Evangelos Mouchos | University of Bristol (original) (raw)

Papers by Evangelos Mouchos

4th European Mineralogical Conference, Dublin, Ireland, 2024

As a result of anthropogenic climate change there is a call to implement a rapid transition to Ne... more As a result of anthropogenic climate change there is a call to implement a rapid transition to Net-Zero greenhouse gas (GHG) emissions. However, reducing emissions is not going to be sufficient for climate stabilisation, and there is a need to remove CO2 from the atmosphere through carbon dioxide removal (CDR). CDR will require more rigorous Monitoring, Reporting and Verification (MRV) because of the complexity of some of the processes and the requirement for CO2 to be stored long-term. With a range of different novel approaches to CDR being developed there are difficulties in ensuring that the quality of each approach is regulated, as well as scalable to make meaningful impacts on climate change. The majority of standards and technology-specific methodologies available for CDR currently lack the scope required to become a governing standard. It is evident, from the formation of alliances and certified methodologies, such as the Enhanced Weathering Alliance and European Biochar Certification, that progress in developing CDR approaches requires collaboration from industry. Yet, as more companies develop new standards there is a risk of making meaningful comparisons of CDR approaches more complex, because of inconsistent MRV methodologies.

Current approaches for CDR can be engineered or nature-based. In both cases monitoring of large temporal and spatial zones is required, and permanence is an important consideration, thus models must be deployed to quantify the evolution of captured CO2. To verify such models, accurate sampling and testing methodologies are critical. At a practical level, engineering specifications are needed to assure quality. If these specifications are not built on proper standards (e.g. CEN and ISO) problems will arise in defining the requirements of the process between customers, producers, and regulators. C-SINK, an EU/UKRI-funded project, aims to deliver a package to support the large-scale deployment of CDR, including pre-standards for a range of different land application technologies, such as enhanced weathering, biochar, artificial soils, and biological CO2 fixation. These technologies introduce key challenges, such as the sources of variance, that must be considered to determine CDR efficiency, ensuring also a robust method for high precision carbon credit calculation. Therefore, field trials will be carried out across Europe to evaluate pre-standards through in situ MRV testing as part of the C-SINK project.

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4th European Mineralogical Conference, Dublin, Ireland, 2024

Implementation of the EU Green Deal and attainment of net-zero greenhouse gas emissions, requires... more Implementation of the EU Green Deal and attainment of net-zero greenhouse gas emissions, requires policies supporting transition from traditional to clean energy sources, which will increase demand on mining key resources, that will likely increase CO2 emissions and waste production. Many previous studies have assessed the potential utilisation of mafic/ultramafic mine waste for CO2 capture (carbonation) via natural or enhanced weathering (EW). EW is the process of utilising fine grained rock material favouring carbon capture, to accelerate carbon biogeochemical cycling by removing higher amounts of CO2 from the atmosphere than are produced in the process. In theory, this is considered a well-defined carbon dioxide removal (CDR) method, but in practice it is still not used on large scale/long period trials, and hence no widely accepted monitoring, reporting & verification (MRV) standards exist to date. More precisely, there are significant gaps in understanding physicochemical controls for carbonation, such as mineral chemistry, particle size, CO2 supply, temperature, soil porosity, porewater pH, saturation and salinity. To consider EW as a viable CDR method, strong evidence is needed that the material sequesters more CO2 than it emits under given conditions. Our research focuses on determining the net CO2 flux from the EW of Ca and Mg-rich mine wastes, considering physicochemical controls for carbonation, under various conditions (e.g. arctic climate). A series of novel laboratory experiments were set up, which indicated the potential for this material to sequester CO2, and allowed development of the method to measure the process. CO2 capture was particularly efficient for tailings, producing higher carbonation rates due to smaller grain size/larger surface area compared to waste rock. These findings will now be tested at field sites in Northern Europe, using a new CDR MRV methodology determining the net CO2 flux generated from mine wastes, under the EU/UKRI-funded C-SINK project.

