Coal Mine Drainage Research Articles

Determination of Trace Element Stability in Sediments Using Redox Gel Probes: Probe Construction and Theoretical Performance

A simple and inexpensive technique is described that can be used to assess the stability of redox-sensitive compounds in the sediments of wetlands and other shallow water environments. In this method, solid redox-sensitive compounds, such as manganese dioxide (MnO 2 ), are incorporated into agar gels held in rigid plastic holders. One surface of the gel remains exposed along the length of the resulting probe. The probes are pushed vertically into sediments and are left in situ for a period of time (days to weeks), after which they are visually inspected and chemically analyzed. The diffusion of nonreactive solutes (e.g., sulfate) in 2% (wt/vol) agar was unaffected by the presence of immobilized MnO 2 particles. The rate of dissolution of particulate MnO 2 in agar gels in the presence of an external diffusing reductant (L-ascorbic acid) could be quantified by digital analysis of pixel density on gel images. Redox gel probes incubated in the sediment of a wetland built to remove manganese from circumneutral pH coal mine drainage demonstrated different patterns of depth-dependent MnO 2 stability along a 15-m transect. MnO 2 gel probe results were consistent with data obtained using sediment cores and porewater diffusion samplers.

THE USE OF WETLANDS TO REMOVE NICKEL FROM MINE DRAINAGE - IS PERPETUAL TREATMENT REALLY POSSIBLE?

Although wetland treatment systems have been shown to be effective for treating both coal and metal mine drainage, the longevity of the treatment has always been a question. Data collected from a wetland in northeastern Minnesota suggests it may be possible to build a wetland that will provide long term treatment. A 7000 square meter overland flow wetland was built in 1992 to treat a mine drainage with an av798798erage pH of 7.2 and an average nickel concentration of 5.1 mg/L. Nickel removal exceeded 90% for the first three years of operation. In 1995, the stockpile which contributed the major input to the wetland was capped, and both flow and concentrations in the drainage were reduced. An intensive study was conducted on one section of the wetland where a large percentage of the overall removal was occurring. Nickel concentrations in the substrate reached 1.5% by weight and the calculated nickel mass in the substrate was about the same as the overall mass removal calculated from the water quality and flow data. Based on a model of substrate accumulation in wetlands, the wetland generates 7 kg of nickel removal capacity each year. Since the annual input of nickel has been reduced to around 10 kg, the projected lifetime of the wetland is about 300 years.

Bacteria in gel probes: comparison of the activity of immobilized sulfate-reducing bacteria with in situ sulfate reduction in a wetland sediment

A novel method was used to examine the microbial ecology of iron-rich wetland sediments receiving neutral-pH coal mine drainage. Gel probes inserted into the sediments allowed analysis of the distribution and activity of bacterial sulfate reduction (BSR). A mixed population of sulfate-reducing bacteria enriched from anoxic wetland sediments was immobilized in low temperature-gelling agarose held in grooved rods or probes. The probes were inserted vertically into sediments and were allowed to incubate in situ for 48 h. After their retrieval, the gels were sectioned and analyzed for residual BSR activity and were compared to in situ BSR rates and chemical porewater profiles. The depth distribution of residual BSR activity in the immobilized cell gel probes differed significantly from the BSR measured in situ. Approximately 51% of the total integrated residual sulfate reduction activity measured in the gel probes occurred between 0 and 7 cm of the upper 20 cm of sediment. In contrast, ca. 99% of the integrated in situ BSR occurred between 7- and 20-cm depth, and only 1% of the total integrated rate occurred between 0- and 7-cm depth. Lactate-enriched bacteria immobilized in the gel may have been atypical of the majority of sulfate-reducing bacteria in the sediment. Agarose-immobilized sulfate-reducing bacteria might also be able to proliferate in the otherwise inhospitable zone of iron reduction, where sulfate and labile carbon compounds for which they are usually outcompeted can diffuse freely into the gel matrix. Gel probes containing particulate iron monosulfide (FeS) indicated that FeS remained stable in sediments at depths greater than 2 to 3 cm below the sediment–water interface, consistent with the shallow penetration of oxygen into surface sediments.

