Iron (III)-silica interactions in aqueous solution: insights from X-ray absorption fine structure spectroscopy

The influence of aqueous silica on the hydrolysis of iron(III) nitrate and chloride salts in dilute aqueous solutions (m_Fe ∼ 0.01 mol/kg) was studied at ambient temperature using X-ray absorption fine structure (XAFS) spectroscopy at the Fe K-edge. Results show that in Si-free iron nitrate and chloride solutions at acid pH (pH < 2.5), Fe is hexa-coordinated with 6 oxygens of H₂O- and/or OH-groups in the first coordination sphere of the metal, at an Fe-O distance of 2.00 ± 0.01 Å. With increasing pH (2.7 < pH < 13), these groups are rapidly replaced by bridging hydroxyls (-OH-) or oxygens (-O-), and polymerized Fe hydroxide complexes form via Fe-(O/OH)-Fe bonds. In these polymers, the first atomic shell of iron represents a distorted octahedron with six O/OH groups and Fe-O distances ranging from 1.92 to 2.07 Å. The Fe octahedra are linked together by their edges (Fe-Fe distance 2.92-3.12 Å) and corners (Fe-Fe distance ∼3.47 ± 0.03 Å). The Fe-Fe coordination numbers (N_edge = 1-2; N_corner = 0.5-0.7) are consistent with the dominant presence of iron dimers, trimers and tetramers at pH 2.5 to 2.9, and of higher-polymerized species at pH > 3.At pH > 2.5 in the presence of aqueous silica, important changes in Fe(III) hydrolysis are detected. In 0.05-m Si solutions (pH ∼ 2.7-3.0), the corner linkages between Fe octahedra in the polymeric complexes disappear, and the Fe-Fe distances corresponding to the edge linkages slightly increase (Fe-Fe_edge ∼ 3.12-3.14 Å). The presence of 1 to 2 silicons at 3.18 ± 0.03 Å is detected in the second atomic shell around iron. At basic pH (∼12.7), similar structural changes are observed for the iron second shell. The Fe-Si and Fe-Fe distances and coordination numbers derived in this study are consistent with (1) Fe-Si complex stoichiometries Fe₂Si_1-2 and Fe₃Si_2-3 at pH < 3; (2) structures composed of Fe-Fe dimers and trimers sharing one or two edges of FeO₆-octahedra; and (3) silicon tetrahedra linked to two neighboring Fe octahedra via corners. At higher Si concentration (0.16 m, polymerized silica solution) and pH ∼ 3, the signal of the Fe second shell vanishes indicating the destruction of the Fe-Fe bonds and the formation of different Fe-Si linkages. Moreover, ∼20 mol.% of Fe is found to be tetrahedrally coordinated with oxygens in the first coordination shell (R_Fe-O = 1.84 Å). This new finding implies that Fe may partially substitute for Si in the tetrahedral network of the silica polymers in Si-rich solutions.The results of this study demonstrate that aqueous silica can significantly inhibit iron polymerization and solid-phase formation, and thus increase the stability and mobility of Fe(III) in natural waters. The silica “poisoning” of the free corner sites of iron-hydroxide colloids should reduce the adsorption and incorporation of trace elements by these colloids in Si-rich natural waters.     

Ozone during stratospheric warmings at Uccle

The day-to-day variations in ozone content at Uccle (51oN) during some stratospheric warming events are ex-amined. In particular, the attention is focused on the timing of commencement of ozone enhancement prior to peak day of warming and on the relationship in the ozone content between the upper and lower stratosphere. These two features are compared with the predictions of ozone transport models. There seems to be an agreement between mod-el predictions and observed features in some cases.     

Managing migration in the Greater Mekong Subregion: Regulation,extra‐legal relation and extortion

One major aim of the Greater Mekong Subregion (GMS) integration programme, supported by the Asian Development Bank (ADB), is to foster regional ‘community’ for sharing resources, people and financial flows. This ‘community’ is the target of both economic growth and poverty reduction. The emphasis on ‘community’ in the ADB's mushrooming quantity of documents raises important questions about what kinds of people are included, in what roles and with what kinds of support and protection. This paper explores these questions in relation to the political economy of regulating ethnic migrants from Myanmar working in Thailand. This paper argues that extra‐legal relations between migrants and state/para‐state agents constitute a crucial part of regulation. In transferring the regulation of migration to the national scale, the ADB inadvertently reinforces national differences between Thais and cross‐border people. Additionally, the complicated and fluctuating implementation of national regulations in both countries leaves migrants subject to violence and extortion from state and quasi‐state agents in Thailand. This paper shows that the dynamics of global capitalism require ‘deportable labour’ supplied by ethnic migrants who are included in the GMS community as the most invisible, vulnerable and exploited members.     