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3rd International Conference on Negative CO2 Emissions, Oxford, UK, 2024

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Goldschmidt, 2019

Phosphorus concentrations within water bodies have strict targets under the European Union Water ... more Phosphorus concentrations within water bodies have strict targets under the European Union Water Framework Directive. The headwaters of the Hampshire Avon in southern England, in the Vale of Pewsey is an agricultural catchment underlain by Upper Greensand (UGS), and flanked by Upper and Lower Chalk. P concentrations in the river are high, and work is underway to investigate the geological versus agricultural origins of this material. It is hypothesised that due to the agricultural nature of the catchment and the release of CaCO3-rich waters to the UGS from weathering and dissolution of surrounding Chalk, that hydroxyapatite, Ca5(PO4)3(OH), would precipitate into the pore space of the UGS. Under different chemical conditions, hydroxyapatite would likely dissolve, representing an anthropogenic P flux to headwaters, which may be an important source of anthropogenic P to the catchment. To investigate hydroxyapatite precipitation and dissolution kinetics, we conducted batch experiments to precipitate the mineral onto sand grains, which was then dissolved in a continuous-flow reactor under various conditions. We also modelled the reactive transport of P along a 1D flow path to simulate hydroxyapatite precipitation and dissolution. Hydroxyapatite rapidly precipitated onto sand grains from an alkaline solution that had high concentrations of Ca and P, thus representing a secondary anthropogenic P mineral if the P is sourced from fertiliser. The dissolution rate of the sand-bound mineral is strongly pH dependent, likely representing the acidic dissolution mechanism of hydroxyapatite. However, within the UGS, pore waters are often close to equilibrium, which results in the dissolution rate having a stronger dependence on the P concentration than on pH. Reactive transport models demonstrate that P behaviour is dynamic, as hydroxyapatite is able to both precipitate and dissolve along a 1D flow path, thus representing an anthropogenic flux of P.

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Goldschmidt, 2023

Phosphorus (P) is a vital element for crop production but excessive amounts in freshwaters can le... more Phosphorus (P) is a vital element for crop production but excessive amounts in freshwaters can lead to eutrophic conditions. Although a suite of regulations on the concentration of P in rivers exist under the EU Water Framework Directive (2000/60/EC) and EU Habitats Directive (92/43/EEC), there is a limited understanding on the natural baseline concentration of P that is derived from the weathering of natural P-bearing minerals within catchments. Focusing on a river catchment underlain by Upper Greensand (UGS), known to contain P-rich nodules, and draining into the Hampshire Avon Special Area for Conservation, drilled core samples were obtained from farmland and woodland sites underlain by the UGS aquifer. Chemical analysis of UGS whole-rock and porewater samples indicates that P content ranges between 0-0.8 wt.%, and soluble reactive P and total dissolved P concentrations range from below detection (<5 μg/L) to >1 mg/L, in a small number of samples. Mineralogical analysis of whole-rock UGS samples showed that the most abundant natural P-bearing mineral form is carbonate fluorapatite (average ~0.1 wt.%) and is commonly present in the form of P nodules. These are found to accumulate in four UGS horizons and when in contact with water they dissolve very slowly producing a natural flux between 9.2 x 10-14 and 1.8 x 10-13 mol PO4 3- s-1 within a 10 m3 UGS profile. By contrast, the most abundant anthropogenic P-bearing mineral is microcrystalline hydroxyapatite (average ~0.01 wt.%), most commonly observed in pore-spaces through which water has percolated from the overlying agricultural land. Mineralogical evidence collected in this study suggests that natural baseline P concentrations in the UGS are very low (~0.2-0.3 μg/L per year). Hence, natural or near-natural P concentrations in the aquifer, deriving solely from the slow dissolution of P nodules, are substantially lower than current concentrations, which exceed the threshold under the EU Water Framework Directive and the EU Habitats Directive. P in UGS porewaters is therefore primarily derived from anthropogenic activity in the Vale of Pewsey, with P migrating vertically through precipitation and dissolution of hydroxyapatite to the water table, rather than from natural weathering of P minerals in the UGS.

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Frontiers in Environmental Science, Sep 19, 2022

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Applied Earth Science, 2017

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Applied Earth Science, 2015

Abstracts from the 38th Annual Winter Meeting of the Geological Society's Mineral Deposits St... more Abstracts from the 38th Annual Winter Meeting of the Geological Society's Mineral Deposits Studies Group held on 18–19th December 2014 at the University of Southampton, UK. The meeting was organised by Dr Robert Knight from the University of Southampton.