CHARACTERIZATION AND RECOURCE RECOVERY POTENTIAL OF PRECIPITATES ASSOCIATED WITH ABANDONED COAL MINE DRAINAGE

CHARACTERIZATION AND RECOURCE RECOVERY POTENTIAL OF PRECIPITATES ASSOCIATED WITH ABANDONED COAL MINE DRAINAGE

SURVEY OF BENTHIC DIATOM COMMUNITIES FROM LOTIC SYSTEMS WITHIN THE WESTERN ALLEGHENY PLATEAU

Over the course of 3 years (1997–1999), 72 stream sites were sampled for epilithic diatom communities. The analysis of these samples has led to the identification of over 325 species of diatoms. In addition to sampling the diatom community, selected physical and chemical parameters were recorded from each stream reach. These parameters included pH, specific conductance, current velocity, SRP, nitrate, silica, and total alkalinity. Canonical Correspondence Analysis (CCA) was used to identify influential environmental parameters and to assess the response of the diatom community to prominent anthropogenic inputs in the region (i.e. coal mine drainage, eutrophication). The initial analyses indicate that pH was the most influential environmental parameter along the first CCA axis. This shift was not unexpected, as acid mine drainage (AMD) in the region leads to a wide range of pH values (2.8–7.93). The highly acidic sites were characterized by species of the genus Eunotia (specifically E. exigua and E. steineckei), Frustulia rhomboides, and Pinnularia subcapitata. Furthermore, Achnanthidium minutissimum was the most widely distributed of the diatom species encountered, being found at 94% of the sites sampled. Streams that fluctuated between acidic and circumneutral pH (termed “teeter‐totter”) had greater abundances of Brachysira vitrea than other streams in this survey. Further implications for the use of these diatom communities as biomonitoring tools and the distribution of assemblages within the Western Allegheny Plateau will be discussed.

Long-term performance of anoxic limestone drains

Ten anoxic limestone drains (ALDs), buried beds of limestone gravel that add alkalinity through dissolution of calcite, have been monitored for a decade. Influent and effluent water quality data have been analyzed to determine the long-term performance of each ALD for treating coal mine drainage. Alkalinity concentrations in the effluent of the ten ALDs ranged from 80–320 mg/L as CaCO3 with near maximum levels of alkalinity being reached after approximately 15 hours of detention. ALDs that received mine water containing less than 1 mg/L of both ferric iron and aluminum have continued to produce consistent concentrations of alkalinity since their construction. However, an ALD that received 21 mg/L of aluminum experienced a rapid reduction in permeability and failed within eight months.

Chemical evolution of coal mine drainage in a non-acid producing environment, Wasatch Plateau, Utah, USA

The causes and problems of coal mine drainage, particularly acid mine drainage, in the Eastern and Interior Coal Provinces of the United States are well documented. West of the Mississippi River, where coal mines account for about 45% of total US coal production and where acid mine drainage is rare, the chemical evolution of coal mine drainage is less well documented and understood. In this investigation, we have used solute and isotopic compositions of non-evolved inflow groundwater and evolved mine discharge water to quantify the chemical evolution of mine discharge water in a western underground coal mine. Water enters the mine from fractures and roof bolt holes, which intercept groundwater in the overlying rock. Carbon-14, and 3H data indicate that these waters recharged between 12,000 and 19,500 years ago. The TDS and solute compositions of roof drip waters are spatially zoned and TDS concentrations range from about 300 to 550 mg l −1. After the water encounters minerals and other substances in the mine, the chemical differences between various mine regions become more pronounced and the TDS of mine drainage water increases to about 850 mg l −1. The TDS of mine drainage is related to water–rock ratios. Mine drainage issuing from the older mined areas, where water–rock ratios are low, has the greatest TDS. Geochemical and isotopic mass balance calculations were performed to quantify chemical reactions in the mine, and to identify sources contributing to the TDS of mine drainage. Chemical reaction pathways evaluated include pyrite oxidation, dissolution of native and rock dust gypsum, dissolution of calcite and dolomite, precipitation of calcite, ion exchange, precipitation of iron hydroxide, and organic decomposition of mining machine emulsion fluid. Solute and isotopic mass transfer reaction calculations demonstrate that the oxidation of pyrite triggers a series of cascading in-mine chemical reactions that are the primary cause of the elevated TDS of mine drainage relative to the TDS of roof-drip water. Pyrite oxidation does not result in acid drainage because of the buffering effect of abundant carbonate minerals. Dissolution of gypsum, both native and gypsum dust previously used as rock dust, is also a significant contributor of SO 4 2−. Ion exchange of Ca 2+ on the sodium zeolite analcime, which occurs in the coal, accounts for an increase in Na + concentrations. Oxidation of fugitive longwall emulsion fluid produces abundant CO 2(g) some of which indirectly affect the TDS of mine drainage.

