Al Speciation Research Articles

Preliminary investigation of aluminium fluoride complexes in aqueous solutions with capillary electrophoresis coupled with electrospray ionization mass spectrometry and with inductively coupled plasma mass spectrometry.

It is crucial to identify and confirm the original species of aluminium ions (Al3+ ) dissolved in water, since they behave differently. Depending on their species, the toxicity differs. Capillary electrophoresis (CE) coupled with electrospray ionization mass spectrometry (ESI-MS) and CE coupled with inductively coupled plasma mass spectrometry (CE/ICP-MS) were explored to identify and determine simple systems of Al species solutions at pH 3.0. The new combinations of techniques, namely, ESI-MS coupled with CE for identification of species and ICP-MS coupled with CE for confirmation, were applied to for the analyses of Al and fluoride (F) solutions. Al monomers, some Al dimers and trimers were detected by CE/ESI-MS. CE/ICP-MS experiments were conducted with the assembled interface. As a result, the calibration line showed R2 = 0.9856, and the detection limits were 35 nL and 0.037 μM. The results were compared with data obtained using MINEQL+. Most of the Al species detected were monomers; some dimers and trimers were detected by CE/ESI-MS, but they were not detected by CE-ICP-MS, probably owing to extremely low concentrations. The Al speciation technique was improved by CE/ESI-MS, and the Al species present at extremely low concentrations were ascertained by CE/ICP-MS. The use of coupled instruments will be one of the most powerful tools for identifying dissolved metal ions.

Modeling key processes affecting Al speciation and transport in estuaries

Assessments of the impacts of aluminium (Al) to aquatic organisms in estuarine waters have suffered from the lack of available models that can accurately predict the presence of toxic physico-chemical forms (species) of Al at adequate spatial and temporal resolution. In the present work, transport and distribution of river-discharged Al species through changing environmental conditions in the Sandnesfjorden estuary, South-Eastern Norway, was predicted using a numerical model system at relatively high spatial (32 m × 32 m in horizontal) and temporal (1 h) resolution. New model code was implemented, including dynamic, salinity-dependent speciation and transformation processes, based on in situ measurements from several Norwegian estuaries as well as experimental data. This is the first time such elemental speciation code including LMM, colloidal, particle and sediment species is utilized in an estuary case in combination with high resolution hydrodynamics and compared to an extensive observational dataset. Good agreement was obtained between modeled and observed total and fractionated Al concentration at several stations along the fjord transect. Without including background contribution of Al from the coastal water, the model predicted too low Al concentrations (by up to approximately a factor 4) near the fjord mouth. The surface Al concentrations were also underestimated due to overestimated near-surface vertical mixing in the hydrodynamic model. The observed correlation between salinity and total Al concentration was well reproduced by the model in situations with low upper layer volume flux, typical under low river flow conditions. In contrast, the predicted surface salinity and total Al concentration were less correlated under high-flux conditions. As the general trends of Al concentrations and speciation were well reproduced, this study demonstrated that by including carefully chosen transfer rates, the model can be used to predict spatio-temporal distribution of total contamination as well as concentration levels of the elemental species.

Soil acidity and aluminum speciation affected by liming in the conversion of a natural pasture from the Brazilian Campos Biome into no-tillage system for grain production

ABSTRACTThe conversion of Pampa Biome soils into no-till system for grain production requires acidity correction, at least to fully neutralize exchangeable aluminum (Al). The aim of the study is to evaluate changes in solid phase acidity and Al speciation in soil solution that was conducted to prepare the soil for the implementation of a no-tillage system in a natural pasture area in Southern Brazil. We collected soil samples from the 0–5, 5–10, 10–15 and 15–20 cm layers in soils subjected, or not, to acidity correction to pH 6.0, as well as in soils with, and without, limestone incorporation through plowing and harrowing. Changes in the solid and solution phase attributes, such as soil acidity, were limited to 5 and 10 cm, respectively, 44 months after surface and incorporated liming. Regardless of liming addition to, or lack of thereof in the soil, Al found in the soil solution was mainly associated with organic carbon. This was the main way to decrease plant toxicity under these conditions, which can be supported by plant behavior, especially that of soybean. Liming induced the soil solution Al to exchange its ligand from organic carbon to hydroxyl.

