The Mechanism Of Adsorption Of Aurocyanide Onto Activated Carbon
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| Release | : 1989 |
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The mechanism of adsorption of aurocyanide onto activated carbon and its subsequent elution are examined in this study, with special reference to the effects of acid and alkali treatment on the system. The results, including a careful analysis of the distribution of all ions in the adsorption and elution processes, are discussed, and evidence for the adsorption and elution mechanisms involved is presented. It is proposed that, under normal plant conditions, aurocyanide is extracted onto activated carbon in the form of an ion pair, M(n+)[Au(CN)2(-)]n, and eluted by hydroxide or cyanide. The hydroxide or cyanide ions react with the carbon surface, rendering it relatively hydrophilic with a decreased affinity for neutral species. Additional adsorption mechanisms are shown to operate under other conditions of ionic strength, pH, and temperature, and it is suggested that this may account in part for the lack of agreement among workers.
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| Release | : 1990 |
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The poor agreement between different workers regarding the exact mechanism involved in the adsorption of aurocyanide onto activated carbon is shown to be due to differences in the experimental conditions they employed. The effects of oxygen and ionic strength are shown to be interrelated. Adsorption under conditions of high ionic strength, as found in gold plants, involves an ion-pair mechanism whereas, under conditions of low ionic strength, a portion of the gold is adsorbed by electrostatic interaction with ion-exchange sites formed through oxidation of the carbon surface by molecular oxygen.
| Author | : Arturo Sabio Ibrado |
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| Total Pages | : 426 |
| Release | : 1992 |
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| Total Pages | : 14 |
| Release | : 1993 |
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Synthetic and commercial activated carbons are characterised for several chemical and physical properties. A range of techniques is used to establish correlations between physicochemical parameters and gold-adsorption activities. The most important parameter in the carbon activation process for a product with a high gold-adsorption activity is the activation temperature. High activation temperatures yield products with large micropore volumes which provides sites that are ideal in size for adsorption. The surface area of an activated carbon is not necessarily a good measure of its adsorption activity. Surface oxygen-containing functional groups are comprised mainly of ethers and hydroxyls. These functional groups line the edges of the micropores imparting a polar character to the pore and aid in the solvation of the adsorbate. Oxidants such as nitric acid result in a proliferation of surface carboxyl groups resulting in a negatively-charged surface that is not conducive to the adsorption of gold.
| Author | : Roop Chand Bansal |
| Publisher | : CRC Press |
| Total Pages | : 498 |
| Release | : 2005-05-24 |
| Genre | : Science |
| ISBN | : 1420028812 |
High surface area, a microporous structure, and a high degree of surface reactivity make activated carbons versatile adsorbents, particularly effective in the adsorption of organic and inorganic pollutants from aqueous solutions. Activated Carbon Adsorption introduces the parameters and mechanisms involved in the activated carbon adsorption
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| Release | : 1980 |
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X-ray photoelectron spectroscopy showed that the adsorption of gold cyanide on carbon in the presence or absence of electrolytes and acids proceeds by the same mechanism. Although the identity of the gold cyanide adsorbate is not known, the mechanism appears to have an initial adsorption stage that involves the adsorption of an ion pair: M(n+)[Au(CN)2(-)]n, where M(n+) is a metal ion (for example Na+, K+ and Ca(2+) that has a lower solubility than the Au(CN)2(-) anion in the adsorption medium, followed by a reduction step in which either a sub-stoichiometric Au(CN)x surface species or a cluster-type compound of gold is formed.
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| Release | : 1993 |
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A polyxanthene and polyquinone have been synthesized and characterized as possible models for activated carbon. These polymers display very high capacities for aurocyanide, which is possibly adsorbed by an ion-exchange mechanism onto carbonium-ion sites. The quinone functionalities play an important role in the adsorption of phenol onto polyquinone. The polyquinone is slightly selective for Au(CN)2- over Ag(CN)2- and base-metal cyanides, whereas the polyxanthene displays no such selectivity. Graphite adsorbs Au(CN)2- only from acidic solution, which results in the adsorption of gold as insoluble AuCN.
| Author | : John Marsden |
| Publisher | : SME |
| Total Pages | : 688 |
| Release | : 2006 |
| Genre | : Science |
| ISBN | : 9780873352406 |
Extensively revised and updated, this edition provides the broad base of knowledge required by all working in the gold extraction and gold processing industries. It bridges the gap between research and industry by emphasizing practical applications of chemical principles and techniques.
| Author | : P. M. Afenya |
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| Total Pages | : 27 |
| Release | : 1993 |
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Activated carbon has been used in a variety of ways for many years. Some of the early applications are in the removal of color, odor taste and objectionable impurities from solutions. In recent years activated carbon has attained new prominence as a material for adsorption of gold and silver cyanides from cyanide-leach gold ores. This new use has a attracted many researchers to investigate the mechanism of aurocyanide adsorption on activated carbon. This paper reviews the chemical and structural characteristics of activated carbon and its mode of adsorption of organic and inorganic species from solutions. Emphasis is given to the study of the mechanism of aurocyanide adsorption. Recent use of X-ray photoelectron spectroscopy for investigating the nature of the adsorbed aurocyanide species will be discussed. [Author's abstract].
| Author | : Ljubisa R. Radovic |
| Publisher | : CRC Press |
| Total Pages | : 442 |
| Release | : 2000-11-09 |
| Genre | : Science |
| ISBN | : 9780824702465 |
"Provides an overview of scientific and technological issues in environmental applications of carbon materials. Emphasizes the versatility of carbon materials in both gas- and liquid-phase environmental applications, including a discussion of emerging technologies. Highlights the power and potential opportunities afforded by NMR spectroscopy for understanding the interaction of carbon materials with adsorbed molecules."
