Personal Research Database

Full Text: 1999\Soi Sci Soc Ame J63, 1626.pdf

Abstract: The influence of pH, ionic strength, ligands (Cl, SO₄, PO₄), and metals (Ni and Pb) on the adsorption of Hg(II) by quartz and gibbsite was investigated to better understand the Hg(II) adsorption process and the impact of metals and ligands on this process. The triple layer model (TLM) was used to simulate Hg(II) adsorption on both surfaces. Mercury(II) adsorption from a 0.6 µM Hg(II) solution varies as a function of pH, increasing to an adsorption maximum with increasing pH before tailing off to a constant level at high pH values. The pH at which maximum Hg(II) adsorption occurs (pH_max ≈ 4.5) is comparable to the pK_a (3.2) for the hydrolysis of Hg²⁺ to form Hg(OH)₂⁰. Further, the Hg(II) adsorption edge shifts to much higher pH values in the presence of 0.001 M and 0.01 M Cl, which also corresponds to the pH at which Hg(OH)₂⁰ is predicted to form. Only minor deviations in the degree of adsorption and the shape of the Hg(II) adsorption edge are influenced by ionic strength, suggesting the formation of inner-sphere surface complexes. However, Hg(II) adsorption can only be successfully modeled with consideration of the formation of both an outer-sphere surface complex [XO‾-HgOH⁺] and an inner-sphere surface complex [XOHg(OH)₂‾]. Swamping concentrations (0.01 M) of SO₄ and PO₄ reduced Hg(II) adsorption on quartz, a result of the predicted formation of Hg(OH)₂SO₄²‾, Hg(OH)₂H₂PO₄‾, and Hg(OH)₂-HPO₄²‾ aqueous species (the adsorption edge and pH_max were not influenced). The presence of SO₄ also decreased Hg(II) retention by gibbsite, which was also attributed to the formation of the Hg(OH)₂SO₄²‾ ion pair, however, the presence of PO₄ increased Hg(II) retention by gibbsite, which was attributed to the formation of a phosphate bridge [AlOPO₃Hg(OH)₂²‾]. Mercury(II) adsorption was decreased in the presence of 14 µM Pb and 48 µM Ni, and most noticeably in the quartz system. The adsorption of Hg(II), when in competition with Pb or Ni, could not be simulated by the TLM without the reoptimization of the Hg(II) outer- and inner-sphere log K_int values. Intrinsic Hg(II) adsorption constants derived from single-element systems could not be employed to simulate adsorption in multi-element, competitive systems.

Shenker, M., Hadar, Y. and Chen, Y. (1999), Kinetics of iron complexing and metal exchange in solutions by rhizoferrin, a fungal siderophore. Soil Science Society of America Journal, 63 (6), 1681-1687.

Full Text: 1999\Soi Sci Soc Ame J63, 1681.pdf

Abstract: Rhizoferrin, a siderophore produced by Rhizopus arrhizus, has been shown in previous studies to be an outstanding Fe carrier to plants. Yet, calculations based on stability constants and thermodynamic equilibrium lead to contradicting conclusions. In this study a kinetic approach was employed to elucidate apparent contradictions and to determine the behavior of rhizoferrin under conditions representing soil and nutrient solutions. Stability of Fe³⁺ complexes in nutrient solution, rate of metal exchange with Ca, and rate of Fe extraction by the free ligand were monitored for rhizoferrin and other chelating agents by Fe-55 labeling. Ferric complexes of rhizoferrin, desferri-ferrioxamine-B (DFOB) and ethylenediamine-di (o-hydroxyphenylacetic acid) (EDDHA) were found to be stable in nutrient solution at pH 7.5 for 31 d, while ferric complexes of ethylenediaminetetraacetic acid (EDTA) and mugineic acid (MA) lost 50% of the chelated Fe within 2 d. Iron-calcium exchange in Ca solutions at pH 8.7 revealed rhizoferrin to hold Pe at nonequilibrium state for 3 to 4 wk at 3.3 mM Ca and for longer periods at lower Ca concentrations. Ethylenediaminetetraacetic acid lost the ferric ion at a faster rate under the same conditions. Iron extraction from freshly prepared Fe hydroxide at pH 8.7 and with 3.2 mM Ca was slow and followed the order. DFOB > EDDHA > MA greater than or equal to rhizoferrin > EDTA. Based on these results we suggest that a kinetic rather than equilibrium approach should be the basis for predictions of Fe chelates’ efficiency. We conclude that the nonequilibrium state of rhizoferrin is of crucial importance for its behavior as an Fe carrier to plants.

Keywords: Rhizopus-arrhizus, Plants

Su, C.M. and Suarez, D.L. (2000), Selenate and selenite sorption on iron oxides: An infrared and electrophoretic study. Soil Science Society of America Journal, 64 (1), 101-111.

Full Text: 2000\Soi Sci Soc Ame J64, 101.pdf

Abstract: We studied selenate and selenite sorption by amorphous Fe oxide [am-Fe(OH)₃] and goethite (α-FeOOH) as a function of time (25 min–96 h), pH (3–12), ionic strength (0.01–1.0 M NaCl), and total Se concentration (0.0001–1.0 M). We examined sorbed selenate and selenite by in situ attenuated total reflectance Fourier transform infrared (ATR–FTIR) spectroscopy, diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy, and electrophoresis to deduce sorption mechanisms. Sorption of both selenate and selenite reached equilibrium in < 25 min and the sorption isotherm was not reversible. Increasing ionic strength decreased selenate sorption but did not affect selenite sorption. The presence of either selenate or selenite lowered the electrophoretic mobility (EM) and decreased the point of zero charge (PZC) of both sorbents, suggesting inner-sphere complexation for both selenate and selenite species. Both in situ ATR–FTIR and DRIFT difference spectra showed bidentate complexes of selenate with am-Fe(OH)₃. The structure of selenite complexes in am-Fe(OH)₃ –solution interface was uncertain due to insensitivity of the in situ ATR–FTIR technique. The DRIFT spectra of selenite on am-Fe(OH)₃ showed ₃ splitting as evidence of complexation. The DRIFT spectra of selenite on goethite showed bridging bidentate complex of selenite. We conclude that the influence of ionic strength on Se sorption cannot be used as a criterion for distinguishing outer- vs. inner-sphere complex formation.

