Mineral Processing
Aghil Haghdadi; Sima Mohammadnejad
Abstract
The presence of copper bearing minerals in cyanidation of gold ores may lead to several challenges in the CIP/CIL circuits. Many solutions have been proposed to address these problems, one being the use of glycine in the cyanidation process. Here, the experimental as well as molecular modelling studies ...
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The presence of copper bearing minerals in cyanidation of gold ores may lead to several challenges in the CIP/CIL circuits. Many solutions have been proposed to address these problems, one being the use of glycine in the cyanidation process. Here, the experimental as well as molecular modelling studies using Density Functional Theory (DFT) have been conducted to investigate the glycine role in cyanidation of copper bearing gold ores. The results show that in the presence of glycine in the solution containing copper-cyanide species and in very low or zero free cyanide content, the dissolution rate of gold is significantly improved (3.02 vs. 0.23 ppm), while no improvement is observed in copper free or cyanide enriched solutions. Molecular modeling has been performed to interpret the laboratory results as well as to identify the mechanisms. The modeling results demonstrate that in cyanide deficient solutions, cyanide complex of copper complexes (E = -319 kCal.mol-1) is replaced by glycine, and the free cyanide produced results in higher gold cyanidation as well as lower copper cyanide formation.
Sina Ghasemi; Sima Mohammadnejad; Mohammad Reza Khalesi
Abstract
The adsorption of gold and copper cyanide complexes on the activated carbon is investigated using the Density Functional Theory (DFT). In order to represent the activated carbon, two fullerene-like model (presenting structural defect sites) and a simple graphene layer containing different functional ...
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The adsorption of gold and copper cyanide complexes on the activated carbon is investigated using the Density Functional Theory (DFT). In order to represent the activated carbon, two fullerene-like model (presenting structural defect sites) and a simple graphene layer containing different functional groups (presenting chemical active sites) are employed. The structural defect sites show a much lower adsorption tendency toward all the cyano complexes comparing to the chemical active sites. The interaction energy for all of the complexes with structural defect sites (concave) is very low. However, the graphene layer with unsaturated active sites displays the highest level of interaction almost for all the complexes except Cu(CN)4-3. The effect of oxygen functional groups on the graphite edges shows a crucial role in the selectivity of gold adsorption over copper complexes. It has increased adsorption energy for Cu(CN)2- in the presence of OH and COOH, and has decreased adsorption energy for Au(CN)2- by OH and increased by COOH. The study results elucidate the lower selectivity for adsorption of gold over copper cyanides by high oxygen content activated carbon. The energy levels of the HOMO and LUMO orbitals show adsorption of unpaired cyanide anions on the activated carbon surface occurs by electron transfer from the complex to the adsorbent and adsorption onto the activated carbon edges by transferring electrons from the absorbent to the complex. The result has clearly demonstrated that the functional groups increase the adsorption tendency for both the gold (only COOH) and copper complexes (OH and COOH) but deteriorate the selectivity of gold over copper cyanides.
Mineral Processing
M. Mohseni; M. Abdollahy; R. Poursalehi; M. R. Khalesi
Abstract
The reactivity of the protonated and hydroxylated sphalerite (1 1 0) surface with xanthate was simulated using the density functional theory (DFT). The difference between the energy of the lowest unoccupied molecular orbital of the sphalerite surface and the energy of the highest occupied molecular orbital ...
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The reactivity of the protonated and hydroxylated sphalerite (1 1 0) surface with xanthate was simulated using the density functional theory (DFT). The difference between the energy of the lowest unoccupied molecular orbital of the sphalerite surface and the energy of the highest occupied molecular orbital of xanthate ( was used to compare the reaction capability of xanthate with fresh and functionalized surfaces. The Mulliken atomic charge analysis was used to provide an in-depth insight into the effects of –H+ and –OH- groups on the reactivity of Zn atoms at the sphalerite surface. The values for different systems showed that the protonated surfaces exposed a higher reactivity with xanthate than the fresh and hydroxylated surfaces. The results of the Mulliken atomic charge analysis demonstrated that after the formation of –H+ and –OH- contained groups on the sphalerite surface, the surface atoms found a new charge due to the reduction and oxidation mechanism. In addition, the results obtained revealed that the electrophilicity of Zn atoms after the ion adsorption could be considered as a key factor in the reactivity of the sphalerite surface with xanthate. The DFT-based calculations also showed that different alkyl groups of xanthate had no significant influence on the reactivity of their head groups. The findings of this research work provided insights into the reactions of the sphalerite surface with xanthate.
