Applied Geochemistry (v.22, #9)
Accelerated weathering of high-level and plutonium-bearing lanthanide borosilicate waste glasses under hydraulically unsaturated conditions by Eric M. Pierce; B.P. McGrail; P.F. Martin; J. Marra; B.W. Arey; K.N. Geiszler (1841-1859).
The US Department of Energy (DOE) has proposed that a can-in-canister waste package design be used for disposal of excess weapons-grade Pu at the proposed mined geologic repository at Yucca Mountain, Nevada. This configuration consists of a high-level waste (HLW) canister fitted with a rack that holds mini-canisters containing a Pu-bearing lanthanide borosilicate (LaBS) waste glass and/or titanate-based ceramic (∼15% of the total canister volume). The remaining volume of the HLW canister is then filled with HLW glass (∼85% of the total canister volume). A 6-a pressurized unsaturated flow (PUF) test was conducted to investigate waste form–waste form interactions that may occur when water penetrates the canisters and contacts the waste forms. The PUF column volumetric water content was observed to increase steadily during the test because of water accumulation associated with alteration phases formed on the surfaces of the glasses. Periodic excursions in effluent pH, electrical conductivity, and solution chemistry were monitored and correlated with the formation of a clay phase(s) during the test. Geochemical modeling, with the EQ3NR code, of select effluent solution samples suggests the dominant secondary reaction product for the surrogate HLW glass, SRL-202, is a smectite di-octahedral clay phase(s), possibly nontronite [Na0.33 Fe2(AlSi)4O10(OH)2 · n(H2O)] or beidellite [Na0.33Al2.33Si3.67O10(OH)2]. This clay phase was identified in scanning electron microscope (SEM) images as discrete spherical particles growing out of a hydrated gel layer on reacted SRL-202 glass. Alpha energy analysis (AEA) of aliquots of select effluent samples that were filtered through a 1.8 nm filter suggest that approximately 80% of the total measurable Pu was in the form of a filterable particulate, in comparison to unfiltered aliquots of the same sample. These results suggest the filterable particles are >1.8 nm but smaller than the 0.2 μm average diameter openings of the Ti porous plate situated at the base of the column. In this advection-dominated system, Pu appeared to be migrating principally as or in association with colloids after being released from the LaBS glass. Analyses of reacted LaBS glass particles with SEM with energy dispersive X-ray spectroscopy suggest that Pu may have segregated into a discrete disk-like phase, possibly PuO2. Alteration products that contain the neutron absorber Gd have not been positively identified. Separation of the Pu and the neutron absorber Gd during glass dissolution and transport could be a criticality issue for the proposed repository. However, the translation and interpretation of these long-term PUF test results to actual disposed waste packages requires further analysis.
Phosphorus fractionation in surficial sediments of Pandoh Lake, Lesser Himalaya, Himachal Pradesh, India by Anshumali; A.L. Ramanathan (1860-1871).
The fractionation of P in Pandoh Lake surface sediments has been investigated for the first time in order to understand its environmental availability and sources, and the eutrophication status of this lake. Inorganic-P is present mainly as authigenic-P (step-III). The authigenic P concentration is higher in winter relative to the summer and monsoon seasons and ranged from 35.9 to 46.9 μg/g. The loosely sorbed or exchangeable-P (step-I), Fe(III)-bound-P (step-II) and detrital inorganic-P (step-IV) were higher in the monsoon season and varied from 3.70 to 11.1 μg/g, 16.9 to 32.0 μg/g and 9.89 to 17.0 μg/g, respectively. Organic-P reached a maximum in the summer season and ranged from 8.00 to 14.9 μg/g. Authigenic-P and detrital inorganic-P show seasonal changes, as pH influences the interaction between P and CaCO3 in the water column. In the winter season, phosphate is precipitated out of the water column and fixed in the sediments as a result of an increase in pH. Calcite-bound-P in the sediments may be redissolved by decreasing pH in the summer season. Relatively high rates of mineralization during the monsoon results in the seasonal pattern of organic-P fractionation to sediment as follows: monsoon = winter < summer. Iron, Ca, organic matter and silt and clay contents seem to play a significant role in regulating the seasonal P budget. Principal component analysis (PCA) was used to identify the factors which influence sedimentary P in the different seasons.