Lithic controls on the removal of iron and remediation of acidic mine drainage

The remediation of streams adversely affected by acidic mine drainage often employs limestone as a neutralization agent. However, metal precipitation on the limestone surface can render it ineffective. This investigation reports preliminary field and laboratory results demonstrating that, in the presence of a mixture of limestone and sandstone, iron preferentially precipitates on the sandstone surface, and iron removal from aqueous solution is greater than with either of the materials alone. First, a river in Tennessee (USA) with preferential iron precipitation was characterized with respect to water quality and lithic surface morphology. Second, a field experiment where lithic samples were placed in an Ohio stream receiving coal mine drainage demonstrated that iron hydroxide preferentially coats quartz-rich lithologies. Finally, laboratory experiments confirmed enhanced iron removal in the presence of mixed lithic surfaces. Based on these results, the use of multiple lithic surfaces, particularly in-stream, has the potential to provide improved methods for the treatment of acidic mine wastes.

Aluminium and iron burdens of aquatic biota in New Zealand streams contaminated by acid mine drainage: effects of trophic level

Concentrations of Al and Fe were determined in samples of filamentous algae, bryophytes and invertebrates from 24 stream sites in North Westland, South Island, New Zealand. Sites were variably contaminated by acid coal mine drainage and ranged in pH from 2.6 to 6.2. Conductivity of stream water ranged from 16 to 944 μS 25 cm −1 and maximum concentrations of total dissolved Al and total Fe measured in two successive years were 35.5 and 32.6 mg l −1, respectively. Metal burdens of algae and bryophytes were not correlated with pH, conductivity or the concentrations of Al and Fe observed in stream water. Metal concentrations in invertebrates were significantly lower than those in plants (mg per g dry wt.), and were similar in herbivore–detritivores (mainly mayfly larvae) and carnivorous species. No evidence was found for the biomagnification of either metal within aquatic food webs. However, invertebrate species exposed to very high concentrations of Al and Fe varied considerably in body burdens, suggesting that groups of insects differ considerably in their physiological or morphological ability to exclude potentially toxic metals.

River water quality in the Humber catchment: an introduction using GIS-based mapping and analysis

The regional water quality of the Humber catchment was mapped for key inorganic chemical determinands using a GIS system and an extensive Environment Agency and LOIS monitoring database. The resultant maps revealed the major factors affecting the general characteristics of regional water quality. Sewage inputs from industrial and domestic sources account for the high concentration of many determinands in urban areas. The concentrations of particulate components increase in tidal zones because of sediment trapping and tidal re-suspension effects. Some determinands also exhibit localized high concentrations related to coal mine drainage, soil pollution caused by past ore mining, bedrock geology, the agricultural use of fertilizers and the ingression of seawater into the estuary.

