Mining and Crude Separation: Heavy Mineral Placer Sands / Float Separation
The most common way that Thorium used to be separated in the west was from placer sands mined for other material such as Titanium Oxide, the companion mineral containing Thorium was mostly Monazite. A placer sand mine is literally the sand placed over time via erosion, wave action from an ancient beach or glaciers in a vein and simply excavated from the deposit. A less common variation is to literally excavate existing or ancient beaches, where great amounts of valuable sand are physically separated for industrial use leaving the monazite byproduct behind.
The historic initial process was to then float the sands with the Monazite grains dropping out because of its heavier weight. The fluid could be water, or water with an additive such as pine extracts to help selectively drop out the minerals.
A typical example of processing the separated minerals is to grind the phosphate minerals into a powder finer than baby powder and then Acid digest them in separation facilities where the acid digested separations are finally inserted into cascade chains of ‘Cameras’ or centrifuges. Once the solution is sent through the cameras, sometimes thousands of cameras, thousands of times, the final product is collected in a cascade from heaviest to lights elements. The form is either a nitrate or an oxide which then can be electrowinned to pure metal.
This is an old process that uses a great deal of acids and requires a tremendous amount of energy to run the centrifuge cameras. There are many new methods of separation that are being explored, such as using ligands to selectively ‘grab’ specific elements that they have been designed to capture. Other approaches use base chemicals instead of acids.
As the separation occurs, the elements that make up the mineral tend to drop out one by one, from heaviest to lightest. Thorium (and then Uranium) are the first to come out of the digestion solution. This Thorium product, usually Thorium Nitrate, can then be sent for further processing to metallic thorium by means of an induction furnace or Electrowinning as described in the next section.