High-Gradient Magnetic Separation of Magnetic Nanoclusters

The capture of magnetic nanoclusters in high-gradient magnetic separation (HGMS) operations, the rate-limiting step in magnetic nanoparticle-based separations and chemical processing, was studied experimentally, and a new model for HGMS capture that extends current single-wire models to column behavior was developed. Clusters >50 nm were captured very efficiently (>99.9%) at high flow rates. When a sufficiently long column was used, the lost particles were almost entirely single nanoparticles that were significantly smaller (<30 nm) than the average cluster size. When these small nanoparticles are removed, capture can be improved significantly. The column model allows quantitative prediction of HGMS capture over a wide range of conditions, whereas analysis of the limiting condition of an infinite number of stages yields new parameters that can be calculated much more simply than with the full-column model. These parameters can be used for quantitative estimates of the maximum capture efficiency and capacity of the HGMS column and can be calculated as simply as previous models that provided only qualitative information.