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Frontiers in Environmental Science, 2022

Phosphorus (P) is a key element which can contribute to the eutrophication of waters draining int... more Phosphorus (P) is a key element which can contribute to the eutrophication of waters draining intensively farmed or populated catchments, driving adverse impacts on ecosystem and human health. An often overlooked source of P in permeable catchments is weathering of P-bearing minerals in bedrock. P release from primary minerals, present when the rock formed, controls background P concentrations in groundwater, but secondary P-bearing minerals may form in aquifers in the presence of anthropogenic P fluxes from agriculture and septic tanks. Using cores from the Upper Greensand (UGS) aquifer, United Kingdom, we show the relative contributions of P from primary and secondary minerals. Bulk rock chemical analysis indicates solid P concentrations of 0-0.8 wt%, while porewater analyses from the same samples indicate phosphate-P concentrations of <5 μg/L-1 mg/L and dissolved organic P concentrations of <5 μg/L-0.7 mg/L. These data, coupled with core stratigraphy, reveal the presence of multiple primary and secondary P-bearing minerals in the UGS, and suggest that secondary P-bearing minerals are largely of anthropogenic origin. The weathering of primary P nodules produces a very low background P flux to surface waters, while the anthropogenic P-bearing minerals undergo rapid dissolution, re-precipitation and re-dissolution cycles, controlled by porewater pH and P concentrations, in turn controlling dissolved P flux to groundwater. We show that secondary P-bearing minerals are a dynamic component of the P transfer system linking anthropogenic activities on the land surface to P in groundwater and surface waters and contributing to the eutrophication of surface waters.

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Applied Geochemistry, 2020

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Mineralogical Magazine, 2016

Rare-earth elements (REE) are viewed as 'critical metals' due to a complex array of produ... more Rare-earth elements (REE) are viewed as 'critical metals' due to a complex array of production and political issues, most notably a near monopoly in supply from China. Red mud, the waste product of the Bayer process that produces alumina from bauxite, represents a potential secondary resource of REE. Karst bauxite deposits represent the ideal source material for REE-enriched red mud as the conditions during formation of the bauxite allow for the retention of REE. The REE pass through the Bayer Process and are concentrated in the waste material. Millions of tonnes of red mud are currently stockpiled in onshore storage facilities across Europe, representing a potential REE resource. Red mud from two case study sites, one in Greece and the other in Turkey, has been found to contain an average of ∼1000 ppm total REE, with an enrichment of light over heavy REE. Although this is relatively low grade when compared with typical primary REE deposits (Mountain Pass and Mount Weld up t...

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Bulletin of the Geological Society of Greece, 2017

The Parnassus-Giona karst bauxite deposits contain significant concentrations of rare earth eleme... more The Parnassus-Giona karst bauxite deposits contain significant concentrations of rare earth elements (400-500 ppm). Preliminary results from a pilot leaching study show that between 19 and 47% of rare earth elements in the bauxite are easily leachable using ion exchange agents such as ammonium sulphate.

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Bulletin of the Geological Society of Greece

Emplacement of the Xanthi Plutonic Complex within the Rhodope Massif of N. Greece created an exte... more Emplacement of the Xanthi Plutonic Complex within the Rhodope Massif of N. Greece created an extensive metamorphic aureole around the plutonite. The aureole contains two areas of intense scapolitization in the contacts between granodiorite and biotitegneiss and between monzonite and sandstone, the latter cross-cut by andesite dykes. This paper reports the results of a mineralogical and geochemical study into the formation of the scapolites and particularly the nature of the plutonite-derived hydrothermal fluids from which scapolites were formed.

