Dissolution of lead- and lead-arsenic-jarosites at pH 2 and 8 and 20 °C: Insights from batch experiments     

Adrian M.L. Smith  William E. Dubbin  Karen A. Hudson-Edwards 《Chemical Geology》2006,229(4):344-361

Lead- and Pb-As-jarosites are minerals common to acidic, sulphate-rich environments, including weathering zones of sulphide ore deposits and acid rock or acid mine drainage (ARD/AMD) sites, and often form on or near galena. The structures of these jarosites are based on linear tetrahedral-octahedral-tetrahedral (T-O-T) sheets, comprised of slightly distorted FeO₆ octahedra and SO₄²⁻ (-AsO₄³⁻ in Pb-As-jarosites) tetrahedra. To better understand the dissolution mechanisms and products of the break down of Pb- and Pb-As-jarosite, preliminary batch dissolution experiments were conducted on synthetic Pb- and Pb-As-jarosite at pH 2 and 20 °C, to mimic environments affected by ARD/AMD, and at pH 8 and 20 °C, to simulate ARD/AMD environments recently remediated with slaked lime (Ca(OH)₂). All four dissolutions are incongruent. Dissolution of Pb-jarosite at pH 2 yields aqueous Pb, Fe and SO₄²⁻. The pH 8 Pb-jarosite dissolution yields aqueous Pb, SO₄²⁻ and poorly crystalline Fe(OH)₃, which does not appear to resorb Pb or SO₄²⁻, possibly due to the low solution pH (3.44-3.54) at the end of the experiment. The pH 2 and 8 dissolutions of Pb-As-jarosite result in the formation of secondary compounds (poorly crystalline PbSO₄ for pH 2 dissolution; poorly crystalline PbSO₄ and Fe(OH)₃ for pH 8 dissolution), which may act as dissolution inhibitors after 250 to 300 h of dissolution. In the pH 2 dissolution, aqueous Fe, SO₄²⁻ and AsO₄³⁻ also form, and in the pH 8 dissolution, Fe(OH)₃ precipitates then subsequently resorbs aqueous AsO₄³⁻. The dissolutions probably proceed by preferred dissolution of the A- and T-sites, which contain Pb, and SO₄²⁻ and AsO₄³⁻, respectively, rather than Fe, which is sterically remote, within the T-O-T Pb- and Pb-As-jarosite structures. These data provide the foundation necessary for further, more detailed investigations into the dissolution of Pb- and Pb-As-jarosites.  相似文献   

Dissolution of jarosite [KFe₃(SO₄)₂(OH)₆] at pH 2 and 8: Insights from batch experiments and computational modelling   总被引：1，自引：0，他引：1  

Adrian M.L. Smith  Karen A. Hudson-Edwards  William E. Dubbin 《Geochimica et cosmochimica acta》2006,70(3):608-621

Jarosite [KFe₃(SO₄)₂(OH)₆] is a mineral that is common in acidic, sulphate-rich environments, such as acid sulphate soils derived from pyrite-bearing sediments, weathering zones of sulphide ore deposits and acid mine or acid rock drainage (ARD/AMD) sites. The structure of jarosite is based on linear tetrahedral-octahedral-tetrahedral (T-O-T) sheets, made up from slightly distorted FeO₆ octahedra and SO₄ tetrahedra. Batch dissolution experiments carried out on synthetic jarosite at pH 2, to mimic environments affected by ARD/AMD, and at pH 8, to simulate ARD/AMD environments recently remediated with slaked lime (Ca(OH)₂), suggest first order dissolution kinetics. Both dissolution reactions are incongruent, as revealed by non-ideal dissolution of the parent solids and, in the case of the pH 8 dissolution, because a secondary goethite precipitate forms on the surface of the dissolving jarosite grains. The pH 2 dissolution yields only aqueous K, Fe, and SO₄. Aqueous, residual solid, and computational modelling of the jarosite structure and surfaces using the GULP and MARVIN codes, respectively, show for the first time that there is selective dissolution of the A- and T-sites, which contain K and SO₄, respectively, relative to Fe, which is located deep within the T-O-T jarosite structure. These results have implications for the chemistry of ARD/AMD waters, and for understanding reaction pathways of ARD/AMD mineral dissolution.  相似文献   

Fluids in early stage hydrothermal alteration of high-sulfidation epithermal systems: A view from the Vulcano active hydrothermal system (Aeolian Island,Italy)     

Adrian J. Boyce  Paolo Fulignati  Alessandro Sbrana  Anthony E. Fallick 《Journal of Volcanology and Geothermal Research》2007

High-sulfidation (HS) epithermal systems have elements in common with passively degassing volcanoes associated with high T, acid fumarole fields or acid crater lakes. They are considered to form in two stages, the first of which involves advanced argillic alteration resulting from intense, strongly acidic fluid–rock interaction. The La Fossa hydrothermal system (Vulcano Island) represents a classic example of such an active HS system and can be considered as a modern analogue of this early stage of alteration, resulting in a core of intense silicic (90–95% pure SiO₂) alteration surrounded by alunitic alteration zones.  相似文献   

How important is the impact of land-surface inundation on seawater intrusion caused by sea-level rise?     

