Legacy mining areas throughout the world contain widespread contaminated surface and groundwater from both anthropogenic and geogenic sources. Abandoned mine waste can contribute harmful solutes to groundwater and surface water, as metals mobilize through oxidation of sulfide minerals. Geogenic contaminant sources, such as geothermal water and mineralization, may also contribute to groundwater pollution in mining areas. To investigate the relationship between various groundwater contamination sources in legacy mining areas we sampled ~30 cold springs in the East Tintic Mountains of Utah and 8 regional hot springs as a proxy for geothermal water during fall 2019 and spring/summer 2020. Water chemistry data were analyzed using a Principal Components Analysis (PCA), revealing two distinct groundwater systems for hot and cold springs with no apparent mixing between the two. Only one cold spring was clearly enriched in multiple metals (Al, Mn, Co, Ni) relative to other springs but was not located proximal to any significant mining waste rock piles. 87Sr/86Sr ratios were analyzed in a subset of samples to identify flowpaths through carbonate or volcanic rocks. Only two springs had 87Sr/86Sr ratios characteristic of the Eocene and Oligocene volcanic rocks that dominate the surface of the study area (0.707 - 0.708), with all others having ratios indicative of underlying Paleozoic carbonate rocks (0.708 -0.710). Groundwater flow through carbonate rocks is dominated by faults and fractures, with faults appearing to act as barriers rather than conduits to flow. Faults create groundwater compartmentalization within the carbonate rock that isolates water contaminated by mining waste, while the carbonate rocks neutralize acid mine drainage. Groundwater compartmentalization explains the lack of widespread contamination despite the presence of large mining waste piles throughout the area. Mixing between geothermal and shallow groundwater may be the source of high Li, B, and SO42- concentrations in a limited number of springs. Our results suggest that contamination from mining waste is highly localized and that that waters discharging from mining areas overlying faulted carbonate rocks may be less contaminated than previously thought. This study has implications for understanding groundwater contamination dynamics in semi-arid regions impacted by mining.

Biological sulphate reduction (BSR) has been identified as a promising alternative technology for the treatment of acid mine drainage. BSR is a process that uses sulphate reducing bacteria to reduce sulphate to sulphide using substrates as nutrients under anaerobic conditions. The performance of BSR is dependent on several factors including substrate, pH, temperature and hydraulic retention time (HRT). In a quest to find a cost effective technology, Mintek conducted bench-scale tests on BSR that led to the commissioning of a pilot plant at a coal mine in Mpumalanga province, South Africa. This current study forms part of the ongoing tests that are conducted to improve Mintek’s process. The purpose of this study was to investigate the robustness of Mintek’s process and to develop a tool that can be used to predict the process’ performance with varying pH, temperature and HRT. Design Expert version 11.1.2.0 was used to design the experiments using the Box-Behnken design. In the design, pH ranged from 4 to 6, temperature from 10 °C to 30 °C and HRT from 2 d to 7 d with sulphate reduction efficiency, sulphate reduction rate and sulphide production as response variables. Experiments were carried out in water jacketed packed bed reactors that were operated in a down-flow mode. The reactors were packed with woodchips, wood shaving, hay, lucerne straw and cow manure as support for sulphate reducing bacteria (SRB) biofilm. Cow manure and lucerne pellets were used as the main substrates and they were replenished once a week. These reactors mimicked the pilot plant. The data obtained were statistically analysed using response surface methodology. The results showed that pH did not have a significant impact on the responses (p>0.05). Temperature and HRT, on the other hand, greatly impacted the process (p<0.05) and the interaction between these two factors was found to be strong. Sulphate reduction efficiency and sulphate reduction rate decreased by over 60 % with a decrease in temperature 30 °C to 10 °C. Generally, a decrease in sulphide production was observed with a decrease in temperature. Overall, a decrease in HRT resulted in a decline of sulphate reduction efficiency and sulphide production but favoured sulphate reduction rate. This study demonstrated that Mintek’s process can be operated at pH as low as 4 without any significant impact on the performance. This decreases the lime requirements and sludge production during the pre-neutralisation stage by close to 50 %. There was, however, a strong interaction between temperature and HRT which can be used to improve the performance especially during the winter season. / Dissertation (MEng)--University of Pretoria, 2020. / Chemical Engineering / MEng / Unrestricted

