The interpretation of leached outcrops as guides to the specific minerals from which they were formed has been developed to a rather high degree by earlier workers, among whom Boswell and Blanchard deserve particular mention. In the present work, a gossan that led to the discovery of a lead deposit is described. Since many hand specimens of the limonite from this gossan lack the characteristic boxwork structures described by the authors above, microscopic investigations of thin and polished sections were carried out. However, the gossan is classified into six types mainly on the basis of its physical properties. At least three of these are correlated with types described by Boswell and Blanchard, one of pyrite derivation and the others from galena. The relative solubility of different limonite types in dilute HC1 was not found to be of as much value as some writers have indicated. The mineral deposits to which the limonite pointed the way have not been sufficiently exposed to allow detailed study, but the presence of tremolite and phlogopite in an area of disseminated mineralization indicates that this portion at least may be of contact metamorphic origin. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

In the Betts process for lead electrorefining the noble impurities originally present in the bullion form a strong and adherent layer of slimes. Within this layer the established ionic concentration gradients can lead to secondary reactions. The following processes were analyzed from a thermodynamic perspective: (A) hydrolysis of the acid (B) precipitation of secondary products (C) reaction of noble compounds. The nature of the concentration gradients within the slimes layer and related secondary processes was studied by using transient electrochemical techniques which include: (A) current interruption, (B) AC impedance, and (C) a variation of SACV (Small Amplitude Cyclic Voltammetry). These studies were complemented by: (A) physico-chemical data on electrolyte properties, (B) "insitu" and "industrially recovered" slimes electrolyte compositions, (C) SEM and X-ray diffraction analysis of the slimes layer. For comparison purposes the electrochemical behaviour of "pure" Pb electrodes was also studied. Upon current interruption the anodic overpotential decays, first abruptly, (as the uncompensated ohmic drop disappears) and then slowly (due to the presence of a back E.M.F. created by ionic concentration gradients that decay slowly). Current interruption measurements showed that: (A) concentration gradients exist across the slimes layer, (B) inner solution potentials within the slimes layer can be larger than those measured from reference electrodes located in the bulk electrolyte, (C) secondary products can shift the inner solution potential to negative values which reverse upon re-dissolution and (D) ionic diffusion is seen upon current interruption but it is complex and difficult to model due to the presence of processes that can support the passage of internal currents. The anodic polarization components were obtained by analyzing the potential and current dependance upon application of a small amplitude sinusoidal waveform. This dependance was found to be linear in the low overpotential region (< 250mV). Thus, upon subtraction of the uncompensated ohmic drop, the remaining polarization is due to the "apparent" ohmic drop of the slimes electrolyte and to liquid junction and concentration overpotentials. These components are directly linked to the electrolysis conditions and to the slimes layer structure. Furthermore, the ratio of these components can be used to obtain the point at which the precipitation of secondary products starts. Changes in this ratio can also be related to the anodic effects caused by the presence of addition agents. AC impedance measurements performed in the presence of a net Faradaic current showed that the impedance increases uniformly as the slimes layer thickens up to the point at which noble impurities start to react. Three electrical analogue models were used to describe the impedance spectra. A steady-state mathematical model that predicts concentration and potential gradients across the slimes layer was developed. Only when a position dependent eddy diffusion term was incorporated in the numerical solution, were reasonable local ionic concentrations and overpotentials obtained. / Applied Science, Faculty of / Materials Engineering, Department of / Graduate

