Acid Rock Drainage Generation Research Articles

Do mature hydrocarbons have an influence on acid rock drainage generation?

The generation of acid rock drainage (ARD) is a biogeochemical process that causes severe ecological impacts, threatening human health worldwide. Microbes involved in acid drainage reactions are generally considered autotrophic but heterotrophic and mixotrophic microorganisms have often been identified at ARD sites. This raises questions about the role of organic matter naturally present at these sites, such as mature hydrocarbons, in promoting the microbial processes underpinning ARD generation. To investigate this, aerobic microcosm experiments were carried out using ARD samples collected at a well-characterised site in northern England (Mam Tor, Derbyshire). Organic analyses indicated the presence of substantial amounts of mature, petroleum-derived hydrocarbons and microbial analyses indicated that the sediment hosts acidophilic bacteria with the capability of degrading petroleum-derived compounds. However, the aerobic microcosm experiments indicated that these petroleum-derived hydrocarbons were not used by the bacterial community and, therefore, are not involved in the reactions that ultimately lead to ARD generation. These observations support a primary role for autotrophs in ARD generation.

Reduction of acid rock drainage using steel slag in cover systems over sulfide rock waste piles.

The extraction of gold, coal, nickel, uranium, copper and other earth-moving activities almost always leads to environmental damage. In metal and coal extraction, exposure of sulfide minerals to the atmosphere leads to generation of acid rock drainage (ARD) and in underground mining to acid mine drainage (AMD) due to contamination of infiltrating groundwater. This study proposes to develop a reactive cover system that inhibits infiltration of oxygen and also releases alkalinity to increase the pH of generated ARD and attenuate metal contaminants at the same time. The reactive cover system is constructed using steel slag, a waste product generated from steel industries. This study shows that this type of cover system has the potential to reduce some of the adverse effects of sulfide mine waste disposal on land. Geochemical and geotechnical characterization tests were carried out. Different proportions of sulfide mine waste and steel slag were studied in leachate extraction tests. The best proportion was 33% of steel slag in dry weight. Other tests were conducted as follows: soil consolidation, saturated permeability and soil water characteristic curve. The cover system was numerically modeled through unsaturated flux analysis using Vadose/w. The solution proposed is an oxygen transport barrier that allows rain water percolation to treat the ARD in the waste rock pile. The results showed that the waste pile slope is an important factor and the cover system must have 5 m thickness to achieve an acceptable effectiveness.

Life cycle assessment of the desulfurisation flotation process to prevent acid rock drainage: A base metal case study

The long-term generation of acid rock drainage (ARD) from sulfide-bearing mine waste is a major environmental liability for the mining sector. Previous studies have demonstrated that these ARD risks can be effectively avoided, and resource recovery simultaneously improved, through the pre-disposal removal of sulfide minerals, by means of flotation.This study uses life cycle assessment to evaluate the broader environmental consequences of incorporating a desulfurisation flotation unit for the pre-disposal treatment of a base metal sulfide tailings wastestream. The desulfurisation flotation process is shown to result in a significant decrease in human toxicity, eco-toxicity, urban land occupation and natural land transformation impacts, but an increase in climate change, fossil fuel depletion and terrestrial acidification impacts. Desulfurisation flotation also offers the opportunity for improved recovery of valuable resources, such as water, residual metals and sulfur. An expanded system boundary would, however, be required to capture the environmental benefits of upstream and downstream utilisation of recovered resources. The study also highlighted the deficiencies of current life cycle impact assessment tools, in terms of their ability to adequately assess the environmental impacts associated with solid mineral wastes. These deficiencies and shortcomings will be the subject of further studies.

