Thesis (M. Sc.)--University of Hong Kong, 1998. / Includes bibliographical references.

Acid mine drainage (AMD) at Stockton Coal Mine, located near Westport, New Zealand, is generated from the oxidation of pyrite within sedimentary overburden exposed during surface mining. The pyrite oxidation releases significant acidity, Fe, and sulphate together with trace metals to the receiving environment. Aluminium is also elevated in drainage waters due to acid leaching from overburden materials. Thirteen AMD seeps emanating from waste rock dumps, and associated sediment ponds were monitored at Stockton Coal Mine to characterise water chemistry, delineate their spatial and temporal variability, and quantify metal loads. Dissolved metal concentrations ranged from 0.05-1430 mg/L Fe, 0.200-627 mg/L Al, 0.0024-0.594 mg/L Cu, 0.0052-4.21 mg/L Ni, 0.019- 18.8 mg/L Zn, <0.00005-0.0232 mg/L Cd, 0.0007-0.0028 mg/L Pb, <0.001-0.154 mg/L As and 0.103- 29.3 mg/L Mn and the pH ranged from 2.04-4.31. Currently this AMD is treated further downstream by a number of water treatment plants employing a combination of ultra fine limestone and calcium hydroxide; however, in the interest of assessing more cost-effective technologies, passive treatment systems were investigated for their treatment and hydraulic efficacy and as potential cost-effective options. Biogeochemical reactors (BGCRs) were selected as the most appropriate passive treatment system for ameliorating AMD at Stockton Coal Mine. Results of mesocosm-scale treatability tests showed that BGCRs incorporating mussel shells, Pinus radiata bark, wood fragments (post peel), and compost increased pH to ≥6.7 and sequestered ≥98.2% of the metal load from the Manchester Seep located within the Mangatini Stream catchment. The following design criteria were recommended for BGCRs incorporating 20-30 vol. % mussel shells as an alkalinity amendment: 1) 0.3 mol sulphate /m3 substrate/day for sulphate removal (mean of 94.1% removal (range of 87.6-98.0%)); 2) 0.4 mol metals/m3/day for metal (mean of 99.0% removal (range of 98.5-99.9%)) and partial sulphate (mean of 46.0% removal (range of 39.6-57.8%)) removal; and 3) 0.8 mol metals/m3/day for metal (mean of 98.4% removal (range of 98.2-98.6%) and minimal sulphate (mean of 16.6% removal (range of 11.9- 19.2%)) removal. At the maximum recommended loading rate of 0.8 mol total metals/m3/day an average of 20.0 kg/day (7.30 tonnes/year) of metals and 85.2 kg acidity as CaCO3/day could be removed from the Manchester Seep AMD by employing BGCRs. The design hydraulic residence time (HRT) would be 3.64 days. On an acidity areal loading basis, a design criterion of 65 g/m2/day was recommended. Tracer studies conducted on the BGCRs indicated ideal flow characteristics for cylindrical drumshaped reactors and non-ideal flow conditions for trapezoidal-shaped reactors indicative of shortcircuiting, channelised flow paths and internal recirculation. Consequently, this resulted in compromised treatment performance in the trapezoidal-shaped reactors. The relaxed tanks in series (TIS) model could be successfully applied to model the treatment performance of drum-shaped reactors; however, the model was unsuccessful for trapezoidal-shaped reactors. Because most pilot and full-scaled vertical flow wetlands (VFWs) have consisted of trapezoidal-prism basins excavated into the ground, the rate-removal methods previously recommended (e.g. mol metals/m3/day) should be applied to BGCR design, evaluation and operation rather than results of hydraulic and reactor modelling. Overall, a staged passive treatment approach is recommended. The first stage should consist of a sedimentation basin to remove sediment, the second stage a BGCR to remove acidity and metals and the third an aerobic wetland to provide oxygenation and tertiary treatment of metals (primarily Fe) from BGCR effluent. Preliminary analysis indicates that BGCRs are potentially a more cost-effective means of treating AMD at Stockton Coal Mine compared with the current active lime-dosing plant by over $125/tonne of acidity ($197/tonne for BGCRs versus $324/tonne for lime dosing (60% efficient)); however, their successful implementation would need to recognise current treatment goals, required areal footprint and inherent maintenance requirements.

