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

The sorption mechanism of Ni(II) on pyrite (FeS2) 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 FeS2 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 (drop Fe-OH), Then, electrostatic interactions between colloidal Ni(ll) and the surface produce a heterogeneous coating of an average thickness of a few nanometres, This film inhibits significantly the oxidation by H2O2 of these two minerals, particularly FeAsS. Copyright (C) 1999 John Whey & Sons, Ltd.