Passive Treatment Of Acid Mine Drainage Research Articles

EFECTO DEL COBRE PARA LA REMOCIÓN DE SULFATO EN UN REACTOR DE LECHO FIJO

Mining of sulfide-rich pyritic ores produce acid mine drainage (AMD), which contains high metal concentrations and have acid pH, causing major environmental problems. Over the last 20 years a variety of passive AMD treatment systems, like anaerobic wetlands, bioreactors and permeable reactive barriers, have been studied. Under controlled conditions bioreactors employ inoculants of sulfate-reducing bacteria (SRB) to treat effluents and capture commercial grade metals. The objective of this research was to evaluate the effect of Cu on the removal efficiency of sulfate in a fixed bed reactor. During 28 d the fixed bed reactor maintained a hydraulic residence time (HRT) of 12 h and an influent rate of 0.67 gCOD/gSO 4 2– . Phase I (synthetic solution with 50 mg Cu/L) lasted 7 d, allowing Cu removal of 99.59 ± 0.43 % and sulfide production of 39.29 mg S 2- /L∙d. Sulfate-reducing activity (SRA) was not affected (40.25 mg S 2- /L∙d) during Phase II (21 d without Cu). Results showed no significant alteration in sulfate and COD removal, as well as sulfur production after the addition of Cu. It is concluded that SRB can be used for AMD treatment.

The role of secondary minerals in remediation of acid mine drainage by Portland cement.

To test the effects of secondary mineral formation on cement neutralisation of acid mine drainage (AMD), cement samples were leached with AMD and dilute sulfuric acid of approximately equal acidity. In both cases the neutralising efficiency of the cements, due to dissolution of portlandite as well as the hydrated calcium silicate and aluminate phases, decreased as secondary minerals accumulated on the cement surfaces. The AMD-leached cement became coated with Fe hydroxides, whereas the H2SO4-leached cement was covered primarily with gypsum. Ettringite and thaumasite also formed within the cement in both cases, however in much greater amounts in cement leached with AMD. The AMD penetrated deeper into the cement than H2SO4 because the higher amounts of ettringite and thaumasite in AMD-leached cement caused expansion and cracking. The cracking, which resulted in a substantial loss of strength of the cement, was enhanced when the cement samples were allowed to dry out. This indicates that cement used for passive treatment of AMD will likely provide better long-term neutralisation in at least partially unsaturated conditions where the cement dries out periodically, facilitating cracking to allow deeper penetration of AMD.

TEKNOLOGI PENGOLAHAN AIR ASAM TAMBANG BATUBARA “Alternatif Pemilihan Teknologi”

Acid Mine Drainage (AMD) treatment systems can be broadly categorised as either active or passive systems, which differ according to their ability to handle Acidity, flow rate and Acidity Load of the influent AMD. Most passive and active systems utilise aggregate carbonate to neutralise the pH and encourage precipitation of metals as hydroxides or sulphide minerals. In addition, passive treatment systems often use organic matter to provide alkalinity and create reducing conditions which favour the precipitation of metal sulphides.Active treatment systems can be engineered to accommodate essentially any acidity, flow rate and acidity load. Active treatment of AMD can be achieved using fixed plants or portable equipment for in-situ treatment. Passive treatment systems are almost invariably used for post closure treatment scenarios, and are best suited to AMD with low Acidity and low flow rates. The key factors in selection and design of active and passive AMD treatment systems are water chemistry including pH, metals, sulphate levels and redox state and flow rate of influent AMD, and the objectives of AMD treatment. Other important factors include capital and operating costs, availability of suitable treatment reagents or materials and sludge management issues. Keywords: Acid Mine Drainage, Active Treatment, Passive Treatment, Coal Mining.

