Oxidation Of Sulfide Minerals Research Articles

Geogenic influence and impact of mining activities on water soil and plants in surrounding areas of Morila Mine, Mali

The Morila Gold mine, a joint venture between AngloGold Ashanti and Randgold Resources, is one of the 10 operating mines in Mali. The mine is located at 180 km southeast of Bamako, Mali, and has been operating since 2001. With the depletion of the orebody, a closure plan was established by the government and shareholders since 2012, and rehabilitation strategies are currently operating. The concentration of major, minor and traces elements were analyzed in 90 water samples (45 water supply boreholes, 13 shallow wells, 20 piezometers of the mine and 12 surface water), 46 stream sediment samples, 10 mine soil samples and 57 plant samples. All the samples were collected from June 2015 to December 2016 in three study areas: Morila mine, an intermittent stream at downstream of the mine and a controlled geochemical background area free of mining activities (located 15 to 20 km upstream of the mine). Chemical water analyses show that arsenic (As: 0.8 to 132 ppb), manganese (Mn: 2.52 to 5200 ppb) and total iron (Fe: 0.462 to 78 ppm) are present at high levels. The ANOVA tests demonstrate significant differences between the three sites for most major ions and trace metals in water, stream sediments and mine soils. The mean concentrations within the mine were significantly higher than those outside mine boundaries. Factor analysis and cluster analysis show a geogenic and pollution factors influencing the soils and the water quality in the study area.Arsenic values were mostly found in groundwater of the village of Sanso (the nearest village to the Morila mine), where 7 of the 10 sources of drinking water boreholes had arsenic contents higher than the standard value of 10 ppb. This arsenic contamination in groundwater and those located in background area could not be linked to mining activities, and attributed to geogenic influences.In stream sediments and soil samples, the values of the analyzed elements were ranged bellow the maximum allowed concentration except for As, Fe, Al and S. Mine soils have high Fe (~10 wt%) and high Al (~3 wt%) concentrations, likely derived from naturally sources. Sulfur contents in soil and stream sediments were high only in the mining environment, and derive from sulfide mineral oxidation. Arsenic contents were elevated in most plant species samples, and concentrations of samples located within the mine were higher than those of the background area. This study indicates that most of the metals and toxic contaminations were from geogenic origin, but mining activities likely also play a substantial role by increasing the level of these contaminants in water, soil and plants within the mining environment.

The critical degree of mineral surface oxidation in copper sulphide flotation

It is well documented that surface oxidation of copper sulphide minerals has some detrimental effects on their flotation performance. However, little work has been done to quantitatively relate surface oxidation to flotation performance, which makes it inherently difficult for processing plants to optimise flotation conditions for oxidised ores. In this study, an array of oxidised chalcopyrite and chalcocite samples was prepared and characterisation of the surface oxidation species was carried out by X-ray Photoelectron Spectroscopy (XPS). The degree of surface oxidation was quantified as the ratio of hydrophilic species to hydrophobic species and correlated with copper sulphide flotation recovery. A quantitative relationship between them was established and a critical degree of oxidation, beyond which flotation becomes impossible, was identified to be 11.7 for chalcopyrite and estimated to be in the range of 1.74–4.85 for chalcocite, indicating that chalcocite flotation is much more sensitive to surface oxidation. This study will enable provision of guidelines to better manage oxidised copper ores to circumvent the loss of recovery and will also help in developing potential solutions that could be applied to flotation of minerals with different degrees of oxidation.

Metagenomes and metatranscriptomes from boreal potential and actual acid sulfate soil materials

Natural sulfide rich deposits are common in coastal areas worldwide, including along the Baltic Sea coast. When artificial drainage exposes these deposits to atmospheric oxygen, iron sulfide minerals in the soils are rapidly oxidized. This process turns the potential acid sulfate soils into actual acid sulfate soils and mobilizes large quantities of acidity and leachable toxic metals that cause severe environmental problems. It is known that acidophilic microorganisms living in acid sulfate soils catalyze iron sulfide mineral oxidation. However, only a few studies regarding these communities have been published. In this study, we sampled the oxidized actual acid sulfate soil, the transition zone where oxidation is actively taking place, and the deepest un-oxidized potential acid sulfate soil. Nucleic acids were extracted and 16S rRNA gene amplicons, metagenomes, and metatranscriptomes generated to gain a detailed insight into the communities and their activities. The project will be of great use to microbiologists, environmental biologists, geochemists, and geologists as there is hydrological and geochemical monitoring from the site stretching back for many years.

