Fig. 12 shows the IR spectra of pyrite, sodium humate and a mixture of sodium humate and pyrite. Upon the addition of sodium humate to pyrite, the peaks attributed to the C@C bond of benzene at 1573 and 1697 cm1 (see Fig. 12a) were shifted to 1600 and 1716 cm1 (see Fig. 12c), respectively, suggesting that sodium humate was chemically adsorbed on the surface of pyrite via the benzene ring of sodium humate.