Liquid axial dispersion and holdup in column leaching

Abstract

The liquid phase hydrodynamics in column and heap leaching is a key design aspect that has attracted some attention, but was not yet completely elucidated. On the other hand, conventional trickle bed catalytic reactors have received enormous attention for many decades; however, the operational variables range in this case is generally far from the column and heap leaching processes. This paper presents a hydrodynamic study performed in a bench scale column, where the axial dispersion and the liquid holdup, as a function of the liquid flow rate, are estimated using residence time distribution experiments. The normalized tracer concentrations are fitted using a non-linear least square method and the piston-dispersion-exchange model that is solved numerically using the finite differences method. The trends of axial dispersion, dynamic and static saturation, and exchange coefficient for mass exchange between mobile and stagnant phases, showed excellent agreement with previous results for low Reynolds number in conventional trickle bed reactors. In this study, these experimental results and empirical correlations are presented. The dynamic saturation of the bed increases with the flow rate while the static saturation decreases slightly. The axial dispersion is weak dependent of the liquid flow rate, but is non-negligible and should be accounted for in the mathematical modeling of heap and column leaching process.