Alan N. Buckley

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.

Metals from Sulfide Minerals: The Role of Adsorption of Organic Reagent in Processing Technologies

The extraction of base metals from sulfide mineral ores is of major industrial and economic importance, and as a consequence considerable effort has been, and continues to be, expended on research to maximize the extraction efficiency. Several unit operations in the extraction process involve interactions at the solid-liquid interface, and these interactions can be modified to achieve enhanced processing efficiency by the adsorption of organic reagents at the surface of the solid phase. In this chapter, the different ways in which organic reagents can interact with a solid surface are first described generally and then more specifically in relation to froth flotation and electrowinning, two of the most important unit operations in base metal production. In addition to a detailed treatment of the relevant adsorption mechanisms, the principal surface analytical techniques that have been used to elucidate these mechanisms are described. For the study of collector adsorption in flotation, both in situ and ex situ techniques are covered, with spectroelectro-chemical studies and UV-visible spectroscopy included in the former, conventional (anode-generated) X-ray photoelectron and secondary ion mass spectroscopies representing the latter, and with FTIR and Raman scattering spectroscopies applicable in both situations. For the study of adsorption of reagents to influence deposit morphology in electrowinning, electrochemical techniques and surface enhanced Raman scattering spectroscopy are emphasized. It is shown that the combination of in situ and ex situ electrochemical and spectroscopic techniques represents a powerful approach for investigating the adsorption of organic reagents in the recovery of metals from sulfide ores.

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.

Re-examining the pitch/coke wetting and penetration test

To produce structurally soundcarbon anodes for use in aluminum smelting, a strong bond between filler and binder coke is necessary. Bond strength results from mechanical interlocking and adhesion of the binder coke to the filler coke. Critical for creating such bonds is the ability of the pitch to wet the coke surface and penetrate the coke porosity during mixing and forming. Wettability is normally assessed from the pitch behavior during the initial stages of a penetration test. In the test, the observed contact angle between a pitch droplet and a bed of fine coke particles is recorded as the temperature is increased. The temperature at which this contact angle becomes 90° is referred to as the wetting temperature of the pitch. The penetration test may be useful to identify pitch and coke combinations that are unlikely to produce baked anodes of acceptable quality with standard paste preparation conditions. It does not, however, provide a measure of the true wettability of a coke by a pitch. The isothermal penetration experiments reported here demonstrate that the observed contact angle of a pitch against a coke bed changes continuously from >90° to <90°, even to 0‡, at a temperature much lower than the wetting temperature derived from the penetration test. The requirements for the measurement of a true contact angle and the difference between the concepts of adhesion and wetting are discussed.

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.