| 1. |
- Peng, Bo, et al.
(författare)
-
Geochemistry of major and trace elements and Pb-Sr isotopes of a weathering profile developed on the Lower Cambrian black shales in central Hunan, China
- 2014
-
Ingår i: Applied Geochemistry. - : Elsevier BV. - 0883-2927 .- 1872-9134. ; 51, s. 191-203
-
Tidskriftsartikel (refereegranskat)abstract
- This paper reports a geochemical study on the major and trace elements and Pb-Sr isotopes of a weathering profile developed in the Lower Cambrian black shales in central Hunan (China). Six weathering horizons were identified and sampled vertically throughout the profile. The chemical composition of the profile consists of variable concentrations of the major elements Fe2O3, FeO, MnO, MgO, CaO, Na2O, and P2O5 and of less variable concentrations of SiO2, TiO2, Al2O3, and K2O. The chemical change caused by weathering is estimated by mass-balance calculations, and the results show that the element mobility is characterised by substantial loss of SiO2, FeO, CaO, K2O, Na2O, LOI, Cr, V, Ba, Cs, Rb, Sr, U, and Th, and moderate loss of Al2O3, MgO, Fe2O3, Ni, Cu, Pb, Tl, Sn, Sc, Ge and REE (Y). The high field strength elements TiO2, Sn, Sc, U, Ga, Ge, Zr, Hf, Nb, and Ta were immobile during weathering. The chemical changes and the Pb-Sr isotopic data suggest that four types of chemical reactions occurred: the oxidation of sulphide minerals (e.g., pyrite) and organic carbon (OS), the dissolution of less resistant clinochlore-Ia, calcite, and P-bearing minerals (DL), the dissolution of detrital albite and microcline (DA), and the transformation of clay (TC) minerals (e.g., muscovite and illite-smectite). These chemical reactions then led to two stages of geochemical processes, an early stage of chemical differentiation and a later stage of chemical homogenisation. The chemical differentiation dominated by the OS, DL, and DA reactions, led to the leaching of mobile elements (e.g., MgO, Na2O, K2O, P2O5, Sr, and REE) and the redistribution of some less mobile elements (e.g., SiO2 and Al2O3). In contrast, the chemical homogenisation, which was caused by TC reactions, led to the leaching of both mobile and less mobile elements from the system and ultimately transformed the weathered black shales into soil. Soils derived from black shales in South China might result from the above two geochemical processes. (C) 2014 Elsevier Ltd. All rights reserved.
|
|
| 2. |
- Xu, Jingzhe, et al.
(författare)
-
Geochemistry of soils derived from black shales in the Ganziping mine area, western Hunan, China
- 2013
-
Ingår i: Environmental Earth Sciences. - : Springer Science and Business Media LLC. - 1866-6280 .- 1866-6299. ; 70:1, s. 175-190
-
Tidskriftsartikel (refereegranskat)abstract
- The geochemistry of major and trace elements (including heavy metals and rare earth elements) of the fresh and weathered black shales, and the soils derived from black shales in the Ganziping mine area in western Hunan province (China) were studied using the following techniques: X-ray fluorescence (XRF), inductively coupled plasma mass spectrometer (ICP-MS) and X-ray diffraction (XRD). The results show that the black-shale soils are significantly enriched with Al2O3 and Fe2O3, and depleted of mobile elements CaO, Na2O and K2O. The soils are also highly enriched with heavy metals U, V, Ni, Ba, Cu, Zn and Pb, that may cause potential heavy-metal contamination of the soils. Composition of the soils is homogeneous compared to the weathered black shales, for which the concentrations of major elements except CaO and Na2O, and trace elements except heavy metals (U, V, Ni, Ba, Cu, Zn and Pb) as well as the mobile Sr, show lower variations than in the weathered black shales. Ratios of Zr/Hf, Ta/Nb, Y/Ho, Nd/Sm, and Ti/(Ti + Zr), of the soils are also less variable, with values constantly similar to that of the fresh and weathered black shales correspondingly. Thus, components of the soils are believed to be contributed from the parent black shales through weathering and pedogenesis. It is concluded that the soils were formed by at least two stages of geochemical processes: the early stage of chemical differentiation and the later stage of chemical homogenization. The chemical differentiation that was taken during black-shale weathering might have caused the depletion of CaO and Na2O, and the enrichment of Al2O3 and Fe2O3; while the chemical homogenization that was taken during pedogenesis led to the depletion of SiO2 and K2O, and to the further enrichment of Al2O3 and Fe2O3. The heavy-metal enrichment (contamination) of the soils was then genetically related to the enrichment of Al2O3 and Fe2O3 in the soils.
|
|
| 3. |
- Yu, Changxun, 1983-, et al.
