Neutral Mine Drainage Research Articles

Temporal dynamics of contaminants in an estuarine system affected by acid mine drainage discharges

The estuary of Huelva is constituted by the common mouth of the Odiel and Tinto rivers, which are extreme cases of acid mine drainage contamination due to the Iberian Pyrite Belt, the world's largest sulfide mineral province. The drained acidic waters are subjected to seawater mixing and thus, to dilution and precipitation processes that drive the load of contaminants entering the oceanic environment. This research reports the distribution of major metal(loid)s present in the highly acidic waters across the entire Tinto and Odiel estuarine systems as they are subjected to acid mine drainage neutralization, until reaching the ocean. The datasets presented are divided in low- and high-flow periods, corresponding to dry/warm and wet/cold seasons, respectively. Iron and Al were almost entirely removed from solution with pH increase at both periods due to their precipitation as schwertmannite and basaluminite, respectively. These mineral phases also, controlled the behavior of As, Cu and Pb, which were removed from solution, with >90 % of their concentration ending up in the particulate phase due to sorption processes. However, at pH >7, As returned entirely to the dissolved phase at both sampled seasons because of desorption, similarly to Cu at the low-flow period. On the other hand, concentrations of Zn, Cd, Mn, Co and Ni in solution decreased only by dilution with seawater, with null partitioning to any sorption processes during estuarine mixing until reaching the Atlantic Ocean.

Adsorption of Cd and Mn from neutral mine effluents using bentonite, zeolite, and stabilized dewatered sludge

This study aimed to investigate the adsorption efficiency of Cd and Mn using natural sorbents—bentonite, zeolite and stabilized digested dewatered waste sludge. The main contributions of the scientific article are in adding to the scientific knowledge of the use of natural and waste sorbents in the removal of heavy metals from neutral mine effluents. Current studies mainly focus on metal removal by sorption using natural sorbents from acid mine drainage. This study investigates sorption in neutral mine drainage. The efficiency of the sorption process was evaluated using the following parameters: efficiency (%) of metal ion removal, Freudlich and Langmuir adsorption isotherm constant. The AES–ICP method (atomic emission spectrometry with inductively coupled plasma) was used for the initial metal analysis of the materials used. The atomic absorption spectrometry (AAS) method was used for the analysis of Cd and Mn in the sorption process. The maximum efficiency of Mn removal by bentonite at the end of the test was approximately 90%. The removal of Mn by zeolite was considerably lower—about 20% compared to the use of sludge—80%. Based on the sorption efficiency, the sludge was suitable for sorption. Much higher levels of Cd sorption were achieved using sludge compared to using natural bentonite and zeolite. The main novelty of the work lies in the sorption of metals using dewatered digested sludge. Previous studies have focused on metal sorption using activated sludge. Most previous studies focused on sorption from acid mine drainage. The novelty of this study is that we focused on the sorption of neutral mine drainages, which are typical for the location we are monitoring.

Sequential hydrotalcite precipitation, microbial sulfate reduction and in situ hydrogen sulfide removal for neutral mine drainage treatment

This study proposed and examined a new process flowsheet for treating neutral mine drainage (NMD) from an open-pit gold mine. The process consisted of three sequential stages: (1) in situ hydrotalcite (HT) precipitation; (2) low-cost carbon substrate driven microbial sulfate reduction; and (3) ferrosol reactive barrier for removing biogenic dissolved hydrogen sulfide (H2S). For concept validation, laboratory-scale columns were established and operated for a 140-days period with key process performance parameters regularly measured. At the end, solids recovered from various depths of the ferrosol column were analysed for elemental composition and mineral phases. Prokaryotic microbial communities in various process locations were characterised using 16S rRNA gene sequencing. Results showed that the Stage 1 HT-treatment substantially removed a range of elements (As, B, Ba, Ca, F, Zn, Si, and U) in the NMD, but not nitrate or sulfate. The Stage 2 sulfate reducing bioreactor (SRB) packed with 70 % (v/v) Eucalyptus woodchip, 1 % (w/v) ground (<1 mm) dried Typha biomass, and 10 % (w/v) NMD-pond sediment facilitated complete nitrate removal and stable sulfate removal of ca. 50 % (50 g-SO4 m−3 d−1), with an average H2S generation rate of 10 g-H2S m−3d−1. The H2S-removal performance of the Stage 3 ferrosol column was compared with a synthetic amorphous Fe-oxyhydroxide-amended sand control column. Although both columns facilitated excellent (95–100 %) H2S removal, the control column only enabled a further ca. 10 % sulfate reduction, giving an overall sulfate removal of 56 %. In contrast, the ferrosol enabled an extra 99.9 % sulfate reduction in the SRB effluent, leading to a near complete sulfate removal. Overall, the process successfully eliminated a range of metal/metalloid contaminants, nitrate, sulfate (2500 mg-SO4 L−1 in the NMD to <10 mg-SO4 L−1 in the final effluent) and H2S (>95 % removal). Further optimisation is required to minimise release of ferrous iron from the ferrosol barrier into the final effluent.

