Kooperativer Bibliotheksverbund

Berlin Brandenburg

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  • 1
    Language: English
    In: Colloids and surfaces, 2012, Vol.399, pp.35-40
    Description: Soil colloid science requires the separation of the colloids from larger particles in suspensions, which is frequently achieved by filtration. However, the results of filtration may be biased due to (i) pore clogging and (ii) the formation of a filter cake. In order to quantify these effects, we filtrated different volumes of soil suspensions containing mainly mineral (M), mainly organic (O) or mineral and organic (MO) colloids through 1.2μm membranes. Turbidity and the concentrations of colloid-bound C, Si and Al were measured in the filtrates and, as a reference, in centrifugates of the suspensions. To exclude the influence of the filter cake and examine only pore clogging effects, we conducted the same filtration experiment with suspensions which have been pre-treated by a centrifugal elimination of particles 〉3μm. Finally, we scanned a membrane after filtration with an electron microscope for the visualisation of possible pore clogging. Turbidity and concentrations of colloid-bound Al and Si in the filtrates of the pre-treated suspensions were one order of magnitude lower than in centrifugates. This discrepancy was most pronounced for M suspensions which indicates that filters preferentially remove mineral colloids. Microscope images revealed no sign for pore clogging and smaller filtrated suspension volumes did not lead to more colloid recovery in pre-treated filtrates. We assume that the colloids are retained within the thick, multilayered structure of the filter without clogging the main pores. When filter cakes are forming (experiment without previous centrifugation), turbidity and concentrations of colloid-bound Al, Si and C decrease with increasing filtration volume. However, the retaining effect of filter cakes seems negligible compared to the retaining effect within the filter. We conclude that the composition of soil colloidal suspensions depends significantly on the technique which is used to remove larger particles. Filtration underestimates the amount of colloids in suspension and centrifugation should be preferred as separation method at least for soils with colloids of similar density, either M or O. ; p. 35-40.
    Keywords: Colloids ; Filtrates ; Centrifugation ; Filtration ; Aluminum ; Turbidity ; Soil Colloids ; Silicon ; Filter Cake ; Soil
    ISSN: 0927-7757
    Source: AGRIS (Food and Agriculture Organization of the United Nations)
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  • 2
    Language: English
    In: Journal of environmental quality, 2009, Vol.38(3), pp.933-9
    Description: Liming is a common technique suggested for the stabilization of shooting range sites. We investigated the effect of an increase in pH on the mobilization of soluble and dispersible (colloidal) Pb, As, and Sb. Our hypothesis was that the addition of divalent cations counteracts the pH-induced mobilization of soluble and colloidal metal(loid)s. We determined soluble (operationally defined as the fraction 〈 10 nm obtained after centrifugation) and dispersible (filter cut-off 1200 nm) As, Pb, Sb, Fe, and C(org) concentrations in the filtered suspensions of batch extracts of topsoil samples (C(org): 8%) from a former shooting range site following a pH increase to values between 3.5 and 7 by adding a monovalent (KOH) or a divalent (Ca(OH)(2)) base. In the Ca(OH)(2)-treated samples, dissolved metal(loid) concentrations were 62 to 98% lower than those titrated with KOH to similar pH. Similarly, Ca reduced the concentration of dispersible Pb by 95%, but had little or no impact on dispersible As and Sb. We conclude that the counterion valency controls the mobility of metal(loid)s by affecting the mobility and sorption capacity of the sorbents (e.g., colloids, organic matter).
    Keywords: Antimony -- Chemistry ; Arsenic -- Chemistry ; Cations, Divalent -- Chemistry ; Lead -- Chemistry ; Soil -- Analysis
    ISSN: 0047-2425
    E-ISSN: 15372537
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  • 3
    Language: English
    In: Journal of environmental quality, 2007, Vol.36(4), pp.1187-93
    Description: Drying of soil may increase the hydrophobicity of soil and affect the mobilization of colloids after re-wetting. Results of previous research suggest that colloid hydrophobicity is an important parameter in controlling the retention of colloids and colloid-associated substances in soils. We tested the hypothesis that air-drying of soil samples increases the hydrophobicity of water-dispersible colloids and whether air-drying affects the mobilization of colloid-associated heavy metals. We performed batch experiments with field-moist and air-dried (25 degrees C) soils from a former sewage farm (sandy loam), a municipal park (loamy sand), and a shooting range site (loamy sand with 25% C(org)). The filtered suspensions (〈1.2 microm) were analyzed for concentrations of dissolved and colloidal organic C and heavy metals (Cu, Cd, Pb, Zn), average colloid size, zeta potential, and turbidity. The hydrophobicity of colloids was determined by their partitioning between a hydrophobic solid and a hydrophilic aqueous phase. Drying increased hydrophobicity of the solid phase but did not affect the hydrophobicity of the dispersed colloids. Drying decreased the amount of mobilized mineral and (organo-)mineral colloids in the sewage farm soils but increased the mobilization of organic colloids in the C-rich shooting range soil. Dried samples released less colloid-bound Cd and Zn than field-moist samples. Drying-induced mobilization of dissolved organic C caused a redistribution of Cu from the colloidal to the dissolved phase. We conclude that drying-induced colloid mobilization is not caused by a change in the physicochemical properties of the colloids. Therefore, it is likely that the mobilization of colloids in the field is caused by increasing shear forces or the disintegration of aggregates.
    Keywords: Desiccation ; Hydrophobic and Hydrophilic Interactions ; Colloids -- Chemistry ; Metals, Heavy -- Analysis ; Soil -- Analysis
    ISSN: 0047-2425
    E-ISSN: 15372537
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  • 4
    Language: English
    In: Soil Science Society of America journal, 2008, Vol.72(6), pp.1694-1707
    Description: Proton nuclear magnetic resonance (1H NMR) relaxometry has been used to analyze pore size distributions of wet porous samples. To make this method applicable to soil samples, knowledge about contribution from the soil solution to the total proton relaxation is needed. We extracted soil solutions from nine soil samples and determined transverse proton relaxation rates, the concentration of Fe, Mn, and total organic C (TOC), and the pH of the solutions. The effects of Fe, Mn, and TOC on the proton relaxation in the soil solution were compared with those of dissolved Fe2+, Fe3+, and Mn2+ and of glucose, D-cellobiose, potassium hydrogen phthalate, sodium alginate, and agar in model solutions. Proton relaxation rates in the soil solutions were up to 20 times larger than in pure water, which was mainly due to dissolved Fe(III) and Mn(II) species. The relaxivities of Fe and Mn in soil solution were reduced to 40 and 70% compared with Fe(III) and Mn(II) in a model solution, respectively. Smaller relaxivities were primarily due to the formation of metal-organic complexes. We conclude that the proton relaxation in soil samples is generally accelerated by the soil solution, and its contribution must be considered to estimate pore sizes from relaxation times. By using the calculated relaxivities of Fe and Mn in soil solution, the contribution of the soil solution to the total proton relaxation can be estimated from the Fe and Mn concentration in the soil solution. ; Includes references ; p. 1694-1707.
    Keywords: Soil Organic Carbon ; Goethite ; Cellobiose ; Soil Solution ; Agar ; Soil Pore System ; Manganese ; Ions ; Iron ; Colloids ; Sampling ; Alginates ; Glucose ; Extracts ; Chemical Concentration ; Chemical Composition ; Nuclear Magnetic Resonance Spectroscopy ; Montmorillonite ; Sodium Alginate ; Pore Size Distribution ; Proton Relaxation ; Potassium Hydrogen Phthalate
    ISSN: 0361-5995
    E-ISSN: 14350661
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