A technique to determine ore variability in a sulphide ore

Ore variability is a big challenge for mineral processing operations, especially in the flotation of complex polymetallic sulphide ores. Processing and blending strategies are determined mostly based on chemical and mineralogical characterization. However, surface characteristics of sulphide minerals is an equally important parameter affecting flotation performance. Changes in surface characteristics of sulphide minerals are usually studied at laboratory scale by using sophisticated equipment, such as ToFSIMs, XPS, etc. In this paper, use of Oxidation Index methodology based on the EDTA extraction technique was evaluated for determination of the presence of secondary copper minerals and surface oxidation of sulphide minerals using a low grade VMS ore deposit from Turkey. These two surface chemistry parameters are known to influence flotation performance significantly, particularly in the copper flotation stage. Therefore, ore variability across the entire ore deposit was evaluated using the relationship between Oxidation Index and flotation performance. The results showed that this methodology can potentially be used as a practical and cost effective method for mapping an ore body regarding variations in surface chemistry of sulphide minerals, prediction of flotation recoveries and selectivity.

Correlation of surface oxidation with xanthate adsorption and pyrite flotation

Various studies have emphasized the importance of surface oxidation of sulfide minerals with regard to xanthate adsorption and their flotation response. However, the correlation between pyrite surface oxidation, xanthate adsorption and its flotation response has not been clearly established. The complexity lies in various intermediate sulfur oxidation products in different solution conditions. Thus, investigation of sulfur oxidation behavior is the key to understand pyrite oxidation. Ion chromatography (IC) and high performance liquid chromatography (HPLC) results showed an increase in the total amounts of occurring sulfur species with increasing slurry pH. Meanwhile, the ratio of S0/sulfur oxyanions was to become lower; X-ray Photoelectron Spectroscopy (XPS) identified the oxidized pyrite surface was rich in SO42− and FeOOH. Both the contact angle results and single mineral flotation data indicated that the more pyrite surface oxidized, the lower hydrophobicity and floatability were. Time-of-flight secondary ion mass spectroscopy (Tof-SIMS) was adopted to analyse xanthate adsorption on the surface of pyrite under conditions of either sufficient oxidation or on freshly polished surface which is assumed little oxidation. A significantly lower intensities of C4H9O and C4H9OCSS was found on the intensely oxidized pyrite surface, indicating xanthate adsorption had strong selectivity on FeS2 rather than FeOOH. The experimental results were further confirmed by theoretical calculation. The self-consistent charge density functional tight binding (SCC-DFTB) calculations indicated that the distances between the xanthate S atoms and surface Fe atoms of FeOOH were larger than the atomic radius of SFe. Essentially, the different electron configurations of their Fe atoms led to the selective adsorption of xanthate on FeOOH and FeS2 surfaces in terms of the coordination chemistry theory. This work provides valuable implications for understanding the correlation of surface oxidation, xanthate adsorption and its floatation behavior to mediate pyrite flotation.