Keywords: ATR–FTIR, attenuated total reflectance–Fourier transform infrared, DRIFT, diffuse reflectance infrared Fourier transform, EM, electrophoretic mobility, EXAFS, extended x-ray absorption fine structure, ICP-AES, inductively coupled plasma-atomic emission spectrophotometry, IR, infrared, PZC, point of zero charge

Manning, B.A. and Suarez, D.L. (2000), Modeling arsenic(III) adsorption and heterogeneous oxidation kinetics in soils. Soil Science Society of America Journal, 64 (1), 128-137.

Full Text: 2000\Soi Sci Soc Ame J64, 128.pdf

Abstract: Arsenite [As(III)] is a soluble and toxic species of arsenic that can be introduced into soil by geothermal waters, mining activities, irrigation practices, and disposal of industrial wastes. We determined the rates of As(III) adsorption, and subsequent oxidation to arsenate [As(V)] in aerobic soil-water suspensions using four California soils, The rate of As(III) adsorption on the soils was closely dependent on soil properties that reflect the reactivity of mineral surfaces including citrate-dithionite (CD) extractable metals, soil texture, specific surface area, and pH, Heterogeneous oxidation of As(III) to As(V) was observed in all soils studied. The recovery of As(V) from As(III)treated soils was dependent on levels of oxalate-extractable Mn and soil texture, After derivation of rate equations to describe the changes in soluble and recoverable As(III) and As(V) in soil suspensions, soil property measurements were used to normalize the empirically derived rate constants for three soils. The fourth soil, which had substantially different soil properties from the other three soils, was used to independently test the derived soil property-normalized model. The soil property-normalized consecutive reaction model gave a satisfactory description of the trends seen in the experimental data for all four soils. Understanding the effects of soil properties on the kinetics of chemical reactions of As(III) and As(V) in soils will be essential to development of quantitative models for predicting the mobility of As in the field.

Keywords: Arsenite, Arsenate, Sorption, Goethite, Ferrihydrite, Absorption, Retention, Stability, Sediments, Manganese

Strawn, D.G. and Sparks, D.L. (2000), Effects of soil organic matter on the kinetics and mechanisms of Pb(II) sorption and desorption in soil. Soil Science Society of America Journal, 64 (1), 144-156.

Full Text: 2000\Soi Sci Soc Ame J64, 144.pdf

Abstract: To improve predictions of the toxicity and threat from Pb contaminated soil, it is critical that time-dependent sorption and desorption behavior be understood. In this paper, the sorption and desorption behavior (pH=5.50, I=0.05 M) of Pb in a Matapeake silt loam soil (Typic Hapludult) were studied by stirred-flow and batch experiments. In addition, we studied the effects of soil organic matter (SOM) on sorption and desorption behavior by treating the soil with sodium hypochlorite to remove the SOM fraction, and using a soil with six times as much SOM (St. Johns loamy sand [Typic Haplaquods]) as the Matapeake soil. Lead sorption consisted of a fast initial reaction in which all of the Pb added to the stirred-flow chamber was sorbed. Following this initial fast reaction, sorption continued and appears to be rate limited (indicated by a decrease in the outflow concentration when the flow rate was decreased, or when the flow was stopped). The total amount of Pb sorbed was 102, 44, and 27 mmol kg^-1 for the St. Johns soil and the untreated and treated Matapeake soils, respectively. Desorption experiments were conducted on the soils with the background electrolyte as the eluent in the stirred-flow chamber. In the St. Johns soil only, 32% of the total sorbed Pb was desorbed, while 47 and 76% of the sorbed Pb was released from the untreated and treated Matapeake soil, respectively. The correlation between SOM in the soils, and the percentage Pb desorbed from the soils suggests that SOM plays an important role in slow desorption reactions of Pb from soil materials. Aging experiments in which sorbed Pb was incubated for 1, 10, and 32 d showed that sorption incubation time had no effect on Pb desorption behavior. Analysis of the treated and untreated Matapeake soils by x-ray absorption fine structure (XAFS) spectroscopy revealed that the local atomic structure of sorbed Pb is distinctly different in the two samples. In the soil treated to remove SOM, the data were well represented by theoretical models using O, Si, and Pb backscattering atoms. In the untreated soil, the XAFS data were best described by O and C backscatterers. These XAFS results confirm that the sorption mechanisms in the two systems are different.

Keywords: CV, Chamber Volume, SOM, Soil Organic Matter, XAFS, X-Ray Absorption Fine Structure

Sui, Y.B. and Thompson, M.L. (2000), Phosphorus sorption, desorption, and buffering capacity in a biosolids-amended Mollisol. Soil Science Society of America Journal, 64 (1), 164-169.

Full Text: 2000\Soi Sci Soc Ame J64, 164.pdf

Abstract: To investigate the impact of biosolids amendments to soil on the sorption, desorption, and buffering capacity of P, laboratory experiments were conducted on soil samples collected from a field study on a Mollisol amended with three levels of biosolids. The potential for sorption of additional P and the binding intensity of P were evaluated by applying the two-surface Langmuir model to sorption isotherms. Over the range of equilibrium P concentrations in this study, the ability of the soil to sorb added P decreased due to biosolids amendment. Addition of biosolids to the soil also decreased indices of the P-binding intensity at both the high-and low-affinity sites. The P equilibrium buffering capacity (PEBC) significantly decreased and the equilibrium P concentration (EPC) significantly increased after biosolids amendment. P desorption from soil samples with and without biosolids amendment was investigated for different equilibration periods and at various liquid/solid ratios. The amount of P that could be desorbed from the soil significantly increased after biosolids amendment. The effects of biosolids amendments on indices of soil P sorption-desorption phenomena (binding energy, PEBC, and EPC) imply a large increase in the P concentration of the soil solution. The increase of soluble forms of P in soil solution of this soil, which was heavily amended with biosolids, could enhance the loss of P in runoff and P movement below the root zone. [Author abstract, 30 Refs, In English]

Keywords: Adsorption, Equation, Kaolinite, Mobility, Phosphate, Soil-Phosphorus, Two-Surface Langmuir

Barnett, M.O., Jardine, P.M., Brooks, S.C. and Selim, H.M. (2000), Adsorption and transport of uranium(VI) in subsurface media. Soil Science Society of America Journal, 64 (3), 908-917.

