The extraction of aurocyanide by activated carbon probably involves the adsorption of neutral ion-pair species [M ^jAuCCN)^. The large hydrophobic aurocyanide anion associates with the cation in order to minimize the disruption of the water structure whereby lowering its free energy

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Thesis (M.S.)--University of Wisconsin--Madison, 1963. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves [141-155]).

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Several conflicting theories of the adsorption of aurocyanide onto activated carbon presently exist. To resolve the mechanism, adsorption and elution of aurocyanide are examined by several techniques, including Mossoauer spectroscopy, X-ray photoelectron spectroscopy, X-ray diffractometry, Fourier Transform Infrared spectrophotometry, ultraviolet-visible spectrophotometry and scanning electron microscopy. The evidence gathered indicates 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. The poor agreement in the literature regarding the mechanism of adsorption of aurocyanide onto activated carbon is shown to be due to the fact that different mechanisms operate under different experimental conditions. The AuCN produced on the carbon surface by acid treatment is shown to react with hydroxide ion via the reduction of AuCN to metallic gold with formation of Au (CN) 2 , and the oxidation of cyanide to cyanate. Other species, such as An(CN)5 and Ag(CN)g adsorb onto activated carbon by a similar mechanism to that postulated for Au(CN)2 . Ion association of MAu(CN) 2 salts in aqueous solution is demonstrated by means of potentiometric titration and conductivity measurements, and various associated species of KAu(CN), salts are shown to occur in organic solvents by means of infrared spectrophoteaietric and distribution measurements. A kinetic model was developed for elution of aurocyanide from activated carbon and was found to predict gold elution performance successfully using the Zadra procedure. The influence of the surface chemistry and structure of activated carbon on adsorption of aurocyanide was investigated by characterization of activated carbons that were synthesized or oxidized under various conditions. Synthetic polymeric adsorbents with characteristics similar to activated carbons were also studied. The evidence suggests that a large micropore volume is important in providing suitable active sites for adsorption. Another important factor is the presence of basic functional groups within the micropore, which act as solvating agents for the ion pair. The aim is to provide a self-consistent adsorption mechanism that accounts for all observations presented in the literature. Interpretation of results in terms of preconceived ideas, and neglect of observations of other authors has greatly contributed to current disagreement in the literature.

As amostras de carvão ativo de bagaço de cana-de-açúcar foram preparadas em temperaturas de carbonização de 500, 600 e 700 ºC, com tempos de ativação de 60 e 120 minutos e concentração de agente ativante (ZnC12) 30 e 60% em relação ao bagaço seco original. Foi utilizado como padrão, para verificação de eficiência, um carvão ativo alemão (Riedel). Estas amostras foram caracterizadas pelas seguintes análises: rendimento; teor e umidade; teor de cinzas; pH; teor de substâncias solúveis em água. Foi também estudado o desempenho destas amostras no descoramento de água de lavagem de cana-de-açúcar, utilizando 1% e 1,5% em peso de carvão ativo. Amostras preparadas a 500 ºC, 60 minutos e concentração de agente ativamente 0%, 30% e 60% em relação ao peso de bagaço seco original foram utilizadas no tratamento de água de lavagem de cana-de açúcar visando a diminuição do potencial poluidor, essas mesmas amostras foram utilizadas para determinação de poder de adsorção, equação e isoterma de Freundlich. Os resultados mostraram ser viável, em escala de laboratório a obtenção de carvão ativo de bagaço de cana-de-açúcar, para utilização no tratamento de água de lavagem de cana-de-açúcar visando diminuir o seu potencial poluidor. / Samples of activated carbon from cane-thrash were prepared in carbonization temperatures of 500, 600 and 700 ºC; activation times of 60 and 120 minutes, and concentrations of activating agent (ZnC12) 30 and 60% in relation to the original dry bagasse. A German activated carbon, was used a standard (Riedel). The samples were characterized by the following analysis: yield, proportion (5) of humidity, proportion of ashes; pH; proportion of solubles in water substances. It was also studied the performance in discolouring sugar-cane washing water using 1% and 1,5% in weight of activated carbon. Samples prepared in 500 ºC, 60 minutes and activating agent concentration of 0%, 30% and 60% in relation to the weight of the original dry bagasse were used in the treatment of sugar-cane washing water the purpose of reducing the polluter potential. They were used to determine the adsorption power, equation and Freundlish isotherm. The results showed it is possible to obtain active carbon from cane-thrash in laboratory scale, to be used in the treatment of sugar-cane washing water with the purpose of reducing its polluter potential.

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