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Karst-bauxite deposits form as a result of the accumulation of residual clay minerals in depressi... more Karst-bauxite deposits form as a result of the accumulation of residual clay minerals in depressions on a karst limestone surface, and their subsequent lateritic weathering. Rare earth elements (REE) become concentrated in the bauxite deposits due to crystallisation of authigenic REE-bearing minerals, accumulation of residual phases and the adsorption of ions on clays and other mineral surfaces. REE are concentrated in the red mud waste generated by alumina production from bauxite through the Bayer process. Red muds thus contain on average 900 ppm REE compared with typical values of <100 ppm to ~500 ppm REE in the bauxites. Extraction of REE from red mud has been shown to be feasible although it is challenging due to the heterogeneous spatial distribution of REE in the bauxites and the need for development of appropriate processing methods. With annual European extraction of bauxite estimated to be approximately 3.5 million tonnes per annum, resulting in approximately 1.4 million...

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Karst-bauxite deposits form as a result of the accumulation of residual clay minerals in depressi... more Karst-bauxite deposits form as a result of the accumulation of residual clay minerals in depressions on a karst limestone surface, and their subsequent lateritic weathering. Rare earth elements (REE) become concentrated in the bauxite deposits due to crystallisation of authigenic REE-bearing minerals, accumulation of residual phases and the adsorption of ions on clays and other mineral surfaces. REE are concentrated in the red mud waste generated by alumina production from bauxite through the Bayer process. Red muds thus contain on average 900 ppm REE compared with typical values of <100 ppm to ~500 ppm REE in the bauxites. Extraction of REE from red mud has been shown to be feasible although it is challenging due to the heterogeneous spatial distribution of REE in the bauxites and the need for development of appropriate processing methods. With annual European extraction of bauxite estimated to be approximately 3.5 million tonnes per annum, resulting in approximately 1.4 million...

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Resent research (2013) commissioned by the Environment Agency (EA) suggested that waters extracte... more Resent research (2013) commissioned by the Environment Agency (EA) suggested that waters extracted from the Upper Greensand (UGS) aquifer had a high background phosphorus (P) concentration, linked to the presence of the mineral apatite in the UGS formation. This work has also suggested that P standards for waters from the UGS region should be higher than those currently in place under the EU Water Framework Directive. This programme was commissioned to evaluate this evidence, and establish whether the P release from the UGS derived from primary (natural) apatite minerals or from the dissolution of P minerals formed in situ in the presence of anthropogenic P arriving in the UGS from overlying fertiliser soils and septic tank seepage. Preliminary analysis of rocks from the Vale of Pewsey indicate that the UGS formation hosts four different forms of P: primary fluorapatite and monazite, secondary hydroxyapatite, and an amorphous P-bearing phase. The primary (detrital minerals) originate from the UGS parent rocks, whereas the secondary (authigenic) minerals and amorphous P-phases are formed in situ from P that is likely to be infiltrated from the anthropogenic sources at the soil surface. Surface P sources include fertilisers, animal wastes, leakage plumes from septic tanks and direct discharges from sewage treatment works. Ongoing work is establishing the relative distribution and abundance of these different mineral forms in the UGS and is seeking to establish the rates at which primary and secondary mineral P sources are dissolved and then form new P-bearing minerals/phases within the rock matrix.

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Recent research has indicated high phosphorus (P) concentrations in waters draining from the Uppe... more Recent research has indicated high phosphorus (P) concentrations in waters draining from the Upper Greensand (UGS) aquifer to surface waters in the Hampshire Avon catchment, compromising the ecological health of the Upper Avon. It has been suggested that a proportion of this phosphorus is derived from natural mineral sources in the UGS, in the form of P-rich apatite nodules. This could be contributing a natural background P concentration to these waters in addition to anthropogenically derived P delivered to surface waters from diffuse agricultural and point source sewage discharges in the catchment.

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European geosciences union general assembly, 2015

Rare earth elements (REE) are considered to be highly “critical” by the European Commission [1], ... more Rare earth elements (REE) are considered to be highly “critical” by the European Commission [1], owing to the concentration of global supply [2] and their use in a wide range of emerging technologies (e.g. smart phones, electric cars and wind turbines). The main source of REE is the mineral bastnäsite, which is primarily extracted from carbonatites. Alternative resources of REE have been identified in a variety of other environments such as alluvial placers, bauxites and ore tailings. The EURARE project (www.eurare.eu), funded by the European Commission, aims to improve understanding of potential REE resources in Europe with the overall objective of establishing the basis for a European REE industry. As a part of this project, alternative sources of rare earth elements in Europe are being considered.

