Langmuir 1994,10, 3582-3586
X-ray Photoelectron and Infrared Spectroscopic Investigation of Sphalerite Activation with Iron Stbphane H. R. Brienne,? Qingsong Zhang,*Ian S. Butler,? Zhenghe Xu,* and James A. Finch*?* Department of Chemistry, McGill University, 801 Sherbrooke Street West, Montreal, Quebec, Canada, H3A 2K6,and Department of Mining and Metallurgical Engineering, McGill University, 3450 University Street, Montreal, Quebec, Canada, H3A 2A7 Received November 9, 1993. In Final Form: June 14, 1994@ The interaction of the sphalerite (ZnS)mineral with ferrous, ferric, and xanthate ions at pH 10 has been studied by using ex situ X-ray photoelectron XPS)and ex situ and in situ infrared (DRIFTS and ATR, respectively) spectroscopy. Interaction occurs with Fez+ but not with Fe3+. The mechanism involves initial adsorption of Fez+,followed by oxidation to Fe3+,and subsequent reaction with xanthate. The final surface product is hydrophobic and may be a factor in the flotation of sphalerite.
Introduction The adsorption of metal ions at solid-liquid interfaces plays a n important role in many industrial processes. In froth flotation, for instance, the activation of sphalerite (ZnS) by addition of solution-phase Cu2+ ions is wellknown.l-s Activation is a process in which a solid surface is modified by the adsorption of metal ions from solution so as to increase the reactivity toward flotation collecting agents, such as xanthates. In practice, however, sphalerite can be activated by other heavy metal ions present as contaminants. This unintentional activation has been attributed to lead6s7and iron ion^^^^ in particular. Despite the economic and fundamental importance of unintentional activation, few detailed studies have been made compared to that of Cu2+ activation. The activation of sphalerite by Cu2+ ions is now well understood: Cu2+ions replace Zn2+ions present on the surface so that the mineral surface behaves like copper sulfide in response to thio-collector ads0rption.l The observation that activation of sphalerite can take place in the absence of Cu2+ions has also been d0cumented.l In a recent communication, sphalerite flotation was reported to occur a t moderately alkaline pH upon addition of ferrous ions.8 A three-step activation mechanism, based on the electrokinetic behavior of the system, was p r o p ~ s e dFirst, .~ adsorption of Fez+, probably as Fe(OH)+, followed by oxidation of the adsorbed Fez+ to Fe3+ at the mineral surface, and finally, reaction between the Fe3+ and xanthate to form a surface-bound hydroxy-xanthate complex. Because ofthe indirect nature ofthe approaches used in the previous studies (i.e., electrokinetic effects and flotation recovery),the proposed mechanism warrants
* Author to whom correspondence should be addressed. t
Department of Chemistry.
* Department of Mining and Metallurgical Engineering.
Abstract published inAdvanceACSAbstracts, August 15,1994. (1)Finkelstein, N. P.; Allison, S. A. In Flotation: A. M . Gaudin Memorial Volume; Fuerstenau, M. C.,Ed.; AIME: New York, 1976; Vol. 1, p 414. (2)Laskowski, J.;Girczys, J. Trans. Inst. Min. Metall.,Sect. C 1972, 81,C118. (3) Mukhejee, A.D.; Sen, P. K. J . Mines, Met. Fuels 1976,24(Oct), 327. (4)Marouf, B.; Bessihre, J.; Houot, R.; Blazy, P. Trans. Inst. Min. Metall. 1986,95,C50. (5)Mielczarski, J. Znt. J . Miner. Process. 1986,16,179. (6) Popov, S. R.; VuEiniC, D. R.; Strojek,J. W.; Denca, A.Znt.J . Miner. Process. 1989,27,51. (7)Houot, R.; Raveneau, P. Int. J . Miner. Process. 1992,35,253. (8)Leroux, M.; Rao, S. R.; Finch, J. A. Can. Inst. Miner. Bull. 1987, 80 (9021,41. (9)Zhang, Q.;Rao, S. R.; Finch, J. A. Colloid Surf. 1992,66,81. @
further examination by direct surface characterization techniques. In the present paper, the sphalerite-iron-xanthate system was studied by using various spectroscopic techniques. The conditions for the adsorption of iron onto sphalerite and the oxidation state of the adsorbed iron have been investigated by X-ray photoelectron spectroscopy (XPS), a technique that has been widely used to examine the interaction of collector molecules with mineral s u r f a c e ~ . ~ J ~The - ~ *adsorption of xanthate on activated sphalerite surfaces was studied by Fourier transform infrared (FTIR) spectroscopy in its ex situ diffusereflectance (DRIFTS) and in situ attenuated total reflectance (ATR) sampling modes. The results of this work are discussed in terms ofthe proposed three-step activation mechanism mentioned above.g
Experimental Section The sphalerite (ZnS)samples were obtained in the form of a copper-lead-zinc ore from Brunswick Mining and Smelting, New Brunswick, Canada, and ground to a 74-37 pm fraction. The separation of sphalerite was accomplished by alternate processing by using a shakingtable and a Mozley separator. The single mineral obtained by this method was treated three times with a 5% HCl solution. Residual sulfur, formed as result of the acid treatment, was removed by washing the samples with acetone,followed by deoxygenated-distilled water. The product was then dried at -340 K and stored under Nz before use. Chemical analysis showed zinc as the dominant heavy metal (63.8%),with minor proportions of Fe (2.8%),Pb (0.38%),and Cu (
