MENVSC / Department of Ecology and Resource Management / See the attached abstract below

MESMEG / Department of Mining and Environmental Geology / Vhembe District has several clay deposits which are traditionally use for clay products such as burnt bricks without taking into account the chemical and mineralogical characteristics of clay being used. The ever-increasing market demand for these clay products cannot be met with the traditional method of clay utilization due to the paucity of scientific information on properties of the clay in the area. Consequently, there is a need to gain better understanding of the characteristics of the clay in Vhembe District and to establish the suitability of the variety of clay for different purposes. The current study was undertaken to better understand the compositional relationship between the clay deposits and surrounding rocks present in the study area. It further aimed at characterizing the clay deposits on the basis of chemical, mineralogy, physical, mechanical, thermal and micro structural properties with a view of evaluating the clays for possible industrial use. A total of thirty-nine clay and rock samples were collected from thirteen different locations across the Vhembe District. Thirteen representative samples from each location were obtained after thorough mixing until homogenization was attained and then quartered for subsequent analyses. The mineralogical and chemical characteristics of the clay and rock samples were determined using XRD and XRF respectively. Thin-sections of the rock samples were prepared and examined under petrographic microscope to better understand the mineral assemblages present in the rocks. The thermal and micro structural properties of the clays were determined using DTA-TGA and SEM analyses and the physical properties which include colour, cation exchange capacity (CEC) and soil pH were assessed. The particle distribution and Atterberg limits tests of the clay samples were also conducted in order to establish their mechanical properties. The petrographic results showed that the clay deposits exhibited an intense weathering and sedimentation processes which incorporated detrital minerals from the surrounding rock units. The rock units which include basalt, granodiorite, gneiss and quartzofeldspathic gneiss were found to be differentiated from subalkaline and/or tholeiitic magmatic composition. Although the value of SiO2 content in rock samples was higher when compared with clay samples, it indicated an ongoing desilicication and allitization processes. The high values of chemical index of alteration (CIA), low values of K/Cs (<6200), Ce* normalized value and higher values of LILE enrichment in the clay deposits indicated oxidizing environments during period of deposition. v The mineralogical composition of the studied clayey deposits showed that smectite (8.25 - 29.32%), kaolinite (14.91 - 59.26%) and chlorite (5.94 -16.54%) were present as clay minerals although associated with other non-clay minerals such quartz, plagioclase, talc and geothite. The chemical composition results revealed high silica and alumina content in most studied clay samples. Their fluxing oxides which include K2O, Na2O, CaO, and MgO, varied slightly from 0.06% to 1.78% in abundance while the Fe2O3 and TiO2 contents in most samples averages at 9.2% and 1.3% respectively. The plasticity index of the studied deposits ranged from 9.50 to 62.00% while liquid limit ranged from 31.34 to 73.62%. The microanalysis using SEM indicated that the microstructure framework of most studied clay exhibited a porous skeleton structure owing to numerous tiny voids. The composite results of SEM and CEC analyses suggested their possible application in water filter and chemical fertilizer industries since they provided passage for water and soil cations transmission. The particle size distribution demonstrated that the studied soils have clayey silt texture with wide range coverage of the well graded and sorted particle sizes. Compressibility and plasticity properties were found to be high in Mukondeni, Mashamba-1, Mashamba-2 and Mashamba-3 clay samples. The thermal behavior of Mukondeni, Mashamba-1, Mashamba-2 and Mashamba-3 samples showed relatively high shrinkage (>9%). The high shrinkage percentage suggests the preponderance of smectite minerals. Other samples which are rich in kaolinite and chlorite minerals exhibited low shrinkage (<2%). The drying trends of the studied clay suggest their suitability for fast drying processes like soft and hard refractoriness, sanitary wares and ceramics. Empirical assessment of most studied clay showed their suitability for pottery-making and manufacturing of roofing tiles and masonry bricks. / NRF

PhD (Environmental Sciences) / Department of Ecology and Resource Management / The presence of arsenic in groundwater has drawn worldwide attention from researchers and public health officials due to its effects on human health such as, cancer, skin thickening, neurological disorders, muscular weakness, loss of appetite and nausea. World Health Organisation (WHO) has set the limit of 10 μg/L for arsenic in drinking water in trying to reduce the effects of arsenic. This was further adopted by South African National Standard (SANS). The present study aims at evaluating arsenic concentration in selected groundwater sources around Greater Giyani Municipality in Limpopo Province and further synthesize clay based adsorbents for arsenic removal using Fe3+ and Mn2+ oxides and hexadecylammonium bromide (HDTMA-Br) cationic surfactant as modifying agents. The first section of the work presented the hydrogeochemical characteristics of groundwater in the Greater Giyani Municipality. The results showed that the pH of the samples ranges from