Iron Removal by a Passive System Treating Alkaline Coal Mine Drainage

The Marchand passive treatment system was constructed in 2006 for a 6,000 L/min discharge from an abandoned underground bituminous coal mine located in western Pennsylvania, USA. The system consists of six serially connected ponds followed by a large constructed wetland. Treatment performance was monitored between December 2006 and 2007. The system inflow was alkaline with pH 6.2, 337 mg/L CaCO₃ alkalinity, 74 mg/L Fe, 1 mg/L Mn, and <1 mg/L Al. The final discharge averaged pH 7.5, 214 mg/L CaCO₃ alkalinity, and 0.8 mg/L Fe. The settling ponds removed 84% of the Fe at an average rate of 26 g Fe m⁻² day⁻¹. The constructed wetland removed residual Fe at a rate of 4 g Fe m⁻² day⁻¹. Analyses of dissolved and particulate Fe fractions indicated that Fe removal was limited in the ponds by the rate of iron oxidation and in the wetland by the rate of particulate iron settling. The treatment effectiveness of the system did not substantially degrade during cold weather or at high flows. The system cost $1.3 million (2006) or $207 (US) per L/min of average flow. Annual maintenance and sampling costs are projected at $10,000 per year. The 25-year present value cost estimate (4% discount rate) is $1.45 million or $0.018 per 1,000 L of treated flow.     

Low Footprint Passive Mine Water Treatment: Field Demonstration and Application

This paper presents iron and manganese removal data from a novel low footprint mine water treatment system. The paper discusses possible design configurations, and demonstrates that the system could treat 1 l/s of mine water containing 7.2 mg/l of Fe to <1 mg/l with a system footprint of 66 m². A conventional lagoon and aerobic wetland system based on standard sizing criteria would require a minimum of 135 m² to achieve the same treatment. Other advantages of the system are that it polishes manganese concentrations, produces ochre that is dense (15% w/v) and free of plant detritus (and therefore amenable to recycling) and that heavy machinery will generally not be required for construction of similar scale systems.     

Determination of Hydraulic Residence Times in Several UK Mine Water Treatment Systems and their Relationship to Iron Removal

In the UK, the Coal Authority has more than 40 mine water treatment systems, most of which are wetland systems with settlement lagoon pretreatment. The purpose of treatment in wetlands is the oxidation of ferrous to ferric iron and the subsequent hydrolysis and precipitation of ferric hydroxide within the wetland. It is generally accepted (Hedin et al., Passive treatment of coal mine drainage, 1994, p 35; Skousen and Ziemkiewicz, Acid mine drainage control and treatment, 1996, p 362; Younger et al., Mine water: hydrology, pollution, remediation, 2002, p 442) that this process proceeds by a first-order rate law, although most systems are designed based on an areal removal rate (10 g/m²/day) developed by the U.S. Bureau of Mines (Hedin et al., Passive treatment of coal mine drainage, 1994, p 35); this design guideline inherently assumes a constant removal rate. Given the actual kinetics of iron removal in wetlands, it follows that residence time will control iron removal; given the wide range of system geometries and aspects, it is logical to ascertain the actual hydraulic residence time of wetlands and settlement lagoons and determine the effect this has on iron removal. To make a preliminary assessment of this link, hydraulic residence time of two Coal Authority wetlands (Lambley and Whittle) and two Coal Authority settlement lagoons (Acomb East, Acomb West and Whittle) were measured using bromide tracer tests. Water samples for iron analysis and flow measurements were taken during each tracer test. The Lambley wetland performs well in terms of residence time, and, as reeds become established and adsorptive processes increase, its iron removal performance (currently 58% removal) may improve, but the low influent iron concentration appears to be a significant impediment to meeting the original performance target. In contrast, the hydraulic performance of the Whittle wetland system is poor, which appears to be due to accumulation of dead plant material coupled with a high length to width ratio. However, performance in terms of iron removal is good (92% removal), which appears to be due to the higher influent iron concentration, and especially the fact that the iron enters the wetland largely in particulate form. The longer residence time of water within the Acomb lagoons (≈12 h) resulted in far more effective iron removal (72% in the east lagoon and 85% in the west lagoon) than the shorter residence time at Whittle (24% iron removal, ≈5 h residence time). Performance (in terms of iron removal) of the settlement lagoon systems appears to be far more closely related to the hydraulic residence time (albeit this conclusion must be tentative, given that only three systems have been investigated, and the Acomb system receives chemical addition). Based on this study, treatment system sizing using 100 m² lagoon area per 1 L/s flow appears to be a more appropriate basis for design rather than an areal iron removal rate.     

