Enhanced Removal of Dolomite Pebble Concentrate by CO2 Generation
The objective of this project is to take advantage of the generation of CO2 gas by dolomite in contact with acid to enhance physical separations based on density, to reject as much dolomite as possible without sacrificing phosphate recovery. The first phase of the project was to obtain samples of high-dolomite phosphate pebble, provided by Mosaic Inc., and to characterize this material to determine the quantities and distribution of magnesium-bearing minerals. It was found that the dolomite was preferentially concentrated in the coarse fraction, and that the dolomite and phosphate minerals were well-liberated from each other even at the coarse sizes. The -6 mesh material had a sufficiently low dolomite content that it was very close to being an acceptable product even without further dolomite separation.
The second phase of the project was to construct an acid-resistant jig, and use it to carry out density separation of dolomite from the phosphate minerals. Studies were first conducted to determine the extent to which jigging could upgrade the phosphate in the absence of acid. It was determined that the jig could achieve significant levels of dolomite removal using only water as the separating media, due to the small difference in density between the apatite particles and the dolomite particles. The phosphate minerals were found to be broadly classifiable into a lower-density and a higher-density form, and the higher-density phosphate was found to be amenable to concentration by jigging.
Subsequent experiments were carried out to determine the extent to which the addition of acid and the generation of carbon dioxide gas could improve jig performance, and whether the performance could be enhanced further by the use of surfactants to help bubbles to adhere preferentially to the dolomite surfaces.