Oxidation Of Sulfide Minerals Research Articles

Formation mechanism of Fe oxyhydroxides and behavior of metals during the oxidation of submarine sulfides at the Wocan-1 hydrothermal field, Carlsberg Ridge

Hydrothermal sulfides undergo complex oxidation process under seawater conditions, which has the potential to impact resource values and marine environments. However, the oxidation process is not fully explored, particularly regarding the transformation of minerals and the behavior of metals. In this paper, we conducted detailed mineralogical and geochemical analyses on a series of samples with varying degrees of oxidation, collected from the Wocan-1 hydrothermal field, Carlsberg Ridge, Northwest Indian Ocean. The principal purpose is to illuminate the formation and transformation of Fe (oxyhydr)oxides, and further to reveal the migration and redistribution of key metals throughout the oxidation process. We identified four types of Fe(−Si) (oxyhydr)oxides with two distinct formation mechanisms. Three Fe (oxyhydr)oxides are the direct oxidation products of pyrite and marcasite, while Fe-Si (oxyhydr)oxide precipitates from low-temperature hydrothermal fluids. Thin Fe (oxyhydr)oxide forms as the secondary product of euhedral pyrite at the early stage of oxidation. Pseudomorphic Fe (oxyhydr)oxide with low Fe contents, occurs as the replacement of euhedral marcasite. Filamentous Fe (oxyhydr)oxide, enriched in trace metals, is attributed to the uniform oxidation of subhedral pyrite-marcasite intergrowth. Moreover, major and trace elements occur multiple migrations and redistributions among primary sulfides, secondary products, and seawater. Notably, Fe (oxyhydr)oxides, through the sequestration mechanism, not only retain Cu and Zn released by the oxidation of primary sulfide minerals, but also scavenge Cu from seawater. However, the dissolution of Pb, As, Mo, and Co exceeds the amount retained during the oxidation, indicating that the potential release of toxic metals into the environment could pose a threat to the local ecosystem. These new insights can provide an initial foundation for the effect of submarine oxidation on economic values of sulfides and ecological environments of deep sea.

Comprehending Spatial Distribution and Controlling Mechanisms of Groundwater in Topical Coastal Aquifers of Southern China Based on Hydrochemical Evaluations

Groundwater quality and availability in coastal aquifers have become a serious concern in recent times due to increased abstraction for domestic, agricultural and industrial purposes. (1) Background: Zhuhai city is selected as a representative coastal aquifer in Southern China to comprehensively evaluate the hydrochemical characteristics, spatial distribution and controlling mechanisms of groundwater. (2) Methods: A detailed study utilizing statistical analyses, a Piper diagram, Gibbs plots, and ion ratios was conducted on 114 surface water samples and 211 groundwater samples. (3) Results: The findings indicate that the pH of most groundwater is from 6.06 to 6.52, indicating a weakly acidic environment. The pH of surface water ranges from 5.35 to 9.86, with most values being weakly alkaline. The acidity in the groundwater may be related to the acidic atmospheric precipitation, an acidic unsaturated zone, oxidation of sulphide minerals and tidal action. The groundwater chemical types are predominantly mixed, followed by Ca-Mg-HCO3 type. Surface water samples are predominantly Na-Cl-SO4 type. The NO3− concentration in groundwater is relatively high, with a mean value of 17.46 mg/L. The NO2− and NH4+ concentrations in groundwater are relatively low, with mean values of 0.46 mg/L and 7.58 mg/L. (4) Conclusions: The spatial distribution of the principal chemical constituents in the groundwater is related to the landform. The chemical characteristics of groundwater in the study area are mainly controlled by the weathering and dissolution of silicate and sulfate minerals, evaporation, seawater mixing and cation exchange. Nitrate in clastic fissure groundwater, granite fissure groundwater and unconfined pore groundwater primarily originates from atmospheric precipitation, agricultural activities of slope farmland and forest land. Nitrate in confined pore groundwater and karst groundwater primarily originates from domestic sewage and mariculture wastewater. Our findings elucidate the processes characterizing the hydrogeology and surface water interactions in Zhuhai City’s coastal system, which are relevant to other catchments with similar geological characteristics.

