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The Youngest Toba Tuff (YTT) supervolcanic eruption occurred 75000 years ago, and resulted in distinctive ash fall deposition in different locations encompassing marine, estuarine, lacustrine, and fluvial sedimentary basins. Of the different sedimentary basins, the YTT crypto‐tephra horizon preserved in the South Kerala Sedimentary Basin (SKSB) of the western coast of India is hosted by a paleo‐estuarine carbonaceous clay layer. Along the eastern margin of SKSB, confined aquifers hosting highly acidic groundwater is associated with this YTT ash and associated organic matter (OM)‐rich carbonaceous clay layer, creating worse acid rock drainage (ARD), which eventually gets neutralised during summer, signalled by the crystallisation of halotrichite. Hydrogeological investigation gave insights on some of the unique geochemical processes, which facilitated the neutralisation of ARD. The main aquifers in the area include laterite and clayey‐sand, which is separated by this impervious layer hosting YTT ash. Wells tapping the clayey‐sand aquifer, beneath this layer, is affected by the ARD condition due to the interaction with pyrite, manifested as low pH of groundwater (3.7). Simultaneously, leaching from YTT ash, which constitutes 11.91% of Al2O3, facilitates Al content to reach groundwater in high concentration (2879.97 ppb). During dry season, when the surface of YTT‐hosting OM‐rich carbonaceous clay layer is exposed, the leached Al interacts with the acid derived from the YTT‐hosting OM‐rich carbonaceous clay layer and results in the precipitation of halotrichite. The two processes, one resulting in ARD condition and the other as formation of halotrichite, occur in succession. Thus, the crystallisation of halotrichite signals the neutralisation of water as well as heralding the potability of water. [ABSTRACT FROM AUTHOR]

It is well known that Acid Rock Drainage (ARD) is a major environmental concern for the mining and civil industry, due to water quality deterioration. Another important issue related to ARD is the integrity of the civil structures percolated by these effluents, especially concrete structures, rock fillings and rock filter/drainage layers. It is expected that the acidic nature of ARD can lead to accelerated weathering processes, reducing the time lifespan of these structures. In the present research we propose to evaluate the sensitivity of two of the most common laboratory rock weathering tests to acidic conditions, the Soxhlet Extractor and Soundness Test. Firstly, three different rock samples were characterized for mineralogy, petrography, and chemical composition. After, they were submitted to Soxhlet Extractor and Soundness (immersion) weathering tests, using ARD, distilled-deionized water (DDW) in the Soxhlet Extractor and ARD, DDW and sulfate as percolating/immersion solutions for the Soundness Test. The results showed that under the ordinary conditions used in these tests, no significant weather variation was observed among all the rocks samples and solutions. Thus, the hypotheses of more intense weathering due to the ARD influence was not corroborated. [ABSTRACT FROM AUTHOR]

Green liquor dregs (GLD) is an alkaline by-product from the pulp and paper industry with a pH between 10 and 14. Today most of the produced GLD in Sweden is landfilled. As a fine-grained alkaline material, it might be possible to use it for acid-generating mining waste remediation. To increase the utilization, quality characteristics and environmental performance need to be determined. In this study samples were collected 5 times from 16 mills during a period of 2.5 years, and were characterized by analyzing dry matter content, loss on ignition (LOI) 550 °C and LOI 950 °C, elemental analysis, pH, electrical conductivity, and calorific value. The results were then evaluated using multivariate statistics (PCA) as well as being compared to other studies and Swedish till. The results show that even if GLD is heterogenous (both within a mill and between different mills) trends can be seen for samples from most mills. When samples do stand out, it is predominately related to the same four mills. Most of the studied parameters showed characteristics favorable for use as a remediant; however, TOC, sulfur, and some of the elements require further study. In general, this study concludes that GLD can be a viable option for the remediation of small orphaned sulfidic mining sites and thus worthy of further studies on the interaction between GLD and acidic mining waste. Overall, GLD can be a good alternative for cost-effective remediation of smaller orphaned mining sites. It is readily available in large quantities, has the qualities needed for remediation of many orphaned acidic mining sites, and can often be locally sourced near the mining site. The use of GLD for mining site remediation is likely also a more sustainable method compared to traditional remediation methods. [ABSTRACT FROM AUTHOR]

Increasing stream metal concentrations apparently caused by climate warming have been reported for a small number of mountain watersheds containing hydrothermally altered bedrock with abundant sulfide minerals (mineralized watersheds). Such increases are concerning and could negatively impact downstream ecosystem health, water resources, and mine‐site remediation efforts. However, the pervasiveness and typical magnitude of these trends remain uncertain. We aggregated available streamwater chemistry data collected from late summer and fall over the past 40 years for 22 mineralized watersheds throughout the Colorado Rocky Mountains. Temporal trend analysis performed using the Regional Kendall Test indicates significant regional upward trends of ∼2% of the site median per year for sulfate, zinc, and copper concentrations in the 17 streams affected by acid rock drainage (ARD; median pH ≤ 5.5), equivalent to concentrations roughly doubling over the past 30 years. An examination of potential load trends utilizing streamflow data from eight "index gages" located near the sample sites provides strong support for regionally increasing sulfate and metal loads in ARD‐affected streams, particularly at higher elevations. Declining streamflows are likely contributing to regionally increasing concentrations, but increasing loads appear to be on average an equal or greater contributor. Comparison of selected site characteristics with site concentration trend magnitudes shows the highest correlation for mean annual air temperature and mean elevation (R2 of 0.42 and 0.35, respectively, with all others being ≤0.14). Future research on climate‐driven controlling mechanisms should therefore focus on processes such as melting of frozen ground directly linked to site mean temperature and elevation. Plain Language Summary: "Mineralized" watersheds contain bedrock with abundant sulfide minerals that, when weathered, often produce naturally acidic and metal‐rich streamwater, known as acid rock drainage (ARD). Increasing metal concentrations have been recently identified in a small number of ARD streams, apparently due to climate change. These trends are concerning because, even at low concentrations, dissolved metals can negatively affect downstream ecosystem health and the quality of water resources. However, we currently do not know how widespread these upward metal trends are regionally, and thus the scope of potential environmental impacts. To address this issue, we aggregated available streamwater chemistry data collected over the past 40 years for mineralized watersheds throughout Colorado. In the 17 sampled ARD streams, we found significant regional upward trends in concentration of ∼2% of the site median per year for two metals of primary environmental concern, zinc and copper. This rate of increase equates to concentrations roughly doubling over the past 30 years. We examined possible driving mechanisms for these marked concentration trends and conclude they are mainly due to increasing sulfide weathering rates (rising metal mass export) rather than simply declining streamflows (less dilution), with melting of frozen ground being a likely major driver of accelerated weathering. Key Points: Sulfate, zinc, and copper concentrations are increasing regionally in streams affected by acid rock drainage throughout ColoradoDeclining streamflows are contributing to increasing concentrations, but increasing loads are likely an equal or greater contributorTrend slopes are positively correlated with mean annual temperature and elevation, suggesting melting of frozen ground is a major driver [ABSTRACT FROM AUTHOR]

