Charles A. Cravotta

Limestone drains to increase pH and remove dissolved metals from acidic mine drainage

Despite encrustation by Fe and Al hydroxides, limestone can be eAective for remediation of acidic mine drainage (AMD). Samples of water and limestone (CaCO3) were collected periodically for 1 a at 3 identical limestone-filled drains in Pennsylvania to evaluate the attenuation of dissolved metals and the eAects of pH and Fe- and Alhydrolysis products on the rate of CaCO3 dissolution. The influent was acidic and relatively dilute (pH 1 mgL ˇ1 ) but was near neutral (pH=6.2‐ 7.0); Fe and Al decreased to less than 5% of influent concentrations. As pH increased near the inflow, hydrous Fe and Al oxides precipitated in the OLDs. The hydrous oxides, nominally Fe(OH)3 and Al(OH)3, were visible as loosely bound, orange-yellow coatings on limestone near the inflow. As time elapsed, Fe(OH)3 and Al(OH)3 particles were transported downflow. The accumulation of hydrous oxides and elevated pH (>5) in the downflow part of the OLDs promoted sorption and coprecipitation of dissolved Mn, Cu, Co, Ni and Zn as indicated by decreased concentrations of the metals in eCuent and their enrichment relative to Fe in hydrous-oxide particles and coatings on limestone. Despite thick (01 mm) hydrous-oxide coatings on limestone near the inflow, CaCO3 dissolution was more rapid near the inflow than at downflow points within and the OLD where the limestone was not coated. The high rates of CaCO3 dissolution and Fe(OH3) precipitation were associated with the relatively low pH and high Fe 3+ concentration near the inflow. The rate of CaCO3 dissolution decreased with increased pH and concentrations of Ca 2+ and HCO3 ˇ and decreased Pco2. Because overall eAciency is increased by combining neutralization and hydrolysis reactions, an OLD followed by a settling pond requires less land area than needed for a two-stage treatment system consisting of an anoxic limestone drain and oxidation-settling pond or wetland. To facilitate removal of hydrous-oxide sludge, a perforated-pipe subdrain can be installed within an OLD. # 1999 Elsevier Science Ltd. All rights reserved.

Assessing mine drainage pH from the color and spectral reflectance of chemical precipitates

The pH of mine impacted waters was estimated from the spectral reflectance of resident sediments composed mostly of chemical precipitates. Mine drainage sediments were collected from sites in the Anthracite Region of eastern Pennsylvania, representing acid to near neutral pH. Sediments occurring in acidic waters contained primarily schwertmannite and goethite while near neutral waters produced ferrihydrite. The minerals comprising the sediments occurring at each pH mode were spectrally separable. Spectral angle difference mapping was used to correlate sediment color with stream water pH (r 2 =0.76). Band-center and band-depth analysis of spectral absorption features were also used to discriminate ferrihydrite and goethite and/or schwertmannite by analyzing the 4 T1 6 A1 crystal field transition (900– 1000 nm). The presence of these minerals accurately predicted stream water pH (r 2 =0.87) and provided a qualitative estimate of dissolved SO4 concentrations. Spectral analysis results were used to analyze airborne digital multispectral video (DMSV) imagery for several sites in the region. The high spatial resolution of the DMSV sensor allowed for precise mapping of the mine drainage sediments. The results from this study indicate that airborne and space-borne imaging spectrometers may be used to accurately classify streams impacted by acid vs. neutral-to-alkaline mine drainage after appropriate spectral libraries are developed. Published by Elsevier Science Ltd.

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 31 and Fe 31 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. Published by Elsevier Science Ltd.

Water-quality trends for a stream draining the Southern Anthracite Field, Pennsylvania

