Mine Drainage Systems Research Articles

Enrichment of dissolved metal(loid)s and microbial organic matter during transit of a historic mine drainage system

Water quality degradation by decommissioned mining sites is an environmental issue recognized globally. In the Ore mountains of Central Europe, a wide array of contaminants is released by abandoned under- and aboveground mining sites threatening the quantity and quality of surface and groundwater resources. Here, we focus on the less-explored internal pollution processes within these mines involving organic carbon and microorganisms in trace metal(loid)s mobilization processes. Over an 18-month period, we conducted hydrological and biogeochemical monitoring at the Reiche Zeche mine, a former lead-zinc-silver mine, in Germany, reaching 230 meters below ground, well below the critical zone. Our results show strong seasonal fluctuations in water availability, concentrations of metal(loid)s, pH, and dissolved organic matter (DOM) components across multiple depths. Excess metal(loid) presence during high flow conditions indicated mobilization behavior deviating from conservative dilution. Our findings reveal strong positive correlations between metal(loid) variability and pH (0.894), and between metal(loid) variability and the DOM fluorescent component C2 (-0.910), a proxy for microbial activity. Accordingly, the microbial processes may significantly contribute to the observed metal(loid) composition and fluxes. By elucidating the intricate roles of hydrological and biogeochemical factors in trace metal(loid) mobilization, our research offers a comprehensive framework for improving mine water management and remediation, potentially informing global environmental policies and sustainable mining practices.

Perancangan Sistem Penyaliran Tambang Pada PIT XYZ PT Karya Bhumi Lestari Jobsite PT Kartika Selabumi Mining Desa Kedang Ipil Kota Bangun II Kabupaten Kutai Kartanegara Provinsi Kalimantan Timur

Water is one of the things that is very influential in the mining process, mining water is water that is at the location and/or comes from the process of mining activities, both mining and processing, including runoff water in the mining area. Surface runoff water is rainwater that overflows into mining areas and is not a result of mining activities. The open pit mining method will cause the formation of a large basin so that it has the potential to become a water storage area, both from surface runoff and groundwater. During extreme weather conditions with high rainfall, water from surface runoff can inundate the ground floor and cause the mining front to become muddy, which can hamper mining activities. Handling waterlogging in mining forts requires good pumping performance, as well as re-planning the mine drainage system for the mine progress area. So that mining activities run smoothly and the mining front is free from puddles of water after rain, the drainage system must be well designed. Based on research that has been carried out, the total area of ​​the Catchment Area is 52.14 Ha with a runoff discharge of 82,567.79 m³/month. The planned discharge using the MF-290 Pump with RPM 1600 is, 290.00 m³/hour or 123,540.00 m³/month. After comparing the MF-290, MF-385 and DND-200 pumps, the MF-290 pump was selected for use. This is because the fuel consumption of the MF-290 is smaller so it saves costs and it is also deemed sufficient to use the MF-290 pump. Pump Ratio on the MF-290 pump April 6.71. May 3.93, June 6.44, July 6.36 and August 8.83, which means the pump is safe to use because the ratio is >1.

Cleaner flotation separation of chalcopyrite from pyrite at low alkalinity: Based on calcium hypochlorite oxidative modification in acid mine drainage system

