Sustainable removal of uranium from acidic wastewater using various mineral raw materials.

Various types of plutonic and volcanic rocks and their alteration products from Greece (serpentinite, magnesite and andesite), have been used for sustainable removal of Uranium (U) from the acidic drainage of Kirki mine, as well as for the pH increase of the polluted solutions. In this light, this study aims at the further understanding and improvement of the ecofriendly reuse of sterile, natural raw materials (including those remaining through industrial processing and engineering testing of aggregate rocks), for remediation of acid mine drainage. The selected rocks constitute such residues of sterile materials were used as filters in experimental continuous flow devices in the form of batch-type columns, in order to investigate acidic remediation properties with special focus on U removal. The initial pH of the wastewater was 2.90 and increased after seven (7) days of experimental application and more specifically from the fourth day onwards. Uranium removal became quantitatively significant once pH reached the value of 5.09. The volcanic rocks appeared to be more effective for U removal than the plutonic ones because of microtextural differences. However, optimum U removal was mainly achieved by serpentinite: while the raw materials rich in Mg strongly reacted and remediated the pH of the drainage water waste. Furthermore, the increase of pH values due to the presence of mineral raw materials, provided increased oxidation potential which deactivated the toxic load of metals, particularly U. Consequently, batch-type serpentinite reaction with the tailing fluid caused a drop in U concentration from an initial value of 254 ppb to the one of 8 ppb, which corresponds to 97% of removal. Andesite presented the second best reactant for experimental remediation, especially when it was mixed with magnetically separated mineral fractions. Despite the fact that the proposed methodology is currently at a relatively low Technology Readiness Level (TRL), it carries the potential to become an extremely effective and low-cost alternative to conventional environmental restoration technologies.

The role of the aggregate shape on the compressive strength of concrete using a new micro geo-informatics methodology.

In this paper the results of an experimental study on the behavior of aggregate shape on the compressive concrete strength was described. The main scope of that work is to answer whether there is a low-cost, low-energy methodology for predicting the behavior of an aggregate within a concrete and therefore its ultimate strength. This was achieved by using a combination of petrographic methods with GIS and MatLab software in a variety of lithologies when simultaneously producing a new micropetrographic index (Mshape) for the first time. For this reason, variable rocks such as sandstones, ultramafic, mafic and volcanic have been collected from Greece which are used as aggregates. Their petrographic characteristics as well as their geometrical properties were studied and hence their influence on concrete production. In the present study, a new micro-petrographic index is proposed based on the present proposed methodology which is able to act as a predictor of the aggregates shape and therefore of their behavior and suitability. Mshape index is strongly correlated with the geometrical indices of shape IE and IF as well as with the concrete strength.

Effectiveness of X-ray micro-CT applications upon mafic and ultramafic ophiolitic rocks.

X-ray micro-computed tomography (µCT) was applied upon selected ophiolitic rock samples from various localities of the Vardar ophiolite outcrops in North Greece. Effectiveness of the µCT application was evaluated through this case study by comparing results with other state-of-the-art techniques (e.g., optical microscopy, mineral chemistry microanalyses, XRD and QEMSCAN) to provide suggestive methodologies for optimum characterization, geological modeling, and visualization of ophiolitic rocks. The research outcomes provide an innovative approach for accurate modal composition calculations, crystal structure and mineral distribution in a 3D perspective, by combining µCT results with mineral chemical analyses. The information obtained is critical for investigating ophiolitic rocks to resolve complex petrogenetic and post-magmatic phenomena, to identify fabrics related to deformation, and furthermore results can also be used for applied research purposes. The obtained µCT results suggest that distributions of mineral's grayscale values strongly rely on three key factors: (i) participation of mineral phases with distinct attenuation coefficient and/or density properties, (ii) coexistence of different mafic minerals or mafic with non-mafic phases, (iii) variability in their mineral chemistry. The ability to analyze and visualize the internal mineral constituents of ophiolitic rocks samples, through the combination of µCT and Energy-Dispersive X-ray spectroscopy (EDS), can lead to advanced 3D stereological rock fabric analyses, which is advantageous compared to 2D methodologies. The µCT allowed to perform rock fabric calculations (best-fit ellipsoids and with volume) upon specified grain size distributions to identify and characterize the 3D morphological properties of the participating crystals and their preferable orientation.