Solid-to-liquid mass transfer as a result of liquid flow through static and dynamic assemblies of mono-sized solid spheres has been simulated. The three-dimensional, transient simulations fully resolve the flow of liquid in the interstitial space between the spheres by means of a lattice-Boltzmann scheme. For the mass transfer process, a finite volume method on Coupled Overlapping Domains (CODs) is used. Spherical grids around the particles allow for resolving the thin scalar concentration boundary layers that are the result of high Schmidt numbers (Sc up to 1000). The spherical grids - one for each sphere - are coupled to an outer cubic grid. Particle-based Reynolds numbers are in the range 1-10; solids volume fractions are 0.15-0.40. The results demonstrate the validity of the COD approach for multi-particle systems, and provide insight in the dependencies of the Sherwood number on the solid-liquid system characteristics. It is shown that for moderate solid-over-liquid density ratios, fluidized particle assemblies have lower Sherwood numbers than fixed beds. (C) 2014 Elsevier B.V. All rights reserved.