  We study the thermalization, injection, and acceleration of ions with
different mass/charge ratios, $A/Z$, in non-relativistic collisionless shocks
via hybrid (kinetic ions-fluid electrons) simulations. In general, ions
thermalize to a post-shock temperature proportional to $A$. When diffusive
shock acceleration is efficient, ions develop a non-thermal tail whose extent
scales with $Z$ and whose normalization is enhanced as $(A/Z)^2$, so that
incompletely-ionized heavy ions are preferentially accelerated. We discuss how
these findings can explain observed heavy-ion enhancements in Galactic cosmic
rays.
