Dissolved Aluminum Concentrations Research Articles

Aluminium in UK rivers: a need for integrated research related to kinetic factors, colloidal transport, carbon and habitat

Dissolved aluminium concentrations ([Al]) in the <0.45 μm filtered fraction are described for 54 UK river sites covering rural, acidic/acid sensitive, agricultural and urban typologies, and wide pH range (4 to 11). High [Al] occurred under acidic conditions and for acid runoff neutralised by bicarbonate rich groundwater. Thermodynamic analysis indicates Al hydroxide/hydroxy-silicate oversaturation at circumneutral pH across the rivers, but undersaturation at lower/higher pH. The oversaturation reflects in part the presence of Al bearing colloids as indicated by (1) [Al] being correlated with components associated with both lithogenic (Fe, Ti and lanthanides) colloids and organic carbon, (2) baseflow studies using cross-flow ultrafiltration and (3) comparison of our data with Acid Waters Monitoring Network (AWMN) information on labile and non-labile Al. Tree harvesting and emission reductions of SO(x) in acidic and acid sensitive catchments in mid-Wales led to acidification reversal, lower [Al] and changing [H(+)] - [Al] relationships. The [Al] decline was confined to acidic conditions while [Al] increased during the later part of the monitoring period with a peak around 2002 for moorland and forested systems. Colloidal production across the flow range was indicated late in the record by comparison of our data with information collected by the AWMN for a site in mid-Wales. This production seems interlinked with organic carbon and with dissolved CO(2) changes. In order for further understanding of Al hydrogeochemistry in river systems there is a need to integrate research that moves from equilibrium to kinetic and colloidal consideration including the critical issues of organic and inorganic controls within the context of bioavailability and aquatic stress. The colloidal Al may well be of low environmental concern to fish and other factors such as habitat may well be critical.

Effects of Acidification on Dewaterability and Aluminum Concentration of Alum Sludge

This study utilizes the Terzaghi-Voigt model to characterize the effects of acidification on the dewaterability of alum sludge. Alum sludge, which was obtained from the sedimentation basins of a water treatment plant using poly aluminum chloride as coagulant, was acidified to different pH levels with sulfuric acid. The dewaterability of the acidified sludge was characterized by expression tests. The results show dewaterability enhancement was insignificant until pH was below 4. Further improvement in dewaterability can be achieved by polymer conditioning. The Terzaghi-Voigt model can be applied to explain the difference in dewaterability between acidified and original sludges. Results also show dissolved aluminum concentrations were controlled by minerals in the influent rather than amorphous aluminum hydroxide.

The kinetics of gibbsite dissolution in NaOH

The dissolution of aluminum hydroxides from bauxite ores constitutes a key process in the aluminum industry. Generally, aluminum minerals in bauxites are present in the form of gibbsite and/or boehmite. Kaolinite, an aluminosilicate that is also present in bauxites, is a critical contaminant of the process. The understanding of the effect of the bauxite composition and of the process variables on the kinetics of dissolution can lead to the development of kinetic models and allow for subsequent process optimization. In this work, gibbsite dissolution in sodium hydroxide was studied in an isothermal batch reactor. Reaction temperature and the initial sodium hydroxide concentration were varied within the ranges 60 to 100 °C and 5 to 10 wt.% (1.2 to 2.5 mol/L), respectively, in accordance with a full 3-level factorial experimental design. For each experimental run, dissolved aluminum concentration was measured along the reaction time (up to 300 min). Kinetic models were developed and implemented in order to describe gibbsite dissolution, assuming that the chemical reaction was the rate-controlling step and that nonporous particles shrank along the time. Parameter estimation was performed with the Particle Swarm method coupled with a Gauss–Newton method. The first-order reversible reaction model was shown to provide good fits of the available experimental data. The estimated activation energy (110 kJ/mol) and heat of dissolution (26.4 kJ/mol) are in good agreement with other values reported in the literature. When conversions are far from equilibrium, it is shown that a simpler first-order irreversible model can also be used with confidence to represent the process.