Oxidative Weathering of Neutral Mine Drainage from Gold Mine Tailings Impoundment: Tracking Formation and Transformation of Biogenic Iron Minerals and the Associated Arsenic

Oxidative Weathering of Neutral Mine Drainage from Gold Mine Tailings Impoundment: Tracking Formation and Transformation of Biogenic Iron Minerals and the Associated Arsenic

Role of indigenous microbial communities in the mobilization of potentially toxic elements and rare-earth elements from alkaline mine waste

This study aims to evaluate the role of indigenous microorganisms in the mobilization of potentially toxic elements (PTE) and rare-earth elements (REE), the influence of the bioavailability of carbon sources that might boost microbial leaching, and the generation of neutral/alkaline mine drainage from alkaline tailings. These tailings, with significant concentrations of total organic carbon (TOC), were mainly colonized by bacteria belonging to the genera Sphingomonas, Novosphingobium and Solirubrobacter, and fungi of the genera Alternaria, Sarocladium and Aspergillus. Functionality analysis suggests the capability of these microorganisms to leach PTE and REE. Bio-/leaching tests confirmed the generation of neutral mine drainage, the influence of organic substrate, and the leaching of higher concentrations of PTE and REE due to the production of organic acids and siderophores by indigenous microorganisms. In addition, this study offers some insights into a sustainable alternative for reprocessing PMC alkaline tailings to recover REE.

OPTIMASI PROSES PENETRALAN AIR ASAM TAMBANG PADA SETTLING POND PT DARMA HENWA TBK JOBSITE PT ARUTMIN INDONESIA SITE ASAM-ASAM

One of method which ussualy used in neutralizing Acid Mine Drainage using neutralizing agents is Settling Pond. This treatment process requires adding neutralizing agents to the waters or through a mixing system and allowing deposits to form in the pond. Many factors and process mechanisms can affect the effluent quality of an Acid Mine Drainage processing system. The purpose of this study is to evaluate the effectiveness and optimize the Acid Mine Drainage neutralization process carried out in Settling Pond 19. The research method used is to make theoretical simulations both modeling using PHREEQC and calculations to simulate various neutralization process options. The results showed that the neutralization process was affected by the quality of the neutralizing agent, the number of doses, the saturation index (precipitation) limit, the dissolution process of the neutralizing agent, the duration of dosing, and the duration of neutralization. According to modeling and theoretical calculations, the technical recommendations for optimizing the Acid Mine Drainage neutralization process to produce effluent quality that meets wastewater quality standards are the duration interval to inject neutralizer from every 60 minutes to every 13.6 minutes with a continuous dosing mechanism; The use of a maximum dose of limestone of 0.22 g/L to avoid oversaturated events, and the use of a limestone dissolution mechanism before the injection process is carried out to reduce the need for retention time for 216 seconds.

Controls on the Generation and Geochemistry of Neutral Mine Drainage: Evidence from Force Crag Mine, Cumbria, UK