Stream flow, chemical and biological data for the northern part of Swatara Creek, which drains a 112 km2 area in the Southern Anthracite Field of eastern Pennsylvania, indicate progressive improvement in water quality since 1959, after which most mines in the watershed had been flooded. Drainage from the flooded mines contributes substantially to base flow in Swatara Creek. Beginning in 1995, a variety of treatment systems and surface reclamation were implemented at some of the abandoned mines. At Ravine, Pa., immediately downstream of the mined area, median SO4 concentration declined from about 150 mg l−1 in 1959 to 75 mg l−1 in 1999 while pH increased from acidic to near-neutral values (medians: c. pH 4 before 1975; c. pH 6 after 1975). Fish populations rebounded from non-existent during 1959–1990 to 21 species identified in 1999. Nevertheless, recent monitoring indicates (1) episodic acidification and elevated concentrations and transport of Fe, Al, Mn, and trace metals during storm flow; (2) elevated concentrations of Fe, Mn, Co, Cu, Pb, Ni, and Zn in streambed sediments relative to unmined areas and to toxicity guidelines for aquatic invertebrates and fish; and (3) elevated concentrations of metals in fish tissue, notably Zn. The metals are ubiquitous in the fine fraction (<0.063 mm) of bed sediment in mining-affected tributaries and the main stem of Swatara Creek. As a result of scour and transport of streambed deposits, concentrations of suspended solids and total metals in the water column are correlated, and those for storm flow typically exceed base flow. Nevertheless, the metals concentrations are poorly correlated with stream flow because concentrations of suspended solids and total metals typically peak prior to peak stream stage. In contrast, SO4, specific conductance and pH are inversely correlated with stream flow as a result of dilution of poorly buffered stream water with weakly acidic storm runoff derived mainly from low-pH rainfall. Declines in pH to values approaching 5.0 during storm flow events or declines in redox potential during burial of sediment could result in the remobilization of metals associated with suspended solids and streambed deposits.

Design and Performance of Limestone Drains to Increase pH and Remove Metals from Acidic Mine Drainage

Publisher Summary This chapter presents data on the construction characteristics and the composition of influent and effluent at 13 underground, limestone-filled drains in Pennsylvania and Maryland to evaluate the design and performance of limestone drains for the attenuation of acidity and dissolved metals in acidic mine drainage. On the basis of the initial mass of limestone, dimensions of the drains, and average flow rates, the initial porosity and average detention time for each drain are computed. Calculated porosity ranged from 0.12 to 0.50 with corresponding detention times at average flow from 1.3 to 33 h. The effectiveness of treatment was dependent on influent chemistry, detention time, and limestone purity. At two sites where influent contained elevated dissolved Al (>5 mg/liter), drain performance declined rapidly. Elsewhere the drains consistently produced near-neutral effluent, even when influent contained small concentrations of dissolved Fe3+ (<5 mg/liter). Rates of limestone dissolution computed on the basis of average long-term Ca ion flux normalized by initial mass and purity of limestone at each of the drains ranged from 0.008 to 0.079 year–1. Data for alkalinity concentration and flux during 11-day closed-container tests using an initial mass of 4 kg crushed limestone and a solution volume of 2.3 liter yielded dissolution rate constants that were comparable to these long-term field rates. An analytical method is proposed using closed-container test data to evaluate long-term performance (longevity) or to estimate the mass of limestone required for a limestone treatment. This method considers flow rate, influent alkalinity, steady-state maximum alkalinity of eflluent, and desired eflluent alkalinity or detention time, and applies first-order rate laws for limestone dissolution (continuous) and production of alkalinity (bounded).

OPTIMIZATION OF LIMESTONE DRAINS FOR LONG-TERM TREATMENT OF MINE DRAINAGE, SWATARA CREEK BASIN, SCHUYLKILL COUNTY, PA

Abstract . Limestone drains were constructed in 1995, 1997, and 2000 to treat acidic mine drainage (AMD) from the Orchard, Buck Mtn., and Hegins discharges, respectively, in the Swatara Creek Basin, Southern Anthracite Coalfield, east-central Pennsylvania. This report summarizes the construction characteristics and performance of each of the limestone drains on the basis of influent and effluent quality and laboratory tests of variables affecting limestone dissolution rates. Data for influent and effluent indicate substantial alkalinity production by the Orchard and Buck Mtn. limestone drains and only marginal benefits from the Hegins drain. Nevertheless, the annual alkalinity loading rates have progressively declined with age of all three systems. Collapsible-container (cubitainer) testing was conducted to evaluate current scenarios and possible options for reconstruction and maintenance of the limestone drains to optimize their long-term performance. The cubitainer tests indicated dissolution rates for the current configurations that were in agreement with field flux data (net loading) for alkalinity and dissolved calcium. The dissolution rates in cubitainers were larger for closed conditions than open conditions, but the rates were comparable for coated and uncoated limestone for a given condition. Models developed on the basis of the cubitainer testing indicate (1) exponential declines in limestone mass and corresponding alkalinity loading rates with increased age of limestone drains and (2) potential for improved performance with enlargement, complete burial, and/or regular flushing of the systems. Additional Key Words: limestone dissolution rate, cubitainer tests, armoring.