Groundtruthing and potential for predicting acid deposition impacts in headwater streams using bedrock geology, GIS, angling, and stream chemistry

Atmospheric acid deposition is of environmental concern worldwide, and the determination of impacts in remote areas can be problematic. Rainwater in central Pennsylvania, USA, has a mean pH of ≈ 4.4. Bedrock varies dramatically in its ability to neutralize acidity. A GIS database simplified reconnaissance of non-carbonate bedrock streams in the Valley and Ridge Province and identified potentially chronically impacted headwater streams, which were sampled for chemistry and brook trout. Stream sites ( n = 26) that originate in and flow through the Tuscarora had a median pH of 5.0 that was significantly different from other formations. Shawangunk streams ( n = 6) and non-Tuscarora streams ( n = 20) had a median pH of 6.0 and 6.3, respectively. Mean alkalinity for non-Tuscarora streams (2.6 mg/L CaCO 3) was higher than the mean for Tuscarora streams (0.5 mg/L). Lower pH and alkalinity suggest that the buffering capability of the Tuscarora is inferior to that of adjacent sandstones. Dissolved aluminum concentrations were much higher for Tuscarora streams (0.2 mg/L; approximately the lethal limit for brook trout) than for non-Tuscarora streams (0.03 mg/L) or Shawangunk streams (0.02 mg/L). Hook-and-line methods determined the presence/absence of brook trout in 47 stream reaches with suitable habitat. Brook trout were observed in 21 of 22 non-Tuscarora streams, all 6 Shawangunk streams, and only 9 of 28 Tuscarora stream sites. Carefully-designed hook-and-line sampling can determine the presence or absence of brook trout and help confirm biological impacts of acid deposition. 15% of 334 km of Tuscarora stream lengths are listed as “impaired” due to atmospheric deposition by the Pennsylvania Department of Environmental Protection. 65% of the 101 km of Tuscarora stream lengths examined in this study were impaired.

STREAM ECOSYSTEM RESPONSE TO LIMESTONE TREATMENT IN ACID IMPACTED WATERSHEDS OF THE ALLEGHENY PLATEAU

Restoration programs are expanding worldwide, but assessments of restoration effectiveness are rare. The objectives of our study were to assess current acid-precipitation remediation programs in streams of the Allegheny Plateau ecoregion of West Virginia (USA), identify specific attributes that could and could not be fully restored, and quantify temporal trends in ecosystem recovery. We sampled water chemistry, physical habitat, periphyton biomass, and benthic macroinvertebrate and fish community structure in three stream types: acidic (four streams), naturally circumneutral (eight streams), and acidic streams treated with limestone sand (eight streams). We observed no temporal trends in ecosystem recovery in treated streams despite sampling streams that ranged from 2 to 20 years since initial treatment. Our results indicated that the application of limestone sand to acidic streams was effective in fully recovering some characteristics, such as pH, alkalinity, Ca2+, Ca:H ratios, trout biomass and density, and trout reproductive success. However, recovery of many other characteristics was strongly dependent upon spatial proximity to treatment, and still others were never fully recovered. For example, limestone treatment did not restore dissolved aluminum concentrations, macroinvertebrate taxon richness, and total fish biomass to circumneutral reference conditions. Full recovery may not be occurring because treated streams continue to drain acidic watersheds and remain isolated in a network of acidic streams. We propose a revised stream restoration plan for the Allegheny Plateau that includes restoring stream ecosystems as connected networks rather than isolated reaches and recognizes that full recovery of acidified watersheds may not be possible.