Contamination and Potential Ecological Risk Assessment of Heavy Metals in the Sediments of Yilong Lake, Southwest China

The concentrations of Al, Ti, As, Cd, Cr, Cu, Ni, Pb, Zn, and Hg and chemical speciation of Cd, Cr, Cu, Ni, Pb, and Zn in four short cores sampled from the Yilong Lake, Yunnan Province were analyzed. The vertical and spatial features in the pollution levels and potential ecological risks of heavy metals in the sediments were studied. Except for the wide concentration ranges of Cd, the metals in the sediments showed narrow variations in their concentrations with coefficients of variation less than 0.3. According to the cluster analysis results, all metals could be classified into two groups:metals in group Ⅰ included As, Cd, Hg, and Pb, while metals in group Ⅱ included Al, Ti, Cr, Cu, Ni, and Zn. The metals in each group exhibited similar vertical variations in each core, but their variations were highly different between the cores. The correlation analysis results demonstrated that the variations in metal concentrations in the sediments were greatly regulated by the sediment texture. Therefore, the enrichment factor (EF) method was used for the differentiation of metals from the natural and anthropogenic sources and for the pollution assessment based on the total metal concentrations. The Cd and Pb in the sediments were mainly presented in the reducible speciation with percentages of 48% and 42%, respectively; Cr, Cu, Zn, and Ni were primarily (68%-82%) associated with the residual speciation. Based on the EF and chemical speciation of metals and their enrichment coefficients of the secondary phase, Cd was the typical pollutant with moderate pollution on average, and the other elements were observed in non-to weak pollution levels. Anthropogenic metals were mainly associated with the extractable speciation in the sediment. Combining the ecological risk index, the sediment quality guidelines, as well as the pollution level and chemical speciation of metals, As, Cu, Hg, Ni, Pb, and Zn in the surface sediments of Yilong Lake should have low potential ecological risk. However, Cd may pose a high potential ecological risk.

Effect of Al speciation on residual turbidity and Al minimization by coagulation with single and dual dosing

Effect of Al speciation on residual turbidity and Al minimization by coagulation with single and dual dosing

Distribution of Aluminum over the Tetrahedral Sites in ZSM-5 Zeolites and Their Evolution after Steam Treatment

Zeolite ZSM-5 is one of the most widely used zeolites, in particular in heterogeneous catalysis. This work investigates the incorporation of Al in the silica framework of monoclinic ZSM-5 and the Al speciation during steam treatment for four ZSM-5 samples with different Si/Al ratios, using ultrahigh field 27Al NMR (22.3 T), 29Si NMR, X-ray diffraction, and IR spectroscopy. 27Al MQMAS NMR at 22.3 T allows identification and quantification of 10 distinct tetrahedral framework resonances which are assigned to the crystallographic sites by their average T–O–T angles, determined from powder XRD patterns for the same samples. A clear Al site preference is observed and found to be dependent on the Si/Al ratio of the parent zeolite. The framework sites facing the intersections in ZSM-5 are found to be most prone to dealumination, whereas Al in the straight and sinusoidal-shaped channels are more stable toward steam treatment at high temperatures. Extra-framework Al species with 5- and 6-fold coordination and two ...

Effect of aluminum (Al) speciation on erythrocytic antioxidant defense process: Correlations between lipid membrane peroxidation and morphological characteristics

Al contamination becomes a growing problem in human society. Accumulation of Al in blood could destroy the structure and disorder function of erythrocyte, and finally cause blood diseases. In the present study, AlCl3 and Al(malt)3 are respectively used in the erythrocyte system, in order to investigate the comparative toxic effect on erythrocyte fragility, the influence on cellular biochemical components and lipid peroxidation level. We find that the osmotic fragility, the number of Heinz bodies, the content of MDA and advanced oxidation protein product of the AlCl3 treated erythrocytes were higher than the Al(malt)3 treated erythrocytes at the same concentrations of Al(Ⅲ). The morphological and membrane protein changes of the AlCl3 treated group show superior to the Al(malt)3 treated group. In summary, we conclude that the comparative effect on the erythrocyte between organic aluminum and inorganic aluminum is significantly different, and the prime comparative difference between the toxic effects of both the compounds is oxidative stress. Further research should focus on in vivo experiments to confirm the differential toxicity and to elucidate the molecular mechanisms underlying Al-induced erythrocyte toxicity in order to prevent hematological disorders.