Streams impacted by historic mining activity are characterized by acidic pH, unique microbial communities, and abundant metal-oxide precipitation, all of which can influence groundwater-surface water exchange. We investigate how metal-oxide precipitates and hyporheic mixing mediate the composition of microbial communities in two streams receiving acid-rock and mine drainage near Silverton, Colorado, USA. A large, neutral pH hyporheic zone facilitated the precipitation of metal particles/colloids in hyporheic porewaters. A small, low pH hyporheic zone, limited by the presence of a low-permeability, iron-oxyhydroxide layer known as ferricrete, led to the formation of steep geochemical gradients and high dissolved-metal concentrations. To determine how these two hyporheic systems influence microbiome composition, we installed well clusters and deployed in situ microcosms in each stream to sample porewaters and sediments for 16S rRNA gene sequencing. Results indicated that distinct hydrogeochemical conditions were present above and below the ferricrete in the low pH system. A positive feedback loop may be present in the low pH stream where microbially mediated precipitation of iron-oxides contributes to additional clogging of hyporheic pore spaces, separating abundant, iron-oxidizing bacteria (Gallionella spp.) above the ferricrete from rare, low-abundance bacteria below the ferricrete. Metal precipitates and colloids that formed in the neutral pH hyporheic zone were associated with a more diverse phylogenetic community of nonmotile, nutrient-cycling bacteria that may be transported through hyporheic pore spaces. In summary, biogeochemical conditions influence, and are influenced by, hyporheic mixing, which mediates the distribution of micro-organisms and, thus, the cycling of metals in streams receiving acid-rock and mine drainage. IMPORTANCE In streams receiving acid-rock and mine drainage, the abundant precipitation of iron minerals can alter how groundwater and surface water mix along streams (in what is known as the “hyporheic zone”) and may shape the distribution of microbial communities. The findings presented here suggest that neutral pH streams with large, well-mixed hyporheic zones may harbor and transport diverse microorganisms attached to particles/colloids through hyporheic pore spaces. In acidic streams where metal oxides clog pore spaces and limit hyporheic exchange, iron-oxidizing bacteria may dominate and phylogenetic diversity becomes low. The abundance of iron-oxidizing bacteria in acid mine drainage streams has the potential to contribute to additional clogging of hyporheic pore spaces and the accumulation of toxic metals in the hyporheic zone. This research highlights the dynamic interplay between hydrology, geochemistry, and microbiology at the groundwater-surface water interface of acid mine drainage streams. [ABSTRACT FROM AUTHOR]

The effective management of sulfide mine waste tailings is a complex task because of the potential for acid rock drainage to harm aquatic ecosystems. Although previous research has explored the environmental consequences of sulfide mine waste tailings and the potential advantages of desulfurization method, there is a lack of studies examining the environmental compliance of desulfurization efforts. To bridge this knowledge gap, a study was conducted at the Ok Ted Mine to evaluate the environmental compliance of the implemented desulfurization process. Ninety samples of sulfide tailing, desulfurized tailing, and sulfide concentrate were collected and analyzed for geochemical and physical properties. The acid-generating capacities were assessed using the Sobek's static test, whereas the particle size, pH, and recovery were evaluated for the overall performance of the desulfurization process. These findings indicated that the desulfurization process significantly reduced the acid-generating capacity and heavy metal concentrations of the sulfide tailings below the regulatory threshold levels. Therefore, the desulfurization approach employed at the Ok Ted Mine comply with the environmental regulaotry requirments. For further assessment, a study is recommended to evaluate the impact of desulfurization on the ecosystem to predict full extent of biodiversity recovery after mine life.

Precipitation infiltrates into the lead–zinc–silver Bunker Hill Mine, oxidizes pyrite, and produces acidic waters that discharge from the mine portal. The metasedimentary geology and alteration from 100+ yr of mining provide a heterogeneous environment for source water infiltration and flow within the mine. A university–industry partnership was developed to trace the mine water sources, flowpaths, and travel times to identify potential areas for infiltration reduction. Snowpack, creek, and mine water samples were collected over a 1-year period for the analysis of δ2H, δ18O, and 3H, along with the in situ measurement of temperature, specific conductance, pH, dissolved oxygen, and flow. The isotope tracers were used to identify the source waters, unmix mine water as it moved deeper in the mine, and examine flowpaths in and near the acid-generating pyritic zone. The results indicate creek water infiltrating relatively quickly through the anthropogenically-modified pathways and causing the largest amount of acidic water in the upper levels of the mine. Slower, natural pathways associated with faults, fractures, and bedding planes produce mostly neutral waters with the source waters typically originating at higher elevations. Travel times ranged from <1 to 22 years with shorter pathways to the upper levels of the mine and increasing contributions deeper in the mine from pathways containing older, higher-elevation snowmelt. These slower and older inflows were identified by depleted δ18O values, smaller 3H concentrations, the dampening of the variability of the isotope signals, and pH increases. Reduction of infiltration zones near the upper workings of the mine likely will decrease the acidic waters in the upper levels of the mine, but the higher elevation infiltration zones will continue to contribute snowmelt-derived waters at all mine levels. [ABSTRACT FROM AUTHOR]

In Peru, socio-environmental conflicts related to the development of mining-metallurgical processes and the responsible disposal of mine tailings have become central issues for accepting mining projects, especially regarding building relationships of trust with the communities. This condition has prompted the Peruvian mining industry to advance in managing alternatives to the conventional surface disposal of mine tailings. A promising and increasingly popular management strategy for mine tailings in Peru is their disposal inside underground mines. This article presents: site-specific conditions, advantages/disadvantages, and lessons learned from practical experiences of mine tailings disposal in underground mines in Peru. In addition, some techniques are highlighted, such as (i) hydraulic fill, (ii) cemented hydraulic fill, and (iii) cemented paste backfill. Finally, this article concludes that the responsible disposal of mine tailings in underground mines is a green mining solution that reduces negative socio-environmental impacts, limiting the generation of acid rock drainage (ARD) and the leaching of metals due to the decrease in contact with oxygen and rainfall, thus mitigating the contamination of surface and underground waters, reducing the footprint of affectation in the territory, and eliminating the emission of particulate matter in the environment. [ABSTRACT FROM AUTHOR]