Influence of atmospheric inputs on the iron distribution in the subtropical North-East Atlantic Ocean

Aerosol (soluble and total) iron and water-column dissolved (DFe, < 0.2 μm) and total dissolvable (TDFe, unfiltered) iron concentrations were determined in the Canary Basin and along a transect towards the Strait of Gibraltar, in order to sample across the Saharan dust plume. Cumulative dust deposition fluxes estimated from direct aerosol sampling during our one-month cruise are representative of the estimated deposition fluxes based on near surface water dissolved aluminium concentrations measured on board. Iron inventories in near surface waters combined with flux estimates confirmed the relatively short residence time of DFe in waters influenced by the Saharan dust plume (6–14 months). Enhanced near surface water concentrations of DFe (5.90–6.99 nM) were observed at the Strait of Gibraltar mainly due to inputs from metal-rich rivers. In the Canary Basin and the transect towards Gibraltar, DFe concentrations (0.07–0.76 nM) were typical of concentrations observed in the surface North Atlantic Waters, with the highest concentrations associated with higher atmospheric inputs in the Canary Basin. Depth profiles showed that DFe and TDFe were influenced by atmospheric inputs in this area with an accumulation of aeolian Fe in the surface waters. The sub-surface minimum of both DFe and TDFe suggests that a simple partitioning between dissolved and particulate Fe is not obvious there and that export may occur for both phases. At depths of around 1000–1300 m, both regeneration and Meddies may explain the observed maximum. Our data suggest that, in deep waters, higher particle concentrations likely due to dust storms may increase the scavenging flux and thus decrease DFe concentrations in deep waters.

Small-Scale Chemical Changes Caused by In-stream Limestone Sand Additions to Streams

In-stream limestone sand addition (ILSA) has been employed as the final treatment for acid mine drainage discharges at Swamp Run in central West Virginia for six years. To determine the small-scale longitudinal variation in stream water and sediment chemistry and stream biota, we sampled one to three locations upstream of the ILSA site and six locations downstream. Addition of limestone sand significantly increased calcium and aluminum concentrations in sediment and increased the pH, calcium, and total suspended solids of the stream water. Increases in alkalinity were not significant. The number of benthic macroinvertebrate taxa was significantly reduced but there was no effect on periphyton biomass. Dissolved aluminum concentration in stream water was reduced, apparently by precipitation into the stream sediment.

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Water-quality data for discharges from 140 abandoned mines in the Bituminous and Anthracite Coalfields of Pennsylvania illustrate relations among pH, sulfate, and dissolved metal concentrations. The pH for the 140 samples ranged from 2.7 to 7.3, with two modes at pH 2.5 to 4 (acidic) and 6 to 7 (near neutral). Generally, flow rates were smaller and solute concentrations were greater for low-pH samples; flow rates increased with pH. Although the pH distribution was similar for the bituminous and anthracite subsets, the bituminous discharges had smaller median flow rates, greater concentrations of sulfate, iron, and aluminum, and smaller concentrations of barium and lead than anthracite discharges with the same pH values. The observed relations between the pH and constituent concentrations can be attributed to (1) dilution of acidic water by alkaline ground water; (2) solubility control of aluminum, iron, manganese, barium, and lead by hydroxide, sulfate, and/or carbonate minerals; and (3) aqueous sulfate-complex formation. The formation of AlSO4 + and AlHSO4 +2 complexes adds to the total dissolved aluminum concentration at pH of equilibrium with aluminum hydroxide or hydroxysulfate minerals and can account for 10 to 20 times greater concentrations of dissolved aluminum in bituminous discharges compared to anthracite discharges at similar pH. Sulfate complexation also can account for 10 to 30 times greater concentrations of dissolved ferric iron concentrations at equilibrium with ferrihydrite (Fe(OH)3) and/or schwertmannite (Fe8O8(OH)4.5(SO4)1.75) at pH of 3 to 5. In contrast, lower barium and lead concentrations in bituminous than anthracite discharges indicates elevated sulfate concentration could decrease mobility of these metals by the formation of insoluble minerals such as barite (BaSO4) or anglesite (PbSO4). Most samples were saturated with barite, but none were saturated with anglesite. Hence, lead concentrations could be controlled by coprecipitation with barite and/or by adsorption to schwertmannite or another sulfate-bearing oxide. Additional

Dust deposition to the surface waters of the western and central North Pacific inferred from surface water dissolved aluminum concentrations

