Hydrochemistry and isotope compositions of groundwater from the Shihongtan sandstone-hosted uranium deposit, Xinjiang, NW China

Groundwaters and surface water in the Shihongtan sandstone-hosted U ore district, Xinjiang, NW China, were sampled and analyzed for their major-, and trace element concentrations and oxygen, hydrogen, boron and strontium isotope compositions in order to assess the possible origins of the waters and water–rock interactions that occurred in the deep aquifer system. The waters in the study district have been grouped into three hydrochemical facies: Facies 1, potable spring-water, is a pH neutral (7.0), Na–Ca–HCO₃ type water with low total dissolved solids (TDS; 0.2 g/l, fresh) and has δ¹⁸O of − 8.3‰, δD of − 48.2‰,δ¹¹B of 1.5‰, and ⁸⁷Sr/⁸⁶Sr of 0.70627. Facies 2 groundwaters are mildly acidic to mildly alkaline (pH of 6.5–8.0, mean 7.3), Na–Ca–Mg–Cl–SO₄ type waters with moderate TDS (8.2 g/l–17.2 g/l, mean 9.3 g/l, brackish) and haveδ¹⁸O values in the − 5.8‰ to − 9.3‰ range (mean − 8.1‰), δD values in the − 20.8‰ to − 85.5‰ range (mean − 47.0‰),δ¹¹B values in the + 9.5‰ to + 39.1‰ range (mean + 17.1‰), and ⁸⁷Sr/⁸⁶Sr values in the 0.70595 to 0.70975 range (mean 0.70826). Facies 3, Aiting Lake water, is a mildly alkaline (pH = 7.4), Na–Ca–Mg–Cl–SO₄ type water with the highest TDS (249.1 g/l, brine) and has δ¹⁸O of − 2.8‰, δD of − 45.8‰,δ¹¹B of 21.2‰, and ⁸⁷Sr/⁸⁶Sr of 0.70840. The waters from the study district show a systematic increase in major, trace element and TDS concentrations and δ¹¹B values along the pathway of groundwater migration which can only be interpreted in terms of water–rock interaction at depth and strong surface evaporation. The hydrochemical and isotopic data presented here confirm that the groundwaters in the Shihongtan ore district are the combined result of migration, water–rock interaction and mixing of meteoric water with connate waters contained in sediments.     

Zero-valent iron and organic carbon mixtures for remediation of acid mine drainage: Batch experiments

A series of laboratory batch experiments was conducted to evaluate the potential for treatment of acid mine drainage (AMD) using organic C (OC) mixtures amended by zero-valent Fe (Fe⁰). Modest increases in SO₄ reduction rates (SRRs) of up to 15% were achieved by augmenting OC materials with 5 and 10 dry wt% Fe⁰. However, OC was essential for supporting SO₄ reducing bacteria (SRB) and therefore SO₄ reduction. This observation suggests a general absence of autotrophic SRB which can utilize H₂ as an electron donor. Sulfate reduction rates (SRRs), calculated using a mass-based approach, ranged from −12.9 to −14.9 nmol L⁻¹ d⁻¹  g⁻¹ OC. Elevated populations of SRB, iron reducing bacteria (IRB), and acid producing (fermentative) bacteria (APB) were present in all mixtures containing OC. Effective removal of Fe (91.6–97.6%), Zn (>99.9%), Cd (>99.9%), Ni (>99.9%), Co (>99.9%), and Pb (>95%) was observed in all reactive mixtures containing OC. Abiotic metal removal was achieved with Fe⁰ only, however Fe, Co and Mn removal was less effective in the absence of OC. Secondary disordered mackinawite [Fe_1+xS] was observed in field-emission scanning electron microscopy (FE-SEM) backscatter electron micrographs of mixtures that generated SO₄ reduction. Energy dispersive X-ray (EDX) spectroscopy revealed that Fe–S precipitates were Fe-rich for mixtures containing OC and Fe⁰, and S-rich in the absence of Fe⁰ amendment. Sulfur K-edges determined by synchrotron-radiation based bulk X-ray absorption near-edge structure (XANES) spectroscopy indicate solid-phase S was in a reduced form in all mixtures containing OC. Pre-edge peaks on XANES spectra suggest tetragonal S coordination, which is consistent with the presence of an Fe–S phase such as mackinawite. The addition of Fe⁰ enhanced AMD remediation over the duration of these experiments, however long-term evaluation is required to identify optimal Fe⁰ and OC mixtures.     

