HOME HELP FEEDBACK SUBSCRIPTIONS ARCHIVE SEARCH TABLE OF CONTENTS		QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Similar articles in this journal Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Anderson, S. J. Articles by Steyer, K. J. Search for Related Content PubMed Articles by Anderson, S. J. Articles by Steyer, K. J. Agricola Articles by Anderson, S. J. Articles by Steyer, K. J.

Effect of Colloidal Goethite and Kaolinite on Colorimetric Phosphate Analysis

Dep. of Crop and Soil Sciences, Michigan State Univ., East Lansing, MI 48824-1325.

^* Corresponding author (ander102{at}pilot.msw.edu).

ABSTRACT

Filtration through 0.45-µm filters provides a convenient and widely used operational separation between dissolved and particulate P, yet colloidal P is included in the filtrate with true dissolved P. In addition, centrifugation is often used to separate solids from solution during PO₄ sorption experiments, but colloids can be present in the supernatant solution. It is not known whether colloid-sorbed PO₄ is detected colorimetrically in solutions that have not been pretreated to release colloidal PO₄. The objectives of this research were to determine whether colloid-sorbed PO₄ is detected colorimetrically and whether the type and size of colloid, the pH during PO₄ sorption, or the sorption reaction time affect the extent to which colloid-sorbed PO₄ is detected colorimetrically. To accomplish these objectives, 10 mg L^–1 suspensions of 40- to 100-nm and 100- to 450-nm kaolinite and goethite were reacted with sodium phosphate solutions (4, 8, and 16 µM PO₄) at pH 4.5 and 7 in 10 mM NaCl for 1 and 10 d. The concentration of PO₄ that was not detected colorimetrically in the presence of colloids (i.e., nonreactive PO₄) was calculated as the difference between PO₄ in colloid-free blanks and colloid-containing samples, whereas PO₄ sorption was measured in samples that had been ultrafiltered through a 4-nm membrane to separate colloids from solution. Nonreactive PO₄, which represents the fraction of sorbed PO₄ for which desorption kinetics are slow compared with the colorimetric analysis time, ranged from 2% to >35% of total PO₄ (P_tot) and from 20 to 100% of sorbed PO₄, depending upon P_tot, colloid type, and reaction time. Nonreactive PO₄ was about two times greater after 10-d than 1-d reaction and about 1.4 times greater for large than small colloids, even though small colloids sorbed more PO₄. Nonreactive PO₄ was greater at pH 4.5 than 7 and was greater for goethite than kaolinite. Nonreactive PO₄ was independent of P_tot, although sorbed PO₄ increased with increasing P_tot. Thus, each type of colloid apparently has a finite capacity to retain sorbed PO₄ in nonreactive sites. Because sorbed PO₄ is not uniformly detected colorimetrically, accurate quantitation of the colloid-sorbed PO₄ will require additional pretreatmeats such as dissolution of the colloids in strong acid.

This article has been cited by other articles:

				A. J. Franzluebbers, J. A. Stuedemann, and S. R. Wilkinson Bermudagrass Management in the Southern Piedmont USA. II. Soil Phosphorus Soil Sci. Soc. Am. J., January 1, 2002; 66(1): 291 - 298. [Abstract] [Full Text] [PDF]