Thesis (Ph. D.)--Virginia Polytechnic Institute and State University, 1990. / Vita. Abstract. Includes bibliographical references. Also available via the Internet.

A dissertation submitted to the Faculty of Engineering, University of the Witwatersrand, Johannesburg, for the Degree of Master of Science. / storage and waste dumps from coal mining tend to spontaneously combust. This is mainly as a result of the oxidation process which is accelerated by the availability of oxygen and the exothermic nature of the oxidation process. In cases of poor ventilation the heat accumulation within the bed is thought to lead to the spontaneous combustion of coal. The work in this dissertation aims to investigate the change in oxygen concentration in a bed of coal and also measure the rate of oxidation (oxygen absorption) in a closed reactor under isothermal conditions. Drying rate of coal under nitrogen was also looked into. An analysis of the oxygen concentration profile in a three metre 20 cm ID plastic column filled up with coal has been carried out. As the coal ages (becomes oxidised) its reactivity towards oxygen decreases and changes in the oxygen concentration profile are noticed. Experiments have been carried out up to 8 months and from the results obtained, a simple pseudo-steady-state model has been developed to describe the diffusion of oxygen into a reacting coal bed. The findings could prove useful in trying to find a solution to coal and waste dump fire control. The second experiment is a simple isothermal oxygen absorption experiment in which the rate of absorption of oxygen on a given coal sample is measured at different initial concentrations of oxygen. The initial concentration of oxygen is varied over a fairly wide range in order to determine the dependence of the rate of oxidation on the oxygen concentration. The rate- limiting step in low temperature oxidation of coal is found to be the absorption of oxygen. Moisture also plays a role in coal oxidation. Drying experiments were also carried out so as to quantify and investigate the rate of loss of moisture. Models have been developed which try to explain the mechanisms involved in the drying process. The modelling suggest that the bound water model is more appropriate to the type of behaviour exhibited during the drying process / Andrew Chakane 2018

A dissertation submitted to the Faculty of Engineering, University of the Witwatersrand, Johannesburg, for the Degree of Master of Science. / Storage and waste dumps from coal mining tend to spontaneously combust. This is mainly as a result of the oxidation process which is accelerated by the availability of oxygen and the exothermic nature of the oxidation process. In cases of poor ventilation the heat accumulation within the bed is thought to lead to the spontaneous combustion of coal. The work in this dissertation aims to investigate the change in oxygen concentration in a bed of coal and also measure the rate of oxidation (oxygen absorption) in a closed reactor under isothermal conditions. Drying rate of coal under nitrogen was also looked into. An analysis of the oxygen concentration profile in a three metre 20 cm ID plastic column filled up with coal has been carried out. As the coal ages (becomes oxidised) its reactivity towards oxygen decreases and changes in the oxygen concentration profile are noticed. Experiments have been carried out up to 8 months and from the results obtained, a simple pseudo-steady-state model has been developed to describe the diffusion of oxygen into a reacting coal bed. The findings could prove useful in trying to find a solution to coal and waste dump fire control. The second experiment is a simple isothermal oxygen absorption experiment in which the rate of absorption of oxygen on a given coal sample is measured at different initial concentrations of oxygen. The initial concentration of oxygen is varied over a fairly wide range in order to determine the dependence of the rate of oxidation on the oxygen concentration. The rate- limiting step in low temperature oxidation of coal is found to be the absorption of oxygen. Moisture also plays a role in coal oxidation. Drying experiments were also carried out so as to quantify and investigate the rate of loss of moisture. Models have been developed which try to explain tile mechanisms involved in the drying process. The modelling suggest that the bound water model is more appropriate to the type of behaviour exhibited during the drying process. / Andrew Chakane 2018

Highly acidic and metal-rich runoff from coal storage facilities can have a dramatic impact on local surface and ground water quality. In order to identify important reactions governing metal transport within subsurface environments subject to infiltration of coal pile runoff, samples of uncontaminated subsoil and aquifer materials adjacent to the D-Area coal stockpile runoff containment basin at the Department of Energy's Savannah River Site were collected and subjected to leaching with the acidic, metalliferous coal pile runoff. Columns were packed to bulk densities of 1.5 Mg m³ and subjected to steady, saturated flows of 0.2 and 1.3 cm h⁻¹, Effluent was collected and multicomponent transport through the subsoil and aquifer materials evaluated. Observed transport was then related to soil chemical and mineralogical properties. Mass balance calculations, a sequential dissolution scheme in which column leaching was terminated and elements partitioned to aqueous, <i>M</i> NH₄CI, and ammonium oxalate in the dark (Ox)-extractable phases, and mineralogical and surface chemical analyses were used to identify important chemical processes and mineralogical alterations. / Ph. D.

