This is a description of a grease table sed in diamond mining to extract diamonds from their ore.
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A grease table is used in the practice of mining for the recovery of uncut diamonds. It works on the principle that diamonds are hydrophobic and their surfaces will not become wetted by water. This causes the diamonds to stick into a layer of grease on a flat surface that is slightly sloped whereas all the other rocks but diamonds will just wash off of the table. It will not work on uncut diamonds that are covered with iron oxide and they get lost in the tailings.
The modern way to extract diamonds from other minerals is using an x-ray florescence tube that causes the raw diamonds to fluoresce in the presence of x-rays. Using this method the diamonds are transported on a conveyor belt along with the other rough minerals are found associated with them. As they pass by the x-ray a jet of air will blow the diamonds and some other minerals off the conveyor belt where the diamonds are hand picked out of the other minerals later.
As the name implies this is actually a table with a slant that is covered with a layer of grease that is usually beef tallow. After running several tons of gravel over this table the grease and diamonds are recovered from the grease by putting the whole mess into a large pot of boiling water. This melts the grease, and the diamonds drop to the bottom of the pot where they are recovered. The grease is recycled back onto the surface of the table ready to run another run of gravel.
Grease tables are usually made of metal although a workable one can also be fabricated out of wood. The table itself is made out of ¾ inch marine plywood that has sides built out of 2 x 10 inch lumber. The deck of the table is coated with a layer of grease that is about one to three millimeters thick in use. Provision is also made so the table can be slanted. The angle is adjustable so you can get the maximum recovery of diamonds.
The gravel has to be classified in size before using the grease table. This is usually 1 -2, 2-4, 4-6, etc in millimeters before running over the grease table. The diamond crystals are periodically removed from the grease with a simple kitchen spatula.
Water is also an important part of the recovery process as it keeps the gravel moving down the table where it falls off the end, and is carried off by another conveyor belt.
In order to maximize your efforts the classified gravel should be run through a jig first to concentrate the heavier minerals found in the gravel, diamond is one of them with a density around 4 grams per cubic centimeter.
As can be seen the basic tools for diamond recovery are quite simple. All of them can be purchased ready made, but if you are handy with tools you can build them yourself. Just remember that recovering diamonds from gravel is nothing more then operating a sand and gravel operation on steroids.