Identification of Sulfate Sources and Biogeochemical Processes in an Aquifer Affected by Peatland: Insights from Monitoring the Isotopic Composition of Groundwater Sulfate in Kampinos National Park, Poland

Temporal and spatial variations of the concentration and the isotopic composition of groundwater sulfate in an unconfined sandy aquifer covered by peatland have been studied to better understand the sources and biogeochemical processes that affect sulfate distribution in shallow groundwater systems influenced by organic rich sediments. The groundwater monitoring was carried out for one year at hydrogeological station Pożary located within the protected zone of the Kampinos National Park. Sulfur (δ34SSO4) and oxygen (δ18OSO4) isotopic composition of dissolved sulfates were analyzed together with oxygen (δ18OH2O) and hydrogen (δ2HH2O) isotopic composition of water and major ions concentration at monthly intervals. The research revealed three main sources of sulfates dissolved in groundwater, namely, (a) atmospheric sulfates—supplied to the aquifer by atmospheric deposition (rain and snow melt), (b) sulfates formed by dissolution of evaporite sulfate minerals, mainly gypsum—considerably enriched in 34S and 18O, and (c) sulfate formed during oxidation of reduced inorganic sulfur compounds (RIS), mainly pyrite—depleted in 34S and 18O. The final isotopic composition and concentration of dissolved SO42− in groundwater are the result of overlapping processes of dissimilatory sulfate reduction, oxidation of sulfide minerals, and mixing of water in aquifer profile.

Hydrogeochemical characteristics, source identification and health risks of surface water and groundwater in mining and non-mining areas of Handan, China

The present work aimed to compare the effects of coal mining and agricultural land uses on the quality of surface water and groundwater in the Handan region in China. For this purpose, the natural water samples were collected from both a mining area and an area without mining in a similar geological setting. The results showed that the contents of total hardness (TH), NO3−, SO42−, Ca, K, Co, Se, Rb, Fe and Ni in groundwater of the mining area (MGW) were significantly higher (1.6–6.1 times) than those in non-mining area (AGW), exhibiting a decreasing trend with the increasing distance from the mining areas. Most elements in surface water from the mining areas (MSW) were higher (1.1–30.8 times) than the non-mining areas surface water (AGW). The medium and high-level pollution in mining area groundwater samples were 16.7% and 50%, while in non-mining area samples were 9.5% and 4.8%, respectively. The lithology of the aquifer [including coal and rock (Permian, Carboniferous, Triassic, Ordovician, and Quaternary)] and watercourses are the main controlling factor of the element variance in groundwater of the Handan area. The Fe and SO42− in the Handan water are derived from sulfide mineral oxidation and the evaporative concentration of sulfate in the aquifer, while the coal mining induced higher NO3− in the mining area (MGW) as compared to the non-mining area (AGW). Interestingly, several samples from the mining areas have met the requirement of Se-supplementation in the water (average = 3.9 μg/L), which is higher than the Hebei groundwater (0.8 μg/L). The high Se in water is associated with the oxidation and leaching of selenium-rich coal and sedimentation of the coal ash. The concentration of Se, Sr, Rb, K, and NO3− generally show a large decline with the distance from mining areas, while Co, Ni and Ca trend are less clear. Unexpectedly, the elevated concentrations of chloride caused a non-carcinogenic risk for potable groundwater use in both the areas, while Pb caused a carcinogenic health risk in the mining areas. The spatial distribution of chemical constituents declines with the distance from mining areas. Noticeably, the elemental enriched coal-rock has caused the pollution of groundwater by rock weathering and percolation.

Desulfurization of the Old Tailings at the Au-Ag-Cu Tiouit Mine (Anti-Atlas Morocco)

Tailings from the abandoned Tiouit mine site in Morocco are mainly composed of sulfides, hematite, and quartz. They contain 0.06–1.50 wt % sulfur, mostly in the form of pyrite, pyrrhotite, and chalcopyrite. The tailings also contain gold (3.36–5.00 ppm), silver (24–37 ppm), and copper (0.06–0.08 wt %). Flotation tests were conducted to reprocess the tailings for Au, Ag, and Cu recovery, and at the same time to prevent acid mine drainage (AMD) generation through the oxidation of sulfide minerals, including pyrite, sphalerite, arsenopyrite, chalcopyrite, galena. The flotation results confirmed that environmental desulfurization is effective at reducing the overall sulfide content in the tailings. The recovery of sulfides was between 69% and 75%, while Au recovery weight-yield was between 2.8% and 4.7%. The test that showed the best sulfur recovery rate and weight-yield was carried out with 100 g/t CuSO4 (sulfide activator) and 50 g/t of amyl xanthate (collector). The goal of this study was also to assess the remaining acid-generating potential (AP) and acid-neutralizing potential (NP) of the desulfurized tailing. The geochemical behavior of the initial tailings sample was compared to that of the desulfurized tailings using kinetic weathering cell tests. The leachates from the desulfurized tailings showed higher pH values than those from the initial tailings, which were clearly acid-generating. The residual acidity produced by the desulfurized tailings was most likely caused by the hydrolysis of Fe-oxyhydroxides.

