Journal of Geochemistry http://www.hindawi.com The latest articles from Hindawi Publishing Corporation © 2014 , Hindawi Publishing Corporation . All rights reserved. Nature of C-(A)-S-H Phases Formed in the Reaction Bentonite/Portlandite Thu, 18 Dec 2014 05:49:55 +0000 http://www.hindawi.com/journals/jg/2014/145425/ Reactions between bentonite/montmorillonite and portlandite have been studied in the context of the engineered barriers of a purpose built repository for the deep geological disposal of spent fuel and high-level radioactive wastes. Portlandite was selected as the representative material of cement leaching in the early alkaline stage expected in a repository when conventional Ordinary Portland Cement (OPC) is used. Eight different batch experiments were performed for a reaction time near to two months, including bentonite or montmorillonite at montmorillonite/portlandite molar ratios of 2 : 1 and 3 : 1 under hydrothermal conditions. Temperatures of reactions were maintained constant at either 60 or 120°C. Calcium silicates hydrates with limited substitution of Al for Si (C-(A)-S-H phases with Al/Si <0.3) were formed with different structures and compositions as a function of the reaction conditions. Orthorhombic 11 Å-tobermorite-type phase was detected in experiments at 120°C while a more disordered monoclinic tobermorite formed at 60°C. These results are useful for the interpretation of experimental data in more complex experiments using concrete or cement pastes and bentonite, where C-(A)-S-H phases of variable compositions can precipitate, in addition to the characteristic cement hydrates and other secondary minerals carbonates. Raúl Fernández, Lorena González, Ana Isabel Ruiz, and Jaime Cuevas Copyright © 2014 Raúl Fernández et al. All rights reserved. Lead Immobilization and Hydroxamate Ligand Promoted Chloropyromorphite Dissolution Sun, 20 Jul 2014 11:51:28 +0000 http://www.hindawi.com/journals/jg/2014/168938/ The immobilization of lead, a major environmental contaminant, through phosphate amendments to form the sparingly soluble lead phosphate mineral chloropyromorphite [Pb5(PO4)3] (CPY) is an effective in situ strategy for soil remediation. An important question is the effect of microbial processes on this remediation. Here, we investigate the role of the microbial siderophore ligand desferrioxamine-D1 (DFO-D1) and its analog acetohydroxamic acid (aHA) in CPY lability using pH-dependent batch dissolution kinetics and model calculations. Both (0.01) M aHA and (0.00024) M DFO-D1 are similarly effective and enhance lead release from CPY by more than two orders of magnitude at pH > 6 compared to in the absence of ligands. This is consistent with model calculations of pH-dependent (aqueous) complexation of lead with hydroxamate ligands. More importantly, pH-dependent ligand sorption is predictive of its ligand promoted dissolution behavior. Our results suggest that organic ligands can significantly increase CPY lability at alkaline pHs in soils and sediments and that addition of P amendments to immobilize Pb as CPY may only be successful at acid pHs. Nadia K. Adam Copyright © 2014 Nadia K. Adam. All rights reserved. Electron Microscopic Studies of Ilmenite from the Chhatrapur Coast, Odisha, India, and Their Implications in Processing Tue, 15 Jul 2014 08:36:14 +0000 http://www.hindawi.com/journals/jg/2014/192639/ Ilmenite from the Chhatrapur coast, Odisha, India, was studied using optical microscope, X-ray diffraction, particle size analysis, and electron microprobe to decipher their micromorphology, texture(s), and elemental composition. The micromorphological features by electron microscope indicate that weathering processes such as mechanical and chemical, affected the placer heavy mineral ilmenite. These detrital ilmenites contain TiO2 in the range of 50.25% to 55.41% and FeO 42.72% to 49.99% in addition to Al2O3, MgO, MnO, CaO, Na2O, Cr2O3, NiO, ZnO, ZrO2, V2O5, and HfO2 (0 to 0.034%). Ti/(Ti + Fe) ratio in the ilmenite varied from 0.413 to 0.5, which indicates the effect of weathering/oxidation confirming microscopic observations. All the results revealed that these ilmenite grains were derived from the gneissic/granitic, basic and high grade metamorphic rocks, belonging to the Eastern Ghats Group of the Precambrian complex of coastal Orissa. D. S. Rao and D. Sengupta Copyright © 2014 D. S. Rao and D. Sengupta. All rights reserved. Geochemical Association of Ni2+, Zn2+, Pb2+, Ag+, Cu2+, and Co2+ Ions in Natural Pyrite Wed, 07 May 2014 08:25:52 +0000 