Mineralogy and trace element geochemistry of gas shales in the United States: Environmental implications

This paper presents a compilation of published mineralogic and trace element data from nine gas shales in the United States. Formations analyzed include the Antrim, Bakken, Barnett, Eagle Ford, Haynesville, Marcellus, New Albany, Utica and Woodford. These mineralogic and trace element data can be used to assess the potential for environmental impacts during hydraulic fracturing. Impacts addressed in this study include: 1) the potential for acid rock drainage generation during gas shale weathering, 2) the distribution of trace elements in gas shales and comparison with regulatory guidelines, and 3) the implications for environmental management of well cuttings. The use of the mineralogic data to assess the fracability of the gas shales is also considered. Compilations of the mineralogy and geochemistry of gas shales can be a valuable resource for managing real and perceived environmental problems associated with their exploitation. Comprehensive environmental assessment to fully address these issues, in addition to other potential environmental impacts, will require collection and collation of additional data on the mineralogy and trace element geochemistry of gas and other hydrocarbon producing shales.

고속도로 건설현장의 산성배수 발생개연성평가 및 피해저감대책: ○○고속도로건설현장

<TEX>${\bigcirc}{\bigcirc}$</TEX>고속도로 건설현장 <TEX>${\bigcirc}$</TEX>공구에 분포하는 암석에 대하여 산성배수 발생개연성을 평가하고 피해 저감대책을 검토하였다. 고속도로건설구간의 지반은 이천리층에 해당하는 사암과 중성내지 산성 화산암으로 구성되어 있으며 이들은 주변의 화강암관입에 수반된 열수 용액에 의해 황화광물을 산점상으로 함유하고 있다. 황화광물의 함량이 높은 화산암과 사암은 산성배수 발생개연성이 높고 중금속(Zn, Pb, As)을 많이 함유한 산성배수가 주변지역으로 유출되어 환경오염을 유발할 개연성이 높은 것으로 나타났다. 건설공사과정중 산성배수가 발생될 개연성이 높은 구역에서 배출되는 배수는 중화 및 중금속 제거처리 후 배수가 이루어져야 하며, 절취면의 안정성 확보를 위하여 산성배수의 발생을 근원적으로 억제할 수 있는 코팅처리기술을 적용한 후 숏크리트, 앵커 등 사면보강공법이 적용되어야 할 것으로 판단된다. 화산암과 사암은 골재로서 활용이 어려우며 지반성토재로 사용할 경우 지하수와 우수의 접촉을 최소화할 수 있는 성토층의 구조를 갖춘 후 활용하여야 한다. Assessment and damage reduction strategy of acidic rock drainage were conducted in a section of <TEX>${\bigcirc}{\bigcirc}$</TEX> highway construction site. The geology of the studied section consists of Icheonri sandstone and intermediate to acidic volcanic rocks. Sulfides occur as a disseminated type in sandstone and volcanics which were altered by the hydrothermal solution of granite intrusion. Volcanics and sandstone with a high content of sulfide were classified as a potentially acid rock drainage(ARD) forming rock. The drainage originated from those rocks may acidify and contaminate the surrounding area during the highway construction. Therefore, the drainage should be treated before it is discharged. A slope landslide hazard due to the ARD was also expected and the coating technology was recommended for the reduction of ARD generation as a preemptive measure before reinforcement work for enhancing slope stability such as shotcrete and anchor. According to the ARD risk analysis, those rocks should not be used as cement aggregate, but only to be used as a bank fill material of a filling-up system that allows minimal contact with rainfall and groundwater.

Acid Rock Drainage and Rock Weathering in Antarctica: Important Sources for Iron Cycling in the Southern Ocean

Here we describe biogeochemical processes that lead to the generation of acid rock drainage (ARD) and rock weathering on the Antarctic landmass and describe why they are important sources of iron into the Antarctic Ocean. During three expeditions, 2009-2011, we examined three sites on the South Shetland Islands in Antarctica. Two of them displayed intensive sulfide mineralization and generated acidic (pH 3.2-4.5), iron-rich drainage waters (up to 1.78 mM Fe), which infiltrated as groundwater (as Fe(2+)) and as superficial runoff (as Fe(3+)) into the sea, the latter with the formation of schwertmannite in the sea-ice. The formation of ARD in the Antarctic was catalyzed by acid mine drainage microorganisms found in cold climates, including Acidithiobacillus ferrivorans and Thiobacillus plumbophilus. The dissolved iron (DFe) flux from rock weathering (nonmineralized control site) was calculated to be 0.45 × 10(9) g DFe yr(-1) for the nowadays 5468 km of ice-free Antarctic rock coastline which is of the same order of magnitude as glacial or aeolian input to the Southern Ocean. Additionally, the two ARD sites alone liberate 0.026 and 0.057 × 10(9) g DFe yr(-1) as point sources to the sea. The increased iron input correlates with increased phytoplankton production close to the source. This might even be enhanced in the future by a global warming scenario, and could be a process counterbalancing global warming.