Removal of Sulfate,Zinc, and Lead from Alkaline Mine Wastewater Using Pilot-scale Surface-Flow Wetlands at Tara Mines,Ireland

Abstract.    Passive treatment systems have primarily been used at abandoned mines to increase pH and remove metals from the drainage water. Two pilot-scale treatment wetlands were constructed and monitored at an active lead/zinc mine (Tara Mines) in Ireland to treat alkaline mine water with elevated sulfate and metal levels. Each system comprised three in-series surface-flow cells that contained spent mushroom compost substrate. Typically, aqueous concentrations of 900 mg L^-1 sulfate, 0.15 mg L^-1 lead, and 2.0 mg L^-1 zinc flowed into the treatment wetlands at c. 1.5 L min^-1. During a two-year monitoring period, removal of sulfate (mean of 10.4 g m^-2 day ^-1 (31%), range of 0-42 g m^-2 day ^-1 (0-81%)), lead (mean of 1.9 mg m^-2 day ^-1 (32%), range of 0-6.6 mg m^-2 day ^-1 (0-64%)) and zinc (mean of 18.2 mg m^-2 day ^-1 (74%), range of 0-70 mg m^-2 day ^-1 (0-99%)) were achieved. These contaminants were somewhat associated with the vegetation roots but more significantly with the substrate. Communities of colonizing macroinvertebrates, macrophytes, algae, and microorganisms contributed to the development of a diverse ecosystem, which proved to be a successful alternative treatment process. The interacting processes within the wetland ecosystems responsible for wastewater decontamination are being further elucidated and quantified using a systems dynamic model.     

Treatment of Mine Drainage with Significant Topographical Constraints: Case Study of the Bodennec Site (France)

The Bodennec lead and zinc mine site produces circumneutral mine drainage that contains 8 mg/L of dissolved iron, while the water quality objective is 3 mg/L at the outlet. The water treatment installation in use, based on three settling ponds, could not reach this objective, but there was insufficient surface area to build additional ponds or a passive treatment plant. A pilot-scale NaOH system, made of a pump controlled by a flow meter, was built on site to assess the feasibility of a low maintenance, low chemical consumption system to inject a small volume of concentrated NaOH solution into the water. The system was supplied with electricity by a solar panel connected to a battery for night-time functioning. No pH probe was needed since the pH in the drainage is stable. A final water treatment plant based on this system was built in 2017.     

Long-term Performance of Passive Acid Mine Drainage Treatment Systems

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

Optimising dewatering costs on a south african gold mine

Many South African Gold Mines are geologically in proximity to the Transvaal Dolomites. This geological unit, is karstic in many areas and is very extensive. Very large volumes of ground water can be found in the dolomites, and have given rise to major dewatering problems on the mines. Hitherto, the general philosophy on the mines has been to acept these large inflows into the mine, and then to pump out from underground at a suitably convenient level. The dolomites constitute a ground water control area which means that Goverment permission is required to do anything with ground water within the dolomite. When the first major inflows occurred, the mines started dewatering the dolomites, and in many areas induced sinkholes, with significant loss of life and buildings. The nett result is that mines have to pump large quantities of water out of the mine but recharge into the dolomite to maintain water levesl. During the past 2 years a number of investigations have been carried out to reduce the very high costs of dewatering. On one mine the cost of removing 130×10³ m³/day is about 1×10⁶ Rand/month. The hydrogeologic model for the dolomites is now reasonably well understood. It shows that surface wells to a depth of up to 150 m can withdraw significant quantities of water and reduce the amount that has to be pumped from considerable depth with significant saving in puming costs. Such a system has a number of additional advantages such as removing some of the large volume of water from the underground working environment and providing a system that can be used for controlled surface dewatering should it be required.     