Biogeochemical stability of organic covers and mine wastes under climate change simulated mesocosms.

Mine environments in boreal and sub-boreal zones are expected to experience extreme weather events, increases in temperature, and shifts in precipitation patterns. Climate change impacts on geochemical stability of tailings contaminants and reclamation structures have been identified as important climate-related challenges to Canadian mining sector. Adapting current reclamation strategies for climate change will improve long-term efficiency and viability of mine tailings remediation/restoration strategies under a changing climate. Accordingly, mesocosm experiments were conducted to investigate associations of climate-driven shifts in microbial communities and functions with changes in the geochemistry of organic covers and underlying tailings. Our results show that warming appears to significantly reduce C:N of organic cover and promote infiltration of nitrogen into deeper, unoxidized strata of underlying tailings. We also observed an increase in the abundance of some nitrate reducers and sulfide oxidizers in microbial communities in underlying tailings. These results raise the concern that warming might trigger oxidation of sulfide minerals (linked to nitrate reduction) in deeper unoxidized strata where the oxygen has been eliminated. Therefore, it would be necessary to have monitoring programs to track functionality of covers in response to climate change conditions. These findings have implications for development of climate resilient mine tailings remediation/restoration strategies.

Acid Mine Drainage Precipitates from Mining Effluents as Adsorbents of Organic Pollutants for Water Treatment.

Acid mine drainage (AMD) is one of the main environmental problems associated with mining activity, whether the mine is operational or abandoned. In this work, several precipitates from this mine drainage generated by the oxidation of sulfide minerals, when exposed to weathering, were used as adsorbents. Such AMD precipitates from abandoned Portuguese mines (AGO, AGO-1, CF, and V9) were compared with two raw materials from Morocco (ClayMA and pyrophyllite) in terms of their efficiency in wastewater treatment. Different analytical techniques, such as XRD diffraction (XRD), Fourier Transform Infrared spectroscopy (FTIR), N2 adsorption isotherms, and Scanning Electron Microscopy (SEM) with Energy Dispersive X-ray (EDX) were used to characterize these natural materials. The adsorption properties were studied by optimizing different experimental factors, such as type of adsorbent, adsorbent mass, and dye concentration by the Box-Behnken Design model, using methylene blue (MB) and crystal violet (CV) compounds as organic pollutants. The obtained kinetic data were examined using the pseudo-first and pseudo-second order equations, and the equilibrium adsorption data were studied using the Freundlich and Langmuir models. The adsorption behavior of the different adsorbents was perfectly fitted by the pseudo-second order kinetic model and the Langmuir isotherm. The most efficient adsorbent for both dyes was AGO-1 due to the presence of the cellulose molecules, with qm equal to 40.5 and 16.0 mg/g for CV and MB, respectively. This study confirms the possibility of employing AMD precipitates to adsorb organic pollutants in water, providing valuable information for developing future affordable solutions to reduce the wastes associated with mining activity.

