Apparatus to extract magnetic particles from suspensions

1. An apparatus for concentrating magnetic particles suspended in a fluid comprising:

a vessel for containing said fluid having an inner base surface that slopes downwards towards a collection region, said collection region including a retrieval well for collecting magnetic particles;

a magnet assembly for positioning under and in proximity with the vessel for attracting magnetic particles to the inner base surface of the vessel, said magnet assembly providing a relatively larger magnetic flux density at a peripheral region thereof;

means for laterally traversing the magnet assembly relative to the vessel between a first position whereby the magnet is generally centered under the vessel and a second position whereby the peripheral portion of the magnet is positioned under the well of the vessel; and

agitation means for agitating said vessel to facilitate movement of the magnetic particles to the well.

2. The apparatus of claim 1 wherein the agitation means comprises rotation means for rotating the vessel.

3. The apparatus of claim 2 wherein the rotation means provides rotation alternately in opposite directions to facilitate relative movement of fluid and vessel.

4. The apparatus of claim 1 wherein the agitation means includes vibrating means to facilitate movement of the magnetic particles along the bottom of the vessel towards the well.

5. The apparatus of claim 1 wherein the magnet assembly comprises a primary magnet, and a backing plate having high magnetic permeability below the primary magnet, for increasing the magnetic flux density at the vessel.

6. The apparatus of claim 5 wherein the magnet assembly further comprises a secondary magnet and secondary backing plate below the backing plate of the primary magnet, and wherein the secondary magnet and secondary backing plate have a larger cross-section than the primary magnet.

7. The apparatus of claim 1 including control means for controlling movements of said vessel and positioning of the magnet relative to the vessel.

8. The apparatus of claim 1 wherein said vessel has a smaller diameter at its top than at its base to facilitate retention of the fluid upon rotation and agitation.

9. A method for concentrating magnetic particles suspended in a fluid comprising:

providing a vessel for containing said fluid having an inner base surface that slopes downwards towards a collection region, said collection region including a retrieval well for collecting magnetic particles;

providing a magnet assembly for positioning under and in proximity with the vessel for attracting magnetic particles to the inner base surface of the vessel, said magnet assembly providing a relatively larger magnetic flux density at a peripheral region thereof;

agitating said vessel to facilitate movement of the magnetic particles to the well; and

traversing the magnet assembly relative to the vessel between a first position whereby the magnet is generally centered under the vessel and a second position whereby the peripheral portion of the magnet is positioned under the well of the vessel.

10. The method of claim 9 wherein agitating the vessel includes rotation.