Addition of alkalinity to acid mine drainage (AMD) results in the neutralisation of acidity and precipitation of dissolved metals as insoluble hydroxides. Two aspects of the current AMD treatment practice at the Stockton Mine could be enhanced. Firstly, residual water quality may be poor due to unreacted alkalinity reagents, particularly CaCO3, resulting in poor water clarity and elevated suspended solids (SS). Secondly, neutralisation to circum-neutral pH may not avoid the discharge of residual metals (Ni and Zn) due to incomplete adsorption and hydroxide precipitation. The aim of this project was to enhance the conventional neutralisation of AMD through addition of humic substances (HS) to reduce residual SS and trace metal concentrations. Humic substances are organically derived and have a high molecular weight. Functional groups on the surface of HS are capable of binding dissolved metals, forming HS-metal complexes. Incorporation of HS complexed metals into settling floc could result in increased metal removal from the dissolved phase. Modified jar testing was used to investigate the effects of HS addition before, after and during (pH 4.5) neutralisation of AMD in two treatment scenarios at the Stockton Mine; the Blackwater Treatment Plant (BTP) using NaOH and Ca(OH)2 and the Mangatini Stream-sump System (MSS) using CaCO3. Supernatant samples collected during the sedimentation period were analysed for basic water quality parameters (turbidity and suspended solids) and dissolved (< 0.45 µm) metal concentrations. The addition of HS to the BTP process before (pH 2.8) and during (pH 4.5) neutralisation resulted in HS precipitation. Precipitated HS subsequently acted as a nucleation site, triggering flocculation of precipitating metal hydroxides, resulting in low turbidity and suspended solids (SS) of less than 2 NTU and 5 mg/L, respectively. The addition of HS after neutralisation (pH 7) did not result in HS precipitation. Intermolecular bridging of HS by the divalent Ca resulted in incorporation of HS into floc when neutralised by Ca(OH)2, resulting in low turbidity and SS. However, in NaOH neutralised conditions, the monovalent Na was unable to bridge HS molecules, resulting in HS remaining dissolved and contributing to elevated turbidity and SS of up to 24.4 NTU and 18.4, respectively. The neutralisation efficiency of CaCO3 is relatively low, thus approximately 1000 mg/L CaCO3 remained unreacted in MSS scenarios, resulting in elevated turbidity and SS. When added after neutralisation, dissolved Solid Energy Humic Acid (SEHA) facilitated flocculation of residual CaCO3 SS, resulting in an up to 75% lower suspended solids than CaCO3 neutralisation alone conditions. Although the results are good, the efficiency of SEHA as a polymer compared unfavorably in a cost: benefit analysis to two commercially available polymers for the removal of residual CaCO3. Neutralisation of AMD in control samples resulted in decreased concentrations of the target metal group (Ni, Zn, Cu, Cd, and Pb) by hydroxide precipitation, co-precipitation, and adsorption. Equilibrium speciation modeling showed that the HS-metal binding affinity controlled the effectiveness of HS addition for metal removal. The low HS complexation affinity of Ni and Zn resulted in no additional metal removal by HS dosing. The removal of Cu was enhanced by over 50% for SEHA 20 during-neutralisation conditions neutralised by both NaOH and Ca(OH)2. Up to 80% lower Cd concentrations were observed for all HS dose conditions when neutralised by Ca(OH)2. Data for CaCO3 HS dosed metal removal was statistically indeterminate. The high detection limit for Pb made any HS dosed removal enhancement difficult to identify, which was unfortunate as Pb has a high HS complexation affinity (Čežı́ková, Kozler et al. 2001; Milne, Kinniburgh et al. 2003). A simple cost: benefit analysis showed that the additional removal of metals by HS dosing was less efficient than conventional neutralisation alone, on a cost basis. Overall, incorporation of HS into AMD treatment results in improved water quality for CaCO3 neutralisation and lower concentrations of metals with a high HS binding affinity, for some conditions. However, further investigation is required to improve the feasibility of HS incorporation into the AMD neutralisation process.