Diatoms have a successful history of use in assessments of wetland biological condition. In North America and across Europe, diatom assemblages are used for routine wetland condition assessments to meet the statutory requirements of the European Water Framework Directive and the National Aquatic Resource Survey by the US Environmental Protection Agency. In South Africa, the use of diatom assemblages as indicators of wetland condition may be a promising alternative to the traditional biotic assemblages employed, such as macroinvertebrates or macrophytes, which have proven to be ineffective. We present a preliminary investigation on the feasibility of diatoms in wetland biological assessments in South Africa by evaluating the use of diatoms as indicators of biological condition for depressional wetlands in the Mpumalanga Highveld region of South Africa. Depressional wetlands typically found in this region are either temporary (seasonally inundated) or permanent depressions. Temporary depressional wetlands are expected to be affected by natural environmental disturbances (e.g., seasonal fluctuations in water-level which may cause changes in water chemistry) as compared to relatively stable permanent ones. Establishing whether diatoms are suitable indicators of natural environmental disturbances in temporary depressional wetlands in this region is necessary for further investigations of anthropogenic disturbances. We sampled epiphytic diatoms from three least human-disturbed temporary depressional wetlands during various stages of inundation and showed that the species composition of epiphytic diatom communities were strong indicators of temporally changing environmental conditions. Using the same diatom and physical and chemical data, we also demonstrated that simplifying the taxonomy by using the functional composition (ecological guilds, life-forms) of the epiphytic diatom communities, can assess temporally changing environmental conditions as effectively as the species composition. Moreover, these functional groups provide valuable ecological information that is not available from the species data. Acid mine drainage (AMD) is the predominant stressor in permanent depressional wetlands of the Mpumalanga Highveld region, where coal mines utilise these wetlands for storage of AMD, which has severe impacts on the structure and function of the ecosystem. In order to develop an approach for impact assessment and management of depressional wetlands in the region, we developed an epiphytic diatom multimetric index (MMI) for AMD impacted permanent depressional wetlands. This is also the first diatom index to quantify AMD impacts in wetland habitats. Data collected from 34 sites that represented a range of conditions along an AMD gradient within the Mpumalanga Highveld was used to select responsive diatom metrics which we combined into a multimetric index. We developed separate MMIs for classes of depressional wetland types in order to account for natural variation among diatom assemblages, and compared their performance with an MMI that did not account for natural variation. To account for natural variation, we classified reference sites based on diatom typologies and hypothesised that by using this approach, we would improve MMI performance. Overall, all MMIs performed considerably well, although grouping sites by diatom typology to account for natural variation improved MMI performance, especially the precision, responsiveness and sensitivity to disturbance. We conclude that diatoms have strong potential for use in wetland ecological assessments in South Africa. The experimental and statistical approaches used in this study should expand our knowledge of diatom ecology and further advance the research and development of diatom bioassessment. / Thesis (PhD)--University of Pretoria, 2017. / Paraclinical Sciences / PhD / Unrestricted

