Method and apparatus for grinding

Grinding apparatus for reducing sizes of mineral particles entrained in a liquid medium, the apparatus comprising:

• a vertical shaft impactor having:
• a rotor, said rotor being rotatable about a predetermined substantially vertical axis and having an outer peripheral edge;
• a first material inlet aligned substantially along said predetermined axis of said rotor for supplying feed material directly to said rotor;
• an impact bed located radially outwardly of said rotor, said impact bed being spaced from the peripheral edge of said rotor and defining a grinding region therebetween, said impact bed being disposed such that feed material supplied to said rotor from said first inlet is flung outwardly against said impact bed;
• and
• a second material inlet for introducing feed material in the form of solid particles in a liquid suspension, said second material inlet being positioned above said grinding region wherein material introduced through said second material inlet is fed into said grinding region without entering said rotor such that said solid particles in a liquid suspension intersect said feed material flung from said rotor at generally right angles thereto, wherein said second material inlet comprises a plurality of pipes for directing said suspension on to a cascade plate located above the rotor such that said suspension cascades into the grinding region.

Grinding apparatus for reducing mineral particle sizes, the apparatus comprising a vertical shaft impactor, the vertical shaft impactor having:

• at least one inlet for feed material in the form of solid particles in a liquid suspension;
• a rotor rotatable about a substantially vertical axis and having an outer peripheral edge, said rotor disposed relative to said at least one inlet to receive a first portion of said feed material therefrom;
• an impact bed located radially outwardly of said rotor, said impact bed being spaced from the peripheral edge of said rotor and defining a grinding region therebetween, said impact bed being disposed such that said first portion of said feed material received from said at least one inlet is flung outwardly towards said impact bed;
• and
• rotor bypass means positioned to receive a second portion of said feed material, said rotor bypass means comprising means defining a first annular region, and means defining a second annular region, said first annular region being located radially outwardly of said second annular region, and said second annular region being separated from but in communication with said first annular region such that said second portion of said feed material can flow from said first annular region to said second annular region, and said second annular region being located above said grinding region and having an open lower portion, such that said second portion of said feed material falls from said second annular region substantially vertically into the path of material being flung outwardly from said rotor.

Grinding apparatus for reducing sizes of mineral particles entrained in a liquid medium, comprising:

• a vertical shaft impactor adapted to receive solids in a liquid suspension, the vertical shaft impactor having:
• a first inlet for feed material;
• a second inlet for feed material, said second inlet being separated from said first inlet;
• a rotor rotatable about a fixed axis, said rotor having an outer peripheral edge and being positioned to receive feed material from said first inlet;
• an impact bed located radially outwardly of said rotor, said impact bed being spaced from the peripheral edge of said rotor and defining a grinding region therebetween, said impact bed being disposed such that feed material received from said first inlet is flung outwardly against said impact bed;
• and
• distribution means for receiving feed material from said second inlet, said distribution means being located above said grinding region such that feed material received thereby fails into the flow of material flung outwardly from said rotor;
• said grinding apparatus further comprising:
• means for supplying raw feed material in liquid suspension to said first inlet of said vertical shaft impactor;
• means for classifying ground material from said vertical shaft impactor into fine particles and oversized particles;
• means for returning said oversized particles to said first and second inlets of said vertical shaft impactor;
• and
• means controllable by an operator of the apparatus for varying the relative proportions of said oversized particles returned to said first and second inlets.