Dissolved Al was determined on ∼3500 surface water samples collected in the NW Pacific during the 2002 Intergovernmental Oceanographic Commission (IOC) Contaminant Baseline survey. In addition, dissolved Al was determined on samples collected at 9 vertical stations occupied along the cruise track. Surface water Al distributions, when converted to annual mineral dust deposition (Measures and Brown, 1996), imply extremely low depositions (mean values ≤0.3 g m−2 yr−1) to surface waters of the subarctic gyre despite the atmospheric transport of large amounts of mineral dust across this region from the desert regions of China. The calculated deposition values are also much lower than the 1–10 g m−2 yr−1 predicted for this region by the GESAMP model (Duce et al., 1991). The lowest mineral dust depositions correspond to the High Nutrient Low Chlorophyll (HNLC) region of the NW Pacific, which implies that the biogeochemical status of this region is the result of low atmospheric micronutrient input, similar to other HNLC regions. In the subtropical gyre the Al‐derived dust deposition (mean values 0.1–0.6 g m−2 yr−1) agrees well with the (&lt;1 g m−2 yr−1) predictions of the GESAMP model. Enriched concentrations of dissolved Al in the coastal waters near Kauai, from fluvial sources, indicate the potential role of remote high islands in adding reactive trace elements to the nearby surface waters. In the vertical profiles, elevated dissolved Al concentrations (4–8 nM) were found to correspond to the potential density of the western Pacific “Subtropical Mode” waters which form in the recirculation zone of the Kuroshio.

Aluminum residual control using orthophosphate

Applying orthophosphate during rapid mix following alum addition is an effective method for reducing residual aluminum concentrations and decreasing the potential for aluminum precipitation in distribution systems. Orthophosphate addition during bench‐scale tests reduced residual dissolved aluminum concentrations by as much as 350 μg/L. The tests involved adding alum and phosphate to Lake Michigan water followed by continuous mixing for up to 8 h. Analysis of filtered samples showed that orthophosphate addition reduced residual aluminum concentrations under all test conditions (pH 7.0–8.0, 4–31oC) except at the lowest temperature, at which aluminum concentrations fell below the detection limit. Orthophosphate loss to floc particles ranged from 22 to 85% of the amount dosed, with greater losses at the lowest pH value tested. Applying orthophosphate before rather than after adding alum resulted in greater phosphate loss to floc particles without improving aluminum removal.

Seasonal variation of dissolved aluminum concentration in harmonic-type Lake Biwa, Japan

Monthly observations performed on a typical harmonic-type lake, Lake Biwa (latitude 35°15′ N, longitude 136°05′ E, Japan), showed that the particulate aluminum concentration varied around a mean value of 0.8 μM, with occasional extraordinarily high values, whereas the dissolved aluminum concentration varied, in the surface layer of the whole lake, between a minimum of 0.01 μM and a maximum of 0.30 μM, depending on the season. Although the variation in dissolved aluminum paralleled the variation in the pH of the lake water, the variation in dissolved aluminum lagged behind the variation in pH by approximately 1 month. A series of laboratory incubation experiments suggested that the supply of dissolved aluminum from, and its removal by, the suspended particulate matter involved a slow, pH-dependent reaction. The stoichiometry and the apparent equilibrium constant of this reaction were evaluated by adopting a zeolite-like structure for the surfaces of the suspended particulates.