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4th European Mineralogical Conference, Dublin, Ireland, 2024

As a result of anthropogenic climate change there is a call to implement a rapid transition to Ne... more As a result of anthropogenic climate change there is a call to implement a rapid transition to Net-Zero greenhouse gas (GHG) emissions. However, reducing emissions is not going to be sufficient for climate stabilisation, and there is a need to remove CO2 from the atmosphere through carbon dioxide removal (CDR). CDR will require more rigorous Monitoring, Reporting and Verification (MRV) because of the complexity of some of the processes and the requirement for CO2 to be stored long-term. With a range of different novel approaches to CDR being developed there are difficulties in ensuring that the quality of each approach is regulated, as well as scalable to make meaningful impacts on climate change. The majority of standards and technology-specific methodologies available for CDR currently lack the scope required to become a governing standard. It is evident, from the formation of alliances and certified methodologies, such as the Enhanced Weathering Alliance and European Biochar Certification, that progress in developing CDR approaches requires collaboration from industry. Yet, as more companies develop new standards there is a risk of making meaningful comparisons of CDR approaches more complex, because of inconsistent MRV methodologies.

Current approaches for CDR can be engineered or nature-based. In both cases monitoring of large temporal and spatial zones is required, and permanence is an important consideration, thus models must be deployed to quantify the evolution of captured CO2. To verify such models, accurate sampling and testing methodologies are critical. At a practical level, engineering specifications are needed to assure quality. If these specifications are not built on proper standards (e.g. CEN and ISO) problems will arise in defining the requirements of the process between customers, producers, and regulators. C-SINK, an EU/UKRI-funded project, aims to deliver a package to support the large-scale deployment of CDR, including pre-standards for a range of different land application technologies, such as enhanced weathering, biochar, artificial soils, and biological CO2 fixation. These technologies introduce key challenges, such as the sources of variance, that must be considered to determine CDR efficiency, ensuring also a robust method for high precision carbon credit calculation. Therefore, field trials will be carried out across Europe to evaluate pre-standards through in situ MRV testing as part of the C-SINK project.

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4th European Mineralogical Conference, Dublin, Ireland, 2024

Implementation of the EU Green Deal and attainment of net-zero greenhouse gas emissions, requires... more Implementation of the EU Green Deal and attainment of net-zero greenhouse gas emissions, requires policies supporting transition from traditional to clean energy sources, which will increase demand on mining key resources, that will likely increase CO2 emissions and waste production. Many previous studies have assessed the potential utilisation of mafic/ultramafic mine waste for CO2 capture (carbonation) via natural or enhanced weathering (EW). EW is the process of utilising fine grained rock material favouring carbon capture, to accelerate carbon biogeochemical cycling by removing higher amounts of CO2 from the atmosphere than are produced in the process. In theory, this is considered a well-defined carbon dioxide removal (CDR) method, but in practice it is still not used on large scale/long period trials, and hence no widely accepted monitoring, reporting & verification (MRV) standards exist to date. More precisely, there are significant gaps in understanding physicochemical controls for carbonation, such as mineral chemistry, particle size, CO2 supply, temperature, soil porosity, porewater pH, saturation and salinity. To consider EW as a viable CDR method, strong evidence is needed that the material sequesters more CO2 than it emits under given conditions. Our research focuses on determining the net CO2 flux from the EW of Ca and Mg-rich mine wastes, considering physicochemical controls for carbonation, under various conditions (e.g. arctic climate). A series of novel laboratory experiments were set up, which indicated the potential for this material to sequester CO2, and allowed development of the method to measure the process. CO2 capture was particularly efficient for tailings, producing higher carbonation rates due to smaller grain size/larger surface area compared to waste rock. These findings will now be tested at field sites in Northern Europe, using a new CDR MRV methodology determining the net CO2 flux generated from mine wastes, under the EU/UKRI-funded C-SINK project.

