FEASIBILITY AND LIMITATIONS OF NANOLEVEL HIGH-GRADIENT MAGNETIC SEPARATION

This work proposes a new separation concept denoted as nanolevel high gradient magnetic separation (HGMS) or magnetic adsorption. A magnetic heteroflocculation model describes the magnetic forces between two sp herical particles with different sizes and magnetic properties, and re veals the feasibilities and limitations of nanolevel HGMS. The adsorbe nt particles, composed of antiferromagnetic magnetite, are modeled as large, immobile spheres on the order of 100-500 nm in radius. The adso rbate, paramagnetic colloidal Fe(OH)(2) particles, are treated as free ly diffusing small spheres on the order of 20-80 nm in radius. The mod el assumes that the magnetite particles are dispersed throughout a por ous, nonmagnetic, solid matrix and that they are free of convective fo rces. The model also assumes that magnetic forces alone act on the Fe( OH), particles, opposed only by Brownian motion. When the magnetic for ce is attractive and overwhelms the randomizing Brownian force, adsorp tion occurs. The results from this model show the importance of the ex ternal held strength, the sizes of the adsorbent and adsorbate particl es, and their magnetic properties in developing a practical nanolevel HGMS process. (C) 1997 Elsevier Science B.V.