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Phosphate Desorption from Goethite in the Presence of Galacturonate, Polygalacturonate, and Maize Mucigel (Zea mays L.)

^a Institute of Ecology, Berlin Univ. of Technology, Salzufer 12, D-10587 Berlin, Germany
^b Institute for Plant Nutrition, Univ. of Hohenheim, Fuwirthstr. 20, D-70593 Stuttgart, Germany

View larger version (15K): [in a new window]   Fig. 1. X-ray diffractogram of the maize mucigel used in this study. Abbreviations: C, calcite; G, gypsum; L, 1:1 layer silicate; Q, quartz.

View larger version (24K): [in a new window]   Fig. 2. Fractional desorption of PO4 in 0.01 M KNO3 background electrolyte at pH 5 with a solid concentration of 2 g L–1: (a) organic matter (OM) sorbed to phosphated goethite and (b) PO4 sorbed to OM-treated goethite. Abbreviations used: P, phosphate; GA, galacturonate; PGA, polygalacturonate; MU, mucigel. Sequence of abbreviations indicates the sequence of sorbate addition. Dashed lines are the model fits using Eq.[1]. Error bars are given as standard errors of three replicate measurements.

View larger version (101K): [in a new window]   Fig. 3. Scanning electron microscopy images of microaggregates of freeze-dried PGA-treated goethite (top) and mucigel-treated goethite (bottom). Insets show representative EDX-spectra of polygalcturonate- and mucigel-treated goethites.

View larger version (20K): [in a new window]   Fig. 4. -Potential of C-free, polygalcturonate- and mucigel-treated goethites during phosphate desorption. After each reaction time about 200 µg of freeze-dried 0.45-µm filter residue were resuspended into 4 mL of 0.01 M KNO3 at pH 5. Sequence of abbreviations indicates the sequence of sorbate addition. Error bars are given as standard errors.

View larger version (17K): [in a new window]   Fig. 5. Difference in the amount of PO4 sorbed (15 d) and desorbed (14 d) between pure goethite and organic matter-treated goethites (P). Abbreviations used: P, phosphate; GA, galacturonate; PGA, polygalacturonate; MU, mucigel. Sequence of abbreviations indicates the sequence of sorbate addition. Error bars denote standard error.