3. Electronic Theses and Dissertations (ETDs) - All submissions
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Item Geochemical characterisation of mine drainage from a copper mine operations at Phalaborwa (South Africa) and Kitwe (Zambia)(2022) Mwelwa KitondoMining and processing of copper minerals form a solid and dependable base for infrastructure, social and economic development of most countries in the Southern African region to which South Africa and Zambia belong, with Phalaborwa and Kitwe as their respective centers of copper mine operations. Copper and its auxiliary metals have benefited man in electrical, electronics, medicine and other spheres associated with modern and easy life. At the far side of societal benefits from an extended copper extractive mining, negative impacts of its operations degrade the environment of which water has always been regarded as the worst impacted target. Phalaborwa and Kitwe study sites are characterised by Cu-sulphide minerals coexisting with carbonate minerals in host ore rocks of volcanic and sedimentary origins, respectively. Phalaborwa is supplemented by large amounts of exploitable iron minerals (Magnetite) and phosphate minerals (Apatite), a recognized residence of REEs. In Kitwe, the exploitable ore deposits are rich in Cu-Co metals. Geochemistry was used, both as a path and a tool, to describe distinct features of a copper mine waste samples, assess potential hazards posed by contaminants resulting from their interaction with oxygen and water, evaluate metal speciation resulting from fractionation of sediments. Analytical results were further complemented by PHREEQC geochemical diagnostic simulations of surface water mixing and predictive simulations of surface water loss through evaporation. Adsorption studies were also used to investigate the recovery capacity of natural magnetite (Mgt) for rare earth elements (REEs) with essential properties for applications in electronics and medicine. Samples, consisting of stream water and sediments, and tailings (dumps) were collected at Kitwe study area. River and dam water and sediments, and a variety of mine solid waste consisting of rocks (Rk), sand, phosphogypsum (PG), carbonatite (Cbt), copper-crust (Cu_crust), magnetite (Mgt) and and tailings ex-concentrator (TexCon) were collected at Phalaborwa study area. Physical (dry) and chemical (wet) sample preparation, of which Toxicity Characteristics Leaching Procedure. (TCLP) and Sequential Extraction (SE) form part, paved the way for qualitative and quantitative analytical determination. A combination of analytical techniques (XRD, XRF, SEM-EDS, LPS, IC, ICP-OES (ICP-MS) and CHNS Analyser) were employed to identify minerals and quantify contaminants. Tailings dumps and sediments samples, from Kitwe, were digested (aqua regia, 3HCl:1HNO3) and leached (TCLP) to assess the effects of vigorous and mild extraction conditions. For both techniques, there were more release of major and trace elements from tailings dumps than sediments. Comparisons of digestion results, (tailings sediments), were: Al (12434<24774 mg kg-1), Ca (58368>5594 mg kg-1), K (6374>1379 mg kg-1), Mg (44622>6153 mg kg-1), Co (407.0>126.7 mg kg-1), Cu (3368>1320 mg kg-1), Fe (24753<27600 mg kg-1), Mn (3790>494.2 mg kg-1) and Zn (40.8<150.0 mg kg-1). The presence of SO42- in phosphogypsum (PG) and copper crust (Cu-crust) minerals, PO43- in sand (Sand) and rock (Rock1) minerals, and CO32- in carbonatite (Cbt) minerals of respective geologic samples was indicative of their association with the amorphous reactive phase whereas quartz, aluminosilicates and magnetite (Mgt) signaled the prominent presence of the crystalline inert phase. The extent of minerals dissolution and their accompanying release of inherent trace elements had a huge bearing on the composition of sample leachates. Cu was abundantly leached out from Cu-crust (45100 mg kg-1), Mgt (424.9 mg kg-1) and TexCon (141.8 mg kg-1). Non geologic samples, in perticular elephant dung (ED), produced leachates with elevated major ions concentration than Mgt, e.g. Ca2+ (1.93>0.33%), Mg2+ (0.78>0.18%), SO42- (964>228 mg L-1), Cl- (124>64 mg L-1). Metal species and positive saturation indices (SI > 1) of mineral precipitates, calculated from PHREEQC computation of surface water parameters, were abundant and more varied in WRD than in rivers. Furthermore, pH and Eh provided a favourable environment for the immobilization of trace metals via adsorption to, and subsequent deposition of scavengers such as iron- and Mn- oxyhydroxides. River sediments, from Phalaborwa, were crystalline (Si, Al, Fe) with silt to silty loam texture and high C/S ratio. Their leaching was reflective of these characteristics and their fractionation consistently released more bioavailable Mn and Cu. Sediments quality, assessed using bioavailable concentrations of trace elements as probable effect quotients (PEQs), was poor (mean PEQ > 0.5) and posed a risk to benthos. Predictive evaporation simulations of Cu_crust leachates indicated, in commensuration with percentages evaporation, worrisome exponential increases in concentration (ca 32%, 120% and 1900% increase at 10%, 50% and 95% evaporation, respectively), and deposition of metal species that could precipitate the deterioration of the aquatic system. Isotherms and kinetics models of REEs adsorption onto natural magnetite together with their thermodynamics were determined. Based on results, Langmuir isotherm model gave the best description of this adsorption process, and every indication pointed at the adsorption as obeying the pseudo-second order kinetic model. Thermodynamics adsorption studies were unanimous in determining the mechanism of REEs adsorption onto Mgt. The percentage recovery was 94.8%. The heats of adsorption, ΔHo (av = 22, min = 17, max = 41 kJ mol-1) and ΔHx, (av = 24, min = 18, max = 40 kJ mol-1), the activation energy, Ea, (av = 51, min = 16, max = 40 kJ mol-1), the activation energy Ea (av = 51, min = 16, max = 102 kJ mol-1), and the adsorption energy obtained from D-R isotherm Es (12 – 15 kJ mol-1) fell, generally, within the category of physisorption/ion exchange mechanism limits found in literature (ΔHo and ΔHx < 80, Ea < 40 and Es < 16 kJ mol-1). Furthermore, REEs adsorption onto Mgt was spontaneous (ΔGo < 0) with dissipative entropy (ΔSo > 0). This study did not seek to compare the two study areas by looking at results of one study site in parallel with results of the other study site, but to allow the evidence of similarities and differences, where possible, to come out with no demanding efforts by searching for aspects that are comparable.