Apparent solubilities of schwertmannite and ferrihydrite in natural stream waters polluted by mine drainage

The apparent solubilities of schwertmannite and ferrihydrite were estimated from the H+, OH−, Fe3+, and SO42− activities of the natural stream waters in Korea and mine drainage in Ohio, USA. Both chemical composition of the stream waters and the mineralogy of the precipitates were determined for samples from two streams polluted by coal mine drainage. This study combines these new results with previous data from Ohio, USA to redetermine solubilities. The activities of the dissolved species necessary for the solubility determinations were calculated from the chemical compositions of the waters with the WATEQ4F computer code.Laboratory analyses of precipitates indicated that the main minerals present in Imgok and Osheep creek were schwertmannite and ferrihydrite, respectively. The schwertmannite from Imgok creek had a variable chemical formula of Fe8O8(OH)8−2x(SO4)x· nH2O, where 1.74 ≤ x ≤ 1.86 and 8.17 ≤ n ≤ 8.62. The chemical formula of ferrihydrite was Fe2O3· 1.6H2O. With known mineralogy of the precipitates from each stream, the activities of H+, OH−, Fe3+, and SO42− in the waters were plotted on logarithmic activity-activity diagrams to determine apparent solubilities of schwertmannite and ferrihydrite. The best estimate for the logarithm of the solubility product of schwertmannite, logKs, was 10.5 ± 2.5 around 15°C. This value of logKs constrains the logarithm of the solubility product of ferrihydrite, logKf, to be 4.3 ± 0.5 to maintain the stability boundary with schwertmannite observed in natural waters.

Environmental risks associated with a contaminated freshwater sediment exposed to a coal-mine drainage water

Environmental risks associated with a contaminated freshwater sediment exposed to a coal-mine drainage water

Relative contributions of abiotic and biological factors in Fe(II) oxidation in mine drainage

The oxidation of Fe(II) is apparently the rate-limiting step in passive treatment of coal mine drainage. Little work has been done to determine the kinetics of oxidation in such field systems, and no models of passive treatment systems explicitly consider iron oxidation kinetics. A Stella II ™ model using Fe(II) init concentration, pH, temperature, Thiobacillus ferrooxidans and O 2 concentration, flow rate, and pond volume is used to predict Fe(II) oxidation rates and concentrations in seventeen ponds under a wide range of conditions (pH 2.8 to 6.8 with Fe(II) concentrations of less than 240 mg L −1) from 6 passive treatment facilities. The oxidation rate is modeled based on the combination of published abiotic and biological laboratory rate laws. Although many other variables have been observed to influence Fe(II) oxidation rates, the 7 variables above allow field systems to be modeled reasonably accurately for conditions in this study. Measured T. ferrooxidans concentrations were approximately 10 7 times lower than concentrations required in the model to accurately predict field Fe(II) concentrations. This result suggests that either 1) the most probable number enumeration method underestimated the bacterial concentrations, or 2) the biological rate law employed underestimated the influence of bacteria, or both. Due to this discrepancy, bacterial concentrations used in the model for pH values of less than 5 are treated as fit parameters rather than empirically measured values. Predicted Fe(II) concentrations in ponds agree well with measured Fe(II) concentrations, and predicted oxidation rates also agree well with field-measured rates. From pH 2.8 to approximately pH 5, Fe(II) oxidation rates are negatively correlated with pH and catalyzed by T. ferrooxidans. From pH 5 to 6.4, Fe(II) oxidation appears to be primarily abiotic and is positively correlated with pH. Above pH 6.4, oxidation appears to be independent of pH. Above pH 5, treatment efficiency is affected most by changing design parameters in the following order: pH>temperature≈influent Fe(II)>pond volume≈O 2. Little to no increase in Fe(II) oxidation rate occurs due to pH increases above pH 6.4. Failure to consider Fe(II) oxidation rates in treatment system design may result in insufficient Fe removal.

Comparison of color, chemical and mineralogical compositions of mine drainage sediments to pigment

Forty-three untreated and actively and passively (wetland) treated coal mine drainage sediments and five yellow-red pigments were characterized using X-ray fluorescence, fusion-inductively coupled plasma atomic emission spectroscopy, X-ray diffraction, and tristimulus colorimeter. Primary crystalline iron-bearing phases were goethite and lepidocrocite, and iron phases converted to hematite upon heating. Quartz was nearly ubiquitous except for synthetic pigments. Gypsum, bassinite, calcite, and ettringite were found in active treatment sediments. Iron concentrations from highest to lowest were synthetic pigment>wetland sediment>natural pigment>active treatment (untreated sediments varied more widely), and manganese was highest in actively treated sediments. Loss on ignition was highest for passively treated sediments. No clear trends were observed between quantified color parameters (L*, a*, b*, and Redness Index) and chemical compositions. Because sediments from passive treatment are similar in chemistry, mineralogy, and color to natural pigments, the mine drainage sediments may be an untapped resource for pigment.

