Al Speciation Research Articles

On the effect of EDTA treatment on the acidic properties of USY zeolite and its performance in vacuum gas oil hydrocracking

USY zeolite catalysts were chemically modified by treatment with aqueous solutions of sodium ethylenediaminetetraacetic acid (EDTA) to study the effect of removal of extraframework aluminum species (EFAl) on hydrocracking performance. The textural, structural and acidic properties were characterized by XRD, elemental analysis, XPS, N2 physisorption, HRTEM, 29Si and 27Al solid-state NMR, ammonia TPD and IR spectroscopy of adsorbed pyridine. The acid catalytic activity of the zeolites was measured by the conversion of propane and 1,3,5-tri-isopropylbenzene. EDTA is a selective agent for the extraction of EFAl from USY preserving the framework Al content. Concomitant with EFAl removal, EDTA enhances the textural properties and changes bulk and surface properties, in particular the Al speciation. Hydrocracking catalysts were prepared from the modified USY zeolites and alumina loaded with a P-promoted NiMo-sulfide phase. Their performance was evaluated in the hydrocracking of a heavy vacuum gas oil under conditions close to the industrial practice. The most active hydrocracking catalyst is obtained by removal of a relatively small amount of EFAl from the USY zeolite. The mild EDTA treatment to achieve this selectively extracts amorphous EFAl species from the mesopore system, resulting in better access to acid sites and an increase of the concentration of strong Brønsted acid sites. Severe EDTA treatment resulted in lower hydrocracking activity which was ascribed to progressive leaching of EFAl synergistically involved in the cracking catalysis. The present study therefore points out the importance of the presence of some EFAl species for the hydrocracking of real feedstocks. This work also shows that even with supports with increased mesoporosity and stronger acid character, higher hydrocracking activity of a real feedstock is not guaranteed.

Forms of Al in soil and soil solution in a long‐term fertilizer application experiment

AbstractUnder the conditions of a long‐term fertilizer experiment, this study aimed to determine the contents of total and exchangeable aluminium in soil as well as the Al concentration in the soil solution. Additionally, Al speciation was evaluated with the use of the MINTEQA2 software. The results obtained indicated that under the conditions of long‐term application of different mineral fertilizers or farmyard manure, the soil reaction changed to a great extent (pH 3.58–6.78). At the same time, the content of total Al in soil fluctuated from 18.85 to 22.13 g/kg and that of exchangeable Al ranged from 1.42 to 102.66 mg/kg. The concentration of Al in the soil solution was highly differentiated (5.19–124.07 μmol/L) as well as that of free aluminium ions (Al3+) (0–16.9 μmol/L). In acidic soils, aluminium complexes with organic matter are the predominant forms of Al in the soil solution. In soils with neutral soil reaction, there were no free aluminium ions. Soil liming and addition of organic amendment were the treatments that restricted the presence of toxic aluminium forms in soil.

The role of hydroxy aluminium sulfate minerals in controlling Al3+ concentration and speciation in acidic soils

Abstract A thermodynamic approach for the complex chemical equilibria investigation of two-phase systems containing hydroxy aluminium sulfate (HAS) minerals in soils has been developed. This approach utilizes thermodynamic relationships combined with original mass balance constraints, where the HAS mineral phases are explicitly expressed. The factors influencing the distribution and concentrations of various soluble aluminium species have been taken into account. The new type of diagrams, based on thermodynamic, graphical and computerized methods, which quantitatively describe the distribution of soluble and insoluble inorganic, and organic, monomeric and polymeric aluminium species in acidic soil solutions in a large range of pH values has been used. The thermodynamics of equilibria of different natural HAS in soils, the conditions under which solids involving common ions can coexist at equilibrium, the acid-base and mineral equilibria and complex formation have been examined. It has been proved that the presence of sulfate ion dramatically alters the HAS mineral solubility under acidic conditions. The obtained data regarding the factors influencing Al speciation, based on the constructed diagrams of heterogeneous chemical equilibria, are in good agreement with the current experimental and theoretical evidence. The proposed approach is intended to determine the dominant processes that are responsible for the Al3+ concentration levels and its speciation in acidic soils.

