A Computational Fluid Dynamic (CFD) model of a lead oxide mass exchanger (PbO MX) was developed. The mass exchanger consisted of a packed bed of PbO spheres. The geometry was created using Discrete Elements Method (DEM) software while the meshing, the solving and the post-processing were done by the commercial CFD package CFX. The dissolution process was modeled by implementing in the code oxygen mass transfer through the boundary layer. The dissolution rate was then predicted for different temperatures. Experiments were also performed at the LBE material test loop known as the DELTA loop. Oxygen concentration at the outlet of the PbO MX was measured for different conditions using a potentiometric oxygen sensor and the dissolution rate was determined for five different temperatures. The experimental data were compared with the numerical model. The temperature dependence of the dissolution rate was then determined in terms of Sherwood number by fitting the simulation results while keeping constant Reynolds number. The results showed that the Sherwood number for PbO MX in flowing LBE varies with Sc^0.323.