Surface spectroscopic study of the adsorption of Ni(II) on pyrite and arsenopyrite at pH 10

The sorption mechanism of Ni(II) on pyrite (FeS 2 ) and on arsenopyrite (FeAsS) has been investigated at pH 10, using complementary methods for surface characterization such as x-ray photoelectron spectroscopy (XPS), Fourier transform mass spectrometry (FTMS), high-frequency dielectric measurements and electrophoretic mobility measurements. At this pH, the surfaces of the minerals are rapidly covered by an oxidation layer composed mainly of Fe(III) oxides on FeS 2 and Fe(III) arsenite and arsenate on FeAsS and presenting negative zeta potentials of -40 and -60 mV, respectively. The first step of the interaction with Ni(II) is the formation of a hydroxylated surface complex through proton exchange with the surface hydroxyl groups (≡Fe-OH). Then, electrostatic interactions between colloidal Ni(II) and the surface produce a heterogeneous coating of an average thickness of a few nanometres. This film inhibits significantly the oxidation by H 2 O 2 of these two minerals, particularly FeAsS.