Sphalerite dissolution kinetics in acidic environment by Patricia Acero; Jordi Cama; Carlos Ayora (1872-1883).
Sphalerite dissolution kinetics were studied by means of long-term (>500 h) flow-through experiments in the pH range of 1–4.2, at 25, 50 and 70 °C and at three different dissolved O2 concentrations, from 0.2 to 8.7 mg L−1 to obtain a dissolution rate law useful to predict sphalerite long-term dissolution behavior in environments affected by acid drainage. The main factor affecting the rate of sphalerite dissolution is pH, whose increase results in a decrease in the dissolution rate, whereas rate is independent of dissolved O2 concentration over the range of 0.2–8.7 mg L−1. In the range of conditions studied, the apparent activation energy was found to be 14.3 ± 1.9 kJ mol−1. A rate law accounting for the effects of pH and temperature on the sphalerite dissolution over this range of conditions is expressed as: R sphalerite = 10 - 6.49 ± 0.02 e - 14.3 ± 1.9 RT a H + 0.54 ± 0.02 where R sphalerite is the sphalerite dissolution rate (mol m−2 s−1), R is the gas constant (kJ mol−1 K−1), T is the temperature (K), and a H + is the activity of H+ ion in the solution. X-ray photoelectron spectroscopy (XPS) analyses of the reacted samples furnish evidence of the formation of a surface layer enriched in S on the sphalerite surface during dissolution. The formation of this layer does not exert any passivating effect on sphalerite long-term dissolution.
Speciation and colloid transport of arsenic from mine tailings by Aaron J. Slowey; Stephen B. Johnson; Matthew Newville; Gordon E. Brown (1884-1898).
In addition to affecting biogeochemical transformations, the speciation of As also influences its transport from tailings at inoperative mines. The speciation of As in tailings from the Sulfur Bank Mercury Mine site in Clear Lake, California (USA) (a hot-spring Hg deposit) and particles mobilized from these tailings have been examined during laboratory-column experiments. Solutions containing two common, plant-derived organic acids (oxalic and citric acid) were pumped at 13 pore volumes d−1 through 25 by 500 mm columns of calcined Hg ore, analogous to the pedogenesis of tailings. Chemical analysis of column effluent indicated that all of the As mobilized was particulate (1.5 mg, or 6% of the total As in the column through 255 pore volumes of leaching). Arsenic speciation was evaluated using X-ray absorption spectroscopy (XAS), indicating the dominance of arsenate [As(V)] sorbed to poorly crystalline Fe(III)-(hydr)oxides and coprecipitated with jarosite [KFe3(SO4, AsO4)2(OH)6] with no detectable primary or secondary minerals in the tailings and mobilized particles. Sequential chemical extractions (SCE) of <45 μm mine tailings fractions also suggest that As occurs adsorbed to Fe (hydr)oxides (35%) and coprecipitated within poorly crystalline phases (45%). In addition, SCEs suggest that As is associated with 1 N acid-soluble phases such as carbonate minerals (20%) and within crystalline Fe-(hydr)oxides (10%). The finding that As is transported from these mine tailings dominantly as As(V) adsorbed to Fe (hydr)oxides or coprecipitated within hydroxysulfates such as jarosite suggests that As release from soils and sediments contaminated with tailings will be controlled by either organic acid-promoted dissolution or reductive dissolution of host phases.
A simulation-based approach for estimating premining water quality: Red Mountain Creek, Colorado by Robert L. Runkel; Briant A. Kimball; Katherine Walton-Day; Philip L. Verplanck (1899-1918).
