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This paper presents an investigation of naturallyoccurring CO2 emissions from the Florina natural analoguesite in Greece. The main objective was to interpretpreviously collected depth sounding data, convert theminto surfaces, and use them as input to develop, for thefirst time, 3D geological models of the Florina basin. Byalso locating the extent of the aquifer, the location of theCO2 source, the location of other natural CO2 accumulations,and the points where CO2 reaches the surface, wewere able to assess the potential for CO2 leakage. Geologicalmodels provided an estimate of the lithological compositionof the Florina Basin and allowed us to determinepossible directions of groundwater flow and pathways ofCO2 flow throughout the basin.Important modelling parameters included the spatial positionsof boundaries, faults, and major stratigraphic units(which were subdivided into layers of cells). We used variousfunctions in Petrel software to first construct a structuralmodel describing the main rock boundaries.We thendefined a 3D mesh honouring the structural model, andfinally we populated each cell in the mesh with geologicproperties, such as rock type and relative permeability.According to the models, the thickest deposits are locatedaround Mesochorion village where we estimate thataround 1000 m of sediments were deposited above thebasement. Initiation of CO2 flow at Florina Basin couldhave taken place between 6.5 Ma and 1.8 Ma ago. The NESWoriented faults, which acted as fluid flow pathways,are still functioning today, allowing for localised leakageat the surface. CO2 leakage may be spatially variable andepisodic in rate. The episodicity can be linked to the timingof Almopia volcanic activity in the area.

The development of three-dimensional geological models has proven to be critical for conceptualizing complex subsurface environments. This is crucial for mining areas due to their various hazards and unstable conditions. Furthermore, three-dimensional (3D) models can be the initial step for the development of numerical models in order to support critical decisions and sustainable mining planning. This paper illustrates the results and the development phases of a 3D geological model within the boundaries of the Kardia lignite deposit in western Macedonia, Greece. It also highlights the usefulness of a Geographic Information System (GIS) methodology in the subsurface geological and hydrogeological analysis regarding the Underground Coal Gasification (UCG) methodology. In addition, the work focuses on the integrated geospatial framework that was developed to support the Coal-to-Liquids Supply Chain (CLSC) integration in unfavorable geological settings. A 3D subsurface geological model of the study area was developed to identify a suitable area for in situ coal conversion and UCG considering criteria related to specific coal thickness and depth. In this context, the suggested integrated geomodelling workflow can positively contribute to the implementation of conventional and innovative mining, saving time and reducing the cost to improve the quality of information needed to support decisions related to UCG implementation. [ABSTRACT FROM AUTHOR]

Natural CO2 fields can be used to identify trapping mechanisms, the fate and the geochemical consequences of geologically stored CO2 in shallow aquifers. The Florina Basin in Greece is regarded as a CO2 naturally leaking analog due to millions of years of gas accumulation in a Tertiary sand formation. This research was conducted in order to identify the CO2 fingerprints and to investigate and evaluate the factors controlling the groundwater quality in the basin. Leaking CO2 is observed in the aquifers and at the surface. The basin is filled with clastic sediments. It can provide information regarding the fate of CO2 and the possible impacts that can be used as reference in demonstration and industrial projects. Water sampling campaigns were conducted to determine the impact of the gas-water long-term interactions in the shallow aquifers. The CO2 has increased the concentration (in relation to other water samples from the basin) of certain elements like Fe, Mn, Na, Cl, and Br but only in few cases exceeds the EU drinking limit. The chemistry of the groundwater in the Florina Basin aquifers was found to be controlled mainly by the CO2-water-rock interactions due to the mineralogy of the aquifers (calcite and silicates including pyroxenes and chlorite). Metal attenuation processes have prevented the aquifers from brine contamination. Considering the Florina Basin is a natural analog for studying the leaking and migration pathways of stored CO2 and that only minor affects have been identified in the groundwater chemistry, the conclusions of this research are promising for the possible usage of a basin of similar geology and lithology for deep CO2 storage. © 2015 Society of Chemical Industry and John Wiley & Sons, Ltd [ABSTRACT FROM AUTHOR]

Μining waste, processing by-products and mine water discharges pose a serious threat to the environment as in many cases they contain high concentrations of toxic substances. However, they may also be valuable resources. The main target of the current review is the comparative study of the occurrence of rare earth elements (REE) in mining waste and mine water discharges produced from the exploitation of coal, bauxite, phosphate rock and other ore deposits. Coal combustion ashes, bauxite residue and phosphogypsum present high percentages of critical REEs (up to 41% of the total REE content) with ΣREY content ranging from 77 to 1957.7 ppm. The total REE concentrations in mine discharges from different coal and ore mining areas around the globe are also characterised by a high range of concentrations from 0.25 to 9.8 ppm and from 1.6 to 24.8 ppm, respectively. Acid mine discharges and their associated natural and treatment precipitates seem to be also promising sources of REE if their extraction is coupled with the simultaneous removal of toxic pollutants. [ABSTRACT FROM AUTHOR]

The Canary Island archipelago holds 2.2 million inhabitants and received more than 14 million tourist visitors in 2019. Its volcanic origin and the presence of recent volcanic activity highlight its potential geothermal interest for heat production, therefore offering an attractive pathway for a renewable energy supply, not only for power generation and deep geothermal exploitation but also for low-enthalpy heating and cooling production. This work investigates nine touristic infrastructures in the Canary Islands which experienced a transition from conventional heat production systems to shallow geothermal energy (SGE) systems. The SGE systems established consisted in ultra-low temperature district heating and cooling (DHC) micro-networks involving, in most cases, small apartment blocks fed by shallow geothermal plants with an average cooling capacity of 602 kW and a heating capacity of 614 kW. The examination of this transition has exhibited an average saving of 374 MWh, 69,235 € and 280 tCO 2 for each installation every year. This work provides evidence of the economical, energetical and environmental advantages of SGE technology in volcanic islands facing both and enormous heating and cooling demand due to tourism, in an energy-dependent system that also faces the challenge of the decarbonization of the heating production sector. • Nine shallow geothermal systems in Canary Islands were examined. • Transition to shallow geothermal energy resulted in 66% energy savings. • Investments showed return rates higher than 13% for all cases studied. • Emissions savings were 256 tCO 2 per installation and year on average. [ABSTRACT FROM AUTHOR]