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Trona ore located in Beypazari is extracted by solution mining method with well pair connected by directional drilling technology. This thesis covers the determination of the dimensions of the initial (vertical) caverns formed in underground by use of a computer modeling (trademark: WinUbro/Poland) on the basis of horizontal and vertical leaching rates. The leaching rates were determined using the trona core samples from the ore deposit. The effect of insoluble content and the thickness of trona layer and solvent temperature on the initial cavern dimension were studied. The outcome of this study showed that the better the trona layer quality from the point of view of thickness and insoluble content, the wider the vertical cavern size is. In 1 m thick trona layer with 20% insolubles, it is possible to develop caverns of 6 m width, which is the minimum size for well pair connection. On the other hand, it is determined that the effective leaching time depends mainly on solvent temperature.

The aim of this study was to study the extraction of zinc from the mineral sphalerite, especially the leaching of concentrate recovered from the Rosh Pinah tailings by means of ferric chloride. To this end, the literature on zinc processing was surveyed and knowledgeable persons were consulted. The study also addressed the leaching kinetics of an upgrade Rosh Pinah tailings dam concentrate as well as those of a synthetic zinc sulphide in a ferric chloride medium. Valuable results were obtained, from the leaching of sphalerite concentrate in ferric chloride medium. An activation energy value of 45.82 kJ/mol was obtained, which compares well with what has been published in the literature. A chemical control model and a diffusion control model were applied to the data obtained. From neither of the models a straight-line relationship could be deduced over the leaching range. At t < 45 minutes it seems that the process is controlled by chemical reaction at the interface; at t > 45 minutes it seems that the process is controlled by diffusion through the product layer. If therefore seems that the rate-controlling step can be related to the process of diffusion through the product layer. The mixed control model proposed by Huang and Rowson, [1-(1-x)1/3+y/6[(1-x)1/3+1-2(1-x)2/3]=kMt, was applied to data obtained during this study. The resultant graphical fit was near perfect, indicating that sphalerite leached in ferric chloride follows a mixed control mechanism for the conditions reported in the study. An activation energy of 20.71 kJ/mol was determined for this model by using the following equation: / Dissertation (MSc)--University of Pretoria, 2006. / Chemistry / unrestricted

Pour progresser dans la compréhension des mécanismes liés aux instabilités des cavités souterraines à partir de la réponse microsismique associée, l'effondrement provoqué d'une cavité saline (~ 200 m en diamètre), créée par dissolution, a été instrumentée sur un site d’exploitation de SOLVAY à Cerville-Buissoncourt (Lorraine, France). Pendant l’expérimentation un vaste ensemble des données a été enregistré (~ 50,000 fichiers d'événements) dont la majorité (80%) est constitué d’essaims microsismiques singuliers. Cette thèse présente une analyse et une interprétation détaillée de cette base de données microsismiques grâce à l’adaptation de méthodologies de traitement originales, dont les résultats améliorent notre compréhension sur la nature de la microsismicité liée aux processus de création et d’effondrement des cavités souterraines, ainsi que sur l’évaluation de l’aléa associé. Les résultats principaux obtenus sont les suivants : les événements microsismiques sont comparables à des petits séismes tectoniques ayant des magnitudes de moment variant entre -3 et 1. (ii) L’ensemble des événements microsismiques montre un mécanisme en cisaillement (double-couple) remarquablement stable et est associé à un régime en faille inverse d’orientation NO - SE, plongeant à environ 35°– 55°. Ce phénomène est probablement lié à la présence de fractures préexistantes sur le site. (iii) L'origine des essaims microsismiques est certainement due à l'incapacité du système à créer des fractures de grandes dimensions capables de libérer des contraintes très importantes. Cela est probablement lié aux propriétés mécaniques du toit de la cavité. (iv) Les périodes d’effondrements du toit de la cavité sont associées à une dynamique de forçage systématique et montrent une réponse microsismique particulière, qui peut-être décrite par des lois statistiques. Les travaux de recherche de cette thèse confirment également, que la surveillance microsismique peut être un outil puissant pour étudier les processus d’instabilité des cavités souterraines, même avec un nombre réduit de capteurs si des outils d’analyse adaptés sont utilisés / In order to improve our understanding of hazardous underground cavities and its microseismic response, the development and collapse of a ~ 200 m wide salt solution mining cavity was monitored at Cerville-Buissoncourt in the Lorraine basin in NE France. The majority of the obtained dataset (~80%) was constituted of numerous unusual microseismic swarming events (~50.000 event files). This thesis presents innovative methods able to treat this specific microseismic data set, whose results provide new and fundamental insights into the principal characteristics of caving and collapsing related microseismicity and hazard assessment of excavated underground formations. The principal results are as follows: (i) the individual microseismic events are comparable to small natural tectonic earthquakes with moment magnitudes Mw ranging from around -3 to 1. (ii) Source mechanisms for most microseismic events are remarkable stable and demonstrate a predominant thrust faulting (double-couple) regime with faults similarly oriented NW-SE, dipping 35°-55° , what might be related to the presence of systematically arranged pre-existing fractures. (iii) The origin of microseismic swarming is suggested in the incapacity to sustain larger strains and to release larger stresses, what seems to be related to the mechanical constitution of the rock strata overlying the cavity (i.e. low strength materials). (iv) Caving and collapsing periods at the cavity roof are associated with systematic, self- reinforcing dynamics and have a distinct microseismic response, clearly observable from statistical analysis, which can be precisely described by empirical laws. The performed analysis and interpretation of the microseismicity at Cerville-Buissoncourt has shown that microseismic monitoring is a useful tool to constrain the mechanical and dynamical characteristics of an evolving and collapsing hazardous underground cavity