Modifier cation (Ba, Ca, La, Y) field strength effects on aluminum and boron coordination in aluminoborosilicate glasses: the roles of fictive temperature and boron content

The field strength of modifier cations has long been known to have important effects on oxide glass properties, but effects on network structure can be complex. For two series of barium, calcium, lanthanum and yttrium aluminoborosilicates with two different B/Si ratios, we report systematic variations in boron and aluminum coordination determined by NMR, and glass transition and heat capacities from differential scanning calorimetry. Data on glasses with different fictive temperatures allow B and Al speciation to be compared on an isothermal basis, rather than as conventionally done for as-quenched structures. Temperature and compositional effects can thus be isolated. These data and comparison to previous studies on glasses with lower B/Si ratios clearly show that higher modifier cation field strength increases the fraction of five- and six-coordinated Al in all compositions. In contrast, the previously documented trend towards more three-coordinated boron (and hence more non-bridging oxygens, NBO) in low B/Si glasses with higher field strength cations reverses in high B/Si and in high NBO compositions. Al and B coordination numbers both decrease with higher fictive temperature in the glasses studied here, suggesting a simple mechanism of coupled structural change.

ALUMINUM SPECIATION OF AMENDED ACID TROPICAL SOIL AND ITS EFFECTS ON PLANT ROOT GROWTH

Exchangeable and soluble soil aluminum (Al) is limiting plant growth in many soils worldwide. This study evaluated the effects of increasing rates of dolomite and magnesium carbonate (MgCO3) on Al3+, pH, dissolved organic carbon, cations, anions, and Al speciation on oil palm Deli dura × AVROS pisifera root growth. Dolomite and MgCO3 additions significantly raised linearly soil solution pH, magnesium (Mg2+), nitrate (NO3 −) and chlorine (Cl−) concentrations; exponentially decreased the activity of phytotoxic Al species [aluminum (Al3+), aluminum sulfate (Al2SO4), and aluminum fluoride (AlF3)]; and reduced manganese (Mn) concentration and activity. High activity of those species exponentially reduced root dry weight. Optimum oil palm growth was achieved at: <50 μM monomeric Al, < 30 μM Mn, and <0.20 unit of the ratio Al+Mn to calcium (Ca)+Mg. High activity of Al species and Mn in acidic soil solution cause significant reduction of the root growth. Soil acidity alleviation either with dolomite or MgCO3 mitigates the toxic effect of Al and Mn.

Internal consistency in aqueous geochemical data revisited: Applications to the aluminum system

Internal consistency of thermodynamic data has long been considered vital for confident calculations of aqueous geochemical processes. However, an internally consistent mineral thermodynamic data set is not necessarily consistent with calculations of aqueous species thermodynamic properties due, potentially, to improper or inconsistent constraints used in the derivation process. In this study, we attempt to accommodate the need for a mineral thermodynamic data set that is internally consistent with respect to aqueous species thermodynamic properties by adapting the least squares optimization methods of Powell and Holland (1985). This adapted method allows for both the derivation of mineral thermodynamic properties from fluid chemistry measurements of solutions in equilibrium with mineral assemblages, as well as estimates of the uncertainty on the derived results. Using a large number of phase equilibria, solubility, and calorimetric measurements, we have developed a thermodynamic data set of 12 key aluminum-bearing mineral phases. These data are derived to be consistent with Na+ and K+ speciation data presented by Shock and Helgeson (1988), H4SiO4(aq) data presented by Stefánsson (2001), and the Al speciation data set presented by Tagirov and Schott (2001). Many of the constraining phase equilibrium measurements are exactly the same as those used to develop other thermodynamic data, yet our derived values tend to be quite different than some of the others’ due to our choices of reference data. The differing values of mineral thermodynamic properties have implications for calculations of Al mineral solubilities; specifically, kaolinite solubilities calculated with the developed data set are as much as 6.75 times lower and 73% greater than those calculated with Helgeson et al. (1978) and Holland and Powell (2011) data, respectively. Where possible, calculations and experimental data are compared at low T, and the disagreement between the two sources reiterates the common assertion that low-T measurements of phase equilibria and mineral solubilities in the aluminum system rarely represent equilibrium between water and well-crystallized, aluminum-bearing minerals. As an ancillary benefit of the derived data, we show that it may be combined with high precision measurements of aqueous complex association constants to derive neutral species activity coefficients in supercritical fluids. Although this contribution is specific to the aluminum system, the methods and concepts developed here can help to improve the calculation of water–rock interactions in a broad range of earth systems.

