Applied Geochemistry (v.17, #8)
Papers to appear (I).
IAGC Memb. Form (XI).
Current Lit Survey (III-X).
Environmental Geochemistry by Ron Fuge (959).
Spatial distribution of heavy metals and arsenic in soils of Aragón (northeast Spain): controlling factors and environmental implications by Ana Navas; Javier Machı́n (961-973).
Legal regulation of heavy metal contents is an important issue in many European countries, where laws still do not exist establishing the heavy metal levels permitted in soils. As a first step to determine the reference levels of heavy metals, it is necessary to know their contents in soils under natural conditions. To achieve this goal in the Autonomous Community of Aragón, a total of 133 sites have been sampled. A balanced allotment of the sampling sites, according to soil spatial distribution in the region, has been carried out by selecting 9 soil types that represent 97.5% of its surface area. Fifteen elements (Cr, Cu, Ba, As, Sb, Hg, Sn, Mn, Fe, Al, Zn, Ni, Co, Cd and Pb) have been analysed by (ICP–AES) after a partial acid extraction. The content of analysed elements has been correlated to some soil parameters such as organic matter, pH, and granulometric fractions. Results of the statistical analyses have shown a large variety and complexity in some of these relationships. The main factors for variation in the heavy metal contents are both the soil type and the lithology. Gypsisols and Calcisols developed on sedimentary rocks have the lowest contents while Leptosols overlying metamorphic and igneous rocks have the highest contents. The spatial distribution of heavy metal contents shows a large variability with the highest contents in the mountain ranges (Iberian and Pyrenees) and the lowest in the plains of the central Ebro valley.
Baselines of certain bioavailable and total heavy metal concentrations in Finland by T. Tarvainen; E. Kallio (975-980).
“Total” (hot aqua regia extraction) and “bioavailable” (acid ammonium acetate EDTA extraction) heavy metal concentrations were measured for 90 basal till samples in Finland. The study covers the whole country. The “total” natural concentrations of several heavy metals in many places exceed the Finnish guideline or limit values designated for contaminated land. The “bioavailable” concentrations are usually only 1–5% of the “total” concentrations. The correlations between “total” and “bioavailable” concentrations were significant for Cr (Pearson's correlation coefficient 0.455∗∗, N=87), Cu (0.452∗∗, N=89), Ni (0.216∗, N=89), Pb (0.325∗∗, N=89), V (0.613∗∗, N=90) and Zn (0.569∗∗, N=89). ∗∗ Signifies that the correlation is significant at the 0.01 level, and ∗ signifies that it is significant at the 0.05 level.
Oxidation and toxicity of chromium in ultramafic soils in Zimbabwe by G.R.C. Cooper (981-986).
Ammonium acetate extractable Cr, identified as Cr(VI) using s-diphenylcarbazide, was detected as the toxic agent in certain stored ultramafic subsoils, that severely affected the growth of maize. The subsoils contained Fe–Mn concretions, which was evidence of oxidation-reduction cycles and had high total Cr contents and significant levels of easily reducible Mn. Before dry storage 8 years previously along with some 100 other bulked soil samples, these subsoils had not been toxic to maize. Some change such as oxidation had occurred during storage. Certain other subsoils containing high total Cr but no concretions (i.e. well aerated subsoils) and topsoils containing high total Cr, were treated with various Mn compounds in an attempt to induce Cr toxicity. Only subsoils treated with oxidizing KMnO4 induced toxicity in maize owing to a measurable release of extractable Cr. The topsoils were not susceptible to oxidation and were not toxic to maize. In order to explain the apparent slow oxidation of Cr in storage in some soils, induced oxidation of Cr in other soils and insusceptibility to oxidation of Cr in yet other soils, a two-stage mechanism is proposed. Firstly, slow hydrolysis under moist field conditions of Cr(III) in chromite or from isomorphically substituted Cr, to Cr(OH)3. Secondly, slow oxidation of Cr(OH)3 to Cr(VI) by the reduction of easily reducible Mn oxides. The first stage pertains to subsoils and not topsoils, presumably because subsoils are generally moister. Only concretionary subsoils that contain specific easily reducible forms of Mn (poorly aerated) are apparently capable of oxidising Cr(III) to Cr(VI) that is soluble and toxic. Where there is an absence of specific easily reducible Mn in subsoils (well aerated), oxidation may be induced by the addition of an oxidising agent. The forms of Mn oxide likely to be present in the different subsoils and topsoil are discussed.
