No description available.

No description available.

No description available.

No description available.

No description available.

No description available.

A research dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science. Johannesburg, 2018. / ABSTRACT Acid mine drainage (AMD) is a serious global problem, particularly focusing on the Witwatersrand Basin, where most abandoned gold mines constituting mine waste containing pyritic rocks exist and leach sulfuric acid into surrounding waters as effluent containing trace elements like Fe, Co, Cu, Ni, Mg, Zn, Ca and U. Using currently available treatment technologies, it would be costly to remediate the approximately 3,000 miles of streams affected by AMD in Johannesburg hence probing a need for further research and new technology development. Therefore, this research explored the possibility of using prawn shells which contain a deacetylated form of chitin with a buffer capacity for use as a polluted mine water adsorbent. The effect of adsorption parameters such as contact time, absorbent dosage, initial pH, initial uranium ion concentration, competing anions and competing cations were investigated. An optimum adsorption of uranium(VI) of 92% was achieved using 1000 mg adsorbent dosage achieved optimum removal efficiency at pH 3, room temperature and 15 mg L-1 after 6 h equilibration time. The kinetics, isotherms followed pseudo second-order and the Freundlich models. The thermodynamic parameters for the adsorption of uranium onto prawn shells showed that the process proceeded in an exothermic nature, that is, adsorption capacity of uranium decreased with an increase in temperature. The desorption studies performed using HNO3 as an eluent gave efficiency of 19 ± 0.01% for 0.5 mg L-1, 37 ± 0.09% for 1 mg L-1 and NaHCO3 desorption capacity of 77.0 ± 0.01% for 0.5 mg L-1, 93.2 ± 0.05% for 1 mg L-1 and 99.7 ± 0.02% for 2 mg L-1, respectively. Consequently, NaHCO3 was found to be a good reagent for the desorption of uranium. The adsorption capacity was observed to be 0.17 mg g-1. At high concentrations the competing species showed an insignificant effect as uranium adsorption reached 97%. In all the experimental conditions, the speciation of uranium was determined using the PHREEQC geochemical modelling code. For instance, negatively charged U-carbonate complexes (e.g. UO2(CO3)22-) were predicted, explaining the potency of NaHCO3 as a desorbent for uranium. In the presence of competing ions, the speciation of uranium did not change significantly and hence the maintenance of elevated xv adsorption. Overall, the results of the study demonstrated that prawn shells are effective for the recovery of UO22+ ions, making them ideal for potential application for the remediation of uranium in liquid waste. Keywords: Uranium; Adsorption; Prawn shells; Acid mine drainage; Modelling / EM2018

A testing apparatus was developed for the determination of the change in permeability of coarse porous media subjected to a decrease in porosity . literature survey was conducted to establish the design criteria for the flow and loading tests. The mthemaUcal model describing flow through course porous media was further developed on a theoretical basis by postulating the layered medium model. Ihis model is a means by which the variability of the particle sizes in the medium is taken into account. The design, construction and operation of the testing apparatus is des:rvx-d. The specimen tested was laded up uo 3,45 MPa; consequently ' the Fbrcheimer aquation in the form of K , Ci/R + Cg was found to yield repeatable values for tiic turbulent friction factor C2, thus providing a means of predicting the change in permeability if the change in porosity and effective particle diameter are known.

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of requirements for the degree of Master of Science. Johannesburg, 2016. / Acid Mine Drainage (AMD) can result in significant and permanent ecological, chemical and physical alterations to the receiving environment. In 2002 a major surface decant of AMD effluent first entered the Tweelopies River upstream of the Krugersdorp Game Reserve, near Johannesburg. Within the game reserve the Tweelopies River intersects the Charles-Fourie Dam. The function of this dam, as a a sink of dissolved AMD contaminants (sulfate and iron), in the contaminated river was investigated in this study between September 2013 and August 2014. A water mass balance approach was used to estimate fluxes of dissolved contaminants. Additionally, compositional changes in sediment chemistry (total Fe, S, Al, Mg, Ca, Cu, Ni, Pb, V, and Zn) were investigated in order to quantify the storage or accumulation of contaminants in the sediment, which would indicate the long-term mitigatory function of the dam. The accumulation of high concentrations of metals and non-metals in the sediment of the dam (including 121.0 g S.kg-1 and 34.7 g Fe.kg-1) indicate that the dam stored both total iron and sulfur (AMD constituents) in the long term. Assuming that there was an average sediment depth of 19.3 cm in the dam, it was estimated that 18 tons of total iron, and 5 tons of total sulfur were present in the sediments of the dam. Additionally, the mass balance indicated that in total the dam acted as a sink for both sulfate and iron (14 853 kg SO42- and 5.5 kg Fe respectively) between September 2013 and February 2014, when the pH of the Tweelopies River was circumneutral (pH 6.1 – 7.6). However, the storage of contaminants in the dam also allowed iron and sulfate to be remobilised from the species and compounds it was stored in in the dam over the 2013-2014 study period. This is the result of changes in the water quality between March and July, when the pH of the river was lower (pH 2.9 – 3.6) and both dissolved iron and sulfate were remobilised (18 219 kg SO42- and 210 kg Fe respectively). In total the dam remobilised sulfate and iron in the 2013-2014 study period (increasing the flux by 0.4% or 3 366 kg and 8.7% or 202 kg Fe respectively). The data collected indicate that pH is the primary driver governing the dam to act as a sink and also remobilise dissolved iron and sulfate from the species and compounds they are stored in in the dam. When the pH is low the dam remobilises AMD constituents and acts as a sink when the pH is circumneutral. Therefore, it is evident that continual neutralisation of the water limits the degree to which the dam remobilises dissolved contaminants from the species and compounds they were stored in and that maintaining a neutral pH in the river should be prioritised by management. Additionally, the concentrations of total Fe, S, Ni, Pb, and Zn in the sediments exceeded the maxima probable effect level for the protection of aquatic life (by 3, 69, 20, 1.6, and 4.9 times respectively). The accumulation of contaminants in the sediment have very likely had a long-term adverse impact upon biodiversity and may present challenges to future rehabilitation efforts. Future management plans should avoid high investment loss to short-term remediation efforts and rather take a long term approach that incorporates these findings. / LG2016

Thesis (M.S.)--Ohio State University. / Includes bibliographical references (leaves 57-59). Available online via OhioLINK's ETD Center