Neutral mine drainage (NMD) at Force Crag mine in north-west England has a circumneutral pH and high levels of Zn contamination. A long-term geochemical and hydrological dataset from this site was analysed using a novel molar mass balance approach, which demonstrated that the water chemistry is dominated by species released by the oxidation of sulphides: sphalerite (Zn, Cd, Ni), galena (Pb, mostly removed by adsorption to ferrihydrite) and pyrite (Fe, mostly precipitates as ferrihydrite). The calculations show that the sphalerite:galena:pyrite oxidation ratio is ~1:2:1, but the mine water chemistry is dominated by Zn due to the removal of Pb and Fe by adsorption/precipitation. The acidity released by pyrite oxidation is neutralised by the dissolution of calcite and, to a lesser extent, chlorite. The presence of pyrite is responsible both for the release of acidity and the removal of some contaminant metals by adsorption on ferrihydrite. The concentrations of sulphate, Zn, Cd and Ni in the mine water decrease with increasing flow due to dilution; modest increases in metal flux with flow probably reflect increased oxidation due to greater amounts of oxygenated water flowing through the mine. In contrast, Al, Pb and Cu concentrations are positively correlated with flow due to the flushing of these metals adsorbed to ferrihydrite particles. The influence of temperature is relatively subtle; metal fluxes are a balance between abiotic oxidation (which increases at higher temperatures and flows) and bacterially mediated oxidation (which is depressed at high flow rates when temperatures decrease below 10 °C). These conclusions apply to NMD mine water throughout the UK and elsewhere in the world, including mines hosted in both limestone and silicate rocks. The molar mass balance approach, together with synchronous flow and geochemistry data, provides crucial information for effective mine-water-treatment system design by elucidating the critical roles of flow rate and temperature in determining contaminant concentrations and loads.

Rationale for alternative water sources for mining regions with high environmental footprint on the example of Levikha village of the Sverdlovsk region

Introduction. Mine drainage has always been one of the main threats to the hydrosphere of mining areas, both during and after active mining. The most common method of mine water neutralization is associated with the slaked lime. On the abandoned Levikha copper-sulphide mine territory (Sverdlovsk region), acid mine drainage discharge reaches 3,000 m³/day. To neutralize acid waters, more than 400 m³/day of water with a neutral pH is required (to produce the slaked lime). Due to the worn out state of water pipe from the river Tagil, heavy losses, and frequent accidents, the neutralization station receives no more than half of the required amount of water. As a result, the neutralization technology is violated, acid mine drainage is not properly cleaned, the regulatory requirements for wastewater are not achieved, and sulfate waters with increased mineralization and metal concentrations are discharged into the river Tagil. Research objective is to substantiate the possibility of finding sources of drinking, household and process water supply for Levikha village and acid mine drainage neutralization stations by applying groundwater. Methods of research include a comprehensive approach containing research results analysis and field and laboratory research data processing. Results and discussion. Promising areas have been identified representing private catchment areas of potential water intakes with the most favorable conditions for underground runoff. A combination of the following factors was the criterion for promising areas and load points: favorable geological and tectonic conditions (the presence of tectonic faults); groundwater inflow testing results (relatively high specific flow rates of wells); geomorphological position (confinement to low relief areas, location near surface sources of groundwater recharge); hydrochemical sampling data (satisfactory chemical composition of groundwater); sanitary and hygienic situation (absence of potential sources of pollution in the local catchment area). Conclusions. The total resources of the five promising sites are 1,340 m3 /day, including 282 m3 /day for drinking purposes. Exploration and development of promising areas no. II (favorable geological and tectonic conditions within it are confirmed by the groundwater inflow testing results) and no. III (favorable sanitary and hygienic conditions) seem to be the most reasonable. These sites might cover half of the village water needs for drinking and household purposes.

Isolation and Identification of Bacterial Communities in Neutral Mine Drainage in Central Slovakian Neovolcanites (Slovakia)

There are several sources of mine drainage left over from past mining sites in the Central Slovakian neovolcanites. The neutral pH and high concentrations of sulphates and multiple potentially hazardous elements, such as zinc or manganese, are typical in this region. However, this environment could be home to specific microbiota. The aim of the study was to characterize bacterial populations in mine drainage in the Central Slovakian neovolcanites. Direct microscopic observations, cultivation methods, MALDI TOF mass spectrometry, and 16S rRNA gene sequencing of isolates were used for identification. Gram-positive and Gram-negative bacteria were almost equally represented in the mine water samples. The most abundant bacterium was the genus Bacillus spp. (43.48%). Another large group of bacteria consisted of Proteobacteria (34.78%), represented by Pseudomonas spp. (17.39%), Serratia spp. (13.04%), and Providencia spp. (4.35%). Our data confirm the presence of Bacillus spp. and Pseudomonas spp. as bacterial species occurring in an environment polluted by potentially hazardous elements, which may indicate their bioremediation potential.