Chromium is an important redox-active element, with significant Cr isotope fractionations driven by redox transformations in the natural environment and quantified through laboratory experiments. Recent work has demonstrated that non-redox-driven transformations can also produce small variations in Cr isotopes, but the role of these processes in controlling environmental Cr isotope variations remains unclear. The highly acidic but biologically diverse acid rock drainage system in Río Tinto, Spain (and affiliated rivers) provides a unique opportunity to examine how non-redox-related processes can substantially affect the isotopic composition of Cr in a natural system. Our results suggest that under conditions where Cr redox transformations are obviated, Cr cycling is largely controlled by formation of Fe-oxyhydroxides and Fe-hydroxysulfates, Cr adsorption, and Cr speciation, with little apparent Cr isotope fractionation between source materials, waters, and sediments. Moderate Cr isotope shifts, however, may be the result of non-redox processes, including adsorption to organic ligands and potentially biological uptake. These results add to a growing body of evidence for the importance of non-redox transformations in contributing to environmental Cr isotope variations, with implications for the use of chromium isotopes in studies of sedimentary Cr isotope records. In particular, this study is a validation of the potential for sulfide weathering in the Proterozoic to deliver relatively unfractionated Cr isotopes to the ocean, despite rising and sustained high oxygen levels. [ABSTRACT FROM AUTHOR]

This study is aimed at investigating acid rock drainage reactions and the impacts of seepage composition on the release and mobility of metals from mine tailing dams. Also, it seeks to inspect potential metal filtering by the soil, specify factors subjecting to metal leaching, and detect leaching metals from neutral mine tailings. To this end, both the geochemical and mineralogical parameters of two selected partially or completely reclaimed sites located adjacent to the western part of Azarbaijan province (Iran) are investigated. The bioavailability of three toxic elements in soil samples overlying the tailing formation collected in the case study (i.e., Agh-darreh) yielded a maximum value because of natural pollution in the riverbed for As (90.22%), Sb (82.26%), and Hg (41.15%). Regarding the As and Sb concentrations in the water of the main branch and the tributary of the Agh-darreh river, As and Sb concentrations in the polluted water of the tributary of the Agh-darreh river after joining to the main branch of Agh-darreh river increased by about 800% and 300% compared to the healthy water of the Agh-darreh river, respectively. Moreover, the concentration of these elements was compared in the bed sediments of the main and subbranches of the Agh-darreh river after joining these two branches. The results revealed that the Agh-darreh subbranch increases the As, Sb, and Hg concentrations in the sediments of the Agh-darreh river bed by 11%, 240%, and 80%, respectively. Overall, recognizing the contaminated areas contributes to providing such solutions, making good infrastructure for the construction of tailing dams, and achieving effluent control by constructing a concrete obstacle to subdue this matter. [ABSTRACT FROM AUTHOR]

Iron-sulfide minerals found in shale formations are stable under anaerobic conditions. However, in the presence of oxygen and water, acid-loving chemolithotrophic bacteria can transform the iron-sulfide minerals into a toxic solution of sulfuric acid and dissolved iron and minerals known as acid rock drainage (ARD). The objective of this study was to disrupt chemolithotrophic bacteria responsible for ARD using chemical treatments and to foster an environment favorable for competing microorganisms to attenuate the biologically induced ARD. Chemical treatments were injected into flow-through microcosms consisting of 501 g of pyrite-rich shale pieces inoculated with ARD bacteria. Three treatments were tested in the microcosms: (1) a sodium hydroxide-bleach mix, (2) a sodium lactate solution, and (3) a sodium lactate-soy infant formula mix. The effectiveness of the treatments was assessed by monitoring pH, dissolved iron, and other geochemical constituents in the discharge waters. The optimal treatment was a sequential injection of 1.5 g sodium hydroxide, followed by 0.75 g lactate and 1.5 g soy formula dissolved in 20 mL water. The pH of the discharge water rose to 6.0 within 10 days, dissolved iron concentrations dropped below 1 mg/L, the median alkalinity increased to 98 mg/L CaCO3, and sulfur-reducing and slime-producing bacteria populations were stimulated. The ARD attenuating benefits of this treatment were still evident after 231 days. Other treatments provided a number of ARD attenuating effects but were tempered by problems such as high phosphate concentrations, short longevity, or other shortcomings. The results of these laboratory microcosm experiments were promising for the attenuation of ARD. Additional investigations and careful selection of treatment methods will be needed for field application. [ABSTRACT FROM AUTHOR]

There is a need to define mine tailings in a clear, precise, multidisciplinary, transdisciplinary, and holistic manner, considering not only geotechnical and hydraulic concepts but also integrating environmental and geochemical aspects with implications for the sustainability of mining. This article corresponds to an independent study that answers questions concerning the definition of mine tailings and the socio-environmental risks linked with mine tailings chemical composition by examining the practical experience of industrial-scale copper and gold mining projects in Chile and Peru. Definitions of concepts and analysis of key aspects in the responsible management of mine tailings, such as characterization of metallic–metalloid components, non-metallic components, metallurgical reagents, and risk identification, among others, are presented. Implications of potential environmental impacts from the generation of acid rock drainage (ARD) in mine tailings are discussed. Finally, the article concludes that mine tailings are potentially toxic to both communities and the environment, and cannot be considered as inert and innocuous materials; thus, mine tailings require safe, controlled, and responsible management with the application of the most high management standards, use of the best available technologies (BATs), use of best applicable practices (BAPs), and implementation of the best environmental practices (BEPs) to avoid risk and potential socio-environmental impact due to accidents or failure of tailings storage facilities (TSFs). [ABSTRACT FROM AUTHOR]