Passive Treatment of Acidic Coal Mine Drainage: The Anna S Mine Passive Treatment Complex

The Anna S coal mine complex in Tioga County, PA, produces drainage with a pH of 2.8–3.6 containing 3–36 mg/L Al, 1–36 mg/L Fe, and 6–9 mg/L Mn. In 2003, the Babb Creek Watershed Association installed two systems that passively treat three discharges from the mine complex. Both systems contain four parallel vertical flow ponds followed by aerobic wetlands. The vertical flow ponds contain a total of 35,483 t of limestone and 4,913 m³ of organic substrate. During the last 6 years, the systems have treated an average of 1,971 L/min of flow to neutral pH with 135–146 mg/L of alkalinity (as CaCO₃), with less than 1 mg/L of Al and Fe, and 2–4 mg/L of Mn. The vertical flow ponds have generated alkalinity at rates of 32–53 g/m²/day as CaCO₃. No seasonal variation in treatment effectiveness has been observed, despite relatively harsh winter seasons. The total cost of the passive systems was $2.5 million (US). The 20 year projected unit treatment cost, including periodic replacement of the organic substrate, is $2.5 million (US). The 20 year projected unit treatment cost, including periodic replacement of the organic substrate, is 403–618 per t (as CaCO₃) of net alkalinity generated.     

Delineating the Origin of Groundwater in the Golgohar Mine Area of Iran Using Stable Isotopes of <Superscript>2</Superscript>H and <Superscript>18</Superscript>O and Hydrochemistry

The Golgohar iron ore mine in southern Iran is a large open pit that uses dewatering (≈4000–5000 m³/day) to prevent flooding. A vast cone of depression has formed, and water from a large area flows into the pit. A study of the different sources of this water was necessary to plan a proper dewatering project. Moreover, the discharged water is saline and contains high levels of contaminants. Based on hydrochemical and isotope (¹⁸O and ²H) analysis, it was concluded that the area’s deep saline groundwater is coming from the Sirjan (Kheirabad) salt playa (north of the mine) by saltwater intrusion while the chemistry of more distant groundwater was due to dissolved minerals.     

International Trials of Vertical Flow Reactors for Coal Mine Water Treatment

Vertical flow reactors (VFRs) were tested at coal mine sites in New Zealand, South Korea, and the USA. The objective was to evaluate the iron removal efficiency and iron removal mechanisms during field trials at low pH and circumneutral pH, and to evaluate the potential use of VFRs as stand-alone systems or in combination with other passive treatment technologies. Total iron and manganese removal efficiencies at circumneutral pH (6–8) often exceeded 90%, with effluent concentrations less than 1 mg/L. This is attributed to both homogeneous and heterogenous Fe(II) oxidation and filtration of the precipitated ferrihydrite. Iron removal efficiencies at moderately acidic conditions (pH 3–4.5) averaged close to 40%, with an average 71.0% removal in one of the trials after iron removal capacity was stabilized. Microbial Fe(II) oxidation and precipitation as schwertmannite together with aggregation of colloidal and nano-particulate Fe(III) are suspected to be the main removal mechanisms. Iron solubility limited removal under very acidic conditions (pH < 3). The reproducibility of the results with respect to previous research confirmed that VFRs can be used as stand-alone passive treatment systems for iron removal from mine waters with a footprint less than half of the area required by a conventional aerobic wetland. A VFR can also provide useful iron pretreatment for other passive treatment systems under circumneutral conditions, but would have to be combined with alkaline generating systems to achieve full iron removal from acidic mine waters.

