Sand milling process and apparatus

Claim 1

PROCESS FOR THE GRINDING OF SOLIDS IN LIQUID, COMPRISING SUPPLYING SOLID PARTICLES TO BE GROUND AND A LIQUID TO A GRINDING ZONE CONTAINING AGITATED PARTICULATE GRINDING MEDIUM; PASSING THE RESULTING SLURRY MEDIUM WITH TICLES TO BE GROUND AND PARTICULATE GRINDING MEDIUM WITH SUBSTANTIALLY UNIMPEDED FLOW UPWARD THROUGH A SEPARATING ZONE; REDUCING THE VERTICAL VELOCITY OF SAID SLURRY PRIOR TO THE OUTFLOW OF SOLID-LIQUID SLURRY FROM SAID SEPARATING ZONE TO A VALUE SUBSTANTIALLY LESS THAN THE VELOCITY OF SAID SLURRY IN SAID GRINDING ZONE AND SUBSTANTIALLY LESS THAN THE SUSPENDING VELOCITY OF SAID GRINDING MEDIUM BUT ABOVE THE SUSPENDING VELOCITY OF THE GROUND SOLID PARTICLES, WHEREBY ENTRAINED PARTICLES OF GRINDING MEDIUM SETLE OUT OF SAID SLURRY IN PREFERENCE TO THE GROUND SOLID PARTICLES; AND THEREAFTER REMOVING FROM THE UPPER PORTION OF SAID SEPARATING ZONE SAID LIQUID AND THE GROUND SOLID PARTICLES FREE FROM AT LEAST MOST OF THE GRINDING MEDIUM.