Detailed mineralogical and textural studies, combined with sequential X-ray diffraction and geochemical modeling, helped to solve the "copper pitch/wad" enigma in the Exótica deposit located downstream of the Chuquicamata porphyry copper deposit. Copper pitch and copper wad are essentially chrysocolla with co-precipitated Mn oxides, mainly birnessite, as well as pseudo-amorphous Mn oxide/oxyhydroxides. Linking the mineralogical, geochemical, and textural evidences with the geological, tectonic, and climatic evolution of the Chuquicamata–Calama area, a four-step genetic model for the evolution of the Exótica deposit is presented: (A) formation of a mature supergene enrichment profile at Chuquicamata (~ 30–25 Ma to ~ 15 Ma) during an erosion-dominated regime (∼900 m of erosion) which was accompanied by acidic (pH ∼2–4) Cu-Mn-Si-dominated rock drainage (ARD) with fluid flow southwards through the Exótica valley towards the Calama Basin, resulting in a strongly kaolinized and chrysocolla/copper wad-impregnated bedrock of the Exótica deposit; (B) deposition of the Fortuna gravels in the Exótica valley (starting ∼19 Ma) intercepted the Cu-Mn-Si-dominated ARD, triggering the main chrysocolla, copper pitch/wad mineralization as syn-sedimentary mineralization by chiefly surficial flow in strongly altered gravels; (C) tectonic freezing and onset of hyper-aridity (∼15–11 Ma) exposed the enriched chalcocite blanket of Chuquicamata to oxidation, resulting in acidic (pH ~ 2–4) and Cu-Si-dominated solutions with less Mn. These solutions percolated in a slightly more reducing groundwater flow path and mineralized relatively unaltered gravels with pure chrysocolla; and (D) ingression of confined chloride-rich groundwater in the upper oxidation zone of Chuquicamata, most likely between 6 and 3 Ma, is responsible for the atacamite/brochantite mineralization (pH ~ 5.5–7) of mainly unaltered gravels in the northern and central part of the Exótica deposit. [ABSTRACT FROM AUTHOR]

Sulphate reducing bacteria (SRB) offer promise for the treatment of mine waste due to their effectiveness removing toxic heavy metals as highly insoluble metal sulphides and their ability to generate alkalinity. The main objective of this study was to develop a treatment composed of a sulphate-reducing bioreactor with a limestone precolumn for the removal of Cu(II) from a synthetic ARD. The purpose of the limestone column was to increase the pH values and decrease the level of Cu in the effluent to prevent SRB inhibition. The system was fed with a pH-2.7 synthetic ARD containing Cu(II) (10–40 mg/L), sulphate (2000 mg/L) and acetate (2.5 g COD/L) for 150 days. Copper removal efficiencies in the two-stage system were very high (95–99%), with a final concentration of 0.53 mg/L Cu, and almost complete removal occurred in the limestone precolumn. In the same manner, the acidity of the synthetic ARD was effectively reduced in the limestone precolumn to 7.3 and the pH was raised in the bioreactor (7.3–8.0). COD consumption by methanogens was predominant from day 0–118, but SRB dominated at the end of the experiment (day 150) when the average COD removal and sulphide production were 74.8% and 61.7%, respectively. Study of the microbial taxonomic composition in the bioreactor revealed that Methanosarcina and Methanosaeta were the most prevalent methanogens while the genera Desulfotomaculum and Syntrophobacter were the dominant SRB. Among the SRB identified Desulfotomaculum intricatum (99% identity) and Desulfotomaculum acetoxidans (96%) were the most abundant sequences of bacteria capable of using acetate. [ABSTRACT FROM AUTHOR]

Increasing variability in precipitation patterns is expected to result from climate change in Canada. This effect has the potential to affect the performances of saturated covers in inhibiting acid rock drainage (ARD) and metal leaching (ML) processes. Because ARD and ML may cause the release of deleterious chemical species into the environment, such climate-change-driven impact was investigated using trickle leach columns. The physical, chemical, and mineralogical characteristics of the tailings as well as chemical composition of the leachate were measured before and after the column study. Results from the experiment showed that higher variability in precipitation regimes could enhance leaching of uranium. Leaching ranged from 67.1 to 90.1% of the total amount of U, with greater values associated with higher variability in precipitation patterns. Lower water levels and prolonged drought periods led to higher oxygen fluxes to the U tailings and dissolution of carbonate-bearing minerals. The release of carbonates could have enhanced uranium leaching through the formation of stable uranium-carbonate complexes in solution. Overall, this study shows that water level variation caused by varying precipitation patterns can significantly affect the drainage chemistry of saturated cover systems for which the level fluctuates freely near the tailings–cover interface.

Halotrichite [FeAl 2 (SO 4) 4 ·22(H 2 O)] is a rare secondary sulfate mineral with its occurrence confined within the sulfide weathering zones. In the South Kerala Sedimentary Basin (SKSB) of SW India, halotrichite, here reported for the first time, is associated with an organic matter (OM)-rich carbonaceous clay layer. Field investigation revealed the prevalence of acid rock drainage (ARD) conditions similar to Martian analogue sites like Rio Tinto. The OM-layer is associated with pyrite forming substratum and Al-rich leachate associated with the Youngest Toba Tuff (YTT) cryptotephra layer. Oxidation of these units results in the formation of halotrichite, which is temporally restricted only to the dry season when the water table lowers and the OM-layer is exposed to air. X-Ray Diffraction (XRD) results for halotrichite show the presence of Al and Fe(II) sulfates. Energy Dispersive X-ray Spectroscopy (EDS) ruled out the existence of pickeringite, the Mg end-member of halotrichite-pickeringite series. XRD results for the OM-layer indicate the presence of kaolinite, quartz, goethite, and lepidocrocite. Hyperspectral analysis of the clay samples confirms that halotrichite is associated with goethite, lepidocrocite, kaolinite, and smectite. Fourier Transform Infrared Spectroscopy (FTIR) analysis revealed the major constituent of the clay sample as kaolinite with traces of quartz, smectite, and OM. Raman spectrum of halotrichite shows the symmetric stretching vibration of SO 4 2− bonded to Fe2+. Association of halotrichite with Fe, Al, and S-rich minerals is also inferred by the study of Raman spectrum of the host clay. Co-existence of halotrichite, goethite, lepidocrocite, and phyllosilicates in the study area is similar to the mineral assemblage found along the Rio Tinto River. On Mars, halotrichite is associated with the layered sulfate deposits, such as those in Valles Marineris and Meridiani Planum, and is categorized as a polyhydrated sulfate. Hence, this study on the halotrichite mineralization in the SKSB can supplement the attempts on deciphering the deposition and formation environment of similar mineralization on Mars. [Display omitted] • Halotrichite, a mineral forming at sulfide weathering zones and Martian analogue sites is reported from South India. • Halotrichite is associated with the younger Toba ash hosting organic matter rich carbonaceous clay layer. • Acidic solution from pyrite oxidation during summer and Al-rich leachate from Toba ash results in halotrichite formation. • Mineralogical and spectral study shows an assemblage of halotrichite, goethite, lepidocrocite and phyllosilicates. • The assemblage is typical to analogue site and this study helps to decipher halotrichite forming environment on Mars. [ABSTRACT FROM AUTHOR]

