Patent ID: 7448500

Claim:
A method of separating particulate material of differing size or density, the method comprising: feeding the particulate material into a rotatable vessel having a volumetric capacity, wherein the particulate material is fed into the vessel so that the particulate material occupies less than 50% of the volumetric capacity; rotating the vessel at a rotation rate to tumble the particulate material, the rotation rate satisfying the relationship 10 - 3 ≤ ω 2 ⁢ L g ≤ 10 - 1 where ω is the rotation rate, L is a diameter of the vessel and g is the acceleration of gravity; and extracting particles of the particulate material at selected radial locations of the vessel; wherein the particulate material is tumbled to produce a continuous or discrete surface avalanching particulate layer to move particles of smaller size or higher density towards the center of the particulate material and particles of larger size or lower density radially outward from the center of the particulate material.