The kinetics of dissolution of ilmenite, containing haematite, in aqueous solutions of sulphuric acid have been studied. Iron was found to leach from the mineral complex at a faster rate than titanium. The rates of solution of both iron and titanium increased, up to certain limiting values, upon abrading the mineral during leaching and were found to be related to the hydrogen ion activity of the leaching solution by a first order dependency. The results have been interpreted in terms of preferential and possibly diffusion-controlled leaching of the haematite with ilmenite being removed both by slow leaching and tearing out from the specimen surface. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

A dissertation submitted to the Faculty of Engineering and the Built Environment at the University of Witwatersrand, Johannesburg, in part fulfillment of the requirements for the degree of Master of Science in Engineering, 17 May 2018 / Traditionally, copper and cobalt are extracted from oxidised ores via hydrometallurgical processing route. The ore is leached in sulphuric acid in reducing conditions. This method co-extracts impurity metal values like iron and manganese, necessitating downstream solution purification, which causes significant valuable losses. Pregnant leach solution purification is performed through step-wise oxidation and acid neutralisation of the leach solution. Cobalt is the most affected component in this process due to high losses incurred during the precipitation stages. Moreover, because the lixiviant is not recycled, the method consumes ominously high quantities of sulphuric acid. As a result, the process must be accompanied by readily available and cost-effective acid-making plant. In the event of an increase in the price of sulphuric acid raw materials or a decline in the ore grade, a source of 50% of the world’s cobalt might be rendered impracticable. This work investigates the viability of using ammoniacal solution as an alternative lixiviant to sulphuric acid. Ammoniacal solution forms soluble complexes with copper and cobalt at pH and potential where iron, manganese and other impurities tend to form precipitates. Because of the preferential leaching, downstream solution purification can be circumvented, thereby reducing valuable losses. Furthermore, because there is no solution altering, multi-step solution purification required, the leach solution retains its initial pre-leaching properties, making it fully recyclable. The recyclable nature of the lixiviant thus reduces lixiviant costs. Furthermore, an advantage of leaching in ammonia is lower equipment costs because ammonia is less corrosive than acid. The feed material used in this study was an oxidised copper-cobalt ore sourced from Katanga Region in the DRC. A size fraction analysis was undertaken in order to determine the deportation of the copper and cobalt metals in the feed material. In the leaching tests conducted, the effect of particle size, temperature, concentration of the reducing agent and concentrations of ammonia and ammonium carbonate were investigated. The results showed that a +63-75μm size fraction had the highest grade of copper and cobalt and was thus used for all the experiments undertaken. The results also indicated that cobalt and copper extraction was highly influenced by temperature. It was found that working at ambient temperature results in poor extraction of the value metal species while raising the temperature to 80°C significantly improves the extraction of both value metals if premature depressurising of the leach vessel is avoided. The results also showed that there was no significant extraction advantage gained from milling finer than -63μm. Moreover, it was found that at 80°C, 2.0M ammonia solution, 0.4M ammonium carbonate, 300rpm, 0.4M reducing agent and 60 minutes pre-treatment and leach time, a peak extraction of 90% could be realised for copper. It was also noted that even better extraction efficiencies could be obtained for copper in the absence of a reducing agent. Optimum cobalt extraction of 85% was obtained at 80°C, 2.0M ammonia solution, 2.0M ammonium carbonate solution, 0.4M ammonium sulphite, 60 minutes pre-treatment time and 60 minutes leaching time. This compares well to about 40-60% recovery reported when leaching in acid. These findings point to the conclusion that ammoniacal solution is a viable alternative to sulphuric acid for hydrometallurgical processing of the copper-cobalt ore. / MT 2018

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This item was digitized as part of the Million Books Project led by Carnegie Mellon University and supported by grants from the National Science Foundation (NSF). Cornell University coordinated the participation of land-grant and agricultural libraries in providing historical agricultural information for the digitization project; the University of Arizona Libraries, the College of Agriculture and Life Sciences, and the Office of Arid Lands Studies collaborated in the selection and provision of material for the digitization project.

Aerosol particles have profound impacts on human health, atmospheric radiation, and cloud microphysics and these impacts are strongly dependent on particle sizes. However, formation and growth of atmospheric particles are currently not well understood. In this work, laboratory and theoretical studies have been performed to investigate the formation and growth of atmospheric particles. The first two parts of the dissertation are a laboratory investigation of new particle formation and growth, and a theoretical study of atmospheric molecular complexes and clusters. The nucleation rate was considerably enhanced in the presence of cis-pinonic acid and ammonia. The composition of the critical cluster was estimated from the dependence of the nucleation rate on the precursor concentration and the time evolution of the clusters was then simulated using molecular dynamic simulations. Results from quantum chemical calculations and quantum theory of atoms in molecules (QTAIM) reveal that formation of strong hydrogen bonding between an organic acid and sulfuric acid is likely responsible for a reduction of the nucleation barrier by modifying the hydrophobic properties of the organic acid and allowing further addition of hydrophilic species (e.g., H2SO4, H2O, and possibly NH3) to the hydrophilic side of the clusters. This promotes growth of the nascent cluster to overcome the nucleation barrier and thus enhances the nucleation in the atmosphere. The last part of this dissertation is the laboratory investigation of heterogeneous interactions of atmospheric carbonyls with sulfuric acid. Direct measurement has been performed to investigate the heterogeneous uptake of atmospheric carbonyls on sulfuric acid. Important parameters have been obtained from the time-dependent or timeindependent uptake profiles. The results indicated that the acid-catalyzed reactions of larger aldehydes (e.g. octanal and 2, 4-hexadienal) in sulfuric acid solution were attributed to aldol condensation in high acidity. However such reactions do not contribute much to secondary organic aerosol (SOA) formation due to the low acidity under tropospheric conditions. On the other hand, heterogeneous reactions of light dicarbonyl such as methylglyoxal likely contribute to SOA formation in slightly acidic media. The reactions of methylglyoxal in the atmospheric aerosol-phase involve hydration and subsequent polymerization, which are dependent on the hygroscopicity, rather than the acidity of the aerosols.

Thesis (M.S.)--University of Missouri, School of Mines and Metallurgy, 1927. / The entire thesis text is included in file. Typescript. Title from title screen of thesis/dissertation PDF file (viewed February 23, 2010) Includes bibliographical references (p. 34).

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Thesis (Ph.D.)--McMaster University, 2006. / Supervisors: M.B. Ives, K.S. Coley. Includes bibliographical references.