H. J. Tobschall

On the mechanistic modeling of As(III) adsorption on gibbsite

Arsenite adsorption on gibbsite was examined as a function of pH, ionic strength (I) and contact time (t(C)). As(III) showed a weak affinity for gibbsite surface. The trends of pH=f(Gamma(ads)) curves have showed a marked deviation from a typical anion adsorption edge showing a maximum Gamma(ads) around pH approximately 8.2. The experimentally derived proton exchange ratio has always converged to zero when 0.26< summation operator [As(III)]<7 microM and 6.2<pH<8.2. The isosteric heat of adsorption, DeltaH(r), exhibited invariant behavior with respect to Gamma(ads). The As(III) adsorption data was quantified by charge distribution multi-site complexation (CD MUSIC) model using the surface complex postulated below:

Application of multi-element relationships in stream sediments to mineral exploration: a case study of Walawe Ganga Basin, Sri Lanka

Abstract This study on the application of multi-element relationships in stream sediments to mineral exploration in the Walawe Ganga Basin presents one of the first of its kind in Sri Lanka. In order to determine the nature of these sediments, multi-element analysis of selected grain size ( Some elements, notably Zr, Hf, Th, U, Ce and La, show very high enrichment factors (e.g. 54 for Zr) as compared to the upper crustal abundance. These are presumably associated with heavy minerals such as zircon, rutile and monazite found in abundance in the stream sediments of the Walawe Ganga Basin. Principal Component Analysis (PCA) of the geochemical data show that multi-element relationships could be effectively used to delineate target areas for mineral exploration. With the use of PCA, this study reveals that areas with associations of calc-silicate/marble and charnockitic rocks are probable source regions for mineral occurrences, particularly in the axial regions of anticlines.

Importance of geomorphology and sedimentation processes for metal dispersion in sediments and soils of the Ganga Plain: identification of geochemical domains

Abstract The Ganga Plain, one of the largest alluvial plains of the earth is under severe environmental stress due to rapid industrial and urban development and exploding population growth. Disposal of industrial and urban wastes and the ignorance of their management have resulted severe environmental problems, especially metal pollution. In the present study, an attempt is made to understand the transport and dispersion processes of metal contaminants in sediments and soils in Kanpur–Unnao industrial region of the Ganga Plain. The significance of geomorphology and monsoon rain is assessed in determining the distribution of contaminated sediments in this area. Three regional geomorphic surfaces (T0, T1 and T2) are identified, each with its characteristic river channel patterns and sediment distribution system which influence the dispersion and accumulation of the metal contaminants. The sediment and water distribution regime depends on the nature of geomorphic features and character of the river channels. Geomorphic features, sedimentation processes, the nature of the river channels and distribution of excess rain water of the monsoon season have given the bases to delineate five geochemical domains in the study area. Each geochemical domain is an independently operating system with its own geomorphic and geochemical characters. Chemical parameters (e.g., pH), metal concentrations, and dispersion of metal-contaminated sediments and soils vary from domain to domain. In comparison to reference values, each domain exhibits its own enrichment of elements, namely the Loni River domain has high contents of C-org, Cd, Cr, Zn; the Ganda Nala domain of C-org, Cu, Cr; the Ganga River domain of C-org, Cr, Cu, Pb, Sn, Zn; the Sewage Network domain of C-org, Cd, Cr, Cu, Pb, Ni, Sn, Zn; and the Pandu River domain of C-org, Cd, Cu, Ni, Zn. Patterns of changes in metal concentrations from one monsoon year to the other and in different seasons of a monsoon flood cycle are also domain specific. Each geochemical domain exhibits its own degree of metal enrichment in sediments and soils by anthropogenic activities and physico-chemical processes. Identification of geochemical domains with their specific physico-chemical processes in the fluvial system of the Ganga Plain will certainly help in assessing the environmental problems and land contamination of this region.

Sources of stream sediments in the granulite terrain of the Walawe Ganga Basin, Sri Lanka, indicated by rare earth element geochemistry

Abstract Thirty-eight samples of stream sediments draining high-grade metamorphic rocks in the Walawe Ganga (river) Basin, Sri Lanka, were analysed for their REE contents, together with samples of metamorphic suites from the source region. The metamorphic rocks are enriched in light REE (LREE) compared to heavy REE (HREE) and are characterised by high La/Lu ratios and negative Eu anomalies. The chondrite-normalised patterns for these granulite-grade rocks are similar to that of the average post-Archaean upper crust, but they are slightly enriched with La and Ce. The REE contents of the N /Sm N and lower La N /Lu N ratios relative to other fractions. The lower La N /Lu N ratio is related to the depletion of heavy minerals in the

The Stream Sediment Geochemistry of the Walawe Ganga Basin of Sri Lanka - Implications for Gondwana Mineralization

