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Geochemical Transactions

Timothy A Doane
The participation of sunlight in the natural chemistry of the earth is presented as a unique field of study, from historical observations to prospects for future inquiry. A compilation of known reactions shows the extent of light-driven interactions between naturally occurring components of land, air, and water, and provides the backdrop for an outline of the mechanisms of these phenomena. Catalyzed reactions, uncatalyzed reactions, direct processes, and indirect processes all operate in natural photochemical transformations, many of which are analogous to well-known biological reactions...
2017: Geochemical Transactions
Samantha L Shumlas, Soujanya Singireddy, Akila C Thenuwara, Nuwan H Attanayake, Richard J Reeder, Daniel R Strongin
The effect of simulated solar radiation on the oxidation of arsenite [As(III)] to arsenate [As(V)] on the layered manganese oxide, birnessite, was investigated. Experiments were conducted where birnessite suspensions, under both anoxic and oxic conditions, were irradiated with simulated solar radiation in the presence of As(III) at pH 5, 7, and 9. X-ray absorption spectroscopy (XAS) was used to determine the nature of the adsorbed product on the surface of the birnessite. The oxidation of As(III) in the presence of birnessite under simulated solar light irradiation occurred at a rate that was faster than in the absence of light at pH 5...
2016: Geochemical Transactions
John C Ayers, Steven Goodbred, Gregory George, David Fry, Laura Benneyworth, George Hornberger, Kushal Roy, Md Rezaul Karim, Farjana Akter
BACKGROUND: High salinity and arsenic (As) concentrations in groundwater are widespread problems in the tidal deltaplain of southwest Bangladesh. To identify the sources of dissolved salts and As, groundwater samples from the regional shallow Holocene aquifer were collected from tubewells during the dry (May) and wet (October) seasons in 2012-2013. Thirteen drill cores were logged and 27 radiocarbon ages measured on wood fragments to characterize subsurface stratigraphy. RESULTS: Drill cuttings, exposures in pits and regional studies reveal a >5 m thick surface mud cap overlying a ~30 m thick upper unit of interbedded mud and fine sand layers, and a coarser lower unit up to 60 m thick dominated by clean sands, all with significant horizontal variation in bed continuity and thickness...
2016: Geochemical Transactions
Iván A Reyes, Ister Mireles, Francisco Patiño, Thangarasu Pandiyan, Mizraim U Flores, Elia G Palacios, Emmanuel J Gutiérrez, Martín Reyes
BACKGROUND: The presence of natural and industrial jarosite type-compounds in the environment could have important implications in the mobility of potentially toxic elements such as lead, mercury, arsenic, chromium, among others. Understanding the dissolution reactions of jarosite-type compounds is notably important for an environmental assessment (for water and soil), since some of these elements could either return to the environment or work as temporary deposits of these species, thus would reduce their immediate environmental impact...
2016: Geochemical Transactions
Yinian Zhu, Bin Huang, Zongqiang Zhu, Huili Liu, Yanhua Huang, Xin Zhao, Meina Liang
BACKGROUND: The interaction between Ca-HAP and Pb(2+) solution can result in the formation of a hydroxyapatite-hydroxypyromorphite solid solution [(PbxCa1-x)5(PO4)3(OH)], which can greatly affect the transport and distribution of toxic Pb in water, rock and soil. Therefore, it's necessary to know the physicochemical properties of (PbxCa1-x)5(PO4)3(OH), predominantly its thermodynamic solubility and stability in aqueous solution. Nevertheless, no experiment on the dissolution and related thermodynamic data has been reported...
2016: Geochemical Transactions
Amanda H Meena, Yuji Arai
BACKGROUND: Reductive precipitation of hexavalent chromium (Cr(VI)) with magnetite is a well-known Cr(VI) remediation method to improve water quality. The rapid (<a few hr) reduction of soluble Cr(VI) to insoluble Cr(III) species by Fe(II) in magnetite has been the primary focus of the Cr(VI) removal process in the past. However, the contribution of simultaneous Cr(VI) adsorption processes in aged magnetite has been largely ignored, leaving uncertainties in evaluating the application of in situ Cr remediation technologies for aqueous systems...