Sulfide oxidation affects the preservation of sulfur isotope signals

Abstract The accumulation of oxygen in Earth’s atmosphere and oceans in the late Archean had profound implications for the planet’s biogeochemical evolution. Oxygen impacts sulfur cycling through the oxidation of sulfide minerals and the production of sulfate for microbial sulfate reduction (MSR). The isotopic signature of sulfur species preserved in the geologic record is affected by the prevailing biological and chemical processes and can therefore be used to constrain past oxygen and sulfate concentrations. Here, in a study of a late Archean analogue, we find that the sulfur isotopic signature in the water column of a seasonally stratified lake in southern China is influenced by MSR, whereas model results indicate that the isotopic signature of the underlying sediments can be best explained by concurrent sulfate reduction and sulfide oxidation. These data demonstrate that small apparent sulfur isotope fractionations (δ34Ssulfate-AVS = 4.2‰–1.5‰; AVS—acid volatile sulfides) can be caused by dynamic sulfur cycling at millimolar sulfate concentrations. This is in contrast to current interpretations of the isotopic record and indicates that small fractionations do not necessarily indicate very low sulfate or oxygen.

Determining the factors controlling the chemical composition of groundwater using multivariate statistics and geochemical methods in the Xiqu coal mine, North China

Studying the hydrogeochemical processes that control groundwater quality in different aquifers helps to identify the sources of inrush water into coal mines. In this paper, 65 mine water samples were collected from Xiqu coal mine during 2016 and 2017 to determine the hydrogeochemical processes and controlling factors of mine water using hydrochemical methods and multivariate statistical analysis. The mine water is acidic to alkaline in nature. The dominant anions in the mine water are SO42− and HCO3−, and cations were dominated by Ca2+ Na+, and Mg2+. The dominant hydrochemical facies of groundwater were SO4–Na·Ca and SO4–Ca·Mg water types. Based on multivariate statistical analysis, four principal components and two clusters were obtained. Concentrations of SO42− showed significant positive correlations with Ca2+, Mg2+, Fe2+ and Fe3+, and strong negative correlations with HCO3− and pH. The mine water chemistry was dominated by the oxidation of iron-bearing sulfide minerals, cation exchange and the dissolution of silicate, carbonate and sulfate minerals. In addition, human activities such as agriculture are also likely to have influences groundwater chemistry at the mine site.

Bio-oxidation of refractory gold ores containing stibnite and gudmundite

Abstract Arsenic and antimony are environmental pollutants associated with several diseases, including skin cancer. One of the main sources of both elements is the oxidation of sulphide minerals, particularly arsenopyrite and therefore any of both elements is a concern in gold mining operations because arsenic- and antimony-bearing sulphides may contain significant gold contents. Bioleaching is considered more environmentally-friendly than chemical processes to recovery gold, particularly from low-grade ores and residues bearing such sulphides. Thus, the current work has investigated the bio-oxidation of both a gold-bearing sulphide concentrate and a flotation tailing by Acidithiobacillus ferrooxidans, at 32 °C, focusing on the behaviour of both arsenic and antimony. Fe2＋ supplementations were required in order to increase the oxidation efficiency and the optimum pH value was 1.75. The cyanidation tests confirmed the refractory nature of the samples under study (21%). The solid products of the bio-oxidation stage showed gold extractions four times as large (85%) as that of the initial sample. The dissolution of antimony was low with no evidence of the formation antimony precipitates. Unlike arsenic, the latter reported mostly to the solid product of the bioleaching step as inert sulphide particles.