Characterization and assessment of potential environmental risk of tailings stored in seven impoundments in the Aries river basin, Western Romania

BackgroundThe objective of this study was to examine the potential environmental risk of tailings resulted after precious and base metal ores processing, stored in seven impoundments located in the Aries river basin, Romania. The tailings were characterized by mineralogical and elemental composition, contamination indices, acid rock drainage generation potential and water leachability of hazardous/priority hazardous metals and ions. Multivariate statistical methods were used for data interpretation.ResultsTailings were found to be highly contaminated with several hazardous/priority hazardous metals (As, Cu, Cd, Pb), and pose potential contamination risk for soil, sediments, surface and groundwater. Two out of the seven studied impoundments does not satisfy the criteria required for inert wastes, shows acid rock drainage potential and thus can contaminate the surface and groundwater. Three impoundments were found to be highly contaminated with As, Pb and Cd, two with As and other two with Cu. The tailings impoundments were grouped based on the enrichment factor, geoaccumulation index, contamination factor and contamination degree of 7 hazardous/priority hazardous metals (As, Cd, Cr, Cu, Ni, Pb, Zn) considered typical for the studied tailings. Principal component analysis showed that 47% of the elemental variability was attributable to alkaline silicate rocks, 31% to acidic S-containing minerals, 12% to carbonate minerals and 5% to biogenic elements. Leachability of metals and ions was ascribed in proportion of 61% to silicates, 11% to acidic minerals and 6% to the organic matter. A variability of 18% was attributed to leachability of biogenic elements (Na, K, Cl-, NO3-) with no potential environmental risk. Pattern recognition by agglomerative hierarchical clustering emphasized the grouping of impoundments in agreement with their contamination degree and acid rock drainage generation potential.ConclusionsTailings stored in the studied impoundments were found to be contaminated with some hazardous/ priority hazardous metals, fluoride and sulphate and thus presents different contamination risk for the environment. A long term monitoring program of these tailings impoundments and the expansion of the ecologization measures in the area is required.

Oxygen influx and geochemistry of percolate water from reactive mine waste rock underlying a sloping channelled soil cover

An ideal engineered soil cover can mitigate acid rock drainage (ARD) by limiting water and gaseous O2 ingress into an underlying waste rock pile. However, the barrier layer in the soil cover almost invariably tends to develop cracks or fractures after placement. These cracks may change water flow and O2 transport in the soil cover and decrease performance in the long run. The present study employed a 10-cmwide sand-filled channel installed in a soil barrier layer (silty clay) to model the aggregate of cracks or fractures that may be present in the cover. The soil cover had a slope of 20%. Oxygen transport through the soil cover and oxidation of the underlying waste rock were investigated and compared to a controlled column test with bare waste rock (without soil cover). Moreover, gaseous O2 transport in the soil cover with channel and its sensitivity to channel location as well as the influence of the saturated hydraulic conductivity of the channel material were modeled using the commercial software VADOSE/W. The results indicted that the waste rock underlying the soil cover with channel had a lower oxidation rate than the waste rock without cover because of reduced O2 ingress and water flushing in the soil cover with channel, which meant a partial soil cover might still be effective to some extent in reducing ARD generation. Gaseous O2 ingress into the covered waste rock was more sensitive to the channel location than to the saturated hydraulic conductivity of the material filling the channel. Aqueous equilibrium speciation modeling and scanning electron microscopy with energy dispersive X-ray analysis indicated that secondary minerals formed as a result of the oxidation of the waste rock included gypsum and goethite in the covered waste rock and schwertmannite and other Fe oxides in the uncovered waste rock. The findings of the study provided insight into the effect of channel flow on O2 transport and oxidation of the covered waste rock, which may help to improve soil cover design and construction to minimise the generation of preferential flow in the barrier layer.

