Coal reverse flotation. Part II. Batch flotation tests

Coal reverse flotation, a process in which coal mineral matter is floated instead of the organic matter, was studied through a series of batch flotation tests on artificial coal/silica mixtures using two coals varying in rank. Dodecyltrimethyl ammonium bromide (DTAB) was utilized as a mineral matter collector, while humic acids (sodium salt) were added as a coal depressant. It was shown that the separation of silica from coal by reverse flotation is a kinetic process in which silica floats first followed by clean coal. The selective recovery of silica was possible only in a very narrow range of DTAB dosages and the amount of DTAB needed for best selectivity was a function of coal rank. A lower rank coal required much higher amine doses than a bituminous coal (depressed with humic acids), which was attributed to the higher amine adsorption on the more hydrophilic coal.