Amending highly weathered soils with finely ground basalt rock by G.P Gillman; D.C Burkett; R.J Coventry (987-1001).
Surface (0–10 cm) samples of 7 soils from tropical coastal Queensland were incubated at room temperature and at field capacity with finely ground (<150 μ) basalt rock for 3 months. The amendment was applied at 0, 1, 5, 25 and 50 t/ha to cover situations of moderate application rates to that where the amendment might be banded to produce high local concentrations. Having an abrasion pH of about 9, the amendment was able to reduce both active acidity (as estimated by an increase in soil pH) and reserve acidity (reduction in % Al saturation of the CEC). Increases in soil pH resulted in increased CEC, depending on the variable charge nature of each soil, accompanied by increases in exchangeable Ca, Mg, and K supplied by the basalt. The amounts of basic cations converted to exchangeable form constituted only a fraction of the amounts applied. Thus the cations held in reserve ensure that the effect of cation enrichment will be prolonged. In some soils phosphate sorption was significantly reduced by crushed basalt application. Furthermore, ‘available’ P as measured by extraction with 0.005 M H2SO4 was increased. These effects appear to be due to the release of silicate from the basalt as well as modest amounts of phosphate in the rock. Three extractants commonly used for estimating Si availability in sugarcane production indicated that all 7 soils contained sub-optimal levels of the element. Application of crushed basalt rock increased extractable Si levels above what is considered sufficient for this crop. The incubated soils were placed in columns and leached with the equivalent of 2750-mm (average wet season) rainfall. Re-analysis showed that the favourable chemical soil properties imparted by the amendment were retained. These results add further support to the contention that the effects of amelioration will continue for some time.
Concentrations of major and trace elements in soil and grass at Shimba Hills National Reserve, Kenya by Paul Sutton; John Maskall; Iain Thornton (1003-1016).
Concentrations of major and trace elements in soils and grass are determined at Shimba Hills National Reserve in Kenya using geochemical mapping techniques. The study investigates the influence of soil and vegetation type on the concentrations of Na, K, Mg, Ca, Mn, P, Co, Cu, Zn, Mo, Ni and Se in soils and grass. The implications are assessed for the nutrition of the sable antelope, of which the Reserve supports the last remaining viable population in Kenya. Low concentrations in surface soils of a number of major and minor elements are attributed to the geochemical nature of the underlying parent materials of sands, sandstone and grits. Within the Reserve, variations in the element status of surface soils are related to the vegetation and soil types. Elevated element concentrations in surface soils in natural forest areas are attributed to the influence of litterfall whilst in grassland areas, soil element status is controlled by soil type and decreases in the order ferralsols > acrisols > arenosols. The general depletion of major and minor elements in soils at Shimba Hills is not reflected as fully in grasses in which nutrient concentrations were of similar magnitude to those reported from other Kenyan conservation areas. Burning of grassland areas leads to elevated concentrations of K, P, Co, Cu and Mo in grasses, elevated soil-plant uptake ratios for P and K and elevated soil pH. It is suggested that increased availability of P in soils at elevated soil pH levels contributes to its enhanced uptake into grass. A tentative assessment of the mineral status of grass at the Reserve using guidelines developed for domestic ruminants indicates deficiencies of Na, K, P and Zn and that the Ca:P ratio exceeds the tolerable range for animals. In addition, the low concentrations of Cu, Co and Zn in surface soils in the Reserve indicate that the potential supply of these elements to plants is limited.
Geochemistry and the mineral nutrition of agricultural livestock and wildlife by Iain Thornton (1017-1028).