A dissertation submitted to the Faculty of Engineering, University of Witwatersrand, in fulfillment of the requirements for the degree of Master Science in Engineering / The Electricity Supply Commission of South Africa (Eskom) have identified open cast coal mine backfill areas as potential disposal sites for the large volumes of coal ash produced by their power stations. As Eskom's power stations are mainly situated in agricultural and coal rich areas of the provinces of Mpumalanga and the Free State, the sterilisation of substantial areas of agricultural soil and coal deposits is thus reduced. The construction of a tailings dam or dump on uncompacted open cast mine backfill creates various problems related to the settlement of the backfill. The scale of the operation, the large particle size and heterogeneous nature of the backfill and its method of placement complicates the prediction for settlement of the backfill. Areas in excess of 74 000 ha could be subjected to opencast mining in Mpumalanga and for future development of these areas more information regarding the magnitude and mechanics of mine backfill settlement is required. This dissertation describes two large scale field tests in which the settlement of mine backfiil was studied during the construction of a test section of an ash tailings dam and the construction of a dry ash dump. / Andrew Chakane 2019

Two coal utility plants in South Africa selected (one from Sasol and another from Eskom) for this study produce large volumes of fly ash (over 40 Mt from Eskom at Tutuka, and 3 Mt from Sasol Synfuels at Secunda annually), and brines as by-products during coal processing. Co-disposal of the brines and fly ashes has been a normal practice in these coal-utility plants for decades. Long-term management of fly ash is necessary and requires an understanding and knowledge of how the different waste materials interact with water and brines in different chemical situations. However the geochemistry of their interactions, the leaching and mobility of elements in these disposal systems has not been fully understood. This work gives insights into the chemical processes taking place in the brine-water/brines systems that govern the concentrations of major and minor elements in ash leachates under different environmental conditions. The possible presence of organic compounds (subsequently referred to as 'organics') in brines and their effects on the leaching chemistry of fly ash was also studied. Sustainability and long term impact of the co-disposal of fly ash and brines on the environment was studied through static (batch tests) modeling of the pH-dependent acid neutralization capacity (ANC) tests and columns modeling for dynamic leach tests. The modeling was based on experimental results from other Sasol-Eskom ashbrine project collaborators. Modeling results of the ANC tests were in good agreement with the reported experimental results, which revealed that the release trends of various elements (including trace, heavy elements and contaminants) contained in fly ash into solution is highly pH dependent. However Na, K, Mo and Li exhibited constant solubilisation which was independent of pH changes from all the scenarios. The presence of different constituents of brines subjected to ANC resulted to different ANC capacities ranging from 0.98 moles H⁺/Kg dry ash (of ash-organics mixed with Mg-brines) to 3.87 H⁺/Kg dry ash for those with the C(4) brines. As expected, those constituents from the cationic brines were found on the lower region of acid addition (in the order Mg-brines < Ca-brines < Na-brines) while the anionic brines were found at the upper region of acid addition (in the order S(6)-brines < Cl-brines < C(4)-brines). In the middle region of acid addition were three important scenarios: that of ash with brine, ash without brines (i.e. ash with DMW) and ash with both ASW organics and combined brines. It was from these three scenarios that a generalization of the effect of brines and organics on the ANC was inferred. The ANC of ash with demineralised water (DMW) was 2.33 mol H⁺/Kg dry ash and that of ash with ASW organics lower at 2.12 mol H⁺/Kg dry ash which was the same value as that of ash with combined brines. This indicated that brines decreased the ANC of ash by about 9.01 % and which could be attributed to the acid-base neutralization process and the dynamics of solid phase dissolutions in response to the acid addition. Both fly ashes exhibited a typical pH > 12 (suspension in demineralised water) and the predominant cation even at this high pH is Ca²⁺ (at concentration > 0.002 mmol/L). This indicates that dissolution of CaO and formation of OH⁻ species at pH > 10 contributes to acid neutralisation capacity of both fly ashes and is the greatest contributor to the acid neutralizing capacity of both fly ashes. Two broad leaching behaviours as a function of pH were observed from the three fly ash-ASW organics-brines scenarios (i) leaching of Ca, Mg, Ni and Sr follows a cationic pattern where the concentration decreases monotonically as pH increases; (ii) leaching of Al, Fe, Ti and Zn follow an amphoteric pattern where the