Mercury mobilization by oxidative dissolution of cinnabar (α-HgS) and metacinnabar (β-HgS)

Cinnabar (α-HgS) and metacinnabar (β-HgS) dissolved at environmentally significant rates in oxygenated slurry experiments simulating a low-flow fluvial system. Based on SO₄²⁻ production, cinnabar dissolution rates were 2.64 to 6.16 μmol (SO₄²⁻) m^− 2 day^− 1, and metacinnabar dissolution rates were 1.20 to 1.90 μmol (SO₄²⁻) m^− 2 day^− 1. Monodentate-bound thiosulfate (S₂O₃²⁻) was identified as an oxidation product on the HgS surface by ATR-IR spectroscopy based on strong infrared absorption bands in the 1140–1145 cm^− 1 and 1006–1014 cm^− 1 regions. The presence of sulfide oxidation intermediates on the HgS surface indicates that SO₄²⁻ concentration underestimates α-HgS and β-HgS dissolution in this setting. Mercury release rates during dissolution were more than two orders of magnitude less than SO₄²⁻ production, but were significant: 0.47 mg (Hg) m^− 2 y^− 1 from cinnabar [6.45 nmol (Hg) m^− 2 day^− 1], and 0.17 mg (Hg) m^− 2 y^− 1 from metacinnabar [2.29 nmol (Hg) m^− 2 day^− 1]. The Hg mobilized during α-HgS and β-HgS dissolution is sufficient to form natural Au–Hg amalgam in downstream placer settings. The proportion of mercury that is not remobilized during α-HgS and β-HgS dissolution likely adsorbs to the dissolving mercuric sulfide. Adsorption of Hg²⁺ to cinnabar was detected in situ by anodic stripping voltammetry using a cinnabar-modified carbon paste electrode following accumulation of Hg²⁺ on the electrode at open circuit potential.     

Chemistry and sulfur isotopic composition of precipitation at Bologna, Italy

Individual and monthly precipitation samples from the polluted atmosphere of Bologna (Emilia-Romagna province) were collected during March 1996 to May 1997 and analyzed for major ions in solution and S isotopes in dissolved SO₄.Weighted mean enrichment factors relative to seawater are found to be 1.0 for Na, 15.2 for K, 105 for Ca, 3.3 for Mg, 17.3 for SO₄ and 663 for HCO⁻₃. Very good positive correlations are observed for the Ca²⁺–Mg²⁺–HCO⁻₃–SO²⁻₄–NO⁻₃ system, indicating that dissolution of Ca (±Mg)-carbonate particles by H₂SO₄ and HNO₃ from combustion of oil and gas is a major process controlling the chemical composition of rain and snow. Na⁺ and Cl⁻ in monthly precipitation derive essentially from sea spray, but the contribution of Na⁺ from continental sources is appreciable in a number of individual rains. NH⁺₄ appears to be on average more abundant in spring and summer precipitation, its main sources being microbial activity in soils and application of fertilizers. K⁺ is probably of continental origin from soil dust.The S isotopic composition of SO₄ is systematically positive, with mean δ³⁴S values of +3.2±1.6‰ (n=40) in individual precipitation and +2.8±1.4‰ (n=12) in monthly precipitation. These isotopic compositions are interpreted in terms of a dominant contribution of S from anthropogenic emissions and subordinate contributions from biogenic and marine sources. Pollutant SO₄ is estimated to have a δ³⁴S value in the range +2.5 to +4.5‰, whereas a distinctive δ³⁴S of −4.5‰ or lower indicates SO₄ from oxidation of biogenic gases.The isotopic and chemical compositions of SO₄ do not depend on wind direction, thus testifying to a mostly local source for pollutant S in the Bologna atmosphere.     

Hydrochemical appraisal of groundwater and its suitability in the intensive agricultural area of Muzaffarnagar district,Uttar Pradesh,India

Muzaffarnagar is an economically rich district situated in the most fertile plains of two great rivers Ganga and Yamuna in the Indo-gangetic plains, with agricultural land irrigated by both surface water as well as groundwater. An investigation has been carried out to understand the hydrochemistry of the groundwater and its suitability for irrigation uses. Groundwater in the study area is neutral to moderately alkaline in nature. Chemistry of groundwater suggests that alkaline earths (Ca + Mg) significantly exceed the alkalis (Na + K) and weak acids exceed the strong acids (Cl + SO₄), suggesting the dominance of carbonate weathering followed by silicate weathering. Majority of the groundwater samples (62%) posses Ca–Mg–HCO₃ type of hydrochemical species, followed by Ca–Na–Mg–HCO₃, Na–Ca–Mg–HCO₃, Ca–Mg–Na–HCO₃–Cl and Na–Ca–HCO₃–SO₄ types. A positive high correlation (r ² = 0.928) between Na and Cl suggests that the salinity of groundwater is due to intermixing of two or more groundwater bodies with different hydrochemical compositions. Barring a few locations, most of the groundwater samples are suitable for irrigation uses. Chemical fertilizers, sugar factories and anthropogenic activities are contributing to the sulphate and chloride concentrations in the groundwater of the study area. Overexploitation of aquifers induced multi componential mixing of groundwater with agricultural return flow waters is responsible for generating groundwater of various compositions in its lateral extent.     