Relations between the geochemical nature of soils and their parent materials and the occurrence of nutritional deficiencies and excesses in grazing livestock have been documented since the 1960s and earlier, with notable work in Australia, New Zealand, United Kingdom, Ireland, USA and the Soviet Union. Studies at Imperial College London, into the development of regional geochemical mapping techniques as a means of delineating nutritional problems commenced in the 1960s and have continued to the present. Research has mainly focussed on deficiencies of Cu, Co and Se in cattle and sheep, and the role of Mo and S in the soil/plant system in both clinical and sub-clinical hypocuprosis in cattle. Exposure to heavy metals, in particular Pb, Zn, Cd and the metalloid As have also received attention in areas contaminated by past mining and smelting activities. Soil and plant factors influencing the dietary supply of both essential trace elements and toxic metals have been studied, including their speciation and bioavailability. Soil ingestion has been recognised as an important exposure pathway of heavy metal contamination to grazing cattle, and as an antagonist of Cu supply and a source of dietary Co in sheep. Relations between soil geochemistry and the mineral status of wildlife species, in particular impala and black rhinoceros, have been established in Kenya and recent work, presented elsewhere in this Symposium, has concerned the supply of nutrients to the Roosevelt sable in Kenya. The compilation of regional and national multi-purpose geochemical atlases, based on the systematic sampling of soils or stream sediments, is now recognised as a priority in many countries of the developed and developing world. This paper explores the opportunities for future research into the application of geochemical maps for the optimisation of land use, efficient livestock production, and improving conservation of wildlife.
Quantitative-spatial assessment of the risks associated with high Pb loads in soils around Lavrio, Greece by A Korre; S Durucan; A Koutroumani (1029-1045).
The advantages of quantitative environmental risk assessment techniques over the more commonly used qualitative approach is widely accepted. Yet, correct implementation of quantitative risk assessment is a difficult task, given the present state of understanding of the environmental processes. One important parameter related to the level of risk is the extent and geographic spread of pollutants. Geographic information systems (GIS) provide a very powerful and highly flexible tool that increases the sophistication of the risk assessment methodology. Through spatial representation, the estimated risk becomes more comprehensive, thus facilitating the decision making process. In addition, valuable qualitative information can be incorporated into the risk assessment procedure with the help of GIS. This paper illustrates a methodology which incorporates a probabilistic risk assessment model within a GIS. The case study utilised to illustrate the methodology is a large industrial area around a number of decommissioned minerals production and processing sites with known high heavy metal loads at Lavrio, Greece. The spatial distribution of Pb concentration in soils was derived from 425 soil samples collected over a total area of 120 km2. A risk assessment model was constructed to simulate and assess the risk associated with high Pb loads in soils in the study area. The methodology consists of a typical exposure assessment model, constructed for adult and child populations. The Pb exposure for both populations is compared with relevant reference dose levels providing hazard quotients. The results of the quantitative risk assessment study are analysed and presented in the form of GIS maps covering the study area.
Groundwater geochemistry of a small reservoir catchment in Central Tunisia by Jean-Pierre Montoroi; Olivier Grünberger; Slah Nasri (1047-1060).
Due to the scarcity of water resources in semiarid sedimentary basins, hill reservoirs are often constructed to recharge groundwater and limit runoff induced water loss. The impact of such reservoirs on groundwater chemistry is investigated in the aquifers of the El Gouazine watershed, Central Tunisia. Three groundwater types are recognised, Ca–HCO3, Na–Cl and Ca–SO4. The strong similarity between host rock and groundwater chemistries indicates significant rock–water interaction. A flowpath, along which the chemical composition of the groundwater evolves, can be identified using the contrast in stable isotope signature between upstream and downstream groundwater. Shallow upstream groundwater is recharged by the infiltration of rainwater with the rate of recharge strongly linked to the permeability of the host lithology. Calcium and HCO3 are supplied to an alluvial aquifer from a more rapidly recharged limestone aquifer with the concentration of Ca and HCO3 ions decreasing by dilution. The alluvial aquifer is also enriched in Ca and SO4 during the downstream flow of groundwater through gypsiferous materials. There is evidence of mixing between meteoric groundwater and evaporated reservoir water. Below the reservoir and partly responsible for reservoir leakage is a sandy aquifer, formed by weathering and erosion of a sandstone host which also supplies water to the alluvial aquifer.
Processes controlling the retention and release of manganese in the organic-rich catchment of Loch Bradan, SW Scotland by Margaret C Graham; Keith G Gavin; John G Farmer; Alexander Kirika; Andrew Britton (1061-1067).