Current concerns about inorganic contaminants in food products have raised consumer awareness of anthropogenic sources of heavy metal contamination in ecosystems and their potential threat to human health. Mining and exploration of mineralized zones is a major source of such contamination. Mining throughout the Patagonia Mountains, Arizona, has left a legacy of surface water contamination by acid mine drainage (AMD). This study assessed the impacts of AMD on soils and plants throughout the study area. Concentrations, transport, and loading of heavy metals (Ag, As, Cd, Co, Cr, Cu, Fe, Mn, Mo, Ni, Pb, Sb, and Zn) in soils and plants was quantified using total concentrations, suggested toxic levels, and plant and soil pollution indices. Pollution indices were modified to include antimony and molybdenum. Pollution indices greater than 100 were found in areas disturbed by mining, remediation sites and beyond. Cattle grazing on grasses contaminated by metals were documented.

Abandoned metal mines in the Tamar catchment, south west England, represent a significant threat to surface water quality via generation of acid mine waters. Currently the River Tamar fails environmental quality standards (EQS) established under the Water Framework Directive (2000/60/EC) for dissolved Cu (x ̅ = 0.19 ± 0.05 μmol L-1) and Zn (x ̅ = 0.19 ± 0.06 μmol L-1, both 1997-2007) downstream of historic mining area of Gunnislake. The aim of this study was to quantify the risk to surface water quality by diffuse drainage generated by mine waste tips. For the first time, a GIS model was compiled and used to generate a priority list of known areas of mine waste, based on physical and environmental factors. The methodology was consistent with European guidance documentation published to meet the requirements of the Mining Waste Directive (2001/21/EC) and has since been applied, in a modified form, to other catchments in south west England. Two study sites, with contrasting mineralogy and hydrology, scored highly in the model and were the subject of field investigations from 2007-2009. These were Devon Great Consols (DGC), an abandoned Cu-As mine near Gunnislake and Wheal Betsy (WB), an abandoned Pb-Ag mine, near Mary Tavy. At each site, surface waters and shallow groundwaters were sampled and analysed for dissolved metals (including Al, Cu, Zn, Mn, Pb, Ni, and Cd), metalloids (As, Sb), major ions and anions. Samples of four selected mine waste tips were also gathered and subjected to a range of laboratory leaching experiments including the novel application of a dynamic upflow percolation test, based on an existing European method (CEN TS 14405). Leachates generated by the waste tips in the field were highly variable and elevated with respect to EQS for Al (up to 1850 μmol L-1), Cu (570 μmol L-1), Zn (34 μmol L-1), Ni (3.8 μmol L-1), Cd (0.17 μmol L-1), Mn (216 μmol L-1), Fe(537 μmol L-1) , As (380 μmol L-1) and Sb (5.4 μmol L-1). Estimated annual fluxes of dissolved metals were predicted using average rainfall data and catchment areas calculated in ArcHydro9 to estimate the annual discharge of waters from the tip. These calculations showed annual contaminant flux from the tips to exceed, or be of the same order of magnitude to, major adit discharges in the catchment (e.g. Cu 50900-66900 mol y-1 at DGC and 470 mol y-1 Cd at WB) and represented a significant contributor to metal flux in the Tamar catchment. Primary sulphide minerals in the waste were generally highly altered and metals (Pb, Cu, Zn, and Mn) and As were found to be strongly associated with secondary iron minerals, precipitated under oxic conditions. In finer wastes, sorption to clay minerals was also found to be very important for the retention of dissolved metals, particularly Pb. Concentrations of contaminants in column field leachates were similar for most metals (Cu, Zn, Mn, Ni and Cd) and may provide a useful tool for prediction of leachate composition. However, sorption and release of metals and As to the secondary phases and clays were highly sensitive to pH change and where laboratory experiments did not replicate field pH, discrepancies between in situ and laboratory results were observed up to two orders of magnitude in scale (particularly for As and Pb).

