Al Chemistry Research Articles

Induced Aggregation, Solvent Regulation, and Supracluster Assembly of Aluminum Oxo Clusters.

ConspectusRecent years have witnessed the development of cluster materials as they are atomically precise molecules with uniform size and solution-processability, which are unattainable with traditional nanoparticles or framework materials. The motivation for studying Al(III) chemistry is not only to understand the aggregation process of aluminum in the environment but also to develop novel low-cost materials given its natural abundance. However, the Al-related clusters are underdeveloped compared to the coinage metals, lanthanides, and transition metals. The challenge in isolating crystalline compounds is the lack of an effective method to realize the controllable hydrolysis of Al(III) ions. Compared with the traditional hydrolysis of inorganic Al(III) salts in highly alkaline solutions and hydrolysis of aluminum trialkyl compounds conducted carefully in an inert operating environment, we herein developed an effective way to control the hydrolysis of aluminum isopropanol through an alcoxalation reaction. By solvothermal/low melting point solid melting synthesis and using "ligand aggregation, solvent regulation, and supracluster assembly" strategies, our laboratory has established an organic-inorganic hybrid system of aluminum oxo clusters (AlOCs). The employment of organic ligands promotes the aggregation and slows the hydrolysis of Al(III) ions, which in turn improves the crystallization process. The regulation of the structure types can be achieved through the selection of ligands and the supporting solvents. Compared with the traditional condensed polyoxoaluminates, we successfully isolated a broad range of porous AlOCs, including aluminum molecular rings and Archimedes aluminum oxo cages. By studying ring expansion, structural transformation, and intermolecular supramolecular assembly, we demonstrate unique and unprecedented structural controllability and assembly behavior in cluster science. The advancement of this universal synthetic method is to realize materials customization through modularly oriented supracluster assembly. In this Account, we will provide a clear-cut definition and terminology of "ligand aggregation, solvent regulation, and supracluster assembly". Then we will discuss the discovery in this area by using a strategy, such as aluminum molecular ring, ring size expansion, ring supracluster assembly, etc. Furthermore, given the internal and external pore structures, as well as the solubility and modifiability of the AlOCs, we will demonstrate their potential applications in both the solid and liquid phases, such as iodine capture, the optical limiting responses, and dopant in polymer dielectrics. The strategy herein can be applied to extensive cluster science and promote the research of main group element chemistry. The new synthetic method, fascinating clusters, and unprecedented assembly behaviors we have discovered will advance Al(III) chemistry and will also lay the foundation for functional applications.

Kinetic Study of the Reactions of AlO with H2O and H2; Precursors to Stellar Dust Formation

AlO is relatively abundant around oxygen-rich Asymptotic Giant Branch (AGB) stars, where it can react with major gas-phase species such as H2 and H2O to form AlOH. These Al-containing species are the likely precursors of refractory alumina nanoparticles, which may provide the nuclei for dust formation. In the present study, the kinetics of these AlO reactions were measured from 295 to 780 K using the pulsed laser photolysis of Al(C5H7O2)3, with time-resolved laser induced fluorescence detection of AlO. The experimental results were interpreted using quantum chemistry calculations and a Master Equation solver for reactions with multiple energy wells. For the recombination reaction AlO + H2O (+ N2) → Al(OH)2, log10(krec,0/cm6 molecule–2 s–1) = −32.9185 + 8.80276 log10(T) – 2.4723(log10(T))2; log10(krec,∞/cm3 molecule–1 s–1) = −19.4686 + 7.62037 log10(T) – 1.47214(log10(T))2; Fc = 0.28 (uncertainty ±13% from 295 to 760 K). For the bimolecular reactions, k(AlO + H2O → AlOH + OH) = (3.89 ± 0.47) × 10–10 exp(−(1295 ± 150)/T) and k(AlO + H2 → AlOH + H) = (5.37 ± 0.52) × 10–13 (T/300)(2.77 ± 0.19) exp(−(2190 ± 110)/T) cm3 molecule–1 s–1. Rate coefficients for Al + H2O → AlOH + H, AlOH + H → AlO + H2 or Al + H2O, and the absorption cross sections of AlOH and AlO were calculated theoretically. Al chemistry around an O-rich AGB star was then investigated using a β-trajectory model, which predicts that AlOH is the major gas-phase Al species beyond two stellar radii and shows that the relative AlO abundance is very sensitive to the AlOH photolysis rate.