Regulatory agencies are often charged with the task of setting site-specific numeric water quality standards for impaired streams. This task is particularly difficult for streams draining highly mineralized watersheds with past mining activity. Baseline water quality data obtained prior to mining are often non-existent and application of generic water quality standards developed for unmineralized watersheds is suspect given the geology of most watersheds affected by mining. Various approaches have been used to estimate premining conditions, but none of the existing approaches rigorously consider the physical and geochemical processes that ultimately determine instream water quality. An approach based on simulation modeling is therefore proposed herein. The approach utilizes synoptic data that provide spatially-detailed profiles of concentration, streamflow, and constituent load along the study reach. This field data set is used to calibrate a reactive stream transport model that considers the suite of physical and geochemical processes that affect constituent concentrations during instream transport. A key input to the model is the quality and quantity of waters entering the study reach. This input is based on chemical analyses available from synoptic sampling and observed increases in streamflow along the study reach. Given the calibrated model, additional simulations are conducted to estimate premining conditions. In these simulations, the chemistry of mining-affected sources is replaced with the chemistry of waters that are thought to be unaffected by mining (proximal, premining analogues). The resultant simulations provide estimates of premining water quality that reflect both the reduced loads that were present prior to mining and the processes that affect these loads as they are transported downstream. This simulation-based approach is demonstrated using data from Red Mountain Creek, Colorado, a small stream draining a heavily-mined watershed. Model application to the premining problem for Red Mountain Creek is based on limited field reconnaissance and chemical analyses; additional field work and analyses may be needed to develop definitive, quantitative estimates of premining water quality.
Immobilization of toxic elements in mine residues derived from mining activities in the Iberian Pyrite Belt (SW Spain): Laboratory experiments by Rafael Pérez-López; José Miguel Nieto; Gabriel Ruiz de Almodóvar (1919-1935).
In the mining environments of the Iberian Pyrite Belt (IPB), the oxidation of sulphide wastes generates acid drainage with high concentrations of SO4, metals and metalloids (Acid Mine Drainage, AMD). These acid and extremely contaminated discharges are drained by the fluvial courses of the Huelva province (SW Spain) which deliver high concentrations of potentially toxic elements into the Gulf of Cádiz. In this work, the oxidation process of mine tailings in the IPB, the generation of AMD and the potential use of coal combustion fly ash as a possible alkaline treatment for neutralization of and metal removal from AMD, was studied in non-saturated column experiments. The laboratory column tests were conducted on a mine residue (71.6 wt% pyrite) with artificial rainfall or irrigation. A non-saturated column filled solely with the pyrite residue leached solutions with an acid pH (approx. 2) and high concentrations of SO4 and metals. These leachates have the same composition as typical AMD, and the oxidation process can be compared with the natural oxidation of mine tailings in the IPB. However, the application of fly ash to the same amount of mine residue in another two non-saturated columns significantly increased the pH and decreased the SO4 and metal concentrations in the leaching solutions. The improvement in the quality of leachates by fly ash addition in the laboratory was so effective that the leachate reached the pre-potability requirements of water for human consumption under EU regulations. The extrapolation of these experiments to the field is a promising solution for the decontamination of the fluvial courses of the IPB, and therefore, the decrease of pollutant loads discharging to the Gulf of Cádiz.
Distribution and turnover of carbon in natural and constructed wetlands in the Florida Everglades by J. Stern; Y. Wang; B. Gu; J. Newman (1936-1948).
Stable and radiocarbon isotopic contents of dissolved organic C (DOC), dissolved inorganic C (DIC), particulate organic C (POC) and plants were used to examine the source and turnover rate of C in natural and constructed wetlands in the Florida Everglades. DOC concentrations decreased, with P concentrations, along a water quality gradient from the agriculturally impacted areas in the northern Everglades to the more pristine Everglades National Park. δ13C values of DOC in the area reflect contributions of both wetland vegetation and sugarcane from agriculture. Radiocarbon ages of DOC, POC and DIC in the Everglades ranged from 2.01 ka BP to “>modern”. The old 14C ages of DOC and POC were found in impacted areas near the Everglades Agricultural Area (EAA) in the northern Everglades. In contrast, DOC and POC in pristine marsh areas had near modern or “>modern”14C ages. These data indicate that a major source of POC and DOC in impacted areas is the degradation of historic peat deposits in the EAA. In the pristine areas of the marsh, DOC represents a mix of modern and historic C sources, whereas POC comes from modern primary production as indicated by positive Δ14C values, suggesting that DOC is transported farther away from its source than POC. High Δ14C values of DIC indicate that dissolution of limestone bedrock is not a significant source of DIC in the Everglades wetlands. As a restored wetland moves towards its “original” or “natural” state, the 14C signatures of DOC should approach that of modern atmosphere. In addition, measurements of concentration and C isotopic composition of DOC in two small constructed wetlands (i.e., test cells) indicate that these freshwater wetland systems contain a labile DOC pool with rapid turnover times of 26–39 days and that the test cells are overall net sinks of DOC.