Investigation of wetting front behavior due to rainfall and ponding head effects in arid region wadi alluvium

Intensive experimental as well as numerical investigations have been carried out in order to develop empirical relationships to predict wetting front travel time and infiltration rate in deep arid region alluvium due to the effect of variable rainfall intensity and ponding head, respectively. A rainfall simulator that is capable of producing variable rainfall intensity up to 160 mm/h and a large diameter infiltrometer were constructed in the study area and then used to test the effect of rainfall and ponding head up to a depth of 3 m. Results of these experiments were utilized to calibrate an unsaturated zone model which was then used to test different scenarios for wetting front movement at depths beyond the scope of these experiments. Empirical infiltration relationships for rainfall and ponding head, respectively, were derived for shallow and deep soil columns from these experiments.     

Iodine concentrations of soils near Trabzon, Turkey: a region of endemic goiter

Iodine contents of soils developed over the major rock formations of the northern zone of the Eastern Pontide Tectonic Belt (Northeastern Turkey) have been investigated with respect to soil-parent rock relationship, effect of topography, elevation, and climate to construe its effect on the health of the local population. Samples were collected from the A and B horizons of the soils developed over the major stratigraphic units constituting the eastern Pontides, including the Lower Basic Complex of Jurassic-Lower Cretaceous age, the Berdiga limestone (Jurassic-lower Cretaceous), the Dagbasi granitoid (Upper Cretaceous), volcano-sedimentary sequence of Upper Cretaceous age, ore-bearing and barren dacites of Upper Cretaceous age, and Neogene alkaline basalts. Chemical analyses of soil samples indicate significantly lower iodine abundances for all the soils studied (5–28 ppm) in comparison to the average abundance of iodine in analogous soils of other parts of the world (22–93 ppm). The concentration of iodine in soils developed over the same geologic formation decrease with increasing elevation. In certain cases, this decrease may reach up to 70%. Goiter is highly common throughout this region in Turkey. The results of this study suggest that the iodine deficiency of region’s soils may be a principal underlying cause for this area of Turkey being an endemic goiter region.     

Ichnology of Bhuban and Boka Bil Formations,oligocene-miocene deposits of Manipur Western Hill,Northeast India

Oligocene-Miocene deposits of Bhuban and Boka Bil Formations, Surma Group, Manipur Western Hill consist of well preserved ichnofossil assemblages. These formations are represented by eight lithofacies such as Massive sandstone (Sm), Rippled marked argillaceous sandstone (Sr), Wavy laminated sandstone-siltstone-silty shale (Sw), Laminated shale (Fl), Massive mudstone (Fm), Trough cross-bedded sandstone (St), Lenticular laminated sandstonesiltstonesilty shale (Sll) and Laminated to massive sandstone-siltstone (Ssc). Fifteen ichnospecies were identified, which further categories into Skolithos, Cruziana, and Skolithos/Cruziana ichnofacies. Overall distribution pattern and behavioural nature of the ichnoassemblage and sedimentological attributes suggests that the sediments of Bhuban and Boka Bil Formations were deposited under frequent fluctuating sea level, moderate to strong energy condition, subtidal to lower intertidal environment, rich in organic nutrients.     

Using δN values in algal tissue to map locations and potential sources of anthropogenic nutrient inputs on the island of Maui, Hawai‘i, USA

Macroalgal blooms of Hypnea musciformis and Ulvafasciata in coastal waters of Maui only occur in areas of substantial anthropogenic nutrient input, sources of which include wastewater effluent via injection wells, leaking cesspools and agricultural fertilizers. Algal δ¹⁵N signatures were used to map anthropogenic nitrogen through coastal surveys (island-wide and fine-scale) and algal deployments along nearshore and offshore gradients. Algal δ¹⁵N values of 9.8‰ and 2.0-3.5‰ in Waiehu and across the north-central coast, respectively, suggest that cesspool and agricultural nitrogen reached the respective adjacent coastlines. Effluent was detected in areas proximal to the Wastewater Reclamation Facilities (WWRF) operating Class V injection wells in Lahaina, Kihei and Kahului through elevated algal δ¹⁵N values (17.8-50.1‰). From 1997 to 2008, the three WWRFs injected an estimated total volume of 193 million cubic meters (51 billion gallons) of effluent with a nitrogen mass of 1.74 million kilograms (3.84 million pounds).     

Tectonic deformation and recrystallisation of oligoclase

Naturally deformed and partially recrystallised oligoclase porphyroclasts were studied in a high voltage electron microscope. The oligoclases had a highly deformed outer mantle zone, which contained high densities of dislocations and albite and pericline deformation twins, and less deformed cores containing fewer dislocations and albite twins but no pericline deformation twins. There was little evidence for recovery; apparently the internal strain energy due to deformation was relieved by recrystallisation. Strain free nuclei developed in areas with the highest defect densities. The resultant new grains had a lower anorthite content than their parents. It is suggested that the recrystallisation processes were aided by strain enhanced diffusion.     

Parametric cubic splines and geologic shape descriptions

Parametric cubic splines provide a versatile means of describing and sampling shapes and curves commonly found in geology. These splines allow the researcher to treat easily curves which are not single-valued in Cartesian or polar coordinates. In addition, they simultaneously provide approximations to positions, slopes, and curvatures of the curve being considered. In conjunction with simple digitizing equipment and a small computer, the method of parametric cubic spline approximation allows the researcher to analyze curves or outlines in cases where the more rapid technique involving video imaging equipment is either not applicable or not available.