     

Assessment and Management of Water Resources for a Lignite Mine

A water resource management study was carried out for the proposed exploitation of lignite in Gujarat, India. The main source of water in the region is monsoon rainfall, which averages 567 mm/yr. The mine will be excavated in benches below groundwater level. Depth of water from the surface varies from 2–5 m. Total groundwater available within the leasehold area is 485 m³/day and water demand for mining purposes will be around 120.5 m³/day (25% of the available groundwater). During the monsoon season, an estimated pumping capacity of 236 L/s should taken care of groundwater seepage and rainwater when the maximum excavated area exists. After rehabilitation and backfilling, a water body will be created in the mined out pit, which will act as a water reservoir and enhance groundwater recharge. The mine should not significantly affect the region's water resources as long as the recommendations outlined in this paper are adopted.     

The Relationship Between Flow Paths and Water Quality in Mine Water Oxidation Ponds in South Korea

Tests were carried out at passive mine water treatment sites in South Korea to determine how flow and pH affected other water quality parameters. Computational flow analysis and tracer tests revealed that the water took surprisingly direct flow routes in the oxidation ponds, while other areas remained stagnant. Furthermore, ferrous iron concentration, dissolved oxygen, pH, electrical conductivity, total dissolved solids, turbidity, and water depth were all directly affected by the flow patterns due to the relationship between retention time and iron precipitation.     

Optimization of Water Pumping and Injection for Underground Coal Gasification in the Meiguiying Mine,China

The Meiguiying mine is a famous underground coal gasification (UCG) mine in China, but there has been a potential safety hazard since it began operating, that groundwater in the overlying aquifer might enter the mine and even extinguish the gasifier. A 3-D hydrogeological model was developed to explore the characteristics of the seepage field of the aquifer and determine an optimal water pumping and injection option for the UCG. The results indicate that more attention should be paid to control induced fractures of the roof due to the increasing water level of the aquifer, and that a pumping rate of 160 m³/day would decrease the water level to a reasonable elevation. Moreover, to maintain the groundwater table and mine safety, 120 m³/day was recommended as a reasonable and economical recharge (re-injection) rate in the study area.     

Abandoned Mine Drainage in the Swatara Creek Basin, Southern Anthracite Coalfield, Pennsylvania, USA: 2. Performance of Treatment Systems

A variety of passive and semi-passive treatment systems were constructed by state and local agencies to neutralize acidic mine drainage (AMD) and reduce the transport of dissolved metals in the upper Swatara Creek Basin in the Southern Anthracite Coalfield in eastern Pennsylvania. To evaluate the effectiveness of selected treatment systems installed during 1995–2001, the US Geological Survey collected water-quality data at upstream and downstream locations relative to each system eight or more times annually for a minimum of 3 years at each site during 1996–2007. Performance was normalized among treatment types by dividing the acid load removed by the size of the treatment system. For the limestone sand, open limestone channel, oxic limestone drain, anoxic limestone drain (ALD), and limestone diversion well treatment systems, the size was indicated by the total mass of limestone; for the aerobic wetland systems, the size was indicated by the total surface area of ponds and wetlands. Additionally, the approximate cost per tonne of acid treated over an assumed service life of 20 years was computed. On the basis of these performance metrics, the limestone sand, ALD, oxic limestone drain, and limestone diversion wells had similar ranges of acid-removal efficiency and cost efficiency. However, the open limestone channel had lower removal efficiency and higher cost per ton of acid treated. The wetlands effectively attenuated metals transport but were relatively expensive considering metrics that evaluated acid removal and cost efficiency. Although the water-quality data indicated that all treatments reduced the acidity load from AMD, the ALD was most effective at producing near-neutral pH and attenuating acidity and dissolved metals. The diversion wells were effective at removing acidity and increasing pH of downstream water and exhibited unique potential to treat moderate to high flows associated with storm flow conditions.     

What Limits the Productivity of Acid Mine Drainage Treatment Ponds?