Loch Bradan, a drinking water reservoir in SW Scotland, frequently exhibits unacceptably high dissolved Mn concentrations. Both the surrounding catchment and the loch sediments are potential sources of Mn to the loch water. This study focused on the catchment soils, which are peaty, and found that redox cycling was an important process with respect to retention of Mn in the top sections (0–15 cm). Under more reducing conditions, reduction to Mn(II) and subsequent complexation by humic substances was observed at greater depth in some soil profiles. Complexation by humic substances is important because lateral water flow can remove soluble complexes and indeed this study observed that about 50% of Mn was humic-complexed in the stream waters feeding into the loch. It was particularly evident that the soil profile with the lowest Mn inventory exhibited the greatest extent of humification and that the remaining Mn was predominantly in a non-easily reducible form.
Environmental geochemistry of abandoned mercury mines in West-Central Nevada, USA by John E Gray; James G Crock; David L Fey (1069-1079).
The Humboldt River is a closed basin and is the longest river in Nevada. Numerous abandoned Hg mines are located within the basin, and because Hg is a toxic heavy metal, the potential transport of Hg from these mines into surrounding ecosystems, including the Humboldt River, is of environmental concern. Samples of ore, sediment, water, calcines (roasted ore), and leachates of the calcines were analyzed for Hg and other heavy metals to evaluate geochemical dispersion from the mines. Cinnabar-bearing ore samples collected from the mines contain highly elevated Hg concentrations, up to 6.9 %, whereas calcines collected from the mines contain up to 2000 mg Hg/kg. Stream-sediment samples collected within 1 km of the mines contain as much as 170 mg Hg/kg, but those collected distal from the mines (>5 km) contain <1 mg Hg/kg, indicating significant geochemical dispersion of Hg downstream from the mines. Sediment samples collected from the Humboldt River basin contain ⩽0.28 mg Hg/kg. Leachate samples of the calcines obtained by using a synthetic water leaching technique contain as much as 1500 μg Hg/l, suggesting that some calcines contain soluble Hg compounds. However, much lower Hg concentrations were found in water samples collected from the Humboldt River system, and these were below the 0.012 μg/l Hg standard used to protect against chronic effects to aquatic wildlife. Mercury transference from these mines to the Humboldt River basin is generally minor because the mines are typically >8 km from the Humboldt River, and Hg is transported and diluted through a large volume of pediment before it reaches the Humboldt River.
Different types of fine-grained sediments associated with acid mine drainage in the Libiola Fe–Cu mine area (Ligurian Apennines, Italy) by E Dinelli; F Tateo (1081-1092).
Different types of fine-grained chemical precipitates were characterized in the surroundings of the pyrite-chalcopyrite mine of Libiola (Northern Italy). Both water chemistry and sediment composition were used to investigate metal mobility near the mine area. Local drainage waters were very acidic (with a pH as low as 2.5) and were rich in dissolved metals (Fe, Al, Cu, Zn, Mn, Ni). Sediments associated with low pH water (pH <4.5) were ochreous mixtures of schwertmannite and goethite with traces of jarosite. Their chemistry was dominated by Fe and they had, compared to other sediments investigated, low concentrations of other metals. When the acidity decreased gradually, other precipitates formed. At a pH of approximately 5, a poorly crystalline, whitish, Al-rich precipitate occurred. At a pH between 6 and 7, a poorly crystalline, blue, Cu (Zn) rich phase was present. These “sequential” precipitation events progressively reduced the metal loading typical of the acidic mine water when there was a gradual mixing with normal water. When a sudden mixing between normal waters (pH ∼8, Ca–HCO3, low metal bearing) and acidic waters took place, a rapid flocculation occurred of mixed precipitates containing Fe, Al and trace elements.
Investigation of contaminant metal dispersal from a disused mine site at Tyndrum, Scotland, using concentration gradients and stable Pb isotope ratios by A.B MacKenzie; I.D Pulford (1093-1103).