>Magister Scientiae - MSc / South African power stations generate large amounts of highly alkaline fly ash (FA). This waste product has a serious impact on the environment. Acid mine drainage (AMD) is another environmental problem associated with mining. AMD has high heavy metal content in addition to high SO/- concentrations. Several studies have shown that 80-90 % of SO/- can be removed when FA is codisposed with AMD rich in Fe and AI. In South Africa, many sources of contaminated mine waters have circumneutral pH and much lower concentrations of Fe and Al (unlike AMD), but are rich in Ca, Mg and SO2-4. This study evaluated sol removal from circumneutral mme water (CMW) collected from Middleburg coal mine using coal FA collected from Hendrina power station. The following parameters were investigated: the effect of the amount of FA, the effect of the final pH achieved during treatment, the effect of the initial pH of the mine water and the effect of Fe and Al on SO/- removal from mine water. The precipitation of ettringite at alkaline pH was evaluated to further reduce the SO/- concentration to below the DWAF limit for potable water. Removal of sol from mine water was found to be dependent on: the final pH achieved during treatment, the amount of FA used to treat the mine water and the presence of Fe and Al in the mine water. Treatment of CMW using different CMW:FA ratios; 5:1, 4:1, 3:1, and 2:1 resulted in 55, 60, 70 and 71 % SO/- removal respectively. Treatment of CMW to pH 8.98, 9.88, 10.21, 10.96, 11.77 and 12.35 resulted in 6, 19, 37, 45, 63 and 71 % SO/- removal respectively. When the CMW was modified by adding Fe and Al by mixing with Navigation coal mine AMD and treated to pH 10, 93 % SO/- removal was observed. Further studies were done to evaluate the effects of Fe and Al separately. Treatment of simulated Fe containing AMD (Fe-AMD) to pH 9.54, 10.2, 11.8, and 12.1 resulted in 47, 52,65, and 68 % SO/- removal respectively. When Al containing AMD was treated to pH 9.46, 10.3, 11.5 and 12 percentage SO/- removal of 39, 51,55 and 67 % was observed respectively. Ion chromatography (IC), inductively coupled plasma-mass spectrometry (ICPMS) and inductively coupled plasma-atomic emission (ICP-AES) analysis of the product water, x-ray diffraction (XRD) and x-ray fluorescence (XRF) spectrometry analysis of FA and solid residues collected after treatment of mine water complemented with PHREEQC thermodynamic modelling have shown that the mechanism of S042 - removal from mine water depends on the composition of the mine water. The sol- removal mechanism from CMW was observed to depend on gypsum precipitation. On the other hand sol- removal from mine water containing Fe and Al was dependent on the precipitation of gypsum and Fe and Al oxyhydroxysulphates. The oxyhydroxysulphates predicted by PHREEQC as likely to precipitate were alunite, basaluminite, ettringite, jarosites and jurbanite. Treatment of CMW with FA to pH 12.35 removed sol- from 4655 ppm to approximately 1500 ppm. Addition of amorphous AI(OH)3 to CMW that was treated to pH greater than 12 with FA was found to further reduce the sol concentration to 500 ppm which was slightly above the threshold for potable water of 400 ppm. The further decrease of sol concentration from 1500 to 500 ppm was due to ettringite precipitation. Mine water treatment using FA was found to successfully remove all the major elements such as Fe, AI, Mn and Mg to below the DWAF limit for drinking water. The removal of the major elements was found to be pH dependent. Fe and Al were removed at pH 4-7, while Mn and Mg were removed at pH 9 and 11 respectively. The process water from FA treatment followed by gypsum seeding and addition of AI(OH)3 had high concentration of Ca, Cr, Mo and B and a pH of greater than 12. The pH of the process water from FA treatment followed by gypsum seeding and addition of AI(OH)3 was reduced by reacting the process water with CO2 to 7.06. The process water from the carbonation process contained trace elements such as Cr, Mo and B above the DWAF effluent limit for domestic use. Carbonation of the process water reduced the water hardness from 5553 ppm to 317 ppm due to CaC03 precipitation, thereby reducing the Ca concentration from 2224 ppm to 126 ppm.

Dabaoshan Mine Site (DMS) is the biggest polymetallic mine in South China. The Hengshi River receives acid mine drain (AMD) waste leaching from the tailings pond and run-off from the treatment plant which flows into the Wengjiang River, Beijiang River, before discharging into the Pearl River. Discharge from the mine site results in heavy metal contamination  near the mine and lower riparian areas along the river course. The present study focuses on the distribution and mobilization of As, Cd, Pb and Zn along the Hengshi River, groundwater, fluvial sediments and soil, with a special focus on As due to its high toxicity and the fact that mining is one of the main anthropogenic sources of As. Heavy metals, grain-size, XRD, %C and S analysis were done in order to determine the physicochemical characteristics of samples. The results were used for geochemical modeling (PHREEQ) and statistical (PCA) analysis to understand and predict the behavior of heavy metals. Potential ecological risk assessment was conducted by calculating contamination degree of heavy metals in soil and sediment and it’s theoretical toxical risk. Near the tailings pond, heavy metal concentration was 2-100 times higher than chinese surface water standard for agricultural use, which decreases downstream, mianly due to dilution, sorption, precipitation and co-precipitation with minerals. In groundwater, heavy metals concentration remained low. Due to the fact that most wells were abandoned or only for household use, potential risk from groundwater is low. The soils were disturbed by industrial or agricultural activities, and heavy metal concentration varied without showing any specific trend along the river. The potential ecological risk of heavy metals are ranked as: Cd&gt;As&gt;Cu&gt;Pb&gt;Zn in sediments; Cd&gt;Cu&gt;Pb&gt;As&gt;Zn in soil. As(Ⅲ) was the predominant species in surface water, and minerals identified in soil and sediment. Arsenic from most sites exceeded the Chinese soil standard for development land. Although arsenic was assumed to have a moderate ecological risk in sediments and low risk in soils, anthropogenic activities, such as land use change and untreated sewage discharge, might reduce and release arsenic into the environment, which poses potential risk to local residents.