Trends and current status of aluminum chemistry in Adirondack headwater streams 30 Years after the Clean Air Act Amendments of 1990

Mobilization of toxic forms of aluminum (Ali) have been one of the most harmful effects of acidic deposition on aquatic ecosystems. Large decreases in acidic deposition levels have resulted in decreases in Ali concentrations in surface waters starting in the 1990s. However, recent studies indicate that fish communities are still being impaired by elevated Ali concentrations in streams, suggesting the need for a present-day assessment of the recovery status of Al chemistry in impacted regions such as the Adirondack region of New York, United States. Therefore, the recovery status of Al was assessed from long-term high-frequency monitoring of three Adirondack streams up through 2019, and multiple resampling of 127 headwater streams throughout the Adirondack region between 2004/2005 and 2018/2019. Results indicated that concentrations of Ali have continued to decrease throughout the Adirondack region, but that harmful conditions still exist in a substantial number of streams during spring snowmelt. In the western Adirondack region, 35 percent of streams during spring snowmelt, (typically the most acidic period), and 10 percent of streams during summer were still experiencing harmful concentrations of Ali (>1.0 μmol L−1) in 2018/2019. In the less-impacted east-central Adirondack region, 10 percent of streams during snowmelt, and 4 percent of streams during summer were experiencing harmful Ali concentrations in 2018. Temporal decreases in Ali concentrations were due in part to a shift in speciation from Ali to non-toxic organically complexed Al as dissolved organic carbon concentrations increased, which was also a response to decreasing acidic deposition. Increased availability of calcium resulting from acid-neutralization processes such as weathering also contributed to the decrease in Ali over the past 5–8 years. The current low levels of acidic deposition may have begun to enhance recovery by increasing the effectiveness of ambient acid-neutralization processes.

Tridentate Ligand with Three Carbanions as Donor Atoms: Formation of Dinuclear, Heptacyclic Complexes of Boron, Aluminum, or Gallium with B-C-B, Al-C-Al, or Ga-C-Ga Three-Center-Two-Electron Bonds.

The trilithium compound 1,3-[PhMe2Si-C(Li)═C(H)]2C6H3Li (2b) reacted with BCl3, AlCl3, or GaCl3 by salt elimination to yield dinuclear heptacyclic compounds (4). Two tridentate tricarbanionic ligands coordinate two B, Al, or Ga atoms and adopt a helical arrangement of the ligands around a central E2 unit. The unusual structures comprise E2C2 heterocycles with two 3c-2e (three-center-two-electron) E-C-E bonds and two C atoms of aromatic rings in the bridging positions. While such a bonding situation is well-documented in Al chemistry, it is rare for B and Ga compounds. Insight into the bonding situation of the molecules is provided by DFT calculations.

Density functional theory studies on the external OH−‐induced barrierless proton dissociation mechanism for the forced hydrolysis reaction of Al3+(aq)

The forced hydrolysis reaction of aqueous aluminum ion (Al3+) is of critical importance in Al chemistry, but its microscopic mechanism has long been neglected. Herein, density functional calculations reveal an external OH−‐induced barrierless proton dissociation mechanism for the forced hydrolysis of Al3+(aq). Dynamic reaction pathway modeling results show that the barrierless deprotonations induced by the second‐ or third‐shell external OH− proceed via the concerted proton transfer through H‐bond wires connected to the coordinated waters, and the inducing ability of the external OH− decreases with increasing hydration layers between Al(H2O)63+ and the external OH−. The OH−‐induced forced hydrolysis mechanism of Al3+(aq) is quite different from its self‐hydrolysis mechanism without OH−. The inducing ability is a unique characteristic of OH−, rather than other anions such as F− or Cl−.

