Bioleaching is an actual economical alternative to treat residues, which allows, depending on the chosen strategy, two possible outcomes: (1) a leachate enriched with target metals, or (2) a residue enriched in target metals through the leaching of interfering components (IC). This work aimed to study the metals released by bioprocessing the Panasqueira mine tailings, as a strategy to increase critical metals' relative concentration in residues. Biostimulation of the local microbiota was compared to a bioaugmentation approach using the autochthonous Diaphorobacter polyhydroxybutyrativorans strain B2A2W2. Inductively Coupled Plasma Mass Spectrometry (ICP-MS) was selected to study the metals released in the leachate through multi-element external standards. A new data treatment method was developed to use a preliminary sweep of intensities to quantify the non-initial target metals concentration in the leachate, based on preliminary ICP-MS intensity measurements. The results demonstrated that biostimulation was an efficient bioleaching strategy for the IC silicon, aluminium, magnesium, selenium, manganese, zinc, iron, and copper, by decreasing concentration, resulting in a relative increase in the gallium and yttrium (10x) levels in the treated residue. The strategy followed to quantify a large number of elements with ICP-MS using a reduced number of data points for calibration proved valid and speeded up the analytical process.

Vibrational and electronic absorption spectra calculated at the (time-dependent) density functional theory level for the bismuth carbide clusters Bi n C + 2n (3 ≤ n ≤ 9) indicate significant differences in types of bonding that depend on cluster geometry.Analysis of the electronic charge densities of these clusters highlighted bonding trends consistent with the spectroscopic information. The combined data suggest that larger clusters (n > 5) are likely to be kinetically unstable in agreement with the cluster mass distribution obtained in gas-aggregation source experiments. The spectral fingerprints of the different clusters obtained from our calculations also suggest that identification of specific Bi n C + 2n isomers of should be possible based on infra-red and optical absorption spectroscopy.

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