Organic geochemistry of the Dongsheng sedimentary uranium ore deposits, China by Jincai Tuo; Wanyun Ma; Mingfeng Zhang; Xianbin Wang (1949-1969).
Organic matter (OM) associated with the Dongsheng sedimentary U ore hosting sandstone/siltstone was characterized by Rock-Eval, gas chromatography–mass spectrometry and stable C isotope analysis and compared to other OM in the sandstone/siltstone interbedded organic matter-rich strata. The OM in all of the analyzed samples is Type III with Ro less than 0.6%, indicating that the OM associated with these U ore deposits can be classified as a poor hydrocarbon source potential for oil and gas. n-Alkanes in the organic-rich strata are characterized by a higher relative abundance of high-molecular-weight (HMW) homologues and are dominated by C 25, C 27 or C 29 with distinct odd-to-even C number predominances from C 23 to C 29. In contrast, in the sandstone/siltstone samples, the n-alkanes have a higher relative abundance of medium-molecular-weight homologues and are dominated by C 22 with no or only slight odd-to-even C number predominances from C 23 to C 29. Methyl alkanoates in the sandstone/siltstone extracts range from C 14 to C 30, maximizing at C 16, with a strong even C number predominance, but in the organic-rich layers the HMW homologues are higher, maximizing at C 24, C 26 or C 28, also with an even predominance above C 22. n-Alkanes in the sandstone/siltstone sequence are significantly depleted in 13C relative to n-alkanes in most of the organic-rich strata. Diasterenes, ββ-hopanes and hopenes are present in nearly all the organic-rich sediments but in the sandstone/siltstone samples they occur as the geologically mature isomers. All the results indicate that the OM in the Dongsheng U ore body is derived from different kinds of source materials. The organic compounds in the organic-rich strata are mainly terrestrial, whereas, in the sand/siltstones, they are derived mainly from aquatic biota. Similar distribution patterns and consistent δ 13C variations between n-alkanes and methyl alkanoates in corresponding samples suggest they are derived from the same precursors. The OM in the organic-rich strata does not appear to have a direct role in the precipitation of the U ore in the sandstone, but an indirect role cannot be excluded. The OM in the U hosting sandstone shows a relatively low hydrogen index, presumably due to oxidation or radiolytic damage.
Arsenic and presumed resistate trace element geochemistry of the Lincolnshire (UK) sedimentary ironstones, as revealed by a regional geochemical survey using soil, water and stream sediment sampling by Neil Breward (1970-1993).
A regional geochemical survey using soils, stream sediment and stream water sampling revealed multi-element geochemical anomalies, though of low environmental mobility, associated with Mesozoic sedimentary ironstones in Lincolnshire, UK. The most prominent of these anomalies were of As and V in soils and sediments, but elevated levels of elements such as Cr, La, Ce and Th were also observed. These were initially thought to be part of a residual resistate element or heavy-mineral suite, but careful examination suggests that these too may be primarily associated with the process of Fe oxide precipitation during the initial formation of the ironstones.
Anglo-Saxon animal husbandry techniques revealed though isotope and chemical variations in cattle teeth by J.A. Evans; S. Tatham; S.R. Chenery; C.A. Chenery (1994-2005).