Efficient and clean flotation separation of copper-sulfur has attracted soaring interest in the beneficiation of sulfide ore. The objective of this work was to examine the influence of calcium hypochlorite (Ca(ClO)2) oxidative modification on the flotation separation of chalcopyrite from pyrite in acid mine drainage (AMD) system. A maximum recovery difference of 69.70 % between both minerals was observed under the recommended conditions (initial pH = 8.5 ± 0.2, [Ca(ClO)2] = 100 mg/L, [EX] = 32 mg/L, and the volume ratio of AMD to pure water = 1:1). A high-grade concentrate with 77.35 % Cu recovery and 29.01 % Cu grade was obtained, demonstrated by mixed-mineral micro-flotation experiments. Analysis of Cu and Fe ions influence indicated that low concentrations of Fe3+ and Cu2+ favored the selective separation of pyrite and chalcopyrite. Moreover, analysis of the pulp ion concentrations showed that Ca(ClO)2 promoted the dissolution of iron ions on the pyrite surface compared to chalcopyrite, thereby enhancing pyrite oxidation. The Ca(ClO)2 interacted more intensively with the pyrite surface, forming a passivated layer that impeded the adsorption of collector, as demonstrated by Zeta potential and contact angle results. The generation of hydrophilic products caused by oxidation on the pyrite surface, such as CaSO4, CaOH+, Fe(Ⅲ)–OOH, and/or Fe2(SO4)3 was confirmed by XPS analysis, further reducing the floatability of pyrite. Furthermore, local electrochemical impedance spectroscopy and scanning electron microscopy analyses further afforded favorable evidence for selective inhibition of pyrite by Ca(ClO)2 in the AMD system. This study provides a new approach to achieve cleaner separation of pyrite and chalcopyrite and offers new perspectives for AMD treatment solutions.

Design and Planning of Mine Drainage Systems at PT. Pertama Mina Sutra Perkasa, Puger District, Jember Regency, East Java, Indonesia

PT. Pertama Mina Sutra Perkasa, a limestone mining company, operates in Grenden Village, Puger District, Jember Regency, East Java Province. Utilizing an open mining system, the company faces challenges related to mine drainage. Based on rainfall analysis from 2013 to 2020. the planned rainfall rate is 25.938 mm/hour, with a rainfall intensity of 5.712 mm/hour, resulting in a runoff water discharge of 0.599 m³/second. The water discharge entering the well at the site is 2159.08 m³/hour. The designed drainage channel has a discharge capacity of 3.109 m³/second, a wet surface area of 0.5 m², a channel bottom slope of 0.03%, a hydraulic radius of 0.25 m, a Manning roughness coefficient of 0.011. a wet cross-section circumference of 2 m, and a flow depth of 0.5 m. The planned well dimensions are 60 m in length, 20 m in width, and 7 m in depth, with a volume of 8400 m³. The current sludge settling pond has three compartments with a total capacity of 393.75 m³. The proposed design for the sludge settling pond includes a length of 60.6 m, a width of 15 m, a depth of 7 m, and a volume of 5454 m³. The actual mud dredging frequency is once every 2 days, while the proposed plan extends this interval to 9 days using a Doosan 340DX type excavator. This comprehensive drainage system design aims to efficiently manage runoff and sedimentation, ensuring sustainable mining operations

Fuzzy Bayesian Network Fault Diagnosis Method Based on Fault Tree for Coal Mine Drainage System

Fuzzy Bayesian Network Fault Diagnosis Method Based on Fault Tree for Coal Mine Drainage System

An Experimental on Filtration and Clogging of Geotextile Filters around Drain Pipes in Fine Tailings

Needle-punched nonwoven geotextiles have been used as filters for decades in mine drainage systems. But the physical clogging of geotextiles by fine particles has continued to receive increasing attention. In this study, the permeation characteristics of a drain pipe wrapped with geotextiles were investigated based on a new radial flow experiment apparatus, and particle size distribution (PSD), pore water pressure (PWP), and scanning electron microscopy (SEM) analyses were employed to identify the geotextile clogging mechanism. The geotextile cleaning methods after clogging were also discussed. The results showed that an exponential decay of hydraulic conductivity (K) with time under different flow conditions. Particles less than 30 μm migrated to the drainage pipe under the action of seepage forces, and a dense and thick cake layer was formed upstream of the geotextile filter. According to microscopic analysis, the clogging process of geotextiles was divided into three stages: pore blockage and cake formation, filter cake dynamic growth and cake layer filtration. Backwash cleaning is a good way to remove a filter cake layer on the surface of geotextiles, which can recover 60% of the hydraulic conductivity (K0).