Results are presented for a study of Pb and Zn concentrations and stable Pb isotope ratios for mining wastes, river sediments and 210Pb-dated peat cores from the vicinity of a derelict Pb/Zn mine at Tyndrum in central Scotland. Mining was carried out at Tyndrum between 1741 and 1862 and the original waste dumps were reworked between 1916 and 1925. Little remains of the original buildings and workings and the contemporary distribution and dispersion pathways of the residual waste are poorly defined. The mine and ore processing waste dumps were readily identified as highly polluted, barren areas, with concentrations of up to 21 and 3.4% Pb and Zn, respectively. The Pb in the waste was characterised by a 206Pb/207Pb atom ratio of 1.146±0.004 and a 208Pb/207Pb ratio of 2.432±0.007. Significant quantities of waste were also found along riverbanks and in river channel sediments in the vicinity of the mine, with concentrations of up to 5.22% Pb and 2.35% Zn. Concentrations of Pb and Zn in river channel sediments decreased markedly with increasing distance downriver from the mining area. However, the decrease in Pb concentrations in the <53 μm fraction was less pronounced, with a relatively high concentration of 0.076% being observed at a distance of 6.5 km from the mine, suggesting significant fluvial transport of this size fraction of waste. The stable Pb isotopic characteristics of the river sediments were consistent with the mine waste being the dominant source, along with minor inputs from local bedrock and vehicle exhaust emissions. The peat core data revealed high levels of Pb deposition throughout the period of the mining operation and very high levels of input in the early 20th century, almost certainly as a result of the reworking of the former waste dumps. As with the river sediments, the isotopic characteristics of the Pb in the peat cores were consistent with a dominant input from the mine waste and minor contributions from bedrock and vehicle exhaust emissions. The results suggest that waste from the mining operation has been a significant source of contaminant heavy metals for several hundred years and continues to be so. The apparent fluvial transport of Pb from the mine site is consistent with previous work suggesting that Tyndrum mine waste is the probable origin of anomalously high levels of Pb deposited in the sediments of Loch Tay, some 25 km to the east. The study highlights the utility of stable Pb isotope analyses in the investigation of sources and environmental dispersion of contaminant Pb.
Geological analogue for circumneutral pH mine tailings: implications for long-term storage, Macraes Mine, Otago, New Zealand by D.A Chappell; D Craw (1105-1114).
Tailings from the Macraes Au mine cyanidation process are stored in an impoundment about 0.6 km2 and 80 m deep whose pH is maintained near 8 by the neutralizing capacity of the gangue minerals. The tailings are sandy (>50 μm particles), have a hydraulic conductivity of about 10−2 m/day, and contain 0.1–1.0 wt.% S and 0.1–1.5 wt.% graphitic C from the primary deposit. Concentrations of As in the pore water of the mixed tailings, which are a combination of various tailings types, range from 0.1 to 20 ppm, HCO3 - is 100 to 200 ppm, and dissolved SO4 is 100–1700 ppm. The mixed tailings will be stored in this impoundment in perpetuity after mining ceases. Confidence in the long-term pH stability of these tailings can be gained from examination of mineralogically and chemically similar geological analogues in the immediate vicinity. A sequence, typically about 5 m thick, of sands and gravels derived from the Macraes mineralized zone 12–28 ka ago contains rounded detrital sulfide mineral grains which are unoxidized despite their close proximity to the surface and the occasional incursion of oxygenated waters. These sediments have a hydraulic conductivity of about 10−4 m/day. Saturating water pH is currently 7–8. Sands with 0.2–0.8 wt.% organic C host SO4-reducing bacteria (SRB), and local cementation by authigenic framboidal pyrite has occurred. SRB were found in water-saturated sediments with decreased hydraulic conductivity and alkaline and anoxic conditions. These bacteria are involved in the formation of authigenic framboidal pyrite, reducing the cycling of dissolved Fe in the sediments. Carbon is not a limiting factor in this process as organic matter is present in the sandstone and ground water contains up to 180 ppm HCO3 -. Comparison of the 28 ka old sediments with the modern tailings suggests that the chemical behaviour of the two will be similar, possibly with the crystallization of authigenic pyrite in the tailings over the long term. As long as the present slightly anoxic and circumneutral pH environmental conditions are maintained in the mixed tailings impoundment, sulfide decomposition and acidification are unlikely.
A baseline survey of the distribution and origin of platinum group elements in contemporary fluvial sediments of the Kentish Stour, England by E de Vos; S.J Edwards; I McDonald; D.S Wray; P.J Carey (1115-1121).
