Adsorption of sulfide ions on cerussite surfaces and implications for flotation
Introduction
As a typical lead oxide mineral, cerussite has been developed as alternative sources of lead metal to address future demands with the gradual depletion of nature lead sulfide ores. In the past years, many techniques, such as flotation, gravity separation combined with flotation, pyrometallurgy and hydrometallurgy, etc., have been attempted to treat lead oxide ores, among which sulfidization xanthate flotation method is the most commonly and commercially used method for concentration and pretreatment of lead oxide minerals [1], [2], [3], [4], [5].
It is generally known that lead oxide mineral is characterized by the higher solubility and more extensive surface hydration compared with its sulfide counterparts, which renders it more difficult to be concentrated via flotation method [6], [7], [8]. As a semi-soluble salt mineral with standard solubility product constant of 7.40 × 10−14 [9], [10], there are lots of dissolved lead ions from the mineral lattice in pulp solutions, which will firstly consume xanthate as lead xanthate precipitation when xanthate is added as a collector to float clean cerussite, so the collector will interact with the cerussite surface until the dissolved lead ions in pulp solutions are exhausted. The interaction of xanthate with the surface of cerussite is considered to an ion-exchange reaction between xanthate and carbonate ions, i.e., forming solid lead xanthate and releasing carbonate ions to the pulp solution. The surface metathetical reaction will continue until the solution equilibrium is reached, and multilayers of lead xanthate are produced in this process, which will continually consume the collector. However, weak-linked surface layer of lead xanthate is easy to be broken away from the surface, which not only reduces the hydrophobicity of the mineral surface, but also removes plentiful surface layers of mineral. Additionally, lead xanthate precipitated from the bulk does not render the mineral hydrophobic [6], [7], [8], [11]. Popov and Vučinić [12], [13], [14] reported that cerussite flotation recovery was improved through decantation of the pulp solution or prolonged agitation in the lead ions solution before xanthate was added, but they are only restricted to laboratory research and may be unsuitable for industrial application. Therefore, sulfidization xanthate flotation method is proposed to commercially treat lead oxide ores.
Sodium sulfide (Na2S) has been widely used as a sulfidizing agent for converting lead carbonate on the mineral surface into lead sulfide since sulfidized cerussite has characteristics similar to galena and can thus be recovered effectively with xanthate-typed collectors [15], [16], [17]. As for galena flotation using xanthate as a collector, it has been a very successful process both in the aspect of theory and practice [18], [19], [20], [21]. Thus, sulfidization is the most critical stage for the sulfidization xanthate flotation of lead oxide minerals. Marabini and Cozza [11] confirmed with the use of transmission IR spectroscopy that xanthate adsorbed onto the surface of sulfidized cerussite, whereas there is no surface adsorption of xanthate when cerussite is not treated with Na2S prior to the xanthate addition. And the role of sodium sulfide in the flotation of oxidized copper, lead, and zinc ores was reviewed by Malghan [22]. Besides, Herrera-Urbina et al. [7], [8] investigated the interaction of cerussite with aqueous hydrosulfide and amyl xanthate and discussed the inhibition mechanism of excess sulfide in solution through zeta potential measurements and electrochemistry analysis. Meanwhile, the method of measuring and monitoring sodium sulfide in flotation pulps was proposed by Malghan [22], and the control system of sulfide concentration was developed to optimize the accurate addition of sulfidizing agents by Gush [23]. Additionally, low grade lead-zinc oxide ores may be pretreated by sulfidization roasting [3] or hydrothermal sulfidization [24] before the collector addition. Furthermore, a favorable flotation result was obtained for treatment of complex and refractory oxide lead-zinc ores by sulfidization xanthate flotation method [1], [2]. Although these studies have been performed on sulfidization, there is still some limitations regarding the interaction mechanism of sulfide ions and the mineral surface.
In this research, X-ray photoelectron spectroscopy (XPS) studies, micro-flotation tests, and surface adsorption were carried out to investigate the interaction between sodium sulfide and cerussite, and to improve the sulfidization mechanism of lead oxide mineral.
Section snippets
Materials and reagents
Cerussite samples were obtained from the Lanping lead-zinc mine in Yunnan province, China following manual removal of gangue minerals such as smithsonite, calcite, and quartz. The pure cerussite samples were manually ground in an agate mortar and then sieved to produce a size range from −74 to +45 μm cerussite for adsorption studies of sulfide ions and micro-flotation tests. The XRF analysis results and the XRD pattern of the pure cerussite samples are shown in Table 1 and Fig. 1, respectively.
XPS studies
X-ray photoelectron spectroscopy (XPS) is a powerful technique to understand the surface speciation, i.e., it can identify both of the chemical composition and chemical state of the element in the measured samples based on the distinctive binding energy of inner electron from each element. In this work, XPS analysis was employed to character the difference of various cerussite samples treated with different concentrations of Na2S·9H2O. The obtained spectra were analyzed by peak fitting and
Conclusions
The present investigation introduced a new discussion on the lead sulfide species formed on the mineral surface after the adsorption of sulfide ions and its implications for cerussite flotation. Based on the results and discussion, the following conclusions can be drawn:
- (1)
An improved flotation recovery of cerussite was obtained after adding Na2S to the pulp, which was attributed to the formation of lead sulfide species on the mineral surface and its activity determined by disulfide and
Acknowledgements
The authors would like to acknowledge the financial support provided by the National Natural Science Foundation of China (No. 51464029), Analysis and Testing Foundation of Kunming University of Science and Technology (No. 20130534 & 20140876), and Academic New Artist Award for Doctoral Post Graduate in Yunnan Province (2014).
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