Abstract.  Acid mine drainage (AMD) treatment ponds are very common in the U.S. Appalachian coal region and are the main source of many headwater streams. Though the water that discharges from these ponds generally meets state and federal water quality standards, there is a distinct lack of productivity in most of these ponds. Our first objective was to compare the productivity of chemically-treated, biologically-treated, and untreated AMD ponds with uncontaminated (reference) ponds. Next, we used principal component analysis and multiple regression of 20 physicochemical characteristics of these ponds to resolve which factor(s) were responsible for inhibiting productivity. We discovered that chemically-treated AMD ponds and untreated AMD ponds exhibited significantly less gross primary productivity (GPP) than reference ponds; biologically-treated ponds (containing AMD that has passed through a wetland) did not vary significantly from reference ponds. Chemically-treated ponds also had significantly less net primary productivity (NPP) than reference ponds. Community respiration did not vary among the pond types. Our test results indicated that soluble reactive phosphate concentration explained most of the variance in both GPP and NPP. Apparently, phosphate availability, not metal toxicity, regulated phytoplankton productivity in these ponds.     

Alkalinity generation and metals retention in a successive alkalinity producing system

Alkalinity generation and metals retention were evaluated during the initial year of operation of a treatment wetland, consisting of four 185 m² inseries cells comprised of alternating vertical-flow anaerobic substrate wetlands (VFs) and surface-flow aerobic settling ponds (SFs). The substrate in the VFs consists of spent mushroom substrate (SMS) and limestone gravel, supplemented with hydrated fly ash in a 20∶10∶1 ratio by volume. Approximately 15±4 L/min of acid mine drainage (AMD) from an abandoned underground coal mine in southeastern Oklahoma, USA, was directed to the system in October 1998 (mean influent water quality: 660 mg L⁻¹ net acidity as CaCO₃ eq., pH 3.4, 215 mg L⁻¹ total Fe, 36 mg L⁻¹ Al, 14 mg L⁻¹ Mn, and 1000 mg L⁻¹ SO₄ ⁻²). Flow through the first VF resulted in substantial increases in alkalinity, decreased metal concentrations and circumneutral pH. 258±84 mg L⁻¹ of alkalinity was produced in the first VF by a combination of processes. Final discharge waters were net alkaline on all sampling dates (mean net alkalinity=136 mg L⁻¹). Total Fe and Al concentrations decreased significantly from 216±45 to 44±28 mg L⁻¹ and 36±6.9 to 1.29±4.4 mg L⁻¹, respectively. Manganese concentrations did not change significantly in the first two cells, but decreased significantly in the second two cells. Mean acidity removal rates in the first VF (51 g m⁻² day⁻¹) were similar to those previously reported.     

Nitrification in Constructed Wetlands Treating Ochreous Mine Water

A survey of ochreous discharges from former coal mines in the UK indicated ammonia contamination at 2–5 mg/L in water from flooded shafts of depths >400–800 m. Although significant, this was much less than historically observed in working mines. No correlation was observed between ammonia and iron concentrations. However, ammonia was removed to some extent in constructed wetlands designed primarily to remove iron. A mechanistic study of wetland removal of ammonia from mine water indicated the main process to be bacterial nitrification, similar (despite great differences in operating conditions) to that occurring in many wastewater treatment works. The study was based on water containing 4–5 mg/L ammonia and some 12–27 mg/L iron from the abandoned Woolley mine in Yorkshire. Notwithstanding relatively high salinity and short residence time, most of the ammonia entering the wetlands was, at least initially, converted to nitrate. Field measurements showed that the conversion efficiency was increased at lower flow rates, higher temperature, and longer flow stabilisation, which are all consistent with bacterial action. Subsurface flow conditions were simulated in column studies, using pre-sterilised gravel and mine water taken from the wetland cells; two strains of bacteria commonly associated with nitrification in domestic wastewaters, Nitrosomonas europaea and Nitrobacter agilis, were able to reproduce the 89% ammonia oxidation observed in the wetlands. It was concluded that the high degree of aeration, neutral pH, and nutrient content of the mine water greatly favoured nitrification. Although more saline and lower in biochemical oxygen demand than organic wastewater, nitrification was not inhibited.     

