Geochemical Characters of Water Coproduced with Coalbed Gas and Shallow Groundwater in Liulin Coalfield of China

To reveal the geochemical characters of water coproduced with coalbed gas and shallow groundwater,water samples were collected from 12 wells of coalbed methane and 7 wells of shallow groundwater.The pH,CODMn,fCO2,total dissolved solids （TDS）,total hardness,and concentrations of metasilicic acid,sodium and kalium,calcium ion,magnesium ion,ammonium iron,bicarbonate ion,carbonate,chloride,sulfate ion,nitrate ion,fluoride,lithium,zinc,nickel,manganese,iron,boron,barium,etc.of the samples were measured.Research results showed the following：（1） Concentrations of TDS,chloride,fluoride,sodium and kalium,ammonium,iron,and barium in the water coproduced with coalbed gas exceeded the national standards of China; however,physical,chemical,and biological properties of shallow groundwater could meet the national standard.（2） The water produced from coalbed contained mainly Na-Cl·HCO3,with average TDS of 4588.5 ppm,whereas shallow groundwater contained a mixture of chemicals including Na.Mg.Ca-HCO3·SO4 and Na.Mg-HCO3·SO4,with average TDS of 663.8 ppm.（3） In general,it was observed that bicarbonate and sodium accumulated in a reducing environment and deeper system,while depletion of hydrogen ions and dissolution of sulfate,calcium,and magnesium occurred in a redox environment and shallow system.（4） Sodium and kalium,ammonium,chloride,and bicarbonate ions were the main ions found in the study area.     

Assessment of chemical properties and hydro-geochemical coefficients at the Qareh Sou Basin,Golestan Province,Iran

This paper focuses on the Qareh Sou Basin in Golestan Province, Iran. Golestan Province is the third largest cereal producer in Iran and water scarcity and salinity are major problems in this area. This study attempts to facilitate the comprehension of system behavior with respect to water quality issues and hydro-geochemical coefficients within the Qareh Sou Basin. This study was carried out during the year 2010. Various parameters, such as pH, EC, chloride, sulfate, bicarbonate, sodium, potassium, calcium and magnesium have been determined for evaluation purposes. Then, Ca/Mg, Na/Cl, Mg/(Ca + Mg), Ca/HCO₃, (Ca + Mg)–(HCO₃ + SO₄), (Na + K)–Cl, (Ca + Mg + Na + K)–Cl, HCO₃ + SO₄, Ca + Mg and chloro-alkaline indices (CAI) were calculated. Results show that cation exchange probably is an important factor in the hydrochemistry and silicate mineral weathering. Also, CAI-1 plot against CAI-2 demonstrates that most of samples have positive values which suggest normal ion exchange in the system. The carbonic acid is the main agent of calcite, limestone and dolomite weathering which occurs in some stations. According to Chadha’s diagram, the type of water is determined as Ca–Mg–HCO₃.     

Evaporative evolution of a Na–Cl–NO<Subscript>3</Subscript>–K–Ca–SO<Subscript>4</Subscript>–Mg–Si brine at 95 °C: Experiments and modeling relevant to Yucca Mountain,Nevada

A synthetic Topopah Spring Tuff water representative of one type of pore water at Yucca Mountain, NV was evaporated at 95°C in a series of experiments to determine the geochemical controls for brines that may form on, and possibly impact upon the long-term integrity of waste containers and drip shields at the designated high-level, nuclear-waste repository. Solution chemistry, condensed vapor chemistry, and precipitate mineralogy were used to identify important chemical divides and to validate geochemical calculations of evaporating water chemistry using a high temperature Pitzer thermodynamic database. The water evolved toward a complex "sulfate type" brine that contained about 45 mol % Na, 40 mol % Cl, 9 mol % NO₃, 5 mol % K, and less than 1 mol % each of SO₄, Ca, Mg, ∑CO₂(aq), F, and Si. All measured ions in the condensed vapor phase were below detection limits. The mineral precipitates identified were halite, anhydrite, bassanite, niter, and nitratine. Trends in the solution composition and identification of CaSO₄ solids suggest that fluorite, carbonate, sulfate, and magnesium-silicate precipitation control the aqueous solution composition of sulfate type waters by removing fluoride, calcium, and magnesium during the early stages of evaporation. In most cases, the high temperature Pitzer database, used by EQ3/6 geochemical code, sufficiently predicts water composition and mineral precipitation during evaporation. Predicted solution compositions are generally within a factor of 2 of the experimental values. The model predicts that sepiolite, bassanite, amorphous silica, calcite, halite, and brucite are the solubility controlling mineral phases.     