The extensive anthropogenic use of the platinum group elements (PGE: Ru, Rh, Pd, Os, Ir and Pt) is the main factor responsible for the widespread dispersion of these elements throughout the environment. Significant quantities of the PGE enter fluvial systems via road runoff, storm drains and wastewater and sewage treatment systems, and may accumulate in fluvial sediments by physical and chemical processes. A baseline survey of contemporary fluvial sediments in the Kentish Stour river, east Kent, England, has been undertaken to document the sources and distribution of anthropogenic PGE in an attempt to constrain some of the physical and chemical parameters that may influence the distribution of these elements. The geology of the catchment of the Kentish Stour is dominated by carbonate and silicate sedimentary rocks, and the river passes through urban and rural land and receives inputs of waste from sewage works. Nine sedimentary rocks, 4 motorway-runoff sediments and 22 river sediments were analysed for PGE by NiS fire assay preconcentration and ICP–MS. The highest element abundances occur in the motorway-runoff sediments (maximum total PGE content of 55 ng/g), whilst the lowest values were recorded in the sedimentary rocks, where some samples contain PGE at concentrations below the limit of detection. The total PGE content of the river sediments ranged from 0.4 to 10.8 ng/g. The distribution and variation in concentrations and ratios of the PGE in the contemporary fluvial sediments of the Kentish Stour correspond strongly with land-use changes (urban versus rural) and with points of discharge from sewage works. The absence of a pure catalytic converter signature in the river sediments, however, indicates that source signatures may be mixed in sewage works or that PGE may chemically fractionate in the fluvial environment.
Isotope dilution ICP–MS analysis of platinum in road dusts from west central Scotland by E Higney; V Olive; A.B MacKenzie; I.D Pulford (1123-1129).
In response to the increased use of catalytic convertors in motor vehicle exhausts systems, recent studies, employing GF–AAS or ICP–MS analysis of platinum group elements (PGEs), have identified a significant increase of Pt and Pd concentrations in road dust and roadside soils leading to concern over potential effects on human health. After deposition, the PGEs are subject to various physical and chemical transformations, potentially resulting in migration into other environmental compartments i.e. soils, the aquatic system and biota. However, the processes involved are poorly understood and the reactivity, bioavailability, and speciation of the PGEs are ill defined. In contrast to environmental studies, in geochemical research, Isotope Dilution ICP–MS (ID ICP–MS) has primarily been used for the quantification of Pt, providing a significant improvement in accuracy by allowing removal from the analyte solution of elements which could potentially give isobaric interference in the mass spectra. In the present work, an ID ICP–MS analytical technique with a detection limit of 0.1 μg kg−1 has been used for determination of concentrations of Pt in road dust samples from west central Scotland. The study highlights potential interference problems that may occur in analysis of Pt in environmental matrices using ICP–MS. Initial application of ID ICP–MS in a study of roadside environments in west central Scotland has revealed significantly enhanced concentrations of Pt, within the range 13–335 μg kg−1, in road dust samples from a trunk road and motorway, representing a significant increase relative to surface soils in this area that are remote from roads, which have Pt concentrations of less than 1.0 μg kg−1. In contrast, lower levels of contamination of 1.8–11.8 μg kg−1 were observed for dust samples from residential areas, in the town of East Kilbride.
The environmental impact of ash management in coal-based power generation by Yvonne Hansen; Philippa J Notten; James G Petrie (1131-1141).
The coal-based power generation industry faces increased pressure to improve its environmental performance in the light of concerns over greenhouse gas emissions, water availability and releases of both acid gases and metals to air and water. Assessment of its environmental performance requires a methodology whereby all environmental impacts can be assessed accurately in full cognisance of their spatial and temporal dimensions, while taking into account the social acceptability of technologies employed. In this work, a methodology is developed to determine the environmental impact associated with solid wastes generated by this industry, and the application of this to the specific case of ash management is demonstrated. This methodology involves a consideration of leachate generation processes from ash impoundments, and subsequent mobility of leached components into groundwater, with due attention given to an analysis of pertinent physico-chemical phenomena. This analysis results in the identification of a time-dependent concentration profile of mobile constituents at the interface between the ash impoundment and the surrounding environment. The integration of leachate prediction modelling with plume dispersion modelling tools provides a measure of the extent to which a land mass is affected by any subsequent leachate migration. In this way it is possible to obtain a time dependent footprint of affected land which could be used as a semi-site specific indicator of the environmental impact of solid waste management practices.
Utilisation of fly ash in a geopolymeric material by J.C. Swanepoel; C.A. Strydom (1143-1148).