Natural and anthropogenic budgets of a small watershed in the massif central (France): Chemical and strontium isotopic characterization of water and sediments

A small watershed (160 km²) located in the Massif Central (France) has been chemically, isotopically and hydrologically studied through its dissolved load, bed sediments and soils. This watershed is underlain by basaltic bedrock and associated soils in which the vegetation is dominated mainly by meadows.Dissolved concentrations of major ions (Cl, SO₄, NO₃, HCO₃, Ca, Na, Mg, K, Al and Si), trace elements (Rb and Sr) and strontium isotopes have been determined for two different hydrologic periods on the main stream of the Allanche river and its tributaries.The major objectives of this study were to characterize the chemical and isotopic signatures of each reservoir occurring in the watershed. Changes in chemical and isotopic signatures are interpreted in terms of fluctuations of the different components inputs: rainwater, weathering products, anthropogenic addition.Water quality may be influenced by natural inputs (rainwater, weathering processes) and anthropogenic additions (fertilizers, road salts, etc.). Precipitation serves as a major vehicle for dissolved chemical species in addition to the hydrosystem and, in order to constrain rain inputs, a systematic study of rainwaters is carried out over a one year period using an automatic collector. Corrections of rainwater addition using chloride as an atmospheric input reference were computed for selected elements and the Sr/Sr ratio. After such corrections, the geochemical budget of the watershed was determined and the role of anthropogenic additions evaluated through the relationship between strontium isotopes and major and trace element ratios. Thus, 10% of Ca and Na originate in rainwater input, 40 to 80% in fertilizer additions and 15 to 50% in rock weatheringThe cationic denudation rates for this watershed are around 0.3 g s^–1 km² during low water discharge and 0.6 g s^–1 km² in high water stage. This led to a chemical denudation rate of 5.3 mm/1000 years.For solid matter, the normalization of chemical species relative to parent rocks shows the depletion or enrichment in soils and sediments. The use of K and Ca as mobile reference illustrates the weathering state of soils and sediments relative to parent rocks. This weathering state for bed sediments range from 15 to 45% for the K normalization and from 2 to 50% for the Ca normalization. For the soils, the weathering state ranges from 15 to 57% for the K normalization and from 17 to 90% for the Ca normalization.     

Elevated naturally occurring arsenic in a semiarid oxidizing system, Southern High Plains aquifer, Texas, USA

High groundwater As concentrations in oxidizing systems are generally associated with As adsorption onto hydrous metal (Al, Fe or Mn) oxides and mobilization with increased pH. The objective of this study was to evaluate the distribution, sources and mobilization mechanisms of As in the Southern High Plains (SHP) aquifer, Texas, relative to those in other semiarid, oxidizing systems. Elevated groundwater As levels are widespread in the southern part of the SHP (SHP-S) aquifer, with 47% of wells exceeding the current EPA maximum contaminant level (MCL) of 10 μg/L (range 0.3–164 μg/L), whereas As levels are much lower in the north (SHP-N: 9%  As MCL of 10 μg/L; range 0.2–43 μg/L). The sharp contrast in As levels between the north and south coincides with a change in total dissolved solids (TDS) from 395 mg/L (median north) to 885 mg/L (median south). Arsenic is present as arsenate (As V) in this oxidizing system and is correlated with groundwater TDS (Spearman’s ρ = 0.57). The most likely current source of As is sorbed As onto hydrous metal oxides based on correlations between As and other oxyanion-forming elements (V, ρ = 0.88; Se, ρ = 0.54; B, ρ = 0.51 and Mo, ρ = 0.46). This source is similar to that in other oxidizing systems and constitutes a secondary source; the most likely primary source being volcanic ashes in the SHP aquifer or original source rocks in the Rockies, based on co-occurrence of As and F (ρ = 0.56), oxyanion-forming elements and SiO₂ (ρ = 0.41), which are found in volcanic ashes. High groundwater As concentrations in some semiarid oxidizing systems are related to high evaporation. Although correlation of As with TDS in the SHP aquifer may suggest evaporative concentration, unenriched stable isotopes (δ²H: −65 to −27; δ¹⁸O: −9.1 to −4.2) in the SHP aquifer do not support evaporation. High TDS in the SHP aquifer is most likely related to upward movement of saline water from the underlying Triassic Dockum aquifer. Mobilization of As in other semiarid oxidizing systems is caused by increased pH; however, pH in the SHP aquifer is near neutral (10–90 percentiles, 7.0–7.6). Although many processes, such as competitive desorption with SiO₂, VO₄, or PO₄, could be responsible for local mobilization of As in the SHP aquifer, the most plausible explanation for the regional As distribution and correlation with TDS is the counterion effect caused by a change from Ca- to Na-rich, water as shown by the high correlation between As and Na/(Ca)^0.5 ratios (ρ = 0.57). This change in chemistry is related to mixing with saline water that moves upward from the underlying Dockum aquifer. This counterion effect may mobilize other anions and oxyanion-forming elements that are correlated with As (F, V, Se, B, Mo and SiO₂). Competition among the oxyanions for sorption sites may enhance As mobilization. The SHP case study has similar As sources to those of other semiarid, oxidizing systems (original volcanic ash source followed by sorption onto hydrous metal oxides) but contrasts with these systems by showing lack of evaporative concentration and pH mobilization of As but counterion mobilization of As instead in the SHP-S aquifer.     

