3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item Purification of coal fly ash leach liquor for alumina recovery(2018) Rampou, MohauOver the years, much work has been done on the extraction of alumina from coal fly ash (CFA). Previous works were motivated by the results of the quantitative analysis of CFA that showed a high content of alumina; comparatively ranking second to the primary bauxite ore. Thereafter, research studies have been dedicated to finding efficient routes of recovering alumina from CFA. Amongst recent studies, a 2-step leach process developed by researchers from the University of Witwatersrand gave promising recovery results. The current work is an extension of the 2-step leaching process, where an attempt is made to purify the leach liquor recovered from this leaching process in order to generate a purer aluminum solution by removing iron and titanium, which are considered as the two major impurities. The aim is to obtain an impurity free solution that can be used to generate smelter grade alumina. In this study, solvent extraction using Primene JMT in kerosene was applied to remove the impurities from the leach solution. Optimum parameters tested during the solvent extraction process included contact time, extractant concentration and the organic to aqueous (O/A) ratios. As expected, most of the titanium was extracted in the organic phase and much of the aluminum remained in the aqueous phase. However, the results showed that most of the iron, which occurred in solution as iron (III) and iron (II), also remained in the aqueous phase. This was an unwanted occurrence, as this residual iron would then co-precipitate with the alumina leading to a contaminated product. Two approaches were then applied for a more effective separation of iron from aluminum. The first approach (Route 1) considered the reduction of the iron (III) species into iron (II) prior to solvent extraction for titanium removal. Alumina crystallization then followed and since iron (II) precipitates at higher pH than aluminum, there was reduced contamination of the alumina product. The second approach (Route 2) firstly considered solvent extraction to remove titanium ions and any iron ions. This was followed by the reduction of residual iron (III) to iron (II). In both approaches, aluminum was crystallized out and iron (II) precipitated using (NH4)2SO4. Titanium (IV) was stripped from the organic phase using NH4OH. The results obtained showed a successful purification of the coal fly ash leach liquor for both processes. Route 1’s disadvantage is that it used more metal iron filings for iron (III) reduction to iron (II) than route 2. Route 2’s disadvantage is that due to the 2-stage stripping applied, it used more excess reagents, therefore implying higher operational costs than route 1. As a result, Route 1 was considered for further tests. The final alumina product generated with the route 1 purification process had a 99.4% Al purity. This purity level meets the smelter grade alumina product specifications. The grade of the final product therefore, indicates that the applied process route was successful.Item Beneficiation of Waterberg Coal(1992) Eroglu, BerrinModern methods of mechanised mining and the necessity for the utilization of total reserves have caused the inclusion of more and more impurities in run of mine coal. This fact, together with the limited supply of naturally clean coal fCI gasification, liquefaction and metallurgical purposes, has made some Iorm l){ beneficiation obligatory at many mines not only in South Africa but also in many other countries. One of the South African Coalfields, Waterherg, contains the continent's largest reserves (approximately 46% of South African known reserves). At the Grootegeluk Coal Mine, approximately 15 m tons of coal per annum are mined by opencast methods. The coal is characterised by containing a high proportion of reactive macerals. The Waterberg Coalfield is currently supplying coal for coke manufacture and middlings for power generation. This coal could also be used for other markets, as Waterberg coal is low in oxygen, contains up to 30% volatile matter. Because it contains 90% vitrinite, it is suitable for direct liquefaction, and possibly coal-water mixtures. However the yield of coal suitable for coking or liquefaction (approx 10% ash) is only 12%, with another 24% of 35% ash coal, currently used for power generation. These yields render mining generally uneconomical if making a simple product. The objective of this project is to ascertain whether the yields of washed coal from the Waterberg Coalfield might be increased by using comminution. Thereafter appropriate beneficiation techniques might be employed on different size fractions. Liberation, float and sink, froth flotation and oil agglomeration processes were examined to identify the best way of treating the coal. Work was carried out on the existing clean coal, middlings and discard fractions. The major objective was to optimise the yield of 10-15% ash coal.The results of the experiment indicate that it is possible to obtain low ash coal from middlings, and middlings from discard for power station. The capital and operating costs for improved new plants are calculated by using available factorised data. The results of experiments on both middlings and discards indicate that yields are significantly higher than those currently obtained, but the cost of obtaining such enhanced yields can be too high for normal commercial application.