Schwertmannite, a ferric oxyhydroxysulfate mineral typically found under acidic, high sulfate and iron aqueous conditions, such as acid mine drainage environments, was studied using analytical high resolution transmission electron microscopy (HRTEM). HRTEM offers advantages over bulk techniques such as powder x-ray diffraction and pair distribution function (PDF) analysis of synchrotron data, in its ability to discern multiple phases within poorly crystalline nanominerals. Based on extensive HRTEM observations of both natural and synthetic schwertmannite samples, the authors suggest that schwertmannite should not be described as a single phase mineral with a repeating unit cell, but as a polyphasic nanomineral with crystalline areas spanning less than a few nanometers within an amorphous matrix. The few visible lattice fringes observable in both natural and synthetic schwertmannite agree well with d-spacings of goethite (and jarosite in natural samples) implying that the transformation from schwertmannite to these phases occurs as a gradual structural reordering at the nanoscale. In the synthetic study, the complete transformation from schwertmannite to goethite nanorods and nanoparticles within 24 hours at 75°C was observed, indicating a low energetic barrier to schwertmannite's phase transformation. We also found that amorphous silica can be intimately entrained within natural schwertmannite, and that high concentrations of arsenic can be held in close association of nanocrystalline regions of the mineral. / Ph. D.

Laboratory experiments were carried out to evaluate the effectiveness of antibacterial substances and antibiotics against Thiobacillus ferrooxidans, the organisms responsible for bacterial mediated acidic mine drainage. Twenty two antibiotics (obtained from Lilly and Co.) and two antibacterial substances were added to: bacterial culture ATCC 19859 grown in 9K medium. Appropriate controls were maintained. Inhibition of iron oxidizing bacteria was recorded in terms of changes in Eh of the medium treated with the compound. Seven antibiotics (A38533A:, A38533B, 197506, 13780, 171541, chloramphenicol and cephalexin) and the two antibacterial substances [N-serve(nitrapyrin) and Dicyandiamide] effectively inhibited the oxidation of Fe²⁻ ions in the medium. The kinetics of Fe²⁻ oxidation with the addition of antibiotics and the antibacterial substances was studied. N-serve [2-chloro-6-(trichloromethyl) pyridine], used as a nitrification inhibitor in agriculture, was highly effective at concentrations greater than 0.1 ml/l. Iron oxidation levels were reduced to levels close to that in uninoculated controls (abiotic oxidation). The use of N-serve to inhibit acid mine drainage (AMD) causing bacteria seems to be both economical and environmentally safe. / Master of Science