<p>Microorganisms mediate many biogeochemical processes critical to the functioning of ecosystems, which places them as an intermediate between environmental change and the resulting ecosystem response. Yet, we have an incomplete understanding of these relationships, how to predict them, and when they are influential. Understanding these dynamics will inform ecological principles developed for macroorganisms and aid expectations for microbial responses to new gradients. To address this research goal, I used two studies of environmental gradients and a literature synthesis.</p><p>With the gradient studies, I assessed microbial community composition in stream biofilms across a gradient of alkaline mine drainage. I used multivariate approaches to examine changes in the non-eukaryote microbial community composition of taxa (chapter 2) and functional genes (chapter 3). I found that stream biofilms at sites receiving alkaline mine drainage had distinct community composition and also differed in the composition of functional gene groups compared with unmined reference sites. Compositional shifts were not dominated by groups that could benefit from mining associated increases of terminal electron acceptors; two-thirds of responsive taxa and functional gene groups were negatively associated with mining. The majority of subsidies and stressors (nitrate, sulfate, conductivity) had no consistent relationships with taxa or gene abundances. However, methane metabolism genes were less abundant at mined sites and there was a strong, positive correlation between selenate reductase gene abundance and mining-associated selenium. These results highlighted the potential for indirect factors to also play an important role in explaining compositional shifts.</p><p>In the fourth chapter, I synthesized studies that use environmental perturbations to explore microbial community structure and microbial process connections. I examined nine journals (2009–13) and found that many qualifying papers (112 of 148) documented structure and process responses, but few (38 of 112 papers) reported statistically testing for a link. Of these tested links, 75% were significant. No particular approach for characterizing structure or processes was more likely to produce significant links. Process responses were detected earlier on average than responses in structure. Together, the findings suggested that few publications report statistically testing structure-process links; but when tested, links often occurred yet shared few commonalities in linked processes or structures and the techniques used for measuring them. </p><p>Although the research community has made progress, much work remains to ensure that the vast and growing wealth of microbial informatics data is translated into useful ecological information. In part, this challenge can be approached through using hypotheses to guide analyses, but also by being open to opportunities for hypothesis generation. The results from my dissertation work advise that it is important to carefully interpret shifts in community composition in relation to abiotic characteristics and recommend considering ecological, thermodynamic, and kinetic principles to understand the properties governing community responses to environmental perturbation.</p> / Dissertation

A research report submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in partial fulfilment of the requirements for the degree of Master of Science in Engineering, 2016 / The aim of this research was to reduce heavy metal and sulfate content of acid mine drainage (AMD) through the methods of passive filtration by combining permeable concrete and organic materials. This was to achieve a low cost, yet effective temporary treatment method for rural/poor communities who are affected by AMD. The acids are filtered through layers of alternating pervious concrete and biological composting layers. The concrete layers target removal of heavy metals such as iron, manganese, potassium, and magnesium, etc. through precipitation as well as reduce sulfate content to a small degree along with total dissolved solids. The concrete layers also aid in raising the pH of the AMD to more acceptable levels. The biological layers achieve sulfate remediation through the metabolism of sulfatereducing- bacteria (SRB). This process however required time and the organic layers were thus thicker and less permeable than the concrete layers in order to allow seepage to take place at a reduced rate. A wide variation of composting layers were tested, including cow manure, chicken manure, sawdust, straw, zoo manure, and leaf compost to find an optimum mix of materials which allows for the greatest sulfate reduction through sulfate reducing bacteria in the shortest possible time. Short as well as Long-term testing of rigs was undertaken to establish effectiveness, limitations and lifespan of the filtration systems. AMD from a mine in the Mpumalanga coal fields with exceptionally high sulfate content was used to test effectiveness of the organic materials over a short period of time. With long term testing conducted with a synthetic AMD, due to limited supply from the mine. The short term testing yielded removal of sulfates in the order of 56% when using kraal manure as the biological reagent mixed with sawdust for added organic carbon. The mix percentages by volume were 80%Sawdust to 20%manure and this setup was able to achieve the 56% removal of sulfates within 14 days. The filter also successfully raised the pH to 8 while removing a significant portion of heavy metals. The long term tests showed complete (100%) remediation of sulfates after a period of approximately sixty days. The tests are continuing to determine their finite lifespan and limitations. The results show promise for using the technology as a low cost, temporary measure to protect locally impacted groundwater, especially for isolated and/or rural communities while a permanent long term solution is sought.

