Reaction Rate Study: Oxidative Pressure Leaching Process

REACTION KINETICS

Reaction rate studies conducted at conditions similar to industrial conditions provides valuable engineering data for full scale reactor design.

In a typical oxidative pressure leaching process, the mass transfer that is required to sustain a heterogeneous reaction takes place at the boundary between two phases, which is called the reaction interface. Obviously one of the phases is solid, so it is the reaction at the solid surface.The total reaction rate of heterogeneous processes is controlled by the rate of the slowest step.

Figure 5 1 below shows a schematic diagram of the sequential process (1 to 6) for the leaching reaction of a solid particle

Dispersion of oxygen into the pulp Fluid film mass transfer Diffusion

Unreacted shrinking core model

The unreacted shrinking core model is applied when the reactant is converted to another solid material leaving behind a product layer around the unreacted particle core.

Figure 5.3: Schematic diagram of shrinking core model

The mathematical description of the shrinking core model under product diffusion control is based on the following assumptions The particle is considered to maintain its shape and size during the entire leaching process The low reaction and product concentrations in solution means the net flux due to diffusion is considered negligible The surface reaction is assumed to be first order and irreversible with respect to the reacting reagent. The reaction reagent is in excess and its concentration may be considered constant during the entire leaching process. The system may be considered to be in quasi steady state.

Considering J to be the flux of B in Reaction 5.2 through a product layer in time t, then from Fick’s law: "J = -4π" "l" ^"2" "D" _"s" "dC" /"dl"