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3rd International Conference on Negative CO2 Emissions, Oxford, UK, 2024

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Goldschmidt, 2019

Phosphorus concentrations within water bodies have strict targets under the European Union Water ... more Phosphorus concentrations within water bodies have strict targets under the European Union Water Framework Directive. The headwaters of the Hampshire Avon in southern England, in the Vale of Pewsey is an agricultural catchment underlain by Upper Greensand (UGS), and flanked by Upper and Lower Chalk. P concentrations in the river are high, and work is underway to investigate the geological versus agricultural origins of this material. It is hypothesised that due to the agricultural nature of the catchment and the release of CaCO3-rich waters to the UGS from weathering and dissolution of surrounding Chalk, that hydroxyapatite, Ca5(PO4)3(OH), would precipitate into the pore space of the UGS. Under different chemical conditions, hydroxyapatite would likely dissolve, representing an anthropogenic P flux to headwaters, which may be an important source of anthropogenic P to the catchment. To investigate hydroxyapatite precipitation and dissolution kinetics, we conducted batch experiments to precipitate the mineral onto sand grains, which was then dissolved in a continuous-flow reactor under various conditions. We also modelled the reactive transport of P along a 1D flow path to simulate hydroxyapatite precipitation and dissolution. Hydroxyapatite rapidly precipitated onto sand grains from an alkaline solution that had high concentrations of Ca and P, thus representing a secondary anthropogenic P mineral if the P is sourced from fertiliser. The dissolution rate of the sand-bound mineral is strongly pH dependent, likely representing the acidic dissolution mechanism of hydroxyapatite. However, within the UGS, pore waters are often close to equilibrium, which results in the dissolution rate having a stronger dependence on the P concentration than on pH. Reactive transport models demonstrate that P behaviour is dynamic, as hydroxyapatite is able to both precipitate and dissolve along a 1D flow path, thus representing an anthropogenic flux of P.

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Goldschmidt, 2023

Phosphorus (P) is a vital element for crop production but excessive amounts in freshwaters can le... more Phosphorus (P) is a vital element for crop production but excessive amounts in freshwaters can lead to eutrophic conditions. Although a suite of regulations on the concentration of P in rivers exist under the EU Water Framework Directive (2000/60/EC) and EU Habitats Directive (92/43/EEC), there is a limited understanding on the natural baseline concentration of P that is derived from the weathering of natural P-bearing minerals within catchments. Focusing on a river catchment underlain by Upper Greensand (UGS), known to contain P-rich nodules, and draining into the Hampshire Avon Special Area for Conservation, drilled core samples were obtained from farmland and woodland sites underlain by the UGS aquifer. Chemical analysis of UGS whole-rock and porewater samples indicates that P content ranges between 0-0.8 wt.%, and soluble reactive P and total dissolved P concentrations range from below detection (<5 μg/L) to >1 mg/L, in a small number of samples. Mineralogical analysis of whole-rock UGS samples showed that the most abundant natural P-bearing mineral form is carbonate fluorapatite (average ~0.1 wt.%) and is commonly present in the form of P nodules. These are found to accumulate in four UGS horizons and when in contact with water they dissolve very slowly producing a natural flux between 9.2 x 10-14 and 1.8 x 10-13 mol PO4 3- s-1 within a 10 m3 UGS profile. By contrast, the most abundant anthropogenic P-bearing mineral is microcrystalline hydroxyapatite (average ~0.01 wt.%), most commonly observed in pore-spaces through which water has percolated from the overlying agricultural land. Mineralogical evidence collected in this study suggests that natural baseline P concentrations in the UGS are very low (~0.2-0.3 μg/L per year). Hence, natural or near-natural P concentrations in the aquifer, deriving solely from the slow dissolution of P nodules, are substantially lower than current concentrations, which exceed the threshold under the EU Water Framework Directive and the EU Habitats Directive. P in UGS porewaters is therefore primarily derived from anthropogenic activity in the Vale of Pewsey, with P migrating vertically through precipitation and dissolution of hydroxyapatite to the water table, rather than from natural weathering of P minerals in the UGS.

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Frontiers in Environmental Science, Sep 19, 2022

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Applied Earth Science, 2017

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Applied Earth Science, 2015

Abstracts from the 38th Annual Winter Meeting of the Geological Society's Mineral Deposits St... more Abstracts from the 38th Annual Winter Meeting of the Geological Society's Mineral Deposits Studies Group held on 18–19th December 2014 at the University of Southampton, UK. The meeting was organised by Dr Robert Knight from the University of Southampton.

