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Authors: Huberts, R
Date: 2011
Language: English
Type: Abstract: Metal sulphate containing acid mine water decantation is generally expected to be an ever increasing challenge as mining activity winds down on the Witwatersrand. The water is contaminated due to by-products of aerobic bacterial action, which catalyses the oxidation of sulphide minerals in the presence of oxygen and water. During the flooding of an abandoned mine, air is replaced with ground water, limiting the access of oxygen as this gas is only sparingly soluble in water. This paper is a theoretical study on how the quality of decanting mine water at a given location may be expected to vary in the longer term.
Identifier: http://hdl.handle.net/10210/16954
Date: 2009
Language: English
Type: Abstract: An integrated procedure for steam extraction followed by volatiles sampling and analysis from the leaves of the Eucalyptus tree was explored. There are two problems to overcome in the extraction from solid plant materials: that of releasing the essential oils from solid matrix and letting it diffuse out successfully, and to model in a manner that can be scaled-up to industrial proportions. Towards this end, the effect of different parameters, such as temperature, pressure and extraction time on the extraction yield were investigated. Temperature (90oC, 97oC, and 99oC) was found to be a significant parameter affecting yield. An increase in yield was observed as pressure was increased and the use of high pressure (150 kPa) in steam generation units permits much more rapid and complete distillation of essential oils over atmospheric pressure. The yield was calculated from the relation between the essential oil mass extracted and the raw material mass used in the extraction. The volatiles, Eucalyptus oil in vapour form, released from the leaves were condensed and analyzed using Gas Chromatography, and eight major components were found to be contained in this species. A mathematical model based on diffusion of essential oil in the leaves was developed. Using a numerical method, the best diffusion coefficient was established for different operating conditions by comparing the model concentration of oil remaining in the leaves with the experimental amount of oil recovered; hence minimizing the sum of squared errors. It was found that one can not simply assume that the oil leached and recovered at the end of a run was the same as that originally present in the leaves. The initial mass of oil was determined by fitting the diffusion model to the data at all temperatures. The Arrhenius model was used to account for the effect of temperature. The resulting expression for the diffusion coefficient as a function of temperature can now be used to model the large scale extraction of the essential oils from Eucalyptus leaves.
Identifier: http://hdl.handle.net/10210/17148
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