An investigation of the Cu (II) adsorption mechanism on pyrite by ARXPS and SIMS

Abstract

The surfaces of polished flats and < 38 μm particles of pyrite were analysed using angle resolved X-ray photoelectron spectroscopy (ARXPS), time of flight secondary ion mass spectrometry (TOF-SIMS), dynamic secondary ion mass spectrometry (dynamic SIMS) and by EDTA oxide/hydroxide chelation after pyrite surface conditioning (20 min in 0.1 M KNO 3 solution, purged with N 2) and after conditioning and subsequent Cu (II) adsorption under different pH and Cu (II) concentration conditions (2.84 × 10 −4 mol dm −3 Cu and 3.43 × 10 −5 mol dm −3 solutions). Solution analyses in conjunction with EDTA results indicate that a 1:1 exchange of Cu(II) ions for Fe(II) ions did not occur during Cu adsorption ruling out ion exchange as the only mechanism. The EDTA extractions indicated no significant Fe hydroxide precipitates on to the surfaces of the pyrite for the conditions used. ARXPS analysis of pyrite flats showed increases in the oxidised S 2 2− ox (E b = 163.5eV) signal on Cu adsorption as compared to only surface conditioning, regardless of pH or concentration. The Cu2p XPS signals for the samples with adsorbed Cu show the presence of Cu(I) ions on the pyrite surfaces where low solution Cu concentrations or low pH were used. It is concluded that oxidised S 2 2− ox species form on the pyrite surface on Cu adsorption rather than polysulfide. The oxidation is accompanied by the reduction of Cu(II) to Cu(I) on the surface of the pyrite. The ARXPS measurements of pyrite flats exposed to 2.84 × 10 −4 mol dm −3 Cu and 3.43 × 10 −5 mol dm −3 solutions at pH 8.5 showed a Cu(I) layer covered by a Cu(II) rich layer indicating the presence of adsorbed Cu(I) covered by precipitated Cu(OH) 2. TOF-SIMS analyses supports the ARXPS results showing strong a correlation between the intensity of the S − fragment and the intensity of the adsorbed Cu(I), in the absence of Cu(OH) 2 precipitation. Dynamic SIMS images provide accurate spatial distributions for adsorbed Cu over the entire pH range and various Cu concentrations and indicate the presence of adsorbed Cu(OH) 2 colloids on Cu adsorption onto a flat pyrite plate at pH 8.5 using 2.84 × 10 −4 mol dm −3 Cu.