Geochemistry of S-type granitic rocks from the reversely zoned Castelo Branco pluton (central Portugal)

The zoned pluton from Castelo Branco consists of Variscan peraluminous S-type granitic rocks. A muscovite>biotite granite in the pluton's core is surrounded successively by biotite>muscovite granodiorite, porphyritic biotite>muscovite granodiorite grading to biotite=muscovite granite, and finally by muscovite>biotite granite. ID-TIMS U–Pb ages for zircon and monazite indicate that all phases of the pluton formed at 310 ± 1 Ma. Whole-rock analyses show slight variation in ⁸⁷Sr/⁸⁶Sr_310 Ma between 0.708 and 0.712, Nd_310 Ma values between − 1 and − 4 and δ¹⁸O values between 12.2 and 13.6. These geological, mineralogical, geochemical and isotopic data indicate a crustal origin of the suite, probably from partial melting of heterogeneous Early Paleozoic pelitic country rock. In detail there is evidence for derivation from different sources, but also fractional crystallization linking some of internal plutonic phases. Least-squares analysis of major elements and modelling of trace elements indicate that the porphyritic granodiorite and biotite=muscovite granite were derived from the granodiorite magma by fractional crystallization of plagioclase, quartz, biotite and ilmenite. By contrast variation diagrams of major and trace elements in biotite and muscovite, the behaviours of Ba in microcline and whole-rock δ¹⁸O, the REE patterns of rocks and isotopic data indicate that both muscovite-dominant granites were probably originated by two distinct pulses of granite magma.     

Composition and applied sedimentology of salt from brines of the Mamfe Basin, Cameroon

Salts produced using brines of the Mamfe Basin were analysed by XRD for their mineral composition and ICP-MS for minor element composition. Halite (NaCl) and dolomite (CaMg (CO₃)₂) constitute the major minerals with minor impurities from Mo and Cd in the chlorides and Sc and Cu in the carbonates. The mineral composition is evidence of dissolution of evaporites with parent brine of marine origin. Other elements analysed are suggested to be adsorbed to these salts and result from water–rock interaction. The elements partitioned based on their correlation to other elements are suggested to derive from sulphates including barite for Ba, sulphides for Pb, Zn, silicates for Zr, Mn and oxides for V, Cr. The electrical conductance of the brines is related to the salt yield by the equation; M = 9 × 10^− 4E− 3.27, and it can be used to estimate salt yield throughout the year. Over 1200 tons of salt consisting dominantly of grade I halite are lost annually as brines across the basin. Purification is required for some minor elements including Ba, Pb, Hg and Cd for use as a condiment. A genetic relation between the parent brine, sulphide minerals and organic matter-rich sediments is proposed.     

Lithogenic concentrations of trace metals in soils and saprolites over crystalline basement rocks: A case study from SW Nigeria

In this study, an assessment of the lithogenic concentrations of trace metals in soils and saprolite over basement rock units in Ibadan, SW-Nigeria is presented in respect of bedrock types and geochemical controls on the weathering-associated release of trace metals. Consequently, soil, weathered and fresh rock samples from the Precambrian Basement of SW Nigeria were collected from three different bedrock units within Ibadan metropolis and subjected to mineralogical and geochemical analyses. The analytical results revealed major proportions of oxides in the range of 18–20% Al₂O₃, 2–6% Na₂O and 1–6% K₂O for weathered profiles over granite-gneiss and pegmatite units, compared to 2–3% Al₂O₃, <0.5% Na₂O and <1.0% K₂O over schist-quartzite. For the trace elements, weathered profiles on granite-gneiss and schist-quartzite settings exhibit similar enrichment trends (enrichment factor, EF l) for most of the trace elements, unlike the pegmatite bedrock. However, enrichments are relatively greater in the top soil unit compared to the intermediate saprolite unit, especially for Pb, Ni, Zn, Cr, Co, Rb, Sr and Ba, a situation attributed to leaching and redistribution within the weathered profiles through pedogenetic process and percolating groundwater.Furthermore, the estimated weathering indices using Ruxton Ratio (RR = {SiO₂/Al₂O₃}) and Chemical Index of Alteration (CIA = 100{Al₂O₃/[Al₂O₃ + CaO + Na₂O + K₂O]}) revealed RR of 2.9–3.7 and CIA of 54–73% for granite-gneiss and pegmatite units, implying medium levels of weathering, compared to RR of 30.8–35.5 and CIA of >60% for schist-quartzite units, which suggest weak chemical weathering. Also, the estimated high percentage loss, especially for Pb, Rb, Sr, Ba relative to the bedrocks, shows that the trace elements can be mobilized within the weathering profiles even at a low degree of chemical weathering. Such weathering-induced release of trace metals is of environmental significance as natural lithogenic input sources and as background reference for future monitoring of possible human/anthropogenic impacts.     