Microbial and chemical characterization of a groundwater flow system in an intermontane basin of southern New Mexico,USA

Groundwater of the southern Jornada del Muerto Basin, an intermontane basin structure associated with the Rio Grande rift located in south-central New Mexico, USA, was analyzed chemically and microbially. A microbial phospholipid fatty acids (PLFA) analysis revealed a sparse microbial population consisting of relatively simple microorganisms with no major population changes along the flow system. A nucleic acid (DNA) analysis of the groundwater resulted in the identification of ten eubacterial and one archeal species. Chemical analyses revealed that sulfate along with calcium, magnesium, iron, and manganese is removed by about an order of magnitude in concentration from the recharge area to the discharge area. The removal of iron, manganese, magnesium, and to some extent calcium can be explained by oxidation reactions and the precipitation of dolomite. Sulfate and additional calcium are most likely removed by the precipitation of gypsum. Thiobacillus spp. are oxidizing metal sulfides that occur as subsurface sulfide mineral deposits to sulfuric acid, which subsequently reacts with calcium carbonate and water to precipitate gypsum. The presence of these sulfide deposits exposed to oxygenated water in the deep groundwater flow system significantly alters its chemical and bacteriological composition. Electronic Publication     

The effects of a gas well blow out on groundwater chemistry

Water wells were sampled near North Madison, Ohio, following a gas well blow out that injected large amounts of CH₄ into near-surface groundwater Chemical analyses showed elevated levels of Fe⁺², Mn⁺², Ca⁺², sulfide, alkalinity, and pH, and low levels of dissolved oxygen, SO₄ ⁻², and NO₃ ⁻ in CH₄-affected wells compared to unaffected wells. Sulfate reduction is quantitatively the most important vehicle for CH₄ oxidation Equilibrium thermodynamic computer models were used to simulate groundwaters from the North Madison area Model results showed that CH₄ is oxidized to HCO₃ ⁻, SO₄ ⁻² is reduced, iron and manganese oxides are reduced and dissolved, and pH increases These simulations are in excellent agreement with trends observed in the field data A laboratory experiment was designed to simulate CH₄ ⁻ perturbed groundwater in the methane-perturbed system, sulfide increased significantly, providing direct evidence for methane oxidation by sulfate reduction Although suitable anaerobic methane-oxidizing bacteria have not been isolated from groundwater aquifers, the combination of field data, laboratory experiment, and computer simulation form a convincing argument that CH₄ perturbation of aquifers can and does affect groundwater chemistry     

Compressive and Tensile Behavior of Polymer Treated Sulfate Contaminated CL Soil

In this study, the compressive and tensile behavior of polymer treated sulfate contaminated CL soil was investigated. Based on the information in the literature, a field soil was contaminated with up to 4 % (40,000 ppm) of calcium sulfate in this study. In addition to characterizing the behavior of sulfate contaminated CL soil, the effect of treating the soil with a polymer solution was investigated and the performance was compared to 6 % lime treated soil. In treating the soil, acrylamide polymer solution (15 g of polymer dissolved in 85 g of water) content was varied up to 15 % (by dry soil weight). Addition of 4 % calcium sulfate to the soil decreased the compressive and tensile strengths of the compacted soils by 22 and 33 % respectively with the formation of calcium silicate sulfate [ternesite Ca₅(SiO₄)₂SO₄)], magnesium silicate sulfate (Mg₅(SiO₄)₂SO₄) and calcium-magnesium silicate (merwinite Ca₃Mg(SiO₄)₂). With the polymer treatment the strength properties of sulfate contaminated CL soil was substantially improved. Polymer treated sulfate soils had higher compressive and tensile strengths and enhanced compressive stress–strain relationships compared to the lime treated soils. Also polymer treated soils gained strength more rapidly than lime treated soil. With 10 % of polymer solution treatment, the maximum unconfined compressive and splitting tensile strengths for 4 % of calcium sulfate soil were 625 kPa (91 psi) and 131 kPa (19 psi) respectively in 1 day of curing. Similar improvement in the compressive modulus was observed with polymer treated sulfate contaminated CL soil. The variation of the compacted compressive strength and tensile strength with calcium sulfate concentrations for the treated soils were quantified and the parameters were related to calcium sulfate content in the soil and polymer content. Compressive stress–strain relationships of the sulfate soil, with and without lime and polymer treatment, have been quantified using two nonlinear constitutive models. The constitutive model parameters were sensitive to the calcium sulfate content and the type of treatment.     