Supergene Oxidized Gold-Silver Deposits in the Americas: Guides for Geologists

Editor’s note: The aim of the Geology and Mining series is to introduce early career professionals and students to various aspects of mineral exploration, development, and mining in order to share the experiences and insight of each author on the myriad of topics involved with the mineral industry and the ways in which geoscientists contribute to each. Abstract Supergene oxidation is a process that has created some of the largest gold and silver orebodies in the Americas, including the Carlin-type (sediment-hosted) gold deposits and Round Mountain in Nevada; Yanacocha and many similar deposits in Peru; Cerro Rico, Bolivia; and Pueblo Viejo, Dominican Republic. Oxidation can make sulfide-bearing gold-silver deposits economic by converting refractory gold-silver–bearing sulfide minerals to minerals that can be leached by dilute cyanide solutions. The use of cyanide heap leaching or tank leaching enabled open-pit mining of low-grade oxidized gold deposits starting in the 1960s. This revolutionized gold mining which, combined with the end of the dollar gold standard in 1971, led to a huge increase in gold production, particularly in the Americas where the technology has been widely applied. During weathering and oxidation of sulfide minerals, particularly pyrite, associated gold and silver form supergene minerals in the oxidation zone but are only transported over short distances (centimeters to meters) due to low solubility of the metals, so they do not form enrichment zones. Gold forms Au0 grains of 1 to 25 µm size and high fineness, as well as invisible gold associated with jarosite and iron oxyhydroxides by sorption or substitution. Silver forms halides and native silver, which may be accompanied by metastable hypogene acanthite. Silver in jarosite, alunite, and Mn oxides is refractory. The economic advantages of near-surface oxidized deposits are that they can be mined by open pit with low costs, commonly not requiring stripping or blasting. Run-of-mine ore is sent directly to leach pads, although some ores may require prior crushing and grinding with agglomeration of fine material such as clays. Oxidized ore is processed by heap leaching using dilute sodium cyanide solution and gold and silver recovered by zinc cementation or on activated carbon. Some ores require grinding and are processed by tank leaching. The hypogene sulfide minerals below the oxidized zone are typically refractory and require at least ultrafine grinding for leaching to be effective, or high-cost oxidation technology for roasting, autoclaving, or bio-oxidation. The sulfide-rich portions of deposits are often not exploited for many decades after discovery, if at all. To explore for supergene oxidized deposits, the exploration geologist requires knowledge of geology, oxide mineralogy, geomorphology, hydrogeology, and the (paleo)-climate, as well as open-pit mining, hydrometallurgy, cyanide leaching, and carbon technology, topics that are introduced here with case studies.

Hydrogeochemical characteristics, driving factors, and health risk assessment of karst groundwater in Southwest Hubei Province, China.

In South China, karst groundwater is an important water resource for industrial, agricultural, and drinking purposes. However, karst aquifers are highly vulnerable to pollution, leading to deteriorating karst groundwater quality and posing potential health risks to local residents. In this study, 22 groundwater samples were collected from a karst aquifer in the southwestern part of Hubei Province. The hydrogeochemical characteristics and their controlling factors were examined, and the potential health risks associated with groundwater pollutant concentrations in karst groundwater were assessed. The results showed that the groundwater is slightly alkaline with low chemical oxygen demand values, indicating good water quality. The groundwater facies type was identified as HCO3-Ca at most sample spots, showing low total dissolved solids concentrations. Substantial spatial variations in Na+, CO3 2-, and NO2 - concentrations were found, whereas spatial variations in the K+, Ca2+, Cl-, HCO3 -, and F- concentrations were small. In addition, the dissolution of gypsum deposits and magnesium carbonate sedimentary rocks at sampling sites resulted in groundwater facies types of HCO3•SO4-Ca and HCO3-Ca•Mg, with low total dissolved solids concentrations. The karst groundwater chemistry in the study area was mainly controlled by water-rock interactions, as well as by the dissolution of gypsum deposits and magnesium carbonate sedimentary rocks at specific groundwater sampling sites. The groundwater Cl- concentrations were mainly affected by atmospheric precipitation. NO3 - was mainly derived from atmospheric precipitation, domestic sewage, septic tanks, and industrial activities, whereas SO4 2- was derived from atmospheric precipitation, sulfate rock dissolution, and sulfide mineral oxidation. These results highlight the absence of potential human health risks of NO3 - and F- to infants, children, and adults, as their concentrations are below the corresponding regional background values. In contrast, the potential health risks of Cl- cannot be ignored, particularly for infants. This study offers scientific guidelines for protecting and allocating local groundwater resources.

Microbial community structure in an uranium-rich acid mine drainage site: implication for the biogeochemical release of uranium.