neutral to weakly alkaline. The dominance of major anionic and cationic species was found to be in the order: HCO3 ->Cl->SO4 2->NO3 - and Na+>Mg2+>Ca2+>K+>Si4+, respectively. Hydrogeochemical facies identified in the study area include CaHCO3 (90%) and mixed CaNaHCO3 (10%) which shows the dominance of water-rock interaction. About 60% of the tested samples contains arsenic concentration above 10 μg/L as recommended by SANS and WHO. Concentration of arsenic was found to be ranging between 0.1 to 172.53 μg/L with the average of 32.21 μg/L. In the second part of this work, arsenic removal efficiency of locally available smectite rich and kaolin clay was evaluated. Results showed that the percentage As(V) removal by kaolin clay was optimum at pH 2 while the percentage As(III) removal was greater than 60% at pH 2 to 12. For smectite rich clay soils, the percentage of As(III) and As(V) removal was found to be optimum at pH between 6 and 8. The adsorption isotherm data for As(III) and As(V) removal by both clays fitted better to Freundlich isotherm. Adsorption of both species of arsenic onto the clay mineral occurred via electrostatic attraction and ion exchange mechanisms. Both clay soils could be regenerated twice using Na2CO3 as a regenerant. Kaolin clay showed a better performance and was selected for further modification. In the third section of this work, Fe-Mn bimetal oxide modified kaolin clay was successfully synthesized by precipitating Fe3+ and Mn2+ metal oxides to the interlayer surface of kaolin clay. Modification of kaolin clay increased the surface area from 19.2 m2/g to 29.8 m2/g and further v decreased the pore diameter from 9.54 to 8.5 nm. The adsorption data fitted to the pseudo second order of reaction kinetics indicating that adsorption of As(III) and As(V) occurred via chemisorption. The adsorption isotherm data was described by Langmuir isotherm models showing a maximum As(III) and As(V) adsorption capacities of 2.16 and 1.56 mg/g, respectively at a temperature of 289 K. Synthesized adsorbent was successfully reused for 6 adsorptiondesorption cycles using K2SO4 as a regenerant. Column experiments showed that maximum breakthrough volume of ≈2 L could be treated after 6 hours using 5 g adsorbent dosage. Furthermore, the concentration of Fe and Mn were within the WHO permissible limit. In the fourth part of the work kaolin clay was functionalized with hexadecyltrimethylamonium bromide (HDTMA-Br) cationic surfactant and its application in arsenic removal from groundwater was investigated. The results revealed that adsorption of As(III) and As(V) is optimum at pH range 4-8. The maximum As(III) and As(V) adsorption capacities were found 2.33 and 2.88 mg/g, respectively after 60 min contact time. Pseudo first order model of reaction kinetics described the adsorption data for As(V) better while pseudo second order model described As(III) adsorption data. The adsorption isotherm data for As(III) and As(V) fitted well to Langmuir model indicating that adsorption of both species occurred on a mono-layered surface. Adsorption thermodynamics model revealed that adsorption of As(III) and As(V) was spontaneous and exothermic. The As(III)/As(V) adsorption mechanism was ascribed to electrostatic attraction and ion exchange. The regeneration study showed that synthesized adsorbent can be used for up to 5 times. In the firth part of the work inorgano-organo modified kaolin clay was successfully synthesized through intercalation of Fe3+ and Mn2+ metal oxides and HDTMA-Br surfactant onto the interlayers of the clay mineral. The batch experiments showed that As(III) removal was optimum at pH range of 4-6, while the As(V) removal was optimum at pH range 4-8. The adsorption data for both species of arsenic showed a better fit to pseudo second order of reaction kinetics which suggest that the dominant mechanism of adsorption was chemisorption. The isotherm studies showed better fit to Langmuir isotherm model as compared to Freundlich model. The maximum adsorption capacity As(III) and As(V) at room temperature as determined by Langmuir model were found to be 7.99 mg/g and 7.32 mg/g, respectively. The thermodynamic studies for sorption of As(III) and As(V) showed negative value of ΔGᴼ and ΔHᴼ indicating that adsorption process occurred spontaneously and is exothermic in nature. The regeneration study showed that the vi inorgano-organo modified kaolin clay can be reused for up 7 adsorption-regeneration cycles using 0.01 M HCl as a regenerant. Thomas kinetic model and Yoon-Nelson model showed that the rate of adsorption increases with increasing flow rate and initial concentration and decreases with increasing of the bed mass. In conclusions, adsorbents synthesized from this work showed a better performance as compared to other adsorbents available in the literature. Among the synthesized adsorbents, inorgano-organo modified clay showed highest adsorption capacity as compared to surfactant functionalized and Fe-Mn bimetal oxides modified kaolin clay. However, all adsorbents were recommended for use in arsenic remediation from groundwater. The following recommendations were made following the findings from this study: 1) routine monitoring of arsenic in groundwater of Greater Giyani Municipality, 2) evaluating the possible link between arsenic exposure and arsenic related diseases within Giyani in order to find the extent of the problem in order to establish the population at risk, 3) The toxicity assessment for HDTMA-Br modified kaolin clay should be carried out, 4) Materials developed in the present study should be modeled and tested at the point of use for arsenic removal, and lastly, 5) this study further encourage the development of other arsenic removal materials that can be used at household level. / NRF