Geochemical reactions and dynamics during titration of a contaminated groundwater with high uranium, aluminum, and calcium

This study investigated possible geochemical reactions during titration of a contaminated groundwater with a low pH but high concentrations of aluminum, calcium, magnesium, manganese, and trace contaminant metals/radionuclides such as uranium, technetium, nickel, and cobalt. Both Na-carbonate and hydroxide were used as titrants, and a geochemical equilibrium reaction path model was employed to predict aqueous species and mineral precipitation during titration. Although the model appeared to be adequate to describe the concentration profiles of some metal cations, solution pH, and mineral precipitates, it failed to describe the concentrations of U during titration and its precipitation. Most U (as uranyl, UO₂²⁺) as well as Tc (as pertechnetate, TcO₄⁻) were found to be sorbed and coprecipitated with amorphous Al and Fe oxyhydroxides at pH below ∼5.5, but slow desorption or dissolution of U and Tc occurred at higher pH values when Na₂CO₃ was used as the titrant. In general, the precipitation of major cationic species followed the order of Fe(OH)₃ and/or FeCo_0.1(OH)_3.2, Al₄(OH)₁₀SO₄, MnCO₃, CaCO₃, conversion of Al₄(OH)₁₀SO₄ to Al(OH)_3,am, Mn(OH)₂, Mg(OH)₂, MgCO₃, and Ca(OH)₂. The formation of mixed or double hydroxide phases of Ni and Co with Al and Fe oxyhydroxides was thought to be responsible for the removal of Ni and Co in solution. Results of this study indicate that, although the hydrolysis and precipitation of a single cation are known, complex reactions such as sorption/desorption, coprecipitation of mixed mineral phases, and their dissolution could occur simultaneously. These processes as well as the kinetic constraints must be considered in the design of the remediation strategies and modeling to better predict the activities of various metal species and solid precipitates during pre- and post-groundwater treatment practices.     

Reactivity of micas and cap-rock in wet supercritical CO2 with SO2 and O2 at CO2 storage conditions

Seal or cap-rock integrity is a safety issue during geological carbon dioxide capture and storage (CCS). Industrial impurities such as SO₂, O₂, and NOx, may be present in CO₂ streams from coal combustion sources. SO₂ and O₂ have been shown recently to influence rock reactivity when dissolved in formation water. Buoyant water-saturated supercritical CO₂ fluid may also come into contact with the base of cap-rock after CO₂ injection. Supercritical fluid-rock reactions have the potential to result in corrosion of reactive minerals in rock, with impurity gases additionally present there is the potential for enhanced reactivity but also favourable mineral precipitation.The first observation of mineral dissolution and precipitation on phyllosilicates and CO₂ storage cap-rock (siliciclastic reservoir) core during water-saturated supercritical CO₂ reactions with industrial impurities SO₂ and O₂ at simulated reservoir conditions is presented. Phyllosilicates (biotite, phlogopite and muscovite) were reacted in contact with a water-saturated supercritical CO₂ containing SO₂, or SO₂ and O₂, and were also immersed in the gas-saturated bulk water. Secondary precipitated sulfate minerals were formed on mineral surfaces concentrated at sheet edges. SO₂ dissolution and oxidation resulted in solution pH decreasing to 0.74 through sulfuric acid formation. Phyllosilicate dissolution released elements to solution with ∼50% Fe mobilized. Geochemical modelling was in good agreement with experimental water chemistry. New minerals nontronite (smectite), hematite, jarosite and goethite were saturated in models. A cap-rock core siltstone sample from the Surat Basin, Australia, was also reacted in water-saturated supercritical CO₂ containing SO₂ or in pure supercritical CO₂. In the presence of SO₂, siderite and ankerite were corroded, and Fe-chlorite altered by the leaching of mainly Fe and Al. Corrosion of micas in the cap-rock was however not observed as the pH was buffered by carbonate dissolution. Ca-sulfate, and Fe-bearing precipitates were observed post SO₂-CO₂ reaction, mainly centered on surface cracks and an illite rich illite-smectite precipitate quantified. Water saturated impure supercritical CO₂ was observed to have reactivity to rock-forming biotite, muscovite and phlogopite mineral separates. In the cap-rock core however carbonates and chlorite were the main reacting minerals showing the importance of assessing actual whole core.     