A multi-disciplinary approach is indispensable for adequate acid rock drainage (ARD), mineral leaching impact, and groundwater management. Groundwater is a valuable resource, and it is critical to protect as well as mitigate the effects of pollution such as ARD in the mining environment. Mine waste storage facilities (waste rocks and tailings) are potential ARD sources capable of degrading groundwater reserves. This research investigated and reported the application of a case study of multivariate statistical and spatial variability of selected parameters associated with ARD in groundwater around WRD and TSF at mine sites. Water quality analysis data of seventy water samples from 10 boreholes located at the WRD and TSF mine were utilised in this study. The correlation matrix and principal components analysis was applied to the data set to determine the associated variability in groundwater in relation to ARD. Geostatistical analysis was used to produce contour maps to ARD principal components of the study site, using ordinary kriging of the best fit models. The application of multivariate statistical and geospatial analysis in groundwater quality assessment with coupled soil and groundwater modelling of flow and transport at waste rock dump and tailings storage sites provides an essential tool for exploratory data analysis, and spatial extent determination of the relationship between various data sets significant to acid rock drainage. [ABSTRACT FROM AUTHOR]

Acid rock drainage (ARD) is one of the most serious and potentially lasting environmental issues for the mining industry. Many researchers investigated the impact of ARD on downstream farmland, but few focused on the soil properties change around waste rock heaps. In this study, a total of 119 soil samples were taken around the 35 waste rock heaps which are scattered in 12 mining sites in an abandoned pyrite mining area (Baihe County, Northwest China). Both rainy and dry seasons of ARD were collected from the discharge outlet of each mining site. The bulk levels of potentially toxic elements (PTEs), including As, Cd, Cu, Ni, Cr, Zn, Pb, Fe, Mn, and F, in waste rock, soil, and ARD samples were analyzed. Leaching concentration and chemical speciation of these PTEs in soils were further investigated. The results show that the ARD had very high pollution loads of PTEs both in the rainy season and dry season, continuously exporting pollutants to the surrounding soils. More than 70% of the soil samples were acidic (pH

There is a need to define mine tailings in a clear, precise, multidisciplinary, transdisciplinary, and holistic manner, considering not only geotechnical and hydraulic concepts but also integrating environmental and geochemical aspects with implications for the sustainability of mining. This article corresponds to an independent study that answers questions concerning the definition of mine tailings and the socio-environmental risks linked with mine tailings chemical composition by examining the practical experience of industrial-scale copper and gold mining projects in Chile and Peru. Definitions of concepts and analysis of key aspects in the responsible management of mine tailings, such as characterization of metallic–metalloid components, non-metallic components, metallurgical reagents, and risk identification, among others, are presented. Implications of potential environmental impacts from the generation of acid rock drainage (ARD) in mine tailings are discussed. Finally, the article concludes that mine tailings are potentially toxic to both communities and the environment, and cannot be considered as inert and innocuous materials; thus, mine tailings require safe, controlled, and responsible management with the application of the most high management standards, use of the best available technologies (BATs), use of best applicable practices (BAPs), and implementation of the best environmental practices (BEPs) to avoid risk and potential socio-environmental impact due to accidents or failure of tailings storage facilities (TSFs).

Increasing variability in precipitation patterns is expected to result from climate change in Canada. This effect has the potential to affect the performances of saturated covers in inhibiting acid rock drainage (ARD) and metal leaching (ML) processes. Because ARD and ML may cause the release of deleterious chemical species into the environment, such climate-change-driven impact was investigated using trickle leach columns. The physical, chemical, and mineralogical characteristics of the tailings as well as chemical composition of the leachate were measured before and after the column study. Results from the experiment showed that higher variability in precipitation regimes could enhance leaching of uranium. Leaching ranged from 67.1 to 90.1% of the total amount of U, with greater values associated with higher variability in precipitation patterns. Lower water levels and prolonged drought periods led to higher oxygen fluxes to the U tailings and dissolution of carbonate-bearing minerals. The release of carbonates could have enhanced uranium leaching through the formation of stable uranium-carbonate complexes in solution. Overall, this study shows that water level variation caused by varying precipitation patterns can significantly affect the drainage chemistry of saturated cover systems for which the level fluctuates freely near the tailings–cover interface. [ABSTRACT FROM AUTHOR]

Protozoa play important roles in microbial communities, regulating populations via predation and contributing to nutrient cycling. While amoebae have been identified in acid rock drainage (ARD) systems, our understanding of their symbioses in these extreme environments is limited. Here, we report the first isolation of the amoeba Stemonitis from an ARD environment as well as the genome sequence and annotation of an associated bacterium, Dyella terrae strain Ely Copper Mine, from Ely Brook at the Ely Copper Mine Superfund site in Vershire, Vermont, United States. Fluorescent in situ hybridization analysis showed this bacterium colonizing cells of Stemonitis sp. in addition to being outside of amoebal cells. This amoeba-resistant bacterium is Gram-negative with a genome size of 5.36 Mbp and GC content of 62.5%. The genome of the D. terrae strain Ely Copper Mine encodes de novo biosynthetic pathways for amino acids, carbohydrates, nucleic acids, and lipids. Genes involved in nitrate (1) and sulfate (7) reduction, metal (229) and antibiotic resistance (37), and secondary metabolite production (6) were identified. Notably, 26 hydrolases were identified by RAST as well as other biomass degradation genes, suggesting roles in carbon and energy cycling within the microbial community. The genome also contains type IV secretion system genes involved in amoebae resistance, revealing how this bacterium likely survives predation from Stemonitis sp. This genome analysis and the association of D. terrae strain Ely Copper Mine with Stemonitis sp. provide insight into the functional roles of amoebae and bacteria within ARD environments. [ABSTRACT FROM AUTHOR]

Abstract Aims/hypothesis Pohang Tertiary mudstone presents the issue of acid rock drainage. This study analyzed the capacity of a mixed slag (70% steel slag + 30% blast furnace slag) to neutralize Pohang Tertiary mudstone’s acid rock drainage. Methods Element analysis, acid neutralization capacity (ANC) test, and net acid generation (NAG) test were conducted on Pohang Tertiary mudstone samples and the mixed slag. The XRF analysis and the XRD analysis on the mixed slag were conducted to measure the CaO content, which indicates the potential of the mixed slag as an acid-neutralizing agent. Results According to the analysis results on the Pohang Tertiary mudstone samples, the total sulfur content was high, which indicates a high risk of acid rock drainage generation. Although there were slight deviations between the samples, overall, the mudstone exhibited a high acid rock drainage generation capacity. The XRF analysis of mixed slag results showed high amounts of CaO content. From the XRD analysis graph, it was clear that a high proportion of minerals with Ca- compounds consisting of basic substances were present. The neutralization capacity of the mixed slag on Pohang Tertiary mudstone was determined by the relationship between maximum potential acidity (MPA) and acid neutralization capacity (ANC). For instance, the mixed slag of 4.5% effectively neutralizes a sulfur content of 1%.