Micromorphology and environmental behavior of oxide deposit layers in sulfide-rich tailings in Tongling, Anhui Province, China

Sulfide-rich tailings produced by mineral processing are prone to oxidation and cause many pollution problems in the surrounding environment; therefore, this issue has become a focus of attention. The Tongling Shuimuchong tailings reservoir contains a large amount of sulfide minerals, especially pyrrhotite and pyrite. This reservoir features obvious oxidation in the surface layer, and the slab is very hard. Mineralogical and environmental geochemical analyses were performed on tailings with different degrees of oxidation in the Shuimuchong tailings reservoir to investigate the influence of the formation of the hard oxidized layer on environmental pollution in the tailings pond. The samples were first subjected to particle-size analysis. The shallow tailings were mainly composed of medium particle; the proportions of coarse particle and fine tailings particles were equal; and the proportions of clay and silt were less than those of the other size fractions. Mineralogical analysis showed that pyrrhotite and pyrite were replaced by residual structures in the oxide layer. The secondary minerals goethite, hematite and jarosite were attached to the edges and fractures of sulfide minerals. The samples were geochemically analyzed to determine the total concentrations of 5 elements, the pH and the major anions. The maximum SO42− concentrations of 33,970 and 32,749 mg/kg were observed at a depth of 40 cm in profiles 1 and 2, respectively. Metal sulfide mineral oxidation in the tailings lowered the pH of the materials to values less than 4. The concentration of HCO3− (122–635 mg/kg) in the tailings samples was very low, and the concentration of CO32− was zero. As (53.2–133.7 mg/kg), Pb (24.2–307.5 mg/kg) and Hg (0.03–0.06 mg/kg) were concentrated in the highly oxidized layer at the surface; the Cd content (0.23–10.5 mg/kg) increased with decreasing oxidation degree of the tailings; and the Cr content (38.0–54.9 mg/kg) fluctuated around a certain value.

Isotopic Composition and Origin of Sulfide and Sulfate Species of Sulfur in Thermal Waters of Jiangxi Province (China)

The reduced sulfur species, sulfide, elemental and thiosulfate were considered in the thermal waters of Jiangxi Province for the first time. It is shown that the sulfur speciation content significantly varies and depends on the pH values. The major part of reduced sulfur refers to sulfide species in the nitric thermal waters, to elemental—in the carbon dioxide thermal waters. The presence of both reduced and oxidized sulfur speciation indicates the possibility of sulfide minerals hydrolysis and disproportionation of the product of this reaction (SO2) with the participation of hot water with the formation of elemental and sulfate sulfur. The isotopic composition of dissolved sulfate and sulfide sulfur speciation has shown that the process of bacterial reduction proceeds in the thermal waters, accompanied by accumulation of relatively heavy sulfur isotope in sulfates. Simultaneously with reduction, the oxidation of both sulfide minerals and newly formed hydrosulfide proceeds with formation of elemental, thiosulfates and also sulfates in the discharge zone was proceeded. It is shown that the process of sulfide oxidation mostly occurs in carbon dioxide thermal waters. Therefore, the elemental sulfur is predominant in carbon dioxide waters. The oxidation process is less significant in the nitric thermal waters, whereby the concentrations of sulfide ion are higher than sulfates. The ambiguous effect of sulfate reduction on the hydrogeochemical environment of the thermal waters is confirmed by the differing value of the carbon isotope ratio of HCO3− in the considered waters. The obtained isotopic composition data 34δS(SO42−) indicate host rocks as a source of sulfates in the thermal waters of Jiangxi Province.

The Potential Role of Halothiobacillus spp. in Sulfur Oxidation and Acid Generation in Circum-Neutral Mine Tailings Reservoirs.