Inhibition of bacterial oxidation of ferrous iron by lead nitrate in sulfate-rich systems

Inhibition of bacterial oxidation of ferrous iron (Fe(II)) by Pb(NO(3))(2) was investigated with a mixed culture of Acidithiobacillus ferrooxidans. The culture was incubated at 30 °C in ferrous-sulfate medium amended with 0-24.2 mM Pb(II) added as Pb(NO(3))(2). Anglesite (PbSO(4)) precipitated immediately upon Pb addition and was the only solid phase detected in the abiotic controls. Both anglesite and jarosite (KFe(3)(SO(4))(2)(OH)(6)) were detected in inoculated cultures. Precipitation of anglesite maintained dissolved Pb concentrations at 16.9-17.6 μM regardless of the concentrations of Pb(NO(3))(2) added. Fe(II) oxidation was suppressed by 24.2 mM Pb(NO(3))(2) addition even when anglesite was removed before inoculation. Experiments with 0-48 mM KNO(3) demonstrated that bacterial Fe(II) oxidation decreased as nitrate concentration increased. Therefore, inhibition of Fe(II) oxidation at 24.2 mM Pb(NO(3))(2) addition resulted from nitrate toxicity instead of Pb addition. Geochemical modeling that considered the initial precipitation of anglesite to equilibrium followed by progressive oxidation of Fe(II) and the precipitation of jarosite and an amorphous iron hydroxide phase, without allowing plumbojarosite to precipitate were consistent with the experimental time-series data on Fe(II) oxidation under biotic conditions. Anglesite precipitation in mine tailings and other sulfate-rich systems maintains dissolved Pb concentrations below the toxicity threshold of A. ferrooxidans.

AMDTreat 5.0+ with PHREEQC titration module to compute caustic chemical quantity, effluent quality, and sludge volume

Abstract Alkaline chemicals are commonly added to discharges from coal mines to increase pH and decrease concentrations of acidity and dissolved aluminum, iron, manganese, and associated metals. The annual cost of chemical treatment depends on the type and quantities of chemicals added and sludge produced. The AMDTreat computer program, initially developed in 2003, is widely used to compute such costs on the basis of the user-specified flow rate and water quality data for the untreated AMD. Although AMDTreat can use results of empirical titration of net-acidic or net-alkaline effluent with caustic chemicals to accurately estimate costs for treatment, such empirical data are rarely available. A titration simulation module using the geochemical program PHREEQC has been incorporated with AMDTreat 5.0+ to improve the capability of AMDTreat to estimate: (1) the quantity and cost of caustic chemicals to attain a target pH, (2) the chemical composition of the treated effluent, and (3) the volume of sludge produced by the treatment. The simulated titration results for selected caustic chemicals (NaOH, CaO, Ca(OH)2, Na2CO3, or NH3) without aeration or with pre-aeration can be compared with or used in place of empirical titration data to estimate chemical quantities, treated effluent composition, sludge volume (precipitated metals plus unreacted chemical), and associated treatment costs. This paper describes the development, evaluation, and potential utilization of the PHREEQC titration module with the new AMDTreat 5.0+ computer program available at http://www.amd.osmre.gov/.ZusammenfassungGrubenwässern von Kohleminen werden häufig basische Chemikalien zudosiert mit dem Ziel der pH-Wert-Anhebung sowie zur Abtrennung von Azidität, gelöstem Aluminium, Eisen, Mangan und assoziierten Metallen. Chemikalienverbrauch und Schlammanfall beeinflussen die Betriebskosten der chemischen Wasserbehandlung. Das Computerprogramm AMDTreat, ursprünglich im Jahre 2003 entwickelt, gestattet es, derartige Kosten auf der Basis der vom Nutzer anzugebenden Menge und Beschaffenheit des unbehandelten Sauerwassers zu berechnen. Zwar kann AMDTreat die Ergebnisse empirischer Titrationstests saurer oder alkalischer Abwässer mit basischen Chemikalien verwenden, um die Behandlungskosten genau abzuschätzen, jedoch sind solche empirischen Daten nur selten verfügbar. Um die Leistungsfähigkeit von AMDTreat in Bezug auf die Abschätzung von (1) Chemikalienmenge und -kosten zur Einstellung des Ziel-pH-Werts, (2) chemischer Beschaffenheit des behandelten Wassers, und (3) Volumen der Wasserbehandlungsschlämme zu verbessern, wurde in der Version AMDTreat 5.0+ nunmehr ein Titrationssimulationsmodul auf der Basis von PHREEQC inkorporiert. Die modellierten Titrationsergebnisse für ausgewählte Alkalien (NaOH, CaO, Ca(OH)2, Na2CO3, oder NH3) können—wahlweise mit oder ohne Belüftung—mit experimentellen Daten verglichen oder aber direkt verwendet werden, um Stoffmengen, Beschaffenheit des behandelten Wassers, Schlammvolumen (gefällte Metalle plus nicht reagierte Ausgangschemikalien) sowie die sich ergebenden Behandlungskosten abzuschätzen. Der Artikel beschreibt die Entwicklung, Bewertung und potentielle Nutzung des PHREEQC-Titrationsmoduls in Verbindung mit dem neuen Computerprogramm AMDTreat 5.0+, verfügbar unter http://www.amd.osmre.gov/.ResumenSustancias alcalinas son comúnmente agregadas a descargas de minas de carbón para incrementar el pH y hacer descender la acidez y las concentraciones de aluminio, hierro, manganeso y metales asociados. El costo anual del tratamiento químico depende del tipo de sustancia y de las cantidades de sustancia usada y de lodo producido. El programa AMDTreat, desarrollado inicialmente en 2003, es ampliamente usado para calcular tales costos sobre la base a los datos de velocidad de flujo y calidad de agua especificadas para el AMD no tratado. Aunque AMDTreat puede usar resultados de la titulación empírica de la acidez o alcalinidad neta del efluente con químicos cáusticos para estimar los costos del tratamiento, tales datos empíricos están raramente disponibles. Un módulo de simulación de titulación usando el programa geoquímico PHREEQC ha sido incorporado a AMDTreat 5.0+ para mejorar la capacidad de AMDTreat para estimar: (1) la calidad y costo de químicos cáusticos para alcanzar cierto pH, (2) la composición química del efluente tratado y (3) el volumen de lodo producido por el tratamiento. Los resultados de la titulación simulada para sustancias cáusticas seleccionadas (NaOH, CaO, Ca(OH)2, Na2CO3 o NH3) sin aireación o con pre-aireación puede ser comparado con, o usada en lugar de, los datos de titulación empírica para estimar las cantidades de sustancias químicas, composición del efluente tratado, volumen del lodo (metales precipitados más sustancias químicas no reaccionantes) y costos de tratamiento asociados. Este trabajo describe el desarrollo, evaluación y potencial uso del modulo de titulación PHREEQC con el nuevo programa AMDTreat 5.0+ disponible en http://www.amd.osmre.gov/.