Freshwater ecotoxicity characterization factors for aluminum

Aluminum (Al) is an abundant, non-essential element with complex geochemistry and aquatic toxicity. Considering its complex environmental behavior is critical for providing a reasonable estimate of its potential freshwater aquatic ecotoxicity in the context of Life Cycle Impact Assessment (LCIA). Al characterization factors (CFs) are calculated using the following: (1) USEtox™ model version 2.1 for environmental fate, (2) MINEQL+ to estimate the distribution of Al between the solid phase precipitate and total dissolved Al, (3) WHAM 7 for Al speciation within the total dissolved phase, and (4) Biotic Ligand Model (BLM) and Free Ion Activity Model (FIAM) for ecotoxicity estimation for seven freshwater archetypes and default landscape properties for the European continent. The sensitivity of the CFs to aquatic chemistry parameters is calculated. New CFs are compared with Dong et al. (Chemosphere 112:26–33, 2014) and default CF calculated by USEtox 2.1. Al CFs vary over 5 orders of magnitude between the seven archetypes, with an arithmetic average CFave of 0.04 eq 1,4-DCB (recommended for use), geometric mean CFgeo of 0.0014 eq 1,4-DCB, and weighted average CFwt of 0.026 eq 1,4-DCB. These values are lower (less toxic) than those for Cu, Ni, Zn, and Pb (with one exception). The effect factor (EF) contributed most to this variability followed by the bioavailability factor (BF), varying over 8 and 4 orders of magnitude, respectively. These revised CFs are 2–6 orders of magnitude lower than those presented by Dong et al. (Chemosphere 112:26–33, 2014) mainly because of consideration of Al precipitation. Freshwater archetype-specific Al CFs for freshwater ecotoxicity that address the effect of Al speciation on bioavailability (BF) and ecotoxicity (EF) have been calculated, and a CF of 0.04 eq 1,4-DCB is recommended for use in generic LCA. For site-specific LCA, the choice of water chemistry and, in particular, pH, and consideration of metal precipitation could significantly influence results. Incorporating estimates of metal speciation and its effect on aquatic toxicity is essential when conducting LCIA. Along with metal speciation estimates, the values derived from the definition of water chemistry parameters must also be included into LCIA. For site-generic assessments, we recommend using the arithmetic average of metal CFs. We also recommend using FIAM as a suitable alternative to BLM to estimate EF if the latter is not available. Consideration of metal speciation is essential for providing more realistic estimates of Al freshwater ecotoxicity in the context of LCIA.

Aluminium (Al) speciation in serum and urine after subcutaneous venom immunotherapy with Al as adjuvant

BackgroundAluminium is associated with disorders and is the commonly used vaccine adjuvant. Understanding the mechanisms of how Al is transported, metabolized or of its toxicity depends on the knowledge of Al-interactions with bioligands, i.e. Al-species. Al-speciation in serum is difficult because of low concentration and the risk of exogenous Al contamination. Furthermore, Al-measurements may be hampered according to various interferences. This study aims for developing quality controlled protocols for reliable Al- and Al-species determination and for investigating probable differences in Al (-speciation) after Al-containing subcutaneous immunotherapy (SIT). MethodsSample donors were recruited either for the control group (“class-0”, they never had been treated with SIT containing an Al-depot extract) or for the SIT-group (“class-1”, they previously had been treated with SIT for insect venom allergy with an Al-depot extract). Blood was drawn for medical reasons and serum prepared. Additionally, some sample donors collected 24-h-urine. They had been informed (and they consented) about the scientific use of their samples. The study was approved by the ethic committee of the “Medical Association Westphalia-Lippe” and of the University of Münster, evaluating the study positively (No. 2013-667-f-S).We applied quality controlled sample preparation and interference-free Al detection by ICP sectorfield-mass spectrometry. Al-species were analysed using size-exclusion-chromatography-ICP-qMS. FindingsAl-concentrations or speciation in urine samples showed no differences between class-0 and class-1. Al-citrate was the main uric Al-species. In serum elevated Al-concentrations were found for both classes, with class-1 samples being significantly higher than class-0 (p = 0.041), but class-0 samples being approximately 10-fold too high compared to reference values from non-exposed persons. We identified gel-monovettes as contamination source. In contamination-free samples from HNO3-prewashed gel-free monovettes (n = 27) there was no difference in the serum Al concentration between the two patient groups (p = 0.669) InterpretationThorough cleaning of sample preparation ware and use of gel-free monovettes is decisive for an accurate Al analysis in serum. Without these steps, wrong analysis and wrong conclusions are likely. We conclude that gel-monovettes are unsuitable for blood sampling with subsequent Al-analysis. Whether Al in serum is elevated after SIT treatment containing an Al-depot extract, or not, remains inconclusive as the non-contaminated sample size was small.