A thesis submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy. September 2014, Johannesburg. / Aims: The adsorptive removal of Cu, Mn, Hg and U by silica and maghemite nanoparticles (NPs) under acid mine drainage (AMD) conditions was investigated with the aim of assessing the applicability of NPs for remediation of AMD-contaminated water. The effect of NPs on metal uptake by algae, an increasingly popular remediation alternative, was also investigated. Methods: NP and algal metal removal were quantified by batch experiments using commercially prepared, bare and amine-functionalised silica-carbon hybrid NPs characterised for size, surface area, porosity, crystallinity, elemental composition and hydrodynamic size. Metal uptake by algae was quantified in the presence and absence of NPs. Results: Silica and maghemite NPs can be used for the adsorptive removal of Cu, Mn, Hg and U from AMD-contaminated surface and ground water. NP metal uptake was rapid and equilibria were attained within 5 minutes with silica and maghemite NPs, and within 45 minutes with amine-functionalised hybrid NPs. Adsorption efficiencies for Cu, Mn, Hg and U at pH 3 were 52, 56, 56 and 49%, respectively with silica and 56, 52, 75 and 50%, respectively, with maghemite NPs. Metal removal was enhanced by >10% in solutions containing ferric, manganese or sulphate ions, although Cu removal was inhibited in solutions with a >1 Mn:Cu ratio. Despite the presence of high affinity amine groups in hybrid NPs, Cu removal was only 52% due to the low surface area of the adsorbent. The comparative study with Hg, however, showed that surface area was not the only determinant of adsorption efficiency: maghemite NPs with a specific surface area ~15 times less than silica adsorbed 21% more Hg. Metal removal by Scenedesmus sp. was enhanced by 12-27% in solutions containing NPs due to the greater sorption surface areas. NPs also modified metal partitioning in algal cells: intracellular concentrations were lower and extracellular concentrations higher in solutions containing NPs relative to controls (no NPs). Conclusion: Silica and maghemite NPs can be applied for the adsorptive removal of Cu, Mn, Hg and U from AMD-contaminated water and to improve the efficiency of phycoremediation by Scenedesmus sp. These findings also point to the possibility of retardation of metals by NPs during their transportation from tailings and contaminated sites. Their partitioning to NPs and the strength of the interactions thereof can determine the prevalence of the metals in solution or in the solid phase.

A dissertation submitted to the Faculty of Engineering and the Built Environment, University of Witwatersrand, Johannesburg, in fulfillment of the requirements for the degree of Master of Science in Engineering. Johannesburg, 2016 / The remediation of acid mine drainage (AMD) has received much attention over the years due to the environmental challenges associated with its toxic constituents. Although, the current methods are able to remediate AMD, they also result in the loss of valuable products which could be recovered and the financial benefits used to offset the treatment costs. Therefore, this research focused on the removal of toxic heavy metals as well as the recovery of acid using a low cost adsorbent and acid retardation process, respectively. In the first aspect of the study, three low cost adsorbents namely zeolite, bentonite clay and cassava peel biomass were evaluated for metal uptake. The adsorption efficiencies of zeolite and bentonite, was found to be less than 50% for most metal ions, which was lower compared to the 90% efficiency obtained with cassava peel biomass. Subsequently, cassava peel biomass was chosen for further tests. The metal removal efficiency using the cassava biomass was in the order Co2+> Ni2+> Ca2+> Mn2+> Fe3+> Mg2+. The highest metal removal was attained at 2% adsorbent loading and 30 ˚C solution temperature. Amongst the equilibrium models tested, the experimental data was found to fit well with the Langmuir isotherm model. Column studies using the immobilized cassava waste biomass suggested that the breakthrough curves of most metal ions did not resemble the ideal breakthrough curve, due to the competitive nature of the ions present in the AMD used in this study. However, the experimental data from the column tests was found to correlate well with the Adam-Bohart model. Sulphuric acid recovery from the metal barren solution was evaluated using Dowex MSA-1 ion exchange resins. The results showed that sulphuric acid can be recovered by the resins via the acid retardation process, and could subsequently be upgraded to near market values of up to 70% sulphuric acid using an evaporator. Water of re-usable quality could also be obtained in the acid upgrade process. An economic evaluation of the proposed process also showed that it is possible to obtain revenue from sulphuric acid which could be used to offset some of the operational costs. / M T 2016