Combining geomechanical and hydrogeological modeling for drainage analysis in Block Caving mine development

Underground caving operations are naturally affected by mud and water inflows. These inflows occur mainly because caving operations are connected to a surface or a previous mining area through a broken subsidence zone where there is potential to accumulate water. Additionally, the surface/groundwater can mix with fine fragments within the broken column, which can generate a sudden mud rush through the drawpoints. A key mitigation measure for this hazard is drainage of the surrounding rock mass. However, an effective mine drainage system can be designed only if the physical behavior of groundwater flow is known. This work proposes a methodology that couples a geomechanical model designed in FLAC3D© with a hydrogeological model developed in FEFLOW©. The geomechanical model determines the spatial and temporal distribution of the stress field and induced strain due to caving. The spatial and temporal distribution of the hydraulic conductivity is analytically defined as a function of the induced strains. Then, the hydrogeological model is linked with the geomechanical model to simulate patterns of groundwater flow through the rock mass during cave propagation. Finally, a drainage chart is presented based on the hydrogeological simulation considering different caving stages and different system recharge due to surface inflows.

An innovative method to degrade xanthate from flotation tailings wastewater in acid mine drainage (AMD) system: Performance, degradation mechanism and pathways

This study objective is to degrade xanthate from flotation tailings wastewater by using a coagulation-flocculation co-Fenton oxidation process in an acid mine drainage (AMD)-H2O2 system. More than 98% sodium butyl xanthate (SBX) removal rate was achieved by the method under optimal conditions. The acids and Fe2+ in AMD were sufficient to initiate a Fenton reaction at the aid of H2O2. Furthermore, iron ions were reduced to an extremely low level (0.19 mg/L) by participating in an oxidation process. Meanwhile, the Cu2+ ions in AMD facilitated the coagulation-flocculation process. Comparison experiments confirmed that the method was superior to the AMD alone (54.26%) and H2O2 alone (32.23%) in terms of performance in degrading SBX. The kinetic results showed that SBX degradation followed a pseudo first-order kinetic model. Additionally, the electron paramagnetic resonance (EPR) and quenching results suggested that hydroxyl radicals (•OH) were the main active species in AMD-H2O2 system. Degradation products were analyzed, and two possible pathways of SBX degradation were proposed. One pathway displayed that the SBX was first transformed into butyl xanthate peroxide (BPX), CO32− and S2O32−, and then further decomposed into CO2, H2O and SO42− under the ongoing •OH attack. Another pathway showed that precipitates consisting of butyl copper xanthate and iron oxide species were generated during the SBX degradation. This study provides a novel perspective on the innovative application of AMD in Fenton oxidation and provides a strong basis for the green and sustainable treatment of xanthate wastewater in tailings.

Comparative Analysis of Actual Conditions and Results of Technical Calculations Using Gumbell Method in Mine Dewatering System: A Case Study on Calculation of Rainfall and Runoff Water Discharge

This research was conducted at PT. Antareja Mahada Makmur on the mining concession owned by PT. Multi Harapan Utama which is located in Sungai Payang Village, Loa Kulu District, Kutai Kartanegara Regency, East Kalimantan Province. The rainfall data used is for 10 years (2012-2021) which comes from the Dewatering Mining Engineering Department. Data analysis was performed by statistically calculating rainfall data using the Gumbell method to obtain the planned rainfall value. Then the calculation of runoff water discharge is carried out to analyze the existing mine drainage system by comparing the actual conditions and the results of technical calculations. Based on the results of the research for rainfall data for 2012 – 2021, Gumbell's calculations plan to collect rainfall of 94.23 mm/day, rainfall intensity of 14.74 mm/hour with a return period of 5 years and a hydrological risk of 89.26%. The total for the Gumbell method runoff discharge is obtained for runoff water entering the Sump 90 Besar of 2.19 m3/second, runoff water entering the Sump 90 Lorong of 3.03 m3/second, and for water discharge runoff that goes into Sump 100 is 3.68 m3/second. The three open channels in the form of trapezoids and culverts have met the theoretical calculation dimensions, with dimensions that are still able to accommodate and drain runoff water discharge. For three dimensions of the actual sump that is currently smaller than the theoretical calculation of the well volume, the sump capacity calculation obtained a recommended sump volume of 47,045 m3 for a 100 sump, for a sump 90 lorong of 43,012 m3, and for a sump 90 besar of 40,635 m3, with recommended dimension improvements. The operating speed of the pump needs to be increased for the Multiflow MF - 420 pump on a sump 90 lorong from 1159 m3/hour to 1224 m3/hour with an efficiency of 65%, Multiflow MF - 420 pump on a sump 90 besar from 1123 m3/hour to 1269 m3/hour with an efficiency of 70 %, for the Multiflow MF - 420 pump at sump 100 from 1282 m3/hour to 1584 m3/hour with an efficiency of 65%.

