Apparatus for dry granular mixtures separation

An apparatus for separating dry granular mixture of particles of different densities into a first fraction and a second fraction, the first fraction having particles of higher density than the second fraction, the apparatus comprising:

• a first end and a second end axially opposite the first end;
• a rotation axis extending along the apparatus from the first end to the second end;
• a channel spiraled about the rotation axis into a plurality of turns successively arranged in an axial direction toward the second end of the apparatus, each turn defining a granular mixture retention volume for receiving the granular mixture and open radially inwardly toward the rotation axis, the channel rotatable about the rotation axis to urge movement of the granular mixture in the axial direction and induce spatial separation of the granular mixture into the first fraction and the second fraction by producing continuous or discrete avalanches in a surface of the granular mixture whereby, within the granular mixture retention volume of each turn, the first fraction is moved toward a center of a volume of the granular mixture and the second fraction is moved radially outward from the center of the volume of the granular mixture, and wherein in the axial direction, the granular mixture retention volume of at least some of the turns decreases relative to preceding turns to induce overflow of the second fraction of the granular material from the at least some of the turns toward the preceding turns during the rotation of the channel about the rotation axis to facilitate backflow of the second fraction toward the first end of the apparatus while continuing to urge movement of the first fraction toward the second end.