Search Results (753)

Following the worldwide increasing demand for Critical Raw Materials (CRMs), the Hellenic Geological Survey (HSGME) implemented a national project focused on the re-evaluation of certain Public Mining Areas in Greece. In this framework, exploration activities, including geological mapping, and mineralogical, geochemical, and geophysical studies, revealed significant mineralization targets which possibly host elevated contents of certain CRMs in the Kimmeria Fe skarn deposit. The mineralization is related to the contact metamorphic aureole of the Oligocene Xanthi pluton. Various skarn minerals form the following paragenetic zones in order of decreasing temperature: (i) garnet–wollastonite, (ii) garnet–clinopyroxene, (iii) garnet–epidote, and (iv) vesuvianite–scapolite. The skarn deposit consists of magnetite-rich ore occurring along with sulfides (chalcopyrite, pyrite, bismuthinite, and molybdenite), scheelite, minor sulfosalts (aikinite, wittichenite, and cubanite) and native elements (Au and Bi). Bulk-rock geochemical analyses yielded significant values, as follows: Fe₂O₃, up to 58 wt%; Cu, up to 6.6 wt%; Bi, up to 1100 ppm; W, up to 670 ppm; V, up to 200 ppm; Mo, up to 200 ppm; and Au, up to 2.1 g/t. Soil and stream sediment geochemistry reveals spatial and linear trends for certain groups of associated elements (i.e., Fe₂O₃-Cu-Bi-W and Mo-W-Zn). These trends reflect the surficial distribution of mineralized zones and imply the existence of partially unexposed mineralization in the western part of the study area, a fact also supported by geophysical evidence. A preliminary drilling project has been proposed to evaluate the qualitative characteristics of the deeper parts of the mineralization, investigate buried ore zones in the western part, and overall, reassess the economic potential of the deposit. Full article

To combat the detrimental impacts of climate change and meet the obligations outlined in the 2015 Paris Agreement, Carbon Capture, Utilization, and Storage (CCUS) has emerged as a crucial technology with significant potential for achieving climate targets. CCUS involves the capture, storage, and utilization of carbon dioxide (CO₂) emissions from existing energy infrastructure, hard-to-abate industries, or directly from the atmosphere, presenting a promising solution for emission reduction. However, fully harnessing the benefits of carbon storage requires the development of technically robust, safe, and cost-effective well control strategies that align with fundamental subsurface policies. This study aims to offer a comprehensive reference guide for carbon storage applications by reviewing relevant research in the field and establishing key subsurface storage policies for carbon storage in saline aquifer formation along with their practical implementation in carbon storage development plans. Additionally, we explore the utilization of optimization techniques employed thus far in the development of effective well control strategies in saline aquifers, presenting mathematical tools utilized and the achieved results. Full article

Accurate predictions of hydrate dissociation conditions are of paramount importance for optimizing mitigation strategies and preventing hydrate formation in oil and gas operations. These predictions are crucial for selecting appropriate thermodynamic inhibitors, reducing operating costs, and minimizing environmental impact. Moreover, they facilitate the practical application of innovative hydrate technologies such as energy storage, gas separation, and carbon capture. To address this need, various commercial PVT software packages, such as MultiFlash, HydraFLASH, CSMGem, and CSMHyd, are commonly used. However, these packages employ different computational approaches, including hydrate modeling, equations of state (EoS), and phase behavior representation, which can influence their prediction capabilities. To assess their accuracy, we conducted an evaluation using a comprehensive database of 400 experimental dissociation pressure data points from both uninhibited and inhibited hydrate former systems. Through our evaluation, we identified the unique strengths and weaknesses of each software package, providing valuable guidance for industry practitioners and researchers who aim to accurately predict hydrate stability conditions, enabling them to implement effective mitigation strategies and exploit technological solutions. Full article

The purpose of this study is to explore the potential influence of cyclic freezing–thawing on the flexural strength of Greek natural stones that are extensively utilized for construction or decoration purposes. Such testing approaches are an indispensable part of the stone selection criteria due to their ability to assess the stone’s durability. It is especially crucial in locations where exposure to freeze–thaw cycles is common. For this study, samples from various types of stones, including limestones, calcite and dolomite marble, cipollino marble, schists, and mylonites, were examined to assess their flexural strength under concentrated loads and their associated values after freeze–thaw cycles in compliance with European standards (EN). The results show that stones of the same type have comparable flexural strength behaviour. Only in a few cases were significant increases or decreases in strength observed. Specific stones demonstrated a substantial reduction in their flexural strength when exposed to freeze–thaw cycling despite their initially calculated high values without having undergone the frost durability test. Full article

