Ferrofluids for Sink Float Separation

The importance of recovering resources from waste materials is an important and pressing problem. The rapid and inexpensive recovery of non-ferrous metals from solid wastes such as automobiles, electrical appliances or indeed any solid waste enables one not only to recycle valuable materials but also to benefit the environment.

The system used for sink-float separations consists of an electromagnet, separation chambers and the means to recover or remove the magnetic fluid coating the recovered materials.

By simply increasing the current in an electromagnet, arranged to produce a field gradient, it is possible to levitate materials of increasing densities to the surface of the magnetic fluid in a systematic way, thereby facilitating separation and recovery.

For example a mixture of metals, such as lead, copper, zinc and aluminium having a wide range of densities can be separated and recovered. The principle behind the process, is that the presence of a field gradient imparts a force to the scrap fragments (V is volume, M magnetisation of the fluid and the magnetic field gradient) which produces levitation thereby overcoming gravitational sedimentation.

The concentration of the ferrite particles is approximately 10% by volume, thereby having a saturation magnetisation of 400 Gauss.