The flotation of fine particles is a technical challenge that the mining industry must address to efficiently exploit certain types of deposit whose ores are finely textured. This issue is of particular importance with the depletion of mineral resources considered as “conventional” with regards to the liberation mesh of minerals of interest. There are two basic approaches to optimise the flotation process for a particular ore, the research for the best working parameters of existing flotation devices and the development of new flotation reagents. The research works in the past decades highlight that, owing to their high hydrodynamic regimes, intensive flotation technologies are more adapted to the treatment of fine particles than conventional mechanical flotation devices. However, due to the short residence time in intensive flotation cells, it is essential that the surface of the minerals of interest has been particularly hydrophobised. In this sense, the improvement of the flotation performance for fine grained ores implies both the use of new flotation technologies and the development of more efficient and more selective flotation reagents. The selected object of studies is a fine grained residue produced after the extraction of gold and tellurium out of the ore from the Kankberg mine which is located in Sweden. This fine material contains low amounts of rare earth elements, in the form of monazite, a phosphate mineral. The thesis works presented in this manuscript consists of developing a reagent that improves the adsorption of the collector on the surface of monazite to facilitate its recovery throughout intensive flotation. The conducted studies emphasise that lanthanum ions significantly promote the adsorption of carboxylate type collectors on the monazite surface thereby increasing the floatability of this mineral. Current knowledge regarding the surface properties of monazite and the mechanism of anionic collectors adsorption on the monazite surface are relatively limited. Therefore, it seems wise to contribute to improving this knowledge during this thesis. A study was carried out to assess the hydroxylation of the monazite surface which is largely considered in the literature as a phenomenon influencing the collector adsorption. The handling of monazite may cause radiation exposure because of the radioactive decay chains of the actinide elements naturally present in the monazite crystal lattice. During this thesis, the synthesis of indurated monazite analogue materials was also investigated to facilitate the conduct of experiments. A protocol of synthesis of monazite powder sufficiently indurated to be mechanically stirred has been developed. Electrophoretic mobility measurements highlight that the surface properties of the synthetic monazite materials were similar to those of natural monazite with complex chemistry showing, in addition, that the presence of several atom substitutions in the monazite crystal lattice has no influence on its electrophoretic mobility.