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
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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
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/25655 |
| Date | January 2018 |
| Creators | Tshikovhi, Fhatuwani Precious |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | Online resource (xv, 79 leaves), application/pdf |
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