The generation of acid mine drainage (AMD) characterized by high acidity and elevated levels of toxic metals primarily results from the oxidation and dissolution of sulfide minerals facilitated by microbial catalysis. Although there has been significant research on microbial diversity and community composition in AMD, as well as the relationship between microbes and heavy metals, there remains a gap in understanding the microbial community structure in uranium-enriched AMD sites. In this paper, water samples with varying levels of uranium pollution were collected from an abandoned stone coal mine in Jiangxi Province, China during summer and winter, respectively. Geochemical and high-throughput sequencing analyses were conducted to characterize spatiotemporal variations in bacterial diversity and community composition along pollution groups. The results indicated that uranium was predominantly concentrated in the AMD of new pits with strong acid production capacity, reaching a peak concentration of 9,370 μg/L. This was accompanied by elevated acidity and concentrations of iron and total phosphorus, which were identified as significant drivers shaping the composition of bacterial communities, rather than fluctuations in seasonal conditions. In an extremely polluted environment (pH < 3), bacterial diversity was lowest, with a predominant presence of acidophilic iron-oxidizing bacteria (such as Ferrovum), and a portion of acidophilic heterotrophic bacteria synergistically coexisting. As pollution levels decreased, the microbial community gradually evolved to cohabitation of various pH-neutral heterotrophic species, ultimately reverting back to background level. The pH was the dominant factor determining biogeochemical release of uranium in AMD. Acidophilic and uranium-tolerant bacteria, including Ferrovum, Leptospirillum, Acidiphilium, and Metallibacterium, were identified as playing key roles in this process through mechanisms such as enhancing acid production rate and facilitating organic matter biodegradation.

Inhibition of acid rock drainage with iron-silicate or phosphate film: in rainy and submerged environments.

Iron phosphate-based coating and iron silicate-based coating were used to inhibit the oxidation of sulfide minerals in rainy and submerged environments. The inhibiting effectiveness of coating agents on the oxidation of iron sulfide minerals was investigated using pyrite and rock samples resulting from acid drainage. The film formed with both surface-coating agents was identified by pyrite surface analysis. It was also confirmed that the formation of coatings varies depending on the crystallographic orientation. The inhibitory effects under rainy and submerged conditions were investigated using column experiments. Submerged conditions accelerated deterioration compared to that under rainy conditions. Iron phosphate coating had a significantly better oxidation-inhibitory effect (84.86-98.70%) than iron silicate coating (56.80-92.36%), and at a concentration of 300mM, H+ elution was inhibited by more than 90% throughout the experiment. Furthermore, methods for effective film formation were investigated in terms of producing Fe3+; (1) application of coating agents mixed with oxidant (H2O2), (2) application of coating agent after the use of the oxidant. In a rainy environment, applying iron phosphate-based coating using the sequential method showed oxidation inhibition effects for cycles 1-9, whereas applying the mixed material showed effects for cycles 9-13. The use of a surface-coating agent after applying an oxidant did not inhibit oxidation. The surface coating agent and the oxidizing agent should be applied as a mixture to form a film.

High-Grade REE accumulation in regolith: Insights from supergene alteration of an apatite-rich vein at the Kapunda Cu mine, South Australia

AbstractThe stratiform and vein-hosted Kapunda Cu deposit in South Australia contains a saprolitized hydrothermal vein with 12.37 wt.% total rare earth oxide (TREO). The vein was analyzed by X-ray diffraction, scanning electron microscopy, synchrotron-based X-ray fluorescence microscopy and electron backscatter diffraction to understand the controls that govern high-grade REE accumulation during periods of intense weathering. Petrological assessments indicate the transformation of an apatite-calcite-aluminosilicate-bearing protolith to a supergene assemblage of Fe-oxides, kaolinite and REE-phosphate minerals that include rhabdophane-(Ce), monazite-(Ce) and florencite-(Ce). This transformation was facilitated by progressive acidification of the weathering fluid, which is indicated by: 1) the increasing crystallinity of authigenic Fe-oxides and kaolinite, which led to REE desorption; 2) the textural evolution and increase in grain size of authigenic REE-phosphates from nanoscopic crystallites, to acicular needles, to micro-scale hexagonal prisms; 3) the late dissolution of REE-phosphates; and 4) the replacement of goethite by jarosite, whose sulfate component originated from the oxidation and weathering of proximal sulfide minerals. Alongside the depletion of pH-buffering carbonate minerals that are indicated by the preservation of calcite menisci, this sulfide dissolution also facilitated acid generation. Results illustrate how highly acidic weathering fluids might facilitate either REE mobilization or REE accumulation in regolith. High-grade REE accumulation under acidic supergene conditions is prioritized when the host-rock contains a significant source of depositional ligands (i.e., phosphate in the form of apatite) that can be readily leached during intense weathering. Exploration companies should therefore assay routinely for REEs in any heavily weathered phosphatic rock, due to the observed efficiency of phosphate minerals as geochemical traps for REE accumulation.