Full Text: 2000\Soi Sci Soc Ame J64, 908.pdf

Abstract: Uranium(VI) adsorption and transport in three natural, heterogeneous subsurface media were investigated in batch and column experiments. The rate of U(VI) adsorption to the natural samples was rapid over the first few hours of the experiments, and then slowed appreciably after 24 to 48 h. The adsorption of U(VI) to the samples was also nonlinear, suggesting a decreasing attraction for the surface with increased surface loading. The extent of adsorption on each of the media was strongly pH-dependent, increasing sharply as the pH increased from 4.5 to 5.5 and then decreasing sharply over the pH range 7.5 to 8.5 as the concentration of dissolved carbonate and U(VI)-carbonate complexes increased. The similarities in the pH-dependent behavior between the three materials despite differences in bulk mineralogy was likely due to the similar Fe contents of the materials. The transport of U(VI) through packed columns of the soils and sediments was significantly retarded but reversible. The local equilibrium assumption and the batch-measured adsorption isotherms dramatically underestimated the degree of retardation observed in the columns. The U(VI) displacement experiments were modeled with the one-dimensional advective-dispersive equation and several different model formulations describing the interactions of U(VI) with the solid phase. These models were able to fit the observed breakthrough curves within 0.1 root mean square error of the initial concentration.

Sarkar, D., Essington, M.E. and Misra, K.C. (2000), Adsorption of mercury(II) by kaolinite. Soil Science Society of America Journal, 64 (6), 1968-1975.

Full Text: 2000\Soi Sci Soc Ame J64, 1968.pdf

Abstract: Adsorption of Hg(II) by kaolinite was investigated as a function of solution pH, ionic strength, and the competitive or complexation effects of ligands (Cl, SO₄, PO₄) and metals (Ni and Pb). Mercury(II) adsorption from a 0.6 µM Hg(II) solution was primarily influenced by pH. The Hg(II) adsorption edge was described by a pH₅₀ (pH where 50% adsorption occurs) of 3.4 and a pH_max (pH where maximum adsorption occurs) of 4.4. At pH values above the pH_max, Hg(II) retention decreased with increasing pH. Chloride and Ni shifted pH₅₀ from 3.4 to 7 and 4.1, respectively. Nickel and Pb reduced the amount of Hg(II) adsorbed throughout the pH range examined. Ionic strength and the presence of SO₄ and PO₄ had relatively little impact on the Hg(II) adsorption envelope. The adsorption of Hg(II) was predicted through the application of the triple layer model (TLM) by assuming that the kaolinite surface was composed of equal proportions of silanol and aluminol groups. The TLM model suggests that the silanol group was responsible for retaining the bulk of the adsorbed Hg(II), through the formation of the ≡SiO^--HgOH⁺ outer-sphere, and the ≡SiOHg (OH)₂^- and ≡SiOHgCl⁰ or ≡SiOHgOHCl^- (Cl system) inner-sphere species. The ≡AlO^--HgOH⁺ outer-sphere complex accounted for a small percentage (<15–35%) of the adsorbed Hg(II). The TLM results suggested that Hg(II) adsorption by both ≡SiOH and ≡AlOH sites on kaolinite should be considered to predict adequately Hg(II) retention.

Keywords: IS, ionic strength, TLM, triple layer model

Matocha, C.J., Sparks, D.L., Amonette, J.E. and Kukkadapu, R.K. (2001), Kinetics and mechanism of birnessite reduction by catechol. Soil Science Society of America Journal, 65 (1), 58-66.

Full Text: 2001\Soi Sci Soc Ame J65, 58.pdf

Abstract: The complex interactions of oxidizable organic ligands with soil Mn(III, IV) (hydr)oxide minerals have received little study by in situ spectroscopic techniques. We used a combination of an in situ electron paramagnetic resonance stopped-flow (EPR-SF) spectroscopic technique and stirred-batch studies to measure the reductive dissolution kinetics of birnessite (delta -MnO₂), a common Mn mineral in soils, by catechol (1,2-dihydroxybenzene). The reaction was rapid, independent of pH, and essentially complete within seconds under conditions of excess-catechol at pH 4 to 6. The overall empirical second-order rate equation describing the reductive dissolution rate was d[Mn(II)]/ dt = k[CAT](1.0)[SA](1.0) where k = 4 (±0.5) (10^-3 L m^-2 s^-1 and [CAT] and [SA] are the initial concentrations in molarity and meters square per liter. In the process, catechol was oxidized to the two-electron o-quinone product. The energy of activation (E.) for the reaction was 59 (±7) kJ mol^-1 and the activation entropy (SI) was -78±225 mol^-1 K^-1, suggesting that the reaction was surface-chemical controlled and occurs by an associative mechanism. Rates of catechol disappearance from solution with simultaneous Mn(II) and o-quinone production were comparable. These data strongly suggest that precursor surface-complex formation is rate-limiting and that electron transfer is rapid, The rapid reductive dissolution of birnessite by catechol has significant implications for C and Mn cycling in soils and the availability of Mn to plants.