Sizing and performance estimation of coal mine drainage wetlands

The effectiveness of wetland treatment of acid mine drainage (AMD) was assessed using three measures of performance: treatment efficiency, area-adjusted removal, and first-order removal. Mathematical relationships between these measures were derived from simple kinetic equations. Area-adjusted removal is independent of pollutant concentration (zero-order reaction kinetics), while first-order removal is dependent on concentration. Treatment efficiency is linearly related to area-adjusted removal and exponentially related to first-order removal at constant hydraulic loading rates (flow/area). Examination of previously published data from 35 natural AMD wetlands revealed that statistically significant correlations exist between several of the performance measures for both iron and manganese removal, but these correlations are potentially spurious because these measures are derived from, and are mathematical rearrangements of, the same operating data. The use of treatment efficiency as a measure of performance between wetlands is not recommended because it is a relative measure that does not account for influent concentration differences. Area-adjusted removal accounts for mass loading effects, but it fails to separate the flow and concentration components, which is necessary if removal is first-order. Available empirical evidence suggests that AMD pollutant removal is better described by first-order kinetics. If removal is first-order, the use of area-adjusted rates for determining the wetland area required for treating relatively low pollutant concentrations will result in undersized wetlands. The effects of concentration and flow rate on wetland area predictions for constant influent loading rates also depend on the kinetics of pollutant removal. If removal is zero-order, the wetland area required to treat a discharge to meet some target effluent concentration is a decreasing linear function of influent concentration (and an inverse function of flow rate). However, if removal is first-order, the required wetland area is a non-linear function of the relative influent concentration. Further research is needed for developing accurate first-order rate constants as a function of influent water chemistry and ecosystem characteristics in order to successfully apply the first-order removal model to the design of more effective AMD wetland treatment systems.

Performance of some diversity and biotic indices in rivers affected by coal mining in northwestern Spain

Diversity and biotic indices are often used to asses freshwater quality. However, few studies have been made of their applicability to mining-derived impact. Biotic indices, in particular, are problematic in this respect because they are devised for specific types of pollution (usually organic). Thus, caution is required when using them in streams contaminated by other classes of pollutants. This study evaluates the performance of several diversity and biotic indices in rivers affected by coal mining in northwestern Spain. The relation between them and a set of environmental variables has been determined by means of correlation (Pearson correlation coefficient). According to the correlation analysis, the variables most related to the biological parameters were by far those indicating mining impact (sulfate and conductivity). In general, the rest of the variables (nitrate, orthophosphate, chloride, distance from the source, among others) were not significantly correlated with th e biological indices. BMWP' (a Spanish version of the BMWP) and family richness of Ephemeroptera, Plecoptera and Trichoptera (EPT family richness) were the indices most succesful in detecting mining impact, as shown by their high correlation with conductivity and sulfate. ASPT' (derived from BMWP'), the Shannon index and family richness were of lesser indicative value. These results suggest that some biotic indices may be a useful tool for monitoring water quality in rivers receiving coal mine drainage. BMWP', in particular, could be a good starting point for devising a biotic index specific to this type of pollution.