Hydrochemistry of Salt Lakes of the Qinghai-Tibet Plateau, China

The authors have carried out scientific investigations of salt lakes on the Qinghai-Tibet Plateau since 1956 and collected 550 hydrochemical data from various types of salt lakes. On that basis, combined with the tectonic characteristics of the plateau, the hydrochemical characteristics of the salt lakes of the plateau are discussed. The salinity of the lakes of the plateau is closely related to the natural environment of lake evolution, especially the climatic conditions. According to the available data and interpretation of satellite images, the salinity of the lakes of the plateau has a general trend of decreasing from north and northwest to south and southeast, broadly showing synchronous variations with the annual precipitation and aridity (annual evaporation/annual precipitation) of the modern plateau. The pH values of the plateau salt lakes are related to both hydrochemical types and salinities of the lake waters, i.e., the pH values tend to decrease from the carbonate type → sodium sulfate subtype → magnesium sulfate subtype → chloride type; on the other hand, a negative correlation is observed between the pH and salinities of the lakes. Geoscientists and biological limnologists generally use main ions in salt lakes as the basis for the hydrochemical classification of salt lakes. The common ions in salt lakes are Ca²⁺, Mg²⁺, Na⁺, K⁺, Cl^? SO₄ ^2?, CO₃ ^2?, and HCO₃ ^?. In this paper, the Kurnakov-Valyashko classification is used to divide the salt lakes into the chloride type, magnesium sulfate subtype, sodium sulfate subtype and carbonate type, and then according to different total alkalinities (K _C = Na₂CO₃ + NaHCO₃/total salt × 100%) and different saline mineral assemblages, the carbonate type is further divided into three subtypes, namely, strong carbonate subtype, moderate carbonate subtype and weak carbonate subtypes. According to the aforesaid hydrochemical classifications, a complete and meticulous hydrochemical classification of the salt lakes of the plateau has been made and then a clear understanding of the characteristics of N–S hydrochemical zoning and E-W hydrochemical differentiation has been obtained. The plateau is divided into four zones and one area. There is a genetic association between certain saline minerals and specific salt lake hydrochemical types: the representative mineral assemblages of the carbonate type of salt lake is borax (tincalconite) and borax-zabuyelite (L₂CO₃) and alkali carbonate-mirabilite; the representative mineral assemblages of the sodium sulfate subtype are mirabilite (thenardite)-halite and magnesium borate (kurnakovite, inderite etc.)-ulexite-mirabilite; the representative mineral assemblages of the magnesium sulfate subtype are magnesium sulfate (epsomite, bloedite)-halite, magnesium borate-mirabilite, and mirabilite-schoenite-halite, as well as large amount of gypsum; The representative mineral assemblages of the chloride type are carnallite-bischofite-halite and carnallite-halite, with antarcticite in a few individual salt lakes. The above-mentioned salt lake mineral assemblages of various types on the plateau have features of cold-phase assemblages. Mirabilite and its associated cold-phase saline minerals are important indicators for the study of paleoclimate changes of the plateau. A total of 59 elements have been detected in lake waters of the plateau now, of which the concentrations of Na, K, Mg, Ca, and Cl, and SO₄ ^2?, CO₃ ^2?, and HCO₃ ^? ions are highest, but, compared with the hydrochemical compositions of other salt lake regions, the plateau salt lakes, especially those in the southern Qiangtang carbonate type subzone (I₂), contain high concentrations of Li, B, K, Cs, and Rb, and there are also As, U, Th, Br, Sr, and Nd positive anomalies in some lakes. In the plateau lake waters, B is intimately associated with Li, Cs, K and Rb and its concentration shows a general positive correlation with increasing salinity of the lake waters. The highest positive anomalies of B, Li, Cs, and K center on the Ngangla Ringco Lake area in the western segment of the southern Qiangtang carbonate type subzone (I₂) and coincide with Miocene volcanic-sedimentary rocks and high-value areas of B, Li, and Cs of the plateau. This strongly demonstrates that special elements such as B, Li, and Cs on the plateau were related to deep sources. Based on recent voluminous geophysical study and geochemical study of volcanic rocks, their origin had close genetic relation to anatectic magmatism resulting from India–Eurasia continent–continent collision, and B–Li (-Ce) salt lakes in the Cordillera Plateau of South America just originated on active continental margins, both of which indicate that global specific tectonically active belts are the main cause for the high abundances of B, Li, and Cs (K and Rb) in natural water and mineralization of these elements.     