Keywords: Electron-Spin-Resonance, Dilute Aqueous Suspensions, Na-Rich Birnessite, Manganese Oxides, Xanes Spectroscopy, Oxidation-State, Hexagonal Birnessite, Surface Complexation, Reaction-Products, Mn(IV) Oxide

Harter, R.D. and Naidu, R. (2001), An assessment of environmental and solution parameter impact on trace-metal sorption by soils. Soil Science Society of America Journal, 65 (3), 597-612.

Full Text: 2001\Soi Sci Soc Ame J65, 597.pdf

Abstract: When studying metal sorption by soils, the potential influence of environmental and solution parameters on the experimental systems cannot be ignored. Characteristics of the soil mineral surfaces are the final determinative factors in whether a metal ion will be sorbed, but soil-solution composition affects both mineral surface properties and whether the metal ions will be in forms that can react with the surfaces. Examples of factors affecting sorption of metals by soil surfaces include ionic strength, cations, anions, and/or organic ligands present in solution, solution pH, and solution metal concentration. In addition, sorption will be affected by external factors such as pressure, temperature, soil/solution ratio, and the manner in which soils to be studied are sampled and stored before investigation. To date, there has been little attempt to standardize experimental protocol, so results obtained using varied systems in different laboratories cannot be readily compared. An initial suggestion that all sorption studies include at least one treatment meeting minimal standards of ionic strength (0.01), background electrolyte (NaNO₃), pH (between 5.5 and 6.0), and temperature (25±3°C) is presented as a first step toward enabling improved ability to make interlaboratory comparisons.

Keywords: DOC, dissolved organic carbon, DOM, dissolved organic matter, I, ionic strength, PDI, potential-determining ion, PZNC, Point of Zero Net Charge

Saha, U.K., Taniguchi, S. and Sakurai, K. (2001), Adsorption behavior of cadmium, zinc, and lead on hydroxyaluminum– and hydroxyaluminosilicate–montmorillonite complexes. Soil Science Society of America Journal, 65 (3), 694-703.

Full Text: 2001\Soi Sci Soc Ame J65, 694.pdf

Abstract: The current imperfect understanding about the adsorption behavior of heavy metals on hydroxyaluminum (HyA)- and hydroxyaluminosilicate (HAS)-interlayered phyllosilicates led us to conduct this study. We examined the adsorption behavior of Cd, Zn, and Pb on synthetically prepared HyA– and HAS–montmorillonite (Mt) complexes in comparison with that on untreated Mt. A very dilute initial metal concentration of 10^-6 M in 0.01 M NaClO₄ background was used in all the adsorption systems. The presence of HyA and HAS polymers on Mt greatly promoted the adsorption of all three metals. Such promoting effects of HyA and HAS polymers on the metal adsorption were, however, not very different from each other. The observed adsorption selectivity sequences of Pb > Zn > Cd on Mt as well as Pb >> Zn  Cd on the complexes resemble the reported metal selectivity sequences on amorphous Fe and Al hydroxides. At different pHs, partitioning the adsorbed metals into strongly and weakly held fractions indicated that specific adsorption rather than nonspecific adsorption might have largely controlled the metal selectivity, particularly on the complexes. This led us to assume a predominant involvement of interlayered HyA or HAS polymers in metal adsorption from such dilute solutions. On Mt, the metals were predominantly adsorbed on the permanent charge sites in an easily replaceable state. However, a substantial involvement of the edge OH^- groups of Mt in specific adsorption of the metals was also evident, especially at higher pH. Obviously, on Mt and on the complexes, the relative abundance of each type of site and their affinity to heavy metals were substantially different.

Keywords: CEC, cation-exchange capacity, HAS, hydroxyaluminosilicate, HRTEM, high-resolution transmission electron microscopy, HSAB, hard–soft acid base, HyA, hydroxyaluminum, IAP, ion activity product, ICP-AES, inductively coupled plasma–atomic emission spectroscopy, M, metal, MT, montmorillonite, SA, strongly adsorbed, TA, total adsorbed, VT, vermiculite, WA, weakly adsorbed, XRD, x-ray diffraction

Scheckel, K.G. and Sparks, D.L. (2001), Temperature effects on nickel sorption kinetics at the mineral-water interface. Soil Science Society of America Journal, 65 (3), 719-728.

Full Text: 2001\Soi Sci Soc Ame J65, 719.pdf

Abstract: In recent years, innovative studies have shown that sorption of metals onto natural materials results in the formation of new mineral-like precipitate phases that increase in stability with aging time. While these findings have demonstrated the usefulness of current state-of-the-art molecular-scale methods for confirming macroscopic data and elucidating mechanisms, basic kinetic and thermodynamic parameters for the formation of the metal precipitates have not been examined. This study examined Ni-sorption kinetics on pyrophyllite, talc, gibbsite, amorphous silica, and a mixture of gibbsite and amorphous silica over a temperature range of 9 to 35 degreesC. Using the Arrhenius and Eyring equations, we calculated the energy of activation (E-a) and enthalpy (H°), entropy (S°), and free energy of activation (G°), related to the formation of the Ni precipitates. Based on values of E-a (93.05 to 123.71 kJ mol^-1) and DeltaS° (-27.51 to -38.70 J mol^-1), Ni sorption on these sorbents was surface-controlled and an associative mechanism, The DeltaH(double dagger) values (90.60 to 121.26 kJ mol^-1) suggest, as indicated by E-a values, that an energy barrier was present for the system to overcome in order for the reaction to occur, Additionally, the large, positive G° values suggest there is an energy barrier for product formation. Although metal precipitation reactions often occur in the natural environment, this study shows that the rate of these reactions depends strongly on temperature.

Keywords: X-Ray-Absorption, Electron-Paramagnetic-Resonance, Surface Precipitation, Dissolution Kinetics, Metal Sorption, Oxide Minerals, Pyrophyllite, Adsorption, Clay, Spectroscopy

Gomes, P.C., Fontes, M.P.F., da Silva, A.G., Mendonça, E.D.S. and Netto, A.R. (2001), Selectivity sequence and competitive adsorption of heavy metals by brazilian soils. Soil Science Society of America Journal, 65 (4), 1115-1121.

