Al2+ (320 keV) ion implantations at room temperature for doses ranging from 3 × 1011 to 3 × 1014 ions cm−2 have been performed in p-type Hg0.78Cd0.22Te. The samples were analyzed by infrared reflectivity providing quantitative results on electrically active defects. A change of type of the free carriers is observed after implantation, for all doses, in a region of thickness greater than the projected range of ions. The dominant phenomena in this change of type seems to be the diffusion of Hg interstitials which takes place during implantation. From 3 × 1011 to 3 × 1013 ions cm−2, the diffusion length of Hg interstitials follows a classical equation with a linear dependence on the squareroot of the implantation time. For doses greater than 3 × 1013 ions cm−2, Hg interstitials diffuse less efficiently. This could be due to the capture of some single interstitials by interstitial dislocation loops as observed by diffuse X-ray scattering.