Обоснование списочного парка насосов и трубопроводных ставов рудничной водоотливной установки

The complex of drainage system of an underground mining enterprise ensures the safety and continuity of mining operations. Deterioration of the level of reliability of the functioning of the mine drainage system can lead to the following serious consequences. The main link of the mine drainage system is a drainage system equipped with pumping units based on the centrifugal pumps. One of the main criteria for the safe operation of a mine drainage system is its equipment with a sufficient number of pumping units. An assessment of the efficiency of the classical methodology for calculating the listed park of pumping units is given, including consideration of the amendment made to it regarding the given water inflow regime. The main drainage installation of the Udachny underground mine, equipped with sectional pumps, was chosen as the object of research. It is established that the list park of pumping units calculated according to the known methods does not allow to ensure a high level of reliability of the operation of the drainage plant. The same picture is typical for the park of discharge pipe sections of the drainage plant. When calculating the list park of pumping units of a drainage system, it is more expedient to consider not the passport performance of the pump, but its average value between major repairs. The number of pumps under repair depends on the average duration of repair work and the average time between failures of the pump. A method is proposed for calculating the optimal number of pumping units and pipe sections of a drainage system from the point of view of ensuring its reliable level of functioning. The results of the performed research will be useful to the specialists responsible for the design of drainage systems for underground mines and coal mines in the Russian Federation.

Watershed Analysis of Potential Flood Discharge in Tlepok Village

Mine drainage system is an effort to control the flow of water entering a work area so as not to interfere with mining activities. This research is intended as a form of implementation of the mine drainage system in the form of a discharge calculation by taking into account the condition of the watershed, then calculating the discharge plan for the return period to predict flood discharge at the research location. For rivers with high flow rates, it is planned to reduce the flood discharge in order to prevent the channel water level from exceeding its capacity. The research location is in Tlepok village, Karangsambung sub-district, Kebumen district, Central Java. In the study, the maximum river flow discharge was 1365.41 m3/s and the planned return period discharge was 520.46 m3/s up to 687.47 m3/s. Based on the calculation results, land conversion planning and river normalization planning were carried out to reduce the discharge in the watershed in Tlepok Village.

Dewatering requirements assessment for the Central Kalimantan NCP open pit gold mine

One of the most critical aspects of open pit mining is the dewatering and mine drainage systems. The NCP Open Pit Gold Mine is located in Central Kalimantan. This study area has a range of rainfall intensities and durations from moderate to heavy. Good dewatering is required to manage runoff water and reduce runoff from entering the pit and mine front loading. The study used daily rainfall intensity data from 1994 to 2018. Using the Mononobe Method, the hydrological data for this area were evaluated by determining the value of the rainfall intensity plan. According to the evaluation of rainfall data from 1994 to 2018, the research area saw a rainfall intensity of 86.23 mm/day over a two-year return period. The majority of water extracted from mines is from precipitation and runoff rather than groundwater. An open channel was made around the open pit, flowing water naturally into the sump to reduce water entering the mining area. The water was pumped into the settling pond with 520 m3/hour and 780 m3/hour capacity pumps.