The Sr concentration and isotope composition of tooth enamel from domesticated animals from two neighbouring Anglo-Saxon settlements, at Empingham (6–7th century) and Ketton (10–12th century) in Rutland, central England, are compared both with each other, and with associated human populations. Data from the Empingham II site form discrete fields in Sr concentration and isotope composition space for cattle, pig and sheep with a partial overlap of the human and pig fields. By contrast there is significant overlap in all the animal and human data fields from the Ketton site. The differences in data distribution between the two sites are attributed to animal husbandry techniques, as the surface geology of the two areas is very similar, implying geological factors are an unlikely cause of the difference. It is suggested that the grazing and feeding patterns of animals at the Empingham II site were controlled and restricted, whereas at the Ketton site the animals grazed and foraged freely over a common area.Strontium isotope variation within cattle molars from the two settlements show marked differences that reflect the nature of their feeding and rearing. The enamel from a cattle molar from the Empingham II site has a well-defined, systematic variation of Sr isotope composition with Sr concentration, whereas no such patterns exist in a comparable cattle molar from Ketton. Chemical and O isotope variations in the cattle tooth from Empingham II show sympathetic variation of Sr and Ba concentrations with Sr isotope composition from cusp to cervix. The cusp has higher Sr and Ba concentrations log (Sr/Ca) ratio of −3.1 and 87Sr/86Sr ratio of 0.71151 where as the cervical region of the enamel has log (Sr/Ca) = −3.3 and 87Sr/86Sr = 0.71061.
Controls on schwertmannite transformation rates and products by Klaus-Holger Knorr; Christian Blodau (2006-2015).
To study the impact of geochemical conditions on the fate of schwertmannite in AMD polluted sediments, pH, concentrations of SO 4 2 - and DOC, and temperature were varied in batch experiments. Schwertmannite transformation was quantified by titration of released acidity and the product investigated with FTIR, XRD, SEM/EDX, and chemical extraction. Rates ranged from 0.0002 d−1 to 0.13 d−1 (transformed fraction/incubation time). Raising pH from 3 to 5 increased transformation by a factor of 5.8 (±2.1) and temperature from 10 to 20 °C by a factor 3.8 (±1.6). Sulphate (20 mmol L−1) and DOC (20 mg L−1) lowered transformation by a factor of 2.5 (±0.4) and 2.4 (±0.5), respectively. The Fe phase was less dissolvable in 1 N HCl but goethite was not detected by XRD. The morphology changed little, even in SO 4 2 - -poor Fe phases. An amorphous, SO4 depleted Fe phase thus formed. Most of the SO4 released from the schwertmannite tunnel structure remained within this phase but changes in IR bands at 1108 cm−1 (ν 3) and 984 cm−1 (ν 1) suggested a relocation of SO4. The study documents the high potential of schwertmannite to buffer pH increase in sediments, particularly at low SO 4 2 - concentrations, and high temperatures.
Dissolution, adsorption and phase transformation in the fluorapatite–goethite system by Åsa Bengtsson; Malin Lindegren; Staffan Sjöberg; Per Persson (2016-2028).
An aqueous system containing fluorapatite (Ca5(PO4)3F), (FAP) and varying amounts of goethite (α-FeOOH) has been investigated. Batch experiments and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy were used to monitor the dissolution products of FAP, as well as the adsorption, and phase transformation of phosphate at the goethite surface over a period of 129 days. The results show that the presence of goethite increases dissolution of FAP, mainly due to the high affinity of phosphate for the goethite surface: Ca 5 ( PO 4 ) 3 F(s) + 3 FeOH + ( 3 + 3 n ) H + ↔ 3 FeH n PO 4 ( n - 2 ) - + 3 H 2 O + 5 Ca 2 + + F - . Besides monitoring the pH changes associated with this reaction, the concentrations of Ca2+ and fluoride were determined. Furthermore, the amount of phosphate adsorbed was quantified from ATR-FTIR spectra. In addition to adsorbed phosphate, phase transformations of goethite into a Fe phosphate phase (FePO4(s)) are seen in the samples with relatively high phosphate to goethite ratios (excess phosphate to available surface sites) equilibrated for 15–129 days.An equilibrium model that takes into account (i) FAP dissolution, (ii) solution complexation, (iii) surface complexation of phosphate species onto goethite and (iv) possible phase transformation Ca5(PO4)3F–CaF2 and FeOOH–FePO4 was designed. This model was found to be in very good agreement with experimental observations and could thus be used to give qualitative and quantitative information about goethite promoted dissolution of FAP under other pH conditions than those studied in the present work.