Hydrogeochemistry of thallium and other potentially toxic elements in neutral mine drainage at the decommissioned Pb-Zn Raibl mine (Eastern Alps, Italy)

Decommissioned mines represent a worldwide concern due to the potential long-term effects related to the dispersion of potentially toxic elements (PTEs) in the environment. In this study, 176 water samples were collected in the period 2018–2021 at the carbonate-hosted Pb-Zn Raibl mine which is affected by neutral mine drainage (NMD). The post-flotation tailings are the main source of PTEs (Zn, Pb and especially Tl) in the river drainage system. Compared to other dissolved PTEs (Zn, Pb, Cd), Tl was found to be more mobile, reaching concentrations up to 120 μg L−1 in waters flowing in the tailings impoundments. Modelling results suggest that Tl is mainly present in the Tl(I) ionic and mobile form thus suggesting that relevant natural attenuation processes for this element are not expected in the investigated area. In contrast, Zn and Pb attenuation pathways appeared to be governed by pH-dependent speciation and sorption processes, whereas elevated Zn concentrations were likely also limited by hydrozincite precipitation. Metalloids such as As and Sb were almost entirely released into the slightly alkaline waters of the mine drainage system, which are generally characterised by longer residence time or standing waters whereas As and Sb concentrations were negligible in the tailings-seepage waters. However, intense rainy events may increase PTE concentrations of one order of magnitude, especially in the tailings impoundment groundwater as a result of a rise in the water table, and PTE total dissolved loads of three orders of magnitude, in the main stream during high flow events, thus representing the most critical factor in regulating the remobilisation and downward dispersion of PTEs in the river drainage system.

Possibilities of remediation of neutral mine drainage - Removal and recovery of potentially hazardous elements

Mine water is one of the factors threatening the environment. The aim of the review article is to discuss and critically evaluate individual strategies for the remediation of neutral mine water. A critical evaluation is an essential tool to determine an appropriate remediation strategy. A wetland system is the preferred method of metal removal. However, the disadvantage is that it takes up more space compared to other methods and has a lower metal removal efficiency compared to active metal removal methods. When creating a suitable strategy, it is also necessary to assess the conditions of the mining site, which partially or completely prevent the use of the selected remediation strategy. The benefit of this review article is the processing of suitable combinations of treatment methods for the removal of potentially hazardous elements and their subsequent recovery. Future research in the field needs to focus on the analysis of the negative aspects of the environment that may disrupt or support the implementation of the selected method of remediation.

Analysis of the Mechanism of Acid Mine Drainage Neutralization Using Fly Ash as an Alternative Material: A Case Study of the Extremely Acidic Lake Robule in Eastern Serbia

Acid mine drainage (AMD) is a waste from mining sites, usually acidic, with high concentrations of sulfates and heavy metal ions. This study investigates the AMD neutralization process using fly ash (FA) as an alternative material. Samples of FA from coal-fired power plants in Serbia (“Nikola Tesla” (EF) and “Kostolac” (KOST)) were analyzed and used. The results were compared with the treatment efficiency of commercial neutralization agent (NaOH). The alkaline nature of FA was the basis for use in the treatment process of the extremely acid Lake Robule (pH 2.46), located in the mining areas of eastern Serbia. The optimal S/L ratio for the AMD neutralization process determined for EF was 25 wt.%, and for KOST it was 20 wt.%. The mechanism of the neutralization process was analyzed using the ANC test and PHREEQC program. The element concentrations and pH values in solutions indicated that FA samples could neutralize Lake Robule with more than 99% of Al, Fe, Cu, Zn, and more than 89% of Pb precipitated. Formation of insoluble (oxy)hydroxide forms (Fe3+ and Al3+ ions) creates favorable conditions for co-precipitation of other trace metals (Cu, Zn, Ni, Pb, and Cd) from AMD, which is further enhanced by cation adsorption on FA particles. FA proved to be a more effective neutralization agent than NaOH due to its adsorption effect, while among the FA samples, KOST was more effective due to the aging process through the carbonization reaction. Using FA as an alternative material is a promising and sustainable method for treating AMD, with economic and environmental benefits.