GROUNDWATER GEOCHEMISTRY IN THE SEMINOLE WELL FIELD, CEDAR RAPIDS, IOWA1

ABSTRACTThe City of Cedar Rapids obtains its municipal water supply from four well fields in an alluvial aquifer along the Cedar River in east‐central Iowa. Since 1992, the City and the U.S. Geological Survey have cooperatively studied the groundwater‐flow system and water chemistry near the well fields. The geochemistry in the alluvial aquifer near the Seminole Well Field was assessed to identify potentially reactive minerals and possible chemical reactions that produce observed changes in water chemistry. Calcite, dolomite, ferrihydrite, quartz, rhodochrosite, and siderite were identified as potentially reactive minerals by calculating saturation indexes. Aluminosiicate minerals including albite, Ca‐montmorillonite, gibbsite, illite, K‐feldspar, and kaolinite were identified as potentially reactive minerals using hypothetical saturation indexes calculated with an assumed dissolved aluminum concentration of 1 microgram per liter. Balanced chemical equations derived from inverse‐modeling techniques were used to assess chemical reactions as precipitation percolates to the water table. Calcite dissolution was predominate, but aluminosilicate weathering, cation exchange, and redox reactions also likely occurred. Microbial‐catalyzed redox reactions altered the chemical composition of water infiltrating from the Cedar River into the alluvial aquifer by consuming dissolved oxygen, reducing nitrate, and increasing dissolved iron and manganese concentrations. Nitrate reduction only occurred in relatively shallow (3 to 7 meters below land surface) groundwater near the Cedar River and did not occur in water infiltrating to deeper zones of the alluvial aquifer.

Long-Term Water Quality and Biological Effects of Alum Treatment of Lake Morey, Vermont

ABSTRACT Lake Morey received one hypolimnetic treatment with alum and sodium aluminate in 1986 to reduce the occurrence of algae blooms caused by internal P loading. Thirteen years of post-treatment monitoring have documented a sustained improvement in water quality in the lake. Comparison of pre-treatment (1977–1985) and post-treatment (1986–1998) data indicated that significant improvements occurred in all water quality variables measured, including spring TP (reduced 66%), summer photic zone TP (reduced 68%), summer photic zone Chi a (reduced 61%), summer Secchi disk transparency (increased 79%), late summer hypolimnetic TP (reduced 83%), and late summer hypolimnetic DO (increased 193%). The one-time alum/aluminate treatment of Lake Morey has thus far succeeded in breaking a cycle of sediment P release and re-precipitation that was initiated during an earlier period in the lake's history. Relative weight loss was observed in samples of large yellow perch during the 3 years immediately following the treatment. Yellow perch condition returned to pre-treatment levels by 1991. Toxicity from elevated dissolved aluminum concentrations in the water column during the summer of treatment may have caused the observed weight loss in fish. The benthic macroinvertebrate community in the upper hypolimnion experienced a 90% decline in density during the year immediately following the alum treatment. The benthic community recovered during subsequent years with density and taxa richness generally exceeding pre-treatment values, possibly in response to improved hypolimnetic DO conditions.

Effect of pH on the measurement of biogenic silica

For investigations of the biogenic silica content of plankton, sediment trap, and sediment samples, alkaline extraction is the most common procedure. Different extraction techniques, with respect to the pH of the leaching agent and the method applied to correct for the release of SiO2 by non-biogenic silica phases as clays or feldspars, are applied. By sequential extraction of marine sediment samples and clay standards with solutions of pH 8 to 14, we investigated the sensitivity of these leaching techniques to the pH of the leaching solution. In addition to the dissolved silica concentration, the temporal increase of the dissolved aluminum concentration of the leaching agent was measured. For sediments of low biogenic silica content, the results are considerably affected by the pH of the leaching agent and relative deviations of more than 300% were observed. Correction by the calculated SiO2/Al2O3 ratios of non-biogenic silica phases had no significant effect on the observed pH dependence. Measurements of samples which exceed ∼10% biogenic silica are only negligibly affected by the pH of the leaching solution. Based on the pH dependence and investigations of a pure Miocene diatom sample, sequential alkaline extraction with a pH of 12.5 is recommended for the determination of biogenic silica.