(författare)
-
Cerium Sequestration in Fractures in the Upper Kilometer of Granitoids, SE, Sweden
- 2013
-
Ingår i: Mineralogical magazine. - : Cambridge University Press. - 0026-461X .- 1471-8022. ; 77:5, s. 2568-2568
-
Tidskriftsartikel (refereegranskat)abstract
- This study seeks to define geochemical processes governing the accumulation and sequestration of Ce in granitoidic fractures down to >700 m depth, revealing past intrusions of oxygenated waters. The fracture coatings (secondary mineral precipitates in open fractures) gathered from the study area (Laxemar, SE Sweden) are characterized by high levels of Ce (Fig. 1b) compared to host rock cocentration (average: 86 ppm, n=65) and show a striking feature of distinct positive Ce anomalies (CeWN*=1.21-3.95, n=8) in the uppermost 20 m of the bedrock (Fig. 1a). Cerium and Mn X-ray absorption spectroscopy (XAS) of selected fracture coatings, together with existing data (e.g. fracture mineralogy and groundwater chemistry), indicate that: (1) Ce(IV) occurs down to c.a. 70 m depth and is exclusively associated with Mn oxides which occur as todorokite and triclinic birnessite as suggested by Mn EXAFS spectra; (2) Since Mn is largely speciated as Mn2+ in the present bedrock groundwaters, the Ce(IV)-bearing Mn oxides most probably resulted from oxidative weathering of wall rock and fracture coating minerals when oxygenated waters intruded into the bedrock (down to several hundred meters depth) during deglacation events (>13000 BP); (3) Unlike other samples, clear XAS features of a poorly-crystalline hexagonalbirnessite-like phase and larger proportion of aqueous Mn2+ were observed in the sample with strikingly positive Ce anomaly (CeWN* = 3.95) (Fig. 1b) at the depth of 0.87 m, suggesting an ongoing dynamic accumulatinon of Ce(IV), i.e. dissolution and reprecipiation of Mn oxides while Ce(IV)- enriched residue largely remained.
|
|
| 4. |
- Yu, Changxun, et al.
(författare)
-
Effect of weathering on abundance and release of potentially toxic elements in soils developed on Lower Cambrian black shales, P. R. China
- 2012
-
Ingår i: Environmental Geochemistry and Health. - : Springer. - 0269-4042 .- 1573-2983. ; 34:3, s. 375-390
-
Tidskriftsartikel (refereegranskat)abstract
- This paper examines the geochemical features of 8 soil profiles developed on metalliferous black shales distributed in the central parts of the South China black shale horizon. The concentrations of 21 trace elements and 8 major elements were determined using ICP-MS and XRF, respectively, and weathering intensity (W) was calculated according to a new technique recently proposed in the literature. The data showed that the black shale soils inherited a heterogeneous geochemical character from their parent materials. A partial least square regression model and EFbedrock (enrichment factor normalized to underlying bedrock) indicated that W was not a major control in the redistribution of trace metals. Barium, Sn, Cu, V, and U tended to be leached in the upper soil horizons and trapped by Al and Fe oxides, whereas Sb, Cd, and Mo with negative EF values across the whole profiles may have been leached out during the first stage of pedogenesis (mainly weathering of black shale). Compared with the Chinese average soils, the soils were strongly enriched in the potentially toxic metals Mo, Cd, Sb, Sn, U, V, Cu, and Ba, among which the 5 first listed were enriched to the highest degrees. Elevated concentrations of these toxic metals can have a long-term negative effect on human health, in particular, the soils in mining areas dominated by strongly acidic conditions. As a whole, the black shale soils have much in common with acid sulfate soils. Therefore, black shale soils together with acid sulfate soils deserve more attention in the context of metal exposure and human health.
|
|
| 5. |
|
|
| 6. |
|
|
| 7. |
- Yu, Changxun, 1983-, et al.
(författare)
-
Retention and transport of arsenic, uranium and nickel in a black shale setting revealed by a long-term humidity cell test and sequential chemica extractions
- 2014
-
Ingår i: Chemical Geology. - : Elsevier BV. - 0009-2541 .- 1872-6836. ; 363, s. 134-144
-
Tidskriftsartikel (refereegranskat)abstract
- The dispersion of acidic solutions with high levels of metals/metalloids, as a result of oxidative weathering of pyritic geomaterials, is a major environmental problem in areas where these materials are widely distributed and/or were historically mined. In this study, four types of materials encountered in an old black-shale mining area (unweathered black shale, weathered black shale, burnt black shale, and lime-mixed burnt black shale) were subjected to a long-term (up to 137 weeks) humidity cell test (HCT) combined with sequential chemical extractions (SCE), with the aim of examining geochemical controls on the release of Ni, U and As in this kind of pyritic settings. By combining the results of HCT and SCE as well as previously collected groundwater data, it is clearly shown that the degree of pyrite oxidation is the only major factor controlling the release of Ni, resulting in its highly elevated concentrations in acidic groundwaters. Although U followed a similar leaching pattern as observed for Ni and occurred abundantly in acidic groundwaters, a major decrease in the chemical fraction targeting exchangeable and carbonate phases, and a correlation of U concentrations with redox potential in groundwaters collectively suggest that the release of U was largely controlled by the solubilization of sorbed/carbonate U phases by oxidation to the highly soluble form (UO22+). As compared to the HCT, the SCE procedures used in this study delivered equally good estimates of Ni, U and S cumulatively leached, suggesting the strength of the SCE in terms of quantification of these elements during the weathering of pyritic geomaterials. Arsenic X-ray absorption near-edge structure spectroscopy shows that during the HCT (oxidation and leaching) of unweathered black shale, As was oxidized from its reduced form (having the oxidation state of -1 and most probably occurs as arsenian pyrite) to As(+5). Compared to the two cationic metals, As was released to a very limited extent and was not detectable in the leachates having pH between 6 and 3. This is because As was speciated exclusively as negatively-charged oxyanions in these leachates as predicted by MINTEQ modeling, thus was effectively attenuated by concurrently formed iron minerals. These minerals include mainly schwertmannite and K-jarosite as observed by SEM-EDS and also predicted by MINTEQ modeling. Elevated levels of As exclusively occurred in the groundwaters from one tube strongly impacted by seawater intrusion. This was regarded as a reflection of loosely-sorbed As oxyanions reliberated through ion exchange with seawater chloride. In this context, sea-level rise on a global scale as a potential driver for arsenic remobilization in low-lying coastal areas deserves further attention.
|
|