No description available.

Surface and groundwaters in contact with mining-exposed pyritic materials have the capacity to generate acid mine drainage (AMD), an acidic, sulfate-rich, metals-laden effluent. The Davis Mine located in northwestern Massachusetts offers a model site to study the processes of natural attenuation of acid mine drainage. These include physico-chemical processes such as dilution and sorption, geochemical processes such as aluminosilicate weathering and biological processes such as transformation and cycling of sulfate, iron and acidity by bacterial metabolism. A focus of recent research undertaken at the site has been characterizing the presence and activity of these bacteria with an aim to stimulate their capacity to attenuate the severity of acidic conditions. To further this investigation, a pilot-scale treatment system was installed, composed of a modified permeable reactive barrier containing organic carbon and limestone. Down-gradient groundwater was sampled over a sixteen-month period for concentrations of dissolved metals, major cations and sulfate, along with pH and redox measurements. The results showed a decrease in dissolved metals, a possible increase in calcium and decrease in sulfate, and measurable increase in pH and corresponding decrease in oxidation-reduction potential. Major decreases in dissolved iron and aluminum were observed, a change which is not entirely consistent with metals removal by combination with biogenic sulfide alone. The additional influence of hydrolysis was proposed and the anticipated action of this alternate process found to bear resemblance to the observed changes. Groundwater composition from the experimental period was compared to previous measurements and significant changes described in pH, iron, aluminum, copper and zinc and to a lesser extent in calcium and sulfate. Comparisons were also made with concurrent surface water compositions and findings of analogous studies. Conclusions that can be drawn include: the pH and redox environment into which a treatment system is placed can greatly influence the reactions which take place, side-reactions which occur in reducing and alkalinity-generating amendments may also have an attenuating effect, and variable processes influence groundwater composition in these biogeochemically complex environments.

No description available.

Acid mine drainage (AMD) is an acidic, iron-rich leachate that causes the dissolution of metals. It constitutes a worldwide problem of environmental contamination detrimental to aquatic life and water quality. AMD, however, is naturally attenuated at Davis Mine in Rowe, Massachusetts. We hypothesize that sulfate-reducing bacteria (SRB) are attenuating AMD. To elucidate the mechanisms by which SRB attenuate AMD, three research projects were conducted using a suite of molecular and geochemical techniques. First we established biological influence on the attenuation of AMD by comparing the microbial community and geochemical trends of microcosms of two contrasting areas within the site: AMD attenuating (AZ) and AMD generating (GZ) zones. The differences in geochemical trends between these zones were related to differences in microbial community membership. SRB were only detected in microcosms of the AZ, while iron oxidizers were only detected in the GZ. This study indicates that biological activity contributes to the attenuation of AMD and that SRB may have a role. To further describe the role of SRB, we determined the rates of sulfate reduction, the abundance, and membership of SRB in the second project. The sulfate reduction rate was weakly correlated with the abundance of SRB. This indicates that the SRB population may be utilizing another electron acceptor. One such electron acceptor would be iron, which was investigated in the third project. When SRB are inhibited, neither accumulation of reduced iron nor the formation of reduced iron sulfide precipitates occurred. Higher concentration of sulfide produced an increase in reduced iron and pH. Therefore, iron reduction mediated by reaction with biogenic sulfide contributes to the attenuation of AMD. This is the first report of the biological enhancement of iron reduction by acidotolerant SRB. The interdisciplinary research described in this dissertation provides evidence that SRB attenuate AMD through sulfate and iron reduction and a greater understanding of SRB in acidic environments. It also demonstrates how the biogeochemical cycling of sulfur is coupled to the iron cycle. Overall, the ubiquity and metabolic versatility of SRB offers boundless potential and exciting opportunities of study in the fields of bioremediation, geomicrobiology, and microbial ecology.

