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• 1
Article
Language: English
In: Environmental Sciences Europe, 2018, Vol.30(1), pp.1-15
Description: Background Aliphatic (poly)hydroxy carboxylic acids [(P)HCA] occur in natural, e.g. soils, and in technical (waste disposal sites, nuclear waste repositories) compartments . Their distribution, mobility and chemical reactivity, e.g. complex formation with metal ions and radionuclides, depend, among others, on their adsorption onto mineral surfaces. Aluminium hydroxides, e.g. gibbsite [α-Al(OH) 3 ], are common constituents of related solid materials and mimic the molecular surface properties of clay minerals. Thus, the study was pursued to characterize the adsorption of glycolic, threonic, tartaric, gluconic, and glucaric acids onto gibbsite over a wide pH and (P)HCA concentration range. To consider specific conditions occurring in radioactive wastes, adsorption applying an artificial cement pore water (pH 13.3) as solution phase was investigated additionally. Results The sorption of gluconic acid at pH 4, 7, 9, and 12 was best described by the “two-site” Langmuir isotherm, combining “high affinity” sorption sites (adsorption affinity constants \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$K_{\text{L1}}$$\end{document} K L1  〉 1 L mmol −1 , adsorption capacities 〈 6.5 mmol kg −1 ) with “low affinity” sites ( \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$K_{\text{L2}}$$\end{document} K L2  〈 0.1 L mmol −1 , adsorption capacities ≥ 19 mmol kg −1 ). The total adsorption capacities at pH 9 and 12 were roughly tenfold of that at pH 4 and 7. The S-shaped pH sorption edge of gluconic acid was modelled applying a constant capacitance model, considering electrostatic interactions, hydrogen bonding, surface complex formation, and formation of solved polynuclear complexes between Al 3+ ions and gluconic acid. A Pearson and Spearman rank correlation between (P)HCA molecular properties and adsorption parameters revealed the high importance of the size and the charge of the adsorbates. Conclusions The adsorption behaviour of (P)HCAs is best described by a combination of adsorption properties of carboxylic acids at acidic pH and of polyols at alkaline pH. Depending on the molecular properties of the adsorbates and on pH, electrostatic interactions, hydrogen bonding, and ternary surface complexation contribute in varying degrees to the adsorption process. Linear distribution coefficients K d between 8.7 and 60.5 L kg −1 (1 mmol L −1 initial PHCA concentration) indicate a considerable mineral surface affinity at very high pH, thus lowering the PHCA fraction available for the complexation of metal ions including radionuclides in solution and their subsequent mobilization.
Keywords: Gibbsite ; Polyhydroxy carboxylic acids ; Gluconic acid ; Tartaric acid ; Adsorption ; Sorption edge ; Sorption isotherm ; Surface complexation ; Nuclear waste repository ; Artificial cement pore water
ISSN: 2190-4707
E-ISSN: 2190-4715
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• 2
Article
Language: English
In: Journal of Soils and Sediments, 2012, Vol.12(8), pp.1269-1279
Description: Issue Title: Special issue: Coevolution of organic substances and soils Sorption of xenobiotics in soils and especially to soil organic matter (SOM) determines their mobility and bioavailability in ecosystems. However, SOM as the major sorbent may be altered in its physicochemical properties upon changes in boundary conditions such as hydration. Hence, the goal of this study was to determine the influence of soil hydration on physicochemical properties of SOM and the resulting effects on sorption of xenobiotics. Samples of a Histosol with 51 % SOM were adjusted to five water contents from 10 to 75 % (w/w based on dry soil mass) and aged for water contact times of 0 weeks to 3 years. The hydrated samples were characterized with respect to thermal properties of SOM and of the incorporated water via differential scanning calorimetry and with respect to hydration-induced swelling via ^sup 1^H-NMR relaxometry, and the sessile drop method was applied to determine their soil-water contact angle. Sorption kinetics and isotherms of naphthalene-2-ol in the pre-treated peat samples were determined in batch experiments. SOM matrix rigidity varied with the water content and increased with water contact time. An initial minimum in SOM rigidity at ~30 % water content became maximum after ~20 weeks, also resulting in the strongest resistance towards water infiltration. We argue that the anomalies at 30 % water content are related to the critical water content for the formation of freezable water w ^sub crit^ in the peat samples, which was 26.2±0.3 %. Conditions for water-assisted molecular bridging were assumably optimal at 30 % water content. Whereas parameters of naphthalene-2-ol sorption reflecting the sorbed amount were mainly altered by the wetting properties of SOM, sorption linearity and hysteresis were influenced by the anomalies in peat matrix properties at a water content around 30 %. The study revealed that the interplay of SOM and water led to highly variable and complex changes in SOM physicochemical properties. These properties may serve as a predictor for sorption of xenobiotics in soil at varying hydration conditions enabling a more precise assessment of the environmental fate of xenobiotics.[PUBLICATION ]
Keywords: Peat ; Rigidity ; SOM-hydration ; Sorption ; WaMB-transition ; Xenobiotics
ISSN: 1439-0108
E-ISSN: 1614-7480
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• 3
Article
Language: English
In: Organic geochemistry, 2012, Vol.47, pp.132-138
Description: Cross-linking of humic substances with organic bridging groups is thought to contribute to the humification of soil organic matter. Model cross-linked humic substances were prepared by cross-linking Amherst soil humic acid by a diepoxide and a polycarboxylic acid, applying procedures established for cross-linking of polymers and textile fabrics. Products of the cross-linking reactions were analyzed by FTIR and ¹³C CPMAS NMR. Physicochemical properties of the products were determined by solubility experiments and thermal analysis. The incorporation of the cross-linker into the matrix of the humic acid by covalent linkages was confirmed by both the disappearance of bands of the reactive functional groups of the cross-linker in the FTIR spectrum and the increase of signals related to the incorporation of the cross-linker into the matrix of the humic acid in the FTIR and ¹³C CPMAS NMR spectra. The formation of covalent ester and ether linkages by the cross-linking reaction was indicated. Water solubilities at pH 6.2 of the cross-linked samples as determined by UV/Vis spectrometry were reduced compared to controls. Fewer water molecule bridges were formed in the cross-linked samples, which was attributed to a lower number of available functional groups and increased distances between humic acid strands caused by the cross-linking molecules. Reduced reactivities of humic acid strands in the cross-linked samples further indicated successful cross-linking. The reactions investigated in this study can be regarded as models for reactions occurring in natural soils to test the significance of cross-linking reactions in the humification process of soil organic matter and the physico-chemical properties and ecological function of organic matter in geosolids. ; p. 132-138.
