Modelling the sorption of Mn(II), Co(II), Ni(II), Zn(II), Cd(II), Eu(III), Am(III), Sn(IV), Th(IV), Np(V) and U(VI) on montmorillonite: Linear free energy relationships and estimates of surface binding constants for some selected heavy metals and actinides

In solution thermodynamics, and more recently in surface chemistry, it is well established that relationships can be found between the free energies of formation of aqueous or surface metal complexes and thermodynamic properties of the metal ions or ligands. Such systematic dependencies are commonly termed linear free energy relationships (LFER). A 2 site protolysis non-electrostatic surface complexation and cation exchange (2SPNE SC/CE) model has been used to model “in house” and literature sorption edge data for eleven elements: Mn(II), Co(II), Ni(II), Zn(II), Cd(II), Eu(III), Am(III), Sn(IV), Th(IV), Np(V) and U(VI) to provide surface complexation constants for the strong sites on montmorillonite. Modelling a further 4 sets of sorption isotherms for Ni(II), Zn(II), Eu(III) and U(VI) provided complexation constants for the weak sites. The protolysis constants and site capacities derived for the 2SPNE SC/CE model in previous work were fixed in all of the calculations. Cation exchange was modelled simultaneously to provide selectivity coefficients. Good correlations between the logarithms of strong ^SK_x−1 and weak ^W1K_x−1 site binding constants on montmorillonite and the logarithm of the aqueous hydrolysis constants ^OHK_x were found which could be described by the following equations: Strong (≡S^SOH) sites:

SlogKX−1=8.1±0.3+(0.90±0.02)log^OHKX     

河南嵩县小南沟金矿床地球化学特征

河南省崇县小南沟金矿是产于熊耳群火山岩中的构造蚀变岩型矿床,矿体受控于近南北向断裂构造中,但其围岩蚀变特点、同位素组成以及流体包裹体成分均与店房稳爆角砾岩型金矿有一定的联系,与熊耳山区产于北东向或近东西向断裂中的蚀变岩型矿床相似,说明小南沟矿床与附近赋存于东西向以及稳爆角砾岩型矿床具有直接的成因联系,它们构成一个统一的成矿体系,其成矿物质来源与赋矿火山岩以及基底古老变质岩有关,成矿作用与燕山期岩浆     

Modeling the adsorption of Cd (II), Cu (II), Ni (II), Pb (II) and Zn (II) onto montmorillonite

The adsorption of five toxic metallic cations, Cd(II), Cu(II), Ni(II), Pb(II) and Zn(II), onto montmorillonite was investigated as a function of pH and ionic strength and a two-site surface complexation model was used to predict the adsorption data. The results showed that in the lower pH range, 3∼6 for Cd, Cu, Ni and Zn, and 3∼4.5 for Pb, the adsorption was greatly affected by ionic strength, while in the higher pH range, the adsorption was not. In the lower pH range, the metallic cations were mainly bound through the formation of outer-sphere surface on the permanently charged basal surface sites (≡X⁻), while in the higher pH range the adsorption occurred mainly on the variably charged edge sites (≡SOH) through the formation of inner-sphere surface complexes. Acid-base surface constants and metal binding constants for the two sites were optimized using FITEQL. The adsorption affinity of the five metallic cations to the permanently charged sites of montmorillonite was Pb > Cu > Ni ≈ Zn ≈ Cd, while that to the variable charged sites was Pb ? Cu > Zn > Cd > Ni.     

Surface complexation modelling of Cd(II), Cu(II), Ni(II), Pb(II) and Zn(II) adsorption onto kaolinite

Proton binding constants for the edge and basal surface sites of kaolinite were determined by batch titration experiments at 25 °C in the presence of 0.1 M, 0.01 M and 0.001 M solutions of NaNO₃ and in the pH range 3-9. By optimizing the results of the titration experiments, the ratio of the edge sites to the basal surface sites was found to be 6:1. The adsorption of Cd(II), Cu(II), Ni(II), Zn(II) and Pb(II) onto kaolinite suspensions was investigated using batch adsorption experiments and results suggested that in the lower pH range the metallic cations were bound through non-specific ion exchange reactions on the permanently charged basal surface sites (X⁻). Adsorption on these sites was greatly affected by ionic strength. With increasing pH, the variable charged edge sites (SOH) became the major adsorption sites and inner-sphere specifically adsorbed monodentate complexes were believed to be formed. The effect of ionic strength on the extent of adsorption of the metals on the variable charged edge sites was much less than those on the permanently charged sites. Two binding constants, log K_(X2Me) and log K_(SOMe), were calculated by optimizing these constants in the computer program FITEQL. A model combining non-specific ion exchange reactions and inner-sphere specific surface complexations was developed to predict the adsorption of heavy metals onto kaolinite in the studied pH range. Linear free energy relationships were found between the edge site binding constants and the first hydrolysis constants of the metals.     

