Adsorption of monoalkyl phosphates at the zircon-aqueous solution interface

The adsorption of a series of monoalkyl phosphates (MAP) of varying alkyl c hain lengths (C-n) on a pure natural sample of zircon (ZrSiO4) at 25 degree s C has been studied as a function of concentration and pH. Electrokinetic (S-potential) studies showed a significant shift of the isoelectric point o f zircon (pH similar to 5.7) to lower pH values, indicating specific intera ctions between zircon and MAP. Diffuse reflectance infrared Fourier transfo rm spectroscopy and pH increment studies suggested that adsorption of MAP o nto zircon proceeded via chelate formation. Adsorption was aided by an attr active lateral alkyl chain interaction energy (phi) of approximately -0.85k T per CH2 group, which suggested that surface aggregates form on the zircon surface. Adsorption isotherms were best described by a Langmuir model, ind icating that attractive lateral alkyl chain interactions were compensated b y repulsive headgroup interactions, resulting in a pseudo-ideal system. (C) 1998 Academic Press.