Interaction of Aluminum Ions with Fused Silica/Water Interfaces in the Presence of Oxalic Acid Tracked by Second Harmonic Generation

Second harmonic generation (SHG) and the χ(3) technique are used to investigate the effect of oxalic acid on the adsorption of aluminum [Al(III)] to the fused silica/water interface. Al(III) adsorption isotherms are measured in the presence and absence of oxalic acid and fit with the Diffuse Layer model to quantify thermodynamic binding parameters. The evolution of charge density throughout the adsorption process is analyzed and used to derive binding mechanisms at the molecular level. It is found that 0.5 mM oxalic acid irreversibly binds to and increases the negative surface charge on the fused silica surface −0.003 C/m2, corresponding to 1.9 × 1012 bound oxalate ions per cm2 under those conditions if oxalate were singly charged at the interface. Oxalic acid decreases the strength of the Al(III) adsorption interaction: the binding constant, Kads, decreases from 60 000 ± 10 000 to 1100 (200) M–1, corresponding to a reduction in the apparent adsorption free energy, ΔGads, from −37.2(4) to −27.3(5) kJ/mol, while surface charge densities at maximum metal coverage, σm, increase from 0.004(2) to 0.014(3) C/m2. Evidence is presented for a change in the dominant charge determining adsorption mechanism that corresponds with a change in Al(III) speciation. These results reveal important information about the surface activity and speciation of Al(III) in the presence of oxalic acid that have direct implications for the mobility, toxicity, and ultimate environmental fate of this metal pollutant.

Toxicity evolution of alum-coagulated municipal wastewater to sea urchin embryogenesis and fertilization

The alum-based coagulation process is a worldwide treatment method in industrial and municipal wastewater (MW) management. In the present study, alum-coagulation was performed on wastewater from the MW plant located south of Naples, Italy, to evaluate any negative impact of MW on marine biota by means of sea urchin bioassays. A series of Jar test experiments (100 rpm for 1 min, 30 rpm for 20 min, and 30 min for settling) was performed using 150 and 450 mg/L of alum concentrations at pH ranging from 5 to 7 and room temperature (20° ± 2°C). Raw and alum-coagulated wastewater samples were analyzed for their COD and TSS, and residual aluminum (RA) concentrations. Toxicity testing of samples (diluted to 1%) by Sphaerechinus granularis sea urchin bioassays (collected in Naples bay) was evaluated to meet the following specifications: (a) acute and/or developmental toxicity, (b) changes in fertilization success, and (c) cytogenetic abnormalities. The results provided the following evidences: (i) the coagulation process at a 150 mg/L alum level in the SG plant was sufficient to meet the discharge standards; (ii) RA was found significantly related to alum dose used in coagulation process and raw wastewater alum concentration; (iii) sea urchin bioassays provided evidence for both embryo toxicity in raw wastewater to a lesser extent, and in alum-coagulated Jar test supernatants, at elevated extent, at a 1% concentration; and (iv) no statistically significant spermiotoxic or cytogenetic effect was observed. Altogether, the results highlighted the influence of wastewater characteristics on developmental toxicity, such as pH-related Al(III) speciation and alum complex formation in wastewater.