In this study, the thermal performance of the parabolic trough collector (PTC) has been addressed under Ouagadougou climate conditions. Thus, after developing a model, the effect of mass flow on PTC performance showed that the Jatropha curcas oil (JCO) temperature difference increases when the mass flow rate ($\dot{m}$) decreases while the thermal efficiency (${\eta }_{th}$) increases. For $\dot{m}$ of 1 kg s⁻¹, a collector length of 46.8 m or collection area of 230 m² is required to obtain an outlet temperature of 210 °C with an average ${\eta }_{th}$ of 82.69%. This paper can support the decision for a demonstration plant implementation regarding JCO use in the CSP plant. Full article

More than 218 million tonnes of mineral construction waste are produced in Germany every year. In view of the shortage of domestic raw materials and an increasing demand for lightweight aggregates and gypsum, it is important to find alternative sources of raw materials for the production of light aggregates. The main focus of our investigations is on construction and demolition waste and industrial by-products, which have so far only been used at a low level. Chemical analyses can be used to classify potential substances in the ternary diagram according to RILEY and to examine their basic suitability. However, the results show that the suitability of a raw material for the production of lightweight aggregates cannot be determined solely on the basis of the classification in the ternary diagram. Experimental investigations are necessary in any case. From the range of residual and waste materials investigated, the rhyolite fractions showed the best bloating properties. Without the addition of bloating agents, bloating values of 1.4 can be achieved. The addition of iron slurry to a reduction in the bloating temperature by about 100 °C, however, is associated with a slight reduction in the bloating value. With our investigations, we were able to show that an expansion of the raw material base for the production of lightweight aggregates is also possible beyond the use of classic, heterogeneous building rubble containing bricks. Full article

This work provides historical information and examines changes in the methods and equipment used in gold recovery and processing operations. Alluvial gold recovery methods, mainly based on gravity separation combined with mercury (amalgamation), have been applied since the early days of mining. Historically, mining gold from the riverbeds was first implemented in Ancient Anatolia (also called “Asia Minor”) and Ancient Greece. As a first attempt to recover gold, the traditional immersion of sheepskin in river water to trap alluvial gold was developed. This technique has been considered a milestone in the famous myth of the Golden Fleece. Since then, gold extraction and processing technologies have evolved. In this respect, Emperor Augustus developed hydraulic gold mining during the period of the Roman Empire. Subsequently, the innovative machines of Georgius Bauer (Agricola) were widely used during the Renaissance, while Spanish colonialists in America improved their techniques by observing the efficient methods of the natives. Finally, the “American Gold Rush” era was perhaps the most crucial period of the alluvial gold mining process. It took place along the rivers of America during the 19th and 20th centuries. Today, in the technologically advanced society, various gold mining machines, including spiral and jig concentrators, provide higher production rates and less environmental harm. Full article

The present research work focuses on the characterization and leachability evaluation of electric arc furnace dust (EAFD) and its vitreous outgrowths produced during vitrification with soda lime recycled glass (SLRG). EAFD is a hazardous industrial waste generated in the collection of particulate material during the steelmaking process via an electric arc furnace. Glasses of various syntheses were obtained during EAFD vitrification with various amounts of silica scrap (50, 60 and 70 wt%). The characterization of the as-received dust was carried out by using granulometry analysis, chemical analysis, X-ray diffraction (XRD), and scanning electron microscopy (SEM), in conjunction with Energy Dispersive X-ray Spectroscopy (EDS). The produced glasses during vitrification were studied by means of chemical and mineralogical analysis, whereas their microstructure in polished sections was examined by SEM/EDS. Their behavior during leaching was determined by the EN 12457-2 compliance leaching test and according to the results, the trace elements detected in the leachates were well below the corresponding regulatory limits. Full article

Lithium iron phosphate (LFP) batteries are becoming a growing trend as a consequence of EU regulations and their advantages over nickel manganese cobalt (NMC) batteries. The use of LFP batteries is expected to increase considerably globally, creating an enormous waste problem. Battery recycling is emphasized in the EU’s battery laws, especially for lithium. Proper recycling of LFP batteries reduces environmental damage and supports the circular economy. Graphite and lithium are acknowledged as essential raw minerals. Recycling LFP batteries can be accomplished using pyrometallurgical and hydrometallurgical techniques. This study investigates the impact of thermal pre-treatments on flotation and leaching to produce an efficient recycling process. Full article

