Physical chemistry mechanisms of CDR system in sulphide mineral flotation

The flotation tests, zeta potential measurements, and Fourier transform infrared spectroscopy (FTIR) analysis on galena, sphalerite, and pyrite were studied in a collecting-depressing-reactivating (CDR) system. In this system, sulphide minerals were first collected and activated by the collector, and then depressed strongly by Ca(OH)₂ in a strong alkaline solution. Finally, they were reactivated by H₂SO₄. The flotation tests of pure minerals showed that in the Ca(OH)₂ depressing process sulphide minerals had similar flotation characteristics because they had already been influenced by the collector. Hence, the flotability differences between them were reduced. However, in the H₂SO₄ reactivating process considerable differences in the flotability between galena and sphalerite/pyrite were produced. That is to say, galena was relatively easy to be reactivated by H₂SO₄, but sphalerite and pyrite were not reactivated at pH > 11. The zeta potentials of sulfide minerals measured by the Zeta Plus presented irreversible characteristics on the change of pH values. The results of the FTIR spectra analysis indicated that the collectors already adsorbed on the mineral surface were removed partially by Ca(OH)₂.