A total of 34 lead ore samples from selected hydrothermal deposits in Wyoming, Montana, and Idaho have been isotopically analyzed and geochronological interpretations made from the results. Leads from along the southeastern flank of the Idaho Batholith appear to have a primary component 2500 my old. Leads from Butte and Cassia counties, Idaho, may be interpreted as having this same primary component with an added component that is estimated to be 1400 to 1600 my old. The radiogenic component of leads along the southeastern flank of the Idaho Batholith commenced development in a closed system 2500 my ago. Radiogenic components of the leads from Butte and Cassia counties commenced development 1900 and 2700 my ago respectively. Preliminary results of analyses from the south end of the Wind River Mtns, Wyoming, and the Little Belt Mtns, Montana, show primary lead ages of about 3200 and 2200 my respectively. Common lead geochronology indicates that the basement rocks of Southern Idaho may be assigned to the Superior Province of North America as defined by Kanasewich (1965). A second Precambrian event was recorded by a change in the lead isotope abundances during the Penokian era. Thus, Southern Idaho had been subjected to several uplifts during parts of Early and Middle Precambrian time. The ages of the anomalous leads from Butte and Cassia counties could represent the times of formation of sedimentary layers which remained closed systems until the time of formation of the ore bodies. A model for continental accretion and growth is discussed. The contribution of the present report to tectonic development models is in the suggestion of a geological sequence which may give rise to anomalous lead suites. This geological sequence is concerned with regional tectonic events which take place in the lower crust and are manifested by igneous activity. Examples of leads with apparent enrichment in the 208 isotope were found during this study and other instances are mentioned. The enrichment is tentatively considered to occur as a result of concentration of the thorium decay product in sedimentary basins. This could occur if the thorium is in more easily weathered minerals than are the uranium isotopes. Evidence supporting naturally occurring lead isotope enrichment phenomena is cited. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Peatlands are an important store of soil carbon, play a vital role in global carbon cycling, and can also act as sinks of atmospherically deposited heavy metals. Large areas of the UK’s blanket peat are significantly degraded and actively eroding, which negatively impacts carbon and pollutant storage. The restoration of eroding UK peatlands is a major conservation concern, and over the last decade measures have been taken to control erosion and restore large areas of degraded peat. In severely eroded peatlands, topography is highly variable, and an appreciation of geomorphological form and process is key in understanding the controls on peatland function, and in mitigating the negative impacts of peatland erosion. The blanket peats of the Peak District, Southern Pennines, UK, embody many problems and pressures faced by peatlands globally, and are amongst the most heavily eroded and contaminated in the world. The near-surface layer of the peat is contaminated by high concentrations of anthropogenically derived, atmospherically deposited heavy metals, which are released into the fluvial system as a consequence of widespread erosion. Whilst not desirable, this legacy of lead pollution and its release, offer a unique opportunity to trace peatland sediment movements and thus investigate the controls on sediment and contaminant mobility. A suite of established field, analytical and modelling techniques have been modified and adapted for use in peatland environments: (i) by incorporating a simple correction for moisture content, field portable XRF has been shown to be an accurate, cost-effective, and rapid tool for assessing in situ lead concentrations in wet organic sediments; (ii) a lightweight time integrated mass flux sampler has been developed for deployment at multiple remote peatland field sites, and has been used to explore spatial and temporal suspended sediment dynamics; and (iii) sediment source fingerprinting and numerical mixing models, traditionally used to determine sources of fine sediment in minerogenic systems, have been used to investigate suspended sediment composition in contaminated organic rich catchments. These modified methods have been successfully employed in combination to address issues of sediment and contaminant release. Several mechanisms and controls have been shown to be important influences on sediment dynamics and Pb release across a range of spatial and temporal scales: (i) the presence of vegetation is key in stabilising the peat’s surface and trapping mobilised sediment; (ii) sediment preparation influences the timing of POC and Pb release; (iii) antecedent water tables may control the timing and the nature of sediment entering the fluvial system during storm events; and (iv) the degree of degradation influences both Pb storage and release. At the landscape scale, peatland restoration significantly mitigates sediment production in eroding peatlands and substantially reduces carbon and pollutant export. At the catchment scale, sediment preparation and hydrological connectivity are important controls on the magnitude and timing of sediment and lead fluxes from eroding peatland catchments. At the plot scale, complex small scale spatial patterns of contaminant storage in eroding headwater catchments can be explained by interactions between topographic setting and vegetation cover, and the mobilisation of sediment by wind and water. This deeper understanding of the multi-scalar dynamics of sediment movements in eroding peatlands is important in the context of: (i) the release and reworking of legacy contamination in organic rich systems; (ii) the response of blanket peats to climate change; (iii) informing future restoration strategies that aim to manage peatland sediment and contaminant fluxes.