The mining that gave rise to Johannesburg as a city has left in its wake pieces of geologically disturbed, disused, and unusable land. These leftover fragments of landscape carry with them, not only memory of the city’s foundations, but scars of the mining processes that now render them unusable - Not only do these vaguescapes have potential for the memory within them to be unearthed, but they are highly polluted, and seek to be reimagined as productive city spaces. The chosen site, an abandoned piece of mineland with a concealed old mine shaft; on the edge of a highway on the fringe of the CBD, is simultaneously highly visible to the city, but forgotten to it. Its positioning is unique in that it allows for the potential for the extraction of the mine pollutants and site remediation to become a highly visible process. Understanding and uncovering layers and traces of the site as means of understanding what is possible on this highly polluted landscape became an important architectural and design generator. The architecture consolidates and reimagines the fragments of ruin, both physical and ephemeral, contained on the site, and curates the users experience through these forgotten traces. Its programme - a colour plant, which extracts useful metallic colour pigments from the contaminated earth, becomes a visceral reminder of these past traces ;and a recording device for the current consequences of past mining activity. The approach is an almost critical speculation. The age of the picturesque landscape is no more. Our effects on the land have depleted the earth and diseased its rhythms. But these unstable consequences hold possibilities that can be engaged with imaginatively; rather than merely re-mediated. How can architecture engage with this instability? The project accepts the presence of rising acid mine water; and imagines a new reality emerging from it. The project is a comment on our own epoch; one where waste, toxicity and radiation are so rife, that they are now a quiet, sinister backdrop to our world. More than an apocalyptic future, this project deals with a dystopian present. The precarious site conditions pose questions for an architecture which can engage with the instability, and not merely withstand it. The architectural concern is to render visible and intensify a consciousness of these traces, to investigate a palimpsest infrastructure. Colour, like architecture is a link between the conscious and the subconscious. It is a mediator between the realms. It holds possibilities for suggesting and molding atmospheres and perceptions. The architecture negotiates all the realms, concerned with past, present and future. It consolidates and makes apparent the traces but it is also developed with an awareness that it becomes part of these traces. It is an intervention which aims to heighten an awareness of the presence of the past in the life of the city; and also as palimpsest infrastructure; as a recording device for the geological happenings of the earth.

A dissertation submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Master of Science in Chemical Engineering, 2016 / In South Africa, the need for water treatment is increasing, especially in the mining sector. As active water treatment technologies are expensive, the mining sector has an increasing need for passive water treatment technology, with low maintenance and operating costs, yet efficient water treatment ability. Literature on passive water treatment suggests that these systems only offer a narrow range of treatment capabilities. Therefore, hybrid water treatment systems could be a solution to low-cost water treatment in South Africa. The Degrading Packed Bed Reactor (DPBR) is one of the units comprising the hybrid treatment group. The DPBR’s main action is to convert sulfates into sulfides and alkalinity. In practice, the main drawback of the DPBR is clogging. Clogging lessens the amount of Acid Mine Drainage (AMD) that comes into contact with Sulfur Reducing Bacteria (SRB) in the DPBR, thereby reducing the efficiency of the bioreactor. In this study, six small-scale DPBRs were constructed. Each was classified according to its unique organic source (manure, straw, vegetable food processing waste, wood shavings, chicken litter and a combined sample with layers of all the carbon sources). Synthetic AMD was fed through the six bioreactors for a period of three months. From the small-scale DPBRs, the permeability, sulfate, iron and pH of the exit samples were measured. On average, the carbon sources removed 50 % of the sulfates and 98 % of the iron from the fed AMD. The different carbon sources showed no significant difference between each other in terms their sulfate and iron removal. The range between the best performing carbon source and the poorest performing carbon source, in terms of sulfate removal, was 17%. For iron removal, the range between the best and poorest performing carbon sources was only 2%. It was found that the permeability of the carbon sources played a larger role in the efficiency of the DPBR than the type of carbon source used. Manure is highly effective in terms of pH improvement, sulfate and iron removal. However, this is at the expense of permeability, as its packing clogs very rapidly. Compost and straw have excellent permeabilities which do not change significantly over long timeframes. This is, however, at the expense of the remedial ability of the packing materials. The combined reactor, in every instance, offers a good compromise between these different behaviours. / GR2016