A regional geochemical and mineralogical study aimed at investigating the mineralization in the western-part of the Walawe Ganga (river) Basin in Sri Lanka is represented in this paper. The river basin is the 3rd largest in the country and has within it a boundary zone between two geologically different crustal blocks, which are marked by granulitic grade rocks and amphibolite grade rocks. Size fractions of stream sediments (< 63 μm; 63–125 μm; 125–177 μm and 177–250 μm) developed on the granulite-grade metamorphic terrain have been analysed at their source for their mineralogical and selected element compositions. Thirty-eight (38) sediment samples and 15 representative probable parent rock samples were chemically analysed giving special emphasis to the High Field Strength trace Elements (HFSE) including the Rare Earth Elements (REE). The granulite grade rocks in the study area is geochemically similar to that of post Archean upper crust. However the stream sediments developed from the high-grade rocks during the intense weathering, are markedly enriched with HFSE and REE. The enrichment of HFSE and LREE is accounted for by the presence of HFSE- and REE- rich accessory mineral phases such as zircon, monazite, apatite, garnet and rutile in the sediments. In some samples, the content of heavy minerals contributes as much as 50 wt. %. These minerals act as a source of elements in the sediments. However, extreme hydraulic sorting of HFSE- and REE-bearing minerals during the sediment deposition cannot be expected within a short distance from near the sources except from a mineralized occurrence. Therefore, the higher enrichment of these elements presumably indicates occurrences of scattered mineral sources such as highly differentiated granites and associated pegmatites within the Walawe Ganga drainage basin. These granitic pegmatites are probably intruded during or soon after the main granulite-facies metamorphic event and similar events are seen in other terrains of East-Gondwana.

Enrichment of high field strength elements in stream sediments of a granulite terrain in Sri Lanka — evidence for a mineralized belt

Abstract Size fractions ( However, geochemical data of these rocks do not correlate with elemental content in stream sediments. Only alkali, alkaline earth and some trace elements such as Cr, Mn, Co, Ni, and Y roughly correlate with the chemical composition of the probable source rocks. Nevertheless, most of the HFSE and related trace elements (e.g. Ti, V, Nb, Zr, Hf, Th, La, Ce) are highly enriched (factor of 10 or more) in sediments compared to the probable source rocks. Compared to the

Geochemical characteristics of sediments from a reservoir (tank) ecosystem in Sri Lanka

Major, trace and selected high field strength element geochemistry of fresh-water sediments from the Malagane tank, Deduru Oya basin, Sri Lanka, has been investigated in this study. Sediment samples were collected from 13 locations and analyzed for their elemental distribution using the X-ray fluorescence technique. The sediments were characterized by relatively low organic matter, ranging from 4.8 to 16.9%. The elemental distributions were compared with those of the average upper continental curst, and it was found that, with a few exceptions, most of the studied elements are either comparable or depleted. Correlation and principal component analyses were applied to identify the relationships among studied elements. Major elements, most trace and light rare earth elemental distribution show strong positive correlation with Al2O3 and TiO2, which indicate that the phyllosilicates and heavy minerals in the sediments are the probable hosts for these elements. The results also indicate that the sediments in the Malagane tank are representative of the materials from the metamorphic rocks in the watershed and were subjected to changes within the tank ecosystem. The results obtained from this study are vital for future pollution management of tank ecosystems in Sri Lanka, since information on elemental distribution within the sediments of tank ecosystem is lacking.

The iodine cycle in the tropical environment — implications on iodine deficiency disorders

Iodine deficiency disorders are a major health problem in a large number of countries most of which lie within the tropical environment. Even though iodine may be abundant in the surface environment, its low bioavailability is the key issue that governs the incidence of IDD. In view of the intense rainfall in the tropical environment, rock weathering with accompanying clay formation and soil leaching is markedly high. Clayey matter and humic substances fix iodine strongly and these are potential geochemical goitrogens that could control the bioavailability of iodine significantly.

Heavy metal release from phosphorite tailings into seawater: a simulated laboratory study.

A number of laboratory experiments were carried out to assess the desorption of trace metals from sedimentary phosphorite samples into artificial seawater. Shaking and percolation experiments have been performed on phosphorite samples from the Cd-rich phosphorite deposits of Hahotoé-Kpogamé (Togo, West Africa) using artificial seawater in the ratio 1:10. The results show that elevated concentrations of trace elements Cd(17-256 micrograms/l), Ni (12-193 micrograms/l), Zn (21-200 micrograms/l) and major elements Al (6-1915 micrograms/l) and Fe (30-1264 micrograms/l) are released into seawater by desorption processes. Maxima of trace metals with high mobility are reached within 4 h indicating the fast desorption kinetics in seawater. Thus, the direct disposal of potentially toxic metal-rich mine tailings may lead to regional coastal water pollution.

Geochemical and mineralogical characteristics of elephant geophagic soils in Udawalawe National Park, Sri Lanka

Geophagy or deliberate ingestion of soils was observed among Asian elephants (Elephas maximus) in the Udawalwe National Park, Sri Lanka, for several years. The geochemical and mineralogical composition of the clayey soil layers which are purposefully selected and eaten by elephants in the park were studied, in order to identify the possible reasons for elephant geophagy. The concentrations of major and trace elements were determined by means of X-ray fluorescence spectrometry in 21 soil samples from eight geophagic sites and six soil samples collected from four non-geophagic sites. The mineralogical composition of selected soil samples was investigated using X-ray diffractometry (XRD). These geochemical analyses revealed that geophagic soils in the study areas are deeply weathered and that most of the elements are leached from the soil layers under extreme weathering conditions. The XRD data showed that the soils of the area consisted mainly quartz, feldspar, and the clay minerals kaolinite, Fe-rich illite, and smectite. Although no significant geochemical differences were identified between geophagic and non-geophagic soils, a clear difference was observed in their clay mineralogical content. Soils eaten by elephants are richer in kaolinite and illite than non-geophagic soils, which contain a higher amount of smectite. It is suggested that elephants in Udawalawe National Park ingest soils mainly not to supplement the mineral contents of their forage but to detoxify unpalatable compounds in their diet.