The role of iron oxides and organic matter on phosphate adsorption in model allophanic synthetic soils

Maria de la Luz Mora G.1, Gerardo Galindo G.2 y Mauricio Escudey C.2

The role of the organic matter and iron oxides in P adsorption process was studied in a synthetic allophane compound under pH 5.5 and 0.1 M KCI. Iron oxide coatings on allophane surfaces produced an increase in both surface acidity and active sites. Associated to this fact there appeared an increase around 40% in P maximun adsorption capacity by means of Langmuir model. The P complexation constants calculated using the Constant Capacitance model showed a higher affinity in those compounds containnig iron oxides. The organic matter decreased P adsorption capacity as a consequece of a blocking effect on the surface.

Keywords: ferrihydrite, organic matter, allophane, P adsorption.
1 Departamento de Ciencias Químicas, Universidad de La Frontera, Casilla 54-D, Temuco, Chile.
2 Departamento de Química, Universidad de Santiago, Santiago, Chile.