (pH< 3, dissolved Zn up to 5000 mg/L). Geochemical modeling suggests that the near-neutral waters—the most voluminous type encountered in the Lexington tunnel—are close to equilibrium saturation with rhodochrosite and hydrous Zn-carbonate (ZnCO₃•H₂O). The Eh of these waters is most likely controlled by redox reactions involving dissolved Mn²⁺ and secondary, Zn-rich, hydrous Mn-oxides. In contrast, the Eh of the acidic waters appears to be controlled by reactions involving Fe²⁺ and Fe³⁺. Most of the acidic waters are saturated with K-jarosite, which forms delicate, straw-like dripstones at several localities. Decaying mine timbers could be an important renewable source of organic carbon for heterotrophic microorganisms, such as iron- and sulfate-reducing bacteria, especially deeper in the mine workings where the ground is saturated with anoxic ground water.     

Predicting Rebound in a Deep Colliery in South Africa

Abstract:  The main challenge facing many of the coal mines in South Africa is the management of mine water following the closure of mining operations. The Sigma Colliery is situated in the Free State Province, adjacent to the town of Sasolburg and bordering the Vaal River, one of the country's largest rivers. The mining includes both opencast and underground operations; however, this paper will only discuss the main underground operations. There are several aquifer systems overlying the deeper mining, which was done by bord and pillar and high extraction mining. Detailed conceptual models of the interactions between several aquifer systems and the rebounding mine voids were constructed using mining and monitoring data. From this, numerical flow models were used to model the complex flow system where rebound of water levels is expected. The results have led to an accurate understanding of the complex flow system and the important controls on the final water levels in the area.     

Evaluation of the Effluent Water Quality Produced at Phosphate Mines in Central Jordan

Abstract.   The effluent water produced by the washing process at the Al-Hisa and Al-Abyad phosphate mines in central Jordan was investigated in summer 2002. Twenty-four effluent and 10 ground water samples were collected and analyzed. There was a significant difference in water chemistry between input (groundwater) and output (effluent water) but, although the investigated area is highly fractured, the stable isotopic results indicated little or no mixing between the effluent water and groundwater in the area. This is attributed to the precipitation of clay-sized particles along the drainage channel. The quality of the effluent from the Al-Hisa mine was better than at the Al-Abyad mine, with electrical conductivity averaging 1474 µS/cm at Al-Hisa and 3250 µS/cm at Al-Abyad. The difference in effluent quality is attributed to slight lithological differences. At both mines, chloride was the predominant ion in the effluent water, with an average concentration of 669 ppm and 1299 ppm at the Al-Hisa and Al-Abyad mines respectively. The concentrations of heavy metals in the high-pH effluent water were very low, presumably due to precipitation and absorption onto suspended fine-grained particles. The effluent water from both mines was found to be relatively low in sodium and radiation, and suitable for the irrigation of salt tolerant plants.     

Giant Mine: Identification of Inflow Water Types and Preliminary Geochemical Monitoring during Reflooding

Abstract:  Between 1948 and 1999, gold ore containing high concentrations of arsenopyrite was mined at the Giant Mine near Yellowknife, Canada. Processing resulted in 215,000 kg of gold and approximately 237,000 tonnes of highly soluble arsenic trioxide, a by-product of the roasting process. The arsenic dust was collected and placed underground in 15 shallow chambers and stopes (within 75m of the surface) with the understanding that the ground would revert to permafrost conditions once mining was completed. Subsequent studies have shown that the ground is unlikely to refreeze naturally; therefore, it has been proposed to actively freeze the arsenic trioxide storage areas to hydraulically isolate them from the post-closure ground water system. However, other arsenic sources (backfilled tailings, etc.) exist deeper in the mine (600 m total depth), so there is a concern that arsenic will leach into the minewater system and ultimately into the environment when the mine is allowed to flood. Therefore, the development and implementation of a remediation plan for the site requires a good understanding of the arsenic distribution and expected release to the mine water. To gain this understanding, a detailed program of surface and underground sampling was carried out to identify or “type” the inflow sources to the mine, and their interaction with arsenic sources both on the surface and within the mine workings. As of July 2005, the mine has been allowed to begin reflooding to reduce pumping costs and remove the need for servicing pumps at the bottom of the mine, thus allowing the main shaft to be taken out of service. Prior to starting reflooding, a multi-level monitoring system was installed in the main shaft and is currently being used to monitor reflooding levels and water chemistry. Samples can be collected from each mine level intersecting the shaft. The system will monitor reflooding rate and test how underground arsenic sources (backfilled tailings, etc.) are affecting water quality in the mine. This geochemical information will be used to assess long-term arsenic loading from sources outside the frozen zone and predict how long mine water treatment will be needed before natural ground water flow can be allowed.     

