ABSTRACT There is currently a ubiquitous drive for South African industries to improve on water usage as large volumes of raw water are consumed and saline effluents (brines) are produced during their operations. This dissertation addresses the use of paste technology to co-dispose brines as well as solid wastes, from the SASOL Secunda complex in a sustainable manner. The findings from this study indicated that the properties of pastes with relatively high solids concentrations (e.g. 70%) are dependent on the physical properties of fly ash, such as carbon content and fineness thus impacting on the transportability of the paste. In order to overcome this effect, the paste with a 65% solids concentration will be less sensitive to the physical properties of the fly ash. Furthermore the chemical composition and salt load of brines affect the transportability and salt retention of paste. It was also observed that salinity of the brine affects the settling rate of the paste. The availability of various brines at SASOL provides an opportunity to investigate the blends of brines that will provide suitable settling and salt retention of paste. The other opportunity identified was the use of SASOL solid wastes such as incineration ash (IA) and gasification ash as additives to improve paste properties. It was also discovered that the mode of salt retention is predominantly chemical rather than physical, which increases the credibility of this technology. The overall conclusion is that paste technology is a potential solution for sustainable co-disposal of ash and brines. Further research areas are proposed to improve the understanding of paste technology and its implementation.

A test facility was constructed to conduct experimental investigation of erosion caused by gas-borne ash particles. The test facility was used to carry out the main objective of the study which was the determination of the critical angle of attack that gives maximum erosion on the target material, mild steel, and the effect of particle velocity and concentration on the erosion of the target material. The tests were carried out using ash samples from three different Eskom fossil-fuelled power stations, namely Matimba Power Station, Matla Power Station and Lethabo Power Station. The selection of the ash samples was based on the ash chemical composition that has the highest content of the chemical elements that have a significant influence in the material erosion of the target material. These chemical elements are quartz and other abrasive materials. These ash samples had a high content of these erosive materials. The first test that was carried out in this study was the determination of the critical angle of attack that gives maximum erosion on the target material. It was decided to start by doing this test because the velocity and concentration tests needed a predefined critical angle of attack that gives maximum erosion on the target material. During the velocity and concentration tests the angle of attack was kept at the predefined critical angle of attack. The results in this study indicate that the critical angle of attack that gives maximum erosion on the target material is at 27º ± 3º orientation of the target surface. The velocity test results indicate that the material erosion rate increases with increasing velocity. The results produced a power relationship between erosion rate and velocity. In this power relationship the velocity exponent for the three ash samples was found to be in the range between 2.42 and 3.64. The concentration test results also indicate that the material erosion rate increases with increasing particle concentration. These results produced a linear relationship between erosion rate and particle concentration.

A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy. Johannesburg, 2015. / The synthesis and applications of carbon nanomaterials (CNMs) such as carbon nanofibres (CNFs), carbon nanotubes (CNTs) and carbon nanospheres (CNSs) have attracted a lot of attention due to their unique chemical and physical properties. For the synthesis of CNMs with desired morphology to occur, one needs to consider three components, namely, the catalyst, carbon source and source of power. However, the cost of the catalysts involved in making CNMs is one of the challenging factors. Due to properties such as high aspect ratio, CNM use as fillers in polymer nanocomposites has been on the forefront to improve the mechanical strength of polymer materials such as polyesters. Due to their hydrophobic nature, the interaction between the filler and matrix tends to be problematic. In this study, we investigated the use of a waste material, coal fly ash as a catalyst for the synthesis of CNMs using the chemical vapour deposition method. The use of CO2 and C2H2 as carbon sources, either independently or together, was also employed. A comparison of two different ashes was also investigated. Lastly, the use of these synthesized and acid treated CNMs as fillers was examined. The catalysts and synthesized CNMs were characterised using SEM, TEM, EDS, laser Raman spectroscopy, XRD, BET, TGA and Mössbauer spectroscopy. The mechanical properties were investigated by testing the tensile, flexural and impact properties. The synthesis of CNMs using fly ash as a catalyst without pre-treatment or impregnating with other metals was achieved. Optimum yields and uniform morphology was obtained at 650 oC, at a flow rate of 100 ml/min using H2 as a carrier gas and C2H2 as a carbon source. Mössbauer spectroscopy revealed that cementite (Fe3C) was the compound responsible for CNF formation. Further, CNMs were formed over fly ash as a catalyst, using CO2 as a sole carbon source, an additive and a carbon source before reacting with C2H2. Duvha was Page | iii found to be a better fly ash catalyst compared to Grootvlei and an optimum loading was achieved at 0.25%. Treating the CNFs with HCl/HNO3 resulted in the highest tensile, flexural and impact strengths. This study / GR 2016