Keywords: Crosslinking ; Humic Acids ; Humification ; Solubility ; Models ; Thermal Analysis ; Fabrics ; Ecological Function ; Polymers ; Nuclear Magnetic Resonance Spectroscopy ; Ph ; Fourier Transform Infrared Spectroscopy ; Soil
ISSN: 0146-6380
Source: AGRIS (Food and Agriculture Organization of the United Nations)
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• 4
Article
Language: English
In: Organic Geochemistry, June 2012, Vol.47, pp.132-138
Description: ► Humic acid was cross-linked in solid-state reactions with a polycarboxylic acid and a diepoxide. ► Cross-linking reduces water solubility. ► Cross-linking alters thermal properties by reducing the number and strength of water bonds. ► These reactions may serve as models for natural cross-linking of soil organic matter. Cross-linking of humic substances with organic bridging groups is thought to contribute to the humification of soil organic matter. Model cross-linked humic substances were prepared by cross-linking Amherst soil humic acid by a diepoxide and a polycarboxylic acid, applying procedures established for cross-linking of polymers and textile fabrics. Products of the cross-linking reactions were analyzed by FTIR and C CPMAS NMR. Physicochemical properties of the products were determined by solubility experiments and thermal analysis. The incorporation of the cross-linker into the matrix of the humic acid by covalent linkages was confirmed by both the disappearance of bands of the reactive functional groups of the cross-linker in the FTIR spectrum and the increase of signals related to the incorporation of the cross-linker into the matrix of the humic acid in the FTIR and C CPMAS NMR spectra. The formation of covalent ester and ether linkages by the cross-linking reaction was indicated. Water solubilities at pH 6.2 of the cross-linked samples as determined by UV/Vis spectrometry were reduced compared to controls. Fewer water molecule bridges were formed in the cross-linked samples, which was attributed to a lower number of available functional groups and increased distances between humic acid strands caused by the cross-linking molecules. Reduced reactivities of humic acid strands in the cross-linked samples further indicated successful cross-linking. The reactions investigated in this study can be regarded as models for reactions occurring in natural soils to test the significance of cross-linking reactions in the humification process of soil organic matter and the physico-chemical properties and ecological function of organic matter in geosolids.
Keywords: Geology
ISSN: 0146-6380
E-ISSN: 1873-5290
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• 5
Article
Language: English
In: Environmental Chemistry, 2014, Vol.11(6), p.709-718
Description:  The supramolecular structure and resulting physicochemical properties of soil organic matter (SOM) significantly control storage and buffer functions of soils, e.g. for nutrients, organic molecules and water. Multivalent cations, able to form complexes, are suggested to form inter- and intramolecular cross-links in SOM. At present, specific effects of the valence and type of cation on SOM properties are incompletely understood. We investigated changes in SOM interfacial properties, its ability to release mobile colloids in aqueous solutions and its sorption affinity towards organic chemicals in dependence on cation–SOM interactions, temperature and aging time.
Keywords: colloids; contact angle; sorption; X-ray photoelectron spectroscopy.
ISSN: 1448-2517
E-ISSN: 1449-8979
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• 6
Article
Language: English
In: Journal of Thermal Analysis and Calorimetry, 2014, Vol.118(2), pp.1203-1213
Description: Multivalent cations are suggested to influence the supramolecular structure of soil organic matter (SOM) via inter- and intra-molecular interactions with SOM functional groups. In this study, we tested the combined effect of cations, temperature treatment, and isothermal aging on SOM matrix properties. Samples from a peat and a mineral soil were either enriched with Na, Ca, and Al or desalinated in batch experiments. After treatment at 25, 40, 60, and 105 °C and after different periods of aging at 19 °C and 31 % relative humidity, we investigated the physicochemical matrix stability and the thermal stability against combustion. We hypothesized that multivalent cations stabilize the SOM matrix, that these structures disrupt at elevated temperatures, and that aging leads to an increase in matrix stability. The results show that cation-specific effects on matrix rigidity started to evolve in the peat only after 8 weeks of aging and were significantly lower than the temperature effects. Temperature treatment above 40 °C caused a non (or not immediately) reversible loss of water molecule bridges (WaMB) and above 60 °C a partly reversible melting process probably of semi-crystalline poly(methylene). Thermal stability increased with increasing cation valence and degree of protonation and was much less affected by temperature. Generally, Na-treated and control samples revealed lower thermal stability and lower increase in matrix rigidity with aging than those treated with Ca, Al, and H. We conclude that drying at elevated temperatures (〉40 °C) may irreversibly change SOM structure via disruption of labile cross-links and melting of semi-crystalline domains.
Keywords: Cation ; Combustion enthalpy ; Differential scanning calorimetry (DSC) ; Soil organic matter (SOM) ; Step transition
ISSN: 1388-6150
E-ISSN: 1588-2926
E-ISSN: 15728943
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