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Relationships among Adsorbed Phosphate, Silica, and Hydroxyl during Drying and Rewetting of Kaolinite Suspension
Author(s) -
BarYosef B.,
Kafkafi U.,
Lahav N.
Publication year - 1969
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1969.03615995003300050017x
Subject(s) - kaolinite , suspension (topology) , adsorption , chemistry , water content , phosphate , moisture , isothermal process , chromatography , nuclear chemistry , mineralogy , organic chemistry , geology , physics , mathematics , geotechnical engineering , homotopy , pure mathematics , thermodynamics
Kaolinite suspensions after 1 week of equilibration with tagged phosphate solution were dried isothermally (24C) from an initial water: clay weight ratio of 24:1 to 0.89:1. At eight points along the drying process triplicate subsamples were removed and kept sealed until the final point of the drying stage was reached. The concentrations of 31 P, 32 P, and silica were determined in the supernatant. The equilibrium concentration of phosphate in the solution remained unchanged along the drying process. The silica concentration increased while drying, but to a lesser extent than would have occurred in the absence of the clay. The pH changed irregularly within the limits of 6.1 ± 0.4. Kaolinite at a moisture content of 0.89 ml water per 1 g clay was rewetted to the initial water content and equilibrated for seven days. Part of the air‐dried kaolinite was oven‐dried (110C) for 48 hours and then rewetted to its original moisture content. The amount of adsorbed P released into the solution when the pH increased from 6.5 to 11.0 was smaller in the oven‐dried clay than in the air‐dried sample. This is attributed to an increase in the negative charge of the surface of the oven‐dried kaolinite. Increasing the pH, the silica was readsorbed to a maximum at pH 9.2, as expected, and released at higher pH values in accordance with the negative surface charge.