Konstantinos Kollias

The Cycladic Blueschist Unit (CBU) of the Aegean (Greece) contains several occurrences of metamorphosed Manganese mineralization within a Triassic volcaniclastic sequence. The latter includes quartz-mica schists intercalated with bimodal metavolcanics and blue-grey marble layers. SHRIMP U-Pb zircon dating has documented the Triassic age (~242 Ma) of the volcanic rocks. Herein we revisit the Mn metallogenic system of the CBU through an extensive study of Mn mineralization at Varnavas area, Northern Attica, and a similar occurrence at central Andros Island (Mparades hill). Manganese mineralogy at both localities is manifested in a typical high-P metamorphic silicate assemblage dominated by piemontite, spessartine garnet, and minor pyroxmangite (rhodonite). At Andros, Mn-rich subdomains contain brecciated braunite micronodules. The preservation of similar nodular form is documented from Varnavas, comprising dominant todorokite, lesser hollandite, pyrolusite, and minor Mn-bearing hematite. The contrasting Mn oxide mineralogy at the two sites is tentatively interpreted as the result of locally incomplete reduction of precursor Mn(IV) phases during metamorphism. Common geochemical characteristics of the Mn-rich rocks include low transition metal concentrations; positive-sloping, PAAS-normalized REE spidergrams; positive Ce anomalies of variable magnitude across individual samples; and high As, Ba, Pb. The geochemical variability recorded is ascribed to the varying mixing of a hydrothermal-sourced, hydrogenous metalliferous component that precipitated penecontemporaneously with the deposition of the host tuffs. The primary Mn precipitates are thought to have been in the form of tetravalent Mn assemblages, which may locally be partially preserved through metamorphism, as appears to be the case in the Varnavas occurrence. All these reveal the interplay between the felsic/intermediate back-arc volcanism and associated hydrothermal activity and the Mn mineralization within the rift setting of the CBU domain.

The prevention of acid generation from sulfidic mine wastes is a problem that challenges the global scientific community for decades. A promising strategy is related to the formation of coating layer around sulfides for inhibiting surface oxidation. In the current research, the conditions favoring the formation of an efficient silicate-based coating around pyrite and arsenopyrite were studied, using batch tests. The coating solutions contained silicate-oxyanions, an oxidant (H₂O₂) and buffered at pH 6. The effect of Si concentration (0.1–50 mM), liquid/solid ratio (5–100 mL/g) and contact time (up to 24 h) was investigated. Pyrite tailings treated with a solution of 1 mM Si/0.1 M H₂O₂ at L/S:100 mL/g for 24 h resulted in the optimum formation of a coating, which reduced the amount of SO₄⁻²-released by 72%, compared to the sample treated in the absence of Si. However, silicate treatment had a negative effect on arsenopyrite tailings inducing As mobilization.

In the framework of the PVadapt H2020 project, a sustainable and fully adaptable building-integrated photovoltaic–thermal (BIPVT) system of substantially lower cost than conventional in-market solutions will be developed. A flexible automated process will be employed to produce PV modules as well as elements with integrated heat pipe-based heat recovery. These active energy components will be combined with passive components with structural, thermal, and other functions to produce prefabricated modules. A smart envelope System, featuring grid connectivity, load prediction/shifting, and insolation/temperature predictive algorithms, will be integrated in the BIPVT to maximize energy efficiency and cost saving. The unit cost of production, the levelized cost of energy (LCOE), and the payback period of the multifunctional BIPVT module will be below 200 €/m², 2 ct/kWh, and 10 years, respectively.

An appealing technique to prevent and/or minimize pyrite oxidation and subsequent acid generation in mine waste sites is the formation of a protective coating on the surface of sulfide grains. To investigate the conditions for the formation of an efficient coating on pyritic tailings, column tests were performed. These tests involved the treatment with a coating solution, which was continuously recycled through the packed bed of tailings. The coating solution was consisted of SiO₄⁻⁴ oxyanions, an oxidant (H₂O₂), and adjusted to pH 6. The effect of the volume of coating solution per mass of material (L/S ratio), Si concentration and treatment duration on coating formation was studied. Based on the results, a protective coating can be developed on the pyrite particles following treatment with a solution of 0.1 mM Si concentration, which resulted in the reduction of sulfate release by 84% compared to non-treated pyrite samples.