Aluminum cycling in a tropical montane forest ecosystem in southern Ecuador

Growth limitation induced by Al toxicity is believed to commonly occur in tropical forests, although a direct proof is frequently lacking. To test for the general assumption of Al toxicity, Al, Ca, and Mg concentrations in precipitation, throughfall, stemflow, organic layer leachate, mineral soil solutions, stream water, and the leaves of 17 native tree species were analyzed. We calculated Al fluxes and modeled Al speciation in the litter leachate and mineral soil solutions. We assessed potential Al toxicity based on soil base saturation, Al concentrations, Ca:Al and Mg:Al molar ratios and Al speciation in soil solution as well as Al concentrations and Ca:Al and Mg:Al molar ratios in tree leaves. High Al fluxes in litterfall (8.77±1.3 to 14.2±1.9kgha−1yr−1, mean±SE) indicated a high Al circulation through the ecosystem. The fraction of exchangeable and potentially plant-available Al in mineral soils was high, being a likely reason for a low root length density in the mineral soil. However, Al concentrations in all solutions were consistently below critical values and Ca:Al molar and the Ca2+:Alinorganic molar ratios in the organic layer leachate and soil solutions were above 1, the suggested threshold for Al toxicity. Except for two Al-accumulating and one non-accumulating tree species, the Ca:Al molar ratios in tree leaves were above the Al toxicity threshold of 12.5. Our results demonstrate high Al cycling through the vegetation partly because of the presence of some Al accumulator plants. However, there was little indication of an Al toxicity risk in soil and of acute Al toxicity in plants likely reflecting that tree species are well adapted to the environmental conditions at our study site and thus hardly prone to Al toxicity.

Effect of aluminum speciation and pH on in-line coagulation/diatomite microfiltration process: Correlations between aggregate characteristics and membrane fouling

Impacts of aluminum speciation and water pH on coagulation/diatomite microfiltration (DMM) process were investigated in this study. Three commonly used Al-based coagulants, aluminum sulfate (AS), poly-aluminum chloride (PACl), and Al13 ([Al13O4(OH)24(H2O)12]7+), were employed to explore the role of Al speciation. Floc characteristics, including particle size and fractal structure under different coagulants and water pH levels, were investigated using a laser diffraction particle sizing device. The results indicated that in the dosage range of 1.0–11.0mg/L, coagulation/DMM could effectively remove particles (97–100%) and DOC (40–80%), and as pH increased from 3.0 to 10.0, its purification efficiency was higher and more stable than separate coagulation. AS contributed to large and loosely structured flocs and thus alleviated the flux declines most effectively, leading to a flux reduction of about 50%, while the reductions for PACl and Al13 were 71% and 73%, respectively. Neutral pH was found most conducive to the hybrid process and alkaline pH (9.0) led to relatively larger flux than strong acidic pH (3.0), especially for AS coagulation system. As pH changed, Al13 led to the least variation in flux declines while both the removal efficiency and filtration flux fluctuated most obviously for AS coagulation system.