Kinetics of montmorillonite dissolution: An experimental study of the effect of oxalate

Low molecular weight organic acids, ubiquitous in soils and sediments, play an important role in the alteration and weathering reactions as they enhance mineral dissolution rates. The dissolution rate of montmorillonite was measured in buffered oxalate solutions over a pH range from 3 to 8 and total oxalate concentrations of 0.1, 0.3 and 1.0mmolL−1 at 25°C in a stirred flow-through reactor. Dissolution rates were obtained based on the release of Si at a steady state under far from equilibrium conditions. From pH4 to 8, the addition of oxalate enhances the montmorillonite dissolution rate up to a maximum of 0.5 logarithmic units at pH7 compared to the experiments in oxalate-free solutions. In order to understand the dissolution mechanism, oxalate adsorption was measured in batch experiments at pH2–11 and Al speciation was modeled with EQ3NR. Oxalate adsorbs onto montmorillonite at pH<8 up to 18μmolg−1 at the highest concentration studied. In addition, DR-FTIR spectroscopy was used to study the interaction of oxalate with montmorillonite. Two mechanisms were consistent with the experimental data: the formation of surface complexes between oxalate and aluminol sites on the surface of the montmorillonite edges, and the decrease of the activity of Al3+ by formation of aqueous Al–oxalate complexes.

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.

Short‐term response of the Ca cycle of a montane forest in Ecuador to low experimental CaCl2 additions

AbstractThe tropical montane forests of the E Andean cordillera in Ecuador receive episodic Sahara‐dust inputs particularly increasing Ca deposition. We added CaCl2 to isolate the effect of Ca deposition by Sahara dust to tropical montane forest from the simultaneously occurring pH effect. We examined components of the Ca cycle at four control plots and four plots with added Ca (2 × 5 kg ha–1 Ca annually as CaCl2) in a random arrangement. Between August 2007 and December 2009 (four applications of Ca), we determined Ca concentrations and fluxes in litter leachate, mineral soil solution (0.15 and 0.30 m depths), throughfall, and fine litterfall and Al concentrations and speciation in soil solutions. After 1 y of Ca addition, we assessed fine‐root biomass, leaf area, and tree growth. Only &lt; 3% of the applied Ca leached below the acid organic layer (pH 3.5–4.8). The added CaCl2 did not change electrical conductivity in the root zone after 2 y. In the second year of fertilization, Ca retention in the canopy of the Ca treatment tended to decrease relative to the control. After 2 y, 21% of the applied Ca was recycled to soil with throughfall and litterfall. One year after the first Ca addition, fine‐root biomass had decreased significantly. Decreasing fine‐root biomass might be attributed to a direct or an indirect beneficial effect of Ca on the soil decomposer community. Because of almost complete association of Al with dissolved organic matter and high free Ca2+ : Al3+ activity ratios in solution of all plots, Al toxicity was unlikely. We conclude that the added Ca was retained in the system and had beneficial effects on some plants.

How do Citrus Crops Cope with Aluminum Toxicity?

World Agriculture faces daunting challenges in feeding the growing population today. Reduction in arable land extent due to numerous reasons threatens achievement of food and nutritional security. Under this back ground, agricultural use of acidic soils, which account for approximately 40 % of the world arable lands is of utmost important. However, due to aluminum (Al) toxicity and low available phosphorous (P) content, crop production in acidic soils is restricted. Citrus, in this context, gains worldwide recognition as a crop adapted to harsh environments. The present paper reviewed Al toxicity and possible toxicity alleviation tactics in citrus. As reported for many other crops, inhibition of root elongation, photosynthesis and growth is experienced in citrus also due to Al toxicity. Focusing at toxicity alleviation, interaction between boron (B) and Al as well as phosphorus and Al has been discussed intensively. Al toxicity in citrus could be alleviated by P through increasing immobilization of Al in roots and P level in shoots rather than through increasing organic acid secretion, which has been widely reported in other crops. Boron-induced changes in Al speciation and/or sub-cellular compartmentation has also been suggested in amelioration of root inhibition in citrus. Despite the species-dependent manner of response to Al toxicity, many commercially important citrus species can be grown successfully in acidic soils, provided toxicity alleviation Agro-biological tactics such as addition of phosphorous fertilizers are used properly.

