Flotation of MnO4− and Fe3+ Ions by the Combined Use of Sodium Silicate and Cationic Surfactant

The removals of MnO4− and Fe3+ ions from an aqueous solution by the combined use of silicate ions(SiO32−) and a cationic surfactant, hexadecyltrimethylammonium chloride (HTAC), were studied by means of ion flotation techniques. The effect of variables such as pH, the surfactant concentration, and the order of addition of the reagents on the floatability of the ions were studied. More than 98 and 97% of the MnO4− and Fe3+ ions, respectively, could be floated under the optimum conditions. The optimum composition of SiO32− and HTAC was found to be about 0.9 in mole fraction of SiO32− for both systems. It was also found that the order of the addition of the reagents markedly affects the floatability. Further, a schematic model of flotation was proposed, taking account of the compositions of the sublate. MnO4− and Fe3+ ion flotations differed from each other in that MnO4− ions combine with SiO32− ions through the double layer of HTAC molecules, which are subsequently coagulated and floated by HTAC, while Fe3+ ions or polynuclear Fe3+ ions combine directly with SiO32− ions, which are subsequently coagulated and floated by HTAC.