A Sodium-Aluminum Hybrid Battery

To effectively harvest the energy from renewable sources such as solar and wind, cheap and long-lasting electric energy storage (EES) devices are essential.1 Among various EES technologies, lithium ion batteries (LIBs) are the most mature technologies with high energy density, high coulombic efficiency and long cycle life. Unfortunately, their high cost and the unevenly distributed global lithium source are major concerns. 2 Thus, beyond lithium technologies based on cheap and naturally abundant elements such as sodium (Na), magnesium (Mg), and aluminum (Al) ion batteries 3, 4 have been intensively studied during the last few years. Among different metals, Al is one of the most earth abundant elements, only second to silicon, resulting in its low price of $0.52/kg, 100 times lower than Li. In addition, Al with three electrons redox couple has distinct advantage over one electron redox couple such as Li and Na and two electrons redox couple such as Mg and Ca, providing a high theoretical specific capacity of 2980 mAh g-1 and a high volumetric capacity of 8040 mAh cm-3. The development of rechargeable Al ion batteries has been hampered by the electrolyte and cathode materials. Due to the low reduction potential of Al (-1.68 V vs. SHE), aqueous electrolytes cannot be used when Al is being used as the anode, since hydrogen will be released before Al can be plated during the reduction process. As an alternative, ambient room temperature ionic liquids with high ionic conductivity and wide electrochemical windows are good candidates for rechargeable Al batteries. Currently, the ionic liquids used for Al deposition are still based on mixtures of anhydrous AlCl3 and organic halide salts.5 It is well-known that only the acidic mixtures show reversible Al deposition/stripping, which poses stringent requirement for the hardwares of the Al batteries.6 To avoid the corrosion issue, pouch cell and special cell configuration have been used.7 Besides electrolytes, Al batteries also face challenges from the cathodes due to the high charge density of the Al3+ ion, making its insertion/extraction into/from the cathode host very difficult. An alternative way to take advantage of metallic Al anode but bypasses the need for efficient Al insertion cathodes is hybrid Al battery.7 It was demonstrated that high voltage and high capacity were possible in a hybrid Al battery with LiFePO4 as the cathode in an acidic ionic liquid electrolyte.7 However, a switch to the more earth-abundant sodium chemistry is more desirable due to the limited Li resources. In this presentation, we report a new hybrid battery using earth-abundant Na and Al chemistry, that is, Al as the anode, Na3V2(PO4)3 (NVP) as the cathode and NaAlCl4 dissolved in acidic ionic liquid as the electrolyte.8 The hybrid battery exhibits a discharge voltage of 1.25 V and a cathodic capacity of 99 mAh g-1 under a current rate of C/10. In addition, the hybrid battery exhibits good rate performance and long cycling stability while maintaining a high coulombic efficiency of 98 %. It is also demonstrated that increasing salt concentration can further enhance the cycling performance of the hybrid battery. X-ray diffraction analysis of the NVP electrodes under different conditions confirms that the main cathode reaction is indeed the Na extraction/insertion. 1. B. Dunn, H. Kamath and J. M. Tarascon, Science, 2011, 334, 928-935. 2. H. L. Pan, Y. S. Hu and L. Q. Chen, Energy Environ. Sci. , 2013, 6, 2338-2360. 3. G. A. Elia, K. Marquardt, K. Hoeppner, S. Fantini, R. Y. Lin, E. Knipping, W. Peters, J. F. Drillet, S. Passerini and R. Hahn, Adv. Mater. , 2016, 28, 7564-7579. 4. T. Gao, X. G. Li, X. W. Wang, J. K. Hu, F. D. Han, X. L. Fan, L. M. Suo, A. J. Pearse, S. B. Lee, G. W. Rubloff, K. J. Gaskell, M. Noked and C. S. Wang, Angew. Chem. Int. Ed. , 2016, 55, 9898-9901. 5. J. S. Wilkes, J. A. Levisky, R. A. Wilson and C. L. Hussey, Inorg. Chem. , 1982, 21, 1263-1264. 6. L. D. Reed and E. Menke, J. Electrochem. Soc., 2013, 160, A915−A917. 7. X. G. Sun, Z. H. Bi, H. S. Liu, Y. X. Fang, C. A. Bridges, M. P. Paranthaman, S. Dai and G. M. Brown, Chem. Commun., 2016, 52, 1713-1716. 8. X. G. Sun, Z. Z. Zhang, H. Y. Guan, C. A. Bridges, Y. X. Fang, Y.-S. Hu, G. M. Veith and S. Dai, J. Mater. Chem. A, 2017, 5, 6589-6596. Figure 1

Anthropogenic fluorine accumulation in the Waikato and Bay of Plenty regions of New Zealand: comparison of field data with projections

Application of phosphate (P) fertilizers to farmland is projected to be causing worldwide accumulation of fluorine (F) in agricultural soils and associated ecosystems, but wide-scale field data have been lacking. We report results of sampling across two large regions of New Zealand involving soils of 298 native and farmed properties. This has enabled the first wide-scale retrospective estimates of anthropogenic F enrichment in pastoral and horticultural soils. Results validate earlier projections: F accumulation in farmed soils has been comparatively rapid (mean increase 2.1 % per year) and widespread. Over 50 years, average total F concentrations in surface soils have doubled from ~220 to 440 mg/kg. Thresholds protective against chronic fluorosis in grazing animals are being substantively passed, indicating that land may be rendered unsuitable for pastoral production in the mid-term future: when sampled 44 % of dairy farm soil samples exceeded 500 mg/kg total F, and 10 % exceeded 650 mg/kg. Potential for F toxicity to plants and wildlife appear to be significant and marginal, respectively, at current soil F concentrations. Relationships between F and other elements suggest P fertilizers are also a source of several elements geochemically linked to F, and that anthropogenic F modifies soil aluminium (Al) chemistry, potentially opening a broad-scale Al exposure pathway to pollinating insects. Findings signal a need for systematic examination of the range of possible affects that may be linked to increasing soil F, which include various types of ecotoxicity, altered Al chemistry, reduced P availability, and potential for increased dietary intakes of F, Al and aluminofluoride (AlFx) species over time.