Behzad Ataie-Ashtiani  Adrian D. Werner  Craig T. Simmons  Leanne K. Morgan  Chunhui Lu 《Hydrogeology Journal》2013,21(7):1673-1677

The influence of sea-level rise (SLR) on seawater intrusion (SWI) has been the subject of several publications, which consider collectively a range of functional relationships within various hydrogeological and SLR settings. Most of the recent generalized analyses of SWI under SLR neglect land-surface inundation (LSI) by seawater. A simple analytical method is applied to quantitatively assess the influence and importance of LSI on SLR–SWI problems under idealized conditions. The results demonstrate that LSI induces significantly more extensive SWI, with inland penetration up to an order of magnitude larger in the worst case, compared to the effects of pressure changes at the shoreline in unconfined coastal aquifers with realistic parameters. The study also outlines some of the remaining research challenges in related areas, concluding that LSI impacts are among other important research questions regarding the SLR–SWI problems that have not been addressed, including the effects of aquifer heterogeneities, real-world three dimensionality, and mitigation measures.  相似文献   

Intrinsic bioremediation of a petroleum-impacted wetland   总被引：4，自引：0，他引：4  

Mills MA  Bonner JS  McDonald TJ  Page CA  Autenrieth RL 《Marine pollution bulletin》2003,46(7):887-899

Following the 1994 San Jacinto River flood and oil spill in southeast Texas, a petroleum-contaminated wetland was reserved for a long-term research program to evaluate bioremediation as a viable spill response tool. The first phase of this program, presented in this paper, evaluated the intrinsic biodegradation of petroleum in the contaminated wetland. Sediment samples from six test plots were collected 11 times over an 11-month period to assess the temporal and spatial petroleum concentrations. Petroleum concentrations were evaluated using gas chromatography-mass spectrometer analyses of specific target compounds normalized to the conservative biological marker, C(30)17alpha,21beta(H)-hopane. The analyses of specific target compounds were able to characterize that significant petroleum biodegradation had occurred at the site over the one-year period. Total resolved saturate and total resolved aromatic hydrocarbon data indicated the petroleum was degraded more than 95%. In addition, first-order biodegradation rate constants were calculated for the hopane-normalized target compounds and supported expected biodegradation patterns. The rapid degradation rates of the petroleum hydrocarbons are attributed to conditions favorable to biodegradation. Elevated nutrient levels from the flood deposition and the unconsolidated nature of the freshly deposited sediment possibly provided a nutrient rich, oxic environment. Additionally, it is suggested that an active and capable microbial community was present due to prior exposure to petroleum. These factors provided an environment conducive for the rapid bioremediation of the petroleum in the contaminated wetland.  相似文献   

A tephra-based correlation of marine and terrestrial records of MIS 11c from Britain and the North Atlantic     

Ian Candy  Gareth Tye  Peter Coxon  Mark Hardiman  Ian Matthews  Adrian Palmer 《第四纪科学杂志》2021,36(7):1149-1161

Resolving marine and terrestrial records of glacial and interglacial stages has long been a challenge for Quaternary studies. We present a tephra-based correlation for MIS 11c of a North Atlantic marine core and a British terrestrial record (Marks Tey). A varved chronology is presented for the annually laminated lake sequence at Marks Tey and the proxy data from this site are plotted on an annual timescale for the first time. This record shows clear evidence for an abrupt cold event and corresponding ecological and landscape response. Varve counting shows that the abrupt event lasted for ca 185 a but the impact on the landscape persisted for ca 560 a. The co-occurrence of a single tephra layer in Marks Tey and ODP 980 allows these two records to be correlated. Furthermore, this synchronisation shows that the abrupt cold event in Marks Tey was coincident with a centennial-scale cold event in ODP 980, as evidenced by an increase in Neogloboquadrina pachyderma (s) percentage. In both ODP 980 and Marks Tey the age of this abrupt event was ca 414 500 a indicating that, at this point in MIS 11c, a widespread cold event occurred in the northeastern Atlantic and the British Isles.  相似文献   

Numerically enhanced conceptual modelling (NECoM) applied to the Malta Mean Sea Level Aquifer     