Synthesis-property-performance relationships of amorphous silica-alumina catalysts for the production of methylenedianiline and higher homologues

Although amorphous silica-alumina catalysts (ASA) are a promising candidate for the replacement of HCl in the production of methylenedianiline (MDA) and higher homologues, their industrial implementation has been hampered by the lack of systematic studies targeting their design. The complexity of both, the materials as well as the reaction, necessitates the development of synthesis-structure-performance relationships to indicate if, and how, the stringent specifications in terms of activity, selectivity, and stability can be met. Herein, we investigate a large set of ASA obtained by coprecipitation, deposition-precipitation, grafting, and from commercial sources. A detailed analysis of their porosity, composition, Al speciation, acidity, and morphology reveals that every synthesis method leads to a unique combination of material properties. Through high-throughput batch experiments we investigate the importance of each of these parameters for the catalytic performance. The properties that determine the activity relate to the specific surface area, which should be as large as possible while featuring tetrahedrally-coordinated aluminum atoms in the silica matrix. In contrast, the selectivity is determined by the employed reaction conditions, namely the reaction temperature and the aniline content of the feed. Continuous tests under industrial conditions reveal that ASA deactivate via fouling during the initial restructuring of aminal. Pore-mouth blockage by fouling was minimized and optimal lifetimes ensured by employing mesopore networks consisting primarily of pyramidal or cylindrical pores. Based on these insights, we demonstrate that ASA can outperform hierarchical zeolites in terms of activity, while approaching industrially attractive oligomer contents and keeping the concentration of byproducts low at a high catalyst lifetime, advertising their potential for large-scale implementation.

Effect of Al Speciation on the Structure of High‐Al Steels Mold Fluxes Containing Fluoride

To design suitable mold fluxes for the casting of high‐Al steels, the structure of mold fluxes based on CaO–SiO2, CaO–SiO2–Al2O3, and CaO–Al2O3 was examined by Raman spectroscopy and magic‐angle spinning nuclear magnetic resonance. The results showed that Si atoms are replaced by Al atoms as the network formers with the increase in Al2O3 in the mold fluxes. This converts the silicate slags (CaO–SiO2 mold fluxes) into aluminosilicates slags (CaO–SiO2–Al2O3 or CaO–Al2O3 mold fluxes). The F− ions in the mold flux containing Al2O3 are classified into three categories, according to function: Bridging F's, Nonbridging F's, and Free‐F's. The Al3+ ion holds three distinct coordination environments: IVAl, VAl, and VIAl. The addition of F affects the coordination environment of Al3+ to form AlO3F and AlO2F2 that accommodate the network structure of slags. The network structure in the CaO–SiO2 mold fluxes is mainly connected through Si–O–Si linkage. However, the network structure of the mold fluxes containing elevated content of Al2O3 is mainly connected through Si–O–Si, Al–O–Al, Al–O–Si, and Al–F–Al linkages. Hence, the structural characteristics of high‐Al steels mold fluxes must be considered during the designing step of the mold fluxes.

Aluminum Activity in Alpine Tundra Soil, Rocky Mountain National Park, Colorado, U.S.A.

Shifts in seasonal aluminum (Al) activity and speciation in poorly buffered alpine tundra soil, attributable to atmospheric deposition of reactive nitrogen, can result in increased Al bioavailability, adversely impacting high-altitude plant and microbial communities. To evaluate seasonal changes in Al soil solution chemistry, intact soil column leaching studies were conducted to determine pore water Al speciation and transport under saturated spring melt-off conditions and unsaturated late summer conditions. These results were compared with aqueous Al speciation in surface and groundwater seep samples collected during the June to August growing season. Analysis of soil column leachates, surface and groundwater seep samples, indicated that Al activity was controlled by the aluminum hydroxyl sulfate suite of minerals, jurbanite, basaluminite, and alunite. Soil pore water collected from saturated soil cores consisted primarily of aluminum fluoride (Al-F) complexes for pore volumes (PV) < 5.0, with aluminum hydroxyl (Al-OH) complexation increasing with continued elution. Leachates collected from unsaturated soil cores exhibited Al-F transport only within the soil wetting front, PV < 1.0, after which, Al-OH complexes were predominant. The presence of fluoride (F−) in the soil pore water in the reactive solution front resulted in notable shifts between Al controlling solid phases and aqueous speciation. Similar shifts in Al speciation and controlling Al solid phases were observed in surface and groundwater seep samples, with sampling date and elevation. Results suggest that Al speciation and transport within alpine tundra soil may be seasonally influenced by soil moisture content and F− release from soil solid phases within the O/A1 soil horizons.