Electrolytic synthesis of aqueous aluminum nanoclusters and in situ characterization by femtosecond Raman spectroscopy and computations

The selective synthesis and in situ characterization of aqueous Al-containing clusters is a long-standing challenge. We report a newly developed integrated platform that combines (i) a selective, atom-economical, step-economical, scalable synthesis of Al-containing nanoclusters in water via precision electrolysis with strict pH control and (ii) an improved femtosecond stimulated Raman spectroscopic method covering a broad spectral range of ca. 350-1,400 cm(-1) with high sensitivity, aided by ab initio computations, to elucidate Al aqueous cluster structures and formation mechanisms in real time. Using this platform, a unique view of flat [Al13(μ3-OH)6(μ2-OH)18(H2O)24](NO3)15 nanocluster formation is observed in water, in which three distinct reaction stages are identified. The initial stage involves the formation of an [Al7(μ3-OH)6(μ2-OH)6(H2O)12](9+) cluster core as an important intermediate toward the flat Al13 aqueous cluster.

Increases in Dissolved Organic Carbon Accelerate Loss of Toxic Al in Adirondack Lakes Recovering from Acidification

Increasing pH and decreasing Al in surface waters recovering from acidification have been accompanied by increasing concentrations of dissolved organic carbon (DOC) and associated organic acids that partially offset pH increases and complicate assessments of recovery from acidification. To better understand the processes of recovery, monthly chemistry from 42 lakes in the Adirondack region, NY, collected from 1994 to 2011, were used to (1) evaluate long-term changes in DOC and associated strongly acidic organic acids and (2) use the base-cation surplus (BCS) as a chemical index to assess the effects of increasing DOC concentrations on the Al chemistry of these lakes. Over the study period, the BCS increased (p < 0.01) and concentrations of toxic inorganic monomeric Al (IMAl) decreased (p < 0.01). The decreases in IMAl were greater than expected from the increases in the BCS. Higher DOC concentrations that increased organic complexation of Al resulted in a decrease in the IMAl fraction of total monomeric Al from 57% in 1994 to 23% in 2011. Increasing DOC concentrations have accelerated recovery in terms of decreasing toxic Al beyond that directly accomplished by reducing atmospheric deposition of strong mineral acids.

Aluminium fractionation and speciation in bulk and rhizosphere of a grass soil amended with mussel shells or lime

Acid soils have a high proportion of Al in the exchange complex and are usually amended with lime to reduce the toxic effect of the free Al (Al3+). To this purpose, in some places like Galicia (NW Spain), there is a high production of wastes such as mussel shells that may substitute the lime. The aim of this work was to study the effect of different amending products derived from mussel shells on the Al chemistry in both bulk and rhizosphere, and on pasture production. The experiments were conducted on plots of an acid soil cultivated with grasses (Dactylis glomerata L., Trifolium repens L. and Lolium perenne L.). Each plot received its own treatment consisting of 1) commercial lime, 2) mussel shells dried and ground till 0–2mm (MDF), 3) mussel shells dried and ground till 2–4mm (MDC), 4) mussel shells heated (550°) and ground till <63μm (MHF), or 5) mussel shells heated (550°C) and ground till 0–2mm (MHC); one plot acted as control and was not treated. Each plot was replicated four times. The soil samples were collected after 16months and submitted to a general characterization. The Al was extracted from the soil by different solutions: ammonium oxalate (Alo=non-crystalline Al), sodium pyrophosphate (Alp=organically bound Al), copper chloride (Alcu=organo-Al complexes of low to medium stability) and ammonium chloride (exchangeable Al); the difference Alp-cu estimated the organo-Al complexes of high stability. From the soil water extracts, the Al was fractionated into acid-soluble (Al-polymers, colloids and organic complexes), non-labile Al (organic monomers) and labile Al (inorganic monomers, namely the species Al3+, Al–OH, Al–F and Al–SO4). For each plot, the production of the total dry matter and of that produced by the sown species, were also determined. With respect to the control, all the amending treatments increased the pH in the rhizosphere (5.11 in the control plots, 5.48–5.89 in the amended plots), which showed pH values higher than the bulk (5.13–5.60 in the amended bulk soil; 5.48–5.89 in the amended rhizosphere). Also the contents of C and N were higher in the rhizosphere than in the bulk, without difference among treatments. Concerning with Al chemistry, all the mussel shells derived products had effects similar to those of the commercial lime, with no difference among them. With respect to the control, in the soil solid phase all the treatments induced an increase in the formation of hydroxyl-aluminium complexes in the bulk (Alo: 3500mgkg−1 in the control, 3700–5500mgkg−1 in the amended plots) and organo-Al complexes of high stability in the rhizosphere (Alp-cu: 3563mgkg−1 in the control, 3550–5000mgkg−1 in the amended plots). The exchangeable Al diminished with all treatments, more in the rhizosphere (1.36cmol(+) kg−1 in the control, 0.24–0.47cmol(+) kg−1 in the amended plots) than in the bulk (2.83cmol(+) kg−1 in the control, 0.46–1.23cmol(+) kg−1 in the amended plots). Concerning the water extracts, the treatments induced an increase of organic complexes (polymers and monomers), more pronounced in the rhizosphere (non-labile Al: 0.17μmolL−1 in the control, 10.7–35.7μmolL−1 in the amended plots) than in the bulk (non-labile Al: 0.25μmolL−1 in the control, 0.25–3.57μmolL−1 in the amended plots). Further, in the treated plots the labile Al was dominated by Al–OH complexes, which are considered toxic but a lower level than the Al3+ and abounded in the control. The production of dry matter due to the sown species was about double in the plots treated with CL and MHF with respect to the control. We conclude that the products derived from mussel shells can substitute the commercial lime in the amending of acid soils, so increasing the value of the shells and limiting the environmental problems derived by their disposal.

