HEATS OF K/Ca AND K/Pb EXCHANGE IN TWO TROPICAL SOILS AS MEASURED BY FLOW CALORIMETRY 1

Appel, Christopher E.; Rhue, Dean; Ma, Liguo; Reve, Bill

doi:10.1097/00010694-200212000-00001

Cited by 13 publications

(9 citation statements)

References 49 publications

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“…1b, d) indicate that as K � Gast, 1972). Consistent with the the amount of K � (preferred ion) on the exchanger above, Appel et al (2002) observed no changes in the decreases, its selectivity increases (going from left to enthalpy of either Ca 2� or Pb 2� adsorption with inright on the figures). Contrarily, the Oxisol-Ca and -Pb creased surface coverage of these ions on this soil.…”

Section: Determination Of Calcium and Lead Selectivitysupporting

confidence: 67%

Selectivities of Potassium‐Calcium and Potassium‐Lead Exchange in Two Tropical Soils

Appel

Lena

Rhue

et al. 2003

Soil Science Soc of Amer J

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Measurement of cation selectivity in soils provides important infor mation about the affinity and binding strength of a particular cationIn many cases, much of the Pb in uncontaminated on soil surfaces. Gaines-Thomas (K GT ) selectivity coefficients were determined for a variety of K/Ca and K/Pb ratios on an Oxisol and Ultisol soil from Puerto Rico. 2� and Pb 2� with increasing surface coverage of these ions. This was attributed to the presence of smectite in the Ultisol, which was able to partially collapse when K � saturated. Some of the Pb sorption in the soils was due to chemisorption. The Oxisol chemisorbed ≈3000 mg Pb kg �1 while that value for the Ultisol was ≈1900 mg kg �1 . The differences were due to the greater quantities of Fe/Al oxides and organic matter in the Oxisol relative to the Ultisol. Scanning electron microscopy-energy dispersive X-ray (SEM-EDX) spectros copy detected discrete Pb-C phase in both soils. The C was from organic matter. Under experimental conditions, any Pb-carbonate phase would not have been stable. It was possible Pb was associated with organic sulfhydral groups. The selectivity exhibited by soil sys tems for various nutrient and heavy metals is important in elucidating how available these metals will be for plant/animal uptake as well as their mobility and stability in the soil environment.

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Section: Determination Of Calcium and Lead Selectivitysupporting

confidence: 67%

Selectivities of Potassium‐Calcium and Potassium‐Lead Exchange in Two Tropical Soils

Appel

Lena

Rhue

et al. 2003

Soil Science Soc of Amer J

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“…The flow calorimeter used in this experiment was the same one used by Appel et al (2002) and Kabengi et al (2006a, b), and its operation has been described in previous work . The only changes to the instrument were in design of the sample cell, which will be described in a future publication (Adrian Gale; personal communication) and that the column effluent in the current experiment passed through a cell with a G-P Gel Combo glass electrode (Corning, Corning, NY) linked to an Accumet 1002 potentiometer (Fisher Scientific, Fairlawn, NJ), enabling the in-line measurement of the effluent solution pH.…”

Section: Instrumentationmentioning

confidence: 99%

Calorimetric Investigation of the Nature of Sulfate and Phosphate Sorption on Amorphous Aluminum Hydroxide

