Purification of contaminated alumina scavengers of aluminum reduction cell effluent dry scrubber systems

In the process of removing metallic and nonmetallic impurities from contaminated alumina scavengers recovered from dry scrubber systems used for purification of aluminum reduction cell effluents, the improvement which comprises preparing a slurry from the contaminated alumina scavenger and a liquid selected from the group consisting of water, polar and nonpolar organic solvents, subjecting the slurry to an ultrasonic treatment at a frequency of at least about 10 kHz for a time period sufficient to remove a desired quantity of metallic and nonmetallic impurities from the alumina scavenger, separating the liquid containing these impurities in dispersed form from the treated scavenger, recovering purified solid alumina of significantly reduced impurity content and recycling the purified alumina to the aluminum reduction cell or to the dry scrubber system.