Toxic Element Contamination Sources in the Surface and Groundwater of the Elbrus Region: Geochemistry and Health Risks

The region surrounding the Elbrus volcano in the Great Caucasus is a popular tourist destination, home to native people and an area of the richest ore mineral resources. Based on the chemical composition of surface water, mineral, and groundwater in the Elbrus area, as well as statistical and thermodynamic calculations, waters with high concentrations of Mn, Cu, Zn, Mo, Ba, W, Pb, and As were identified, possible mineral phases that may lead to these metal concentrations in water were estimated, and risks to human health were assessed. Two main sources of surface water pollution have been identified: (1) water from tailings that are enriched due to oxidation of sulfide minerals is considered a source of As (181 µg/L) and Mo (2070 µg/L) pollution in the area of the Tyrnyauz W-Mo deposit; and (2) CO2-rich waters of deep horizons discharge on the earth surface with high concentrations of As (828 µg/L) and W (504 µg/L). It has been shown that compared to all toxic elements studied, only Mo and As have adverse non-carcinogenic effects on adult health. The estimated carcinogenic risk of As in the mine area was 1.7 × 10−3 and exceeded the generally accepted range of 10−4 to 10−6. In order to minimize the health risks, regular monitoring of water quality is required when mining activities on the Tyrnyauz W-Mo deposit are renewed.

Effect of Power and Exposure Time on the Microwave-Assisted Roasting of Refractory Gold Ore

Reserves of high-grade gold ore worldwide are decreasing, and some industries have started processing refractory gold ore. Refractory gold ore contains sulfide minerals such as pyrite (FeS2), chalcopyrite (CuFeS2), galena (PbS), and sphalerite (ZnS). Gold in refractory ores occurs as fine-size gold-bearing sulfide minerals. In this study, the microwave-assisted roasting method has been investigated as a pretreatment for a refractory gold ore. This method can provide rapid heating radiation, cause micro-cracks, and trigger the decomposition of sulfide minerals. The presence of additive helps in the oxidation of sulfide minerals. The microwave-assisted roasting was carried out using variations in microwave power and time. Microwave power between 300 - 600 watts significantly affected the increase in roasting temperature and weight loss of refractory gold ore. The highest temperature reached 567°C in roasting at 800 watts for 30 minutes. The optimum condition for microwave roasting was achieved at 400 watts of power with a roasting time of 30 minutes. Metals extraction of Cu, Zn, Pb, and Fe reached 97.2%, 82.7%, 16.1%, and 2.1% in water leaching.

Probing the exchange of CO2 and O2 in the shallow critical zone during weathering of marl and black shale

Abstract. Chemical weathering of sedimentary rocks can release carbon dioxide (CO2) and consume oxygen (O2) via the oxidation of petrogenic organic carbon and sulfide minerals. These pathways govern Earth's surface system and climate over geological timescales, but the present-day weathering fluxes and their environmental controls are only partly constrained due to a lack of in situ measurements. Here, we investigate the gaseous exchange of CO2 and O2 during the oxidative weathering of black shales and marls exposed in the French southern Alps. On six field trips over 1 year, we use drilled headspace chambers to measure the CO2 concentrations in the shallow critical zone and quantify CO2 fluxes in real time. Importantly, we develop a new approach to estimate the volume of rock that contributes CO2 to a chamber, and assess effective diffusive gas exchange, by first quantifying the mass of CO2 that is stored in a chamber and connected rock pores. Both rock types are characterized by similar contributing rock volumes and diffusive movement of CO2. However, CO2 emissions differed between the rock types, with yields over rock outcrop surfaces (inferred from the contributing rock volume and the local weathering depths) ranging on average between 73 and 1108 tCkm-2yr-1 for black shales and between 43 and 873 tCkm-2yr-1 for marls over the study period. Having quantified diffusive processes, chamber-based O2 concentration measurements are used to calculate O2 fluxes. The rate of O2 consumption increased with production of CO2, and with increased temperature, with an average O2:CO2 molar ratio of 10:1. If O2 consumption occurs by both rock organic carbon oxidation and carbonate dissolution coupled to sulfide oxidation, either an additional O2 sink needs to be identified or significant export of dissolved inorganic carbon occurs from the weathering zone. Together, our findings refine the tools we have to probe CO2 and O2 exchange in rocks at Earth's surface and shed new light on CO2 and O2 fluxes, their drivers, and the fate of rock-derived carbon.