The biogeochemistry of acid mine drainage (AMD) derived from waste rock associated sulfide mineral oxidation is relatively well-characterized and linked to Acidithiobacillus spp.. However, little is understood about the microbial communities and sulfur cycling before AMD develops, a key component of its prevention. This study aimed to examine circum-neutral mining impacted water (MIW) communities and its laboratory enrichments for sulfur oxidizing bacteria (SoxBac). MIW in situ microbial communities differed in diversity, structure and relative abundance consistent with site specific variations in total aqueous sulfur concentrations (TotS; ~2–17 mM), pH (3.67–7.34), and oxygen (22–93% saturation). However, the sulfur oxidizer, Halothiobacillus spp. dominated seven of the nine total SoxBac enrichment communities (~76–100% relative abundance), spanning three of the four mines. The presence and relative abundance of the identified sixteen known and five unclassified Halothiobacillus spp. here, were the important clustering determinants across parent MIW and enrichment communities. Further, the presence of Halothiobacillus spp. was associated with driving the pH <4 in enrichment experiments, and the combination of specific Halothiobacillus spp. in the enrichments affected the observed acid to sulfate ratios indicating differential sulfur cycling. Halothiobacillus spp. also dominated the parent communities of the two acidic MIWs providing corroborating evidence for its active role in net acid generation within these waters. These results identify a putative indicator organism specific to mine tailings reservoirs and highlight the need for further study of tailings associated sulfur cycling for better mine management and environmental stewardship.

Adsorption characteristics of Acidianus manzaensis YN25 on chalcopyrite: Surface thermodynamics and the extended DLVO theory

The adsorption of Acidianus manzaensis YN25 on chalcopyrite was investigated experimentally and theoretically. A. manzaensis showed high adhesion affinity to the chalcopyrite under acidic condition, but low adhesion affinity under neutral and alkaline conditions. The microbe-mineral adhesion was assessed by the surface thermodynamics and the extended DLVO theory. The experimental results were in agreement with the theory. Moreover, A. manzaensis grown on chalcopyrite, sulfur, and ferrous ion showed similar adsorption phenomena. The adsorptive capacity of A. manzaensis increased with increasing temperature and decreasing pH respectively, and within the range of investigation, the best adsorption was achieved at pH 2.0 and 65 °C. This study provided new insights for bio-catalytic oxidation of sulfide minerals by the thermophilic acidophilic archaea.

Long-term acid generation and heavy metal leaching from the tailings of Shimokawa mine, Hokkaido, Japan: Column study under natural condition

The leaching from mine tailings results in contamination of nearby groundwaters and rivers by hazardous metals like copper (Cu), zinc (Zn), and iron (Fe). In this study, unweathered tailings samples at depths of 1 to 3 m were collected from a tailings dam of an abandoned mine located in the north of Hokkaido, Japan. The mechanisms of long-term tailings weathering were assessed through leaching of hazardous metals by three column experiments. Measurements of mineralogical and chemical constituents, observation by scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDX), sequential extraction of the tailings, and chemical analyses of the leachates were carried out to determine the processes responsible for the leaching of Cu, Zn, Fe, and sulfate ion (SO42−). The contents of Cu, Zn, and Fe in the tailings were mainly associated with ion exchangeable and sulfide fractions. The pH values of the effluents from the columns were 3.0–3.7 throughout the experiments over 84 weeks, and approximately 15–23% of Cu, 35–45% of Zn, 2.5–4% of Fe and 15–20% of S were leached. Higher concentrations of Cu, Zn, Fe, and SO42− at the beginning of the experiments were observed, which could be attributed to the dissolution of soluble sulfate minerals present in the tailings. This indicates that the formation and dissolution of secondary soluble sulfate minerals contributed to Cu and Zn leaching. The continuous leaching of Cu, Zn, Fe, and SO42− suggests the oxidation of pyrite and other sulfide minerals. During these processes, ferrihydrite, goethite, lepidocrocite, and maghemite were formed and these minerals also acted as a sink for Cu and Zn by adsorption, and/or co-precipitation. These results mean the significance of the long-term behavior of hazardous metals released from mine tailings dams, which could provide helpful information on the management of tailings dams after mine closure.