Several recent studies have shown that acid mine drainage (AMD) may be a promising source of rare earth elements (REEs), which are essential feedstocks for many high tech applications and defense products. AMD is a longstanding environmental challenge and is currently the primary pollutant of water in the Appalachian coal mining region. Acid generated during the coal mining process tends to leach several transition metals from the surrounding rock strata. While iron, aluminum, and manganese have traditionally been noted as the predominant metals in AMD, recent studies have also shown that REEs are also present, albeit in trace concentrations, often less than 5 μg/L. The recovery of REEs from AMD can be both an economic and environmental advantage; however, the low REE concentrations and high contamination from other metals makes the concentration and purification of REEs quite difficult. This research seeks to develop and optimize a process capable of producing mixed rare earth concentrates with purities exceeding 90% from an AMD feedstock. Parallel efforts by other members of the research team showed that a solid preconcentrate, nominally 0.1 to 2% REE, can be readily produced from AMD; however, that pre-concentration process cannot provide the further enrichment needed to generate high purity oxides suitable for downstream markets. In this project, solvent extraction was investigated as secondary process used to further enrich the low grade preconcentrate to a purity exceeding 90%. Initially, laboratory-scale batch solvent extraction tests were performed on synthetic REE solutions to determine the influence of various process parameters (e.g. pH, extractant dosage, diluent type, and feedstock concentration). Next, the separation of REEs from major AMD gangue elements was investigated using synthetic leachate solutions with concentrations similar to those expected from the pre-concentrate samples. This process showed that the grade targets could easily be met when combining optimal parameters from each step. From this preliminary work with synthetic solutions, an optimal SX process was developed and validated using a real leachate generated from a pre-concentrate sample. By integrating leachate preparation, solvent extraction, scrubbing, stripping, and oxalic acid precipitation, an oxide containing 90.5% rare earth oxides was generated. Details on the process development, experimental optimization, and opportunities for process improvement are described. / Master of Science / Rare earth elements (REEs) are essential for many modern industries, high-tech applications, and defense products. The U.S. consumes approximately 11% of the global REE demand; however, the US supply chain is heavily reliant on imported Chinese feedstocks. This lack of a domestic supply chain exposes the US to both price and supply volatility, which are prevalent in the international markets. This supply issue is further compounded by a lack of suitable domestic feedstocks. REEs are rarely concentrated into mineable ore deposits, and in some cases the extraction and processing of conventional REEs deposits entails considerable environmental risk. As a result of these challenges, numerous federal agencies and private companies have recently sought to identify promising alternative resources. One potential alternative resource is acid mine drainage (AMD), which is a common environmental challenge associated with coal and hard rock mining. Prior studies have shown that acid mine drainage contains REEs; however, other metals, such as iron, aluminum, and manganese, preclude REE recovery using conventional processing techniques. As such, the goal of this research is to develop and optimize a process capable of recovering and concentrating REEs from an AMD feedstock. The research conducted in this thesis predominantly included laboratory testing using synthetic AMD samples. The complexity of the synthetic AMD progressively increased from very simple, single element solutions to complex multi-component mixtures. Through this research, data and information from these controlled experiments was used to design a multi-step solvent extraction process capable of producing final REE products exceeding 90% purity. In the last stage of the research, the final process was validated using actual AMD recovered from an operating mine site. The validation test showed that the process was effective in meeting its initial objectives: the grade of the final rare earth oxide was determined to be 90.5%. This laboratory-scale experimental work represents the first step of process needed to develop and deploy a commercial technology capable of producing REE products from AMD feedstocks.

The production of acid mine drainage (AMD) is catalyzed by iron-oxidizing bacteria primarily of the species Thiobacillus ferrooxidans. By inhibiting these bacteria, the production of AMD can be greatly reduced. One compound found to be effective in the inhibition of T. ferrooxidans is nitrapyrine. N-Serve, a product of Dow Chemical, Inc., is the commercially available form of nitrapyrine. This compound has been widely used in agriculture for nitrification inhibition. The purpose of this study was to determine the effectiveness of N-Serve in reducing the production of AMD under simulated field conditions. A column study was completed using a coal mine waste and a hard-rock mine waste. Eight columns containing 7kg of rock were established for each substrate. Three doses of NServe (22% nitrapyrine) were applied once at the beginning of this study: a high dose 2200 mg/kg, a medium dose 220 mg/kg, and a low dose 22 mg/kg. Duplicate columns were included for each N-Serve dose including two untreated columns to serve as a control for each substrate. Beginning the week after treatment, the columns were leached once a week for 29 weeks with deionized, distilled water (equivalent to 2.5 cm precipitation). Only the highest NServe dose produced a column leachate of significantly better quality than that of the controls. The acidity in the high-dose coal mine columns averaged less than 50 percent of the acidity in the control effluent from week 6 through the end of the study. A monolithic controlled release system utilizing acrylonitrile rubber was successfully developed and tested for use with nitrapyrine. This formulation should withstand the rigors of the environment and with minor modification could produce a variety of release rates. / Master of Science

Alkaline fly ash has been studied as a liming agent within coal refuse fills to reclaim acid-forming refuse. Previous studies focused on bulk blending ash with acid-forming (pyritic) refuse. A better representation of field conditions is a "pancake layer" of ash above the refuse. A column study was initiated to evaluate the leachate chemistry from acid-forming refuse-ash bulk blends vs. ash over refuse layers. An acidic and an alkaline ash were blended with, or layered over, acid-forming refuse and sandstone and packed into columns which were leached with deionized water twice a week for 24 weeks under unsaturated conditions. Leachates were analyzed for pH, electrical conductivity, and a suite of elements with a focus on the oxyanions of As, Cr, Mo, and Se. A sequential extraction procedure revealed a significant portion of the elements in the residual fraction for the refuse/spoil substrates and in metal-oxide bound fractions for the ashes prior to leaching, and a general trend for a greater proportion of oxyanion elements to be associated with metal oxide fractions after leaching. Bulk-blended treatments maintained higher leachate pH than corresponding layered treatments. The acidic ash and refuse pancaked treatments exhibited relatively high initial concentrations of most elements analyzed. Pancake layers of ash over refuse are an inadequate co-disposal method to prevent and mitigate acid mine drainage. Blending alkaline ash with refuse to acid-base accounting specifications should improve leachate quality overall, but there may be water quality concerns for loss of Se and other soluble ions during initial leaching events. / Master of Science