Full Text: 2001\Soi Sci Soc Ame J65, 1115.pdf

Abstract: Heavy-metal cations can be introduced into agricultural soils by application of fertilizers, liming materials, sewage sludge, composts, and other industrial and urban waste materials. Therefore, heavy-metal adsorption reactions, in a competitive system, are important to determine heavy-metal availability to plants and their mobility throughout the soil. This study was conducted to evaluate the selectivity sequence and estimate the competitive adsorption of several heavy metals in seven soils with different chemical and mineralogical characteristics. Distribution coefficients (K_d), which represent the sorption affinity of metals for the solid phase, were obtained for each soil and heavy-metal cation. On the basis of these K_d, the selectivity sequence was evaluated. The most common sequences were Cr > Pb > Cu > Cd > Zn > Ni and Pb > Cr > Cu > Cd > Ni > Zn. Chromium, Pb, and Cu were the heavy-metal cations most strongly adsorbed by all soils, whereas Cd, Ni, and Zn were the least adsorbed, in the competitive situation. Selectivity sequences related to valence for the trivalent Cr. For metals of the same valence, sequences did not exactly follow the order of electronegativity. For individual elements, the Misono softness parameter and hydrolysis properties of the heavy-metal cations may have influenced the sequences. Correlation analysis showed that soil characteristics that may have affected the heavy-metals adsorption, represented by the distribution coefficients, were pH and cation-exchange capacity (CEC) for Cd and Cr, organic carbon, clay, and gibbsite contents for Cu, pH and CEC for Ni and Pb.

Keywords: ALF, Alfisol, CEC_ef, effective cation-exchange capacity, CEC_tot, total cation-exchange capacity, Gibb, gibbsite, Goet, goethite, Hem, hematite, Kao, kaolinite, K_d, distribution coefficients, OC, organic carbon, OX1, Oxisol number 1, OX2, Oxisol number 2, OX3, Oxisol number 3, OX4, Oxisol number 4, UL1, Ultisol number 1, UL2, Ultisol number 2, ΣOxi, sum of oxide content

Notes: highly cited

Grafe, M., Eick, M.J. and Grossl, P.R. (2001), Adsorption of arsenate(V) and arsenite(III) on goethite in the presence and absence of dissolved organic carbon. Soil Science Society of America Journal, 65 (6), 1680-1687.

Full Text: 2001\Soi Sci Soc Ame J65, 1680.pdf

Abstract: The environmental fate of arsenic (As) is of utmost importance as the public and political debate continues with the USEPA’s recent proposal to tighten the As drinking water standard from 50 to 10 g L^-1. In natural systems, the presence of dissolved organic C (DOC) may compete with As for adsorption sites on mineral surfaces, hence increasing its potential bioavailability. Accordingly, the adsorption of arsenate [As(V)] and arsenite [As(III)] on goethite (alpha -FeOOH) was investigated in the presence of either a peat humic acid (Hap), a Suwannee River Fulvic Acid (FA) (international Humic Substances Society, St. Paul, MN), or citric acid (CA). Adsorption edges and kinetic experiments were used to examine the effects of equimolar concentrations of organic adsorbates on As adsorption. Adsorption edges were conducted across a pH range of 3 to 11, while the kinetic studies were conducted at pH 6.5 for As(V) and pH 5.0 for As(III). Both Hap and FA decreased As(V) adsorption, while CA had no effect. Humic acid reduced As(V) between pH 6 and 9 by approximate to 27%. Fulvic acid inhibited As(V) adsorption between pH 3 and 8 by a maximum of 17%. Arsenite adsorption was decreased by all three organic acids between pH 3 and 8 in the order of CA > FA approximate to Hap. The different pH regions in which Hap and FA decreased As(V) adsorption suggest that more than one functional group on these complex organic polymers may be responsible for binding to the alpha -FeOOH surface. Similarly, the relative surface affinity of the As(III or V) species and that of the competing organic ligand as a function of pH may play a major role in the outcome of As adsorption on alpha -FeOOH. The results of these experiments suggest that DOC substances are capable of increasing the bioavailability of As in soil and water systems in which the dominant solid phase is a crystalline iron oxide.

Keywords: Chromate Retention Mechanisms, Competitive Adsorption, Fulvic-Acid, Phosphate, Sorption, Minerals, Oxide, Soils, Complexation, Gibbsite

Goldberg, S. (2002), Competitive adsorption of arsenate and arsenite on oxides and clay minerals. Soil Science Society of America Journal, 66 (2), 413-421.

Full Text: 2002\Soi Sci Soc Ame J66, 413.pdf

Abstract: Arsenic adsorption on amorphous Al and Fe oxides and the clay minerals, kaolinite, montmorillonite, and illite was investigated as a function of solution pH and As redox state, i.e., arsenite [As(III)] and arsenate [As(V)]. Arsenic adsorption experiments were carried out in batch systems to determine adsorption envelopes, amount of As(III), As(V), or both adsorbed as a function of solution pH per fixed total As concentration of 20 µM As. Arsenate adsorption on oxides and clays was maximal at low pH and decreased with increasing pH above pH 9 for Al oxide, pH 7 for Fe oxide and pH 5 for clays. Arsenite adsorption exhibited parabolic behavior with an adsorption maximum around pH 8.5 for all materials. There was no competitive effect of the presence of equimolar arsenite on arsenate adsorption. The competitive effect of equimolar arsenate on arsenite adsorption was small and apparent only on kaolinite and illite in the pH range 6.5 to 9. The constant capacitance model was able to fit the arsenate and arsenite adsorption envelopes to obtain values of the intrinsic As surface complexation constants. These intrinsic surface complexation constants were then used in the model to predict competitive arsenate and arsenite adsorption from solutions containing equimolar As(III) and As(V) concentrations. The constant capacitance model was able to predict As adsorption from mixed As(III)-As(V) solutions in systems where there was no competitive effect.