Hydrobiogeochemical interactions in `anoxic' limestone drains for neutralization of acidic mine drainage

Processes affecting neutralization of acidic coal mine drainage were evaluated within `anoxic' limestone drains (ALDs). Influents had pH≤3.5 and dissolved oxygen <2 mg/l. Even though effluents were near neutral (pH>6 and alkalinity>acidity), two of the four ALDs were failing due to clogging. Mineral-saturation indices indicated the potential for dissolution of calcite and gypsum, and precipitation of Al 3+ and Fe 3+ compounds. Cleavage mounts of calcite and gypsum that were suspended within the ALDs and later examined microscopically showed dissolution features despite coatings by numerous bacteria, biofilms, and Fe–Al–Si precipitates. In the drain exhibiting the greatest flow reduction, Al-hydroxysulfates had accumulated on limestone surfaces and calcite etch points, thus causing the decline in transmissivity and dissolution. Therefore, where Al loadings are high and flow rates are low, a pre-treatment step is indicated to promote Al removal before diverting acidic mine water into alkalinity-producing materials.

Field determination of Fe 2+ oxidation rates in acid mine drainage using a continuously-stirred tank reactor

A gravity-fed, battery-powered, portable continuously-stirred tank reactor has been developed to directly measure aqueous reaction rates in the field. Dye and tracer experiments indicate the reactor is well-mixed. Rates of Fe 2+ oxidation at untreated and passively treated coal mine drainage sites in Pennsylvania were measured under ambient conditions and with the addition of either O 2 gas or NaOH solutions. Rates at 5 sites ranged from below the detection limit for this technique (approximately 10 −9 mol L −1 s −1) to 3.27±0.01×10 −6 mol L −1 s −1. Uncertainties in rates ranged from 70% near the lower limit of measurement to as little as 1% at higher rates of reaction. Multiple linear regressions showed no universal correlations of rates to Fe 2+, dissolved O 2, and pH ( Thiobacillus populations were not measured), although data for two more acidic sites were found to fit well for the model log rate=log K+a log [Fe 2+]+b log [OH −]+c log [O 2]. Field rates of Fe oxidation from this and other studies vary by 4 orders of magnitude. A model using the ambient field rate of Fe oxidation from this study successfully reproduced independently-measured Fe 2+ concentrations observed in a passive wetland treatment facility.

Insect faunas of acidic coal mine drainages in Westland, New Zealand

Insect faunas at 10 stream sites affected by acidic drainage from abandoned coal mines were examined in North Westland. Stream water pH ranged from 2.6 to 4.2 and concentrations of dissolved aluminium and iron were elevated at all sites. Larval Ephemeroptera, Plecoptera, Trichoptera, Megaloptera, Coleoptera and Diptera were found at various sites, with species of Chironomidae (Diptera), Scirtidae (Coleoptera), Kokiriidae and Oeconesidae (both Trichoptera) below pH 3. The occurrence of caddisfly larvae belonging to four families at pH>3.6 is noteworthy and consistent with the hypothesis that many New Zealand stream insects are habitat generalists that tolerate a wide range of physico-chemical conditions.

VALIDITY OF MANGANESE AS A SURROGATE OF HEAVY METALS REMOVAL IN CONSTRUCTED WETLANDS TREAUNG ACIDIC MINE WATER

The evaluation of manganese as a surrogate for heavy metal behavior in two wetland treatment systems receiving acidic coal mine drainage in central Pennsylvania was investigated. The use of manganese as an indicator is based on physical/chemical treatment processes quite different from wetland treatment. The treatment systems represented one anoxic, subsurface flow system and one oxic surface flow system. Water quality parameters measured included pH, alkalinity, acidity, and a suite of metals. Correlation and linear regression analysis were used to evaluate the ability of a candidate predictor variable (indicator) to predict heavy metal concentrations and removal. The use of manganese as a predictor of effluent quality proved to be poor in both wetland treatment systems, as evidenced by low linear R{sup 2} values and negative correlations. Zinc emerged as the best predictor of the detectable heavy metals at the anoxic wetland. Zinc exhibited positive strong linear correlations with copper, cobalt, and nickel (R{sup 2} values of 0.843, 0.881, and 0.970, respectively). Effluent pH was a slightly better predictor of effluent copper levels in the anoxic wetland. Iron and cobalt effluent concentrations showed the only strong relationship (R{sup 2} value = 0.778) in the oxic system. The lack of good correlationsmore » with manganese strongly challenges its appropriateness as a surrogate for heavy metals in these systems.« less