Identifying sources of acid mine drainage and major hydrogeochemical processes in abandoned mine adits (Southeast Shaanxi, China).

Acid mine drainage (AMD) has resulted in significant risks to both human health and the environment of the Han River watershed. In this study, water and sediment samples from typical mine adits were selected to investigate the hydrogeochemical characteristics and assess the environmental impacts of AMD. The interactions between coexisting chemical factors, geochemical processes in the mine adit, and the causes of AMD formation are discussed based on statistical analysis, mineralogical analysis, and geochemical modeling. The results showed that the hydrochemical types of AMD consisted of SO4-Ca-Mg, SO4-Ca, and SO4-Mg, with low pH and extremely high concentrations of Fe and SO42-. The release behaviors of most heavy metals are controlled by the oxidation of sulfide minerals (mainly pyrite) and the dissolution/precipitation of secondary minerals. Along the AMD pathway in the adit, the species of Fe-hydroxy secondary minerals tend to initially increase and later decrease. The inverse model results indicated that (1) oxidative dissolution of sulfide minerals, (2) interconversion of Fe-hydroxy secondary minerals, (3) precipitation of gypsum, and (4) neutralization by calcite are the main geochemical reactions in the adit, and chlorite might be the major neutralizing mineral of AMD with calcite. Furthermore, there were two sources of AMD in abandoned mine adits: oxidation of pyrite within the adits and infiltration of AMD from the overlying waste rock dumps. The findings can provide deeper insight into hydrogeochemical processes and the formation of AMD contamination produced in abandoned mine adits under similar mining and hydrogeological conditions.

Risk assessment for the long-term stability of fly ash-based cementitious material containing arsenic: Dynamic and semidynamic leaching

Fly ash from municipal solid waste incineration (MSWIFA) contains leachable heavy metals (HMs), and the environmental risk of contained HMs is an important concern for its safe treatment and disposal. This paper presents a dynamic leaching test of fly ash-based cementitious materials containing arsenic (FCAC) in three particle sizes based on an innovative simulation of two acid rainfall conditions to investigate the long-term stability of FCAC under acid rain conditions. As well as semi-dynamic leaching test by simulating FCAC in three scenarios. Furthermore, the long-term stability risk of FCAC is evaluated using a sequential extraction procedure (SEP) and the potential risk assessment index. Results showed that the Al3+ in the FCAC dissolved and reacted with the OH− in solution to form Al(OH)3 colloids as the leaching time increased. Moreover, the oxidation of sulfide minerals in the slag produced oxidants, such as H2SO4 and Fe2(SO4)3, which further aggravated the oxidative dissolution of sulfides, thereby resulting in an overall decreasing pH value of the leachate. In addition, due to the varying particle sizes of the FCAC, surface area size, and adsorption site changes, the arsenic leaching process showed three stages of leaching characteristics, namely, initial, rapid, and slow release, with a maximum leaching concentration of 2.42 mg/L, the cumulative release of 133.78 mg/kg, and the cumulative release rate of 2.32%. The SEP test revealed that the reduced state of HMs in the raw slag was lowered substantially, and the acid extractable state and residual state of HMs were increased, which was conducive to lessening the risk of FCAC. Overall, the geological polymerization reaction of MSWIFA is a viable and promising solution to stabilize mining and industrial wastes and repurpose the wastes into construction materials.