Relationship between residual Al species, floc operational parameters and coagulation performance during reservoir water treatment by PAC–PDMDAAC

This study investigated the relationship between removal efficiency, floc operational parameters and residual Al species when polyaluminum chloride–polydiallyl dimethyl ammonium-chloride (PAC–PDMDAAC) was applied in coagulation of a reservoir water. Various residual Al fractions (total Al, dissolved Al, dissolved monomeric Al, dissolved organically-bound Al and dissolved organic monomeric Al, suspended/particulate Al) were separated and measured in purified water samples. The fundamental floc operational parameters were characterized via floc size, growth rate, and strength factor in this study. Turbidity and organic matter removal were also determined as supporting data. Experimental results demonstrated that the mass ratio of Al to PDMDAAC (MR) and solution pH manifested a significant influence on residual Al speciation distribution. Residual Al content and floc operational parameters exhibited a linear correlation. In addition, moderate floc size, strength factor, growth rate and removal efficiency were favorable to the reduction of residual Al concentration for one coagulant under various pH conditions. For different coagulation system under the same pH condition, the higher the values of floc operational parameters and removal performance, the lower the residual Al content. The Al speciation was altered before and after coagulation. A majority of total Al in treated water was in the dissolved form. In dissolved Al form, the monomeric Al and organically bound Al were presented at a higher proportion under conditions of 4<pH<6 and pH>7, respectively.

Properties of impurity-bearing ferrihydrite I. Effects of Al content and precipitation rate on the structure of 2-line ferrihydrite

The association of Al with ferrihydrite (Fh) may have a considerable effect on the composition, structure, and surface properties of Fh nanoparticles, and thus impact its reactivity and interaction with pollutant species. Aluminous Fh is abundant in natural environments, but the mode of association of Al with this nanomineral is not yet fully understood. Al3+ speciation may vary from true chemical substitution for Fe3+, to adsorption or surface precipitation, and/or to formation of a mixture of two (or more) individual nanoscale phases. The conditions of formation (i.e. slow vs. rapid precipitation) may also affect the nature of Fh nanoparticles in terms of their crystallinity, phase purity, and Al speciation. In this study we used a variety of laboratory (TEM, NMR, ICP-AES) and synchrotron-based techniques (X-ray total scattering and PDF analysis, scanning transmission X-ray microscopy, Al K-edge XANES spectroscopy) to characterize two synthetic Al-bearing Fh series formed at different precipitation rates in the presence of 5–40mol% Al. We find that Al is dominantly octahedrally coordinated in the synthetic Fh samples and that up to 20–30mol% Al substitutes for Fe in the Fh structure, regardless of the synthesis method we used. Formation of separate aluminous phases (e.g., gibbsite) was most significant at Al concentrations above 30mol% Al in slowly precipitated samples. However, small amounts (<6% of total Al) of Al-hydroxide phases were also detected by NMR spectroscopy in samples with lower Al content (as low as 15mol% Al), particularly in the Fh series that was precipitated slowly. Furthermore, it appears that the amount of Al incorporated in Fh is not affected by the synthesis methods we used and is more likely controlled by the accumulated strain caused by Al substitution in the Fh lattice. Given the prevalence of naturally occurring aluminous ferrihydrite, assumptions about ferrihydrite reactivity in natural environments should consider the impact of Al substitution on reduction potential, Fe bioavailability, as well as sorption reactions.