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Frontiers in Environmental Science, 2022

Phosphorus (P) is a key element which can contribute to the eutrophication of waters draining int... more Phosphorus (P) is a key element which can contribute to the eutrophication of waters draining intensively farmed or populated catchments, driving adverse impacts on ecosystem and human health. An often overlooked source of P in permeable catchments is weathering of P-bearing minerals in bedrock. P release from primary minerals, present when the rock formed, controls background P concentrations in groundwater, but secondary P-bearing minerals may form in aquifers in the presence of anthropogenic P fluxes from agriculture and septic tanks. Using cores from the Upper Greensand (UGS) aquifer, United Kingdom, we show the relative contributions of P from primary and secondary minerals. Bulk rock chemical analysis indicates solid P concentrations of 0-0.8 wt%, while porewater analyses from the same samples indicate phosphate-P concentrations of <5 μg/L-1 mg/L and dissolved organic P concentrations of <5 μg/L-0.7 mg/L. These data, coupled with core stratigraphy, reveal the presence of multiple primary and secondary P-bearing minerals in the UGS, and suggest that secondary P-bearing minerals are largely of anthropogenic origin. The weathering of primary P nodules produces a very low background P flux to surface waters, while the anthropogenic P-bearing minerals undergo rapid dissolution, re-precipitation and re-dissolution cycles, controlled by porewater pH and P concentrations, in turn controlling dissolved P flux to groundwater. We show that secondary P-bearing minerals are a dynamic component of the P transfer system linking anthropogenic activities on the land surface to P in groundwater and surface waters and contributing to the eutrophication of surface waters.

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Applied Geochemistry, 2020

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Mineralogical Magazine, 2016

Rare-earth elements (REE) are viewed as 'critical metals' due to a complex array of produ... more Rare-earth elements (REE) are viewed as 'critical metals' due to a complex array of production and political issues, most notably a near monopoly in supply from China. Red mud, the waste product of the Bayer process that produces alumina from bauxite, represents a potential secondary resource of REE. Karst bauxite deposits represent the ideal source material for REE-enriched red mud as the conditions during formation of the bauxite allow for the retention of REE. The REE pass through the Bayer Process and are concentrated in the waste material. Millions of tonnes of red mud are currently stockpiled in onshore storage facilities across Europe, representing a potential REE resource. Red mud from two case study sites, one in Greece and the other in Turkey, has been found to contain an average of ∼1000 ppm total REE, with an enrichment of light over heavy REE. Although this is relatively low grade when compared with typical primary REE deposits (Mountain Pass and Mount Weld up t...

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Bulletin of the Geological Society of Greece, 2017

The Parnassus-Giona karst bauxite deposits contain significant concentrations of rare earth eleme... more The Parnassus-Giona karst bauxite deposits contain significant concentrations of rare earth elements (400-500 ppm). Preliminary results from a pilot leaching study show that between 19 and 47% of rare earth elements in the bauxite are easily leachable using ion exchange agents such as ammonium sulphate.

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Bulletin of the Geological Society of Greece

Emplacement of the Xanthi Plutonic Complex within the Rhodope Massif of N. Greece created an exte... more Emplacement of the Xanthi Plutonic Complex within the Rhodope Massif of N. Greece created an extensive metamorphic aureole around the plutonite. The aureole contains two areas of intense scapolitization in the contacts between granodiorite and biotitegneiss and between monzonite and sandstone, the latter cross-cut by andesite dykes. This paper reports the results of a mineralogical and geochemical study into the formation of the scapolites and particularly the nature of the plutonite-derived hydrothermal fluids from which scapolites were formed.

