Geochemical investigations of noble metal-bearing ores: Synchrotron-based micro-analyses and microcosm bioleaching studies.

Auriferous sulphide ores often incorporate micro-fine (or invisible) gold and silver particles in a manner making their extraction difficult. Nobel metals are lost in the tailings due to the refractory nature of these ores. Bioleaching is an environment-friendly alternative to the commonly used and toxic cyanidation protocols for gold extraction from refractory ores. In this paper, we investigate gold and silver bioleaching from porphyry and epithermal mineralisation systems, using iron-oxidizing bacteria Acidithiobacillus ferrooxidans. The invisible Au, sequestered in refractory ores, was characterised in situ by synchrotron micro X-Ray Fluorescence (SR-µ-XRF) and X-ray Absorption Spectroscopy (XAS), offering information on Au unaltered speciation at the atomistic level within the ore matrices and at a micro-scale spatial resolution. The SR-µ-XRF and XAS results showed that 10-20 µm sized elemental Au(0) nuggets are sequestered in pyrite, chalcopyrite, arsenopyrite matrices and at the interface of a mixture of pyrite and chalcopyrite. Moreover, the preliminary bioleaching experiments of the two types of ores, showed that Acidithiobacillus ferrooxidans can catalyse the dissolution of natural heterogeneous Fe-rich geo-matrices, sequestering Au and Ag and releasing particulate phases or partially solubilising them within 60 days. These results provide an understanding of noble metal sequestration and speciation within natural ores and a demonstration of the application of synchrotron-based micro-analysis in characterizing economic trace metals in major mineral structures. This work is a contribution to the ongoing efforts towards finding feasible and greener solutions of noble metal extraction protocols.

Wind erosion on arable lands, associated with extreme blizzard conditions within the hilly area of Eastern Romania.

The removal of wind-blown soils from cultivated fields is often expensive. It physically removes the most fertile portion of the soil that can lead to yield reduction in areas where wind erosion is a recurring problem. Soil nutrients and surface-applied chemicals can also be carried along with soil particles, contributing to off-site impacts. An extreme blizzard event has been investigated as case study within the Moldavian Plateau of eastern Romania. The results obtained, based on 45 snow core samples, show that the deposited sediment widely varied depending on land-use. The highest mean value of 5967 g m-2 occurred on fallow land and it sharply decreased under winter wheat (445 g m-2) and pasture (345 g m-2). Regarding the major subunits of the Moldavian Plateau, the Jijia Rolling Plain (JRP) was the most affected, with mean value of 7547 g m-2. The Barlad Plateau (BP) and the Falciu Rolling Plain (FRP) are depicted by smaller values, namely: 395 g m-2 and 386 g m-2. By using remote sensing it was estimated that 208,990 ha under fallow from JRP (34% of the total) were heavily subjected to wind erosion with a mean soil loss of 2.04 t ha-1, while the depositional area comprised 175,440 ha (29% of the total). The deposited soil is loamy compared with the general clayey-loamy texture of local soils. The main source of the wind-blown material is represented by the close proximity fields under fallow of the depositional areas.

Fractional Factorial Design Study on the Performance of GAC-Enhanced Electrocoagulation Process Involved in Color Removal from Dye Solutions.

The aim of this study was to determine the effects of main factors and interactions on the color removal performance from dye solutions using the electrocoagulation process enhanced by adsorption on Granular Activated Carbon (GAC). In this study, a mathematical approach was conducted using a two-level fractional factorial design (FFD) for a given dye solution. Three textile dyes: Acid Blue 74, Basic Red 1, and Reactive Black 5 were used. Experimental factors used and their respective levels were: current density (2.73 or 27.32 A/m²), initial pH of aqueous dye solution (3 or 9), electrocoagulation time (20 or 180 min), GAC dose (0.1 or 0.5 g/L), support electrolyte (2 or 50 mM), initial dye concentration (0.05 or 0.25 g/L) and current type (Direct Current-DC or Alternative Pulsed Current-APC). GAC-enhanced electrocoagulation performance was analyzed statistically in terms of removal efficiency, electrical energy, and electrode material consumptions, using modeling polynomial equations. The statistical significance of GAC dose level on the performance of GAC enhanced electrocoagulation and the experimental conditions that favor the process operation of electrocoagulation in APC regime were determined. The local optimal experimental conditions were established using a multi-objective desirability function method.