Using a Mine Dewatering System to Increase Cooling Capacity and Energy Recovery of Underground Refrigeration Plant: A Case Study

Heat stress in deep hot mines is a factor that often determines the possibility of technical mining of natural resources. One of the solutions enabling miners to work in such mines is air cooling. Cooling systems vary, and their selection depends on the type of mine and the mining methods used. Limited air cooling capabilities exist in electric-powered coal mines. The main solution for air cooling is based on movable spot air coolers. Such systems commonly use surface or underground refrigeration plants. An underground refrigeration plant (URP) equipped with compressor chillers does not achieve more than 2.5–3.0 MW of cooling capacity due to the limited heat rejection capacity of return air streams in a typical coal mine. The method discussed in this paper, using mine water to discharge waste heat from the underground refrigeration plant, provides a measurable benefit for optimizing the mine air cooling system. The main purpose of this research is to study the feasibility and effect of water diversion from the actual mine drainage system to the underground refrigeration plant. The water drainage system in an underground mine is called the dewatering system of the mine. The heated water in the condensers of the chillers is directed back to the mine’s central dewatering system. The recovery from water discharged to the surface contributes to optimising energy consumption for a mine air cooling and the sustainable discharge of wastewater. In addition, using the total water flow from the mine dewatering system to reject heat in compressor chillers, compared with the traditional solution, can improve the cooling capacity of URP. These findings may provide beneficial guidance for practical applications in deep hot mines with small natural water inflow.

TECHNICAL DESIGN OF MINE DRAINAGE SYSTEM IN LIMESTONE MINING AT UP. PARNO, KARANGASEM VILLAGE, PONJONG DISTRICT, GUNUNGKIDUL DISTRICT, REGION YOGYAKARTA SPECIAL

UP. Parno is a limestone mining company operating in Karangasem Village, Ponjong District, Gunungkidul Regency. UP. Parno has an IUP with an area of 5.7 hectares by implementing an open mining system (surface mining) with the quarry method. Surface mining affects the surface due to climate. When it rains, the falling rainwater can pool in the mining area and around the lower mining openings. If it is dry, no rainwater enters the mining area. Thus, an adequate mine drainage system design is needed. Water discharge is the main thing to determine a good mine drainage system design. Based on the results of the calculation of rainfall data from 2011 to 2020, it is known that the planned rainfall is 101.70 mm/day, and the rainfall intensity is 43.77 mm/hour with a five-year return period of rain. The purpose of making an open channel is to drain rainwater that enters the mining area and drain runoff so that the mine road does not stagnate. The designed open channel has dimensions of b = 1.50 m; B = 1.00 m; d = 0.60 m; h = 0.50 m; a = 0.60 m. Culverts function to drain water from open channels that cut off haul roads. The culverts required are made of smooth cement surface, with a diameter of 0.35 m. The water flowing by the open channel will go to the settling pond to be purified first before flowing into the river around the mining area. The settling pond is designed to consist of three compartments with an area of 264 m2 each and 666 m3 volume. Dredging of sediment in settling ponds must be carried out every 10 months and 13 days.

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.

Trace element uptake in fresh and aged aluminium oxyhydroxysulfates and hydroxides: Implications for mine drainage-affected environments

Aluminium oxyhydroxysulfates and hydroxides are known to precipitate from mining-generated acidic, neutral and basic pH drainage waters that are enriched in potentially toxic metal(loid)s. Their role as medium-term (1 year) sinks of Al, As, Cu and Ni at pH values of 4, 7 and 10 was assessed using batch experiments. X-ray diffraction analysis showed that basaluminite initially formed at pH 4 and 7, whereas at pH 10, bayerite or nordstrandite (both Al(OH)3) formed. After 12 months of ageing at 20 °C, some of the pH 4 basaluminite recrystallised to form alunite, the pH 7 basaluminite recrystallised to form gibbsite, and the bayerite/nordstrandite was unchanged. At pH 4, the basaluminite took up As but did not take up Ni or Cu. By the end of the 12 months, some As was released from the basaluminite or alunite, and some Cu was taken up by these phases. At the beginning of the pH 7 experiments, As, Cu and Ni were taken up in the basaluminite, and these were retained in the gibbsite that replaced the basaluminite after 12 months. In the pH 10 experiments, only As was expelled from the bayerite/nordstrandite after 12 months. The differences in uptake of As, Cu and Ni are attributed to their aqueous speciation relative to the net surface charge of the Al oxyhydroxsulfates and hydroxides. Release of As from the pH 4 and pH 10 phases at 12 months was likely due to incorporation within the poorly crystalline original phases, followed by progressive release as the phases transformed to more crystalline minerals (at pH 4) or become more crystalline (at pH 10) with ageing. The results have significant implications for the mineralogy of Al oxyhydroxysulfates and hydroxides, and the cycling of As, Cu and Ni, in mine drainage systems.