Legacy of contamination with metal(loid)s and their potential mobilization in soils at a carbonate-hosted lead-zinc mine area

Chemical weathering of carbonate-hosted Pb–Zn mines via acid-promoted or oxidative dissolution generates metal-bearing colloids at neutral mine drainage sites. However, the mobility and bioavailability of the colloids associated with metals in nearby soils are unknown. Here, we monitored the mobility of metal(loid)s in soils affected by aeolian deposition and river transport in the vicinity of a carbonate-hosted Pb–Zn mine. Using chemical extraction, ultrafiltration, and microscopic and spectroscopic analysis of metals we find that contamination levels of the soil metals cadmium (Cd), lead (Pb) and zinc (Zn) were negatively correlated with metal extractability. However, nano-scale characterization indicates that colloid-metal(loid) interactions induced potential mobilization and increased risk from metal(loid)s. Dynamic light scattering (DLS) and HRTEM-EDX-SAED analysis further indicate that organic matter (OM)-rich nano-colloids associated with calcium (Ca), silicon (Si) and iron (Fe) precipitates accounted for the majority of the dissolved metal fractions in carbonate-hosted Pb–Zn mine soils. More stable nano-crystals (ZnS, ZnCO3, Zn-bearing sulfates, hematite and Al–Si–Fe compounds) were present in the pore water of aeolian-impacted upland soils rather than in river water-impacted soils. Our results suggest that future work should consider the possibility that potential mobilization of metal(loid)s induced by the weathering and transformation of these metal-bearing nano-crystals to metal-bearing amorphous colloids, potentially elevating metal mobility and/or bioavailability in river water-impacted agricultural soils.

Lignite fly ash utilization for acid mine drainage neutralization and clean-up

Two fly ashes (FAs) originating from Kardia and Megalopolis power plants are used for the first time to amend the acid mining drainage (AMD) from the abandoned Ermioni and the active Kassandra Greek mining sites. The fly ashes employed are of type C, with Kardia fly ash (KFA) being mostly calcareous and Megalopolis’ (MFA) mostly siliceous. Both FAs were tested for their pH-regulating and metal-ions-removal efficiency. Regarding the acidity reduction both FAs proved equally efficient; by regulating the FA to AMD solution ratio, final pH values between 6 and 12.5 were attained using KFA while weakly acidic (pH = 6) to neutral solutions were produced in the case of MFA. Except for chromium ions, both FAs, also, proved equally effective in (heavy-)metal-removal for loadings higher than 5 g/50 mL acid waters. KFA, particularly, cleaned up the acid mine drainage solution from all metals even at a 0.5 g/50 mL loading. For KFA, metal removal was attributed to precipitation while in the case of MFA retention was found to occur via adsorption and/or complexation as well. Both FAs and AMD are largely produced as side effects of the two major Greek economic activities, i.e., electricity production and mining; using FAs to assess the AMD environmental impact can contribute to circular economy and, therefore, is of significant financial interest for Greece.

Comparative study of acid mine drainage neutralization by calcium hydroxide and concrete sludge–derived material

A novel neutralizing agent (PAdeCS) was produced from concrete sludge generated during the production of secondary concrete products by centrifugal molding, and the effect on actual acid mine drainage (AMD) was evaluated. The effect was compared with a conventional neutralizing agent (i.e., calcium hydroxide). Nine reaction tanks were temporarily installed and operated, imitating the treatment of actual AMD. The amount of discharged water and sediment generated was evaluated. The amount of PAdeCS required to neutralize the actual mine wastewater was 1.5 times that of Ca(OH)2, and the amount of sludge generated was less with PAdeCS than with Ca(OH)2. The coagulation sedimentation performance of PAdeCS is greater than that of Ca(OH)2, determined by comparing the thickness of the sludge layer and the transparency of the supernatant. The reduction of CO2 emissions for the substitution of Ca(OH)2 and CaCO3 by PAdeCS was evaluated, and the neutralization performance of this novel neutralizing agent prepared from concrete sludge in AMD was determined.