Biological sulfate reduction (BSR) is an attractive approach for the bioremediation of sulfate-rich wastewater streams. Many sulfate-reducing microorganisms (SRM), which facilitate this process, have been well-studied in pure culture. However, the role of individual members of microbial communities within BSR bioreactors remains understudied. In this study we investigated the performance of two up-flow anaerobic packed bed reactors (UAPBRs) supplemented primarily with acetate and with lactate, respectively, during a hydraulic retention time (HRT) study set up to remediate sulfate-rich synthetic wastewater over the course of 1,000 + days. Plug-flow hydrodynamics led to a continuum of changing volumetric sulfate reduction rates (VSRRs), available electron donors, degrees of biomass retention and compositions of microbial communities throughout these reactors. Microbial communities throughout the successive zones of the reactors were resolved using 16S rRNA gene amplicon sequencing which allowed the association of features of performance with discrete microorganisms. The acetate UAPBR achieved a maximum VSRR of 23.2 mg.L−1. h−1 at a one-day HRT and a maximum sulfate conversion of the 1 g/L sulfate of 96% at a four-day HRT. The sulfate reduction reactions in this reactor could be described with a reaction order of 2.9, an important observation for optimisation and future scale-up. The lactate UAPBR achieved a 96% sulfate conversion at one-day HRT, corresponding with a VSRR of 40.1 mg.L−1. h−1. Lactate was supplied in this reactor at relatively low concentrations necessitating the subsequent use of propionate and acetate, by-products of lactate fermentation with acetate also a by-product of incomplete lactate oxidation, to achieve competitive performance. The consumption of these electron donors could be associated with specific SRM localised within biofilms of discrete zones. The sulfate reduction rates in the lactate UAPBR could be modelled as first-order reactions, indicating effective rates were conferred by these propionate- and acetate-oxidising SRM. Our results demonstrate how acetate, a low-cost substrate, can be used effectively despite low associated SRM growth rates, and that lactate, a more expensive substrate, can be used sparingly to achieve high VSRR and sulfate conversions. We further identified the preferred environment of additional microorganisms to inform how these microorganisms could be enriched or diminished in BSR reactors.

Protozoa play important roles in microbial communities, regulating populations via predation and contributing to nutrient cycling. While amoebae have been identified in acid rock drainage (ARD) systems, our understanding of their symbioses in these extreme environments is limited. Here, we report the first isolation of the amoeba Stemonitis from an ARD environment as well as the genome sequence and annotation of an associated bacterium, Dyella terrae strain Ely Copper Mine, from Ely Brook at the Ely Copper Mine Superfund site in Vershire, Vermont, United States. Fluorescent in situ hybridization analysis showed this bacterium colonizing cells of Stemonitis sp. in addition to being outside of amoebal cells. This amoeba-resistant bacterium is Gram-negative with a genome size of 5.36 Mbp and GC content of 62.5%. The genome of the D. terrae strain Ely Copper Mine encodes de novo biosynthetic pathways for amino acids, carbohydrates, nucleic acids, and lipids. Genes involved in nitrate (1) and sulfate (7) reduction, metal (229) and antibiotic resistance (37), and secondary metabolite production (6) were identified. Notably, 26 hydrolases were identified by RAST as well as other biomass degradation genes, suggesting roles in carbon and energy cycling within the microbial community. The genome also contains type IV secretion system genes involved in amoebae resistance, revealing how this bacterium likely survives predation from Stemonitis sp. This genome analysis and the association of D. terrae strain Ely Copper Mine with Stemonitis sp. provide insight into the functional roles of amoebae and bacteria within ARD environments.

Blending of potentially acid generating (PAG) waste rock with non-PAG waste rock to create a rock mixture which performs as non-PAG is a possible approach to permanent prevention of acid rock drainage (ARD) for PAG waste rock. In 2012, a field weathering study using 300 kg samples was implemented at Teck Coal's Quintette Project located in northeastern British Columbia, Canada to test the prevention of acid generation in the PAG waste rock by dissolved carbonate leached from overlying non-PAG waste rock and direct neutralization of acidic water from PAG waste rock by contact with non-PAG waste rock. After eight years of monitoring the experiments, the layered non-PAG on PAG barrels provided proof-of-concept that as the thickness of the PAG layer increases relative to the thickness of the non-PAG layers, acidic waters are more likely to be produced. The PAG on non-PAG layering has resulted in non-acidic water and no indications of metal leaching despite accelerated oxidation in the PAG layer shown by sulfate loadings. The study has demonstrated that the scale of heterogeneity of PAG and non-PAG materials is a critical consideration for providing certainty that rock blends designed to be non-PAG will perform as non-PAG in perpetuity. This is contrary to the standard paradigm in which an excess of acid-consuming minerals is often considered sufficient alone to ensure ARD is not produced. [ABSTRACT FROM AUTHOR]

A critical analysis of experimental and computational studies on the actual ecological problem of the formation of acidic drainage waters in dumps of sulfide-containing rocks has been carried out. The focus is placed onto assessing reasons for changes in the oxidation rate of pyrite (r), which is the most common sulfide. The dependences of r on temperature, pH, and contents of O2 and Fe3+ in the solution remain almost the only ones expressed in the form of equations. The slow stage of Fe2+ oxidation in acidic solutions cannot control r under natural conditions, because this process is accelerated by iron-oxidizing bacteria. The value of r also changes depending on the type and content of isomorphic admixtures in pyrite, decreases under the influence of some ligands and other sulfides (galvanic effect), and varies with time. The effect of time is usually explained by the formation of a surface protective layer of reaction products, but a probable alternative explanation is the dissolution (disappearance) of surface defects. Depending on the content and activity of minerals that produce and neutralize acid, the weathering of dumps can proceed with the formation of acidic or near-neutral solutions. Scenarios of the processes are predicted using static and kinetic tests, which have significant disadvantages because of the differences between the laboratory and field conditions. The use of mathematical modeling for this purpose is promising, but so far it is limited due to the simplification of models and calculation errors. However, the simulation has clearly showed that the value of r in the dumps is controlled by the rate of O2 delivery, which in turn depends on the pore size, the degree of pore filling with water, and the temperature and pressure gradients. To prevent and recultivate acidic drainage waters, materials are used that isolate individual grains of sulfides (microencapsulation) or the entire dump from O2 penetration, alkaline materials that neutralize acid, bactericides that reduce the activity of iron-oxidizing bacteria, and bioreactors in which metal sulfides are deposited under the action of sulfate-reducing bacteria. [ABSTRACT FROM AUTHOR]

Acid mine drainage (AMD) or acid rock drainage (ARD) refers to the effluents from coal and metal mines. AMD is a common phenomenon which occurs naturally as a process of rock weathering, but is increased in large scale due to human activities such as construction contracts (transportation corridors, dam build, etc.) and mining operations. This phenomenon denotes the acidic water that is produced during exposure of sulphide minerals (mainly pyrite) to air and water through a natural process, and creates sulphuric acid. AMD is a hazard to animals, aquatic life and human beings as it increases the acidity and dissolves metals. Preventing and treating AMD is an important issue in a mine site not only during operation life but also after the mine is abandoned.