Novel cost effective full scale mussel shell bioreactors for metal removal and acid neutralization

Acid mine drainage (AMD) impacted waters are a worldwide concern for the mining industry and countries dealing with this issue; both active and passive technologies are employed for the treatment of such waters. Mussel shell bioreactors (MSB) represent a passive technology that utilizes waste from the shellfish industry as a novel substrate. The aim of this study is to provide insight into the biogeochemical dynamics of a novel full scale MSB for AMD treatment. A combination of water quality data, targeted geochemical extractions, and metagenomic analyses were used to evaluate MSB performance. The MSB raised the effluent pH from 3.4 to 8.3 while removing up to ∼99% of the dissolved Al, and Fe and >90% Ni, Tl, and Zn. A geochemical gradient was observed progressing from oxidized to reduced conditions with depth. The redox conditions helped define the microbial consortium that consists of a specialized niche of organisms that influence elemental cycling (i.e. complex Fe and S cycling). MSB technology represents an economic and effective means of full scale, passive AMD treatment that is an attractive alternative for developing economies due to its low cost and ease of implementation.

Oxycline formation induced by Fe(II) oxidation in a water reservoir affected by acid mine drainage modeled using a 2D hydrodynamic and water quality model — CE-QUAL-W2

The Sancho reservoir is an acid mine drainage (AMD)-contaminated reservoir located in the Huelva province (SW Spain) with a pH close to 3.5. The water is only used for a refrigeration system of a paper mill. The Sancho reservoir is holomictic with one mixing period per year in the winter. During this mixing period, oxygenated water reaches the sediment, while under stratified conditions (the rest of the year) hypoxic conditions develop at the hypolimnion. A CE-QUAL-W2 model was calibrated for the Sancho Reservoir to predict the thermocline and oxycline formation, as well as the salinity, ammonium, nitrate, phosphorous, algal, chlorophyll-a, and iron concentrations. The version 3.7 of the model does not allow simulating the oxidation of Fe(II) in the water column, which limits the oxygen consumption of the organic matter oxidation. However, to evaluate the impact of Fe(II) oxidation on the oxycline formation, Fe(II) has been introduced into the model based on its relationship with labile dissolved organic matter (LDOM). The results show that Fe oxidation is the main factor responsible for the oxygen depletion in the hypolimnion of the Sancho Reservoir. The limiting factors for green algal growth have also been studied. The model predicted that ammonium, nitrate, and phosphate were not limiting factors for green algal growth. Light appeared to be one of the limiting factors for algal growth, while chlorophyll-a and dissolved oxygen concentrations could not be fully described. We hypothesize that dissolved CO2 is one of the limiting nutrients due to losses by the high acidity of the water column. The sensitivity tests carried out support this hypothesis. Two different remediation scenarios have been tested with the calibrated model: 1) an AMD passive treatment plant installed at the river, which removes completely Fe, and 2) different depth water extractions. If no Fe was introduced into the reservoir, water quality would significantly improve in only two years. Deeper extractions (3m above the bottom) would also improve the water quality by decreasing the hypoxic zone. However, extractions at the epilimnion would increase the amount of hypoxic water in the reservoir.

The Use of Mussel Shells in Upward-Flow Sulfate-Reducing Bioreactors Treating Acid Mine Drainage

In this study, sulfate-reducing bioreactors (SRBRs) efficiently treated acid mine drainage (AMD) for a contiguous period of 5 months. The AMD was sourced from an active coal mine on the South Island of New Zealand and typically had a pH < 3, 1,700 mg/L of sulfate, 50 mg/L of Fe, 18 mg/L of Al, 15 mg/L of Mn, 4 mg/L of Zn, and lower concentrations of other contaminants. Two alkalinity-generating materials (mussel shells and limestone) and two hydraulic retention times (HRTs) of 3 and 10 days were evaluated. Influent and effluent water quality parameters were monitored weekly. Each SRBR system successfully increased the pH (≥6) and the alkalinity (≤350 mg/L CaCO3) of the water while removing substantial amounts of dissolved metals at both HRTs (≥90 % Al, ≥86 % Fe, ≥87 % Cu, ≥99 % Zn). Mn removal was lower and ranged from 19 to 55 %. Increasing the HRT from 3 to 10 days significantly improved effluent water quality in terms of pH, alkalinity, and metals and sulfate removal. SRBRs using mussel shells in their reactive mixtures were more effective than those using limestone, with a higher (60–113 %) alkalinity generation and a better (3–5 %) metal removal. This study showed that mussel shells are an inexpensive and sustainable alternative to mined limestone for AMD passive treatment, and that better treatment efficiency resulted from a longer HRT.