Algoma-type banded iron formation (BIF), Abitibi Greenstone belt,Quebec, Canada

A typical Algoma-type banded iron formation (BIF) occurs in Orvilliers, Montgolfier, and Aloigny townships in the Abitibi Greenstone belt, Quebec, Canada. The BIF is composed of millimeter to decimeter thick beds of alternating fine-grained, dark gray to black, well laminated, magnetite-rich (and/or hematite) beds and quartz–feldspar metasedimentary (graywacke) beds. The BIF is well defined by magnetic anomalies. These BIF layers are commonly associated with decimeter to meter thick horizons of metasedimentary rocks and mafic to intermediate volcanic rocks, which are locally crosscut by dikes of felsic or mafic intrusive rocks and, as well, narrow dikes of lamprophyre. The upper and lower contacts of the BIF are gradational with the adjacent graywacke. All geological units in the area are metamorphosed to the greenschist facies of regional metamorphism. Magnetite is mainly associated with subordinate amounts of hematite, quartz, Na-rich plagioclase, and muscovite. The fine-grained magnetite content is composed of 77% to 89% of the principal iron oxide minerals present. The magnetite occurs as disseminated idiomorphic to sub-idiomorphic small crystals, which average 20 μm ± 5 μm in size. Hematite is the second most abundant iron oxide mineral. Although less abundant, red jasper occurs in cherty horizons with strongly folded fragments and within fault zones. This particular Algoma-type iron formation stratigraphically extends more than 36 km along strike. It dips sub-vertically with a true width from 120 m to 600 m. The origin of the BIF is closely linked to regionally extensive submarine hydrothermal activity associated with the emplacement of volcanic and related subvolcanic rocks in an Archean greenstone belt.     

神木煤田延安组1~(-1)、1~(-2)及2~(-2)煤层的煤岩学特征及煤相划分

根据鄂尔多斯盆地神木煤田延安组1~(-1)、1~(-2)及2~(-2)煤层的平均光泽和结构特征,划分出了12种宏观煤岩类型。显微研究表明,该区煤中均质镜质体的含量较高,且多为草本植物和灌木类所组成,因此认为根皮镜质体的大量存在是该区煤的主要煤岩特征之一。此外,一些过渡型显微组分,如半镜质体和半丝质体的含量也相对高。依据因子分析和聚类分析结果并结合凝胶化指数和结构保存指数,划分出4种沼泽相:开阔水域水生植物淤泥相、深覆水草甸沼泽相、浅覆水草本灌木混生沼泽相和陆地森林沼泽相。     

Radiogenic Isotope Geology,by Alan P. Dickin,Cambridge University Press,Cambridge, UK, 1995 (paperback edition, 1997), $95.00 (U.S., cloth), ISBN 0 521 43151 4, $44.96 (U.S., paper), ISBN 0 521 59891 5

Mathematical Geosciences -     

A tyrannosaur trackway at Glenrock,Lance Formation (Maastrichtian), Wyoming

During the Campanian and Maastrichtian ages (86–66 million years ago), tyrannosaurids were the predominant large carnivorous dinosaurs throughout the Northern hemisphere. Despite the abundance of skeletal material, the fossil-footprint record of tyrannosaurids has been limited. Here we report a tyrannosaurid trackway in the Lance Formation, Wyoming. The trackway consists of three sequential tracks on a sandstone surface. Based on the age and size of the footprints, the trackmaker can be identified as either a sub-adult Tyrannosaurus rex or a Nanotyrannus lancensis. The trackway offers a record of a tyrannosaurid pace length, which permits the speed of the trackmaker to be calculated at 4.5–8.0 km/h. This result discounts previous speculation that tyrannosaurid walking speeds were notably slower than those of other large theropods.     

