Adsorption of Phosphate on Goethite. An Undergraduate Research Laboratory Project
Lorena Tribe
Pennsylvania State University Berks–Lehigh Valley, Reading, PA 19610-6009
Beatriz C. Barja
INQUIMAE, Facultad de Ciencias Exactas y Naturales, Universidad Buenos Aires Ciudad Universitaria–Pab. II, 1428 Capital Federal, Argentina
We present a freshman laboratory experiment on the adsorption of phosphate on goethite as a case study that opens the doors to the discussion of surface properties, interphases, acid–base equilibrium, molecular structure, and solid state chemistry, among other topics. We also describe a pedagogical implementation of this experiment that allows the students to work cooperatively, enhancing the feeling of community of the course. In this work students approach the study of adsorption of phosphate on an iron oxide as a function of pH, total ligand concentration, and ionic strength of the solution. This is achieved by adding an aqueous solution of sodium phosphate of known concentration to a suspension of goethite, allowing the system to equilibrate and then determining the concentration of phosphate not adsorbed on the surface of the oxide in the supernatant solution. These experiments are performed in different pH and ionic strength conditions to evaluate the role of these variables on the adsorption processes. Students were able to observe that the adsorption of phosphate increased with decreasing pH while it was not appreciably affected by the ionic strength of the solution.
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