Keywords: EM, Electrophoretic Mobility, EXAFS, X-Ray Absorption Fine Structure, FTIR, Fourier Transform Infrared Spectroscopy, PZC, Point of Zero Charge

Waltham, C.A. and Eick, M.J. (2002), Kinetics of arsenic adsorption on goethite in the presence of sorbed silicic acid. Soil Science Society of America Journal, 66 (3), 818-825.

Full Text: 2002\Soi Sci Soc Ame J66, 818.pdf

Abstract: The potential toxicity and availability of As in the environment is dependent on several factors including redox potential, pH, and the presence of ligands that can compete for adsorption sites on mineral surfaces. Silicic acid is a ligand ubiquitous in natural systems and strongly chemisorbs to Fe oxides. However, there are relatively few studies examining its influence on As adsorption on Fe oxides. This study examined the influence of silicic acid (0.10 and 1.0 mM) on the adsorption kinetics of arsenite and arsenate (0.10 mM) on goethite over a range of common soil pH values (4, 6, and 8). The rate of arsenic(III and V) and silicic acid adsorption was greatest at pH values near their pK₁ value. However, silicic acid sorption was characterized by biphasic kinetics with rapid adsorption followed by a much slower adsorption reaction. The rate and total quantity of arsenite adsorption decreased in the presence of silicic acid at all pH values and concentrations of silicic acid. Approximately 40% less arsenite was adsorbed in the presence of 1.0 mM silicic acid at all pH values. At 0.10 mM, silicic acid had less of an effect on arsenite adsorption. In contrast, only the rate and not the total quantity of arsenate was reduced in the presence of silicic acid. The rate of arsenate adsorption decreased as pH and silicic acid concentration increased. This was attributed to a decrease in the goethite’s surface potential upon specific adsorption of silicic acid and deprotonation of the arsenate molecule creating an unfavorable electrostatic field. These results demonstrate the importance of evaluating As speciation, reaction kinetics, and the influence of naturally occurring ligands on the adsorption of As on variable charge surfaces.

Keywords: FESEM, Field Emission Scanning Electron Microscopy, PZC, Point of Zero Charge, TGA, Thermal Gravimetric Analysis, XRD, X-Ray Diffraction

Violante, A. and Pigna, M. (2002), Competitive sorption of arsenate and phosphate on different clay minerals and soils. Soil Science Society of America Journal, 66 (6), 1788-1796.

Full Text: 2002\Soi Sci Soc Ame J66, 1788.pdf

Abstract: Sorption and desorption of AsO₄ on or from different soil components may have a dominant role in regulating As mobility in soils. The objectives of this work were to provide information on the factors that influence the competitive sorption of AsO₄ and PO₄ in soil. We studied the competitive sorption of PO₄ and AsO₄ on selected phyllosilicates, metal oxides, synthetic organo-mineral complexes, and soil samples as affected by pH (4.0–8.0), ligands concentration, surface coverage of the oxyanions on the samples and the residence time. We found that Mn, Fe, and Ti oxides and phyllosilicates particularly rich in Fe (nontronite, ferruginous smectites) were more effective in sorbing AsO₄ than PO₄. In fact, by adding AsO₄ and PO₄ as a mixture (AsO₄/PO₄ molar ratio of 1) more AsO₄ than PO₄ was usually sorbed on birnessite, pyrolusite, goethite, nontronite, and ferruginous smectite, but more PO₄ than AsO₄ was sorbed on noncrystalline Al precipitation products, gibbsite, boehmite, allophane, and kaolinite. For example, at pH 5.0 the sorbed AsO₄/sorbed PO₄ molar ratio (rf) was 1.81 for birnessite, 1.05 for nontronite, but was only 0.45 for kaolinite and 0.14 for allophane. For montmorillonite, illite, and vermiculite the rf values were slightly <1. For soil samples, particularly rich in kaolinite, halloysite, allophane, and containing relatively large amounts of organic C, the rf values were usually much <1. For all the samples, the rf values increased by decreasing the pH and with the residence time of the oxyanions. The sorption of AsO₄ (or PO₄) on goethite and gibbsite decreased by increasing the initial PO₄/AsO₄ (or AsO₄/PO₄ molar ratio) up to 2.0. However, PO₄ inhibited AsO₄ sorption more on gibbsite than on goethite, whereas AsO₄ prevented PO₄ sorption more on goethite than on gibbsite. The data reported in this paper suggest that the mobility, the bioavailability, and the toxicity of As in soil environments may be greatly affected by the nature of soil components, pH, presence of anions (PO₄), and residence time.

Keywords: AlD, Al Extracted by Na-Dithionite-Citrate, AlO, Al Extracted by NH₄-Oxalate, EGME, Ethyleneglycol Monoethylether, FeD, Fe Extracted by Na-Dithionite-Citrate, FeO, Fe Extracted by NH₄-Oxalate, IEP, Isoelectric Point, IMt-2, Montana illite, KGa-1, Georgia kaolinite, OOMWW, Olive Oil Mill Waste Water, PZC, Point of Zero Charge, PZSE, Point of Zero Salt Effect, RF, Molar Ratio, SWy-1, Wyoming Montmorillonite, TEM, Transmission Electron Microscopy, XRD, X-Ray Diffraction

Saha, U.K., Liu, C., Kozak, L.M. and Huang, P.M. (2004), Kinetics of selenite adsorption on hydroxyaluminum- and hydroxyaluminosilicate-montmorillonite complexes. Soil Science Society of America Journal, 68 (4), 1197-1209.