The application of artificial neural network model to predicting the acid mine drainage from long-term lab scale kinetic test

Acid mine drainage (AMD) is one of the common environmental problems in the coal mining industry that was formed by the oxidation of sulfide minerals in the overburden or waste rock. The prediction of acid generation through AMD is important to do in overburden management and planning the post-mining land use. One of the methods used to predict AMD is a lab-scale kinetic test to determine the rate of acid formation over time using representative samples in the field. However, this test requires a long-time procedure and large amount of chemical reagents lead to inefficient cost. On the other hand, there is potential for machine learning to learn the pattern behind the lab-scale kinetic test data. This study describes an approach to use artificial neural network (ANN) modeling to predict the result from lab-scale kinetic tests. Various ANN model is used based on 83 weeks experiments of lab-scale kinetic tests with 100% potential acid-forming rock. The model approaches the monitoring of pH, ORP, conductivity, TDS, sulfate, and heavy metals (Fe and Mn). The overall Nash-Sutcliffe Efficiency (NSE) obtained in this study was 0.99 on training and validation data, indicating a strong correlation and accurate prediction compared to the actual lab-scale kinetic tests data. This show the ANN ability to learn patterns, trends, and seasonality from past data for accurate forecasting, thereby highlighting its significant contribution to solving AMD problems. This research is also expected to establish the foundation for a new approach to predict AMD, with time efficient, accurate, and cost-effectiveness in future applications.

Geochemistry of neutral mine drainage at sulfide deposits ‒ example of the „Grot“ Pb-Zn mine, South-Eastern Serbia

This study examines the chemistry of mine waters of the ?Grot? Pb? ?Zn mine and identifies the hydrogeochemical factors that influence the formation of mine waters chemical composition. Eleven mine water samples were collected at six locations across the area of Kriva Feja in order to determine their chemical composition. Data analysis revealed that the waters belong to the HCO3 -?SO4 2-?Ca2+ and SO4 2-?Ca2+ water types, with neutral pH values. The concentrations of metals in these waters (zinc, lead, barium, copper, chromium) are generally low, and most of the samples meet drinking water quality criteria (USEPA standards). Modelling using the PHREEQC software indicates that the dominant processes in the formation of the chemical composition of these waters are the dissolution of carbonate minerals and the oxidation of sulphide minerals. Carbonate minerals have a scarcer occurrence compared to sulphide minerals, such as galena, sphalerite and pyrite, which are dominantly distributed. The low intensity of sulphide mineral oxidation is interpreted to result from a rapid water exchange and reduced contact time between the water and the rock. The occurrence of this process is localized only in the ore body zone. This study highlights the importance of kinetics (in terms of the chemical reaction rate) as the main factor influencing the oxidation of sulphide minerals and, subsequently the quality of mine waters.

Old Sulfidic Ore Tailing Dump: Ground Features, Mineralogy, Biodiversity—A Case Study from Sibay, Russia

The Urals (Russia) are among the largest mining areas in the world, with millions of tons of mine waste deposited. An old sulfidic tailing dump formed over decades of mining activities at the Sibay ore-processing plant is a typical cause of acid mine drainage (AMD) formation, posing a threat to ecosystems of neighboring environments. In this study, the formation of oxidized surface soil layers in four zones of the Sibay tailing dump was revealed, and their chemical–mineralogical and physical–mechanical characteristics were analyzed. According to the results of the metabarcoding of hypervariable regions of the 16S rRNA genes, oxidation in soil layers was associated with the activity of sulfur- and iron-oxidizing acidophiles represented by a few genera: Ferroacidibacillus, Sulfoacidibacillus, Sulfobacillus, and Ferroplasma. The structure of the microbial communities in soil layers differed depending on the zone and depth of sampling. In the samples characterized by the weak oxidation of sulfide minerals, microbial communities were dominated by bacteria of the genus Pseudomonas. The data obtained in this research are of importance to predict the oxidation/leaching processes in mine wastes and their negative environmental impacts in the mining region, as well as to develop technologies for processing these raw materials.

Applying industrial side streams in the neutralization of acid generating sulfide-rich sediments – The impact on pH and leaching of harmful elements