Acid mine drainage (AMD) results from the oxidation of pyretic mineralogy, exposed by mining operations to oxygen and water. This reaction produces sulfuric acid and liberates heavy metals from the surrounding mineralogy and impairs water quality and freshwater communities. The U.S. Army Corps of Engineers has begun an ecosystem restoration project to remediate the abandoned mine land (AML) impacts to the North Fork Powell River (NFP) and is utilizing the ecotoxicological rating (ETR) system to delineate these affects to focus restoration efforts. The ETR was developed to summarize the integrative data into a single number ranging from 0 to 100, which is descriptive of the environmental integrity of a sampling station. The ETR is conceptualized to work as an academic grading scale (0 through 100), rating reference stations with A's (90-100) and B's (80-89) and impacted stations with C's (70-80), D's (60-70) and failures (F = 60). Two rounds of ETR investigations have evaluated seven headwater tributaries to the NFP including investigations of Ely and Puckett's Creek from 1997 and 1998. This thesis contains the results of the second series of ETR investigations at 41 stations in Cox Creek, Jone's Creek, Reed's Creek, Summers Fork, Straight Creek, and areas in the NFP. Eight stations were recommended for reclamation; CC 03, JCRF2 02, JCRF2 01, RCPS 09B, RCPS 11B, SULF 01, SU 02, and SU 01. Summers Fork was the most severely impacted watershed of the second round of ETR investigations. An effort to streamline the ETR to the most ecologically predictive parameters was successful in creating a system more time and cost efficient then the initial ETRs and exclusive of benthic macroinvertebrate surveys. The Modified ETR streamlined the ETR to just 5 parameters including; mean conductivity, mean Asian clam survival, mean aluminum (Al) and manganese (Mn) in the water column, and mean habitat score to describe the AMD impacts to small headwater streams. Also, an investigation was conducted to determine the mode of toxicity, (i.e., exposures to metal contaminated surface waters or sediments) by which Al and iron (Fe) dominated AMD impairs benthic macroinvertebrate communities. It was found that water column exposures both within and beyond the zone of pH depression are the most likely mode by which AMD impairs the benthic macroinvertebrate communities of the NFP. / Master of Science