Full Text: 2004\Soi Sci Soc Ame J68, 1197.pdf

Abstract: A lack of understanding about the selenite adsorption behavior on hydroxyaluminum (HyA)- and hydroxyaluminosilicate (HAS)- interlayered phyllosilicates led us to conduct the present study. The kinetics of selenite adsorption on montmorillonite (Mt), HyA(OH/ Al = 2.0)-Mt, HAS1(OH/Al = 2.0, Si/Al = 0.24)-Mt, and HAS₂(OH/ Al = 2.0, Si/Al = 0.48)-Mt were studied at pH 4.5, with an initial selenite concentration of 0.025 mM, a clay concentration of 0.5 g L^-1, temperatures of 288, 298, 308, and 318 K, and background electrolyte concentration of 10^-2 M NaNO₃. Of the six different kinetic models tested, the second-order rate equation best described the kinetic data obtained for the initial fast reaction (5-30 min) followed by a slow reaction (30-180 min) in the adsorption systems. Elevated temperatures brought about a substantial increase in the rate constants. Compared with Mt, different HyA/HAS-Mts had 2 to 21 times higher rate constants for the fast reaction and up to five times higher rate constants for the slow reaction. Silication of HyA-Mt to form HAS1-Mt and HAS2-Mt substantially lowered the rate constants for both the fast and slow reactions. For the fast reaction, Mt had the highest activation energy and HyA-Mt had the lowest activation energy (around four times lower than Mt), silication increased the activation energy of selenite adsorption on the HAS-Mts. The pre-exponential factor, an index of the frequency of selenite collision with the clay surface, was remarkably lower for the HyA/HAS-Mts in comparison with Mt. The data obtained in the present study are of fundamental significance in understanding the role of Al interlayering and coating and silication of Al polymers on expansible phyllosilicates in influencing the dynamics of Se in soil and related environments.

Keywords: Hydroxy-Aluminosilicate Ions, Expansible Layer Silicates, Phosphate Adsorption, Charge Characteristics, Aluminum Hydroxides, Anion Adsorption, Proto-Imogolite, Electric Charge, Iron-Oxides, Surface

? Bolster, C.H. and Hornberger, G.M. (2007), On the use of linearized Langmuir equations. Soil Science Society of America Journal, 71 (6), 1796-1806.

Full Text: 2007\Soi Sci Soc Ame J71, 1796.pdf

Abstract: One of the most commonly used models for describing solute sorption to soils is the Langmuir model. Because the Langmuir model is nonlinear, fitting the model to sorption data requires that the model be solved iteratively using an optimization program. To avoid the use of optimization programs, a linearized version of the Langmuir model is often used so that model parameters can be obtained by linear regression. Although the linear and nonlinear Langmuir equations are mathematically equivalent, there are several limitations to using linearized Langmuir equations. We examined the limitations of using linearized Langmuir equations by fitting P sorption data collected on eight different soils with four linearized versions of the Langmuir equation and comparing goodness-of-fit measures and fitted parameter values with those obtained with the nonlinear Langmuir equation. We then fit the sorption data with two modified versions of the Langmuir model and assessed whether the fits were statistically superior to the original Langmuir equation. Our results demonstrate that the use of linearized Langmuir equations needlessly limits the ability to model sorption data with good accuracy. To encourage the testing of additional nonlinear sorption models, we have made available an easily used Microsoft Excel spreadsheet (ars.usda.gov/msa/awmru/ bolster/Sorption_spreadsheets) capable of generating best-fit parameters and their standard errors and confidence intervals, correlations between fitted parameters, and goodness-of-fit measures. The results of our study should promote more critical evaluation of model fits to sorption data and encourage the testing of more sophisticated sorption models.

Keywords: Nonlinear Least-Squares, Purpose Adsorption-Isotherms, Phosphorus Sorption Capacity, Estimating Michaelis-Menten, Minnesota River-Basin, Regression-Analyses, Runoff Phosphorus, Calcareous Soils, Curve-Fit, Constants

? Bolster, C.H. and Hornberger, G.M. (2008), On the use of linearized Langmuir equations. Soil Science Society of America Journal, 72 (6), 1848.

Full Text: 2008\Soi Sci Soc Ame J72, 1848.pdf

Warren, J.G. (2009), Investigating phosphorus sorption onto kaolinite using isothermal titration calorimetry. Soil Science Society of America Journal, 73 (2), 560-568.

Full Text: 2009\Soi Sci Soc Ame J73, 560.pdf

Abstract: The mechanism of P sorption onto soils has a strong impact on bioavailability and transport potential. Assessment of sorption energy via isothermal titration calorimetry (ITC) can potentially provide information on P sorption mechanisms. This study used ITC to examine P sorption onto poorly crystalline Georgia kaolinite at pH 4.3 and 6.3. A complementary sorption and desorption isotherm was also conducted at the same kaolinite/solution ratio as the titration experiment. In addition, other ITC experiments were performed to help interpret the kaolinite-P thermograms. Thermograms (measured heat response) for titration of P into pH 4.3 kaolinite indicated initial fast exothermic followed by slower endothermic reactions, both reactions decreased with further P additions. By the eighth titration, the net reaction turned from exothermic to endothermic, indicating that the endothermic reaction now dominated. The complementary sorption isotherm indicated a statistically significant “breakpoint” at this same P addition. In contrast, pH 6.3 kaolinite exhibited only exothermic reactions during P titrations. Based on sorption isotherms, solution thermodynamic modeling, and supporting ITC experiments, the exothermic reaction indicated P sorption onto kaolinite by ligand exchange and dissolution or protonation of kaolinite while the endothermic reaction indicated Al phosphate precipitation. Sequential desorption isotherm results showed that although the pH 4.3 and 6.3 kaolinite desorbed the same amount of P when normalized for initial surface P concentrations, kaolinite at pH 4.3 desorbed P at a greater rate than at pH 6.3. Compared with traditional solid-state techniques, ITC provides continuous data collection as reactions are occurring, rather than discrete observations.

Keywords: Amorphous Aluminum Hydroxides, Anion-Exchange, Availability, Bioavailability, Data Collection, Desorption, Dissolution, Endothermic, Eutrophication, Flow Calorimetry, Impact, Ionic-Strength, Isotherm, Isotherms, Kaolinite, Mechanism, Modeling, Phosphate, Phosphate Adsorption, Phosphorus, Soils, Sorption, Sorption Isotherm, Thermodynamic, Transport

? Tsao, T.M., Wang, M.K. and Huang, P.M. (2009), Automated ultrafiltration device for efficient collection of environmental nanoparticles from aqueous suspensions. Soil Science Society of America Journal, 73 (6), 1808-1816.

