at which centrifugal force on material in the cylinder is equal to or greater than the force of gravity the water and soluble components of the saltcake combine in the mill to form a brine in which the insoluble particles are kept in suspension by the rotation of the cylinder saltcake and water are fed continuously to the cylinder and a portion of the slurry is continuously withdrawn the slurry goes to a pair of concentric trommel screens the outer screen having a finer mesh than the inner screen in one embodiment of the invention the outer screen was 30 mesh and the inner screen was 12 mesh particles having a diameter from 4 inches to 12 mesh are fifty to eighty percent by weight metallic aluminum and are recycled in the same manner as dross the particles are melted in a furnace and the aluminum is cast into rsi recycled secondary ingot sows rsi is used for example in the automotive industry particles passing through the inner screen and not the outer screen e g 12 mesh to 30 mesh are twenty five to fifty percent metal and are used as exothermics by the steel industry the amount of aluminum recovered from the trommel screens especially the amount of 12 mesh 30 mesh particles of aluminum is monitored to control the feed rate of saltcake and water to the cylinder in the mill for optimum aluminum production maximum total aluminum and minimum 30 mesh.