Lime Effects on Soil Acidity, Crop Yield, and Aluminum Chemistry in Direct‐Seeded Cropping Systems

Soil acidification threatens dryland crop production in the inland Pacific Northwest (IPNW). Our objective was to assess the efficacy of lime to lower soil acidity, alter Al chemistry, and increase crop yield in a direct‐seeded system. Treatments of subsurface banded fertilizer (120–168 kg N ha−1 yr−1) alone or with subsurface banded lime (224 kg ha−1 yr−1), or a one‐time broadcast application of lime (7000 kg ha−1) or elemental S (1000 kg ha−1) were initiated in spring 2002. Grain yield was measured annually from 2002 to 2005 in a spring barley (Hordeum vulgare L.)–spring wheat (Triticum aestivum L.)–winter wheat rotation. Soil was sampled in spring 2004 to assess pH and model Al speciation. Low pH was evident at the depth of fertilizer placement (5–10 cm). Broadcast lime increased pH in the surface 15 cm, although reductions in Al3+ activity [(Al3+)] occurred only in the 0‐ to 5‐cm layer. Relative to banded N, there was no increase in pH at the 5‐ to 10‐cm depth where banded lime was placed. At the 0‐ to 5‐cm depth, lower pHs were observed with broadcast S (4.6) compared with the banded N control (5.1) or banded lime (5.0). There was no effect of treatment on yield. Modeling suggests that soluble Al is dominated by organic matter–Al complexes (fulvic acid, FA; FA2Al+ and FA2AlOH0). Solid‐ and solution‐phase organic complexes may control (Al3+) at pH &lt;5.5. Although acidification is a concern in the IPNW, the high organic matter content in direct‐seeded soils may buffer against Al phytotoxicity.

The Chemistry of Aluminum(I), Silicon(II), and Germanium(II)

Although tetrameric Al(I) compounds have been known for a long time, the monomeric Al(I) compounds that are analogous to carbenes are very recent entrants in Al(I) chemistry. They possess novel str...

Evolution of soil solution aluminum during transport along a forested boreal hillslope

Aluminum (Al) transfer from soils to surface waters is a crucial determinant of aquatic biodiversity in acidified and/or naturally acid surface waters. Defining how landscapes and acid deposition influence Al export depends on our understanding of the mobilization of Al within catchments. This paper documents the evolution of Al chemistry in water during its transport through a hillslope by using soil water chemistry combined with hydrometric data. Al levels moving laterally from upslope mineral soils were low (&lt;0.1 mg·L−1). This is not consistent with a vertically infiltrating acidification front mobilizing Al from across the catchment. As water moves laterally downslope into the peaty soils of the riparian zone (RZ), Al increased along with organic acids and iron. The RZ in this study was thus a net source of Al to soil solution on all 9 sampling occasions where Al was measured, as well as a net source of dissolved organic carbon (DOC) on another dozen measurement occasions. The potential for Al concentrations being modified during transport through the RZ needs to be accounted for in efforts to relate acid deposition to toxic stream Al concentrations. Organic carrying capacity was in excess of Al for all samples. Only samples from the deeper mineral soils showed supersaturation; however, none of the samples showed degrees of supersaturation high enough for spontaneous mineral precipitation. A key area for further research is how the RZ can sustain a larger Al pool than upslope mineral soils when the supply of Al from these upslope soils to lateral flux is currently lower than that from the RZ. Two possibilities are either episodic downslope transport during periods of high lateral flow, or drainage‐induced changes in hydrology that transformed the RZ from an accumulator of Al to a source of Al.