Reactivity of organic-rich sediment in seawater at 350°c, 500 bars: experimental and theoretical constraints and implications for the guaymas basin hydrothermal system

Hydrothermal alteration of organic-rich diatomaceous sediment by seawater was modelled experimentally at 350°C, 500 bars and seawater/sediment mass ratio of 3. The experiment was performed to assess the effect of organic matter reactivity on solution speciation and sediment alteration processes at an elevated temperature and pressure and provide requisite data to better understand the chemistry of hydrothermal fluids issuing from vents in the Guaymas Basin, Gulf of California.Seawater chemistry changed greatly during the experiment. In particular, Na, Mg and SO₄ decreased, while ∑ CO₂, ∑ NH₃, ∑ H₂S, SiO₂, Ca, K, H₂, CH₄ and heavy and base metals increased. Moreover, owing to the thermal alteration of sediment organic matter, organic acids, phenolic derivatives and phthlate were released to solution. Examination of solid alteration products revealed the effects of extensive dissolution and precipitation processes characterized by total elimination of diatoms and formation of cristobalite, quartz (?), pyrite, pyrrhotite, mixed layer chlorite/smectite and calcite. Plagioclase feldspar (An₄₀) recrystallized to a more albitic form owing to Na fixation and Ca cycling to calcite. A graphitic residue was also present in the products of the experiment.Mg and Na fixation reactions during the experiment generated significant H⁺, although the pH measured at 25°C was approximately 6.2. SO₄ reduction and thermal alteration and dissolution of organics, however, consume H⁺ and are chiefly responsible for the near neutral pH for the overall reaction. Speciation calculations including ammine and acetate protonation reactions give a pH at experimental conditions of approximately 5.1, while mineral solubility relations involving virtually all alteration phases require a pH of 5.57 to 5.94. A near neutral pH at experimental conditions constrains the mobility of Fe, Mn, Zn, Cu and Ni, which existed in solution as chloro-complexes. Dissolved concentrations of Pb and Al, in contrast, covaried with dissolved organics, especially acetate, suggesting organo-metallic complex formation.     

Mineral species control of aluminum solubility in sulfate-rich acidic waters

The identification of the mineral species controlling the solubility of Al in acidic waters rich in sulfate has presented researchers with several challenges. One of the particular challenges is that the mineral species may be amorphous by X-ray diffraction. The difficulty in discerning between adsorbed or structural sulfate is a further complication. Numerous studies have employed theoretical calculations to determine the Al mineral species forming in acid sulfate soil environments. The vast majority of these studies indicate the formation of a mineral species matching the stoichiometry of jurbanite, Al(OH)SO₄·5H₂O. Much debate, however, exists as to the reality of jurbanite forming in natural environments, particularly in view of its apparent rare occurrence. In this work the use of Al, S and O K-edge XANES spectroscopy, in combination with elemental composition analyses of groundwater precipitates and a theoretical analysis of soluble Al concentrations ranging from pH 3.5 to 7, were employed to determine the mineral species controlling the solubility of Al draining from acid sulfate soils into Blacks Drain in north-eastern New South Wales, Australia. The results indicate that a mixture of amorphous Al hydroxide (Al(OH)₃) and basaluminite (Al₄(SO₄)(OH)₁₀·5H₂O) was forming. The use of XANES spectroscopy is particularly useful as it provides insight into the nature of the bond between sulfate and Al, and confirms the presence of basaluminite. This counters the possibility that an Al hydroxide species, with appreciable amounts of adsorbed sulfate, is forming within these groundwaters.Below approximately pH 4.5, prior to precipitation of this amorphous Al(OH)₃/basaluminite mixture, our studies indicate that the Al³⁺ activity of these acidic sulfate-rich waters is limited by the availability of dissolved Al from exchangeable and amorphous/poorly crystalline mineral species within adjacent soils. Further evidence suggests the Al³⁺ activity below pH 4.5 is then further controlled by dilution with either rainwater or pH 6-8 buffered estuarine water, and not a notional Al(OH)SO₄ mineral species.     

The influence of sulfur deposition rates on sulfate retention patterns and mechanisms in aerated forest soils