Flotation separation of chalcopyrite and pyrite via Fenton oxidation modification in a low alkaline acid mine drainage (AMD) system

The selective flotation separation of pyrite and chalcopyrite, and the comprehensive utilization of AMD play a vital role in the cleaner production of copper sulfide ore. In this paper, flotation separation of chalcopyrite and pyrite via Fenton oxidation modification in a low alkaline acid mine drainage (AMD) system was investigated. The results of micro-flotation experiment displayed that the maximum recovery difference between chalcopyrite and pyrite was 74.6% at recommended test conditions. The artificial mixed-mineral flotation experiment further confirmed the desirable flotation separation of minerals. Zeta potential, FTIR spectra analysis, contact angle measurement and adsorption amount analysis results confirmed that the hydrophilic species caused by Fenton oxidation could seriously hinder the interaction between pyrite surfaces and EX collector. Whereas, the Fenton oxidation had feeble influence on the floatability of chalcopyrite. The XPS study indicated that Fenton oxidation significantly increased the contents of SO42- on pyrite surfaces, and the concentration of SO42- increased from 5.9% to 37.65%. Meanwhile, this modification promoted the deep transformation of Fe chemical states mainly from Fe(Ⅱ)-S to Fe(III)–OOH and Fe2(SO4)3. As a result, the contents of Fe(III)–OOH and Fe2(SO4)3 reached 50.04% and 29.19%, respectively. For chalcopyrite, a small amount of oxide/hydroxide species were formed during this processing, and the chalcopyrite can interact with EX collector effectively. Thus, flotation separation of chalcopyrite and pyrite via Fenton oxidation modification in a low alkaline AMD system mainly attributes to the significant differences in the number and species of hydrophilic species.

Thermal Transformation of Natural Schwertmannite in the Presence of Chromium

Schwertmannite is a metastable mineral playing a crucial role in the immobilization of metal(oid)s in acid mine drainage (AMD) systems. High temperatures associated with wildfires could lead to a sudden schwertmannite transformation, changing the mobility of metal(oid)s. The objective of the present study was to examine the thermal transformation from schwertmannite to hematite, and the subsequent effect on the chromium partitioning. The immobilization of arsenate after thermal transformation and its implications on chromium mobility was also evaluated. Natural schwertmannite, with increasing contents of chromium, was thermally treated between 200 to 800 °C. Transformation products were characterized by solid-phase techniques and selective chemical extractions. Results indicated a transformation to hematite at temperatures above 400 °C. The presence of chromium barely affected the temperature at which the transformation occurred, although partitioning of chromium in the mineral changed with temperature. As the temperature increased from 25 °C to 400 °C, chromium was less mobile and less outcompeted by arsenic adsorption, suggesting a larger contribution of inner-sphere complexes with increasing temperature. At temperatures above 600 °C, non-mobile forms strongly associated with neo-formed hematite were found. Finally, neo-formation of hematite led to a decrease in arsenic adsorption, implying a potentially enhanced arsenic mobility in AMD systems upon wildfires.

Metagenomic Mining for Esterases in the Microbial Community of Los Rueldos Acid Mine Drainage Formation.