A research report submitted to the Faculty of Science in partial fulfillment of the requirements for the degree of Master of Science, 2016. / South African gold mines are associated with the generation of a lot of mine waste in the form of milled rock (tailings). Tailings contain the mineral pyrite which, when exposed to air and water, cause acid mine drainage (AMD). Due to the large environmental impact (footprint and scale) ofthe tailings storage facilities (TSFs) on soils and groundwater, there has been much research done in phytoremediation. Some plants, such as Eucalyptus, used in this method are able to control seepage by using their extensive roots but this may inadvertently extract some contaminants from the water and accumulate them in the above ground parts of the tree. Upon harvesting of these plants, there is the potential for them to be used as biofuel for the generation of bioenergy, and by industry or the public as timber/construction wood, firewood, charcoal, generation of electricity, etc. In this study, three species of Eucalyptus trees grown by the University of the Witwatersrand in three site-species trials on AMD were evaluated for their concentrations of elements in leaves, bark, branches/twigs and stem wood, in order to determine the safety of the biomass for fuel, and the potential for environmental pollution (dissemination of metals) that could be caused by combustion. The study focused on Eucalyptus camaldulensis, E. grandis x camaldulensis hybrid and E. dunnii trees grown for eight years in three different trial sites, with one trial ("Mispah") situated at AngloGold Ashanti's Vaal River Mining Operations (VR, near Orkney - Klerksdorp) and two trial("Madala", "Red Soil") situated at the West Wits Mining Operations (WW, near Carletonville). The sites were typical of soils on the mine properties (WW Madala: Clovelly, WW Red Soil: Hutton, VR Mispah: Hutton and Mispah), and impacted by seepage from adjacent TSFs. Three entire above-ground trees were harvested per species (three trees per site, nine in total), weighed fresh and after drying. Samples of leaves, bark, twig/small branches, and main stem wood were analysed for their elemental contents; alongside a Certified Reference Material (CRM) (Orchard Leaves no. 1571); using Leco CNS analyser, Inductively Coupled PlasmaOptical Emission Spectroscopy (ICP-OES) and Inductively Coupled Plasma-Mass Spectroscopy (ICP-MS) to determine the concentrations of major and trace elements such as Aluminium (AI), Barium (Ba), Calcium (Ca), Iron (Fe), Potassium (K), Magnesium (Mg), Manganese (Mn), Sodium (Na), Nickel (Ni), Phosphorus (P), Sulphur (S), Strontium (Sr), Titanium (Ti), Zinc (Zn), Vanadium (V), Chromium (Cr), Cobalt (Co), Copper (Cu), Arsenic (As), Gold (Au), Mercury (Hg), Lead (Pb), Uranium (U), carbon (C) and ash content. The CRM was used to validate the two analytical methods. There was variation in the concentrations of nutrients measured. There were no significant differences noted in the metallloids concentrations between all the Eucalyptus 11\ species studied (p>O.05). Variation between sites could not be determined as there were no replicates available to perform the comparison. The World Health Organisation (WHO) maximum permissible level (MPL) in plants for arsenic (As) is 1 mg/kg. The MPL was exceeded in all tissues of all three Eucalyptus species studied. Arsenic concentrations of 5.09, 4.36 and 5.48 mg/kg were found in the wood of E. camaldulensis, E. grandis x camaldulensis and E. dunnii respectively. A risk assessment performed found that there was no evidence that there will be adverse effects caused by supplying fuelwood from these contaminated Eucalyptus trees. Even though high arsenic concentrations were recorded in this study, if the wood is used as fertilizer in a vegetable bed, the transfer of the arsenic to the common vegetables is below the daily oral reference dose. The general trend in the concentration of metals and metalloids in different plant tissues was in the order of leaves > bark > branches/twigs > wood. The results of the biomass exposure assessment showed that the exposure through use of the ash as fertiliser was lower than the oral reference dose for Mn, Fe, Ba and As. The biomass risk assessment showed that the best-performing tree, in terms of wood production on AMO, was the E. camaldulensis. The risk of other metallioids was not evaluated as there was no good agreement between the results recorded with those certified of the CRM. It is suspected that the CRM used was old. / AC2016