Thiol collectors

The adsorption of collectors on sulfide mineral occurs by two separate mechanisms chemical and electrochemical. The former results in the presence of chemisorbed metal xanthate (or other thiol collector ion) onto the mineral surface. The latter yields an oxidation product (dixanthogen if collector added is xanthate) that is the hydrophobic species adsorbed onto the mineral surface. The chemisorption mechanism is reported to occur with galena, chalcocite and sphalerite minerals, whereas electrochemical oxidation is reportedly the primary mechanism for pyrite, arsenopyrite, and pyrrhotite minerals. The mineral, chalcopyrite, is an example where both the mechanisms are known to be operative. Besides these mechanisms, the adsorption of collectors can be explained from the point of interfacial energies involved between air, mineral, and solution. 

Buckley, A. N., 1994. A survey of the application of X-ray photoelectron spectroscopy to flotation research. Colloids Surf, 93 159 - 172 Buckley, A. N. and Woods, R., 1995. Identifying chemisorption in the interaction of thiol collectors with sulphide minerals by XPS adsorption of xanthate on silver and silver sulphide. Colloids and Surfaces A Physicochemical and Engineering Aspects, 104,2 - 3 Buckley, A. N. and Woods, R., 1996. Relaxation of the lead-deficient sulphide surface layer on oxidized galena. Journal of Applied Electrochemistry, 26(9) 899 - 907 Buckley, A. N. and Woods, R., 1997. Chemisorption—the thermodynamically favored process in the interaction of thiol collectors with sulphide minerals. Inert. J. Miner. Process, 51 15-26... 

Chander, S. and Fuerstenau, D. W., 1975. Sulphide minerals with thiol collectors the chalcocite diethy dilhiophosphate system. 11th International Mineral Processing Congress, 1 583 - 603 Chander, S., Wie, J. M., Fuerstenau, D. W., 1975. On the native floatability and surface properties of naturally hydrophobic solids, hr P. Somasunfaran and R. G. Grieves(eds.), Advances in Interfacial Phenomena of Particulate/Solution/Gas Systems. AIME Symp., Ser., 150(71) 183-188... 

The most widely applied activation procedure is that involving the use of copper(II) ions to enhance the floatability of some sulfide minerals, notably the common zinc sulfide mineral sphalerite.2 Sphalerite does not react readily with the common thiol collectors, but after being treated with small amounts of copper it floats readily owing to the formation of a surface layer of CuS." A similar procedure is often adopted in the flotation of pyrrhotite (FeS), pyrite (FeS2), galena (PbS) and stibnite (Sb2S3). In the context of coordination chemistry, the major contribution has been to the understanding of the chemistry involved in the deactivation of these minerals, a procedure often adopted in the sequential flotation of several minerals from a complex ore. 

Goh, S.W., Buckley, A.N., Lamb, R.N., Woods, R. (2006) The ability of static secondary ion mass spectrometry to discriminate submonolayer from multilayer adsorption of thiol collectors. Min. Eng., 19,571-581. 

The 1930s saw the development of theories to elucidate collector-mineral interaction and to explain the selectivity for sulfide mineral flotation of thiol collectors such as the xanthates. Three propositions were put forward, and each was promoted and defended by its proponents with considerable vigor and intensity. 

Figure 1. Schematic representation of the mixed-potential mechanism for the interaction of thiol collectors with sulfide minerals in which the anodic process is chemisorption (a), a single-step reaction to form a metal collector compound (b), the latter reaction occurring in two stages, comprising oxidation of the mineral (c), ion exchange with the collector (d), and formation of the dithiolate (e). (FrOTi Woods.

In later studies, Mielczarski and co-workers " investigated surfaces after treatment with xanthate under potential control. This approach allows better definition of monolayer and multilayer conditions. The spectra observed for copper, " chalcocite, and silver electrodes in ethyl xanthate solutions after the potential was held in the prewave region indicated the presence of an additional species containing sulfur, carbon, and oxygen, but the authors considered this surface species not to be xanthate itself but an adsorbed impurity derived from the thiol collector. As pointed out in Sections IV, VII. 1, and VII.2, this assignment is not consistent with the results of other studies. 

In the concept promoted by Taggart, the formation of a hydrophobic surface is governed by the solubility of the metal thiol compounds. In order to overcome the difficulty that flotation occurs at collector concentrations that are orders of magnitude less than those at which one would expect a metal thiol compound to deposit from solubility considerations based on bulk species, Taggart and Hassialis considered that the concentration of the metal ion be taken as that in the lattice of the mineral. Sutherland and Wark pointed out the fallacy of this reasoning and reaffirmed the conviction that, to explain the floatability at low collector concentrations, an adsorption process must be operative. 

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