Vegetation effects on pedogenetic forms of Fe, Al and Si and on clay minerals in soils in southern Switzerland and northern Italy

The older forest type Quercetum– Betuletum (oak/birch; Q-type vegetation) in southern Switzerland and northern Italy was to a large extent replaced by chestnut forests ( Castanea sativa; C-type vegetation) in roman times. When laurophylloid vegetation (L-type vegetation) invaded some of these chestnut systems during the last few decades, it caused detectable changes in organic chemistry. The invasion of the L-type vegetation was predominately due to increased winter temperatures. We tested whether these vegetation changes led to measurable long-term and short-term responses of the mineral matrix by comparing soils under Q-type with C-type vegetation (probing for long-term effects; > 100–2000 years) and soils under C-type with L-type vegetation (short-term effects; a few decades). To do so, we examined soil characteristics including the dithionite-, oxalate- and pyrophosphate-extractable forms of Fe, Al and Si as well as the phyllosilicate mineralogy of the clay fraction with a pair-wise comparison procedure. On L-type patches, short-term changes resulted in higher contents of secondary, poorly crystalline Fe. The accumulation of pedogenetic Fe probably results from a lower availability of organic complexing moieties under L-type vegetation and thus leading to a reduced removal. As soil acidity did not change with the vegetation types, a strong effect of organic compounds on Fe and Al chemistry must be assumed. A correlation analysis confirmed that metal binding to organic matter was different between L-type stands (correlation of Fe and Al with organic matter was less significant) and C-type stands. The differences in clay phyllosilicate assemblage between the different vegetation sites were rather small. There was, however, a trend towards higher contents of hydroxy-interlayered vermiculite (HIV) under L-type vegetation when compared to C-type sites. It seems that Al-polymers fixation in interlayers of 2:1 clay minerals was increased or their removal hindered at sites having L-type vegetation. Changes in the long-term (response to C-type vegetation) were only measurable for the pyrophosphate-extractable Si content (formation of phytolithe?). The colonisation of laurophyllous species led in the short-term to significant alterations of the soil system that were even more pronounced than the long-term effect of chestnut on soil quality.

Aluminum dynamics in forest soil waters in Norway

We report on weekly aluminum (Al) concentration measurements in soil water from forested catchments monitored throughout Norway since 1986. Originating in acidification research, and thus accompanied by many other chemical variables, they constitute a comprehensive data set suited for analysis of short- as well as long-term variations in a geographic perspective. The Al time series at 21 sites are characterized by high temporal variability, seasonal behavior, and episodic events with peak values in the range 200–800 μmol/l, mostly caused by sea salts blown inland in storms, with a subsequent release of Al after cation exchange. Despite a clear south–north gradient in possible acidification over Norway, we found no indication of such south–north trends in Al chemistry, neither in mean values, maximum values, nor time trends. We identified two main drivers for variation in Al concentrations. The first one was sea salts, where Al was released to the soil solution after cation exchange. The second driver was high production of DOC, where Al was driven into the soil solution by complexation with DOC. There appears to be little risk for aluminum toxicity to trees in Norwegian forests. Except during occasional episodes, aluminum concentrations generally lay far below the supposed threshold values for toxic effects on Norway spruce, Scots pine and birch. Much dissolved aluminum was non-labile, and thus relatively non-toxic. Although the Ca 2+ / labile Al ratio was often below 1.0, considerable doubt exists as to the applicability of this variable in the field.

