A THEORY FOR AGGLOMERATION AND SEDIMENTATION OF FERROMAGNETIC PARTICLES SUSPENDED IN A HYDROCARBON LIQUID AND EXPOSED TO A MAGNETIC-FIELD

Recently S.C. Saxena, R.S. Miao, M.J. McNallen and M. Shalaby, AIChEJ. , 40 (1994) 1594 [1] have shown that an iron powder suspended in a hyd rocarbon liquid (Therminol-66) can be effectively separated by sedimen tation after magnetization in an external magnetic field. A simple two -step mechanistic model is developed here to analyze quantitatively th e separation process data involving the settling rates of group agglom erates. In the first step, the ferromagnetic particles are magnetized, arranged and then pulled together in the magnetic field to form 'part icle agglomerates'. In the second step, these particle agglomerates se ttle under gravity only and grow further in size by collision to form 'group agglomerates'. These group agglomerates settle at a much faster rate because of their large size than the original particles in the u ntreated powder or the particle agglomerates formed in the magnetic fi eld. The proposed mathematical model in conjunction with the experimen tal data of Saxena and coworkers [1] has enabled the average diameters of particle agglomerates and group agglomerates to be estimated. It i s concluded that this technology has the promise and potential to be e mployed effectively to separate fine micron size catalyst particles of magnetizable materials suspended in a hydrocarbon liquid. More detail ed investigations are warrented to form a basis for elaborate detailed and sound design of separation unit equipment as well as for better u nderstanding of the structural characteristics of particle and group a gglomerates.