Stable isotope ratios were used as a tracer for S flow and transformations in an irrigation experiment with 5 different German forest soils. Seventy-five lysimeters constructed from soil cores, 15 from each site, were irrigated over 20 months with SO₄-rich artificial canopy throughfall, simulating 3 different S input levels: 35 kg S ha⁻¹ in treatment I, 63 kg S ha⁻¹ in treatment II, and 131 kg S ha⁻¹ in treatment III. The δ³⁴S value of the irrigation SO₄ was more than 22‰ higher than those of total S in the untreated soils. Mass and isotope balances for different soil S compounds were used to assess the patterns and mechanisms of S retention in individual soil horizons and their dependence on S deposition levels. Independent of the S deposition level, on average 12±5 kg ha⁻¹ of the applied S were bound organically by the microbial biomass in all soils. Immobilization of irrigation SO₄ occurred predominantly in the topsoil horizons with the formation of C-bonded S being more prevalent than the synthesis of organic sulfates. Tracer retention via formation of organic soil S compounds accounted for up to 50% of the irrigation SO₄ in treatment I, from 16 to 25% in treatment II, and less than 20% in treatment III. The dominant process of inorganic S retention in the soils appeared to be adsorption of SO₄, but precipitation of aluminum hydroxy sulfate minerals constituted a second potential inorganic retention process in some soils. Sulfate adsorption increased with increasing sesquioxide content of the soils and with increasing S deposition rates. In soils with high sesquioxide contents, typically more than 70% of the irrigated S was retained inorganically, whereas in the soil with the lowest sesquioxide content, generally less than 50% of the labeled irrigation S was detected in inorganic form. In the latter soil, the sesquioxide content was not high enough to fully adsorb the elevated SO₄ inputs in treatments II and III. Consequently, increased tracer S export with the seepage water SO₄ was observed in the experimental variants with elevated SO₄ deposition rates. In soils with high sesquioxide contents, the elevated SO₄ inputs in treatments II and III were fully retained in the soil horizons in inorganic form during the 20 months of the experiment and thus increased seepage water export of labeled SO₄ was not observed. The ability to inorganically retain tracer S in the mineral soil horizons was identified as the major factor regulating the extent of tracer S export with the seepage water at 60 cm depth. The high retention of labeled S in all soils combined with the comparatively low recovery of irrigation SO₄ with the seepage water implies that the mean transit time of S in the uppermost 60 cm of the acid forest soils varies between several years and many decades, much longer than previously thought.     

The control of Phanerozoic atmosphere and seawater composition by basalt–seawater exchange reactions

We present results from a long term geochemical cycling model, with a focus on the sensitivity of atmospheric carbon dioxide, oxygen, and the major element composition of seawater to seafloor spreading rates. This model incorporates rock weathering, basalt–seawater exchange reactions, and the formation and destruction of chemical sediments and organic matter. Hydrothermal reactions between seafloor and seawater involving calcium, magnesium, sodium, potassium, sulfate and carbon are the high temperature counterparts to low temperature redox, weathering, precipitation and diagenetic reactions. A major source of uncertainty is the extent to which these exchange fluxes are controlled by seafloor spreading rate. In addition, the return fluxes of these components to the atmospheric and primary silicate reservoirs reflect not only the overall rates of subduction and metamorphism, but the distribution of the overlying sedimentary burden and authigenic minerals formed during basalt alteration as well. In particular, we show how the stoichiometry of exchange fluxes (Mg/Ca and SO₄/Ca) may buffer atmospheric CO₂ and O₂ concentrations.     

The post-depositional reactivity of iron and managanese in the sediments of a macrotidal estuarine system

Four cores of anoxic sediments were collected from the Seine estuary to assess the early diagenesis pathways leading to the formation of previously reactive phase. Pore waters were analyzed for dissolved iron (Fe) and manganese (Mn) and different ligands (e.g., sulfate, chloride, total inorganic carbon). The anoxic zone is present up to the first centimeter depth, in these conditions the reduction of Mn and Fe oxides and SO₄ ²⁻ was verified. The sulfate reduction was well established with a subsequent carbon mineralization in the NORMAI94 core. The chemical speciation of Mn and Fe in the dissolved and solid phases was determined. For the dissolved phase, thermodynamic calculations were used to characterize and illustrate the importance of carbonate and phosphate phases as sinks for Fe and Mn. The ion activity product (IAP) of Fe and Mn species was compared to the solubility products (Ks) of these species. In the solid phase, the presence of higher concentration of calcium carbonate in the Seine sediments is an important factor controlling Mn cycle. The carbonate-bound Mn can reach more than 75% of the total concentration. This result is confirmed by the use of electron spin resonance (ESR) spectroscopy. The reduction of Fe is closely coupled to the sulfate reduction by the formation of new solid phases such as FeS and FeS₂, which can be regarded as temporal sinks for sulfides. These forms were quantified in all cores as acid volatile sulfide (AVS: FeS+ free sulfide) and chromium reducible sulfide (CRS: FeS₂+elemental sulfur S⁰).     