Full Text: 2009\Soi Sci Soc Ame J73, 1808.pdf

Abstract: Environmental nanoparticles exist in the hydrosphere, pedosphere, biosphere, and atmosphere. Their biogeochemical and ecological impacts are some of the fastest growing areas of research today. However, efficient separation of environmental nanoparticles remains difficult. The objective of this study was to develop an automated ultrafiltration device (AUD) for efficient collection of environmental nanoparticles. The AUD utilizes an automated hydraulic ram to facilitate collection of nanoparticles using the ultrafiltration membrane with pore size in the range of 1 to 100 nm. Zeolite A was used as a model nanoparticle sample to demonstrate the efficiency of the AUD. The size distribution and mean particle sizes determined by zeta-sizer analysis on the collected nanoparticles and their transmission electron micrographs indicate the adequacy of the AUD developed in this study in collecting nanoparticles (1-100 nm). Because of its ability to reduce the time needed for sample collection, coupled with the quantity of nanoparticles collected, the AUD was far more efficient than the conventional syringe method for collecting nanoparticles. The AUD has the characteristics of automation, easy operation, and high efficiency in the separation of nanoparticles and would, thus, facilitate future research and developments in environmental nanoscience and nanotechnology and their impacts on the ecosystem.

Keywords: Cross-Flow Ultrafiltration, River Superfund Complex, Size Analysis, Heavy-Metals, Colloids, Fractionation, Water, Microfiltration, Oxides, Nanotechnology

? Wang, Y.J., Cui, Y.X., Zhou, D.M., Wang, S.Q., Xiao, A.Y., Wang, R.H. and Zhang, H.L. (2009), Adsorption kinetics of glyphosate and copper(II) alone and together on two types of soils. Soil Science Society of America Journal, 73 (6), 1995-2001.

Full Text: 2009\Soi Sci Soc Ame J73, 1995.pdf

Abstract: Glyphosate [N-(phosphonomethyl)glycine] is a nonselective, postemergence herbicide that contains multiple functional groups, which can form strong coordination with metal cations to give bidentate and tridentate complexes. The complexation of glyphosate with metal cations may affect their distribution and bioavadability in sods. Adsorption kinetics of glyphosate and Cu(II) alone and together were studied using a continuous flow experimental setup on two soils with different characteristics at pH5.5. Four kinetic models, i.e., the Lagergren first-order, pseudo-second-order, Elovich, and power function equations, were successfully used to describe their adsorption kinetics. Among the four models, the Lagergren first-order kinetic model fit the experimental data of glyphosate and Cu(II) adsorption the best. Glyphosate significantly increased the adsorption quantity of Cu(II) on the Red soil (a Hapludult or Udic Ferrosol), due to the fact that Cu(II) was adsorbed on the sites where glyphosate had been strongly adsorbed. Glyphosate decreased the adsorption of Cu(II) on the Wushan soil (a Haplaquept or Anthrosol), however, because adsorption of glyphosate on this soil was weak and the complex of glyphosate and Cu(II) tended to be highly soluble in water, thus preventing Cu(II) from exchanging with Ca²⁺ and Mg²⁺ ions on the soil surface. On the other hand, the presence of Cu(II) decreased the adsorption of glyphosate on both soils, which may be attributed to the lower affinity of the Cu(II)-glyphosate complex to the soils than glyphosate alone.

Keywords: Adsorption, Adsorption Kinetics, Characteristics, Complexation, Coordination, Copper(II), Cosorption, Cu(II), Data, Distribution, Elovich, Experimental, First Order, First-Order Kinetic Model, Flow, FTIR, Function, Functional Groups, Goethite, Herbicide, Ions, Kinetic, Kinetic Model, Kinetic Models, Kinetics, Metal, Model, Models, Montmorillonite, Power, Pseudo Second Order, Pseudo-Second-Order, Soil, Soils, Sorption, Surface, Water, Zinc

? Ren, W.J., Wang, M.E. and Zhou, Q.X. (2011), Adsorption characteristics and influencing factors of chlorimuron-ethyl in two typical Chinese soils. Soil Science Society of America Journal, 75 (4), 1394-1401.

Full Text: 2011\Soi Sci Soc Ame J75, 1394.pdf

Abstract: The adsorption of chlorimuron-ethyl in two typical northeastern Chinese soils before and aft er removal of organic matter and removal of organic matter plus iron/aluminum oxides was investigated using batch equilibrium methods, and the effect of pH on the adsorption was also evaluated. The adsorption kinetics were fitted well with the Elovich and pseudo-second-order kinetic models (R(2) = 0.973-0.985) and the adsorption isotherms conformed to the Linear, Freundlich, and Langmuir models (R(2) > 0.963). The mineral fraction appeared to dominate adsorption of chlorimuron-ethyl in brown earth (BE; Alfisols), while organic matter was the major component for the adsorption in black soil (BS; Mollisols). The adsorption of chlorimuron-ethyl in the original and treated soils all decreased with increasing pH. Moreover, the effect of pH on the adsorption of chlorimuron-ethyl in soil minerals was stronger than that in organic matter at acidic conditions.

Keywords: Adsorption, Adsorption Isotherms, Adsorption Kinetics, Bensulfuron-Methyl, Desorption, Equilibrium, Ethametsulfuron-Methyl, Freundlich, Isotherms, Kinetic, Kinetic Models, Kinetics, Langmuir, Metsulfuron-Methyl, Organic Amendment, pH, Removal, Soil, Soils, Sorption, Sorption, Desorption Behavior, Sulfonylurea Herbicides, Tandem Mass-Spectrometry, Thifensulfuron-Methyl