Coagulation of Iron Oxide Particles in the Presence of Organic Materials

Abstract

Experiments using hematite particles (70 nm in diameter) in the presence of organics (phthalic acid, fatty acids, polyaspartic acid, fulvic and humic acid) reveal important features of particle coagulation dynamics. A light scattering technique was used to determine quantitatively the initial coagulation rates of hematite particles. Electrokinetic measurements were taken to obtain the sign and magnitude of electrical potential at the oxide/aqueous solution interface. Adsorption experiments were carried out to evaluate affinities of aqueous molecules for the metal oxide surface. Intrinsic equilibrium constants for surface complexes are derived from a Surface Complex Formation/Diffuse Layer Model (SCF/DLM) accounting for interfacial electrostatic charge and potential. Small organic molecules, such as phthalate, show specific chemical reaction with the hematite surface and influence colloidal hematite coagulation kinetics by altering interfacial charge and potential. For fatty acids, hydrophobic interaction, in addition to covalent and electrostatic interaction, offers a plausible explanation for observed systematic changes in hematite stability and electrokinetic data. In the presence of polyelectrolytes, such as polyaspartic acid, fulvic and humic acids, a combination of specific chemical, electrostatic, and hydrophobic energies of carboxyl segments favors adsorption, and these materials have a relatively great impact on particle coagulation and stability.

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