Abstract Coal mine waste rocks produced during mining and beneficiation can affect the environment due to land degradation and acid mine drainage generation. However, proper characterization and treatment of mineral processing wastes creates options for safe disposal, enhancing the environmental performance. The aim of this study was to use static and kinetic tests to assess properties of coal waste produced at the Moatize Mine in Mozambique, one of the largest "world-class" coal deposits. The study included sampling and characterization of coarse and fine wastes generated during coal beneficiation. Both materials were analyzed in terms of granular properties, static procedures - immediate composition, sulfur forms, mineralogical composition, elemental composition, acid-base balance - and kinetic behavior in humidity cell tests. The conjugation of these techniques indicates that these wastes have a low water acidification potential and low geochemical mobility of toxic elements. Therefore, it was concluded that fine and coarse wastes could be used in land shaping procedures.

Placement methods and material availability during waste rock pile (WRP) construction may create significant heterogeneities in physical and geochemical parameters (such as grain size, permeability, mineralogy, and reactivity) and influence the internal pile structure. Due to the enormous scale of WRPs, it is difficult to capture the influence of heterogeneities on mine drainage composition and evolution. Although laboratory- or field-scale experimental studies have provided much insight, it is often challenging to translate these results to full scale WRPs. This study uses a numerical modeling approach to investigate the influence of physical and chemical heterogeneities, structure, and scale on the release of acid rock drainage (ARD) through 2D reactive transport simulations. Specifically, the sensitivity of drainage quality to parameters including grain size distribution, sulfide mineral weathering rates, abundance and distribution of primary minerals, and pile structure as a function of construction methods are investigated. The geochemical model includes sulfide oxidation, pH buffering by calcite dissolution, and ferrihydrite and gypsum as secondary phases. Simulation results indicate that the implications of heterogeneity and construction method are scale-dependent; when grain size distribution trends observed in a pile's core are applied to the entirety of a pile, results between push- and end-dumping methods vary substantially—however, predicted drainage for different construction methods become more similar when features such as traffic surfaces, structural variation, and multiple benches are also considered. For all scales and construction methods investigated, simulated results demonstrate that pile heterogeneity and structure decrease peak mass loading rates 2 to 3-fold, but cause prolonged ARD release compared to the homogeneous case. These findings have implications for the economics of planning water treatment facilities for life of mine and closure operations.

Mining areas are among the most polluted industrial sites, the surface waters being often affected by acid rock drainage. Mine and processing wastes represents one of the main sources of acidic waters. The seepages form Bloaja tailings management facilities have a low pH and increased total dissolved solids. Chemical analyses show high Zn, Cu and Pb concentrations of the contact water with the pyrite concentrate deposited on Bloaja Old tailings management facility. These polluted waters are discharged in the watercourses, decreasing the quality of surface water. Despite of the remediation of Bloaja New tailings management facility, the waste waters seepages have a conspicuous environmental impact on watercourses from Lăpuș River basin. [ABSTRACT FROM AUTHOR]

Characterization of metamorphic rocks to evaluate waste material acid rock drainage potential is particularly challenging as commonly used laboratory methods can result in its significant underprediction. Static tests were conducted for over 300 samples from the Touro copper project and indicate that carbon-based methods frequently overestimate acid neutralization potential due to the presence of both graphite and manganese–iron carbonates. The Modified Sobek method more accurately accounts for the buffering capacity of carbonates and does not account for graphite, although aluminosilicate dissolution kinetics need to be evaluated in the context of sulfide oxidation rates. Historic sulfur assays for the project relied on methods insufficient to fully digest metamorphosed sulfides and required correction. The more aggressive Leco method provides accurate sulfur estimates and has now been adopted for the project. Static test metrics such as the net neutralization potential or neutralization potential ratio, therefore, can give misleading results when incorrect characterization methods are employed. Such metrics should be considered as screening level, used with caution, and complemented with careful field and laboratory kinetic tests. Preliminary humidity cell testing of five Touro samples suggests that terminal pH values for cells that have become acidic closely match predicted net acid generation (NAG) pH values. The NAG pH test avoids some of the challenges associated with sulfur and carbon predictions in metamorphic rocks as it directly buffers sulfide oxidation acidity with available material neutralization potential. As such, NAG pH has been adopted as the accepted project metric for segregating acid-generating from non-acid-generating waste. Supplementary material: All Touro project static and kinetic test data are available at https://doi.org/10.6084/m9.figshare.c.5389948 Thematic collection: This article is part of the Hydrochemistry related to exploration and environmental issues collection available at: https://www.lyellcollection.org/cc/hydrochemistry-related-to-exploration-and-environmental-issues [ABSTRACT FROM AUTHOR]

Aims/hypothesis: Pohang Tertiary mudstone presents the issue of acid rock drainage. This study analyzed the capacity of a mixed slag (70% steel slag + 30% blast furnace slag) to neutralize Pohang Tertiary mudstone's acid rock drainage. Methods: Element analysis, acid neutralization capacity (ANC) test, and net acid generation (NAG) test were conducted on Pohang Tertiary mudstone samples and the mixed slag. The XRF analysis and the XRD analysis on the mixed slag were conducted to measure the CaO content, which indicates the potential of the mixed slag as an acid-neutralizing agent. Results: According to the analysis results on the Pohang Tertiary mudstone samples, the total sulfur content was high, which indicates a high risk of acid rock drainage generation. Although there were slight deviations between the samples, overall, the mudstone exhibited a high acid rock drainage generation capacity. The XRF analysis of mixed slag results showed high amounts of CaO content. From the XRD analysis graph, it was clear that a high proportion of minerals with Ca- compounds consisting of basic substances were present. The neutralization capacity of the mixed slag on Pohang Tertiary mudstone was determined by the relationship between maximum potential acidity (MPA) and acid neutralization capacity (ANC). For instance, the mixed slag of 4.5% effectively neutralizes a sulfur content of 1%. [ABSTRACT FROM AUTHOR]