Feasibility of reprocessing gold tailings: Integrated management approach for the control of contaminated neutral mine drainage

Sulfide ore processing generates finely ground mine tailings that often contain sulfide minerals such as pyrite, pyrrhotite, arsenopyrite, and gersdorffite. These minerals can generate acid mine drainage or contaminated neutral drainage (CND) due to weathering (aqueous oxidation by oxygen, and bacterial activity). Contaminated neutral mine drainage affects the surrounding environment by contaminant release (e.g., As, Ni, Fe, Cu, and Zn), which is one of the most challenging environmental issues for the mining industry. This paper examines the feasibility of desulfurization by flotation at the laboratory scale as a sustainable tailings management approach to prevent CND generation from tailings produced by the Amaruq mine (Nunavut, Canada). The flotation tests were conducted using a five-level statistical experimental design (DOE) using five parameters that include: collector dosage (PAX), activator dosage (CuSO4), frother dosage (MIBC), pH, and solid content (Cs). The response surface methodology (RSM) was used to predict sulfur recovery and to choose the optimal conditions of flotation. The mineralogical properties of the samples before and after reprocessing were investigated by combining optical microscopy, X-ray diffraction spectroscopy (XRD), and the quantitative evaluation of materials by scanning electron microscopy (QEMSCAN®). The trace element (As, Co, Ni, etc.) microanalysis of the identified minerals was quantified using electron probe micro-analyser (EPMA), and the bulk chemical composition was analyzed using induction furnace, X-ray fluorescence, and ICP-AES/MS. Finally, the geochemical behavior of the initial (WTT) and desulfurized (DWT) tailings was evaluated using kinetic weathering cells. The main results demonstrated that sulfur recovery can reach up to 97 % using the following optimal conditions: pH of 11.5, PAX dosage of 158 g/t, CuSO4 dosage of 300 g/t, MIBC dosage of 55 g/t, and Cs of 29.3 %. Moreover, the residual sulfides within the desulfurized tailings were completely locked within the non-sulfide gangue minerals as analyzed by QEMSCAN® and optical microscopy. Kinetic testing was performed on WTT and DWT to assess their contaminant release rates (especially As, Ni, Cu, Fe, and Zn).The desulfurized material did not cause any significant risk of contaminated mine drainage generation. All released contaminants were below the limits of Quebec provincial legislation.

Mobility of Be, Bi, F, Ga, Ge and W in Surface Water and the Water Quality Impact on Epilithic Diatoms Downstream of the Historical Yxsjöberg Mine Site, Sweden

There is a potential risk that the geochemical cycles of several critical metals will be affected when mining of these metals increases to meet the demand of green technology. The geochemistry of Be, Bi, Ga, Ge, and W, herewith called CM5, is lacking, yet is necessary to ensure responsible mine waste and water management. Beryllium, Bi, and W are all considered immobile, but in previous studies of skarn tailings in Yxsjöberg, Sweden, all three elements were mobilized. The tailings are enriched in CM5, together with pyrrhotite, calcite, and fluorite. The mobility and environmental impact of CM5 and F in surface waters downstream of the Yxsjöberg mine site, Sweden, were studied using monthly water samples from seven locations and analysis of diatoms at five of these locations. Bismuth, Ge, and W were present at low concentrations, transported in the particulate phase, and likely settled in the sediments hundreds of meters from the tailings. Beryllium and F were present at high concentrations and dominantly transported in the dissolved phase. At these pH conditions (5.6), Be should form insoluble hydroxides; however, elevated concentrations of dissolved Be were observed more than 5 km from the mine site. Diatoms downstream of the mine site were negatively affected by the mine drainage. The release of low quality neutral mine drainage will continue for hundreds of years if remediation actions are not undertaken since only a small portion of the tailings have weathered during 50–100 years of storage.

Start-Up and Performance of a Full Scale Passive System In-Cluding Biofilters for the Treatment of Fe, as and Mn in a Neutral Mine Drainage

Passive mine drainage treatment plants are the scene of many chemical and biological reactions. Here, the establishment of iron (Fe), arsenic (As), and manganese (Mn) removal was monitored immediately after the commissioning of the Lopérec (Brittany, France) passive water treatment plant, composed of aeration cascades and settling ponds followed by pozzolana biofilters. Iron and As were almost completely removed immediately after commissioning, while Mn removal took more than 28 days to reach its maximum performance. Investigations were performed during two periods presenting strong variations in feeding flow-rates: from 2.8 m3.h−1 to 8.6 m3.h−1 and from 13.2 m3.h−1 to 31.3 m3.h−1. Design flow rate was reached during the first week of the second period. Dissolved Fe and As were not affected by the decrease in residence time while Mn was only slightly affected. Microbial communities in biofilter presented similarities with those of the pond sludge, and genera including Mn-oxidizing species were detected. Proportion of bacteria carrying the aioA gene encoding for As(III)-oxidase enzyme increased in communities during the second period. Results suggest Mn removal is mainly associated with bio-oxidation whereas removal of Fe and As could be mainly attributed to chemical oxidation and precipitation of Fe, possibly helped by As(III) bio-oxidation.