http://www.hindawi.com/journals/jg/2014/161850/ The natures of competitive adsorption of six metal ions on the natural pyrite surface have been studied with an objective to provide strong foundations towards mode of association/occurrence of trace elements on pyritic surface. Some parameters, for instance, adsorption edge, mechanism, correlation coefficient, monolayer coverage, pH, and thermodynamic parameters, have been considered here. The significant results are the order of increasing trend of adsorption edges which has been found to be Pb2+ < Cu2+ < Ni2+ < Zn2+ < Co2+ < Ag+. Nonuniformity in variation of adsorption edge of a particular metal ion in presence of a second metal ion in solution is evident from the study. However, in case of Ag2+ and Co2+ ions two adsorption edges are observed. These variations have been explained based on the formation of hydroxo complexes which are pH dependent. The competitive monolayer coverage of each metal ion as a function of pH has shown variation in the extent of adsorption. Computed higher correlation coefficient in a binary system indicates retardation in adsorption of metal ion in presence of a second metal ion. Further the adsorption of metal ions on pyrite surface showed exothermic processes due to the spontaneous nature at low temperature. Our study has strongly revealed promising adsorbent characteristics of natural pyrite with considerable geochemical and environmental implications. Mrinal K. Baruah, Probhat Kotoky, and Gobin C. Borah Copyright © 2014 Mrinal K. Baruah et al. All rights reserved. Electro-Thermal and Semiconductivity Behaviour of Natural Sintered Complex Carbonate Ore for Thermo-Technological Applications Wed, 05 Mar 2014 09:38:15 +0000 http://www.hindawi.com/journals/jg/2014/451782/ The polymetal (Zn, Pb, Fe, Ca, Mg, Cd, Ba, Ni, Ti, and SiO2) complex Umm-Gheig carbonate ore is subjected to sintering treatment at 573, 773, 973 and 1273 K respectively for four hours. Chemical, spectral, X-ray and differential thermal analyses are applied for the native ore as well as for the samples preheated and sintered. The current versus applied DC voltage (–) characteristics, bulk density , percent shrinkage (%), activation energy and energy gap are established for the sintered ore. The electrical conductivity , thermal conductivity () and thermoelectric power coefficient have been investigated as a function of applied temperature for the sintered ore materials. The electrical conduction is mainly achieved by free electrons near or in conduction band or n-type. As the sintering temperature increases the conduction of the ore is also increased due to the recombination process taking place between the electrons and holes. Electrons hopping between Fe2+ and Fe3+ are the main charge carriers. The formation of Fe3O4 at high sintering temperature acts as an active mineralizer, thus inducing an increased degree of crystallinity and a more ordered crystal structure is produced. Loutfy H. Madkour Copyright © 2014 Loutfy H. Madkour. All rights reserved. Spatial Distributions of Humic Substances and Evaluation of Sediment Organic Index on Lake Dalinouer, China Thu, 02 Jan 2014 08:25:59 +0000 http://www.hindawi.com/journals/jg/2014/502597/ The aim of this study is to examine and interpret the spatial distribution of sedimentary humic substances in Lake Dalinouer. Humic substances in sediments were analyzed separately in different fractions: humins (HM), humic acid (HA), fulvic acid (FA), and different forms of organic carbon. The results showed that total organic carbon (TOC) contents varied from 7.25 to 65.54 g kg−1 with a mean of 36.37 ± 17.74 g kg−1. It was found that high TOC concentrations were at lake’s center and low TOC concentrations occurred at the estuary of inflows. Different redox conditions caused by water depth were of the most important factors which might influence TOC contents. Concentrations of HM, HA, and FA in sediments were detected in range of 6.40–58.16 g kg−1, 0.27–3.50 g kg−1, and 0.27–4.26 g kg−1, respectively. Of them, HM was the dominant form and accounted for 74–94% of TOC and 80–90% of humus. Organic Sediment Index (OSI) was used to assess the organics accumulation, and the value of OSI ranged from 0.001 to 0.30, which indicated that Lake Dalinouer was relatively clean. The relative high degree of humidification was found in the eastern of lake, where it should be taken into consideration seriously. Dekun Hou, Jiang He, Changwei Lü, Wei Wang, and Fujin Zhang Copyright © 2014 Dekun Hou et al. All rights reserved.