Hyperfiltration of nickel sulphate solutions through silty sandstone and its effect on hydraulic conductivity by G.J. Houben; F. Wagner (2029-2044).
Hyperfiltration (reverse osmosis) and subsequent precipitation of minerals from the hyperfiltrated solution are processes that potentially decrease the hydraulic conductivity of porous media. These processes were demonstrated by hyperfiltrating NiSO4 solutions through fine-grained sandstone. The mineral precipitates occur in very small (mm sized) layers at the high-pressure side of the samples where they create zones of lowered hydraulic conductivity (2–3 orders of magnitude lower than initial). The total amount of precipitates is very small compared to the dissolved mass which was passed through the membrane. Hyperfiltration-induced precipitates and the resulting lowering of hydraulic conductivities were observed at solute saturations as low as 10%. Nevertheless, at saturations higher than 50% the conductivity reduction strongly increased. Full reversibility of the hydraulic conductivity reduction by extensive re-flushing with water was only obtained at low initial solute saturations (10%). This indicates that precipitated minerals in many pores are susceptible only to very slow, diffusion-controlled re-dissolution.
Adsorption of aromatic carboxylate compounds on the surface of synthesized iron oxide-coated sands by K. Hanna (2045-2053).
The complex mineral assemblages of silica and Fe minerals play a significant role in the transport of compounds in soils and sediments. Five coated sands including Goethite, Lepidocrocite, Ferrihydrite, Hematite and Magnetite were synthesized by a heterogeneous suspension method and characterized by FTIR spectroscopy, XRD, BET surface area and chemical analyses. The synthesis results showed that the degree of coating (mg Fe/g sand) varied with the mineralogy of Fe coating phases, which may have different affinities towards the silica surface. Batch experiments were conducted with two compounds (2,5-dihydroxybenzoic acid and 1-hydroxy-2-naphthoic acid) to quantify the contributions to adsorption from different oxide coatings and compare adsorption characteristics of selected organic acids. Sorption of these compounds to coated sands was examined versus a wide range of conditions (time, pH, ionic strength and sorbate concentration). Because of the attachment of Fe oxide, the coated sand had higher specific surface area, involving a better adsorption efficiency of organic compounds. Mineral surface charge and pH proved to be important for the adsorption of these compounds. The batch results indicated that the degree of coating was the most significant factor enhancing the sorption of aromatic compounds on the surface of sand and the mineralogy of the Fe phase was of less importance.
Fe-solid phase transformations under highly basic conditions by Nikolla P. Qafoku; Odeta Qafoku; Calvin C. Ainsworth; Alice Dohnalkova; Susan G. McKinley (2054-2064).
Hyperalkaline and saline radioactive waste fluids with elevated temperatures from S-SX high-level waste tank farm at Hanford, WA, USA accidentally leaked into sediments beneath the tanks, initiating a series of geochemical processes and reactions whose significance and extent was unknown. Among the most important processes was the dissolution of soil minerals and precipitation of stable secondary phases. The objective of this investigation was to study the release of Fe into the aqueous phase upon dissolution of Fe-bearing soil minerals, and the subsequent formation of Fe-rich precipitates. Batch reactors were used to conduct experiments at 50 °C using solutions similar in composition to the waste fluids. Results clearly showed that, similarly to Si and Al, Fe was released from the dissolution of soil minerals (most likely phyllosilicates such as biotite, smectite and chlorite). The extent of Fe release increased with base concentration and decreased with Al concentration in the contacting solution. The maximum apparent rate of Fe release (0.566 × 10−13 mol m−2 s−1) was measured in the treatment with no Al and a concentration of 4.32 mol L−1 NaOH in the contact solution. Results from electron microscopy indicated that while Si and Al precipitated together to form feldspathoids in the groups of cancrinite and/or sodalite, Fe precipitation followed a different pathway leading to the formation of hematite and goethite. The newly formed Fe oxy-hydroxides may increase the sorption capacity of the sediments, promote surface mediated reactions such as precipitation and heterogeneous redox reactions, and affect the phase distribution of contaminants and radionuclides.
