ABSTRACT
Metal-deficient polysulfides have been argued for a long time to be responsible for the low kinetics of chalcopyrite leaching to extract copper. It has been shown that chalcopyrite surfaces are the source of sulfur that is oxidized to form polysulfides and elemental sulfur. Electronic structure calculations were performed for HxSnx-2 (x = 0, 1, 2 and n = 1...20), aiming to understand the effect of the pH on the growing chains and the formation of elemental sulfur. The estimated pKa1 of the H2Sn polysulfides converges from 4.2 (n = 3) to 3.4 (n ≥ 8), and the estimated pKa2 converges from 7.6 (n = 3) to 4.1 (n ≥ 8). The initial steps of the formation of polysulfide chains are more favored for protonated species. The elemental sulfur formation due to the decomposition of polysulfides to form smaller chains is mostly favored for protonated species with n smaller than 12. For larger chains, the decomposition is thermodynamically favored for polysulfides with any degree of protonation. The consequences of these results to the understanding of the mechanism of the chalcopyrite leaching process are discussed with the focus on the pH effect and the formation of elemental sulfur.
ABSTRACT
The use of theoretical calculation to determine structural properties of fulvate-metal complex (zinc, copper and iron) is here related. The species were proposed in the ratio 1:1 and 2:1 for which the molecular structure was obtained through the semi-empirical method PM6. The calculation of thermodynamic stability ([Formula: see text]) predicted that the iron complex were more exo-energetic. Metallic ions were coordinated to the phtalate groups of the model-structure of fulvic acid Suwannee River and the calculations of vibrational frequencies suggested that hydrogen bonds may help on the stability of the complex formation.
Subject(s)
Benzopyrans/chemistry , Coordination Complexes/chemistry , Copper/chemistry , Iron/chemistry , Zinc/chemistry , Hydrogen Bonding , Hydrogen-Ion Concentration , Models, Molecular , Molecular Conformation , ThermodynamicsABSTRACT
The combined use of ESI-MS (electrospray ionization-mass spectrometry) and theoretical calculations for the determination of citrate:metal (metal=Cu and Fe) structures are reported. Mass spectrometry allowed to determine the stoichiometry 1:1 and 2:1 of the complexes, corroborating the theoretical calculations. The species found in the ratio 2:1 had their calculated structures readjusted, from what was originally simulated, since the deprotonation of citric acid differed from what was before simulated. The thermodynamic stability (ΔH(aq.)(0)) of the complexes optimized at the B3LYP/LANL2DZ level was more exoenergetic than for the complexes found by the PM6 semi-empirical method.
Subject(s)
Citrates/chemistry , Coordination Complexes/chemistry , Copper/chemistry , Ferric Compounds/chemistry , Mass Spectrometry , Spectrometry, Mass, Electrospray Ionization , ThermodynamicsABSTRACT
The combined use of ESI-MS, FTIR-ATR and theoretical calculations for the determination of metal-citrate (metal=Cd and Pb) structures are reported. Mass spectrometry allowed to determine the stoichiometry 1:1 and 2:1 of the complexes, corroborating the theoretical calculations. The species found in the ratio 2:1 had their molecular structures readjusted, since the deprotonation of citric acid differed from what was simulated. The calculations of thermodynamic stability (ΔH(0)(aq.)) for the complexes obtained by B3LYP/LANL2DZ were more exoenergetic than those found by PM6. However, for both methods, the stability of the complexes follows a trend, that is, the lowest-energy isomers in PM6 are also the most stable in B3LYP/LANL2DZ. The infrared analysis suggested that carboxyl groups are complexation sites and hydrogen bonds can help in the stability of the complexes. The vibrational frequencies in B3LYP/LANL2DZ had a good correlation with the experimental infrared results.