Dissolution of Fluorapatite by Pseudomonas fluorescens P35 Resulting in Fluorine Release

ABSTRACT Chemical weathering of fluorine-bearing minerals is widely accepted as the main mechanism for the release of fluorine (F) to groundwater. Here, we propose a potential mechanism of F release via microbial dissolution of fluorapatite (Ca5(PO4)3F), which has been neglected previously. Batch culture experiments were conducted at 30°C with a phosphate-solubilizing bacteria strain, Pseudomonas fluorescens P35, and rock phosphates as the sole source of phosphate for microbial growth in parallel with abiotic controls. Rock phosphates consisted of 55–91% of fluorapatite and 5–10% of dolomite before microbial dissolution as indicated by X-ray diffraction (XRD). Mineral composition and morphology changed after microbial dissolution characterized by the disappearance of dolomite and the development of etched cavities on rock phosphate surfaces. The pH of media used was approximately 7.4 at the beginning and increased gradually to 7.7 in abiotic controls; with the inoculum, the pH decreased to acidic values of 3.7–3.8 after 27 h. Phosphate, calcium, and fluoride were released from the rock phosphate to the acidified medium. At 42 h, the concentration of F reached 8.1–10.3 mg L−1. The elevated F concentration was two times higher than the F levels in groundwater in regions diagnosed with fluorosis, and was toxic to the bacteria, as demonstrated by a precipitous decrease in live cells. Geochemical modeling demonstrated that the oxidation of glucose (the carbon source for microbial growth in the medium) to gluconic acid could decrease the pH to 3.7–3.8 and result in the dissolution of fluorapatite and dolomite. Dolomite and fluorapatite remained unsaturated, while concentrations of dissolved phosphorus (P), calcium (Ca), and F increased throughout the time course Fluorite reached saturation [saturation index (SI) 0.22–0.42] after 42 h in rock phosphate–amended biotic systems. However, fluorite was not detected in XRD patterns of the final residue from microcosms. Given that phosphate-solubilizing bacteria are ubiquitous in soil and groundwater ecosystems, they could play an important role in fluorapatite dissolution and the release of F to groundwater.