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Karst-bauxite deposits form as a result of the accumulation of residual clay minerals in depressi... more Karst-bauxite deposits form as a result of the accumulation of residual clay minerals in depressions on a karst limestone surface, and their subsequent lateritic weathering. Rare earth elements (REE) become concentrated in the bauxite deposits due to crystallisation of authigenic REE-bearing minerals, accumulation of residual phases and the adsorption of ions on clays and other mineral surfaces. REE are concentrated in the red mud waste generated by alumina production from bauxite through the Bayer process. Red muds thus contain on average 900 ppm REE compared with typical values of <100 ppm to ~500 ppm REE in the bauxites. Extraction of REE from red mud has been shown to be feasible although it is challenging due to the heterogeneous spatial distribution of REE in the bauxites and the need for development of appropriate processing methods. With annual European extraction of bauxite estimated to be approximately 3.5 million tonnes per annum, resulting in approximately 1.4 million...

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Karst-bauxite deposits form as a result of the accumulation of residual clay minerals in depressi... more Karst-bauxite deposits form as a result of the accumulation of residual clay minerals in depressions on a karst limestone surface, and their subsequent lateritic weathering. Rare earth elements (REE) become concentrated in the bauxite deposits due to crystallisation of authigenic REE-bearing minerals, accumulation of residual phases and the adsorption of ions on clays and other mineral surfaces. REE are concentrated in the red mud waste generated by alumina production from bauxite through the Bayer process. Red muds thus contain on average 900 ppm REE compared with typical values of <100 ppm to ~500 ppm REE in the bauxites. Extraction of REE from red mud has been shown to be feasible although it is challenging due to the heterogeneous spatial distribution of REE in the bauxites and the need for development of appropriate processing methods. With annual European extraction of bauxite estimated to be approximately 3.5 million tonnes per annum, resulting in approximately 1.4 million...

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Resent research (2013) commissioned by the Environment Agency (EA) suggested that waters extracte... more Resent research (2013) commissioned by the Environment Agency (EA) suggested that waters extracted from the Upper Greensand (UGS) aquifer had a high background phosphorus (P) concentration, linked to the presence of the mineral apatite in the UGS formation. This work has also suggested that P standards for waters from the UGS region should be higher than those currently in place under the EU Water Framework Directive. This programme was commissioned to evaluate this evidence, and establish whether the P release from the UGS derived from primary (natural) apatite minerals or from the dissolution of P minerals formed in situ in the presence of anthropogenic P arriving in the UGS from overlying fertiliser soils and septic tank seepage. Preliminary analysis of rocks from the Vale of Pewsey indicate that the UGS formation hosts four different forms of P: primary fluorapatite and monazite, secondary hydroxyapatite, and an amorphous P-bearing phase. The primary (detrital minerals) originate from the UGS parent rocks, whereas the secondary (authigenic) minerals and amorphous P-phases are formed in situ from P that is likely to be infiltrated from the anthropogenic sources at the soil surface. Surface P sources include fertilisers, animal wastes, leakage plumes from septic tanks and direct discharges from sewage treatment works. Ongoing work is establishing the relative distribution and abundance of these different mineral forms in the UGS and is seeking to establish the rates at which primary and secondary mineral P sources are dissolved and then form new P-bearing minerals/phases within the rock matrix.

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Recent research has indicated high phosphorus (P) concentrations in waters draining from the Uppe... more Recent research has indicated high phosphorus (P) concentrations in waters draining from the Upper Greensand (UGS) aquifer to surface waters in the Hampshire Avon catchment, compromising the ecological health of the Upper Avon. It has been suggested that a proportion of this phosphorus is derived from natural mineral sources in the UGS, in the form of P-rich apatite nodules. This could be contributing a natural background P concentration to these waters in addition to anthropogenically derived P delivered to surface waters from diffuse agricultural and point source sewage discharges in the catchment.

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European geosciences union general assembly, 2015

Rare earth elements (REE) are considered to be highly “critical” by the European Commission [1], ... more Rare earth elements (REE) are considered to be highly “critical” by the European Commission [1], owing to the concentration of global supply [2] and their use in a wide range of emerging technologies (e.g. smart phones, electric cars and wind turbines). The main source of REE is the mineral bastnäsite, which is primarily extracted from carbonatites. Alternative resources of REE have been identified in a variety of other environments such as alluvial placers, bauxites and ore tailings. The EURARE project (www.eurare.eu), funded by the European Commission, aims to improve understanding of potential REE resources in Europe with the overall objective of establishing the basis for a European REE industry. As a part of this project, alternative sources of rare earth elements in Europe are being considered.

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