A new view on gold speciation in sulfur-bearing hydrothermal fluids from in situ X-ray absorption spectroscopy and quantum-chemical modeling

Despite the common belief that Au^I complexes with hydrogen sulfide ligands (H₂S/HS⁻) are the major carriers of gold in natural hydrothermal fluids, their identity, structure and stability are still subjects of debate. Here we present the first in situ measurement, using X-ray absorption fine structure (XAFS) spectroscopy, of the stability and structure of aqueous Au^I–S complexes at temperatures and pressures (T–P) typical of natural sulfur-rich ore-forming fluids. The solubility of native gold and the local atomic structure around the dissolved metal in S–NaOH–Na₂SO₄–H₂SO₄ aqueous solutions were characterized at temperatures 200–450 °C and pressures 300–600 bar using an X-ray cell that allows simultaneous measurement of the absolute concentration of the absorbing atom (Au) and its local atomic environment in the fluid phase. Structural and solubility data obtained from XAFS spectra, combined with quantum-chemical calculations of species geometries, show that gold bis(hydrogensulfide) Au(HS)₂⁻ is the dominant Au species in neutral-to-basic solutions (5.5  pH  8.5; H₂O–S–NaOH) over a wide range of sulfur concentrations (0.2 < ΣS < 3.6 mol/kg), in agreement with previous solubility studies. Our results provide the first direct determination of this species structure, in which two sulfur atoms are in a linear geometry around Au^I at an average distance of 2.29 ± 0.01 Å. At acidic conditions (1.5  pH  5.0; H₂O–S–Na₂SO₄–H₂SO₄), the Au atomic environment determined by XAFS is similar to that in neutral solutions. These findings, together with measured high Au solubilities, are inconsistent with the predominance of the gold hydrogensulfide Au(HS)⁰ complex suggested by recent solubility studies. Our spectroscopic data and quantum-chemical calculations imply the formation of species composed of linear S–Au–S moieties, like the neutral [H₂S–Au–SH] complex. This species may account for the elevated Au solubilities in acidic fluids and vapors with H₂S concentrations higher than 0.1–0.2 mol/kg. However, because of the complex sulfur speciation in acidic solutions that involves sulfite, thiosulfate and polysulfide species, the formation of Au^I complexes with these ligands (e.g., AuHS(SO₂)⁰, Au(HS₂O₃)₂⁻, Au(HS_n)₂⁻) cannot be ruled out. The existence of such species may significantly enhance Au transport by high T–P acidic ore-forming fluids and vapors, responsible for the formation of a major part of the gold resources on Earth.     

Permo-Carboniferous volcanism in late Variscan continental basins of the Bohemian Massif (Czech Republic): geochemical characteristic

Extensive Permo-Carboniferous volcanism has been documented from the Bohemian Massif. The late Carboniferous volcanic episode started at the Duckmantian–Bolsovian boundary and continued intermittently until Westphalian D to Stephanian B producing mainly felsic and more rarely mafic volcanics in the Central Bohemian and the Sudetic basins. During the early Permian volcanic episode, after the intra-Stephanian hiatus, additional large volumes of felsic and mafic volcanics were extruded in the Sudetic basins. The volcanics of both episodes range from entirely subalkaline (calc-alkaline to tholeiitic) of convergent plate margin-like type to transitional and alkaline of within-plate character. A possible common magma could not be identified among the Carboniferous and Permian primitive magmas, but a common geochemical signature (enrichment in Th, U, REE and depletion in Nb, Sr, P, Ti) in the volcanic series of both episodes was recognized. On the other hand, volcanics of both episodes differ in intensities of Nb, Sr and P depletion and also, in part, in their isotope signatures. High ⁸⁷Sr/⁸⁶Sr (0.707–0.710) and low ε_Nd (−6.0 to −6.1) are characteristic of the Carboniferous mafic volcanics, whereas low ⁸⁷Sr/⁸⁶Sr (0.705–0.708) and higher ε_Nd ranging from −2.7 to −3.4 are typical of the Permian volcanics. Felsic volcanics of both episodes vary substantially in ⁸⁷Sr/⁸⁶Sr (0.705–0.762) and ε_Nd (−0.9 to −5.1). Different depths of magma source or heterogeneity of the Carboniferous and Permian mantle can be inferred from variation in some characteristic elements of the geochemical signature for volcanics in some basins. The Sr–Nd isotopic data with negative ε_Nd values confirm a significant crustal component in the volcanic rocks that may have been inherited from the upper mantle source and/or from assimilation of older crust during magmatic underplating and ascending of primary basic magma. Two different types of primary magma development and formation of a bimodal volcanic series have been recognized: (i) creation of a unique magma by assimilation fractional crystallization processes within shallow-level reservoirs (type Intra-Sudetic Basin) and (ii) generation and mixing of independent mafic and felsic magmas, the latter by partial melting of upper crustal material in a high-level chamber (type Krkonoše Piedmont Basin). A similar origin for the Permo-Carboniferous volcanics of the Bohemian Massif is obvious, however, their geochemical peculiarities in individual basins indicate evolution in separate crustal magma chambers.     