2016: Geochemical Transactions
Tianyu Gao, Yougang Shen, Zhaoheng Jia, Guohong Qiu, Fan Liu, Yashan Zhang, Xionghan Feng, Chongfa Cai
BACKGROUND: In soils and sediments, manganese oxides and oxygen usually participate in the oxidation of ferrous ions. There is limited information concerning the interaction process and mechanisms of ferrous ions and manganese oxides. The influence of air (oxygen) on reaction process and kinetics has been seldom studied. Because redox reactions usually occur in open systems, the participation of air needs to be further investigated. RESULTS: To simulate this process, hexagonal birnessite was prepared and used to oxidize ferrous ions in anoxic and aerobic aqueous systems...
December 2015: Geochemical Transactions
Rebecca B Chesne, Christopher S Kim
[This corrects the article DOI: 10.1186/1467-4866-15-6.].
2015: Geochemical Transactions
Matthew H H Fischel, Jason S Fischel, Brandon J Lafferty, Donald L Sparks
BACKGROUND: Manganese-oxides are one of the most important minerals in soil due to their widespread distribution and high reactivity. Despite their invaluable role in cycling many redox sensitive elements, numerous unknowns remain about the reactivity of different manganese-oxide minerals under varying conditions in natural systems. By altering temperature, pH, and concentration of arsenite we were able to determine how manganese-oxide reactivity changes with simulated environmental conditions...
2015: Geochemical Transactions
Christopher H House
BACKGROUND: Due to the biogeochemical fractionation of isotopes, organic material can be heterogeneous at the microscale. Because this heterogentiy preserves in the rock record, the microscale measurement of carbon isotopes is an important frontier of geobiology. Such analyses via secondary ion mass spectrometry (SIMS) have been, however, held back by the lack of an appropriate homogeneous synthetic standard that can be shared between laboratories. Such a standard would need to yield a carbon signal intensity within the same instrument dynamic range as that found for typical rocks, exhibit minimal matrix effects under typical SIMS conditions, and be widely available...
2015: Geochemical Transactions
Aurélie Chagneau, Francis Claret, Frieder Enzmann, Michael Kersten, Stephanie Heck, Benoît Madé, Thorsten Schäfer
BACKGROUND: In geochemically perturbed systems where porewater and mineral assemblages are unequilibrated the processes of mineral precipitation and dissolution may change important transport properties such as porosity and pore diffusion coefficients. These reactions might alter the sealing capabilities of the rock by complete pore-scale precipitation (cementation) of the system or by opening new migration pathways through mineral dissolution. In actual 1D continuum reactive transport codes the coupling of transport and porosity is generally accomplished through the empirical Archie's law...
2015: Geochemical Transactions
Sylvain Grangeon, Alejandro Fernandez-Martinez, Fabienne Warmont, Alexandre Gloter, Nicolas Marty, Agnieszka Poulain, Bruno Lanson
BACKGROUND: Vernadite is a nanocrystalline and turbostratic phyllomanganate which is ubiquitous in the environment. Its layers are built of (MnO6)(8-) octahedra connected through their edges and frequently contain vacancies and  (or) isomorphic substitutions. Both create a layer charge deficit that can exceed 1 valence unit per layer octahedron and thus induces a strong chemical reactivity. In addition, vernadite has a high affinity for many trace elements (e.g., Co, Ni, and Zn) and possesses a redox potential that allows for the oxidation of redox-sensitive elements (e...
2015: Geochemical Transactions
Huiqin Zhang, Yan Li, Xin Wang, Anhuai Lu, Hongrui Ding, Cuiping Zeng, Xiao Wang, Xiaolei Wu, Yong Nie, Changqiu Wang
BACKGROUND: Mn oxides occur in a wide variety of geological settings and exert considerable influences on the components and chemical behaviors of sediments and soils. Microbial reduction of Mn oxides is an important process found in many different environments including marine and freshwater sediments, lakes, anoxic basins, as well as oxic-anoxic transition zone of ocean. Although the pathway of Mn anaerobic reduction by two model bacteria, Geobacter and Shewanella, has been intensively studied, Mn bio-reduction is still the least well-explored process in nature...
2015: Geochemical Transactions
Hao-Jie Cui, Hai-Zheng Huang, Baoling Yuan, Ming-Lai Fu
BACKGROUND: Organic dye pollution in water has become a major source of environmental pollution. Mn(III/IV) oxides have attracted a great deal of attention to remove organic dye pollutants due to their unique structures and physicochemical properties. Numerous studies have reported the removal of dye by various Mn(III/IV) oxides through catalytic degradation and adsorption. The crystalline structures of manganese oxides and solution pH may exert substantial impact on the removal of dyes...