Geopolymer concretes synthesised from composite class F fly ashes and a mixed alkaline activator were optimised by use of Taguchi orthogonal design method. The optimised mix achieved a compressive strength at the age of 28 days of 70 and 58 MPa after initial curing at 70??C for 12 hours and at 23??C for 24 hours, respectively. The resultant Geopolymer has an amorphous aluminosilicate structure. Efflorescence and the potential risk of alkali-silica reaction for the Geopolymer used in this study are both very low. The research confirmed that the Geopolymer concrete developed in this study is far superior to Portland cement concrete when exposed in a sulphuric acid environment. The standard immersion tests finally selected for this research were in 10% sulphuric acid for 56 days and in 1% sulphuric acid for one year. Geopolymer concrete samples retained their shape without softening though they experienced a mass loss of about 5% and a strength loss of some 30%. Portland cement concrete recorded a mass loss of some 40% in a 10% sulphuric acid for 28 days. The penetration rate of sulphuric acid into the Geopolymer concrete was found to approximately follow Fick’s first law of diffusion and a linear relationship between the neutralisation depth and the square root of immersion time (in day) was established. The degradation processes of Geopolymer concrete in sulphuric acid environments were intensively studied. The first stage involved the preferential liberation of alkali ions. The tetrahedral aluminium in the Si-O-Al configuration was removed and converted to octahedral aluminium. Consequently, the original units of Si(1Al) degraded to a silica polymorph structure in the corroded Geopolymer, which continued to serve a cementitious role. In contrast, in the case of Portland cement concrete, the acid solution dissolved the hydration products of the cement paste. The residual reaction products were found to be soft and have no structural strength. Geopolymers with alkaline activators of mixed sodium hydroxide and sodium silicate did not exhibit any cracking problems. Class F fly ash with low calcium content was found to be suitable for developing a Geopolymer binder able to withstand sulphuric acid attack.

Thesis (M.S.)--Oregon State University, 1984. / Typescript (photocopy). Includes bibliographical references (leaves 38-41). Also available on the World Wide Web.

Thesis (Ph. D.)--Lehigh University, 2000. / Includes vita. Includes bibliographical references (leaves 160-165).

Thesis (M.Inst.Agrar. (Animal Production (Animal and Wildlife Sciences)) -- University of Pretoria, 2009. / Abstract in English. Includes bibliographical references.

published_or_final_version / Earth Sciences / Doctoral / Doctor of Philosophy

No description available.

Agricultural soils in Nova Scotia are usually limed in order to raise soil pH to ensure optimum availability of soil nutrients. Wood ash, produced by burning wood-based fuels, is promoted as a substitute for agricultural lime. This study individually assessed two wood ash sources available to Nova Scotia producers through on-farm sampling as well as greenhouse bioassay and incubation experiments. The variables measured were soil pH, plant-available and total element concentrations in soil, total element concentrations in above ground plant tissue, botanical composition and pasture condition scores (PCS). Soil pH was significantly increased after the application of wood ashes, however the effect was short-lived for one ash (NewPage). Agricultural lime was the most effective at increasing pH. Total soil concentrations of Al, Cr, K and Na remained elevated one year after ash application to NewPage sites. Brooklyn Power ash contained excessive levels of Zn, Cd, Pb and As.