Integrated hydrochemical method of water quality assessment for irrigation in arid areas: application to the Jilh aquifer, Saudi Arabia

Water samples from 72 wells tapping the Jilh aquifer were collected and analyzed for 10 different water quality parameters. Using these data, a regional irrigation water quality was assessed using three techniques: (i) United States Department of Agriculture method (USDA), (ii) Food and Agriculture Organization (FAO) guidelines for water quality assessment, and (iii) Water-Types approach. The USDA method revealed that the aquifer water salinity, as represented by electrical conductivity, EC_w, ranges from high salinity (C3: EC_w > 0.75–2.25 dS/m) to a very high salinity (C4: EC_w > 2.25 dS/m). The sodium adsorption ratio (SAR) varied from low (S1) to very high (S4) sodicity. Therefore, the water of the Jilh aquifer is dominantly of the C4–S2 class representing 56% of the total wells followed by C4–S1, C4–S3, C3–S1 and C4–S4 classes at 19%, 14%, 8%, and 3% of the wells respectively. The FAO system indicated moderate to severe restriction on the use for irrigation and slight to moderate ion toxicities for Na⁺, Cl⁻, B⁺, NO₃⁻ and HCO₃⁻. It is clear that, both USDA and FAO systems condemn the Jilh groundwater as hazardous for irrigation due to its high salt content, unless certain measures for salinity control are undertaken. The dominant salt constituents in the water are Mg–Cl₂, Na–Cl and Ca–Cl₂ as per the Water-Types method. However, due to the complexity in classifying the aquifer groundwater for irrigation, a simplified approach acknowledging three class groups (I-suitable water, II-conditionally suitable water and III-unsuitable water) adopted from the three methods, is suggested in this paper. The simplified approach combines C–S classes of the USDA method among these three groups according to the lowest ratings. The salinity of the FAO method has been split arbitrarily into slight and moderate subclasses with values of 0.7–2.25 and >2.25 dS/m, respectively; to match with the C3-class of the USDA system. The Water-Types were classified assuming that Ca–Cl₂ is the least hazardous salt, followed by Mg–Cl₂ and Na–Cl. Using this integrated hydrochemical method, the majority of the wells (92%) contain unsuitable water for irrigation (Group III) while the remaining wells (8%) are in Group II with water considered conditionally suitable for irrigation.     

Characterization of the reactivity of riverine heterogeneous sediments using a facies-based approach; the Rhine–Meuse delta (The Netherlands)

Large groundwater resources are found in densely populated lowland areas, which consist often of young unconsolidated and reduced sediments. When anthropogenic activities lead to oxygenation of the aquifer, breakdown of the main reduced fractions, i.e. sedimentary organic matter (SOM) and pyrite, could lead to severe groundwater deterioration such as acidification, heavy metal mobilization, and increased hardness. The characterization of the reactive properties of these sediments is important in predicting groundwater deterioration, but is often complicated by the high degree of heterogeneity of these sediments. In this study, the potential reduction capacity (PRC, based on SOM and pyrite content), the potential buffer capacity (PBC, based on carbonate content), potential acidification capacity (PAC, based on the potential acid production by sulfide oxidation), and the measured reduction capacity (MRC) of five facies, which are typical of the riverine sediments in the Rhine–Meuse delta (The Netherlands) were determined. A universal facies-classification model was used to classify the deposits into more homogeneous sub-units based on lithologic and geogenic properties, with a further sub-division into oxic or anoxic redox environment based upon groundwater data and field observations. The bulk chemical data show strong variation across facies for the median values of PRC (186–9093 mmol O₂ kg⁻¹), PBC (17–132 mmol O₂ kg⁻¹), and PAC (36–1530 mmol H⁺ kg⁻¹). The MRC was measured as reactivity to molecular O₂ exposure and was 0.5–567.3 mmol O₂ kg⁻¹. Steady-state oxidation rates were in the wide range of 0.001–10.355 mmol O₂ kg⁻¹ day⁻¹ but were typically about 3–8 times faster in fine facies than in coarse facies. Both the PRC and MRC depend strongly on grain size, but also on the syn/post-depositional environment and redox conditions. The main part of the PRC consists of SOM, but pyrite reactivity is higher than SOM reactivity as shown by the relative depletion of pyrite in oxic subfacies and the preferential oxidation during the oxidation experiments. Some facies are very prone to acidification because the PAC is higher than the PBC, but the oxidation experiments also show that acidification could already start before the PRC is fully exhausted. This study, is one of the few that combines bulk chemical data, groundwater data, and reactivity measurements and shows that a facies-based approach is a practical tool in characterizing the reactivity of heterogeneous deposits.     