The increasing use of rare-earth elements (REEs) in renewable technologies such as electric vehicles and wind turbines is driving a rapid rise in their economic importance. This work investigated the separation of REEs (Nd, Pr, Sm, and Dy) from NdFeB magnets using high-performance solid-phase extraction chromatography. More than 99% of the REEs were extracted from an Fe-rich sulfate-based leach liquor using a three counter-current stage solvent extraction of 34.7 vol.% and O/A 1.5. The REE-loaded H₂SO₄ strip solution was separated into a high-purity Nd and Pr fraction from separate Sm and Dy fractions in a single stage using a D2EHPA-impregnated column and H₂SO₄ gradient elution. Full article

Manganese oxide minerals have a remarkable range of applications. This investigation delves into their potential utility in energy storage, particularly as supercapacitors. The study centers on natural manganese oxides sourced from the Drama region (Greece), evaluating their electrochemical promise and devising strategies for addressing the remediation of mining waste sites. Samples were collected from abandoned mining sites at Kato Nevrokopi area, Drama region. Techniques such as X-ray diffraction (XRD) were employed to probe the structural characteristics of the minerals. Electrochemical studies involved the preparation of electrodes using natural and heat-treated nsutite (hausmannite). Then, the designed electrodes were subjected to cyclic voltammetry tests and charge-discharge measurements. Results showed superior electrochemical performance for the hausmannite-based electrode due to its greater structural homogeneity. Full article

As Europe addresses decarbonization, huge coal mining areas shall be reclaimed and appropriately valorized, creating the post-mining areas. This work assesses their resilience and safety by methodologically addressing multi-hazards threatening closed and abandoned mines. The current work modifies an indicator-based semi-quantitative multi-hazard method towards post-mining risk assessment, described as the (1) identification of the hazards, (2) assessment of the interactions, and (3) quantification of the level of interactions. The methodology can appropriately quantify the multi-hazard severity for various scenarios. However, it has limitations, not considering appropriately the hazards’ sequence and missing an objective criterion for scenario comparison. Full article

This study examines some relevant limnological and hydrogeochemical characteristics of the most emblematic pit lake of the Iberian Pyrite Belt (IPB). Corta Atalaya (CA) open pit mine is known for its large size and for being one of the most important exploitations of copper in Europe. Despite its historical importance, little is known about the lake formed in this open pit. During this study, the pit lake presented a surface area of 16 ha, a maximum depth of 106 m, and a 5.8 hm³ volume of acid and metal-enriched water. CA pit lake shows permanent chemical stratification (meromictic lake), where three layers with different density and chemical composition can be differentiated: (i) a superficial layer of 5 ± 2 m water depth, with electric conductivity (EC) between 5.4–6.64 mS/cm, and oxygenated and Fe(III)-rich mixolimnion; (ii) an intermediate layer (between 5–30 m, chemocline), exhibiting strong vertical changes in parameters such as temperature (T) and EC, which show an increase with depth; and (iii) a thick bottom layer from 30 m to 106 m depth, with anoxic, elevated EC (47 mS/cm) and T (32 °C) values, and a concentration of Fe as Fe(II) (monimolimnion).The characterization of the water column is essential to know the potential sources of strategic and critical raw materials, and to evaluate their possible recuperation, thereby activating a circular economy. Full article

Hydrogen is increasingly being recognized as a crucial element in reducing carbon emissions in the metallurgical industry. Its use in the steel sector is gaining momentum through various initiatives at high TRL levels. Moreover, hydrogen shows promise in other metal production processes as well. One application involves utilizing hydrogen for effective selective reduction copper from copper slags with a low amount of iron being reduced. Hydrogen can also be employed in the pre-reduction of manganese ore, leading to the carbon-free production of manganese metal through aluminothermic reactions. Additionally, hydrogen can be used in the processing of bauxite residue, where iron is partially or completely reduced to separate an iron-rich fraction, allowing for alumina recovery via leaching. Full article

The conventional lithium extraction method involves the calcination of a-spodumene at 1050 °C so that it can be converted to the more-reactive b-spodumene and then a sulfuric acid roasting step at 250 °C. Lithium is finally extracted via leaching with water. This method is energy-intensive, leading to high capital and operational costs. In this study, the direct calcination of a-spodumene with the use of sodium carbonate and calcium oxide was examined, aiming to significantly reduce the calcination temperature and completely omit the sulfuric acid roasting step, thereby radically redesigning the lithium extraction process. The calcination product was then leached with different leaching agents, such as water and sulfuric acid, and at different temperatures. The efficiency of the additives was evaluated through the results of lithium extraction achieved during the leaching step. Different leaching agents and temperatures were investigated. The maximum lithium extraction achieved was 96%, obtained after calcination using a sodium carbonate/spodumene mixture and leaching with sulfuric acid at 90 °C. High lithium extractions, up to 83%, can also be achieved under the same calcination conditions and after leaching with sulfuric acid at lower temperatures, such as 40 °C, and for shorter leaching times. Full article