concentration increases at acidic and alkaline pH, although Al showed some anomaly from pH 11 where the concentration decreased with the increase in pH. Al showed an amphoteric pattern in which its release increased between pH 12.8 and 11 for all the scenarios and then decreased with decrease in pH down to neutral pH of 7. The batch leaching simulation results from hydrogeochemical modeling also showed that mineral dissolution, precipitation and new phase formation during ash-organics-brines interactions was controlled by pH. The newly formed phases however remain in equilibrium with the ash-brines-organics mixture. Each individual mineral phase dissolution/precipitation/formation system controls the concentration and speciation of the respective constituent elements as evidenced by the log C-pH diagrams obtained from the modeled scenarios. The ash-brines-organics interactions do exhibit and affect the mineralogical chemistry of fly ash. However the extent to which these interactions occur and their effect, varies from one scenario to another, and are dependent on the amounts and type of the constituent brine components. Organics do have a significant effect on dissolution characteristics of few minerals such as calcite, mullite, kaolinite, Ni₂SiO₄, and SrSiO₃ due to complexation effect. The effect is quantitatively conspicuous for calcite mineral phase and for the formation of some new phases such as Fe(OH)₃(am)-CF and portlandite. The composition of the liquid phase from acid neutralisation capacity experiments was successful.Hydrogeochemical modeling was used as a means to provide insights and understanding of the complex reactions taking place, speciation and mineralogical changes occurring. These changes would serve to predict future environmental scenarios when pH conditions change. In this study, an extension of the application field of PHREEQC hydrogeochemical code for modeling and simulation of equilibrium; kinetic and transport mechanisms associated with the interaction of water; and organics and brines with fly ash during their co-disposal is successfully demonstrated. The parameters associated with these mechanisms were used as inputs into the PHREEQC program using modified Lawrence Livermore National Laboratory (LLNL) database for inorganic brines and MINTEQ.V4 database for organics, and used to model the results of ANC test data for the fly ashes. A special reference is made to two separate modeled mineralogical ash recipes from two of the South African power utility plants' fly ash systems, namely, Tutuka and Secunda. The effects of brines in the leaching of major, minor and trace elements at various pH values and the mineralogical changes associated with the intermediate and final products from the interactions of ash-brines systems under different scenarios are qualitatively and quantatively discussed. Multiphase saturation characteristics have been determined for mineral species in contact with water and brines. The modeling results indicated that several mineral phases could be controlling the species concentration in the leachates, and the ANC and column modeling results corroborated well in many aspects with the experimental results obtained from collaborating institutions (South Africa Universities and Research institutions). In addition, application of the PHREEQC model to the ash heap under different disposal systems was carried out to predict the heap leachate composition and geochemical transformations taking place in a period of time. Pore water chemical analysis, and moisture content analysis revealed that contact of the ash with water is a crucial factor in the mobilization of the contaminants with time. Maximum weathering/dissolution of the ash is observed in the top layer (1-3) m and at the point of contact with the subsurface water level which was in good agreement with the model results. The surface layer and the very lowest layers of the dump in contact with lateral flows experience the highest degree of weathering leading to depletion of species. The geophysical transformation of fly ash was also captured through the porosity change calculations and the results revealed that geochemical reactions do affect the porosity of fly ash during the weathering processes. These modelling results were in agreement with the hydraulic tests and salt leaching tests conducted during Sasol-Eskom ashbrine project in Phase I which suggested that salts captured in the ash will become mobile and leach from the fly ash over time. The data therefore indicates that ash dumps may not act as sustainable salt sinks. These findings may have some bearing on engineering decisions on fly ash reuse. From the above observations, it is apparent that release of large quantities of the salts in the ash depends on the extent of its interaction with brines being used for irrigation or with water, either through plug-in flow after a rainfall event or contact with groundwater. The results revealed effects of brine-water contact time with fly ash, the flow volume and velocity, the pH, the degree of saturation, hydrogeology and ash heap geometry as important factors that affect fly ash