Naturally occurring contaminants in the Piedmont and Blue Ridge crystalline-rock aquifers and Piedmont Early Mesozoic basin siliciclastic-rock aquifers, eastern United States, 1994–2008

Groundwater quality and aquifer lithologies in the Piedmont and Blue Ridge Physiographic Provinces in the eastern United States vary widely as a result of complex geologic history. Bedrock composition (mineralogy) and geochemical conditions in the aquifer directly affect the occurrence (presence in rock and groundwater) and distribution (concentration and mobility) of potential naturally occurring contaminants, such as arsenic and radionuclides, in drinking water. To evaluate potential relations between aquifer lithology and the spatial distribution of naturally occurring contaminants, the crystalline-rock aquifers of the Piedmont and Blue Ridge Physiographic Provinces and the siliciclastic-rock aquifers of the Early Mesozoic basin of the Piedmont Physiographic Province were divided into 14 lithologic groups, each having from 1 to 16 lithochemical subgroups, based on primary rock type, mineralogy, and weathering potential. Groundwater-quality data collected by the U.S. Geological Survey (USGS) National Water-Quality Assessment (NAWQA) Program from 1994 through 2008 from 346 wells and springs in various hydrogeologic and land-use settings from Georgia through New Jersey were compiled and analyzed for this study. Analyses for most constituents were for filtered samples, and, thus, the compiled data consist largely of dissolved concentrations. Concentrations were compared to criteria for protection of human health, such as U.S. Environmental Protection Agency (USEPA) drinking water maximum contaminant levels and secondary maximum contaminant levels or health-based screening levels developed by the USGS NAWQA Program in cooperation with the USEPA, the New Jersey Department of Environmental Protection, and Oregon Health & Science University. Correlations among constituent concentrations, pH, and oxidationreduction (redox) conditions were used to infer geochemical controls on constituent mobility within the aquifers. Of the 23 trace-element constituents evaluated, arsenic, manganese, and zinc were detected in one or more water samples at concentrations greater than established human health-based criteria. Arsenic concentrations typically were less than 1 microgram per liter (μg/L) in most groundwater samples; however, concentrations of arsenic greater than 1 μg/L frequently were detected in groundwater from clastic lacustrine sedimentary rocks of the Early Mesozoic basin aquifers and from metamorphosed clastic sedimentary rocks of the Piedmont and Blue Ridge crystalline rock aquifers. Groundwater from these rock units had elevated pH compared to other rock units evaluated in this study. Of the nine samples for which arsenic concentration was greater than 10 μg/L, six were classified as oxic and three as anoxic, and seven had pH of 7.2 or greater. Manganese concentrations typically were less than 10 μg/L in most samples; however, 8.3 percent of samples from the Piedmont and Blue Ridge crystalline-rock aquifers and 3.0 percent of samples from the Early Mesozoic basin siliciclastic rock aquifers had manganese concentrations greater than the 300-μg/L health-based screening level. The positive correlation of manganese with iron and ammonia and the negative correlation of manganese with dissolved oxygen and nitrate are consistent with the reductive dissolution of manganese oxides in the aquifer. Zinc concentrations typically were less than 10 μg/L in the groundwater samples considered in the study, but 0.4 percent and 5.5 percent of the samples had concentrations greater than the health-based screening level of 2,000 μg/L and one-tenth of the health-based screening level, respectively. The mean rank concentration of zinc in groundwater from the quartz-rich sedimentary rock lithologic group was greater than that for other lithologic groups even after eliminating samples collected from wells constructed with galvanized casing. Approximately 90 percent of 275 groundwater samples had radon-222 concentrations that were greater than the proposed alternative maximum contaminant level of 300 picocuries per liter. In contrast, only 2.0 percent of 98 samples had combined radium (radium-226 plus radium-228) concentrations greater than the maximum contaminant level of 5.0 picocuries per liter, and 0.6 percent 2 Contaminants in Crystalline-Rock Aquifers and Siliciclastic-Rock Aquifers, Eastern United States, 1994–2008 of 310 samples had uranium concentrations greater than the maximum contaminant level of 30 μg/L. Radon concentrations were highest in the Piedmont and Blue Ridge crystalline-rock aquifers, especially in granite, and elevated median concentrations were noted in the Piedmont Early Mesozoic basin aquifers, but without the extreme maximum concentrations found in the crystalline rocks (granites). Although the siliciclastic lithologies had a greater frequency of elevated uranium concentrations, radon and radium were commonly detected in water from both siliciclastic and crystalline lithologies. Uranium concentrations in groundwater from clastic sedimentary and clastic lacustrine/evaporite sedimentary lithologic groups within the Early Mesozoic basin aquifers, which had median concentrations of 3.6 and 3.1 μg/L, respectively, generally were higher than concentrations for other siliciclastic lithologic groups, which had median concentrations less than 1 μg/L. Although 89 percent of the 260 samples from crystalline-rock aquifers had uranium concentrations less than 1 μg/L, 0.8 percent had uranium concentrations greater than the 30-μg/L maximum contaminant level, and 6.5 percent had concentrations greater than 3 μg/L.