Response of soil water hydrochemistry and δ13CDIC to changes in spatio-temporal variations under different land covers in SW China karst catchment

Abstract Soil water plays a crucial role in biogeochemical processes within karst ecosystems. However, geochemical variations of soil waters under different land covers and the related karst critical zone processes are still unclear. In this study, five land covers, including grassland, dry land, shrub land, reforestation land, and bamboo land in the Qingmuguan karst area of Chongqing Municipality, Southwest (SW) China were investigated in order to better understand the spatio-temporal variations of soil water geochemistry and its controlling mechanisms. The hydrochemistry of soil water and stable carbon isotopic compositions of dissolved inorganic carbon (δ13CDIC) in soil water were analyzed by a semi-monthly sampling strategy. The results show that there is remarkable spatio-temporal variation in the hydrochemistry and δ13CDIC of soil waters under different land covers in the studied area. Soil waters collected from shrub, dry, and afforestation lands have higher total dissolved solids (TDS), Ca2+, and HCO3− concentrations and heavier δ13CDIC, which is probably associated with the stronger carbonate dissolution caused by higher soil CO2 and carbonate content in soils under these land covers. However, lower TDS, Ca2+, and HCO3− concentrations as well as δ13CDIC values but higher SO42− concentrations are found in soil waters collected from bamboo land and grassland. The reason is that higher gypsum dissolution or oxidation of sulfide minerals and less soil CO2 input occurs in soils under these two land covers. Under the shrub, dry, and afforestation lands, higher concentrations of Ca2+ and HCO3− in soil waters occur in rainy seasons than in dry seasons, which are probably linked to higher CO2 input due to stronger microbial activities and root respiration in the wet summer seasons. In addition, seasonal variations of NO3− concentrations in soil waters from the dry land are observed, and much higher NO3− concentration occurs in the rainy seasons than that in the dry seasons, which suggest that the agricultural fertilization may lead to high NO3− in soil water. On the vertical soil profile, except for the bamboo land, soil waters under different land covers commonly show an increasing trend of main ion concentrations with the increase of depth. This vertical variation of hydrochemistry and δ13CDIC values in soil waters is primarily controlled by the intensity of carbonate dissolution related to carbonate content in soils and soil CO2 production. The soil waters under different land covers have great variations in δ13CDIC values which ranged from −20.68‰ to −6.90‰. Also, the [HCO3−]/([Ca2+] + [Mg2+]), [NO3−]/[HCO3−], and [SO42−]/([Ca2+] + [Mg2+]) molar ratios in soil waters show a large amplitude of variation. This suggested that carbonic acids could not be a unique dissolving agent and sulfuric/nitric acids may play a role in the weathering of carbonate in the Qingmuguan karst area.

Pyrite oxidization accelerates bacterial carbon sequestration in copper mine tailings

Abstract. Polymetallic mine tailings have great potential as carbon sequestration tools to stabilize atmospheric CO2 concentrations. However, previous studies focused on carbonate mineral precipitation, whereas the role of autotrophic bacteria in mine tailing carbon sequestration has been neglected. In this study, carbon sequestration in two samples of mine tailings treated with FeS2 was evaluated using 13C isotope, pyrosequencing and DNA-based stable isotope probing (SIP) analyses to identify carbon fixers. Mine tailings treated with FeS2 exhibited a higher percentage of 13C atoms (1.76±0.06 % for Yangshanchong and 1.36±0.01 % for Shuimuchong) than did controls over a 14-day incubation, which emphasized the role of autotrophs in carbon sequestration with pyrite addition. Pyrite treatment also led to changes in the composition of bacterial communities, and several autotrophic bacteria increased, including Acidithiobacillus and Sulfobacillus. Furthermore, pyrite addition increased the relative abundance of the dominant genus Sulfobacillus by 8.86 % and 5.99 % in Yangshanchong and Shuimuchong samples, respectively. Furthermore, DNA SIP results indicated a 8.20–16.50 times greater gene copy number for cbbL than cbbM in 13C-labeled heavy fractions, and a Sulfobacillus-like cbbL gene sequence (cbbL-OTU1) accounted for 30.11 %–34.74 % of all cbbL gene sequences in 13C-labeled heavy fractions of mine tailings treated with FeS2. These findings highlight the importance of the cbbL gene in bacterial carbon sequestration and demonstrate the ability of chemoautotrophs to sequester carbon during sulfide mineral oxidation in mine tailings. This study is the first to investigate carbon sequestration by autotrophic bacteria in mine tailings through the use of isotope tracers and DNA SIP.