Aluminium chemistry in ploughed podzolic forest soils

Mechanical site preparation has been used to ensure efficient reforestation of clear-felled areas in Finland since the 1960s. About 18% (3.94 million ha) of the total forest land in Finland (21.9 million ha) has been site-prepared, of which one-third has been deeply tilled. In the present study, long-term effects of deep tilling on the chemical properties of soil and soil solution chemistry were evaluated at two forest sites that had been ploughed 17 and 31 years ago and planted with Norway spruce (Picea abies (L.) Karst.) seedlings. Particular interest was focused on the possible mobilisation of soil aluminium in the spodic B horizons exposed upon tilling. Mechanisms controlling Al solubility in the tilled soil profiles were also examined. Decreased concentrations of soil extractable Al, mainly inorganic secondary Al, in the exposed Bs horizons of tilts and furrows and increased concentrations of organically complexed Al in the O horizons buried within the tilt indicate that some Al was mobilised at the ploughed forest sites. Accumulation of organic C on top of the tilts and furrows with the relatively high Norway spruce fine root biomass in the tilts indicated that the release of Al was mainly due to acidity produced by ecosystem internal processes such as organic acids excreted by roots or released during decomposition of aboveand belowground litter. Ploughing did not affect the processes controlling activity of Al in soil solution. In the undisturbed and disturbed Bs horizons, Al solubility was controlled by secondary minerals while in the O and Ah/E horizons, solubility control by organically bound Al was observed. Although the soil exchangeable Al pool was small, the Al Ca exchange based on the Gaines-Thomas equation succesfully described the relationship between these cations in soil solution and on exchange sites in the studied O and Bs horizons. In the O horizons, exchangeable Al had nonacidic properties similar to those of base cations, and the soil solution pH was explained by weak organic acid dissociation using the Henderson-Hasselbach equation. The changes observed in soil chemical properties in the ploughed soil were consistent with the processes determining the Al chemistry in soil solution, and in accordance with the theory of podzolization. It may be expected that soil formation processes will in the course of time result in the development of a new spodic horizon in the tilts and furrows. Although the time elapsed since ploughing was only a few decades in this study, the occurrence of changes observed suggest that plant-derived organic matter and plant-soil interactions are already modifying the properties of ploughed podzols.

Compost, Limestone, and Gypsum Effects on Calcium and Aluminum Transport in Acidic Minespoil

Combining limestone (CaCO 3 ) application with compost or gypsum (CaSO 4 .2H 2 O) can substantially increase subsoil Ca and decrease subsoil Al saturation in highly weathered acidic soils because of increased Ca mobility and formation of nontoxic Al-organic matter complexes. However, little is known about the effect of these surface amendments on subsoil chemistry in acidic minespoils that are high in SO 4 . This study used small segmented laboratory columns to analyze the effect of surface incorporated compost, CaCO 3 , and gypsum on Ca and Al chemistry in the highly acidic minespoil material (pH 2.5) below the zone of incorporation. Compost did not affect subsoil Al and Ca chemistry but caused a small increase in subsoil pH. Because of the high acidity in the spoil material CaCO 3 solubility in the amended layer was high and was not increased by compost. Adding gypsum increased Ca leaching into the subsoil compared with CaCO 3 alone, but extractable Ca was higher only after extensive leaching. Increases in extractable Ca in the subsoil were strongly correlated to decreases in extractable Al and Fe, indicating cation-exchange processes. However, significant losses of Al in unamended spoil columns and the small impact of CaCO 3 and gypsum on total Al leaching indicated that Al chemistry was also influenced by a solid phase. Solubility calculations pointed to a jurbanitelike solid phase buffering Al activity in the subsoil, even after extensive leaching. Because of this buffering effect and the high acidity of the spoil material, none of the surface treatments would be expected to alleviate subsoil phytotoxicity in highly acidic minespoil material.

Hyperspectral Mapping of Mineral Assemblages Associated with Gold Mineralization in the Central Pilbara, Western Australia

The Indee district, located in the Central Pilbara tectonic zone of the North Pilbara terrain in Western Australia, contains Archean lode gold deposits and epithermal gold systems. Hydrothermal alteration assemblages associated with these deposits contain the minerals pyrophyllite, white mica, chlorite, and tourmaline. Known prospects are surrounded by flat areas of poorly exposed calcretized bedrock, calcretes, rock float, and sandy soils. Two adjacent lines of airborne hyperspectral data (HyMap®) were acquired. To produce mineral abundance maps, these data were processed to correct for atmospheric and illumination conditions and then calibrated to reflectance data using field spectra. This analysis successfully mapped the distribution of pyrophyllite, white mica, Mg chlorite, Fe chlorite, calcite, dolomite, kaolinite, tourmaline, hematite, and goethite. Alteration assemblages associated with the Camel 2 deposit, which is located along the Mallina shear zone, were found to be characterized by pyrophyllite and Al-rich white mica, the latter having an AlOH absorption feature at 2.194 μ m. In contrast, alteration assemblages associated with epithermal deposits south of the Mallina shear zone are characterized by Al-poor white mica with a longer wavelength absorption feature at 2.210 μ m, the shift reflecting the change in Al chemistry (Tschermak substitution). Tourmaline is also present near the epithermal-like deposits, suggesting that it may be an integral part of these systems. Fe chlorite is associated with both the mesothermal and epithermal systems but is also pervasive as a regional metamorphic mineral. Regolith-related carbonates are common throughout the area and their compositions are determined by the hyperspectral processing. Mineral abundance images were verified by PIMA® (portable infrared mineral analyser) analysis of ground samples, and assays of rocks in previously unknown areas of pyrophyllite and white mica confirmed the presence of anomalous gold. These results show that mineral maps and compositional information derived from hyperspectral analysis are extremely valuable for exploration, even in poorly exposed, regolith-dominated districts such as Indee.

