In this manuscript, the chemi-ionization (CI) processes in atom - Rydberg atom collisions are examined. We obtained the cross-sections, as well as rate coefficients for CI processes in potassium and sodium collisions for principal quantum numbers 5⩽n⩽25 in the 500 K ⩽T⩽1500 K temperature region. The presented data could be useful for the improvement of analysis and modelling of weakly ionized layers of different atmospheres and cosmic objects where these and other CI processes could change excited state populations and the free electron density, consequently affecting the optical characteristics.