transformation and weathering. Overall, the ash heap modeling enhanced the understanding of the ash-brines interactions and demonstrated that leachate composition is determined by the following factors; (i) the mass flows from the pores of fly ash, (ii) the surface dissolution of the mineral phases, (iii) the various chemical reactions involved during the ash-brine and ash-water interactions, (iv) the interactions with a gas phase (atmospheric CO₂), (v) the composition of the initial fly ash, and (vi) by the leachate flow and hydrodynamics as captured in the conceptual model. Any ash handling system should therefore be designed to take these criteria into consideration to prevent environmental contamination. The modeling results also gave indications that the ash-brine co-disposal in dry ash systems would be an unsustainable way of locking up brine salts in the long run. In this Thesis, modeling results were used to support experimental data which further reaffirmed the important role hydrogeochemical modeling plays in liquid and solid waste management. Furthermore, hydrogeochemical modeling complements the work of analytical/environmental scientists as well as guiding the future solid waste management and engineering decisions. / Thesis (Ph.D.)-University of KwaZulu-Natal, Westville, 2012.

Structural and functional changes in the macroinvertebrate community of a fly ash receiving stream were investigated during the final year of fly ash basin operation and for 10 months after fly ash discharges to the stream were terminated. Minimal changes were observed in the benthic community until the basin reached 77% of capacity, at which time the number of macroinvertebrate taxa, density of organisms, diversity, and relative abundance of Ephemeroptera all declined sharply. Ephemeroptera (mayflies) exhibited the greatest sensitivity to the fly ash effluent, while the beetle, Psephenus herricki (Coleoptera) was very resistant to the effects of fly ash. Recovery responses of the macroinvertebrate community were observed one month after fly ash discharges to the stream ended, while full recovery required 10 months. Based on the results of the field study, the toxicity of fly ash constituents (fly ash particulates, pH excursions, and heavy metals) was examined in three species of aquatic insects: Stenonema pudicum (Ephemeroptera), Hydropsyche slossonae (Trichoptera), and Psephenus herricki. Fly ash particulates were not acutely toxic to the three species at concentrations of 4000 mg/l. Stenonema pudicum was consistently the most sensitive species to acidic and alkaline pH extremes and heavy metals (Cd, Cr, Cu, Zn, and a metal mixture), while Psephenus herricki was consistently the most resistant species tested. Alkaline pH extremes and elevated heavy metal concentrations are believed to be responsible for the observed changes in the macroinvertebrate community of the receiving stream during the final two months of basin operation, while elevated heavy metal concentrations were responsible for earlier perturbation of the stream community. / Ph. D.

Ph.D. (Geography) / The focus of Aeolian research has mainly been on wind-blown dust from desert and arid areas. Numerous dust emission schemes have been developed over the years aimed at accurately estimating dust emission rates from various soil types and land use surfaces. Limited research has been done on wind-blown dust from smaller area sources – such as mine tailings and ash storage facilities. Lately, the concern about the environmental and health impacts, caused by dust from mine tailings storage facilities and ash disposal sites, has become more prominent, calling for better methods in determining dust emissions and their related impacts. This thesis established a practical approach for wind-blown dust emissions estimation and dispersion modelling from mine waste and ash storage facilities for the purpose of legal compliance assessment. Extensive research on the physics of wind erosion has been done over the past decade, compelling the re-evaluation of previously applied techniques. The latest and most widely applied dust emission schemes are evaluated to determine, through systematic testing of parameterisation and validation, using empirical mine waste and coal ash data, a best-practice prescription for quantifying wind-blown dust emissions and determining effects on a local scale using commercially available dispersion models. The applicability of two dust-flux schemes, (one developed by Marticorena and Bergametti (1995) and the simplified Shao 2004 scheme, as reported in 2011) for the quantification of wind-blown dust emissions, were tested using site specific particle size distribution data, bulk density and moisture content from six gold- and one platinum- tailings storage facilities and from two ash storage facilities. The availability of the required input parameters and the uncertainty associated with these parameters, were tested. The dependency of the Shao et al. (2011) model on plastic pressure (P) and the coefficient cy, both of which are not easily determined, added to the uncertainty of the emission rates. In this study, P and cy were