Study on the kinetics of iron oxide leaching by oxalic acid

The presence of iron oxides in clay or silica raw materials is detrimental to the manufacturing of high quality ceramics. Although iron has been traditionally removed by physical mineral processing, acid washing has been tested as it is more effective, especially for extremely low iron (of less than 0.1% w/w). However, inorganic acids such as sulphuric or hydrochloric acids easily contaminate the clay products with SO₄²⁻ and Cl⁻, and therefore should be avoided as much as possible. On the other hand, if oxalic acid is used, any acid left behind will be destroyed during the firing of the ceramic products. The characteristics of dissolution of iron oxides were therefore investigated in this study.The dissolution of iron oxides in oxalic acid was found to be very slow at temperatures within the range 25–60 °C, but its rate increases rapidly above 90 °C. The dissolution rate also increases with increasing oxalate concentration at the constant pH values set within the optimum range of pH2.5–3.0. At this optimum pH, the dissolution of fine pure hematite (Fe₂O₃) (105–140 μm) follows a diffusion-controlled shrinking core model. The rate expression expressed as 1 − (2 / 3)x − (1 − x)^2 / 3 where x is a fraction of iron dissolution was found to be proportional to [oxalate]^1.5.The addition of magnetite to the leach liquor at 10% w/w hematite was found to enhance the dissolution rate dramatically. Such addition of magnetite allows coarser hematite in the range 0.5–1.4 mm to be leached at a reasonable rate.     

Permian basaltic rocks in the Tarim basin, NW China: Implications for plume–lithosphere interaction

There are large areas of Permian basaltic rocks in the Tarim basin (PBRT) in northwestern China. Precise Ar–Ar dating of these rocks revealed an eruption age span of 262 to 285 Ma. Most of the PBRT is composed of alkaline basaltic rocks with high TiO₂ (2.43%–4.59%, weight percent), high Fe₂O₃ + FeO (12.63%–17.83%) and P₂O₅ (0.32%–1.38%) contents. Trace elements of these rocks have affinities with oceanic island basalts (OIB), as shown in chondrite normalized rare earth elements (REE) diagrams and primitive mantle normalized incompatible elements diagrams. The rocks show complex Sr–Nd isotopic character based on which they can be subdivided into two distinct groups: group 1 has relatively small initial (t = 280 Ma)⁸⁷Sr/⁸⁶Sr ratio ( 0.7048) and positive εNd(t) (3.42–4.66) values. Group 2 has relatively large initial ⁸⁷Sr/⁸⁶Sr ratio (0.7060–0.7083) and negative εNd(t) (from − 2.79 to − 2.16) values. Lead isotopes are even more complex with variations of (²⁰⁶Pb/²⁰⁴Pb)t, (²⁰⁷Pb/²⁰⁴Pb)t and (²⁰⁸Pb/²⁰⁴Pb)t ranging from 17.9265 to 18.5778, 15.4789 to 15.6067 and 37.2922 to 38.1437, respectively. Moreover, these two groups have different trace elements ratios such as Nb/La, Ba/Nb, Zr/Nb, Nb/Ta and Zr/Hf, implying different magmatic processes. Based on the geochemistry of basaltic rocks and an evaluation of the tectonics, deformation, and the compositions of crust and lithospheric mantle in Tarim, we conclude that these basaltic rocks resulted from plume–lithosphere interaction. Permian mantle plume caused an upwelling of the Tarim lithosphere leading to melting of the asthenospheric mantle by decompression. The magma ascended rapidly to the base of lower crust, where different degrees of assimilation of OIB-like materials and fractionation occurred. Group 1 rocks formed where the upwelling is most pronounced and the assimilation was negligible. In other places, different degrees of assimilation and fractionation account for the geochemical traits of group 2.     