Benthic invertebrates in the headwaters of the Wye and Severn: effects of forestry and clear-felling

Abstract. Invertebrate communities were recorded in three surveys between 1974 and 1994 of headwaters of the Wye and Severn at Plynlimon: the Afon Gwy (unforested), the Afon Hore (initially forested) and the Afon Hafren (forested throughout). The data cover periods before and after the clear-felling of a large area of coniferous forest in the catchment of the Hore. All three streams contained invertebrates characteristic of acidic, upland conditions and had similar species richness. Differences in assemblage composition within streams between surveys could be related to differences in method or timing of sampling. All assemblages were dominated by Insecta, particularly Plecoptera and Diptera, whereas Ephemeroptera, Moilusca, Crustacca and some families of Trichoptera (notably Hydropsychidae and Philopotamidae) were poorly represented. The forested streams (Hafren and Hore) contained similar assemblages which differed from those in the unforested stream (Gwy) in containing lower densities of Ephemeroptera and Oligochacta and much higher densities of nemourid and leuctrid Plecoptera. Clear-felling of the Hore catchment resulted in changes in physical and chemical conditions (including a reduction of stream pH, and increases in dissolved aluminium concentration and summer water temperature) but no related change in the invertebrate assemblage. The apparent failure of invertebrates to respond as expected to substantial changes in local environmental conditions may reflect either a lack of understanding of causal links between invertebrates and environmental factors, or the over-riding influence of the dynamics of recruitment to populations.

Geochemical response of acid groundwater to neutralization by alkaline recharge

Solute transport and chemical neutralization (pH 3 to 7) within a shallow heterogeneous aquifer producing acid mine drainage (AMD) are examined at an abandoned surface coal mine in West Virginia. The aquifer is undergoing partial neutralization by mixing with alkalinity from a leaking sludge disposal pond, extending in preferential zones controlled by aquifer heterogeneity. Hydraulic heads interpolated from wells indicate leakage from a central alkaline (pH 7.1, 0.72 meq/L alkalinity) sludge pond is a principal source of recharge. Chemically-conservative sodium, added to AMD during treatment and leaked into the aquifer with the sludge, develops a dispersion plume over a restricted portion of the aquifer that correlates with pH, hydraulic head, and dissolved metals distributions. Concentrations of aluminum, iron, sulfate and acidity display higher concentrations downgradient from the pond as sludge alkalinity is consumed along flow paths. Before reaching springs, most dissolved iron is oxidized and hydrolyzed, likely precipitating in the aquifer as a ferric hydroxide or hydroxysulfate phase. The spatial pattern of iron and aluminum concentrations suggests accelerated oxidation caused by gas transport along the outer slopes of the spoil. Dissolved aluminum concentrations increase with total acidity, suggesting that dissolution of silicate minerals results from acidity released by iron hydrolysis. Neutralization reactions and higher pH are favored in more highly permeable portions of the spoil, where ferrihydrite and aluminum hydroxysulfate minerals (such as basaluminite) are supersaturated. In acid-producing zones at pH < 4.5, jurbanite is near equilibrium and an aluminum-sulfate phase with similar properties may limit aluminum concentrations, but become undersaturated in zones of advancing neutralization. At this particular site, ferrous iron produced by pyrite oxidation is almost completely oxidized over short transport distances, allowing hydrolysis of iron and aluminum should sufficient alkalinity be added to these acid waters.

CHUM: a hydrochemical model for upland catchments

CHUM (CHemistry of the Uplands Model) simulates soil-water chemical interactions and water flows in upland catchments with acid soils. The chemical interactions are described with the equilibrium speciation code WHAM, which emphasises the interactions of inorganic chemical species with solid-phase and dissolved organic matter, and also considers inorganic solution speciation and sorption reactions of fulvic acid. Of special significance is the treatment of aluminium chemistry; control of dissolved aluminium concentrations is assumed to be due primarily to complexation reactions with solid phase organic matter, whereas previous models have postulated equilibrium with mineral phases or simple ion-exchange. In addition, CHUM takes nitrogen transformations and weathering (dissolution) reactions into account. The catchment is conceptualised as a series of columns consisting of two soil horizons and an underlying permeable or fractured bedrock zone. Water flows are described with a hydrological submodel that distinguishes immobile water present in soil micropores (which is in chemical equilibrium with the soil solids) from mobile drainage water. The mobile water can move vertically from one horizon to another, from one column to the column immediately downslope, or as outflow from a column adjacent to a stream or lake. Solutes exchange between the mobile and immobile compartments. The model runs on a daily time-step. The fundamentals of the model are given, together with a description of its application to a site in the English Lake District.

