78 research outputs found
Mechanisms of corrosion in surface layers at solid-solution interfaces
No full textThis review is focussed on solids in the broad categories of oxides, both simple (e.g. binary) and complex (e.g. silicates, aluminosilicates, titanates), and sulfides as ceramics, minerals and surface coatings. Mechanisms of surface reaction, corrosion and leaching associated with protons, hydroxide, water and simple cations and anions are considered. A variety of mechanisms that have some generality in determining the kinetics and reaction products at the solid-solution interfaces is illustrated. The focus of the experimental studies is on the surface layers; their development, distribution of species, depth and control. Mechanisms discussed and illustrated include: diffusion; protonation and ion transfer to solution; lattice reaction; ion exchange (leaching); precipitation; surface oxidation; surface reconstruction; intergranular films and grain boundaries. Theoretical models for the first four mechanisms are presented
Surface analysis methods in materials science.
No full textThe idea for this book stemmed from a remark by Philip Jennings of Murdoch University in a discussion session following a regular meeting of the Australian Surface Science group. He observed that a text on surface analysis and applica tions to materials suitable for final year undergraduate and postgraduate science students was not currently available. Furthermore, the members of the Australian Surface Science group had the research experience and range of coverage of sur face analytical techniques and applications to provide a text for this purpose. A of techniques and applications to be included was agreed at that meeting. The list intended readership of the book has been broadened since the early discussions, particularly to encompass industrial users, but there has been no significant alter ation in content. The editors, in consultation with the contributors, have agreed that the book should be prepared for four major groups of readers: - senior undergraduate students in chemistry, physics, metallurgy, materials science and materials engineering; - postgraduate students undertaking research that involves the use of analytical techniques; - groups of scientists and engineers attending training courses and workshops on the application of surface analytical techniques in materials science; - industrial scientists and engineers in research and development seeking a description of available surface analytical techniques and guidance on the most appropriate techniques for particular applications. The contributors mostly come from Australia, with the notable exception of Ray Browning from Stanford University
Kinetic factors for oxidative, and non-oxidative dissolution of iron sulfides
No full textThe dissolution behaviour of iron sulfides is significant in the minerals industry for both the recovery of more precious metals and the treatment of waste materials (pyrite being the major contributor to acid rock drainage). The dissolution behaviour of pyrrhotite, Fe(1-x) S, and troilite, FeS, in deoxygenated acid was studied using approaches established for the study of binary metal oxides in acid conditions. A feature of pyrrhotite (Fe1-xS) is that a relatively slow dissolution rate (10-8 mol m-2 s-1) can increase suddenly by three orders of magnitude (to 10-5 mol m-2 s-1) in the same solution. The sudden increases have been shown to be due to the onset of non-oxidative dissolution. Correlation was found between the non-oxidative dissolution of pyrrhotite and that of ionic and semi-conducting binary metal oxides dissolving in acid with reaction controlled kinetics. In both situations -log (Rate) was proportional to pH, implying that the rate-determining step is ionic transfer across the surface - electrolyte interface. The strongly ionic nature of the S2- bonding within semi-conducting troilite is made evident by dissolution rates of the order of 10-4-10-3 mol m-2 s-1. As with ionic oxides with dissolution rates of this magnitude, the dissolution kinetics of troilite are no longer reaction-controlled, but are controlled by bulk solution diffusion factors
Diagnostic leaching of galena and its oxidation products with EDTA
No full textMany authors have used EDTA as a means of determining the extent of oxidation of flotation pulps. However, there have been few documented studies of the reaction mechanisms in the interaction of EDTA with sulphide minerals and their oxidation products. This paper examines the use of EDTA to extract lead oxidation products from galena. In the first instance, it will be demonstrated that all oxygen containing galena oxidation products (i.e. sulphate, hydroxide, oxide, and carbonate, but not polysulphide or sulphur) are rapidly solubilized in EDTA. Secondly, it is shown that EDTA does not extract lead from un-reacted galena. Continued extraction of lead with increasing conditioning time is due to continued galena oxidation, not to the extraction of lead from galena. Argon gas purging minimises this oxidation whereas the use of air or nitrogen gas purging do not. Using mformation gathered from these experiments, an improved EDTA extraction technique was developed and compared with other techniques used within the mining industry. © 2002 Elsevier Science Ltd. All rights reserved
Collectorless flotation of pyroxene in Merensky ore: residual layer identification using statistical ToF-SIMS analysis
No full textIn Merensky (Bushveld Complex, South Africa) ore flotation, normally more than 2% of the gangue minerals,principally pyroxene with minor chromite, reports to the concentrate diluting the PGM recovery and contributing to subsequent processing costs. Understanding and controlling the mechanisms that cause this misreporting remains a primary target in PGM flotation. The orthopyroxene in Merensky ore can develop floatable properties through chemical interactions in the flotation system, principally through inadvertent copper-collector complexation, but this paper shows that this mechanism does not fully account for the true flotation of large pyroxene (20–150 µm) particles. Statistical comparison of ToF-SIMS analysis of particles from concentrate and tails reveals no significant difference in Cu and collector (IBX, DTP) signals between these streams but surface exposure of Mg and Si is favoured in the concentrate. Flotation of pyroxene without collector has confirmed this statistical discrimination. Hydrophobic talc-like residual layers, probably from partial serpentinisation of the pyroxene, seen in XRD differences between the concentrate and tails, explain this flotation mechanism
Surface chemical mechanisms of inadvertent recovery of chromite in UG2 ore flotation: residual layer identification using statistical ToF-SIMS analysis
No full textIn the UG2 ore (Bushveld Complex, South Africa) flotation, normally more than 3% of the gangue minerals,principally chromite with talc and pyroxene, report to the concentrate diluting the PGM recovery and contributing to subsequent processing costs. Previous studies have identified residual talc-like layers onorthopyroxene surfaces in Merensky ore flotation contributing to inadvertent flotation of relatively large particles (20–150 µm) of this mineral. Chromite (75–150 µm) from flotation of UG2 ore has been similarly examined. Statistical comparison of ToF-SIMS analysis of particles from concentrate and tails reveals no significant difference in Cu, Pb, Ni and collector (IBX and DTP) signals between these streams but surface exposure of Mg and Si is favoured in the concentrate. The flotation rate of coarse chromite correlates with the exposures of magnesium and silicon in patches on the chromite surface; higher exposures give earlier flotation. Conversely, there is a negative correlation with signals corresponding to the chromite surface, i.e.Cr, Fe, Al. Flotation of chromite without collector has confirmed this statistical discrimination. Hydrophobictalc-like residual layers, similar to those found on orthopyroxene surfaces, probably from partial alteration,explain this flotation mechanism
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