Thermodynamic controls on the kinetics of microbial low-pH Fe(II) oxidation.

Acid mine drainage (AMD) is a major worldwide environmental threat to surface and groundwater quality. Microbial low-pH Fe(II) oxidation could be exploited for cost-effective AMD treatment; however, its use is limited because of uncertainties associated with its rate and ability to remove Fe from solution. We developed a thermodynamic-based framework to evaluate the kinetics of low-pH Fe(II) oxidation. We measured the kinetics of low-pH Fe(II) oxidation at five sites in the Appalachian Coal Basin in the US and three sites in the Iberian Pyrite Belt in Spain and found that the fastest rates of Fe(II) oxidation occurred at the sites with the lowest pH values. Thermodynamic calculations showed that the Gibbs free energy of Fe(II) oxidation (ΔG(oxidation)) was also most negative at the sites with the lowest pH values. We then conducted two series of microbial Fe(II) oxidation experiments in laboratory-scale chemostatic bioreactors operated through a series of pH values (2.1-4.2) and found the same relationships between Fe(II) oxidation kinetics, ΔG(oxidation), and pH. Conditions that favored the fastest rates of Fe(II) oxidation coincided with higher Fe(III) solubility. The solubility of Fe(III) minerals, thus plays an important role on Fe(II) oxidation kinetics. Methods to incorporate microbial low-pH Fe(II) oxidation into active and passive AMD treatment systems are discussed in the context of these findings. This study presents a simplified model that describes the relationship between free energy and microbial kinetics and should be broadly applicable to many biogeochemical systems.

Life cycle assessment analysis of active and passive acid mine drainage treatment technologies

Acid mine drainage (AMD), resulting from open-cast coal mining, is currently one of the largest environmental challenges facing the mining industry. In this study, a life cycle assessment (LCA) was conducted to evaluate the environmental impacts associated with the construction, operation and maintenance of different AMD treatment options typically employed. LCA is a well-reported tool but is not documented for AMD treatment systems despite their ubiquitous implementation worldwide. This study conducted detailed LCA analysis for various passive and active AMD treatment approaches implemented or considered at a major coal mine in New Zealand using a comparative functional unit of kg acidity removed per day for each treatment option. Eight treatment scenarios were assessed including active limestone and hydrated lime treatments, and compared to passive treatments using limestone and waste materials such as mussel shells. Both midpoint and endpoint LCA impact categories were assessed. Generally, the active treatment scenarios demonstrated greater LCA impacts compared to an equivalent level of treatment for the passive treatment approaches. Lime slaking had the greatest LCA impacts, while passive treatment approaches incurred consistently less impacts except for one passive treatment with a purchased energy scenario. A 50% reduction in transportation distances resulted in the lowest LCA impacts for all scenarios. This study highlights the importance of evaluating the environmental and social impacts of AMD treatment for the mining industry.

Technical note: Development of a Linear Flow Channel Reactor for sulphur removal in acid mine wastewater treatment operations

