Sima Mohammadnejad; Davood Alavi; Seyed Mohammad Javad Koleini
Abstract
In this work, the mechanism of zinc hydroxide and ammine complexation in caustic and ammonia leaching is investigated by molecular modelling using the density functional theory method. The speciation of zinc complexes is defined based on the thermodynamic data and Pourbiax diagrams. The mechanism of ...
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In this work, the mechanism of zinc hydroxide and ammine complexation in caustic and ammonia leaching is investigated by molecular modelling using the density functional theory method. The speciation of zinc complexes is defined based on the thermodynamic data and Pourbiax diagrams. The mechanism of Zn+2 complexation by hydroxide and ammine ligands is simulated by molecular modeling. The structure of reactants in the form of individual clusters is modelled using the density function theory. In order to compare the hydroxide and ammine species structures, the geometry studies are carried out as well. The ammoniacal salt effectiveness to improve the dissolution and stability of the ammine species is studied. The ligand single molecule interaction with a smithsonite molecule is done for a better understanding. Molecular modeling show that the zinc hydroxide species are more stable based on the higher reaction free energies. The reaction free energies decrease by adding the OH- and NH3 ions to the complexes from -30.12 kcal/mol to -16.943 kcal/mol, and -22.590 kcal/mol to 66.516 kcal/mol, respectively. The Zn-OH bonds are shorter than Zn-NH3, and the ammine species show more regular structures in comparison with the hydroxide structures. The change of free energies in the presence of ammoniacal salts indicate that the sulfate ions can significantly improve the dissolution of zinc oxide in ammonia. The smithsonite interaction with ammonia and hydroxide reveal that hydroxide ions lead to a higher interaction energy than ammonia (-36.396 vs. -28.238), which is consistent with the higher stability of hydroxide species. The results obtained well-explain the experimental results obtained before, and can be effectively used to optimize the alkaline leaching of zinc oxide ore.
M. Hasani; Seyed M. J. Koleini; A. Khodadadi
Abstract
In the present work, the extraction of zinc from a sphalerite concentrate using sodium nitrate as an oxidant in a sulfuric acid solution was investigated. The effective parameters such as the temperature, sulfuric acid and sodium nitrite concentrations, stirring speed, particle size, and solid/liquid ...
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In the present work, the extraction of zinc from a sphalerite concentrate using sodium nitrate as an oxidant in a sulfuric acid solution was investigated. The effective parameters such as the temperature, sulfuric acid and sodium nitrite concentrations, stirring speed, particle size, and solid/liquid (S/L) ratio were analyzed. The dissolution rate increased with increase in the sulfuric acid and sodium nitrite concentrations and temperature but decreased with increase in the particle size and S/L ratio. Moreover, the stirring speed had a significant effect on the leaching rate. Under the optimum conditions, 74.11% of zinc was obtained. The kinetic data obtained was analyzed by the shrinking core model (SCM). A new SCM variant captured the kinetic data more appropriately. Based on this model, the activities of the reactants control the diffusion but the two concentrations affect the second order reaction rate or diffusion in both directions. At 75 ˚C, the R2 values in the surface chemical reactions and diffusion were 0.78 and 0.89, respectively. Using the new model, however, the R2 value 0.989 was obtained. The reaction orders with respect to [H2SO4], [NaNO3], S/L ratio, and particle size were 1.603, 1.093, ‒0.9156, and ‒2.177, respectively. The activation energy for the dissolution was 29.23 kJ/mol.
M. R. Tavakoli Mohammadi; Seyed M. J. Koleini; M. Abdollahy
Abstract
Efforts to increase the mass transfer coefficient, enhance the contact area, and decrease the power input of contractors have given risen to the development of the pre-dispersed solvent extraction (PDSE) contactor and the devise of the new dissolved nitrogen PDSE (DNPDSE) contactors. The studies conducted ...
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Efforts to increase the mass transfer coefficient, enhance the contact area, and decrease the power input of contractors have given risen to the development of the pre-dispersed solvent extraction (PDSE) contactor and the devise of the new dissolved nitrogen PDSE (DNPDSE) contactors. The studies conducted after the design of the new contactor to determine the working conditions for its suitable performance (2.5-3.5 bar pressure, 0.1 L/min sparger flow rate, and 1.5 L of the aqueous phase) showed that for all the evaluated conditions (i.e. the pressure, polyaphron type, and dilution percentage), the recovery in the DNPDSE contactor was higher than that in the PDSE one. In addition, pictures of the performance modes of the two contactor indicated the presence of the organic phase in the form of colloidal gas aphrons (CGAs) in the DNPDSE contactor and of polyaphron aggregations in the PDSE one. This is a good reason for the increased copper recovery in the DNPDSE contactor. The best recovery for the extraction process in the DNPDSE contactor was achieved using the anionic polyaphron of sodium dodecylbenzene sulphonate (NaDBS) with five-fold dilution at 3.5 bar.
sima razmjouee; mahmood abdollahy; seyed mohammad javad koleini
Abstract
Using microflotation method, this study explored the collectorless flotation of Chalcocite and its dependence on the redox potential of pulp . Electrochemical studies were performed by cyclic voltammetry in specific potential ranges and at different pH values. The results show that significant ...
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Using microflotation method, this study explored the collectorless flotation of Chalcocite and its dependence on the redox potential of pulp . Electrochemical studies were performed by cyclic voltammetry in specific potential ranges and at different pH values. The results show that significant floatability of Chalcocite occurs in the specific reducing conditions. By increasing potentials, on the other hand, the floatability of Chalcocite is reduced. The effect of pH was also examined: At pH=4, the maximum recovery of 73%, was obtained at E= -222 mV (Eh= -17); and at pH=9, the maximum recovery of 71% was obtained at E= -501 mV (Eh= -296). On the basis of the results obtained, the possible mechanisms of collectorless flotation of Chalcocite in different conditions were discussed.