Characterization of flocs generated by preformed and in situ formed Al13 polymer

During coagulation process, preformed and in situ formed Al13 polymer are the predominant aluminum hydrolysis species at the optimal pH condition for polyaluminum chloride (PACl) containing high content of Al13 and AlCl3 (AC), respectively. The structure and morphology of the flocs generated by preformed and in situ formed Al13 polymer were investigated from the viewpoint of the relationship between Al speciation and flocs surface structure. The results showed that at pH 6 the predominant composition of PACl and AC flocs were Al13 polymer aggregate and amorphous Al hydroxide, respectively. The flocs generated by preformed Al13 polymer had a better crystalline structure than those from in situ formed one, while they had smaller size and smoother surface structure than those formed by in situ formed Al13 polymer. During weak acidic pH condition and at high dosage of Al coagulant adsorption onto precipitated Al hydroxides was the main pathway for kaolin particle removal. Preformed Al13 polymer showed a stronger charge neutralization ability, while the flocs generated from in situ formed Al13 polymer exhibited a higher adsorption capacity for kaolin particles. Al species distribution during coagulation process governs the floc character and coagulation efficiency of Al coagulant. The present study further conduces to the understanding of coagulation mechanism and puts forward a basis for coagulant selection during water treatment process.

The effect of additional poly-diallyl dimethyl ammonium-chloride on the speciation distribution of residual aluminum (Al) in a low DOC and high alkalinity reservoir water treatment

To provide insight into aluminum (Al) speciation in treated water and to investigate the factors that can affect it, specific Al fractions have been isolated and analyzed in finished water samples for the coagulation treatment of a low DOC and high alkalinity reservoir water in Ji’nan (China). The organic poly-diallyl dimethyl ammonium-chloride (PDMDAAC) was added into poly-aluminum chloride (PAC) to produce the dual-composite coagulant (PAC–PDMDAAC). The particulate and organic matter removal during coagulation process was also measured as supporting data. It was intended to examine the influence of hydroxyl to Al molar ratio and PDMDAAC to Al mass ratio on the coagulation performance as well as the content and speciation distribution of residual Al in treated water. Experimental results demonstrated that the coagulation effect and Al fractions were quite different for single PAC and composite PAC–PDMDAAC coagulation system. The additional PDMDAAC can improve impurity removal and decrease the residual total Al concentration of the effluent. Yet, the deterioration of DOC removal at higher dosages and the increment of organically bound Al fraction in treated water can also be noticed by PDMDAAC introduction. The prehydrolyzed degree (basicity) and Al to PDMDAAC mass ratio in composite PAC–PDMDAAC should be determined by virtue of water quality and a preferential aim for coagulation. Majority of the total Al in treated water was particulate Al. In the dissolved Al fraction, organically bound Al forms were present at a higher proportion.

Antioxidative responses of cell suspension cultures of two Coffea arabica varieties to low aluminum levels at pH 5.8

The effects of aluminum (Al) on the activities of antioxidant enzymes and ferritin expression were studied in cell suspension cultures of two varieties of Coffea arabica, Mundo Novo and Icatu, in medium with pH at 5.8. The cells were incubated with 300 µM Al3+, and the Al speciation as Al3+ was 1.45% of the mole fraction. The activities of superoxide dismutase (SOD), catalase (CAT), and glutathione S-transferase (GST) were increased in Mundo Novo, whereas glutathione reductase (GR) and guaiacol peroxidase (GPOX) activities remained unchanged. SOD, GR, and GST activities were increased in Icatu, while CAT activity was not changed, and GPOX activity decreased. The expression of two ferritin genes (CaFer1 and CaFer2) were analyzed by Real-Time PCR. Al caused a downregulation of CaFER1 expression and no changes of CaFER2 expression in both varieties. The Western blot showed no alteration in ferritin protein levels in Mundo Novo and a decrease in Icatu. The differential enzymes responses indicate that the response to Al is variety-dependent.

