Flotation has produced the majority tonnage of REE materials, and is currently used in China, USA, and Australia. It is economical, effective, well understood, and the industry standard of REE mineral processing. The end product is a somewhat pure REE mineral concentrate, which, due to impurity issues, generally is unsalable and must be used for in-house processing into other concentrates and products.
The procedure is somewhat analogous to a washing your dirty clothes in a household machine.…with the fabric being the equivalent of the non-valuable rock phase, and the dirty bits being the REE minerals that collect on the bubbles.
In REE flotation the following basic steps are utilized:
1. The pH of the ground rock slurry is adjusted to proper values.
2. Chemical reagents are added which will minimize recovery of the non-REE phases.
3. Chemical reagents are added to selectively modify the surface of the REE mineral. The goal is to make the REE mineral surface very repellant to water.
4. The now chemically modified ground rock slurry is put into a tank, it can be either square or round, and copious quantities of air bubbles are introduced into the system.
5. The now water-repellent REE grains are attracted to the bubbles, and attach themselves to the bubble surface.
6. The bubbles are analogous to a conveyer belt which transfers the REE minerals from the ground ore slurry (pulp) to the REE mineral concentrate tanks. Also note that the loaded bubble must not be too heavy or it will not float, this implies that the REE mineral size must be sufficiently small, and the ore must be ground sufficiently fine. Grains too fine are blocked from reaching the bubbles by hydraulic action and will not attach.
7. The REE mineral bubbles are collected and transferred to other flotation tanks for refloating and further upgrading. After this has been done a sufficient number of times, and the REO grade is satisfactory, the REO mineral concentrate is stored in bins or piles awaiting the next stage of processing.
Froth flotation at lab scale
The development of a flotation procedure has many requirements that must be followed, a few of which are listed below:
1. Mineralogy studies must be carried out on the ground ore to determine the characteristics of the REE minerals, the minerals one wishes to not recover, and the overall amenability to flotation.
2. The right staff is crucial, as a wide knowledge of chemical reagents, grinding technologies, and flotation machines are required.
3. The ground ore slurry must contain the right size mineral grains. Both the average and the size distribution of the REE minerals must be appropriate for the flotation equipment used. Occasionally, separating the ground ore into several more narrow size fractions will lead to improved overall flotation performance, as the flotation equipment can be better matched to process needs.
4. The test work needs to start out with lab-sized batch studies, and once successful, move on to small continuously operated pilot plants.