A major water quality problem in smolt farms: combined effects of carbon dioxide, reduced pH and aluminium on Atlantic salmon ( Salmo salar L.) smolts: physiology and growth

Hatchery reared Atlantic salmon ( Salmo salar L.) smolts (mean start weight 80 g) in soft freshwater were exposed to three levels of carbon dioxide partial pressure for 38 days (25 days for the high group) in an open flow system: 0.5 mm Hg (1.8 mg/l CO 2; pH 6.6; control group), 2.7 mm Hg (9.3 mg/l CO 2; pH 6.0; medium group) and 5.7 mm Hg (19.4 mg/l CO 2; pH 5.7; high group). The different pH levels were a consequence of the addition of carbon dioxide to the water. Water temperature was 6–8 °C and effluent oxygen levels above 9 mg/l. During the experiment, the total aluminium concentration in the water was relatively stable in the range 115–140 μg/l. Labile Al concentration was low in all groups (about 10 μg/l). Despite this, the mean gill aluminium deposition was five times and seven times higher in the medium and high carbon dioxide groups, respectively, compared with the control group ( p<0.05). Mean respiration frequency was significantly increased both in the medium and high carbon dioxide groups compared to the control group ( p<0.05). The main gill lesions observed in the groups with elevated CO 2 were focal to diffuse hypertrophy and hyperplasia of chloride cells and adhesion of lamellae. Even though no significant differences were found in mean plasma cortisol concentrations in the medium group compared to the control group at any sampling time, mean plasma chloride and gill Na +,K +-ATPase activity in the medium group were lower than controls on day 19 ( p<0.05) and the mean condition factor was significantly reduced on day 38 ( p<0.05). The overall specific growth rate (SGR) for the medium group was −0.06%/day compared to 0.26%/day for the control group between days 3 and 38. After 38 days, accumulated mortality for the control group and the medium group was 0.4% and 4%, respectively. Days 2 and 19 mean plasma cortisol and hematocrit were significantly increased in the high group, and mean plasma chloride concentration was significantly reduced compared to the control group. There was a significant depression in gill Na +,K +-ATPase activity between days 2 and 19 ( p<0.01) in the high CO 2 group, to a level of approximately 30% of control levels. The specific growth rate for this group was negative (−0.25%/day) between days 3 and 38. Accumulated mortality in the high group was 42% after 25 days and the experiment was discontinued for ethical reasons. The present investigation has shown that the build-up of carbon dioxide, reduction in pH and the changes in Al chemistry may be detrimental to Atlantic salmon smolts even at low concentrations. Further investigations are, however, needed to study combined effects of aluminium, pH and carbon dioxide and effects of each parameter in isolation on Atlantic salmon smolts.

Aluminium chemistry in two contrasted acid forest soils and headwater streams impacted by acid deposition, Vosges mountains, N.E. France.

Al chemistry was studied in two acidic watersheds, one with a podzol, the other with an acid brown soil, in the Vosges mountains (N.E. France), by analysing both leaching and centrifugation soil solutions and spring waters over 3 yr. In the podzol, Al was mobilized in the eluvial horizons under the predominant influence of organic acidity, then leached down the profile as organic and F-bound Al. Strong undersaturation with respect to proto-imogolite and imogolite showed that the proto-imogolite theory of podzolization could not apply. Al was transferred from the soil to spring water mostly as Al3+ and Al-F. Al3+, as well as additional minor species (AlOH2+, AlSO4 +), originated from the redissolution of the top of the spodic horizons under the influence of both soil solution acidity and the occurrence of mobile anions derived from atmospheric deposition. Conversely, in the acid brown soil, Al mobilization was regulated by nitrate and occurred mainly as Al3+. Most of Al was retained in the deep soil and only traces of monomeric Al reached spring water. In the podzol eluvial horizons, soil solutions were undersaturated with respect to all relevant mineral phases and their chemical composition agree with the concept of a mobilization of Al from the solid soil organic Al and a control of Al3+ activity by complexation reaction with the solid and soluble soil organic matter and F. In the acid brown soil, soil solutions were found to be in equilibrium with natural alunite, and the formation of this mineral, if confirmed, would account for the occurrence of 'open' vermiculites instead of the expected hydroxy-Al interlayered vermiculites. Al solubility control in surface water of both watersheds remains unclear. The Al-F species in both watersheds and the likely control of Al solubility by alunite in the acid brown soil emphasize the influence of acid deposition on Al chemistry in acid watersheds.