Mine influenced waters (MIW) pose a broad range of potential environmental impacts, which often also carry financial and social consequences. MIWs are often high in solids content, and can have highly acidic or alkaline pH and high contents of metals or other problematic constituents (e.g., traces of chemicals used in minerals processing or water treatment). Acid mine drainage (AMD) is a common type of MIW characterized by low pH. Release of untreated MIWs like AMD to surface waters, for example, can lead to problems such as a sedimentation and siltation, undesirable changes in pH and/or precipitation of metals and salts, and addition of particular stressors for various aquatic organisms. As such, these waters are frequently captured and treated on-site in systems requiring extensive piping. Polyethylene (PE) pipes are popular in mining, including MIW, applications because they are chemically inert, and have relatively low costs, low density, and high flexibility. However, PE material is susceptible to abrasion. To combat this problem and offer a single pipe option for a variety of mining applications, Gerodur MPM Kunststoffverarbeitung GmbH and Co. KG.(Gerodur) has developed a novel liner for PE pipes. The liner is made of a rubber-like material that is resistant to mechanical abrasion by slurries or high-solids waters, but its susceptibility to mineral scale buildup has not been specifically evaluated. In order to evaluate scale buildup on the lined PE versus traditional PE pipe material, two studies were undertaken and are reported in this thesis. A short-term field study was conducted in the Reiche Zeche underground mine in Freiberg, Germany – an inactive lead-zinc mine. Water quality varies considerably between different zones in this mine, but is characterized by very high dissolved solids, which is typical for AMD. For this study, the pipe materials were exposed to waters in six locations for three weeks; and were then analyzed for weight gain and scale composition. Results showed that there was only a marginal difference in the scale build up when comparing the two piping materials. In a follow-up study in the laboratory, the two pipe materials were exposed over a total of 16 weeks to three idealized AMD water qualities: an untreated AMD made to simulate the most extreme condition observed in the field study, the same AMD following passive treatment (i.e., neutral pH), and the same AMD following active treatment (i.e., slightly basic pH). Exposure was done in pipe-loop apparatuses such that samples could be subjected to different flow and sedimentation conditions (i.e., gentle mixing only on the sides of the water reservoir, gentle mixing and sedimentation on the bottom of the reservoir, and constant flow and possible sedimentation within the pipe-loop tubing itself). Results of this study indicated that factors such as water chemistry and flow velocity had significant effect on the quantity and chemistry of scale. However, there was very little difference in propensity for scale build up between the two materials. This liner was designed in an effort to resist mechanical abrasion. Because scale build up is not exacerbated by the liner, it may provide a means for uniform applications across mines with contiguous abrasive and scale prone waters. That is, it could eliminate the need to have various specialized piping materials on a site to handle these problems individually, streamlining the pumping and piping network installation and operation. / Master of Science / Mine influenced waters (MIW) are a potential danger to the environment, and a company’s financial and social standings. MIW’s come in many different varieties, and can contain harmful contaminants from the mine site. One of the most common MIW’s is characterized by low pH, and is commonly referred to as Acid Mine Drainage (AMD). In addition to the problematic pH, AMD can have excessive dissolved solids such as metals, salts, and sediment. Polyethylene (PE) pipes are popular in mining applications because they do not react to most chemicals, and have low costs, low density, and high flexibility. However, PE material is susceptible to losing wall thickness through abrasion caused by slurries and solids in water. Gerodur MPM Kunststoffverarbeitung GmbH and Co. KG.(Gerodur) has developed a liner for PE pipes to address the abrasion problem. The liner is made of a rubber-like material that is resistant to mechanical abrasion, but its susceptibility to mineral scale buildup has not been specifically evaluated. To study the differences between the new liner versus traditional PE pipe, two studies were completed and are reported in this thesis. The first was a short field study conducted in an underground mine in Freiberg, Germany. Though the water throughout the mine varies, it generally has high dissolved solids as seen in most AMD. In the mine, traditional and lined pipes were exposed to waters in six different locations for three weeks, and weight gain and scale composition were tested. Results showed very little difference in both quantity, and content of scale. To further test the material, a longer lab study was conducted. The two materials were exposed for 16 weeks to three different simulated waters. One simulated untreated AMD, AMD treated to a neutral pH, and finally AMD treated to a basic pH. Results showed that the water chemistry and flow did have an effect on the quantity and chemistry of the scale. It also supported that there was very little difference in the scale on the two materials when exposed to the same water conditions. Because the material did not make scale worse, it can be applied to waters with high abrasion and scaling potential. This could be an asset to the mining community because it eliminates the need for v multiple pipe materials. It simplifies the mining process by allowing one pipe material to be applied uniformly across a mine site.