The efficacy of passive treatment systems for remediating acid rock drainage can be limited by the seasonal flux of discharge and metal concentrations that may not have been considered during treatment design. A review of passive treatment options for acid rock drainage indicates reduced efficacy due to seasonal periods of increased drainage and metal concentrations that lead to mineral precipitation, surface passivation, and flow bypass. In select cases, passive treatment systems prematurely failed due to seasonal flux or experienced substantially reduced treatment efficacy and life of the system. Complimentary systems are needed to minimise impacts from seasonal flux of drainage and metal concentrations to improve treatment efficacy and preserve the life of a multi-component system or a downstream primary system. Multi-component systems are possible with integration of existing treatment systems and design of new treatment options to tailor treatment to site specifications. [ABSTRACT FROM AUTHOR]

High throughput sequencing data collected from acid rock drainage (ARD) communities can reveal the active taxonomic and functional diversity of these extreme environments, which can be exploited for bioremediation, pharmaceutical, and industrial applications. Here, we report a seasonal comparison of a microbiome and transcriptome in Ely Brook (EB-90M), a confluence of clean water and upstream tributaries that drains the Ely Copper Mine Superfund site in Vershire, VT, USA. Nucleic acids were extracted from EB-90M water and sediment followed by shotgun sequencing using the Illumina NextSeq platform. Approximately 575,933 contigs with a total length of 1.54 Gbp were generated. Contigs of at least a size of 3264 (N50) or greater represented 50% of the sequences and the longest contig was 488,568 bp in length. Using Centrifuge against the NCBI “nt” database 141 phyla, including candidate phyla, were detected. Roughly 380,000 contigs were assembled and ∼1,000,000 DNA and ∼550,000 cDNA sequences were identified and functionally annotated using the Prokka pipeline. Most expressed KEGG-annotated microbial genes were involved in amino acid metabolism and several KEGG pathways were differentially expressed between seasons. Biosynthetic gene clusters involved in secondary metabolism as well as metal- and antibiotic-resistance genes were annotated, some of which were differentially expressed, colocalized, and coexpressed. These data can be used to show how ecological stimuli, such as seasonal variations and metal concentrations, affect the ARD microbiome and select taxa to produce novel natural products. The data reported herein is supporting information for the research article “Characterization of an acid rock drainage microbiome and transcriptome at the Ely Copper Mine Superfund site” by Giddings et al. [1].

Pyrite oxidation, Acid Rock Drainage (ARD) generation, and associated release and transport of toxic metals are a major environmental concern for the mining industry. Estimation of the metal loading in ARD is a major task in developing an appropriate remediation strategy. In this study, an expert system, the Multi-Output Adaptive Neuro-Fuzzy Inference System (MANFIS), was used for estimation of metal concentrations in the Shur River, resulting from ARD at the Sarcheshmeh porphyry copper deposit, southeast Iran. Concentrations of Cu, Fe, Mn and Zn are predicted using pH, sulphate (SO4) and magnesium (Mg) concentrations in the Shur River as input to the MANFIS. Three MANFIS models were implemented, Grid Partitioning (GP), the Subtractive Clustering Method (SCM) and the Fuzzy C-Means Clustering Method (FCM).A comparison was made between these three models and the results show the superiority of the MANFIS-SCM model. The results obtained indicate that the MANFIS-SCM model has potentialfor estimation of the metals with high a degree of accuracy and robustness.

Passive treatment systems provide lower cost alternatives for remediation of mine drainage; however, acidic drainage increases treatment difficulty because of higher metal concentrations and proton competition for reactive substrates. A silica fiber functionalized with (3-aminopropyl) triethoxysilane (Si + APTES) and a naturally-occurring, microporous silicate mineral (clinoptilolite of the zeolite family) were evaluated in the laboratory as potential reactive substrates for passive treatment of mild (≥ pH of 3) acid rock drainage. Column permeability experiments with spun, 10-µm median diameter, silica fiber and loosely packed, 3.6-mm median diameter clinoptilolite indicate greater permeability and stability of clinoptilolite under flowing conditions. Batch sorption experiments with silica fiber (Si), Si + APTES, and clinoptilolite in a synthetic Fe(II)–SO4, pH 3.0 solution indicate an Fe specific sorption efficacy of Si + APTES > clinoptilolite > Si at equivalent surface areas. Specific sorption normalized to packing densities indicate greater sorption per volume for clinoptilolite. Sorption results for Si + APTES and clinoptilolite did not produce isotherms described by the Langmuir or Freundlich models, likely because of surface heterogeneity and precipitation reactions. Column sorption experiments under flowing conditions indicate an Fe removal efficacy of clinoptilolite > Si + APTES for permeable packing densities. Si + APTES demonstrated high specific sorption of Fe in batch sorption experiments and has potential use in low-flow, passive treatment of mildly acidic solutions. The balance of minimal surface preparation, greater permeability, structural stability, large surface area, micropore structure, and ion-exchange properties make clinoptilolite a better reactive substrate for passive treatment of mildly acidic solutions in high- or low-flow conditions. [ABSTRACT FROM AUTHOR]

Previous tests using a growth medium and olive mill wastewater (OMWW) have shown that it supplies carbon and electron donors suitable for sulphate reducing bacteria (SRB). We assessed the co-treatment of acid mine drainage (AMD) and OMWW using SRB-enriched bioreactors and identified the most abundant bacterial populations present under optimized conditions. The process requires a neutralizing agent to create optimal pH conditions for successful removal of the AMD's main contaminants. Concentrations of SO42−, Al, Fe, Cu, Zn, and Mn decreased to below Portugal's maximum admissible values for irrigation waters, and all but Mn were reduced to less than Portugal's emission limit values (ELVs) for wastewater discharges. Phenol concentrations—the main pollutants in OMWW—dropped to values between 1/10 and 1/5 their initial concentrations in batch tests using mixtures of AMD and OMWW, and to 1/2 their initial concentrations in flow-through tests. The final total phenol concentrations were still above the ELV for wastewater discharges, but phenols are not regulated in irrigation waters, and OMWW is used by some producers to irrigate soils. Six main SRB groups were identified as likely having a fundamental role in the bioremediation process: the genera Desulfovibrio, Sulfurospirillum, and Acetobacter and the families Sphingomonadaceae, Prevotellaceae, and Deferribacteraceae. [ABSTRACT FROM AUTHOR]