Acid mine drainage (AMD) systems are extremely acidic and are metal-rich formations inhabited by relatively low-complexity communities of acidophiles whose enzymes remain mostly uncharacterized. Indeed, enzymes from only a few AMD sites have been studied. The low number of available cultured representatives and genome sequences of acidophiles inhabiting AMDs makes it difficult to assess the potential of these environments for enzyme bioprospecting. In this study, using naïve and in silico metagenomic approaches, we retrieved 16 esterases from the α/β-hydrolase fold superfamily with the closest match from uncultured acidophilic Acidobacteria, Actinobacteria (Acidithrix, Acidimicrobium, and Ferrimicrobium), Acidiphilium, and other Proteobacteria inhabiting the Los Rueldos site, which is a unique AMD formation in northwestern Spain with a pH of ∼2. Within this set, only two polypeptides showed high homology (99.4%), while for the rest, the pairwise identities ranged between 4 and 44.9%, suggesting that the diversity of active polypeptides was dominated not by a particular type of protein or highly similar clusters of proteins, but by diverse non-redundant sequences. The enzymes exhibited amino acid sequence identities ranging from 39 to 99% relative to homologous proteins in public databases, including those from other AMDs, thus indicating the potential novelty of proteins associated with a specialized acidophilic community. Ten of the 16 hydrolases were successfully expressed in Escherichia coli. The pH for optimal activity ranged from 7.0 to 9.0, with the enzymes retaining 33–68% of their activities at pH 5.5, which was consistent with the relative frequencies of acid residues (from 54 to 67%). The enzymes were the most active at 30–65°C, retaining 20–61% of their activity under the thermal conditions characterizing Los Rueldos (13.8 ± 0.6°C). The analysis of the substrate specificity revealed the capacity of six hydrolases to efficiently degrade (up to 1,652 ± 75 U/g at pH 8.0 and 30°C) acrylic- and terephthalic-like [including bis(2-hydroxyethyl)-terephthalate, BHET] esters, and these enzymes could potentially be of use for developing plastic degradation strategies yet to be explored. Our assessment uncovers the novelty and potential biotechnological interest of enzymes present in the microbial populations that inhibit the Los Rueldos AMD system.

Geochemical Assessment of Gypsum Scale Formation in the Hydrated Lime Neutralization Facility of the Daedeok Mine, South Korea

Scale is widely observed in the hydrated lime mine drainage treatment plant of the Daedeok Mine in South Korea. In order to understand the environment in terms of the formation of scale minerals, scale and water were collected from the AMD treatment facility and analyzed. In addition, the saturation index was calculated based on geochemical modeling to predict the minerals that could be produced in the AMD treatment facility, and the results were then compared with an analysis of onsite scale minerals. Furthermore, the onsite mine drainage was neutralized from pH 3 to pH 9 in the laboratory, and the precipitates produced were identified. The changes in the Ca2+ and SO42− concentrations were also identified over time for each pH. The results of geochemical modeling predicted the possible precipitation of gypsum, anhydrite, and bassanite after AMD neutralization. Scanning electron microscope/energy dispersive X-ray spectroscopy (SEM/EDS) analysis results showed that the main mineral in scale formed at the AMD treatment facility was gypsum, produced by the reaction of SO42− and Ca2+ from lime during AMD. The laboratory neutralization experiment showed that gypsum was produced in all neutralization ranges from pH 3 to pH 9, and the higher the neutralization pH, the greater the amount of gypsum produced. It was demonstrated that simulated amounts of 2 g/L and 7 g/L gypsum at pH 5 and 9 were well matched with the experimental results. Iron (Fe), a major pollutant in the mine drainage system, was rapidly precipitated in the form of iron hydroxides after neutralization. As gypsum is produced slowly and continuously for a long period of time, it results in the growth of scale throughout the flow path. As a method of minimizing gypsum production in the AMD treatment facility using hydrated lime, it is recommended that the facility should be operated at the lowest pH possible, which will also enable the removal of major pollutants, such as iron and aluminum.