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 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

M. Tech. Chemical Engineering

The changes that have taken place in the British Coal Industry over the last five years have meant that in many coalfileds the last deep mines have closed. When a coalfield is abandoned and dewatering ceases, groundwater levels rebound, threatening surface waters with polluting discharges. However, the sparse data sets available limit modelling with existing techniques. A lumped parameter model GRAM (Groundater Rebound in Abandoned Mineworkings) has been developed. This model conceptualises a coalfield as a group of 'ponds'. Each pond is an area of the coalfield that has been extensively worked and can be considered as a single hydraulic unit. The ponds are connected by pipes which represent major inter-connecting roadways along which flow is assumed to be turbulent. Discharge to the surface is also represented using pipes. Flow through the pipes can be calculated using the Prandtl and Nikuradse of the Colebrook-White pipeflow equations. The storage coefficient can vary vertically to represent both worked Coal Measures and the intervening unworked strata. GRAM is able to predict the timing and volume of discahrges. An iron component gives an indication of the water quality evolution of the discahrges. Monte Carlo simulation allows the variables that have most error in their estimation to be represented by probability distributions. The Dysart-Leven Coalfield in eastern Fife, Scotland has not been mined since 1985. However, dewatering has continued to protect the workings in the Frances Colliery. In 1994 British Coal decided the Frances would never reopen, there is therfore no longer a need to continue dewatering. GRAM has been used to produce estimates of the quantity, timing and location of dischargges from the Dysart-Leven Coalfield should pumping cease. MODFLOW has also been applied to the coalfield with less success. Water quality modelling was also attempted using GRAM's iron component, however, conclusive results will not be obtained until the three variables over which ther is most uncertainty have been calibrated against existing discharges.

Bibliography: p. 368-375. / xv, 375 p. : ill. (chiefly col.), maps ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Laboratory tests using a wide range of additives have been undertaken to develop hardpans more akin to naturally occurring duricrusts. Some additives have developed cements which have the low permeability and porosity characteristics required, while maintaining a high level of resistance to both chemical and physical breakdown. / Thesis (Ph.D.)--University of Adelaide, Dept. of Geology and Geophysics, 1999

Bibliography: p. 368-375. / xv, 375 p. : ill. (chiefly col.), maps ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Laboratory tests using a wide range of additives have been undertaken to develop hardpans more akin to naturally occurring duricrusts. Some additives have developed cements which have the low permeability and porosity characteristics required, while maintaining a high level of resistance to both chemical and physical breakdown. / Thesis (Ph.D.)--University of Adelaide, Dept. of Geology and Geophysics, 1999

Thesis (M.Sc.)(Microbiology)--University of Pretoria, 2008. / Includes summary. Includes bibliographical references.

The treatment of acid mine drainage (AMD) by sulfate-reducing bacteria (SRB) has been reported in the literature as a possible alternative to chemical treatment. The overall objective of this study was to implement such a treatment process at the mine site and specifically within the open mine pit itself. The first step of this study was to characterize process parameters. To accomplish this, a reactor was designed and built to simulate hydrodynamic conditions found in the mine pit. This reactor contained a 6$ sp{ prime prime}$ deep gravel bed in which a mixed population of SRB was inoculated. The operation of this reactor demonstrated that treatment of a continuous flow of AMD by SRB was possible, however, the response to changes in the composition of the AMD and to flow conditions was limited. The results indicated that further studies should be directed at the gravel bed itself since this was where the SRB are located and is the active site within the system. / The role of various physical parameters of a gravel bed in the biological treatment of AMD by SRB was examined. This was accomplished by using gravel of different sizes (0.25$ sp{ prime prime}$ vs. 0.5$ sp{ prime prime})$ and composition (granite vs limestone) to form 12$ sp{ prime prime}$ beds in a series of column reactors. The difference in size results in variations in the total surface area, the void volume and various volume ratios within the system. The effect of potential geological buffering by limestone was examined by using and comparing with beds composed of granite. / The gravel beds were inoculated with a mixed culture of SRB and overlaid with 6 L of AMD. After the SRB were established, a series of experiments were performed in which 16.7%, 25%, 75% and 100% of the water column was replaced with an equivalent quantity of fresh AMD. Changes in pH, ORP, electric conductivity, and concentrations of metal and sulfate were monitored for at least 28 days. Sulfate and metal removal at days 7 and 28 of each experiment were compared. The SRB can tolerate a wide range of disturbances, however, an increase in the load of fresh AMD decreased the performance of the system. The results indicated that the total surface area is of greater importance than the void volume in the overall treatment process by SRB. / A dimensionless number was constructed to describe the relationships between the physical parameters of the gravel bed. A plot of the proportion of sulfate removed and this dimensionless number could provide essential information for the sizing of a gravel bed for the purposes of sulfate reduction. This was done for each type of gravel and comparison of the two curves indicated that there was no significant difference between the two gravels. / The importance of the physical substrate for the SRB has been reported in the literature. However, no known attempt has been made to quantify the relationships between the physical parameters and the biological activity. Such information would be useful for the sizing of wetlands and other passive treatment system that uses SRB activity for the purposes of treating AMD. This study is a step towards filling this void.