A review of principles and applications of magnetic flocculation to separate ultrafine magnetic particles

•The principles of magnetic separation have been critically reviewed.•Both external and interparticle forces for ultrafine particles are reviewed and compared.•Suspensions stability of the particles factors are described and analyzed.•Various modeling of magnetic flocculation are introduced and some of the applications are illustrated. Magnetic separation has been used in industries to concentrate or remove magnetic minerals/particles for many years. The separation of ultrafine magnetic particles is significantly influenced by aggregation between particles due to various external and interparticle forces, such as gravity, magnetic attraction, van der Waals, electrical double-layer, hydrodynamic, and Brownian diffusion forces. This review focuses on the principles of the magnetic flocculation and separation of micrometer-sized particles in solution. Potential energies between particles are linked to the particle aggregation (i.e. stability), sedimentation and dispersion in applied magnetic fields. Prediction and control of magnetic flocculation are achieved by simulating particle motions around the surface of the magnetic separators using various mathematical models, with some large-scale applications of magnetic flocculation are being demonstrated.