Tidal inlet sequence, Sundance Formation (Upper Jurassic), north-central Wyoming

The sandstones and coquinas of the upper 20 m of the Sundance Formation are interpreted as a tidal inlet, back-barrier shoal and sandy tidal-flat sequence deposited at the close of marine Jurassic sedimentation in north-central Wyoming. The barrier strandline maintained a generally E-W trend as it prograded to the north. The lateral migration of inter-barrier tidal inlets along the regressive shoreline of the late Sundance sea caused the coquinas and sandstones of the uppermost Sundance Formation to be deposited as tabular, laterally-extensive units. Tidal bundles, sigmoidal reactivation surfaces, herringbone cross-lamination and abundant mud drapes within the sandstones are evidence of considerable tidal influence during the deposition of the uppermost Sundance Formation. Earlier models, which attach an offshore environment of deposition to the sequence, do not explain the tabular geometries of the sandstone and coquina units and their conformable stratigraphic relationship with the overlying non-marine sediments of the Morrison Formation.     

Silicification in the Belt Supergroup (Mesoproterozoic), Glacier National Park, Montana, USA

Nodular cherts can provide a window on the original sediment composition, diagenetic history and biota of their host rock because of their low susceptibility to further diagenetic alteration. The majority of Phanerozoic cherts formed by the intraformational redistribution of biogenic silica, particularly siliceous sponge spicules, radiolarian tests and diatom frustules. In the absence of a biogenic silica source, Precambrian cherts necessarily had to have had a different origin than Phanerozoic cherts. The Mesoproterozoic Belt Supergroup in Glacier National Park contains a variety of chert types, including silicified oolites and stromatolites, which have similar microtextures and paragenesis to Phanerozoic cherts, despite their different origins. Much of the silicification in the Belt Supergroup occurred after the onset of intergranular compaction, but before the main episode of dolomitization. The Belt Supergroup cherts probably had an opal-CT precursor, in the same manner as many Phanerozoic cherts. Although it is likely that Precambrian seas had higher silica concentrations than at present because of the absence of silica-secreting organisms, no evidence was observed that would suggest that high dissolved silica concentrations in the Belt sea had a significant widespread effect on silicification. The rarity of microfossils in Belt Supergroup cherts indicates that early silicification, if it occurred, was exceptional and restricted to localized environments. The similarity of microtextures in cherts of different ages is evidence that the silicification process is largely controlled by host carbonate composition and dissolved silica concentration during diagenesis, regardless of the source of silica.     

The Wenchuan Earthquake (May 12, 2008), Sichuan Province,China, and resulting geohazards

On Monday, May 12, 2008, a devastating mega-earthquake of magnitude 8.0 struck the Wenchuan area, northwestern Sichuan Province, China. The focal mechanism of the earthquake was successive massive rock fracturing 15 km in depth at Yingxiu. Seismic analysis confirms that the major shock occurred on the Beichuan–Yingxiu Fault and that aftershocks rapidly extended in a straight northeast–southeast direction along the Longmenshan Fault zone. Fatalities approaching a total of 15,000 occurred, with a significant number resulting from four types of seismically triggered geohazards—rock avalanches and landslides, landslide-dammed lakes (“earthquake lakes”), and debris flows. China Geological Survey has identified 4,970 potentially risky sites, 1,701 landslides, 1,844 rock avalanches, 515 debris flows, and 1,093 unstable slopes. Rock avalanches and landslides caused many fatalities directly and disrupted the transportation system, extensively disrupting rescue efforts and thereby causing additional fatalities. Landslide-dammed lakes not only flooded human habitats in upstream areas but also posed threats to potentially inundated downstream areas with large populations. Debris flows become the most remarkable geohazards featured by increasing number, high frequency, and low triggering rainfall. Earthquake-triggered geohazards sequentially induced and transformed to additional hazards. For example, debris flows occurred on rock avalanches and landslides, followed by landslide-dammed lakes, and then by additional debris flows and breakouts of the landslide-dammed lakes and downstream flooding. Earthquake-induced geohazards occurred mainly along the fault zone and decreased sharply with distance from the fault. It can be anticipated that post-earthquake geohazards, particularly for debris flows, will continue for 5–10 years and even for as long as 20 years. An integrated strategy of continuing emergency response and economic reconstruction is required. The lesson from Wenchuan Earthquake is that the resulted geohazards may appear in large number in active fault regions. A plan for geohazard prevention in the earthquake-active mountainous areas is needed in advance.