Experimental determination of pyrite and molybdenite oxidation kinetics at nanomolar oxygen concentrations

Constraining the rate at which sulfide minerals undergo oxidative weathering at low atmospheric O2 is crucial for understanding the evolution of the Archean and Proterozoic biosphere when O2 was a trace atmospheric gas. However, recent studies attempting to constrain sulfide oxidation rates, atmospheric O2 sinks, and trace metal delivery to seawater under Archean conditions are limited by the need to extrapolate from experimental pyrite oxidation kinetics determined at much higher O2 levels. Extrapolation of those data sets to Archean levels of O2 (<10−5 present atmospheric level or PAL prior to 2.4 Ga) leads to more than an order of magnitude uncertainty in sulfide mineral oxidation rates, hampering efforts to quantify oxidative weathering under early Earth conditions. To quantify sulfide oxidation kinetics at low pO2, we conducted aqueous pyrite and molybdenite oxidation experiments at ∼2–1200 nM dissolved O2 and pH values 1.83, 5.08, and 8.58. Our experimental approach used LUMOS O2 sensors to extend the pO2 range explored by oxidation experiments down to 10−5 PAL pO2, the limit of the sensors, which is up to three orders of magnitude lower than the pO2 range explored in previous work. From these experiments, we use 28 independent rate measurements to derive a new rate law for the oxidation of pyrite as a function of pO2: rpyrite=10-8.83(±0.27)O20.50±0.04H+-0.25±0.02, Where rpyrite is the rate of oxidation in mol/m2 sec, and the activities of dissolved [O2] and [H+] are in (mol/L). Our results most closely match the previous rate law presented by Williamson and Rimstidt (1994), but indicate a stronger pH dependence than previous studies. We also present the first kinetic rate law for molybdenite oxidation at low O2, based on 13 independent rate measurements: rmolybdenite=10-8.3(±2.3)O20.5±0.3, Where rmolybdenite is the rate of oxidation in mol/m2 sec, and the activity of dissolved [O2] is in (mol/L). We find molybdenite oxidation to be nearly as rapid as pyrite oxidation even at low concentrations of dissolved O2 (equivalent to <10−5 PAL pO2), in contrast to previous work which argued for a threshold effect for molybdenite oxidation. Both pyrite and molybdenite oxidation kinetics exhibit a constant half-order dependence on dissolved O2 down to nanomolar levels of O2. We show that this behavior is best explained by a reaction mechanism in which O2 undergoes dissociative adsorption to the sulfide mineral surface. This mechanism helps to resolve major uncertainties regarding the reaction mechanism of O2 with pyrite and molybdenite mineral surfaces and provides a strong theoretical basis for the robust extrapolation of present results to higher and lower O2 concentrations.

Characteristics of interactions between black shale and water

Some geological engineering problems are caused by weathering of black shale within dispersed sulfide minerals (mainly pyrite), in which some weathering products such as acid water and expansive sulfates play an important role. These effects are essentially manifested through oxidation of sulfide minerals. Complex chemical reactions occur simultaneously and influence mutually in water-rock interaction process. Chemical weathering of black shale is a factor leading to engineering problems such as landslides and acid corrosion. The objectives of present study are to understand the process of water-rock interactions between black shale and water. The semi-immersion simulation experiment is mainly used to explore the chemical weathering characteristics of black shale under natural conditions.