High‐shear impellers (HSIs) are mixers used in industrial stirred tanks to incorporate powders in... more High‐shear impellers (HSIs) are mixers used in industrial stirred tanks to incorporate powders into liquids and break down particle agglomerates. A detailed numerical study of two commercial ring‐style HSIs of laboratory scale was carried out and their performance was compared with the Rushton turbine (RT). It was found that power and pumping numbers or their ratio cannot be simply connected for properly selecting an impeller in applications where highly localized viscous dissipation is desirable. The ratio of the average viscous dissipation in the impeller swept volume to the mean in the entire volume at two constant values of power input turned out to be lower for HSIs compared to that evaluated for RT. However, at higher power input, the dimensionless average viscous dissipation in the blade swept volume was found to be similar for the HSI of two rings and the RT, corroborating the high local viscous dissipation of this HSI when operated at higher speeds.
ABSTRACT A systematic electrochemical study at controlled potential, using a rotating cylinder el... more ABSTRACT A systematic electrochemical study at controlled potential, using a rotating cylinder electrode reactor, was carried out on a synthetic solution with composition 0.2mol/L Na2S2O3, 0.05mol/L CuSO4, 0.025mol/L EDTA, 0.6 mo/L NH3, 1 × 10− 3mol/L AgNO3, which simulates actual leaching solution, to determine the conditions which permit the selective silver electroseparation with a minimum interference from the copper ions. The presence of 10 ppm of gold (5 × 10− 4M Au(I)) was found to enhance the gold–silver alloy deposition, with negligible effect on the copper ions. Those results were compared to that obtained with solutions originating from a previously characterized sulfide concentrate leach, in order to determine the influence of other impurities present in the pregnant solution, on the selective silver electrodeposition, obtaining averaging current efficiencies of 80%, with 90% of silver in the formed deposit and less than 5% of both, copper and lead, with only minor quantities of iron and zinc. Additionally, it was shown that the resulting solution could be recycled back to the leach stage, obtaining similar performances to those produced by the fresh solution, implying that it was not significantly altered in its composition, by the electroseparation process.
... In the reverse scan, two oxidation peaks (A1 and A2) may be noted. It is possible that A2 is ... more ... In the reverse scan, two oxidation peaks (A1 and A2) may be noted. It is possible that A2 is associated to the oxidation of thiosulfate ( [Breuer and Jeffrey, 2003] , [Byerley et al., 1973] , [Molleman and Dreisinger, 2002] , [Pedraza et al., 1988] and [Rolia and Chakrabarti, 1982] ). ...
The chemistry of precious metal ammoniacal thiosulfate leaching is very complex, especially with ... more The chemistry of precious metal ammoniacal thiosulfate leaching is very complex, especially with additives, such as EDTA, which are used to stabilize the major reactants in this system. Lead, which is co-extracted in these solutions, can be a large consumer of both EDTA and thiosulfate, decreasing the leaching capacity for gold and silver. In this research, thermodynamic analyses for different
High‐shear impellers (HSIs) are mixers used in industrial stirred tanks to incorporate powders in... more High‐shear impellers (HSIs) are mixers used in industrial stirred tanks to incorporate powders into liquids and break down particle agglomerates. A detailed numerical study of two commercial ring‐style HSIs of laboratory scale was carried out and their performance was compared with the Rushton turbine (RT). It was found that power and pumping numbers or their ratio cannot be simply connected for properly selecting an impeller in applications where highly localized viscous dissipation is desirable. The ratio of the average viscous dissipation in the impeller swept volume to the mean in the entire volume at two constant values of power input turned out to be lower for HSIs compared to that evaluated for RT. However, at higher power input, the dimensionless average viscous dissipation in the blade swept volume was found to be similar for the HSI of two rings and the RT, corroborating the high local viscous dissipation of this HSI when operated at higher speeds.
ABSTRACT A systematic electrochemical study at controlled potential, using a rotating cylinder el... more ABSTRACT A systematic electrochemical study at controlled potential, using a rotating cylinder electrode reactor, was carried out on a synthetic solution with composition 0.2mol/L Na2S2O3, 0.05mol/L CuSO4, 0.025mol/L EDTA, 0.6 mo/L NH3, 1 × 10− 3mol/L AgNO3, which simulates actual leaching solution, to determine the conditions which permit the selective silver electroseparation with a minimum interference from the copper ions. The presence of 10 ppm of gold (5 × 10− 4M Au(I)) was found to enhance the gold–silver alloy deposition, with negligible effect on the copper ions. Those results were compared to that obtained with solutions originating from a previously characterized sulfide concentrate leach, in order to determine the influence of other impurities present in the pregnant solution, on the selective silver electrodeposition, obtaining averaging current efficiencies of 80%, with 90% of silver in the formed deposit and less than 5% of both, copper and lead, with only minor quantities of iron and zinc. Additionally, it was shown that the resulting solution could be recycled back to the leach stage, obtaining similar performances to those produced by the fresh solution, implying that it was not significantly altered in its composition, by the electroseparation process.
... In the reverse scan, two oxidation peaks (A1 and A2) may be noted. It is possible that A2 is ... more ... In the reverse scan, two oxidation peaks (A1 and A2) may be noted. It is possible that A2 is associated to the oxidation of thiosulfate ( [Breuer and Jeffrey, 2003] , [Byerley et al., 1973] , [Molleman and Dreisinger, 2002] , [Pedraza et al., 1988] and [Rolia and Chakrabarti, 1982] ). ...
The chemistry of precious metal ammoniacal thiosulfate leaching is very complex, especially with ... more The chemistry of precious metal ammoniacal thiosulfate leaching is very complex, especially with additives, such as EDTA, which are used to stabilize the major reactants in this system. Lead, which is co-extracted in these solutions, can be a large consumer of both EDTA and thiosulfate, decreasing the leaching capacity for gold and silver. In this research, thermodynamic analyses for different
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Papers by ALEJANDRO ALONSO