ARD generation and corrosion potential of exposed roadside rockmass at Boeun and Mujoo, South Korea

Acid rock drainage (ARD) is a longstanding problem often associated with the resulting corrosion due to the acidity generated from sulfidic oxidation. To evaluate characteristics of ARD and corrosion, samples from the road side rock mass of Boeun and Mujoo were analysed using X-ray diffraction, acid/base accounting and Leaching tests. The results indicated that many samples had a pyritic origin and can be regarded as acid-generating rocks. The Leaching test showed that the average pH of the leachates of samples from both Boeun and Mujoo were moderately acidic, ranging from 3 to 4. Interestingly, as acidity increases from pH 4, the SO4−, Fe, Al and Mg concentrations increase abnormally. Samples from roadside slope of Mujoo showed high corrosive potential. Maximum sulfide oxidation rate of a sample taken from Mujoo was as high as 5,166 mg/kg/week.

Evaluación de la reactividad de sulfuros de hierro y residuos mineros: una metodología basada en la aplicación de la voltamperometría cíclica

The mining industry around the world produces an important amount of wastes, which by their high toxic metal and iron sulfide content present a serious environmental problem. Iron sulfide oxidation under weathering conditions provokes the main environmental problem of the mining industry, the generation of Acid Rock Drainage (ARD). Up to now the prediction methodologies do not allow the study of important factors that influence the generation of ARD, producing in some cases erroneous or uncertain conclusions. This paper shows the utilization of cyclic voltammetry using carbon paste electrodes (CPE-Mineral) as an alternative tool in the study of the oxidation capacity of iron sulfides and mining wastes. This electrochemical technique constitutes a novel methodology to establish and understand the factors involved during generation of ARD. Results of several studies including selected sulfide samples and sulfide mining wastes have been described in order to show the capacity of this methodology as a complementary tool in the prediction of the generation of ARD.

Utilization of Atikokan coal fly ash in acid rock drainage control from Musselwhite Mine tailings

A site-specific study is carried out to assess the suitability of utilizing Atikokan coal fly ash (AFA) as a buffering material to control and mitigate the generation of acid rock drainage from reactive Musselwhite Mine tailings. The physical, chemical, and mineralogical properties of the fly ash and mine tailings are determined via experiments, followed by six kinetic column permeation tests to monitor the leaching properties of the coal fly ash and coal fly ash – mine tailings mixtures. The results of the experiments indicate that the hydraulic conductivities of high-calcium AFA and the ash–tailings mixtures are significantly reduced upon contact with acidic drainage. The pH of the pore fluid has increased from acidic (pH 4) to alkaline (pH 8 and above). Chemical analyses after the kinetic column permeation tests further indicate that concentrations of regulated elements in the leachate from the ash–tailings mixtures are well below the guideline limits set by the Ontario environmental authority for accelerated flow conditions.Key words: coal fly ash, mine tailings, hydraulic conductivity, pH, heavy metals, acid rock drainage.

Variations in moisture content for a soil cover over a 10 year period

The Equity Silver mine is located in north-central British Columbia and is the site of a large, well-instrumented soil cover. The soil-cover site was designed to prevent the generation of acid rock drainage from the acid-generating waste rock disposed of at this site. The cover was designed to act as an oxygen barrier by maintaining a layer of saturated soil above the waste rock. The cover consists of a compacted till placed over the waste rock and covered with a non-compacted layer of the same material. Neutron probes and thermal conductivity sensors were used to monitor the moisture content of the cover soil over a 10 year period. Weather data at the site were also collected. A review of the data collected has shown that saturation was maintained in the lower, 0.5 m thick compacted layer of the cover, as per the original cover design. The upper cover layer (0.3 m of noncompacted till) was subject to seasonal variations in moisture content, with drying in the summer months and wetting in the fall and spring. Variations in the moisture of the upper layer correlated well with the weather data collected at the site. Spatial variations were noted in the water contents measured over the cover, but a nearly saturated lower layer appears to have been maintained throughout the area monitored.Key words: soil cover, neutron probes, moisture profile, mine waste covers.

