Flotation of diaspore and aluminosilicate minerals applying novel carboxyl hydroxamic acids as collector

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Three novel carboxyl hydroxamic acids including ortho-carboxyl tetrachlorobenzohydroxamic acid (OCB), ortho-carboxyl hexahydrobenzohydroxamic acid (OHB) and ortho-carboxyl tetrahydrobenzohydroxamic acid (OTB), were synthesized and tested as collectors for flotation of diaspore, kaolinite and illite contained in diasporic bauxite from China. Subsequently, their flotation mechanism to diaspore and aluminosilicate minerals was investigated by zeta potential measurements and FT-IR spectrum checking. The results of flotation experiments show that by using carboxyl hydroxamic acid as collectors, the pulp pH value has significant influence on their collecting performance as the floatability of either diaspore or aluminosilicates varies sharply with their change, and the appropriate pH value for the flotation of diaspore gets close to neutral condition where diaspore presents good floatability while kaolinite and illite exhibits poor performances. Additionally, the floatability of diaspore and aluminosilicates is in the descending order of diaspore, kaolinite, and illite in the presence of three collectors, and their collecting capacity to three minerals is in the ascending order of OTB, OHB and OCB. Of three synthesized carboxyl hydroxamic acids, OCB has the strongest collecting capability to diaspore while relatively weak to aluminoscilicate minerals, whose good selectivity for the flotation between diaspore and aluminosilicates is possibly suited for direct flotation desilication of diasporic bauxite. Moreover, the optimum pH value for diaspore flotation associated with FT-IR spectrum and zeta potentials indicate that the adsorption interaction between the synthesized collectors and diaspore is dominantly a kind of chemical bonding one in the form of three cycle chelate rings due to the coordination of carboxyl and hydroxamate to the metal aluminum atoms, where the oxygen atoms contained in carboxyl and hydroxamate of the polar group have the stereo conditions to form five to seven membered rings. By contrast, the adsorption interactions of the carboxyl hydroxamic acid on the surfaces of aluminosilicate minerals are mainly dominated by means of hydrogen bonds.