both interpolated using the range limits provided by Shao (2004) for natural soils. By calculating P, using the salt and calcium carbonate content, similar values were obtained. The minimally disturbed dust fraction, as required by the Shao et al. (2011) scheme were derived from particle size distribution analysis but found to be more representative of the fully disturbed particle size faction (𝜂fi) and therefore needed to be corrected to represent the minimally disturbed particle size faction (𝜂mi) through the application of a correction factor, CF𝜂mi. Specific attention was given to the quantification of the threshold friction velocity (u*t) and the threshold velocities (u*), and how these two parameters relate to each under variable wind speed and time durations. This was tested using sub-hourly averaged meteorological data, one set reflected 5-minute intervals and the other 10-minute intervals. Dependent on the frequency and strength of the sub-hourly wind gusts, the resulting dust-flux rates were found to vary significantly when based on hourly averaged wind data in comparison with 5- and 10-minute wind data. Dispersion models are useful tools in air quality management. Whereas ambient monitoring provides actual ambient concentrations for specific pollutants at set locations, atmospheric dispersion models can be used to simulate any number of pollutants and determine the impacts at any location within the modelling domain. These dust-flux schemes of Marticorena and Bergametti (1995) and Shao et al. (2011) have been coupled with the US EPA regulatory Gaussian plume AERMOD dispersion model for the simulation of ground level concentrations resulting from wind-blown dust from mine tailings facilities. For this study, two Case Studies were evaluated; one included two of the gold mine tailings and the second focused on the platinum tailings. Simulated ambient near surface concentrations were validated with ambient monitored data for the same period as used in the model. For the Marticorena and Bergametti (1995) dust-flux scheme, only z0 had to be adjusted to provide a good fit with measured data – whereas the Shao et al. (2011) scheme resulted in significantly higher concentrations, resulting in an over-prediction of the measured data. By applying the correction factor, CF𝜂mi, to the minimally disturbed dust fraction, the predicted concentrations improved considerably. The coupling of the dust-flux schemes with a regulatory Gaussian plume model provided simulated ground level PM10 concentrations in good agreement with measured data. The best correlation was found under conditions of high wind speeds when the prevailing wind was from the direction of the tailings storage facility. This thesis demonstrates that simulated impacts from complex source groups can be performed, within an acceptable range of certainty, using widely applied dust-flux schemes. These dust-flux schemes, developed primarily for large-scale desert and arid areas, have been demonstrated to be applicable also to small-scale sources, of the order of 1 km2, and can be coupled to regularly available dispersion models for impact evaluations of wind-blown dust. The value of this improved approach to the mining and mineral processing industries are substantial, allowing for more accurate health risks and adverse environmental assessments from wind-blown dust from large material storage piles, a source category that has hitherto been difficult to quantify.

MENVSC / Department of Ecology and Resource Management / South Africa is highly dependent on coal for production of electricity. The combustion of coal for electricity generation produces waste by-products which include fine ash (fly ash) and coarse ash. Fly ash (FA) is produced in large amounts while its utilization is low due to its classification as a hazardous material. Sasol produces about 7 million tons of FA, while Eskom produces about 28 million tons of coal FA annually. FA is a fine by-product from pulverized coal with detrimental effects on plants, soil or land, animals and human beings, and pollutes the air. The present investigation focuses on the examination of the chemical elements bioaccumulation and phytoremediation potential of Indian mustard (Brassica juncea) and Spinach (Spinacia Oleracea L). X-ray fluorescence (XRF) was used to analyze the elemental composition of FA and soil, Scanning Electron Microscope (SEM) to examine the morphology, while X-ray diffraction (XRD) analysis was used to evaluate the mineralogy of FA. The concentrations of metal and non-metal species that are released from FA on contact with water at different conditions were quantified using ICP-MS. Pot culture experiment was conducted to grow Brassica juncea and Spinacia Oleracea L. using FA and soil as growth medium. Leachates from the pots were collected and analysed using ICP-MS. Plant parts from harvested Brassica juncea and Spinacia Oleracea L. were cut separately and analysed using ICP-MS for the concentrations of different metal and non-metal species in plant parts. Plant parts were also used to estimate biomass and chlorophyll content (leaves). To prepare these plant samples