2015: Geochemical Transactions
Yinian Zhu, Zongqiang Zhu, Xin Zhao, Yanpeng Liang, Liuqin Dai, Yanhua Huang
BACKGROUND: The substitution of Ca(2+) in Ca-hydroxylapatite by toxic Cd(2+) can cause the forming of Cd-hydroxylapatite and is a significant issue in a great variety of research areas, which hence needs an understanding of the essential physicochemical characteristics. Unfortunately, the solubility product and thermodynamic data for Cd-hydroxylapatite in water under a variety of conditions now are lacking. Little information has been reported by previous researchers. Additionally, the dissolution mechanism of Cd-hydroxylapatite has never been studied...
2015: Geochemical Transactions
Huaiyan Zhao, Xinran Liang, Hui Yin, Fan Liu, Wenfeng Tan, Guohong Qiu, Xionghan Feng
BACKGROUND: Todorokite, a 3 × 3 tectomanganate, is one of three main manganese oxide minerals in marine nodules and can be used as an active MnO6 octahedral molecular sieve. The formation of todorokite is closely associated with the poorly crystalline phyllomanganates in nature. However, the effect of the preparative parameters on the transformation of "c-disordered" H(+)-birnessites, analogue to natural phyllomanganates, into todorokite has not yet been explored. RESULTS: Synthesis of "c-disordered" H(+)-birnessites with different average manganese oxidation states (AOS) was performed by controlling the MnO4 (-)/Mn(2+) ratio in low-concentrated NaOH or KOH media...
2015: Geochemical Transactions
Nadav Knossow, Barak Blonder, Werner Eckert, Alexandra V Turchyn, Gilad Antler, Alexey Kamyshny
BACKGROUND: We studied the annual variability of the concentration and isotopic composition of main sulfur species and sulfide oxidation intermediates in the water column of monomictic fresh-water Lake Kinneret. Sulfate concentrations in the lake are <1 mM and similar to concentrations that are proposed to have existed in the Paleoproterozoic ocean. The main goal of this research was to explore biogeochemical constrains of sulfur cycling in the modern low-sulfate fresh-water lake and to identify which processes may be responsible for the isotopic composition of sulfur species in the Precambrian sedimentary rocks...
2015: Geochemical Transactions
Clinton W Noack, Jinesh C Jain, John Stegmeier, J Alexandra Hakala, Athanasios K Karamalidis
In this work, the geochemistry of the rare earth elements (REE) was studied in eleven outcrop samples and six, depth-interval samples of a core from the Marcellus Shale. The REE are classically applied analytes for investigating depositional environments and inferring geochemical processes, making them of interest as potential, naturally occurring indicators of fluid sources as well as indicators of geochemical processes in solid waste disposal. However, little is known of the REE occurrence in the Marcellus Shale or its produced waters, and this study represents one of the first, thorough characterizations of the REE in the Marcellus Shale...
2015: Geochemical Transactions
Mark E Hodson, Liane G Benning, Bea Demarchi, Kirsty E H Penkman, Juan D Rodriguez-Blanco, Paul F Schofield, Emma A A Versteegh
BACKGROUND: Many biominerals form from amorphous calcium carbonate (ACC), but this phase is highly unstable when synthesised in its pure form inorganically. Several species of earthworm secrete calcium carbonate granules which contain highly stable ACC. We analysed the milky fluid from which granules form and solid granules for amino acid (by liquid chromatography) and functional group (by Fourier transform infrared (FTIR) spectroscopy) compositions. Granule elemental composition was determined using inductively coupled plasma-optical emission spectroscopy (ICP-OES) and electron microprobe analysis (EMPA)...
2015: Geochemical Transactions
Zhijun Zhang, Jing Lai, Hui Yin, Xionghan Feng, Wenfeng Tan, Fan Liu
BACKGROUND: Although most reported biogenic Mn oxides are hexagonal birnessites, other types of biogenic Mn oxides also commonly occur in the environment. However, sorption characteristics and underlying mechanisms of the adsorption of heavy-metal ions on these biogenic Mn oxides are still rarely addressed. In this study, the sorption mechanisms of Cu(II) on a low valence biogenic Mn oxide, poorly crystallized bixbyite-like Mn2O3 (α-Mn2O3), were investigated. RESULTS: The maximum adsorption capacity of Cu(II) onto this biogenic Mn oxide at pH 6...
2015: Geochemical Transactions
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