Restructuring of polygalacturonate on alumina upon hydration—Effect on phosphate sorption kinetics

Mikutta, Christian; Krüger, Jaane; Schaumann, Gabriele E.; Lang, Friederike

doi:10.1016/j.gca.2006.03.007

Cited by 5 publications

(3 citation statements)

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“…This is consistent with the conclusions drawn for mineral soil samples [6] and peat samples [8]. Mikutta et al [58] studied the hydration of polygalacturonate (PGA) coatings on alumina (Al 2 O 3 ) and concluded from their NMR and DSC results that the PGA chains reorient into the pore space upon swelling.…”

Section: Comparison Of the Results Determined By 1 H Nmr And Cryo Nmrsupporting

confidence: 83%

Proton NMR Relaxometry as a Useful Tool to Evaluate Swelling Processes in Peat Soils

Jaegera¹

2010

TOMRJ

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Dramatic physical and physico-chemical changes in soil properties may arise due to temperature and moisture variations as well as swelling of soil organic matter (SOM) under constant conditions. Soil property variations may influence sorption/desorption and transport processes of environmental contaminants and nutrients in natural-organic-matterrich soils. Notwithstanding the studies reported in literature, a mechanistic model for SOM swelling is unavailable yet. The objective of the present study was the evaluation of the swelling of peat soils, considered as SOM models, by 1 H NMR relaxometry and differential scanning calorimetry (DSC). Namely, information on the processes governing physical and physicochemical changes of peat during re-hydration were collected. The basic hypothesis of the present study was that the changes are slow and may affect water state as well as amounts of different water types into the peats. For this reason, such changes can be evidenced through the variations of mobility and thermal behaviour of the involved H 2 O molecules by using 1 H NMR relaxometry and DSC. According to the experimental results, a mechanistic model, describing the fundamental processes of peat swelling, was obtained. Two different peats re-wetted at three temperatures were used. The swelling process was monitored by measuring spin-spin relaxation time (T2) over a hydration time of several months. Moreover, DSC, T1-T2 and T2-D correlation measurements were done at the beginning and at the end of the hydration. Supplementary investigations were also done in order to discriminate between the swelling effects and the contributions from soil solution, internal magnetic field gradients and/or soil microorganisms to proton relaxation. All the results revealed peat swelling. It was evidenced by pore size distribution changes, volumetric expansion and redistribution of water, increasing amounts of nonfreezable and loosely bound water, as well as formation of gel phases and reduction of the translational and rotational mobility of H 2 O molecules. All the findings implied that changes of the physical and physicochemical properties of peats were obtained. In particular, three different processes having activation energies comprised in the interval 5-50 kJ mol-1 were revealed. The mechanistic model which was, then, developed included water reorientation in bound water phases, water diffusion into the peat matrix and reorientation of SOM chains as fundamental processes governing SOM swelling. This study is of environmental significance in terms of re-naturation and re-watering of commercially applied peatlands and of sorption/desorption and transport processes of pollutants and nutrients in natural organic matter rich soils.

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Section: Comparison Of the Results Determined By 1 H Nmr And Cryo Nmrsupporting

confidence: 83%

Proton NMR Relaxometry as a Useful Tool to Evaluate Swelling Processes in Peat Soils

Jaegera¹

2010

TOMRJ

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Section: Comparison Of the Results Determined By 1 H Nmr And Cryo Nmrsupporting

confidence: 83%

Proton NMR Relaxometry as a Useful Tool to Evaluate Swelling Processes in Peat Soils~!2009-07-26~!2009-12-04~!2010-06-15~!

