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.

Carbon dioxide (CO₂) has reached a higher level of emissions in the last decades, and as it is widely known, CO₂ is responsible for numerous environmental problems, such as climate change. Thus, there is a great need for the application of CO₂ capture and storage, as well as of CO₂ utilization technologies (CCUS). This review article focuses on summarizing the current CCUS state-of-the-art methods used in Europe. Special emphasis has been given to mineralization methods/technologies, especially in basalts and sandstones, which are considered to be suitable for CO₂ mineralization. Furthermore, a questionnaire survey was also carried out in order to investigate how informed about CO₂ issues European citizens are, as well as whether their background is relative to their positive or negative opinion about the establishment of CCUS technologies in their countries. In addition, social acceptance by the community requires contact with citizens and stakeholders, as well as ensuring mutual trust through open communication and the opportunity to participate as early as possible in the development of actions and projects related to CO₂ capture and storage, at all appropriate levels of government internationally, as citizens need to understand the benefits from such new technologies, from the local to the international level.

In West Macedonia (Greece), CO₂ accounts as one of the largest contributors of greenhouse gas emissions related to the activity of the regional coal power plants located in Ptolemaida. The necessity to mitigate CO₂ emissions to prevent climate change under the Paris Agreement’s framework remains an ongoing and demanding challenge. It requires implementing crucial environmentally sustainable technologies to provide balanced solutions between the short-term needs for dependency on fossil fuels and the requirements to move towards the energy transition era. The challenge to utilise and store CO₂ emissions will require actions aiming to contribute to a Europe-wide CCUS infrastructure. The Horizon 2020 European Project “STRATEGY CCUS “examines the potential for CO₂ storage in the Mesohellenic Trough from past available data deploying the USDOE methodology. Research results show that CO₂ storage capacities for the Pentalofos and Eptachori geological formations of the Mesohellenic Trough are estimated at 1.02 and 0.13 Gt, respectively, thus providing the potential for the implementation of a promising method for reducing CO₂ emissions in Greece. A certain storage potential also applies to the Grevena sub-basin, offering the opportunity to store any captured CO₂ in the area, including other remote regions.

Pleistocene alkaline basaltic lavas crop out in the region of Volos at the localities of Microthives and Porphyrio. Results from detailed petrographic study show porphyritic textures with varying porosity between 15% and 23%. Data from deep and shallow water samples were analysed and belong to the Ca-Mg-Na-HCO₃-Cl and the Ca-Mg-HCO₃ hydrochemical types. Irrigation wells have provided groundwater temperatures reaching up to ~30 °C. Water samples obtained from depths ranging between 170 and 250 m. The enhanced temperature of the groundwater is provided by a recent-inactive magmatic heating source. Comparable temperatures are also recorded in adjacent regions in which basalts of similar composition and age crop out. Estimations based on our findings indicate that basaltic rocks from the region of Volos have the appropriate physicochemical properties for the implementation of a financially feasible CO₂ capture and storage scenario. Their silica-undersaturated alkaline composition, the abundance of Ca-bearing minerals, low alteration grade, and high porosity provide significant advantages for CO₂ mineral carbonation. Preliminary calculations suggest that potential pilot projects at the Microthives and Porphyrio basaltic formations can store 64,800 and 21,600 tons of CO₂, respectively.

Greece is considered amongst the world’s top marble producers in the global carbonate ornamental stone market. Selected Greek carbonate ornamental stones considered in our study suite are characterized by their distinctive and in some cases unique appearance, having a significant impact on their commercial value. Their wide range of colour varieties and their physico-mechanical properties are closely related to their mineral assemblage, chemical constitution, petrographic properties, structural defects, which in turn depend highly upon their metamorphic/diagenetic grade and in some cases hydrothermal processes that affected them. This study endeavors to feature the petrographic, mineralogical and geochemical properties of the main Greek carbonate ornamental stones from selected localities and their by-product waste material used as aggregates. The documented data aims to serve a better understanding of the dynamic Greek marble industry by relating their mineral and chemical properties with their physico-mechanical and aesthetic characteristics.

Underground geological energy and CO₂ storage contribute to mitigation of anthropogenic greenhouse-gas emissions and climate change effects. The present study aims to present specific underground energy and CO₂ storage sites in Greece. Thermal capacity calculations from twenty-two studied aquifers (4 × 10⁻⁴–25 × 10⁻³ MJ) indicate that those of Mesohellenic Trough (Northwest Greece), Western Thessaloniki basin and Botsara flysch (Northwestern Greece) exhibit the best performance. Heat capacity was investigated in fourteen aquifers (throughout North and South Greece) and three abandoned mines of Central Greece. Results indicate that aquifers present higher average total heat energy values (up to ~6.05 × 10⁶ MWh_(th)), whereas abandoned mines present significantly higher average area heat energy contents (up to ~5.44 × 10⁶ MWh_(th)). Estimations indicate that the Sappes, Serres and Komotini aquifers could cover the space heating energy consumption of East Macedonia-Thrace region. Underground gas storage was investigated in eight aquifers, four gas fields and three evaporite sites. Results indicate that Prinos and South Kavala gas fields (North Greece) could cover the electricity needs of households in East Macedonia and Thrace regions. Hydrogen storage capacity of Corfu and Kefalonia islands is 53,200 MWh_(e). These values could cover the electricity needs of 6770 households in the Ionian islands. Petrographical and mineralogical studies of sandstone samples from the Mesohellenic Trough and Volos basalts (Central Greece) indicate that they could serve as potential sites for CO₂ storage.