Siew Wei Goh

Interaction of thiol collectors with pre-oxidised sulfide minerals

Abstract In order to determine whether pre-oxidation results in a change in the identity of the products of the interaction of sulfide minerals with flotation collectors, chalcocite or galena surfaces that had been exposed to air were treated with diethyl dithiophosphate (DTP) or iso -butyl xanthate (BX), respectively, in a borate buffer solution of pH 9.2. The resulting surfaces were studied by means of X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectroscopy (ToF-SIMS). The metal oxidation products formed on each mineral surface during the exposure to air were removed by immersion in water or the buffer solution alone and, to avoid this happening in collector solutions, most experiments were carried out with solutions saturated with the ion of the metal component of the mineral. Immersion of chalcocite surfaces in copper-saturated 10 −5 mol dm −3 dithiophosphate solution for 40 s, or of galena surfaces in lead-saturated 10 −4 mol dm −3 xanthate solution for 8 min, resulted in the formation of chemisorbed DTP or BX. Immersion of chalcocite or galena in similar DTP or BX solutions for longer periods gave rise to CuDTP or Pb(OH)BX, respectively, in addition to the chemisorbed collector. In each case, the products of interaction of the mineral with the collector were the same for freshly exposed and pre-oxidised surfaces. The results indicate that the mechanism for the formation of the chemisorbed layer on the pre-oxidised surfaces would have been ion exchange with copper–oxygen or lead–oxygen species followed by reorganisation adjacent to the mineral surface, rather than dissolution of the metal–oxygen species in the aqueous medium followed by chemisorption of the collector at the oxide-free surface.

XPS, Static SIMS and NEXAFS Spectroscopic Investigation of Thiol Adsorption on Metals and Metal Sulfides

Examples are presented of the complementary nature of conventional XPS, synchrotron XPS, ToF-SIMS and NEXAFS spectroscopy when applied to the adsorption of MBT on metals and metal sulfides. Conventional XPS could detect chemisorption via S 2p spectra, detect the onset of multilayer formation via the relevant metal Auger or core level photoelectron spectra, and determine metal thiolate stoichiometry from thick multilayers. Surface-optimised synchrotron XPS allowed precise chemisorbed MBT S 2p binding energies to be obtained. Angle-dependent N and C NEXAFS spectra revealed adsorbate orientation, even for an abraded but relatively smooth surface. Cu L 3 -edge spectra detected some Cu(II) and hence Cu(MBT) 2 in multilayers on chalcocite. Static SIMS data confirmed the interaction of both N and exocyclic S with surface metal atoms for silver metal and chalcocite.

Ex Situ Surface Chemical Characterization in Minerals Processing Research: The Effect of Hydrophilic Organic Solvents on Sulfide Mineral Surfaces

In both the concentration of a valuable metalliferous ore component by froth flotation, and the extraction of the corresponding metal from flotation concentrates by leaching, fine mineral particles are involved. However, there are a number of advantages of investigating, in the laboratory, the influence of surface chemical composition on these plant processes by using single piece specimens with a relatively smooth surface of area ~10 mm rather than ~0.1 mm particulate samples. In such investigations, to emulate the surface of particles from comminution mills, single piece specimen surfaces prepared by abrasion as well as fracture are usually characterised.