Effect of aluminum speciation on arsenic removal during coagulation process

The effect of Al speciation on arsenate [As(V)] removal during coagulation process was investigated from the viewpoint of Al hydrolysis species transformation. The As(V) removal efficiency of preformed Al13 was compared with that of in situ formed Al13 considering various Al dosages and pH values. The mechanisms of As(V) removal by Al salt coagulation were explored, and adsorption ability of the flocs formed from Al13 species were evaluated. The results showed that As(V) removal efficiency was positively correlated with the content of Al13 species during coagulation process. Weak acidic condition (pH 5–7) is the optimal pH range to remove As(V) because Al13 species, especially for AlCl3, is largely in situ formed from the transformation of monomeric Al species. Through regulating Al speciation, pH adjustment could improve As(V) removal and AlCl3 could benefit most from this. In contrast, the improvement induced by pH control for polyaluminum (PACl) was slighter because Al speciation of PACl was less dependent upon water pH. This present study confirmed that adsorption on formed hydroxide flocs was the most active mechanism for As(V) removal by Al based coagulants. The flocs generated from in situ formed Al13 presented better As(V) adsorption ability than the flocs generated from preformed Al13. These findings are important to understand the coagulation mechanisms of arsenic removal by Al based coagulants.

Quantification analysis of polymeric Al species in solutions with electrospray ionization time-of-flight mass spectrometry (ESI-TOF-MS)

With the help of Ferron colorimetric method and 27Al NMR spectroscopy, quantification analysis method of electrospray ionization time-of-flight mass spectrometry (ESI-TOF-MS) on Al speciation was developed and thus Al species in polymeric Al solutions were quantitatively analyzed. Based on the speciation results of mononuclear Al solution and purified Al 13 solution, Al species obtained with ESI-TOF-MS in polymeric Al solutions were classified into three categories as low polymers (i.e., Al 1–Al 10), mid polymers (i.e., Al 13–Al 20), and high polymers (i.e., Al 21–Al 31). Among these polymers, only a certain number of Al species have relative high content and constitute the dominant component of polymeric Al solutions. The quantification analysis results of ESI-TOF-MS agree well with those obtained by the other two traditional methods, which proves the feasibility of the novel method on Al species analysis. Additionally, ESI-TOF-MS can provide more information on Al speciation than 27Al NMR spectroscopy and Ferron colorimetric method, and the quantification analysis results can clearly explain the difference between the two traditional methods.

Predicting Al, Cu, and Zn concentrations in the fine roots of trembling aspen (Populus tremuloides) using bulk and rhizosphere soil properties

We compared the predictions of Al, Cu, and Zn concentrations in fine roots of trees using properties of the bulk and rhizosphere soils to find the best approach to assess the ecological risks of metals to trees. Predictions were made from 18 trembling aspens ( Populus tremuloides Michx.) equally distributed on six sampling sites using multiple linear regressions with soil Al, Cu, and Zn speciation data and chemical and microbial properties as explanatory variables. Fine root Al, Cu, and Zn concentrations ranged, respectively, from 2137 to 7480, from 7.03 to 206, and from 41.2 to 360 µg·g dry root mass–1. No significant prediction was obtained for Al. The soil total water-soluble Cu and Zn concentrations better predicted the metal concentrations in fine roots than the concentration of labile metal species. The concentrations of reactive Zn, water-soluble organic C, and NH4+ together with microbial biomass of N were the other significant explanatory variables. The best regression models for Cu and Zn were obtained in the rhizosphere and explained, respectively, 79.2% and 95.7% of the variation of metal concentrations in fine roots. This work pointed out that the rhizosphere properties and processes need to be considered to correctly assess the ecological risks of metals to tree.