Finding means of utilising waste products is a very important field of research at the moment. In this study, fly ash, a waste product of the electricity and petrochemical industries, was investigated as a basic ingredient of a new geopolymeric material. The similarity of fly ash to natural pozzolans has encouraged the use of this waste product in the synthesis of geopolymers, which, in turn, can best be viewed as consisting of a polymeric Si–O–Al framework. Manufacturing of the geopolymers was conducted by mixing fly ash, kaolinite, sodium silicate solution, NaOH and water. The samples were cured at 40, 50, 60 and 70 °C for different time intervals (6, 24, 48 and 72 h). The optimum condition was found to be at 60 °C for a period of 48 h. Compressive strength measurements show a maximum strength of almost 8 MPa after 28 days. Infrared spectroscopic measurements were obtained of the samples after 7 and 28 days. X-ray diffraction measurements show quartz as the main constituent with the largest part of the geopolymer structure being amorphous and glass-like.
Outlier-resistant errors-in-variables regression: anomaly recognition and grain-size correction in stream sediments by Robert C Szava-Kovats (1149-1157).
Regression analysis is a well-established method to correct for grain size differences in suites of sediments. However, distortion caused by the presence of outliers and imprecision in both variables can hinder many common regression models from performing adequately. Median sum of weighted residuals (MSWR) regression is strongly outlier-resistant and accounts for imprecision in both variables for each member of a dataset. In a case study of Ni and Pb normalisation for a suite of stream sediments in NE Estonia, the ability of MSWR regression to detect anomalies was compared to ordinary least squares, weighted least squares, least absolute deviation and least median of squares regression. MSWR regression not only revealed more anomalous samples than the other methods, but also was able to distinguish anomalies in samples at comparatively low heavy metal concentration. This feature is particularly significant when tracking heavy metal dispersion downstream from point sources.
Evaluation of the use of modified coal ash as a potential sorbent for organic waste streams by C.D Woolard; J Strong; C.R Erasmus (1159-1164).
Fly ash was modified by hydrothermal treatment with 7 M NaOH. The resultant product displayed an 8-fold increase in surface area. The primary crystalline component of the modified fly ash was identified by X-ray diffraction to be hydroxysodalite (Na6Al6Si6O24 •8H2O). The cation exchange capacity of the modified ash was significantly increased over that of the raw fly ash (188 vs 2 meq g−1). Adsorption experiments showed that the modified fly ash adsorbed a cationic dye (methylene blue) to a much greater extent than an anionic dye (alizarin sulfonate). Saturation adsorption revealed that the capacity of the ash for methylene blue had increased 10-fold during modification when compared to the raw ash. Adsorption is thus ascribed to be a surface effect rather than involving incorporation into the channels of the hydroxysodalite structure.
Ozonation of diesel fuel in unsaturated porous media by Byung-Tae Lee; Kyoung-Woong Kim (1165-1170).
The objectives of this study were to determine the feasibility of ozonation in unsaturated porous media, and consequently to observe its features and to identify possible limiting factors. Diesel fuel was chosen to represent a complex organic contaminant that is widespread in the environment. In this experiment, the effects of several ozonation features were investigated. Sand was spiked with commercially available diesel fuel (17.024 g diesel/kg dry sand), and packed into a column. Ozone was supplied into the column in a downward direction. When the sand was treated for 7 h at 20 mg ozone/l of air, 40% of the diesel was removed. As the ozone concentration increased from 5 to 20 mg ozone/l, the removal efficiency increased. The removal rate varied significantly depending on the ozone concentration and the treatment duration. At higher ozone concentration, significant quantities of ozone were consumed by the intermediates produced by the ozonation process, and therefore, the removal efficiency and the apparent removal rate of diesel became lowered. The low removal efficiency of diesel results from the high concentrations of normal alkanes. Total hydrocarbon concentration (THC) in the effluent gas was measured using a total hydrocarbon analyzer. The THC decreased with the period of exposure and increasing ozone concentration. Ozonation decreased the gas-extractable fraction and accordingly, the THC decreased. Water-extractable fractions formed by the action of ozone were further oxidized by ozone. Due to the reduction of WEOC (water-extractable organic C) caused by ozone treatment, the potential spread of contamination can be reduced.