The rapid development of advanced technologies has led to an increase in demand for critical elements that are essential in the manufacturing of high-tech products. Among these critical elements, manganese (Mn), cobalt (Co), and nickel (Ni) are used in the production of batteries, electronics, and other advanced applications. The demand for these elements has been growing exponentially in recent years, driven by the rise of electric vehicles, renewable energy, and other emerging technologies. However, the United States is heavily dependent on foreign sources of critical minerals and on foreign supply chains, resulting in the potential for strategic vulnerabilities to both economy and military. To address this problem and reduce the Nation's vulnerability to disruptions in the supply of critical minerals, it is important to develop critical minerals recycling technologies. A systematic study was conducted to develop a process for producing high-purity Mn, Co, and Ni products from an acid mine drainage (AMD). As major contaminants, Fe and Al in the solution were sequentially precipitated and eliminated by elevating the pH. After that, a pre-concentrated slurry containing Mn, Co, Ni, and Zn was obtained by collecting the precipitates formed in the pH range of 6.50 to 10.00. The pre-concentrated slurry was redissolved for further purification. Sodium sulfide was added into the redissolved solution to precipitate Co, Ni, and Zn selectively while retaining Mn in the solution. Almost 100% of Co, Ni, and Zn but only around 15% of Mn were precipitated using a sulfur-to-metal molar ratio of 1 at pH 4.00. The sulfide precipitate was calcined and then completely dissolved. The critical elements existing in the dissolved solution were efficiently separated using a two-stage solvent extraction process. Ultimately, Co and Ni products with almost 94% and 100% purity were obtained by sulfide and alkaline precipitation, respectively. AMD also contains rare earth elements (REEs), which can be recovered through selective chemical precipitation. REE removal improved at pH 4.0 after converting ferrous to ferric ions with H2O2. Aluminum species in the solution hindered REE adsorption on ferric precipitates, and ferrous ions reduced REE adsorption on aluminum precipitates at lower pH, but at higher pH, REE removal increased due to ferrous ion precipitation. Various tests and analyses were conducted to understand the partitioning mechanisms of REE during the precipitation process of AMD. Sulfide precipitation is crucial to separate Mn from other elements, but the presence of contaminants like Fe and Al can affect sulfide precipitation efficiency. The effects of Al3+ iii and Fe2+ on the precipitation characteristics of four valuable metals, including Mn2+, Ni2+, Co2+, and Zn2+, were investigated by conducting solution chemistry calculations, sulfide precipitation tests, and mineralogy characterizations. It was found that the ability of the valuable metals to form sulfide precipitates followed an order of Zn2+ > Ni2+ > Co2+ > Mn2+. The sulfide precipitate of Zn2+ was the most stable and did not re-dissolve under the acidic condition (pH 4.00 ± 0.05). In addition, the sulfide precipitation of Zn2+ was barely affected by the contaminant metal ions. However, in the presence of Al3+, the precipitation recoveries of Mn2+, Ni2+, and Co2+ in a solution containing all the valuable metals were noticeably reduced due to simultaneous hydrolysis and competitive adsorption. The precipitation recoveries of Ni2+ and Co2+ in solutions containing individual valuable metals also reduced when Fe2+ was present, primarily due to competitive precipitation. However, the recovery of Mn2+ was enhanced due to the formation of ferrous sulfide precipitate, providing abundant active adsorption sites for Mn species. In the solution containing all the valuable metals, Fe2+ promoted the recoveries of the valuable metals due to the higher concentration of Na2S and the formation of ferrous sulfide precipitate. / Doctor of Philosophy / The rapid development of advanced technologies has increased the demand for critical elements essential in manufacturing high-tech products. In this study, a process was developed for producing high-purity Mn, Co, and Ni products from an acid mine drainage (AMD). A product with around 30 wt.% Mn was produced. Co and Ni products with 94% and 100% purity were also obtained. However, when developing the process, it was found that a portion of the REEs is often lost to the precipitates of the dominant metal contaminant ions (Fe and Al) in the staged precipitation. It was found that the REE removal increase was realized through adsorption onto the surfaces of the ferric precipitates. In sulfide precipitation, the presence of Fe and Al in the solution can significantly influence the separation efficiency of the critical elements. The effect of Al3+ on the sulfide precipitation is due to the simultaneous hydrolysis of aluminum and sulfur ions. The reduction of the recovery of valuable metals caused by the Fe2+ is due to the form of iron sulfides.