Recovery of non-ferrous metals by means of permanent magnets

Abstract

A technique for recovery of non-ferrous metals from municipal solid waste has been demonstrated. The technique may also be applied to separating non-ferrous metals from each other or to separating non-ferrous metals contained in automobile scrap. The apparatus has no moving parts and consumes no electrical power. It consists of an inclined ramp on which non-ferrous metals are deflected to one side as they slide down. Deflection results from eddy currents induced by permanent magnets embedded in the ramp surface. A detailed theory has been developed that allows to predict the deflection of metallic particles from the straight-down path as a function of all the relevant physical parameters. The deflection was measured on circular discs of aluminum, copper, zinc, brass, lead, and stainless steel as a function of the ramp inclination, disc thickness, disc diameter, distance of the discs to the magnet face, and initial velocity. Good agreement with theoretical predictions is observed in all cases. Tests have also been conducted on the heavy-fraction remaining after air classification of municipal solid waste. A laboratory separator has been tested at heavy fraction feed rates of 1 ton per hour which correspond to a feed rate of 15 tons per hour of municipal solid waste to a resource recovery plant. The concentration of non-ferrous metals contained in the heavy fraction is increased from 15 percent to 90 percent in a single pass with corresponding recovery efficiencies of 80 percent. Separator efficiency is given as a function of feed rate and moisture content.