Effect of pH on floc properties and membrane fouling in coagulation–ultrafiltration hybrid process with different Al-based coagulants

Impacts of pH on floc properties and membrane fouling in coagulation–ultrafiltration process with different Al-based coagulants were investigated. Polyaluminum chloride (PAC) was prepared with alkali-titration method and Al speciation distribution was tested with Al-Ferron method. Three kinds of coagulants (AC(AlCl3), PACb, and PACc) consisted primarily of Ala (monomeric species), Alb (medium polymer species), and Alc (colloidal or solid species), respectively, were used as coagulants under pH conditions of 4.0, 6.0, and 8.0. Floc properties were evaluated using a laser diffraction particle sizing device and ultrafiltration experiments were conducted by a dead-end batch unit. The results indicated that pH condition and aluminum species had significant influence on size and fractal dimension value of flocs. For the three Al species, relatively low pH condition was favorable to form larger flocs, while it would diminish the floc growth rate. And the loosest flocs were formed at pH 4.0. Under the same pH conditions, Ala tended to form the largest flocs and Alc achieved the loosest floc structure. For each coagulant, membrane fouling under different pH conditions was in the following order: pH 4.0 > pH 8.0 > pH 6.0. Alb and Alc showed a wider tolerance for changes of pH conditions than Ala. And under the same pH conditions, Alc achieved the lightest membrane fouling.

The Interplay of Al and Mg Speciation in Advanced Mg Battery Electrolyte Solutions.

Mg batteries are an attractive alternative to Li-based energy storage due to the possibility of higher volumetric capacities with the added advantage of using sustainable materials. A promising emerging electrolyte for Mg batteries is the magnesium aluminum chloride complex (MACC) which shows high Mg electrodeposition and stripping efficiencies and relatively high anodic stabilities. As prepared, MACC is inactive with respect to Mg deposition; however, efficient Mg electrodeposition can be achieved following an electrolytic conditioning process. Through the use of Raman spectroscopy, surface enhanced Raman spectroscopy, (27)Al and (35)Cl nuclear magnetic resonance spectroscopy, and pair distribution function analysis, we explore the active vs inactive complexes in the MACC electrolyte and demonstrate the codependence of Al and Mg speciation. These techniques report on significant changes occurring in the bulk speciation of the conditioned electrolyte relative to the as-prepared solution. Analysis shows that the active Mg complex in conditioned MACC is very likely the [Mg2(μ-Cl)3·6THF](+) complex that is observed in the solid state structure. Additionally, conditioning creates free Cl(-) in the electrolyte solution, and we suggest the free Cl(-) adsorbs at the electrode surface to enhance Mg electrodeposition.

Alunite dissolution rates: Dissolution mechanisms and implications for Mars

Alunite (KAl3(SO4)2(OH)6) is a hydrated aluminous sulfate mineral associated with acidic, oxidizing aqueous environments on Earth. Additionally, orbiting spacecraft and rovers on Mars have reported spectral data that indicate a range of mono- and polyhydrated sulfate phases and hydroxysulfate phases, suggesting such conditions also existed on Mars in the past. This study examines alunite dissolution rates in aqueous systems with varying pH, temperature, and solution chemistry conditions. Alunite dissolution rates in dilute solutions are 2–3 orders of magnitude slower than jarosite dissolution rates measured under analogous conditions. Similar to jarosite, alunite dissolution rates vary as a function of activity of H+ and OH− following the rate law log r (molm−2s−1)=−0.133(±0.02)pH−10.65(±0.07) at pH<5 and log r=0.194(±0.04)pH−12.53(±0.26) at pH>5. However, minimum alunite dissolution rates are shifted to higher pH (5–5.5), likely due to differences in Fe and Al speciation. Alunite and jarosite rates converge in saturated NaCl and CaCl2 brines as the activity of water decreases, suggesting that differences in water exchange rates with Fe3+ and Al3+ control dissolution rates in dilute solutions, while metal–Cl− complexation occurs at similar rates within the brines. Particle lifetimes based on measured dissolution rates in dilute solutions show that alunite particles are expected to be preserved two orders of magnitude longer than jarosite particles over a range of pH and temperature conditions. In particular, alunite is more likely to be preserved in neutral to moderately alkaline systems compared to jarosite, which is expected to be preserved in more acidic conditions. Alunite dissolution produced amorphous Al-rich alteration products at moderate to high pH. Unlike jarosite, alunite dissolution does not show a clear trend as a function of temperature; alunite dissolution rates do not increase with increasing temperature, likely due to lower alunite solubility at higher temperature. Therefore, alunite is expected to be more prevalent in hydrothermal systems compared to jarosite.