Environmental impact of metal mining—biotechnological aspects of water pollution and remediation—an Indian experience

The role of chemolithotrophs such as Acidithiobacillus ferrooxidans in the generation of acid rock drainage from abandoned sulfidic mines and tailing dumps is discussed. Case studies with respect to an Indian copper mine and mill tailings are illustrated. Acid production potentials of mined sulfide ores and tailings in the presence of A. ferrooxidans are established and it is shown that calcareous gangue effectively neutralized bacterial acid generation. The role of sulfate reducing bacteria in the remediation of acid rock drainage is brought out.

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

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.

English

Excavation through sulfidic geologic materials during construction activities has resulted in acid rock drainage (ARD) related problems across the state of Virginia. The most extensive documented disturbance at a single location resulted from construction of the Stafford Regional Airport in Stafford, Virginia. Beginning in 1998 over 150 ha of sulfidic Coastal Plain sediments were disturbed, including steeply sloping cut surfaces and spoils. This disturbed area remained barren for over two years before being recognized as sulfidic. In addition to the development of acid sulfate soils, the generation of ARD degraded metal and concrete structures and heavily damaged a receiving stream with water quality effects noted over 1000 m downstream from the site. In December 2001 the existing surface soils were composite sampled from 32 map units across the site. In February 2002 a water quality monitoring program was established with 16 locations in and around the airport. In the spring and fall of 2002, after determining liming requirements using potential peroxide acidity (PPA), the site was treated with lime-stabilized biosolids, straw-mulch, and acid- and salt- tolerant grasses. By October 2002 the site was fully revegetated ( 90% living cover) with the exception of a few highly acidic outcrops and seep areas. Water quality quickly responded to treatment, although some N release was noted as a secondary effect. Surface soil sampling in September 2003 indicated that post- amendment pH values across the site increased from values 7.0. Continued monitoring of the water and soils will be used to evaluate the multi-year efficacy of this treatment. Stafford Regional Airport illustrates the importance of accurately assessing sulfide hazards, and establishing optimal handling and treatment procedures prior to construction.

Determination of the Diffusion Coefficient of Oxygen for a Cover System Including a Pulp and Paper By-Product

Abstract Among the several solutions that have been proposed to curb the problem posed by the generation of acid rock drainage (ARD), the placement of covers with capillary barrier effect (CCBE) has received particular attention. With the creation of a capillary barrier, oxygen has to migrate through a nearly saturated layer, a much slower process than in air. As a consequence, its availability is drastically reduced, reducing ARD generation. An experimental procedure was developed to obtain the diffusion coefficient of oxygen through compacted deinking residues, an organic matter-rich by-product of paper recycling. With the oxygen concentrations obtained as a function of time, it was possible to deduce the diffusion coefficients based on the best reproductions of laboratory results, using the computer code POLLUTE v.6. As expected, it was found that the diffusion coefficient—and the associated flux—is highly influenced by the degree of saturation of the sample. Beyond a threshold in the vicinity of 85%, a one order of magnitude drop in the diffusion coefficient was observed. A comparison of the results obtained with previously published data shows that deinking residues constitute a very effective oxygen barrier material due both to its ability to maintain a high degree of saturation and to rapidly consume oxygen. Given the latter, special care was needed in defining the most appropriate equipment design, sample preparation method, and testing procedure.

