Enhancement of gas-liquid mass transfer in hydrometallurgical leaching systems.

摘要

The influence of gas-liquid reactions on oxygen mass transfer in three hydrometallurgical leaching systems under typical operating conditions has been investigated and assessed in terms of enhancement factors and Hatta numbers.; Mass transfer rates and interfacial areas were determined simultaneously in order to obtain the parameters necessary for the evaluation of the enhancement factors. The progress of Fe(II) oxidation was followed by sampling and titration, whereas the progress of Cu(I) oxidation was followed by measuring the rate of oxygen consumption using gas mass flowmeters. Reactant concentrations in the two copper systems were estimated using a speciation routine based on the minimization of Gibbs free energy.; Hatta numbers obtained from Fe(II) oxidation tests under a flat interface were greater than 3, situating the reaction in the very fast regime. However, similar values evaluated from tests carried out in a well-agitated reactor fell between 0.3 and 3, categorizing the reaction in the intermediate regime. An instantaneous reaction model in the two copper systems successfully modeled experimental results from well-agitated reactor tests. Results of speciation calculations indicate that metallic copper existed prior to the introduction of oxygen when the metallic copper charge exceeded 5 g/L in sulphate media. However, all of the metallic copper was converted to Cu(I) in ammoniacal media. Enhancement factors estimated from flat interface data indicated that the reactions in the two systems fall under the very fast reaction regime, complementing the well-agitated reactor test results.; Based on the results, it is concluded that oxygen mass transfer rates may be determined using the gas-liquid reactions typically taking place in certain hydrometallurgical systems. The Hatta numbers and enhancement factors obtained indicate that all solutions are depleted of oxygen at the high concentrations of Fe(II) and Cu(I) in both sulphate and ammoniacal media, and therefore, the use of oxygen solubility in solving the kinetic equations appears to be suspect. The nature of the gas-liquid interface (stagnant film versus surface renewal) has a notable effect on both the kinetics of Fe(II) oxidation and oxygen mass transfer. In the two Cu(I) systems, oxygen mass transfer is enhanced several times over the maximum possible rate of physical absorption under the same conditions. Finally, with some modifications it would be possible to evaluate mass transfer parameters directly from the rate of Cu(I) oxidation in either sulphate or ammoniacal media. (Abstract shortened by UMI.)