for analysis, the powdered plant sample (0.5 g) was digested through aqua regia (HCL:HNO3 = 3:1 (v/v)) to near dryness using hotplate and filled to 100 mL of MilliQ water. The samples were filtered and directly used to determine the chemical elements concentrations. Blanks and internal standards were used for quality assurance during analysis. Chemical elements that are present in FA and sometimes in higher concentrations are associated with detrimental effects in plants, animals and human beings, hence phytoremediation is vital. Bioconcentration factor (BCF) was used to estimate the metal species accumulation ability of the plants from the FA, FA/soil mixtures, while translocation factor (TF) was used to assess the plant species potential for phytoremediation of coal fly ash dumps. Analysis of Varience (ANOVA) was used to statistically test data using Graphpad software package. Relationship between chemical elements in soil, FA and FA+soil growth media and also different plant parts (root, stem and leaf) of B. juncea and S. Oleracea L were calculated using the t - test, ANOVA-Bartlett test, Mann-Whitney Test and Kruskal-Wallis Statistic (KW) depending on each data set. The physicochemical characterization of coal fly ash showed that FA from Grootvlei power station can be classified as class F with an alkaline pH level of 10.62. It showed that particle morphology of this FA had a lower degree of sphericity with irregular agglomerations of many particles while there were dominant spherical particles and smaller sharp needle like particles. It is also an alumino-silicate material as confirmed by the high SiO2 and Al2O3 content, while soil leachates had an average/neutral pH of 7.22 with very high amounts of Si. In both soil and FA, elements that were expected to be readily available to plants included Ca, Si, K, Ba, Mo, Na, Al, Mg, Sr and non-essential elements (Si, Ba, Na, Al, Sr), which, if uptaken by plants’ roots can have negative impacts in plants. Physicochemical analysis of soil, FA and FA+soil leachates showed that the alkalinity of the FA changed over time and there was also a decrease in the EC due to dissolution iv of soluble major oxides, which was promoted by continuous water irrigation. The soil and FA+soil growth media showed similar results. Chemical elements like B, Mn, Fe and Ba were occurring at higher concentrations in leachates for most weeks in the pot culture experiments. However, it was observed that in the eleventh week of leachate collection all these chemical elements decreased to very low concentrations. This suggest that these chemical elements can be reduced over time as plants are being irrigated which is either due to uptake by plants or washed off with water. Statistically, there was a significant difference for different chemical elements of leachates from different growth media for each plant species (B. juncea and S. Olearcea L.). The overall growth rate shows that S. Oleracea L was better than that of B. juncea especially in the FA media over time, while the biomass of the two plant species showed similar results. After all, even though S. Oleracea L had carotenoid content below detection limits, it had higher chlorophyll b than B. juncea for all growth media in general. But, statistically there was no significant difference between the two plant species in terms of growth rate and biomass; even between the plant parts denoting similar growth performance for the two plant species under study. The bioaccumulation potential of the two plant species showed that chemical elements such as Fe, Mn, Ba, Zn and B were highly accumulated by the different parts of the plants. However, the chemical elements such as of Mo, Ni, Cu, and Cr showed the least concentrations. This trend was similar for all growth media and both plant species but this changes over time for different growth media and plant species as increasing and decreasing trends can be noticed. This led to no significant difference between plant species and also growth media, statistically. High BCF values of Fe, Mn, Ba, Zn and B were observed in the different parts of the plants for both plant species. However, Mo, Ni, Cu, and Cr had BCF values less than 1 for most growth media over time. BCF values in plant parts differed with time, growth media and plant species. Translocation of chemical elements shows that the B. juncea plant proved to be an effective phytoremediation plant species since it is effective in translocation of many chemical elements for different growth media to shoots while S. Oleracea L failed to translocate most chemical elements from stem to leaves although it translocated some from root to shoots. Hence, it can be concluded from the study that both species can be used in phytoremediation of coal fly ash dumps but with B. juncea being the most effective accumulator and translocator of many chemical elements. However, it can be recommended that chelating agents like ethylene diamine tetra acetic acid (EDTA) be introduced to solubilize chemical elements from growth media matrix into growth media solution to facilitate the quick transport of chemical elements into xylem, and increase