Summary: Here we consider a magnetized plasma composed of electrons of low mean density and of one species of multicharged ions. Starting with the Vlasov-Fokker-Planck equations for both particles, we derive a diffusion model for the electrons, with explicit transport coefficients which are related to the ions. Finally, we study the kinetic boundary layers in the case of a bounded domain in space variables. For that purpose, we are led to study a Milne problem and to introduce a generalized extrapolation length.