Where sulphate removal is targeted in the biological treatment of acid mine drainage wastewaters, a step additional to sulphate reduction is required to prevent the complete oxidation of sulphide back to sulphate. This linearisation of the biological sulphur cycle has presented a technological bottleneck, particularly in passive treatment operations. We report an investigation of sulphur production in floating sulphur biofilms as a means for addressing this problem. These 50 μm to 500 μm structures may be seen to form on the surface of sulphidic, organic waters and in which sulphide is partly oxidised to So and polysulphide. A Linear Flow Channel Reactor was developed in which the formation of the floating sulphur biofilm could be optimised and studied under controlled conditions. In this study the sulphide feed was sourced from a lignocellulose packed bed reactor treating a synthetic acid mine water (2 000 mg∙l -1 Na 2 SO 4 solution) and the Liner Flow Channel Reactors (surface area 1.1 m 2 and 2.2 m 2 ) were operated in a controlled environment chamber. The floating sulphur biofilm was harvested by settling to the bottom of the reactor where it remained largely unreacted until removed. It was shown that up to 88% of sulphide in the feed stream may be removed in this way and that this was achieved mainly by oxidation of sulphide to sulphur (including a polysulphide fraction). A mass balance accounting for the process showed that up to 66% of total sulphur species entering the system were recovered as So. Oxidation of sulphide to thiosulphate and sulphate was not found to be significant. A fraction of fine particulate sulphur is released into the stream on harvesting of the biofilm which does not readily settle in the reactor and may thus be lost to the mass balance account. The effects of temperature, loading rate and reactor surface area were investigated in optimising the performance of the reactor. Scale-up application studies in the use of the Linear Flow Channel Reactor in an acid mine drainage passive treatment environment have been undertaken in field studies. Keywords: floating sulphur biofilms, acid mine drainage, AMD passive treatment, linear flow channel reactor, sulphur biotechnology

Environmental assessment and management of metal-rich wastes generated in acid mine drainage passive remediation systems

As acid mine drainage (AMD) remediation is increasingly faced by governments and mining industries worldwide, the generation of metal-rich solid residues from the treatments plants is concomitantly raising. A proper environmental management of these metal-rich wastes requires a detailed characterization of the metal mobility as well as an assessment of this new residues stability. The European standard leaching test EN 12457-2, the US EPA TCLP test and the BCR sequential extraction procedure were selected to address the environmental assessment of dispersed alkaline substrate (DAS) residues generated in AMD passive treatment systems. Significant discrepancies were observed in the hazardousness classification of the residues according to the TCLP or EN 12457-2 test. Furthermore, the absence of some important metals (like Fe or Al) in the regulatory limits employed in both leaching tests severely restricts their applicability for metal-rich wastes. The results obtained in the BCR sequential extraction suggest an important influence of the landfill environmental conditions on the metals released from the wastes. To ensure a complete stability of the pollutants in the studied DAS-wastes the contact with water or any other leaching solutions must be avoided and a dry environment needs to be provided in the landfill disposal selected.

우분과 참나무 폐목을 이용한 산성광산배수의 처리에 관한 연구

Although facilities for the passive treatment of AMD (Acid Mine Drainage) are currently operating in Korea, their removal efficiency for heavy metals is relatively low in average (only 80%). Passive treatment system is composed of oxidation tank, SAPS (Successive Alkalinity Producing System), and wetland. In the treatment system adopted in korea, SAPS (Successive Alkalinity Producing System) plays a major role to remove about 65% of heavy metals through a precipitation. However, the efficiency of SAPS is limited due to the use of mushroom compost (MC) as a organic material and of limestone as a neutralizer. Therefore, this research was performed to search for alternative organic materials through the field test. We tested two types of mixed organic materials: 1) cow manure and spent oak (herein, CO) and 2) cow manure and sawdust (herein, CS). For comparison mushroom compost (herein, MC) was also tested. The result showed that the average Fe removal efficiency was 91.38% with CO, 85.19% with CS, and 91.58% with MC. Thus, CO can be effectively used as an alternative of MC in the SAPS system for heavy metals removal.

Alkalinity Generation in a Novel Multi-stage High-strength Acid Mine Drainage and Municipal Wastewater Passive Co-treatment System

Passive co-treatment of high-strength acid mine drainage (AMD) and municipal wastewater (MWW) was examined in a laboratory-scale, four-stage continuous flow reactor system with a total residence time of 6.6 d. Synthetic AMD of pH 2.60 and an acidity of 1,870 mg/L (as CaCO3) was mixed at a 1:2 ratio with raw MWW (pH 7.67, 288 mg/L alkalinity (as CaCO3), and 265 mg/L BOD5) from the City of Norman, Oklahoma and introduced into the system. Alkalinity generated by limestone dissolution and bacterial SO4 2− reduction (BSR) processes was sufficient to support various metal removal processes and produce an effluent with circumneutral pH (6.98) and a net alkalinity of 10.4 mg/L (as CaCO3). Alkalinity generation from limestone dissolution was comparable with conventional AMD passive treatment systems. BSR proceeded at a relatively high rate (0.56 mol/m3 day) despite inhibitory pH and metals concentrations. Results indicate that the diverse electron donors in the MWW may be as suitable for BSR and their supporting microbial communities as commonly used substrates, presenting an opportunity to use a common waste as a resource for passive treatment.