Reclamation of Disturbed Sulfidic Coastal Plain Sediments Using Biosolids at Stafford Regional Airport in Virginia

Excavation through sulfidic geologic materials during construction activities has resulted in acid rock drainage (ARD) related problems across the state of Virginia. The most extensive documented disturbance at a single location resulted from construction of the Stafford Regional Airport in Stafford, Virginia. Beginning in 1998 over 150 ha of sulfidic Coastal Plain sediments were disturbed, including steeply sloping cut surfaces and spoils. This disturbed area remained barren for over two years before being recognized as sulfidic. In addition to the development of acid sulfate soils, the generation of ARD degraded metal and concrete structures and heavily damaged a receiving stream with water quality effects noted over 1000 m downstream from the site. In December 2001 the existing surface soils were composite sampled from 32 map units across the site. In February 2002 a water quality monitoring program was established with 16 locations in and around the airport. In the spring and fall of 2002, after determining liming requirements using potential peroxide acidity (PPA), the site was treated with lime-stabilized biosolids, straw-mulch, and acid- and salt- tolerant grasses. By October 2002 the site was fully revegetated ( 90% living cover) with the exception of a few highly acidic outcrops and seep areas. Water quality quickly responded to treatment, although some N release was noted as a secondary effect. Surface soil sampling in September 2003 indicated that post- amendment pH values across the site increased from values 7.0. Continued monitoring of the water and soils will be used to evaluate the multi-year efficacy of this treatment. Stafford Regional Airport illustrates the importance of accurately assessing sulfide hazards, and establishing optimal handling and treatment procedures prior to construction.

An investigation of Acid Rock Drainage (ARD) occurrence in a gold mine located in a Southeastern Brazil region

This work is aimed at evaluating the potential of Acid Rock Drainage (ARD) from two Brazilian gold sulfidic ore samples, by means of using three of the most traditional ARD prediction techniques: Standard Acid Base Accounting and Modified Acid Base Accounting, as static methods, and humidity cells, as a kinetic method. Samples were submitted to chemical and mineralogical characterization that indicated the presence of traces of sulfide minerals, such as pyrite, arsenopyrite, pyrrhotite and of carbonates, calcite and dolomite. While the Standard ABA results were inconclusive, the Modified ABA NNP results and NP/AP ratio suggested a tendency of TP01 and WP01 being acid generators, this tendency being slightly stronger for sample WP01. So, a kinetic test was conducted to elucidate the results. The humidity cells results for samples TP01 and WP01 indicated the probable sulfide oxidation to produce acid, subsequently neutralized by alkalinity generated by the carbonates. Based on the results, one can conclude that although sample WP01 has a slightly higher ARD generation potential than TP01, these samples can be at different stages of ARD process, or better, TP01 is at a more advanced stage of ARD production than WP01. The determinant role of the kinetic tests is highlighted by the results.

Estimating ground water discharge by hydrograph separation.

Iron Mountain is located in the West Shasta Mining District in California. An investigation of the generation of acid rock drainage and metals loading to Boulder Creek at Iron Mountain was conducted. As part of that investigation, a hydrograph separation technique was used to determine the contribution of ground water to total flow in Boulder Creek. During high-flow storm events in the winter months, peak flow in Boulder Creek can exceed 22.7 m3/sec, and comprises surface runoff, interflow, and ground water discharge. A hydrograph separation technique was used to estimate ground water discharge into Boulder Creek during high-flow conditions. Total ground water discharge to the creek approaches 0.31 m3/sec during the high-flow season. The hydrograph separation technique combined with an extensive field data set provided reasonable estimates of ground water discharge. These estimates are useful for other investigations, such as determining a corresponding metals load from the metal-rich ground water found at Iron Mountain and thus contributing to remedial alternatives.

Microorganisms, biotechnology and acid rock drainage — emphasis on passive-biological control and treatment methods

Acid rock drainage (ARD) resulting from the natural oxidation of sulfide mineral wastes has become a major concern to the mining industry, both during the operational period and after mine closure. ARD is generally characterized by high acidity and high concentrations of dissolved metals and sulfates. If the generation of acid cannot be prevented or controlled, it must be treated to eliminate acidity and to reduce the concentration of heavy metals and suspended solids before release to the environment. Microorganisms play an important catalytic role in the generation of ARD. Several prevention, control and treatment technologies that are based on microbiological activities have been developed. The role of microorganisms and biotechnology in the generation of ARD and their role in the methods used for prevention, control and treatment are discussed in this paper. Recently developed passive and biological treatment processes that have been implemented at mine sites are emphasized in this paper. Benefits, limitations and design criteria for passive biological processes are also presented.