Browsing by Author "Gaylard, Peter"

Now showing 1 - 4 of 4
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    Atmospheric leaching of a saprolytic nickel laterite ore in chloride solutions
    (2008) Field, Karen Louise; Gaylard, Peter
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    Leaching of selected PGMs : a thermodynamic and electrochemical study employing less aggressive lixiviants
    (2008) Kriek, R J; Gaylard, Peter; Nicol, Mike; Nikoloski, Aleks
    Historically the platinum group metals (PGMs) have been, and are still being dissolved by means of rather aggressive methods, e.g. aqua regia. Limited research has been conducted into the dissolution of the PGMs using different oxidizing agents. The dissolution of gold on the other hand has been afforded extensive research, and numerous papers and review articles have been published on the subject. The last number of years has seen the biggest application by volume of the PGMs as part of autocatalysts towards the degradation of harmful motor vehicle exhaust gases. This has subsequently sparked research into the recovery of specifically platinum, palladium, and rhodium from spent autocatalysts. Currently pyrometallurgical recovery of PGMs is being employed predominantly. A hydrometallurgical process on the other hand is, based on current technology, still a rather aggressive process that makes for high maintenance costs and an unpleasant environment. Gold has traditionally been dissolved by making use of cyanide, which is still the major route for gold dissolution. Due to environmental concerns lixiviants such as thiosulphate (S2O3 2-), thiourea (H2NCSNH2), and thiocyanate (SCN-) are gaining acceptance due to them being more environmentally friendly and giving good recoveries. These ‘softer’ alternatives have however not been tested on the PGMs. It is therefore the aim of this study to obtain an improved understanding of the leaching of the PGMs using lixiviants less aggressive than aqua-regia. These lixiviants include (i) SCN-, (ii) S2O3 2-, (iii) H2NCSNH2, and (iv) AlCl3/HCl. A thermodynamic study highlighted the fact that thermodynamic data for platinum-, palladium- and rhodium complexes are basically non-existent. To therefore obtain a clearer thermodynamic understanding of the leaching of the platinum group metals by means of these alternative lixiviants, future detailed speciation and thermodynamic investigations need to be conducted. An exploratory electrochemical investigation focusing on open circuit potentials and potentiodynamic scans, showed AlCl3 / HCl / NaOCl to be a good candidate for the leaching of the platinum group metals followed by SCN- / Fe3+ and CS(NH2)2 / Fe3+. Actual leach results, employing virgin autocatalysts as sample material, again highlighted the potential of AlCl3 / HCl / NaOCl as being a good lixiviant system. The surprise package, however, has been SCN- / Fe3+ that rendered very good results for Pd and Pt.
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    Thermodynamic behaviour of sulphur and chlorine as minor elements in metallurgical melts
    (2006) Du Toit, Adam Jacobus; Gaylard, Peter; Jahanshahi, Sharif; Nell, Johan
    This thesis is presented on the equilibrium studies that have been carried out on a series of slags, specifically chosen to cover the range of composition and conditions appropriate to the melters of the platinum group metals (PGM) producers of South Africa. New measurements have been made on the ferric to ferrous ration, sulphide capacity as well as the chloride capacity mainly for the PGM melter-type slags.
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    The use of life cycle assessment in the evaluation of environmental performance in the base metal refining industry
    (1999) Forbes, Patricia Belinda Crosby; Gaylard, Peter; Petrie, James
    In the last decade, life cycle assessment has come into consideration as an environmental decision support tool for the design and operation of industrial processes. The usefulness of this technique for the purpose of environmental management was assessed by means of a case study carried out at the base metal refinery of impala Platinum Limited. An assessment was first carried out on the historic performance of the process. This was then extended to evaluate some possible impacts of future changes in operating practice and technology.