Jaeger¹,

Shchegolikhina²,

As³

et al. 2010

TOMRJ

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Dramatic physical and physico-chemical changes in soil properties may arise due to temperature and moisture variations as well as swelling of soil organic matter (SOM) under constant conditions. Soil property variations may influence sorption/desorption and transport processes of environmental contaminants and nutrients in natural-organic-matterrich soils. Notwithstanding the studies reported in literature, a mechanistic model for SOM swelling is unavailable yet. The objective of the present study was the evaluation of the swelling of peat soils, considered as SOM models, by 1 H NMR relaxometry and differential scanning calorimetry (DSC). Namely, information on the processes governing physical and physicochemical changes of peat during re-hydration were collected. The basic hypothesis of the present study was that the changes are slow and may affect water state as well as amounts of different water types into the peats. For this reason, such changes can be evidenced through the variations of mobility and thermal behaviour of the involved H 2 O molecules by using 1 H NMR relaxometry and DSC. According to the experimental results, a mechanistic model, describing the fundamental processes of peat swelling, was obtained. Two different peats re-wetted at three temperatures were used. The swelling process was monitored by measuring spin-spin relaxation time (T2) over a hydration time of several months. Moreover, DSC, T1 -T2 and T2 -D correlation measurements were done at the beginning and at the end of the hydration. Supplementary investigations were also done in order to discriminate between the swelling effects and the contributions from soil solution, internal magnetic field gradients and/or soil microorganisms to proton relaxation. All the results revealed peat swelling. It was evidenced by pore size distribution changes, volumetric expansion and redistribution of water, increasing amounts of nonfreezable and loosely bound water, as well as formation of gel phases and reduction of the translational and rotational mobility of H 2 O molecules. All the findings implied that changes of the physical and physicochemical properties of peats were obtained. In particular, three different processes having activation energies comprised in the interval 5 -50 kJ mol -1 were revealed. The mechanistic model which was, then, developed included water reorientation in bound water phases, water diffusion into the peat matrix and reorientation of SOM chains as fundamental processes governing SOM swelling. This study is of environmental significance in terms of re-naturation and re-watering of commercially applied peatlands and of sorption/desorption and transport processes of pollutants and nutrients in natural organic matter rich soils.

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“…Recently, the influence of the acidic polysaccharides on the processes of ionic sorption by the iron oxides and hydroxides has been addressed (Mikutta et al, 2006a). In particular, it has been shown that polygalacturonic acid (PGA) can increase the bioavailability of important ions such as phosphate by competing for the same sorption sites of the iron oxides and hydroxides and by reducing the intra-particle diffusion of phosphate because PGA blocks mineral pores of < 10 nm (Mikutta et al, 2006a(Mikutta et al, , 2006b. However, in nature, the formation of mucilages on the root surface occurs gradually and involves calcium (Ca) ions in the soil liquid phase or adsorbed on inorganic matrices in close contact with the roots.…”

Section: Introductionmentioning

confidence: 99%

Role of root exudates on the sorption of arsenate by ferrihydrite

Castaldi

Garau

Lauro

et al. 2015

European J Soil Science

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Iron oxy-hydroxides in soil are known to have a large affinity for arsenate (As(V)) inorganic species. At the soil-root interface such mineral components are embedded by mucilaginous material that is secreted from continuously growing root cap cells. In order to determine the role of plant mucilages in As(V) sorption by iron oxy-hydroxides, we layered a calcium (Ca)-polygalacturonate network (CaPGA) on to amorphous iron (Fe) (III) hydroxide (ferrihydrite, Fh) particles. The scanning electron micrographs of the CaPGA network coating the ferrihydrite (Fh-CaPGA) show a regular structure with a honeycomb-like pattern where interlacing fibrils form a porous system. The FT-IR spectra of Fh-CaPGA suggest that CaPGA fibrils are retained by the surface Fe(III) nuclei of Fh through electrostatic interactions. The sorption experiments carried out at pH 4.3 and 5.8 indicated a smaller amount of As(V) sorbed by Fh-CaPGA than by Fh alone, being less after 3 and 24 hours of reaction by about 70 and 30%, respectively. The sorption of As(V) by Fh was also studied in the presence of caffeic acid (CAF), an important root exudate. Simultaneous sorption kinetics show that As(V) sorption by Fh is almost independent of CAF concentration, indicating a greater affinity of arsenate ions towards the Fh surfaces. However, the amount of As(V) sorbed by the Fh coated by CaPGA, in the presence of 0.25, 0.5 and 1.0 mm CAF, is markedly smaller by about 20, 27 and 40%, respectively, than that found in the As(V)-CAF-Fh ternary systems. This is caused mainly by redox reactions involving CAF and the surface Fe(III) nuclei of Fh leading to the formation of CAF oxidation products which prevent As(V) sorption.

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Restructuring of polygalacturonate on alumina upon hydration—Effect on phosphate sorption kinetics

Cited by 5 publications

References 58 publications

Proton NMR Relaxometry as a Useful Tool to Evaluate Swelling Processes in Peat Soils

Proton NMR Relaxometry as a Useful Tool to Evaluate Swelling Processes in Peat Soils

Proton NMR Relaxometry as a Useful Tool to Evaluate Swelling Processes in Peat Soils~!2009-07-26~!2009-12-04~!2010-06-15~!

Role of root exudates on the sorption of arsenate by ferrihydrite

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