Dynamics of the Galionella spp. and Leptothrix spp. Communities of Polluted Mine Drainage Water in Slovinky and Markušovce (Slovakia)

Tailings ponds Slovinky and Markušovce (Slovakia) belong to the group of high-risk areas threatening human health and the environment due to the high concentrations of potentially toxic elements. The aim of this study was to identify iron bacteria living in these extreme environments and to assess the impact of selected physicochemical parameters of drainage water, flowing from tailings ponds, on the dynamics of their population. The material deposited on the Slovinky and Markušovce tailings pond showed a circumneutral pH. The values of electrical conductivity and total dissolved solids were significantly higher in drainage water in Slovinky compared to Markušovce. The concentration of total iron was notably higher in drainage water in Markušovce than in Slovinky. Direct microscopic observations showed the presence of iron-oxidizing bacteria as Gallionella spp. and Leptothix spp. exhibiting significant seasonal changes in their prevalence. The differences in the environmental characteristics of drainage waters did not affect the dynamics of iron-oxidizing bacteria populations, but cultivable heterotrophic bacterial community showed significantly lower abundance in Markušovce drainage water. The findings contribute to the understanding of bacterial diversity in neutral mine drainage waters and demonstrate an important role of environmental factors in shaping the microbial population in mine environments.

Infrared thermographic investigation of the oxidation behaviour of sulfide minerals from antimony-bearing rocks exemplified by the Podkozara deposit, Bosnia-Herzegovina

To date, prediction of the drainage chemistry of geologic materials at mine sites commonly relies upon well-established mineralogical and geochemical test work. Antimony (Sb) deposits require water quality risk assessments that consider the contaminant's solubility and mobility behaviour. To investigate the oxidation reaction of sulfides, a newly designed infrared (IR) thermographic test protocol was used to visualise oxidising sulfide minerals and to classify the rock types from the Podkozara Sb project, Bosnia-Herzegovina according to their oxidation reactivity. Furthermore, the sample materials were geochemically and mineralogically analysed using pXRF, powder XRD, ICP-AES, ICP-MS and NAGpH techniques. Four rock types have been recognised in the deposit: (i) stibnite mineralised quartz veins (SMQV); (ii) stibnite mineralised carbonate rocks (SMCR); (iii) pyritic phyllites; and (iv) mylonitic marbles. As indicated by the defined rock types, stibnite and pyrite are the only two sulfide minerals detected in the sample materials, causing reactions of varying intensities during IR testing. The intensity and duration of the oxidation reaction depends on various factors, including the sulfide mineral itself, the ore content and galvanic reactions between the sulfide minerals. Based on IR testing, it could be demonstrated that SMQV and SMCR are highly reactive and have a high risk for sulfide oxidation and associated Sb release into waters in any pH environment. Pyritic phyllites and tailings show less oxidation reaction intensities and no oxidation reactions could be recorded for marbles. Tailings pose a low risk and pyritic phyllites as well as marbles do not show a risk at all for Sb deportment. For pyritic phyllites, however, a release of Fe must be considered. In addition, underground mine and local surface waters were analysed for their pH, Eh as well as dissolved metal, metalloid and sulfate contents. The mine waters possess especially strongly elevated Sb values (5–244 μg/L) at neutral to alkaline pH values (7.0–8.1). Thus, in the Podkozara deposit, there is a general excess of neutralising carbonate minerals that result in adequate buffering of generated sulfuric acid, limiting mobility of base metal cations in solution but this supports the mobilisation of Sb into mine waters. In this study, complementary conventional mineralogical and geochemical testing as well as novel IR visualisation of possible sulfide oxidation have revealed useful information on the likelihood of different rock types causing metalliferous drainage issues. In particular, IR thermographic testing provides valuable insights on the presence of oxidising Sb- and Fe-sulfides in ores and wastes. This information can be used to prepare suitable mitigation strategies for Sb-rich neutral mine drainage waters and serves as a sample pre-selection for long-term environmental studies and tests. Furthermore, this analysis shows that different management and separate disposal plans will be needed for different lithological wastes.