Optimising the rehabilitation of polluted mine tailings and water by an organic medium passive acid mine drainage treatment in South Africa

Up to the present polluted Acid Mine Drainage (AMD) also known as Acid Rock Drainage (ARD) from South Africa's gold mines was treated by the precipitation of heavy metals with lime and expensive caustic soda where the residues accumulate in the treated water. This water then is dispersed into wetlands for natural remediation. The environmental damage to soil is irreversible and can sterilise soil in a very short period while acting as a plant toxin. This study about AMD as one of the biggest environmental problem is carried out using organic and mechanical treatment with an organic medium.

Attenuation of pyrite oxidation with a fly ash pre-barrier: Reactive transport modelling of column experiments

Conventional permeable reactive barriers (PRBs) for passive treatment of groundwater contaminated by acid mine drainage (AMD) use limestone as reactive material that neutralizes water acidity. However, the limestone-alkalinity potential ceases as inevitable precipitation of secondary metal-phases on grain surfaces occurs, limiting its efficiency. In the present study, fly ash derived from coal combustion is investigated as an alternative alkalinity generating material for the passive treatment of AMD using solution-saturated column experiments. Unlike conventional systems, the utilization of fly ash in a pre-barrier to intercept the non-polluted recharge water before this water reacts with pyrite-rich wastes is proposed. Chemical variation in the columns was interpreted with the reactive transport code RETRASO. In parallel, kinetics of fly ash dissolution at alkaline pH were studied using flow-through experiments and incorporated into the model. In a saturated column filled solely with pyritic sludge–quartz sand (1:10), oxidation took place at acidic conditions (pH 3.7). According to SO42- release and pH, pyrite dissolution occurred favourably in the solution-saturated porous medium until dissolved O2 was totally consumed. In a second saturated column, pyrite oxidation took place at alkaline conditions (pH 10.45) as acidity was neutralized by fly ash dissolution in a previous level. At this pH Fe release from pyrite dissolution was immediately depleted as Fe-oxy(hydroxide) phases that precipitated on the pyrite grains, forming Fe-coatings (microencapsulation). With time, pyrite microencapsulation inhibited oxidation in practically 97% of the pyritic sludge. Rapid pyrite-surface passivation decreased its reactivity, preventing AMD production in the relatively short term.

English

The Old Bevier Aerobic Wetland in Macon County, Missouri, was constructed between 1990 and 1991 by the Missouri Department of Natural Resources' Land Reclamation Program for the purpose of treating acid mine drainage (AMD). The principal source of the AMD is from an underground mine that operated during the 1920's through 1950's, which was partially exposed during surface mining in the 1950's. Limestone bedding of an AMD collection system provided alkalinity similar to an anoxic limestone drain (ALD). Because the original aerobic wetland failed when a critical dilution water supply became unavailable, the total acidity of the AMD overwhelmed the limited neutralization ability of the aerobic wetland. The aquatic vegetation deteriorated and treatment became ineffective. The Missouri Land Reclamation Program with the assistance of the Office of Surface Mining, Mid-Continent Regional Coordinating Center rehabilitated the Old Bevier Aerobic Wetland in 2001, incorporating newer technologies to improve the performance. The new system, Old Bevier II treatment facility, consists of a 2-stage vertical flow pond (VFP) with associated oxidation cells and aerobic wetlands. This paper discusses the performance of this passive AMD treatment system, updating an earlier report. The new treatment system has operated with nearly continuous net alkaline discharge and a high iron removal rate. Also discussed are measures to improve AMD collection and treatment by the facility.

Hydraulic Conductivity of Substrates Used for Passive Acid Mine Drainage Treatment

Hydraulic Conductivity of Substrates Used for Passive Acid Mine Drainage Treatment