Sulfation of calcitic and dolomitic lime mortars in the presence of diesel particulate matter

The sulfation of four types of calcitic and dolomitic lime mortars exposed to SO₂ in the presence of particulate matter from diesel vehicle exhaust emissions has been investigated. The binders mineralogy and mortars texture are the main factors influencing the formation of deleterious sulfate salts. The type of binder also influences the pore size distribution and the total porosity of the mortars: for equal aggregate (quartz or dolomite), dolomitic lime mortars have smaller pores and higher porosity than calcitic ones. During the first 24 h exposure to SO₂, calcitic lime mortars undergo a higher weight increase than dolomitic ones due to rapid formation of gypsum on their surface. However, at the end of the sulfation test (10 days), dolomitic mortars show a higher weight increase due to massive formation of epsomite and gypsum, which is facilitated by their higher porosity and the high reactivity of Mg phases in the porous and partially carbonated binder. Control samples (not covered with diesel particulate matter) also develop calcium and magnesium sulfates upon long term exposure to SO₂. This is due to the presence of uncarbonated Ca and Mg hydroxides that promote SO₂ fixation as sulfates. However, the amount and size of sulfate crystals are significantly smaller than those observed on samples covered with diesel particulate matter. These results show that diesel particulate matter enhances the sulfation of lime mortars and demonstrate that sulfation of dolomitic lime is an important mechanism for the in situ formation of highly soluble and deleterious hydrated magnesium sulfates (epsomite and hexahydrite). The use of dolomitic limes in the conservation of monuments exposed to air pollution in urban environments may therefore pose a significant risk.     

Early oxidation of organic matter in pelagic sediments of the eastern equatorial Atlantic: suboxic diagenesis

Pore water profiles of total-CO₂, pH, PO^3?₄, NO^?₃ plus NO^?₂, SO^2?₄, S^2?, Fe²⁺ and Mn²⁺ have been obtained in cores from pelagic sediments of the eastern equatorial Atlantic under waters of moderate to high productivity. These profiles reveal that oxidants are consumed in order of decreasing energy production per mole of organic carbon oxidized (O₂ > manganese oxides ~ nitrate > iron oxides > sulfate). Total CO₂ concentrations reflect organic regeneration and calcite dissolution. Phosphate profiles are consistent with organic regeneration and with the effects of release and uptake during inorganic reactions. Nitrate profiles reflect organic regeneration and nitrate reduction, while dissolved iron and manganese profiles suggest reduction of the solid oxide phases, upward fluxes of dissolved metals and subsequent entrapment in the sediment column. Sulfate values are constant and sulfide is absent, reflecting the absence of strongly anoxic conditions.     

Ferric iron in sediments as a novel CO2 mineral trap: CO2–SO2 reaction with hematite

Thermodynamic simulations of reactions among SO₂-bearing CO₂-dominated gas, water and mineral phases predict that Fe^III in sediments should be converted almost entirely to dissolved Fe^II and siderite (FeCO₃), and that SO₂ should simultaneously be oxidized to dissolved sulfate. The reactions are however, subject to kinetic constraints which may result in deviation from equilibrium and the precipitation of other metastable mineral phases. To test the prediction, a laboratory experiment was carried out in a well stirred hydrothermal reactor at 150 °C and 300 bar with hematite, 1.0 m NaCl, 0.5 m NaOH, SO₂ in quantity sufficient to reduce much of the iron, and excess CO₂. The experiment produced stable siderite and metastable pyrite and elemental S. Changes in total dissolved Fe are consistent with nucleation of pyrite at ∼17 h, and nucleation of siderite at ∼600 h. Dissolution features present on elemental S at the conclusion of the experiment suggest nucleation early in the experiment. The experiment did not reach equilibrium after ∼1400 h, as indicated by coexistence of hematite with metastable pyrite and elemental sulfur. However, the results confirm that Fe^III can be used to trap CO₂ in siderite if partly oxidized S, as SO₂, is present to reduce the Fe with CO₂ in the gas phase.     

酸溶-电感耦合等离子发射光谱法测定密西西比型铅锌矿床矿石中的铅

密西西比型(MVT)铅锌矿床的主要矿物有方铅石、闪锌矿,常伴生有重晶石、萤石等矿物,使得MVT型矿石在酸处理过程中易生成不溶于水和酸的硫酸铅钡复盐,故而检测矿样中铅的含量偏低。本文建立了采用盐酸-硝酸-氢氟酸体系酸溶分解MVT型矿石,电感耦合等离子体发射光谱法(ICP-OES)测定铅含量的分析方法。实验比较了盐酸-硝酸-氢氟酸、盐酸-硝酸-氢氟酸-高氯酸、盐酸-硝酸-硫酸三种酸溶体系的溶样效果,并通过X射线衍射论证了方法的可行性。结果表明,盐酸-硝酸-氢氟酸体系克服了复盐硫酸铅钡和硫酸铅沉淀的生成,适量的氢氟酸促进了Pb SO4的溶解,X射线衍射表征也表明此种酸溶体系的沉淀中不含有Pb SO4,可更彻底地分解MVT型矿石。本方法精密度(RSD)为0.3%~0.6%,实际样品的加标回收率为96.0%~99.2%,铅的最佳检测范围为0.01%~20.0%。     

