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Acid Polysaccharide Coatings on Microporous Goethites

Controls of Slow Phosphate Sorption

Dep. of Soil Science, Institute of Ecology, Berlin Univ. of Technology, Salzufer 12, D-10587 Berlin, Germany

View larger version (31K): [in a new window]   Fig. 1. Phosphate sorption kinetics of freeze-dried and nondried pure and PGA-coated goethites. Solid lines show the predicted values using the combined model of Eq. [1]. Values in parentheses refer to the initial C content in mmol C g–1.

View larger version (16K): [in a new window]   Fig. 2. Apparent diffusion constants (D/r2)app of freeze-dried pure and PGA-coated goethites versus the CO2 micropore volume present before phosphate sorption. Bidirectional error bars indicate SE. Values in parentheses indicate the C content in mmol C g–1.

View larger version (24K): [in a new window]   Fig. 3. Polygalacturonate-C desorption from goethites during phosphate sorption for 3 wk. Solid lines indicate the fit of Eq. [1] to the C desorption data of goethites with high C loadings. Coefficients of determination were >0.97. Average SE of total organic C measurements was 27 µmol g–1; the maximum SE recorded was 78 µmol g–1 (n = 80).

View larger version (20K): [in a new window]   Fig. 4. Changes in the molar ratio of PGA-C desorbed and phosphate sorbed of freeze-dried and nondried PGA-coated goethites with high C loadings during phosphate sorption for 3 wk. The mean SE of the molar Cdes/Psorb ratios was 0.2. The x axis is in logarithmic scale.

View larger version (16K): [in a new window]   Fig. 5. -Potential changes during phosphate sorption of freeze-dried uncoated and PGA-coated goethites at the highest PGA-level. The solid lines show linear regressions. Error bars are SE. Values in parentheses represent the C loading in mmol C g–1. Initial -potentials (mV) at pH 5 in 0.01 M KNO3 were: G1: 29.8 ± 3.5, G2: 29.1 ± 0.5, G1 (1.76): –29.0 ± 3.6, G2 (1.43): –28.5 ± 1.2. The x axis is in logarithmic scale.

View larger version (31K): [in a new window]   Fig. 6. Plots of phosphate sorbed versus PGA-C desorbed for (a) freeze-dried and (b) nondried PGA-coated goethites. Values in parentheses refer to the amount of PGA-C initially present in the samples in mmol C g–1.