Lotti  Francesca  Borsi  Iacopo  Guastaldi  Enrico  Barbagli  Alessio  Basile  Paolo  Favaro  Lorenzo  Mallia  Adrian  Xuereb  Rachel  Schembri  Michael  Mamo  Julian Alexander  Sapiano  Manuel 《Hydrogeology Journal》2021,29(4):1517-1537

Conventional hydrogeological practice is to formulate a conceptual model, which is often the basis of a numerical model. The numerical model is then used to test groundwater management strategies. A workflow is proposed, employing the numerically enhanced conceptual model (NECoM) of the Mean Sea Level Aquifer (MSLA) on the island of Malta. The Malta MSLA is overexploited and under threat of salinization. Data (heads, chloride concentrations, electrical conductivity logs, tidal tests and qualitative analyses) were assimilated into a fast-running numerical model. Simultaneously, strategies for optimal acquisition of further data were examined through the modelling process. The model was delivered through the Energy and Water Agency, with suggestions for flexible model deployment. These workflows will, hopefully, spawn model improvements through further revision of the base concepts. The model allows the agency to make predictions, which have uncertainties that are quantified and reduced through data assimilation as new data become available. Contemplated management plans can therefore be properly assessed before implementation. The proposed NECoM approach can be generalized since it bases model usage on the premise that modelling should make maximum use of existing data by assimilating its information content, thereby highlighting the uncertainties of decision-critical predictions that remain because of data insufficiency. Thus, the presently disjointed process of modelling on the one hand, and data acquisition on the other, can be better aligned. Conceptual and numerical model development become parallel, rather than sequential, activities. Together, they enable predictions of future system behaviour for which bias is reduced and uncertainties quantified.

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Geological and hydrogeological reconstruction of the main aquifers of the Maltese islands     

Barbagli  Alessio  Guastaldi  Enrico  Conti  Paolo  Giannuzzi  Miriana  Borsi  Iacopo  Lotti  Francesca  Basile  Paolo  Favaro  Lorenzo  Mallia  Adrian  Xuereb  Rachel  Schembri  Michael  Mamo  Julian Alexander  Sapiano  Manuel 《Hydrogeology Journal》2021,29(8):2685-2703

Hydrogeology Journal - Geological and hydrogeological conceptualizations of the five main aquifers of Malta were performed by means of characterization of the groundwater bodies’ geometries...  相似文献   

A machine learning approach for regional geochemical data:Platinum-group element geochemistry vs geodynamic settings of the North Atlantic Igneous Province     

Jordan J. Lindsay  Hannah S.R. Hughes  Christopher M. Yeomans  Jens C.Ø. Andersen  Iain McDonald 《地学前缘(英文版)》2021,12(3):101098

Whilst traditional approaches to geochemistry provide valuable insights into magmatic processes such as melting and element fractionation, by considering entire regional data sets on an objective basis using machine learning algorithms(MLAs), we can highlight new facets within the broader data structure and significantly enhance previous geochemical interpretations.The platinum-group element(PGE) budget of lavas in the North Atlantic Igneous Province(NAIP) has been shown to vary systematically according to age, geographic location and geodynamic environment.Given the large multi-element geochemical data set available for the region, MLAs were employed to explore the magmatic controls on these shifting concentrations.The key advantage of using machine learning in analysis is its ability to cluster samples across multi-dimensional(i.e., multi-element)space.The NAIP data set is manipulated using Principal Component Analysis(PCA) and t-Distributed Stochastic Neighbour Embedding(t-SNE) techniques to increase separability in the data alongside clustering using the k-means MLA.The new multi-element classification is compared to the original geographic classification to assess the performance of both approaches.The workflow provides a means for creating an objective high-dimensional investigation on a geochemical data set and particularly enhances the identification of metallogenic anomalies across the region.The techniques used highlight three distinct multi-element end-members which successfully capture the variability of the majority of elements included as input variables.These end-members are seen to fluctuate in prominence throughout the NAIP, which we propose reflects the changing geodynamic environment and melting source.Crucially, the variability of Pt and Pd are not reflected in MLA-based clustering trends, suggesting that they vary independently through controls not readily demonstrated by the NAIP major or trace element data structure(i.e., other proxies for magmatic differentiation).This data science approach thus highlights that PGE(here signalled by Pt/Pd ratio) may be used to identify otherwise localised or cryptic geochemical inputs from the subcontinental lithospheric mantle(SCLM) during the ascent of plume-derived magma, and thereby impact upon the resulting metallogenic basket.  相似文献   

Lithospheric foundering and underthrusting imaged beneath Tibet     

Min Chen  Fenglin Niu  Jeroen Tromp  Adrian Lenardi  Cin-Ty A. Lee  Wenrong Cao  Julia Ribeiro 《《地质学报》英文版》2018,92(Z1):48-48

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