Iron geochemical zonation in a tidally inundated acid sulfate soil wetland

Tidal inundation is a new technique for remediating coastal acid sulfate soils (CASS). Here, we examine the effects of this technique on the geochemical zonation and cycling of Fe across a tidally inundated CASS toposequence, by investigating toposequence hydrology, in situ porewater geochemistry, solid-phase Fe fractions and Fe mineralogy. Interactions between topography and tides exerted a fundamental hydrological control on the geochemical zonation, redistribution and subsequent mineralogical transformations of Fe within the landscape. Reductive dissolution of Fe(III) minerals, including jarosite (KFe₃(SO₄)₂(OH)₆), resulted in elevated concentrations of porewater Fe²⁺ (> 30 mmol L^?1) in former sulfuric horizons in the upper-intertidal zone. Tidal forcing generated oscillating hydraulic gradients, driving upward advection of this Fe²⁺-enriched porewater along the intertidal slope. Subsequent oxidation of Fe²⁺ led to substantial accumulation of reactive Fe(III) fractions (up to 8000 μmol g^?1) in redox-interfacial, tidal zone sediments. These Fe(III)-precipitates were poorly crystalline and displayed a distinct mineralisation sequence related to tidal zonation. Schwertmannite (Fe₈O₈(OH)₆SO₄) was the dominant Fe mineral phase in the upper-intertidal zone at mainly low pH (3–4). This was followed by increasing lepidocrocite (γ-FeOOH) and goethite (α-FeOOH) at circumneutral pH within lower-intertidal and subtidal zones. Relationships were evident between Fe fractions and topography. There was increasing precipitation of Fe-sulfide minerals and non-sulfidic solid-phase Fe(II) in the lower intertidal and subtidal zones. Precipitation of Fe-sulfide minerals was spatially co-incident with decreases in porewater Fe²⁺. A conceptual model is presented to explain the observed landscape-scale patterns of Fe mineralisation and hydro-geochemical zonation. This study provides valuable insights into the hydro-geochemical processes caused by saline tidal inundation of low lying CASS landscapes, regardless of whether inundation is an intentional strategy or due to sea-level rise.     

Impact of natural water chemistry on public drinking water in Japan

Drinking water from Japan (Toyama, Kumamoto, Osaka, and Tokyo Prefecture) and France (Volvic water) was evaluated for taste and health properties using an index based on major and trace mineral content and organoleptic components. Although various reports point to calcium (Ca²⁺) as a key ingredient imparting good taste and magnesium (Mg²⁺) and sulfate (SO₄ ^2?) as causing unpleasant taste in drinking water, recent sensory threshold experiments have indicated that other major ions and minerals directly or indirectly contribute to good taste, including potassium (K), silica (SiO₂), and phosphorous (P). The present study examined major and trace constituents in water to accurately quantify water taste, flavor, and health effects in good-tasting (Volvic, Toyama, and Kumamoto water) and average-tasting water (Osaka and Tokyo water). Trace metal, volatile organic carbon, non-purgeable organic carbon and total inorganic carbon levels were evaluated as parameters influencing the sensory properties of the drinking water. All of the representative good-tasting water contained higher amounts of tasty minerals (Ca²⁺, K⁺, SiO₂) and lower amounts of unsavory, rough (Mg²⁺ and SO₄ ^2?), and bitter (Cl^?) minerals. Stiff diagrams of the water samples indicated that good-tasting water was generally bicarbonate (HCO₃ ^?) type. Seasonal variations in physicochemical parameters did not change the order of abundance of cations and anions but did affect the concentration of various ions present in the water. Trace metals also affected water flavor. Mn facilitates acetaldehyde formation and Fe is associated with polyphenolic oxidation and formation of organoleptic flavor constituents. Trihalomethanes (THMs) may also cause unpleasant drinking water flavors or odors. THMs concentrations for all samples were below 5.7 μg/L, meeting the safety and taste requirements for good drinking water. The Japanese samples were compared against Volvic water, which was used as a standard for good-tasting water. Total dissolved solids concentrations were below 300 mg/L for all specimens, in compliance with World Health Organization guidelines. The results are discussed on the basis of the balance between inorganic major ions and trace minerals and THMs concentration thresholds.