Investigative study into the hydrodynamics of heap leaching processes

Three mathematical models (mixed side-pore diffusion (MSPD) and profile side-pore diffusion (PSPD) with uniform or distributed pore lengths) are derived in dimensionless form to simulate the transport of solutes through the flowing channels and the stagnant pores of an unsaturated heap. Model parameters are determined from experimental tracer residence-time distributions using the least-squares minimization approach. It is shown that the residence-time distribution curves display a long tail resulting from the very slow mass transfer (or diffusion) into the 1- to 6-cm-long stagnant pores, which take up 5 times more space than the flowing liquid. The very large coefficients of determination (R-2 > 0.99) confirm the validity of all models and especially that of the PSPD model with a distributed pore length. The effects of five factors (agglomeration, addition of binder, particle size, solution flow rate, and bed height) are examined. Data from experimental residence-time distributions prove that the advection time is directly proportional to the column height and inversely proportional to the flow rate. The two estimated parameters (stagnant liquid holdup and pore length) are only marginally affected by any change in crush size, agglomeration technique, or operating conditions. This, in turn, suggests that the model can predict and/or simulate the hydrodynamic behavior in taller columns and, possibly, heaps.