Method and apparatus for washing and grading sand

1. A method of washing and grading particulate material comprising:

washing and grading a feed material on a first vibrating screen;

collecting oversize material from the first vibrating screen as a first product and collecting undersize material and water from the first vibrating screen in a first sump;

pumping the undersize material and water from the first sump into a first hydrocyclone, thereby removing fine contaminants from the material;

passing the underflow from the first hydrocyclone onto a second vibrating screen, and collecting oversize material from the second vibrating screen as a second product;

passing the overflow from at least the first hydrocyclone into a settling tank, and collecting sludge in a lower end of the settling tank and removing the sludge therefrom;

collecting water overflowing from the settling tank into a water storage reservoir and delivering water from the storage reservoir to the first and second vibrating screens; and

collecting undersize material and water from the second vibrating screen in the first sump;

wherein the first and second vibrating screens comprise respective sections of a split screen vibrating screen.

2. The method of claim 1 , comprising adding a portion of the overflow from at least the first hydrocyclone to the sump of the first and/or second vibrating screens to control the water level and/or content of the material in the sump or sumps.

3. The method of claim 1 , comprising collecting undersize material and water from the second vibrating screen in a second sump and passing material and water from the second sump into a second hydrocyclone.

4. The method of claim 1 , comprising adding a flocculent to the settling tank to facilitate the settling out of suspended solid material in the settling tank.

5. The method of claim 1 , comprising adding water from the water storage reservoir to the feed material in a wash box upstream of the first vibrating screen.

6. An apparatus for washing and grading sand comprising:

a first vibrating screen having a deck arranged to receive a feed material, said first vibrating screen configured so that oversize material passing over said deck of said first vibrating screen can be collected as a first product, and undersize material and water can be collected in a first sump of said first vibrating screen before being pumped to a first hydrocyclone;

a second vibrating screen receiving an underflow from said hydrocyclone upon a deck thereof, said second vibrating screen configured so that oversize material passing over said deck of said second vibrating screen can be collected as a second product;

a settling tank configured to receive an overflow from at least said first hydrocyclone; and

a water storage reservoir for receiving water overflowing from said settling tank while sludge is collected and removed from a lower end of said settling tank, wherein water passed from said water storage reservoir to said first and second vibrating screens to washes and fluidizes material thereon;

wherein said first and second vibrating screens comprise respective sides of a split deck vibrating screen, said first sump being common to said first and second vibrating screens.

7. The apparatus of claim 6 , wherein water from said water storage reservoir is added to the feed material in a wash box upstream of said first vibrating screen.

8. The apparatus of claim 6 , wherein a portion of the overflow from at least said first hydrocyclone is added to said sump of said first and/or second vibrating screens to control the water content of the material in said sump or sumps.

9. An apparatus for washing and grading sand comprising:

a first vibrating screen having a deck arranged to receive a feed material, said first vibrating screen configured so that oversize material passing over said deck of said first vibrating screen can be collected as a first product, and undersize material and water can be collected in a first sump of said first vibrating screen before being pumped to a first hydrocyclone;

a second vibrating screen receiving an underflow from said hydrocyclone upon a deck thereof, said second vibrating screen configured so that oversize material passing over said deck of said second vibrating screen can be collected as a second product;

a settling tank configured to receive an overflow from at least said first hydrocyclone; and

a water storage reservoir for receiving water overflowing from said settling tank while sludge is collected and removed from a lower end of said settling tank, wherein water passed from said water storage reservoir to said first and second vibrating screens to washes and fluidizes material thereon;

wherein said first vibrating screen has a first sump receiving undersize material and water therefrom and said second vibrating screen has a second sump, separate from said first sump, receiving undersize material and water therefrom, said first sump having a respective pump for pumping material and water therefrom into said first hydrocyclone, said second sump having a respective pump for pumping material and water therefrom into a second hydrocyclone, the overflow from both said first and second hydrocyclones being collected in said settling tank.

10. The apparatus of claim 6 , further comprising a dosing apparatus for adding a flocculent to said settling tank to facilitate the settling out of suspended solid material in said settling tank.

11. The apparatus of claim 6 , wherein a first flow control valve is provided for controlling the addition of a water from said storage reservoir to said first vibrating screen and a second control valve is provided for controlling the addition of water from said storage reservoir to said second vibrating screen.

12. The apparatus of claim 6 , wherein said first and second vibrating screens, at least said first hydrocyclone, said settling tank and said water storage reservoir are mounted on a common chassis.

13. The apparatus of claim 6 , further comprising a further hydrocyclone configured to receive undersize material and water from said sump of said second vibrating screen, the underflow from said further hydrocyclone being delivered onto said deck of a third vibrating screen, wherein the oversize material from the third vibrating screen is collected as a third product.

14. The apparatus of claim 13 , wherein said second and third vibrating screens comprise respective sides of a split deck vibrating screen having a common sump.

15. An apparatus for washing and grading sand comprising:

a first vibrating screen having a deck arranged to receive a feed material, said first vibrating screen configured so that oversize material passing over said deck of said first vibrating screen can be collected as a first product, and undersize material and water can be collected in a first sump of said first vibrating screen before being pumped to a first hydrocyclone;

a second vibrating screen receiving an underflow from said hydrocyclone upon a deck thereof, said second vibrating screen configured so that oversize material passing over said deck of said second vibrating screen can be collected as a second product;

a settling tank configured to receive an overflow from at least said first hydrocyclone; and

a water storage reservoir for receiving water overflowing from said settling tank while sludge is collected and removed from a lower end of said settling tank, wherein water passed from said water storage reservoir to said first and second vibrating screens to washes and fluidizes material thereon;

wherein said first and second vibrating screens comprise respective sides of a split deck vibrating screen, said first sump being common to said first and second vibrating screens;

wherein said first and second vibrating screens, at least said first hydrocyclone, said settling tank and said water storage reservoir are mounted on a common chassis; and

wherein said settling tank and said water storage reservoir are arranged at substantially the same height as the split deck screen.

16. The apparatus of claim 15 , wherein water from said water storage reservoir is added to the feed material in a wash box upstream of said first vibrating screen.

17. The apparatus of claim 15 , wherein a portion of the overflow from at least said first hydrocyclone is added to said sump of said first and/or second vibrating screens to control the water content of the material in said sump or sumps.

18. The apparatus of claim 15 , further comprising a further hydrocyclone configured to receive undersize material and water from said sump of said second vibrating screen, the underflow from said further hydrocyclone being delivered onto said deck of a third vibrating screen, wherein the oversize material from the third vibrating screen is collected as a third product.