Classification by ferrofluid density separation

Claim 1

A method of separating substantially non-magnetic particles of different densities where alone or in combination, the product of the difference in particle density and particle diameter is at most 5 gr/cm 2 or the difference in particle density is at most 0.1 gr/cm 3 or the particle diameter is at most 1 cm comprising: immersing said particles in a ferrofluid with a magnetic dipole moment of M, M being computed from the ratio of particle attraction forces (F ss ) to particle separation forces (F 1 ) to be applied by the magnetized ferrofluid, and said ratio being made less than 10 where: ##EQU10## M = magnetic dipole moment per unit volume of ferrofluid ρ2 = density of the more dense particles ρ1 = density of the less dense particles D = dimeter of the particles g = acceleration of gravity; cm/sec 2 a = center to center spacing between particles applying a magnetic field to said ferrofluid capable of overcoming the forces produced by gravity and interparticle magnetic attraction to levitate the least dense particles in said ferrofluid, whereby the particles are classified into relatively pure fractions; and collecting the individual fractions.

Claim 2

A method of separating substantially non-magnetic particles of different densities where alone or in combination, the product of the difference in particle density and particle diameter is at most 5 gr/cm 2 or the difference in particle density is at most 0.1 gr/cm 3 or the particle diameter is at most 1 cm comprising: immersing said particles in a ferrofluid with a magnetic dipole moment of M, M being computed from the ratio of particle attraction forces (F ss ) to particle separation forces (F 1 ) to be applied by the magnetized ferrofluid, and said ratio being made less than 10 where: ##EQU10## M = magnetic dipole moment per unit volume of ferrofluid ρ2 = density of the more dense particles ρ1 = density of the less dense particles D = dimeter of the particles g = acceleration of gravity; cm/sec 2 a = center to center spacing between particles applying a magnetic field to said ferrofluid capable of overcoming the forces produced by gravity and interparticle magnetic attraction to levitate the least dense particles in said ferrofluid, whereby the particles are classified into relatively pure fractions; and collecting the individual fractions.