et al. 2013

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The fate and transport of sulfate and phosphate in the environment are largely mediated by how these anions react with soil colloids, especially metal (hydr)oxides. The overall objective of this study was to use flow calorimetry to compare and better understand sulfate and phosphate sorption and sorption mechanisms on amorphous aluminum hydroxide (AHO). This was performed by measuring the in situ heats of NO 3 -and Cl -and K + and Na + exchange before and after reaction of AHO with sulfate and phosphate, by measuring heats of sulfate and phosphate sorption on AHO, and by determination of the amount of sulfate and phosphate sorbed. The AHO used in our study was synthesized in-house and was amorphous. All solutions used in our experiments had pH of 5.8 and ionic strengths of 50 mmol/L. Sulfate and phosphate treatment of the AHO reduced anion exchange by 61% and 77%, respectively, relative to the measured heats of NO 3 -and Cl -exchange before SO 4 2-or H 2 PO 4 -treatment. Sulfate and phosphate treatment of the AHO did not change measured heats of K + and Na + exchange. The molar heats of sorption were 2.9 ± 1.4 kJ/mol for sulfate and −6.5 ± 3 kJ/mol for phosphate. The thermodynamic exchange (NO 3 -and Cl -and K + and Na + ) and sorption (SO4 2-and H 2 PO 4 -) data obtained by the flow calorimeter differentiated between outer-and inner-sphere SO4 2-and H 2 PO 4 -sorption mechanisms in situ and indicated that these ligands irreversibly sorbed on AHO by most likely forming monodentate complexes, bidentate bridging complexes, and Al-hydroxy surface precipitates. P hosphate and sulfate are ligands of environmental concern.Elevated concentrations of phosphate in fresh water can lead to eutrophication (Pierzynski et al., 2000), and sulfate in drinking water is a potential contaminant at concentrations more than 250 mg/L (Freeze and Cherry, 1979). The fate and transport of these anions in soils and in the environment are largely mediated by how they react with soil metal (hydr)oxides. A better understanding of the mechanisms that govern sulfate and phosphate sorption on metal hydr(oxides) has implications for water and soil quality as well as nutrient availability. The reactivity of aluminum (hydr)oxides, which are considered some of the most reactive solid phases for oxyanion sorption in soils, with respect to sulfate and phosphate sorption is largely governed by charge characteristics of the aluminum hydr(oxides) and the chemical properties of the sorbing oxyanions (McBride, 1994).Phosphate sorption by aluminum (hydr)oxides exhibits an initial rapid uptake. Both monodentate and bidentate phosphate surface complexes have been proposed based on spectroscopic, thermodynamic, and quantum mechanical analysis (Bleam et al.. Hydroxyl ions on the surface of aluminum (hydr)oxides can coordinate to one, two, or even three Al cations in the solid. The singly coordinated hydroxyls readily protonate/deprotonate to form surface charge, whereas the doubly and triply coordinated hydroxyls are much less active in this respect. At pH bel...

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“…Briefl y, this involves the use of a calorimeter for the detection of changes in heat emitted (exotherm) or absorbed (endotherm) as a solute is added to a solution or suspension. Such instruments have been used in the investigation of sorption mechanisms and thermodynamics (Kabengi et al, 2006a;Cai et al, 2006;Kaya, 2004;Rhue et al, 2002;Miltenburg and Golterman, 1998;Zou et al, 1997), ion exchange (Kabengi et al, 2006b;Appel et al, 2002), and surface charge (Kabengi et al, 2006b). Calorimetric techniques are not "stand alone," however; correct interpretation of the data involves some knowledge of the system being studied and complimentary solution or solid-state data.…”

Section: Investigating Phosphorus Sorption Onto Kaolinite Using Isothmentioning

confidence: 99%

Investigating Phosphorus Sorption onto Kaolinite Using Isothermal Titration Calorimetry

Penn

Warren

2009

Soil Science Soc of Amer J

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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.

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HEATS OF K/Ca AND K/Pb EXCHANGE IN TWO TROPICAL SOILS AS MEASURED BY FLOW CALORIMETRY 1

Cited by 13 publications

References 49 publications

Selectivities of Potassium‐Calcium and Potassium‐Lead Exchange in Two Tropical Soils

Selectivities of Potassium‐Calcium and Potassium‐Lead Exchange in Two Tropical Soils

Calorimetric Investigation of the Nature of Sulfate and Phosphate Sorption on Amorphous Aluminum Hydroxide

Investigating Phosphorus Sorption onto Kaolinite Using Isothermal Titration Calorimetry

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