Geochemistry and Isotopic Composition of H2S-rich Water in Flooded Underground Mine Workings,Butte, Montana,USA

Abstract.   Groundwater being pumped from the flooded West Camp mine workings of Butte, Montana, is elevated in hydrogen sulfide (H₂S), has a circum-neutral pH, and has high arsenic but otherwise low metal concentrations. The daily flux of H₂S and As pumped from the extraction well are each estimated at roughly 0.1 kg. Isotopic analysis of coexisting aqueous sulfide and sulfate confirms that the H₂S was produced by bacterial sulfate reduction. the mine waters are close to equilibrium saturation with amorphous FeS, amorphous ZnS, siderite, rhodochrosite, calcite, and goethite, but are undersaturated with orpiment (As₂S₃). The higher solubility of orpiment relative to other mental sulfides allows concentrations of dissolved arsenic (~ 100 g/L) that are well above human health standards. The West Camp waters differ markedly from the acidic and heavy metal-rich mine waters of the nearby Berkeley pit-lake. These differences are partly attributed to geology, and partly to mining history.     

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.     

Reclamation of Abandoned Coal Mine Waste in Korea using Lime Cake By-Products

Abstract.  There are hundreds of abandoned coal mines in Korea's steep mountain valleys. Enormous amounts of coal waste from these mines were dumped on the slopes, contaminating streams with sediment and acid mine drainage. A limestone slurry by-product (lime cake), which is produced during the manufacture of soda ash, was investigated for its potential use in reclaiming the coal waste. The lime cake is fine grained, has low hydraulic conductivities (10^-8 to 10^-9 cm sec^-1), high pH, high electrical conductivity, and trace amounts of heavy metals. A field experiment was conducted; each plot was 20 x 5 m in size on a 56% slope. Treatments included a control (waste only), lime (CaCO₃), and lime cake. The lime requirement (LR) of the coal waste to pH 7.0 was determined; treatments consisted of adding 25, 50, and 100% of the LR. The lime cake and lime were applied either as a layer between the coal waste and topsoil or mixed into the topsoil and waste. Each plot was hydroseeded with grasses, and planted with trees. In each plot, soils, surface runoff, and subsurface water were collected and analyzed, and plant cover was measured. Lime cake treatments increased the pH of the coal waste from 3.5 to 6, and neutralized the pH of the runoff and leachate of the coal waste from 4.3 to 6.7. Moreover, the surface cover of seeded species was significantly increased; sufficient acidity in the coal waste was neutralized in the 25% LR plots to allow seed germination.     

Using the DRASTIC System to Assess the Vulnerability of Ground Water to Pollution in Mined Areas of the Upper Silesian Coal Basin

Abstract  An attempt was made to use the U.S. EPA DRASTIC ranking system to assess the vulnerability of ground water in the Upper Silesian Coal Basin. Analysis of the various system components indicate that several DRASTIC factors would have to be modified to consider the effects of mining, subsidence, and ground water rebound.     

A Tragic Disaster Caused by the Failure of Tailings Dams Leads to the Formation of the Stava 1985 Foundation

Abstract.   This paper summarizes the dynamics and causes of the Stava disaster, and highlights some risky design procedures that led to the 19 July 1985 tailings dam failure. It then presents the Stava 1985 Foundation, which was formed to focus attention on such risks and to strengthen the culture of respect for human lives and safety.