A novel low pH sulfidogenic bioreactor using activated sludge as carbon source to treat acid mine drainage (AMD) and recovery metal sulfides: Pilot scale study

In this work a pilot scale sulfidogenic bioreactor was used to treat acid mine drainage (AMD) from Zijinshang copper mine. In this process, S²⁻ produced in the Up-flow Anaerobic Sludge Bed (UASB) reactor were recycled in the two precipitation tanks for copper and iron precipitation, activated sludge from local waste water treatment plant was used as the carbon source. The reactor were steady operated in acid condition (with no pH control) for 4 month, AMD with a copper concentration of 100–120 mg/L, iron concentration of 170–200 mg/L, sulfate concentration of 2000–2500 mg/L and pH of 2.34–2.56, were feeding into the reactor under a feed rate of 1 m³/days and HRT of 3 days, copper and iron removal were 60.95%, 97.83% respectively. The precipitant in the precipitation tank containing 15.7% Cu and 22.66% Fe, thus indicating a recovery possibility of copper by pyrometallurgy process. From these results we can conclude that an SRB process would be a viable method of treating Zijinshan AMD.     

Groundwater Source Discrimination and Proportion Determination of Mine Inflow Using Ion Analyses: A Case Study from the Longmen Coal Mine,Henan Province,China

Complex hydrogeological conditions in China’s coal mines have contributed to frequent mine water disasters. A simple and effective method to determine water inflow sources and paths is therefore essential. The Longmen Mine, located in Henan Province, in central China was used as a case study. A Piper diagram and cluster analysis were used to screen the characteristic values of 18 water samples from potential aquifers. A comprehensive fuzzy evaluation of the groundwater ions was carried out to determine the main source of the total mine inflow. Then, based on conservation of ionic masses, a matrix function was established to calculate the groundwater recharge composition. Finally, using measured water inflows for the Cambrian limestone aquifer, the calculated and observed results were compared. The results showed that the Carboniferous Taiyuan Formation limestone aquifer (the L₇ limestone aquifer) accounts for 60.8% of the total mine inflow, while the Cambrian limestone and roof sandstone aquifers account for 34.8 and 4.4% of the inflow, respectively. The normal mine inflow totals about 19,200 m³/day, of which 6,840 m³/day is from the Cambrian limestone aquifer. This agrees well with the calculated value of 6,720 m³/day. Thus, the method is feasible and reliable.     

Assessing Pilot-Scale Treatment Facilities with Steel Slag-Limestone Reactors to Remove Mn from Mine Drainage

Pilot-scale mine water treatment facilities were operated for over four years at the Ilwol mine, South Korea. A steel slag-limestone reactor (referred to as the slag reactor) was tested and a successive alkalinity producing system (SAPS) and a SAPS incorporating slag from a basic oxygen steelmaking furnace were compared. The SAPS decreased Mn from 23.3 to 7.4 mg L^?1 on average because the alkalinity generated led to saturation with rhodochrosite. Adding a slag reactor removed Mn down to levels of 0.002–1.8 mg L^?1 from influent Mn as high as 17.1 mg L^?1 with a residence time of 5–25 h. Mn-containing carbonates and oxides were precipitated, which was supported by the geochemical modelling and observed with scanning electron microscopy with energy dispersive spectroscopy. The increased alkalinity in the SAPS before the slag reactor helped remove Mn at a pH range of 8.0–8.3. Mn removal rates and Mn-standardized Mn removal rates in the slag reactor were 0.76 mg L^?1 h^?1 and 0.105 h^?1 in average, respectively. The passive treatment of Mn using an Fe-pretreatment and alkalinity-generation system, a slag-limestone reactor, and a wetland rather than a SAPS including slag, an oxidation-settling pond, and a wetland is suggested to consistently meet the effluent standards for Mn and pH.