Study of interactions between relevant organic acids and aluminium in model solutions using HPLC and IC

The interactions of different organic acids such as citric, malic, oxalic, and fulvic with aluminium were studied using ion-exchange chromatography (IC) and high performance liquid chromatography (HPLC). The experiments were carried out at low pH (1.5-3.1). The results of IC experiments on the interaction between Al and oxalate, citrate, and malate were compared with model chemical equilibrium calculations. The strongest effect on Al speciation was observed with oxalic acid and fulvic acid. These two ligands formed more than one type of complex with Al. In contrast, there was no significant effect of malic acid on Al speciation and a rather weak effect caused by citric acid. The studies show that the formed complexes are stable even at low pH.

The impact of fluoride on Al abundance and speciation in boreal streams

The impact of fluoride on the abundance and speciation of aluminium (Al) was investigated in three boreal streams characterised by overall high concentrations of fluoride and dissolved organic matter. Stream-water sampling was carried out several times a year for at least 4years, and a chemical equilibrium model (Visual MINTEQ) was applied in order to model the proportion of colloidal and organically/inorganically complexed Al in the waters. The Al concentrations in filtered (0.45μm) water samples were inversely correlated with pH, and reached values up to approximately 1mg/L during low pH conditions (pH<6.0). In a stream with high fluoride concentrations, as compared to a similar stream with only moderately elevated fluoride concentrations, the Al concentrations were consistently elevated. For the stream with high concentrations of fluoride and Al, the model predicted both high concentrations and proportions of Al-fluoride complexation. This prediction indicates that high fluoride levels contribute to raise both the Al abundance and the ratio of inorganic to organic Al complexation in stream water. In contrast, for another stream with high fluoride concentrations and consistently high (near neutral) pH, there was no evidence of fluoride affecting Al concentration or complexation. These results show that it is important to focus future studies on the role of high levels of dissolved fluoride on both the speciation and the toxicity of Al in stream water.

Aluminium (Al) fractionation and speciation; getting closer to describing the factors influencing Al3+ in water impacted by acid mine drainage

Acid mine drainage (AMD) severely impacts the water chemistry of a receiving resource, changing the occurrence, speciation and toxicity of metals such as Aluminium (Al). The toxicity of Al is determined by its speciation represented by the labile monomer Al fraction or Al3+. The purpose of the study was to combine fractionation and Visual MINTEQ speciation to calculate the effect of AMD altered water chemistry on Al speciation and Al3+ concentration. Water in rivers impacted by AMD presented with monomeric Al (Almon) concentrations between 0.35 and 15.37mgL−1 which existed almost exclusively in the toxic labile form (98%). For the reference site, Almon was less than 2% (10μgL−1), suggesting significantly lower Al toxicity. Principal component analysis plots illustrated that labile Al was directly related to the total Al and iron concentrations and strongly influenced by parameters such as pH, electrical conductivity, sulphate and dissolved organic carbon. Visual MINTEQ modelling was used to determine the primary Al species distribution. The dominant form of Al in AMD impacted water was AlSO4+, which increased proportionally with the sulphate and Al3+ concentration. Heavily impacted areas, presented with an average of 1mgmL−1 Al3+, which poses a potential human health risk. A novel centrifugal ultrafiltration method was investigated as an alternative to determining Almon to simplify the speciation of Al. Monomeric and centrifugal ultrafiltrated (<10kD) Al fractions were significantly similar (p=0.74), suggesting that ultrafiltration may present a time, energy and cost saving alternative to organic extraction of Almon.