Acid sulfate soils can cause severe environmental harm due to a low pH and mobilization of harmful elements. Acid sulfate soil material is formed when oxidation of sulfide minerals causes a drop in pH to <4.0 for mineral oil materials and <3.0 for organic soil materials or when the soil materials contain enough sulfide to potentially do so.Two dredged, acid sulfate soil materials from Finland were used in this laboratory study. Chemical analyses were performed to determine the pre-incubation characteristics of both fresh dredged sediment samples and oxidized samples after 23 weeks of incubation. Total element concentrations were determined after digestion in aqua regia by ICP-MS or ICP-OES. The leachable concentration of elements was determined by using the two-stage shaking test (method SFS-EN 12457-3). The leaching of harmful elements (Cd, Co, Ni, Mn, and Zn) was high in the acidified dredged spoil samples. Also, the leaching of S was high. The soluble concentration was dependent on total concentration, pH, and the mobility of the elements.During a 23-week oxidation period, the impact of various amounts of industrial side streams (alkaline ashes, industrial lime residues) as neutralizing agents on the acid-generating dredged sediments was investigated in the laboratory. Calcite was used as a reference material. pH measurements were carried out during the incubation period. The leaching of elements was determined with a modified method based on the SFS-EN 12457-2 standard before and after oxidation.The untreated dredged spoils and the samples treated with too low amounts of neutralizing agents, acidified to pH < 4 during the oxidation period. Thus, harmful elements were leached out. However, the 100 % theoretical calculated neutralization need was suitable to prevent acidification and thus the leaching of harmful substances from the neutralized acid-generating dredged spoils. However, the leaching of Mo increased at neutral pH values. The results showed that industrial side streams can be applicable for the neutralization of acid sulfate soil materials. However, the legislation must also be considered.

Oxidation of sulfide mineral and metal extraction analysis in the microwave-assisted roasting pretreatment of refractory gold ore

The recovery of gold from refractory ore could guarantee sustainable development in the gold industry. However, there are many challenges in the treatment of ore, such as environmental pollution and low recovery. In this regard, the current research focuses on the pretreatment of refractory gold ore and investigates the effect of microwave power, the role of additives, and water on the oxidation and decomposition of sulfide minerals. Pretreatment using microwave-assisted roasting with NaClO3 as an additive to the oxidizing agent is a new method of processing refractory gold ore. Oxidation was studied through sulfur and chlorine mass balance analysis and the degree of metal extraction from sulfide minerals. SEM analysis was carried out to complete the study of the phase change of compounds in the oxidation of mineral sulfides. Roasting of refractory gold ore with a composition of 180 kg NaClO3 and 180 kg water/ton ore reached a temperature of 470 °C at a microwave power of 400 watts for 30 minutes. Total oxidized sulfur reached 90.6%, while only 10.4 % of the sulfur was released, and chlorine release was 49.5%. In addition, water leaching was conducted to investigate the extraction rate of metals after roasting. The results showed that the water leaching extraction of Cu, Zn, Pb, and Fe reached 84.3%, 97.6%, 22.8%, and 8.4%, respectively. Applying microwaves with appropriate concentrations of additives and water resulted in high oxidation of sulfide minerals (>90%) and low sulfur emissions in roasting refractory gold ore with relatively low power, temperature, and time. Moreover, leaching this roasted gold ore resulted in gold extraction of 92.5%; however, leaching of refractory gold without pretreatment resulted in gold extraction of only 47.5%.

Expression, Purification and Characterization of a Novel Rusticyanin from the Psychrotolerant Acidithiobacillus ferrivorans

Rusticyanin plays a crucial role in ferrous oxidation of sulfide minerals during bioleaching for industrial metal extraction. Diverse isoforms of rusticyanin have been found, but until now, except for type-A rusticyanin, other isoforms or sources of rusticyanin have been scarcely investigated. Here, a rusticyanin (gene locus 0470) from the psychrophilic Acidithiobacillus ferrivorans was gene-cloned, expressed, purified, and assembled in vitro. All forms of the protein exhibit extreme acid stability, even at pH 0.3. The stability of the protein is obviously enhanced after binding of the copper cofactor; the oxidation state is more stable than the reduced state. The protein has characteristic UV-vis peaks and EPR signals similar to type-A or type-B rusticyanin but is different with a small position shift and an obvious intensity change. The vibrational spectrum of the apoprotein was more different than these between the oxidation and reduced states of the protein. The ferrous oxidation kinetic rate constant of the protein is obviously faster than that of both the type-A and type-B rusticyanins previously reported. Further bioinformatics analysis reveal their changes in sequence and molecule: the mutations related to the peculiar shield belt mostly account for the variation in the properties of the protein, and the classification of the protein as a new isoform, type-C rusticyanin, is proposed.