Episodic flow–duration analysis: a method of assessing toxic exposure of brook trout (Salvelinus fontinalis) to episodic increases in aluminum

Episodic flow–duration curves were developed that summarize stream flow data by considering the duration of sustained flows at or above specified levels. These curves and relationships between dissolved aluminum concentrations and stream flow were combined for five Appalachian (Pennsylvania) streams to determine the frequency of occurrence of acutely toxic aluminum conditions for brook trout (Salvelinus fontinalis). Concentrations of total dissolved aluminum (AlTD) increased with stream flow in all streams, but reached a plateau or decreased during extreme high flows in some streams. AlTDwas dominated by inorganic monomeric species in all streams except Benner Run and Baldwin Creek. Episodic AlTDconcentrations and durations were compared with a toxicity curve developed using caged wild and hatchery-reared brook trout. Results predicted that lethal episodes occurred on Linn, Stone, and Roberts runs, but not on Benner Run and Baldwin Creek. With the exception of Stone Run, brook trout populations were largest in streams without predicted lethal episodes (Benner Run and Baldwin Creek) and were smallest in streams with predicted lethal episodes (Linn and Roberts runs). This analysis could be adapted for prediction of toxic conditions in streams for other pollutants where toxicity varies with both concentration and duration of exposure.

Determination of Aluminum Concentration in Molten Zinc by the E.M.F. Method Using Zirconia Solid Electrolyte.

Control of the dissolved aluminum concentration in a hot dip galvanizing bath is of great importance for producing galvannealed steel sheets. Since aluminum has much greater affinity for oxygen than zinc, the oxygen potential of Zn-Al-O bath may be determined only by the following equilibrium reaction; Al2O3(s)=2Al(in Zn)+3O(in Zn) when the aluminum concentration in the bath is relatively low. Aluminum sensor based on the emf method using the zirconia solid electrolyte has been devised by utilizing the above equilibrium relation.In this paper, emf measurements have been carried out in Zn-Al-O baths having aluminum concentration of 0.02-0.50 mass% under an air atmosphere by using some of the most appropriate combinations of zirconia solid electrolyte and liquid reference electrode for Zn-O baths.From the analysis of such emf values at temperatures between 450-500°C, the following relationships between aluminum concentration and cell emf for two reference electrodes were obtained; E/mV=57.19 ln[Al]/mass%+506.4, 0.02≤[Al]/mass%≤0.30 (In-In2O3 as ref. electrode)E/mV=68.27 ln[Al]/mass%+270.4, 0.05≤[Al]/mass%≤>0.20 (Zn-ZnO as ref. electrode)The external AC voltage applied on these sensors immediately after immersion into the bath showed to be effective to their responsibility and stability. The emf measurements were also carried out in Zn-Mn-O and Zn-Cr-O baths, respectively, and it has been ascertained that the sensors work much better in these baths, even though the partial oxygen pressure PO2 of the bath is as low as 10-40 Pa at 450°C. The posssibility of the present aluminum sensor has been ascertained experimentally.

Aluminium speciation variations in an acidic upland stream draining the Hafren spruce forest, Plynlimon, Mid-Wales

The speciation of aluminium in an acidic stream, draining a spruce plantation-forest in Mid-Wales, is examined using an established model based on an equilibrium thermodynamic approach. Trivalent aluminium and aluminium complexes with fluoride, with dissolved organic matter and with silica were abundant: aluminium hydroxy-fluorides and sulphates were much less so. There is a large scatter in the results, primarily due to variations in stream water chemistry at a given pH, rather than to an effect of temperature. It is concluded that aluminium silica complexes can be an important part of the total dissolved aluminium concentration: at pHs > 5, they comprise typically 20% of the total dissolved aluminium in the stream water.