Magister Scientiae (Biodiversity and Conservation Biology) - MSc (Biodiv and Cons Biol) / The demand for better quality produce by consumers is on the increase, as higher heavy metal concentrations pose a problem in agriculture. They result in decreased yield and unsuitable food for human consumption. This brings about a negative economic effect as such products become unprofitable on the domestic or export markets thus affecting productivity of farms.Four heavy metals (Cd, Cu, Pb and Zn) have been shown to be a problem in the farming areas in Cape Town. Pot and field studies were carried out on the effects and concentrations of cadmium and lead on Phaseolus vulgaris. Field studies included collecting plant samples from the Joostenbergvlakte/ Kraaifontein farming areas and measuring the heavy metal concentrations within the different organs of the plants. Pot experiments were carried out, where Phaseolus vulgaris var. Contender were grown and then heavy metals were administered to these plants together with two heavy metal mitigation techniques, precipitation with phosphate and mobilisation with EDTA to see if they were successful in combating heavy metal pollution.Samples taken from farms in the Joostenbergvlakte/ Kraaifontein area revealed that cadmium, lead and zinc concentrations were higher than the legal standard in the edible fruits. In the pot experiment, results revealed that cadmium reduced the chlorophyll index as well as the shoot fresh mass and changes in mineral uptake were seen. Lead did not affect growth or the chlorophyll index. The high cadmium treatment resulted in a marked increase in sodium concentration in the shoots. The phosphate treatments and EDTA treatments both resulted in increased cadmium concentrations in the roots and shoots. The higher phosphate and lead treatments also reduced lead concentrations in the roots. Low phosphate and the EDTA treatments increased the shoot sodium concentrations.

Fracture of a pacemaker lead is one of the most common causes of pacemaker malfunction. Lead fractures are seen in approximately 4 % of patients with pacemakers. We present a rare case of complete severance of the tip of a dual chamber pacemaker atrial lead. A 62 years old male presented for a routine device check of his pacemaker, which was originally implanted in 2002 for sick sinus syndrome and had a generator change in 2010. Device check showed a dual chamber pacemaker with right atrial and right ventricular leads and a remaining battery life of 8.6 years. Patient was not pacemaker dependent. Ventricular lead showed normal sensing, impedance and pacing threshold. Atrial lead showed unusually high impedance of 2175 ohms and no capture on testing at voltages as high as 7.5 mV. Further evaluation was done due to abnormal atrial lead test. An EKG was obtained showing normal sinus rhythm and atrial pacing spikes with no capture. Chest X-ray revealed a complete severance and dislocation of the atrial lead tip and an intact ventricular lead. A detailed history was obtained, and patient denied any trauma to the chest or upper extremities, chest pain, shortness of breath, palpitations, syncope or presyncope. Upon further history, patient reported a recent visit to theme park and enjoying high thrill rides. On examination, there were no signs of trauma, erythema, swelling, warmth, drainage or erosion at implant site. The pacemaker setting was changed from DDDR to VVIR, with plans to cap the proximal port of the fractured lead and placing a new atrial lead. Pacemaker lead fractures are reported with an incidence rate of 0.1 to 4.2 % per patient year [1]. The most common site of lead fracture is at the site of entry (40%) followed by between the entry site and generator (28%), close to the generator site (23%) and only (7%) are intravascular fractures [1]. Trauma and subclavian crush syndrome are the most commonly reported causes of pacemaker lead fractures. Pacemaker lead fracture due to physical exertion is an uncommon cause of lead malfunction [2]. Few cases have been reported of traumatic lead fracture due to the blunt chest trauma [3]. Patients with a lead fracture may present with symptoms of dizziness, syncope, chest discomfort, palpitations or, less commonly extra cardiac symptoms like hiccups or may completely be asymptomatic as seen in our patient. Diagnosis can be made by electrogram during device check, ECG and careful review of chest imaging such as chest x ray or fluoroscopy. Treatment is placement of a new lead with or without extraction of the fractured lead. This rare case of pacemaker lead fracture after a theme park ride indicates there may be a risk to pacemaker leads with high velocity amusement park rides which are becoming popular. This may have clinical implications such as a need for caution during amusement park visits and routine pacemaker interrogations after such visits especially in pacemaker dependent patients. References: 1: Alt E, Völker R, Blömer H: Lead fracture in pacemaker patients. Thorac Cardiovasc Surg.1987, 35:101-4.10.1055/s-2007-1020206 2: ohm J: Displacement and fracture of pacemaker electrode during physical exertion. Report on three cases. Acta Med Scand.1972, 192:33-5.10.1111/j.0954-6820.1972.tb04774 3: Bőhm A1, Duray G, Kiss RG: Traumatic Pacemaker lead fracture. Emerg Med J.2013, 30:686.10.1136/emermed-2012-202090.

No description available.