Neutralization by limestone is a common treatment for acid mine drainage (AMD). The effectiveness of using limestone to treat AMD can be reduced by aluminum (Al) and iron (Fe) oxyhydroxide coatings that form on the limestone, because the coatings inhibit the transport, and thus neutralization, of hydrogen ions (H+) derived from acid mine drainage. I used mixed flow reactor experiments to investigate the effect of Al coatings on the diffusion of H+ to the surface of limestone and to quantify how those Al coatings affect the limestone dissolution rate. Experiments used acidic Al sulfate solutions with initial Al concentrations ranging from 0.002 M to 0.01 M (32 to 329 ppm) and pH values ranging from 3.7 to 4.2, which are typical of conditions found at AMD sites. Cleaved pieces of Iceland spar calcite were used as a proxy for limestone. The pH was measured in the effluent to determine the rate of H+ consumption. Effluent solutions were analyzed for Al, calcium (Ca) and sulfur (S) using inductively coupled plasma optical emission spectroscopy (ICP OES). Examination of the precipitated coatings using x-ray diffraction indicated that amorphous poorly crystalline gibbsite is the primary Al coating but scanning electron microscope analysis also suggests the possible presence of a poorly crystalline sulfur containing phase, such as hydrobasaluminite. The experimental data were used to calculate the diffusion coefficient of H+ through the Al coatings. The calculated diffusion coefficient for H+, assuming a gibbsite and/or hydrobasaluminite layer, ranged between 10-13 to 10-11 m2/sec, that are significantly lower than in pure water. / Master of Science / Acid mine drainage (AMD) is an acidic discharge characterized by low pH and high concentrations of toxic metals that can have an impact on the aquatic environments. A common treatment method for AMD is the use of limestone drains to neutralize the pH. However, the neutralization capacity of limestone drains can be reduced by coatings of aluminum (Al) that form on the limestone during treatment. I used mixed flow reactor experiments to investigate the effect of Al coatings on the diffusion of H⁺ to the surface of limestone and to quantify how those Al coatings affect the limestone dissolution rate. I measured pH in the effluent to determine the rate of H⁺ consumption during the reaction of the solutions with calcite. I also analyzed effluent solutions for Al, Ca and S concentrations. Examination of the produced coatings with x-ray diffraction suggests amorphous poorly crystalline gibbsite as the primary Al coating but scanning electron microscope analysis also suggests the presence of poorly crystalline hydrobasaluminite, a sulfur-bearing phase. The experimental results were used to model the decline in the limestone neutralization rate as the coatings grow thicker over time under different pH conditions and Al concentrations similar to those found in AMD. Finally, the diffusion coefficient for H⁺ , assuming a gibbsite and/or hydrobasaluminite layer, ranged between 10⁻¹³ to 10⁻¹¹ m²/sec, which is orders of magnitude smaller than the diffusion coefficient in pure water.

M. Tech. (Chemical Engineering, Faculty of Engineering and Technology), Vaal University of Technology / Acid mine drainage (AMD) is a serious problem associated with mining activities, and it has the potential to contaminate surface and ground water. The aim of this study was to evaluate the performance of constructed wetland and photocatalysis in treating AMD. Three identical unvegetated upflow constructed wetlands packed with natural zeolite (clinoptilolite) and coarse silica sand were made of a cylindrical plastic pipe, and the slurry photocatalyst was prepared using quartz material. A hydro-alcohol thermal method was used to prepare an anatase core-void-shell TiO2 photocatalyst. The results showed that the three unvegetated upflow constructed wetlands (CW) had relatively similar percentage removal of heavy metals despite their varying concentrations within the AMD. The removals were: Fe (86.54 - 90.4%); Cr (56.2 - 64.5%); Mg (56.2 - 67.88%); Ca (77.1 - 100%); and 100% removal was achieved for Be, Zn, Co, Ni, and Mn. The removal of sulphate was also 30%. Heavy metals concentration in CW packing material was significantly higher in the outlet of the constructed wetlands than in the inlet. The adsorption isotherms revealed that the experimental data fitted the Langmuir Isotherms better, which suggested a monolayer coverage of heavy metals on the surface of the adsorbents; thermodynamic studies showed that the nature of adsorption taking place was physical; the kinetics models showed that the adsorption was first order reaction. A higher photocatalytic reduction (62%) of Cr(VI) was obtained at pH 2, 30 mg/l Cr(VI) initial concentration, and three hours of irradiation time. It was also found that the presence of Fe(III) enhanced the reduction of Cr(VI). The core-void-shell TiO2 photocatalyst showed a better activity than the commercial P25 Degussa for the reduction of Cr(VI) to Cr(III). The kinetic studies showed that the reduction of Cr(VI) was first order reaction. Photocatalytic reduction of Cr(VI) in real AMD sample was achieved only for the Douglas North Discharge (DND) sample (68%), and the Fe(III) reduction was found to be 83%. Therefore it was concluded that the combination of constructed wetland and UV/ TiO2 photocatalysis employing anatase core-void-shell TiO2 as a photocatalyst has a potential to reduce the toxicity of Cr(VI)-laden acid mine drainage.

Please read the abstract in the section 00front of this document / Dissertation (MSc)--University of Pretoria, 2007. / Geography, Geoinformatics and Meteorology / MSc / Unrestricted