Sulfur and carbon isotope geochemistry of coal and derived coal-combustion by-products: An example from an Eastern Kentucky mine and power plant by Erika R. Elswick; James C. Hower; Ana M. Carmo; Tao Sun; Sarah M. Mardon (2065-2077).
The isotopic compositions of S (δ 34S) and C (δ 13C) were determined for the coal utilized by a power plant and for the fly ash produced as a by-product of the coal combustion in a 220-MW utility boiler. The coal samples analyzed represent different lithologies within a single mine, the coal supplied to the power plant, the pulverized feed coal, and the coal rejected by the pulverizer. The ash was collected at various stages of the ash-collection system in the plant. There is a notable enrichment in 34S from the base to the top of the coal seam in the mine, with much of the variation due to an upwards enrichment in the δ 34S values of the pyrite. Variations in δ 34S and in the amount of pyritic S in the coal delivered to the plant show that there was a change of source of coal supplied to the plant, between week one and week two of monitoring, supporting a previous study based on metal and sulfide geochemistry for the same plant. The fly ash has a more enriched δ 34S than the pulverized coal and, in general, the δ 34S is more enriched in fly ashes collected at cooler points in the ash-collection system. This pattern of δ 34S suggests an increased isotopic fractionation due to temperature, with the fly ash becoming progressively depleted in 34S and the flue gas S-containing components becoming progressively enriched in 34S with increasing temperatures. Substantially less variation is seen in the C isotopes compared to S isotopes. There is little vertical variation in δ 13C in the coal bed, with δ 13C becoming slightly heavier towards the top of the coal seam. An 83–93% loss of solid phase C occurs during coal combustion in the transition from coal to ash owing to loss of CO2. Despite the significant difference in total C content only a small enrichment of 0.44–0.67‰ in 13C in the ash relative to the coal is observed, demonstrating that redistribution of C isotopes in the boiler and convective passes prior to the arrival of the fly ash in the ash-collections system is minor.
Characterisation of concentrates of heavy mineral sands by micro-Raman spectrometry and CC-SEM/EDX with HCA by Anna Worobiec; E. Anna Stefaniak; Sanja Potgieter-Vermaak; Zbigniew Sawlowicz; Zoya Spolnik; René Van Grieken (2078-2085).
The effectiveness of electrostatic separation of zircon and TiO2 phases during the processing of heavy mineral concentrates derived from heavy mineral sands depends upon the chemical, physical and mineralogical characteristics of the concentrates. Here the authors’ demonstrate the use of combined micro-Raman spectrometry (MRS), scanning electron microscopy (SEM) and computer controlled scanning electron microscopy coupled with an energy-dispersive X-ray detector (CC-SEM/EDX), followed by hierarchical cluster analysis (HCA) to determining these characteristics on samples from the non-magnetic fraction of the Richards Bay (South Africa) heavy mineral concentrate. All samples were found to be predominately comprised a heterogeneous population of grains of zircon and rutile and other TiO2 polymorphs with diverse physicochemical properties. Combined MRS and CC-SEM/EDX enabled the identification of textural characteristics which impacted on the efficiency of electrostatic separation of zircon and rutile concentrate streams.
Carbon and hydrogen isotopic variations of natural gases in the southeast Columbus basin offshore southeastern Trinidad, West Indies – clues to origin and maturity by Giselle A. Norville; Richard A. Dawe (2086-2094).
Natural gas can have two distinct origins, biogenic and thermogenic sources. This paper investigates the types and maturities of natural gas present in the SE Columbus basin, offshore Trinidad. The chemical composition and the isotope ratios of C and H were determined for approximately 100 samples of natural gas from eight areas within the SE Columbus basin. These compositions and isotopic data are interpreted to identify the origins of gas (biogenic, thermogenic) and maturity. The data showed that the gases in the SE Columbus basin are of both biogenic and thermogenic origin with a trend of mainly thermogenic to mixed to biogenic when moving from SW to NE across the basin. This trend suggests differential burial of the source rock. The presence of mixed gas indicates there was migration of gas in the basin resulting in deeper thermogenic gas mixing with shallow biogenic gas.