Separation of Nonmagnetic Metals From Solid Waste by Permanent Magnets. Pt. 1. Theory

A new method of separating nonmagnetic metals (Al, Cu, Sn and Zn) from solid waste is described. The process makes use of the much higher electrical conductivity of metals as compared to that of glass, ceramics and wood. The separation is achieved by means of a ramp which has permanent magnets embedded in its surface. The magnets are arranged in stripes of alternating polarity at 45 degrees to the ramp axis. Nonconducting particles will slide straight down the ramp, whereas conducting particles will be deflected laterally. The amount of deflection has been calculated as a function of the length and inclination of the ramp, the period and strength of the magnets at the ramp surface, the conductivity, density, shape, size and initial velocity of the particles and the coefficient of sliding friction between particles and ramp. The deflection is proportional to the ratio of electrical conductivity to mass density and varies sub stantially as the 3/2 power of the ramp length. If the particle diameter is small compared to the magnet period, the deflection varies as the square of the diameter. In the converse case the deflection is substantially independent of the particle size. 15 ref.--AA.