(3) Magnetic fluids hydrocyclones. Magnetic fluids hydrocyclones can be employed to enhance the separation and classification of natural non-magnetic mineral particles by treating the water-based mag- netic fluids, that is, ferrofluids, as medium. By putting the hydro- cyclone in an outside magnetic field, magnetic fluids hydrocyclones combine the centrifugal separation principle with the magnetohy- drostatic suspension principle, and can successfully enhance the hydrocyclone separation with magnetic force, especially for the particles with size of < 100 μm.(4) Electrochemical hydrocyclones. Electrochemical hydrocyclones, which combine the electro-deposition process with the centrifugal separation process, are primarily utilized for the electrolytic re- covery of valuable metals, such as the gold, silver, and copper, from dilute solutions.(5) Flocculant-assisted hydrocyclones. Several Flocculants can ag- glomerate particles in hydrocyclones feed to form flocs, which re- sults in that the flocculant dosage is proportional to the solid con- centration in underflow, whereas is inversely proportional to the solid concentration in overflow. Therefore, the flocculant can en- hance the hydrocyclone separation. Different kinds of flocculant can enhance the separation efficiency in various degree. Compared with addition of flocculant to the pump outlet, the addition of flocculant to the pump outlet yields higher separation efficiency.(6) Hydrocyclones enhanced by flotation. Not only hydrocyclones can be successfully used to extend the flotation limit, but also the flo- tation could be effectively employed to enhance the hydrocyclone separation of dissolved solid particles, oil and fibres. To date, available hydrocyclones enhanced by flotation are main used for oil removal from liquid, and can be classified into two groups ac- cording to the approaches adding air bubbles: (i) the hydrocyclone using an air-liquid mixing pump and an air-liquid separation pot; and (ii) the air-injection hydrocyclone. For both of them, there does exist an optimum air-liquid ratio for hydrocyclone separation. For the air-injection hydrocyclones, (i) the vortex finder diameter of the air-injection hydrocyclone should be larger than the hydrocyclone without air injection. (ii) The micro-pore diameter is proportional to the separation efficiency. (iii) The best separation efficiency can be got by the first one third fine-cone injection.