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Scholars Day 2005, Wednesday, April 13

Influence of Solution Composition on Phosphate Sorption on Gypsum

Phosphate is common in aquatic systems at concentrations typically below 20 ug L-1. In impacted systems, concentrations may reach 1 mg L-1 or more, causing excess growth of phytoplankton and ultimately eutrophication. In an effort to minimize the impact of anthropogenic sources of phosphate, we investigated its sorption by gypsum. Results in all the sample electrolyte solutions conform to an L-shaped isotherm. This suggests that gypsum has an affinity for phosphate, but a limited number of sorption sites exist. Evaluating the data using the Langmuir isotherm indicates that phosphate sorption is slightly preferred at pH 6 for both Ca and Na backgrounds, and little difference in sorption is seen between the Ca and Na solutions at equivalent pH values. Sorption did not fit well to a Langmuir isotherm for the 0.01 M Ca solution. Phosphate’s affinity for Ca may be producing the precipitation of a Ca-phosphate phase.

Presenter: Carolyn Schutt (Undergraduate Student)
Topic: Geology
Location: 218 Lennon
Time: 1:30 pm (Session III)

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