Chemistry and sulfur isotope investigation of industrial wastewater contamination into groundwater aquifers, Piteå County, N. Sweden

The possible contamination of a groundwater system with industrial wastewater originating from a paper mill factory has been investigated in Piteå, N. Sweden. Six samples were collected from the wastewater in the waste dump and twelve samples from the adjacent groundwater were analyzed for chemistry and sulfur isotopes. The industrial wastewater is a saline water consisting mainly of Na–HCO₃–SO₄, having a high pH and showing δ³⁴S values between 7‰ and 9‰ affected by bacterial sulfate reduction. The groundwaters are relatively dilute, dominated by Na⁺, Ca²⁺ and HCO₃⁻, but with varying concentrations as exemplified by sulfate with concentrations varying between 3 and 69 mg L^− 1 while the δ³⁴S values range from − 0.5‰ to 14.3‰. The data suggest that the main S sources in the waters are the bedrock sulfides and/or atmospheric deposition, which, sometimes, are overlapped by bacterial sulfate reduction. Contamination from the waste dump does not occur.     

A low δLi lower crustal component: Evidence from an alkalic intraplate volcanic series (Chaîne des Puys, French Massif Central)

The intraplate volcanic suite of the Chaîne des Puys (French Massif Central) shows a complete petrologic range, from alkali basalts to trachytes. The significant variations of trace elements and radiogenic isotopes along the series strongly support the occurrence of crustal assimilation associated with fractional crystallization (AFC). The least contaminated basalts are clearly related to a HIMU-type reservoir (²⁰⁶Pb/²⁰⁴Pb > 19.6; ⁸⁷Sr/⁸⁶Sr < 0.7037; ε_Nd > + 4). The behavior of radiogenic isotopes suggests that the most likely crustal contaminants are meta-sediments located in the lower crust.The Li isotopic compositions of the lavas range from high δ⁷Li (> + 7‰) in basalts to lighter values in more evolved lavas (down to δ⁷Li ≈ 0‰). The mantle component, expressed in the least evolved lavas, has a heavy Li isotopic signature, in good agreement with previous δ⁷Li measurements of OIB lavas with HIMU affinities. The evolution of Li isotopic compositions throughout the volcanic series is in agreement with the AFC model suggested by the Sr–Nd–Pb isotopic systems. Although the behavior of Li isotopes during assimilation processes is currently poorly constrained, our calculations suggest that at least a portion of the lower crust beneath the Chaîne des Puys is characterized by a light Li isotopic composition (δ⁷Li < − 5‰).     

Geochemistry of sulphate-bearing water of Akra Kaur Dam,Gwadar, Balochistan,Pakistan and its assessment for drinking and irrigation purposes

This paper is an attempt to study the geochemistry of Akra Kaur Dam (AKD) water, north of Gwadar city, southern Balochistan. Representative water samples were collected from AKD reservoir to assess the suitability of water for drinking and agriculture purposes. The major ionic composition is suggestive for freshwater. The average ionic composition demonstrate SO₄ > Ca > Na > Cl > HCO₃ > Mg > K. The plots on Piper diagram reflected Ca–Mg–SO₄ type of water facies. High Ca/SO₄ and Ca/Mg ratios revealed that the water has influence of gypsum dissolution. The negative ratio of chloro-alkaline indices indicated reverse exchange between Ca and Mg in water occurred with Na and K in rocks. The pH, electrical conductivity, total dissolved salts, Ca, Mg, Na, K, HCO₃, Cl and SO₄ concentrations in the dam water were below the permissible limit, however, Na and SO₄ were above the desirable limit, set by the World Health Organization. Important parameters such as residue sodium carbonate, sodium percent, sodium adsorption ratio, permeability index, magnesium content and Kelley’s ratio were calculated to evaluate the suitability of water for irrigation purpose. The result were compared with standard permissible limits and found satisfactory. The health and agriculture hazards of sulphate-bearing water were also discussed.     

Correlation between local structure and molar ratio of Au (III) complexes in aqueous solution: An XAS investigation

The local and geometrical structure around gold (III) e.g., Au³⁺ ions in aqueous solution with different OH⁻/Cl⁻ molar ratios, has been investigated by X-ray absorption spectroscopy (XAS). X-ray absorption near-edge structure (XANES) spectra of [AuCl_n(OH)_4−n]⁻ solutions have been calculated and the multiple-scattering spectral features have been attributed to Cl d-states, axial water molecules and the replacement of Cl⁻ ligands by OH⁻ ligands. A square–planar geometry for [AuCl_n(OH)_4−n]⁻ with two axial water molecules has been identified. Moreover, a spectral correlation between XANES features and the type of planar atoms has been identified. By extended X-ray absorption fine structure spectra (EXAFS), the planar Au bond distances in the solutions have also been determined, e.g., 2.28 Å for Au–Cl and 1.98 Å for Au–O, respectively. The same EXAFS analysis provides evidence that the peak at about 4.0 Å in solutions with the lowest OH⁻/Cl⁻ molar ratio arises from collinear Cl–Au–Cl multiple-scattering contributions. For the first time, a complete detailed reconstruction of the hydration structure of an Au ion at different pH values has been achieved.