An innovative approach for the removal of heavy metal ions such as Pb2+ and Cd2+ from aqueous solution was evaluated. It was established that alkaline filtration, which is in essence the combination of alkaline precipitation and membrane filtration, could drastically increase both the efficiency and completeness of Pb2+ or Cd2+ ions removal, producing water whose metal concentration satisfying drinking water standard from a simulation wastewater containing 5 ppm or more Pb2+ or Cd2+ ions. Filtration with three different membranes, including microfiltration (MF), ultrafiltration (UF), and nanofiltration (NF) membranes, were studied at three different pH levels, i.e., 7.0, 8.5, and 10, in terms of metal ion rejection, flux, and permeate pH and at varied dissolved inorganic carbon (DIC) concentration. Increasing the pH of the feed in the tested range would lead to the decrease of metal ion concentration in permeate while flux was in general unaffected. When the feed pH was 10, the Pb2+ concentration in permeate was below 10 ppb regardless of the DIC concentration and membrane for filtration. The effects of DIC concentration were significant but complex. It was found that MF, UF, NF could all effectively reject Pb2+ ions at pH 8.5 and pH 10 although only NF was charged. A hypothesis was proposed to explain the mechanism of alkaline filtration based on experimental data.

Colloid-borne Heavy Metals in the Drainage Gallery of an Abandoned Zn-Pb-Ag Mine (in German). The colloid inventories and the colloid-borne heavy metals in the Rothschönberger Stolln adit, the main drainage gallery of the Freiberg, Germany, mining district, were investigated. This adit runs from Freiberg to the village of Rothschönberg, where it flows into the river Triebisch, a tributary of the river Elbe. The water of the adit is a typical mine water from a flooded ore mine. The main reason for choosing the Rothschönberger Stolln adit for colloid investigations was that ample knowledge concerning the origin of the water and the geology of its catchment area exists. The aim was to characterize the colloids at the mouth of the adit and to elucidate if important contaminants occur in a colloid-borne form. A colloid concentration of about 1 mg/L was found. The particles have a size of 50 to 150 nm. They primarily consist of iron and aluminum oxyhydroxide and carry trace elements such as Pb, As, Cu, Y, La. The contaminants Pb and As are almost entirely colloid-borne. Colloids can have both a retarding and a stimulating influence on the transport of contaminants. The existence of colloids should be taken into account if mine waters flow to the biosphere or if mine waters are to be purified by permeable reactive barriers.

Over the last decade, impressive development in lead halide perovskites (LHPs) have made them leading candidate materials for photovoltaics (PVs), X-ray scintillators, and light-emitting diodes (LEDs). The success of LHPs NCs in lighting and display applications is mainly originated from their high photoluminescence quantum yield (PLQY), narrow emission, sizable bandgap, and cost-effective fabrication. Consequently, a comprehensive understanding of the design principles of LHP NCs will fuel further innovations in their optoelectronic applications. This dissertation centers on the synthesis and self-assembly of LHP NCs. At first, we investigate the capability of colloidal synthetic routine to engineer the shape, size, and dimensionality of the resulting LHPs NCs (chapter 2), including 0D nanospheres, 2D nanoplates, and 3D nanocubes. Starting from the LHPs NCs, nanoplates (chapter 3), nanowires (chapter 4), and superstructures (chapter 5) are successfully achieved via various self-assembly strategies. In chapter 3, we present a liquid-air interfaces-assisted self-assembly technique to obtain micro-scale CsPbBr3 nanoplates from as-synthesized nanoscale NCs. The AC-HRTEM offered an atomic-level observation during the structural evolution and revealed an oriented attachment-mediated assembly mechanism. The assembled CsPbBr3 nanoplates exhibited ultrahigh stability under X-ray energy dispersive spectroscopy (EDS) mapping conditions (300-kV electron beam), and the first atomic-resolution EDS elemental mapping data of LHP NCs were acquired. In chapter 4, we demonstrate an efficient green-chemistry approach for the self-assembly of CsPbBr3 NCs into 1D nanowires and nanobelts via the light induction. As an elegant and promising green-chemistry approach, light-induced self-assembly represents a rational method for designing perovskites. In chapter 5, we will explore the self-assembly of CsPbBr3 NCs into superstructures to overcome the ‘green gap’ to achieve a pure green emission with high PLQY for realizing next-generation vivid displays. In summary, we systematically investigated the mechanisms of LHP NC self-assembly, the kinetics of their morphological evolution and phase transitions, and driving forces that govern the self-assembly process. The assembled LHP NCs manifest desirable properties (e.g., superfluorescence, improved photoluminescence lifetime, enhanced stability against moisture, light, electron-beam irradiation, and thermal-degradation) that translate into dramatic improvements in device performance.