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Journal of Minerals & Materials Characterization & Engineering, Vol. 1, No.2, pp131-140, 2002Printed in the USA. All rights reserved131 ADSORPTION OF SURFACTANT DISPERSED Nanometer MAGNETITE J. Y. HWANG Michigan Technological University, Institute of Materials Processing 1400 Townsend Drive, Houghton, MI 49931 ABSTRACT Processing of fine particles in a slurry is a difficult problem. Methods to make fine particles magnetic have been developed recently and may offer a solution to this problem. Particles of nonmagnetic Materials can be selectively rendered magnetic through surface interactions with magnetic reagents, which are prepared by dispersing nanoscale magnetite (about 10 nm diameter) with surfactants. When adsorption occurs, the magnetic susceptibility of the material isincreased. Magnetic enhancement at several orders of magnitude can be achieved. Selectivity of the adsorption can be controlled by the functional groups of magnetic reagents and various surface interaction mechanisms. This approachallows a new degree of freedom for the processing of fine particles, even with conventional magnetic means. Separation and filtration are examples of theapplications.Keyword: nanomaterial, dispersion, flocculation, magnetic reagent, magnetic enhancement, separation.
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J. Y. Hwang Vo1. 1, No. 2 132 INTRODUCTION The behavior of fine particles in a slurry is difficult to control, presenting a serious problem for the processing of fine particles in many industries. At fine particle sizes, gravitational force is weak. Electrostatic force, although strong in dry conditions, can rarely be applied for particles in an aqueous slurry. The applications using magnetic force are limited because most materials are diamagnetic to weakly paramagnetic. Without being able to use these forces effectively, the movement of fine particles can hardly be controlled. There are methods to agglomerate fine particles into flocs, which allows effective applications of gravitational force [1, 2]. Co-flocculation of fine particles with magnetic particles also allows the use of magnetic force [3, 4]. However, these approaches may not be desirable because there are many processes which require fine particles to stay in the dispersed state. Thus, there is a need to develop methods to control the movement of individual particles. Methods to increase the magnetic properties of fine particles are introduced in this study. Based on the magnetic reagent technology developed at Michigan Technological University [5, 6, 7], it has been found that magnetic properties of particles can be increased by several orders of magnitude through the adsorption of a magnetic reagent. Thus, a new degree of freedom can be utilized for the processing of fine particles of nonmagnetic materials. Through the use ofmagnetic means, movement of fine particles with enhanced magnetic properties can be controlled. These particles can be separated, collected, immobilized, or filtered. Manyapplications can then be developed. MAGNETIC REAGENT AND ITS FUNCTIONS A magnetic reagent is a composite of magnetic materials and surface active agents. The surface active agents contain functional groups which can react with magnetic materials and other materials. Under appropriate conditions, the agents can serve as a bridge to couplemagnetic materials to other materials. Thus, the composite of magnetic materials and surface active agents with the capabilities to couple other materials is a magnetic reagent. In many applications, a magnetic reagent is prepared by building two layers of surfactants on colloidal (Nanometer size in most cases) magnetite. The inner layer surfactant has a functional group with an affinity to magnetite. Fatty acid, such as oleic acid, is an example. After coveringthe surface of magnetite with the inner layer of surfactants, an outer layer surfactant can be built on top of the inner layer surfactant through hydrophobic interactions. The functional group of the outer layer will orient outward from the magnetite and provide the capability for coupling withnonmagnetic Materials. Since the functional group of the outer layer can be tailored, selectivity on the coupling can then be controlled.