  We present a theoretical study of resonance characteristics in graphene from
adatoms with $s$ or $p_z$ character binding in top, bridge, and hollow
positions. The adatoms are described by two tight-binding parameters: onsite
energy and hybridization strength. We explore a wide range of different
magnitudes of these parameters by employing T-matrix calculations in the single
adatom limit and by tight-binding supercell calculations for dilute adatom
coverage. We calculate the density of states and the momentum relaxation rate
and extract the resonance level and resonance width. Top position with large
hybridization strength or, equivalently, small onsite energy, induces
resonances close to zero energy. Bridge position, compared to top, is more
sensitive to variation in the orbital tight-binding parameters. Resonances
within the experimentally relevant energy window are found mainly for bridge
adatoms with negative onsite energies. The effect of resonances from top and
bridge position on the density of states and momentum relaxation rate is
comparable and both positions give rise to power-law decay of the resonant
state in graphene. Hollow position with $s$ orbital character is affected from
destructive interference which is seen from very narrow resonance peaks in the
density of states and momentum relaxation rate. The resonant state shows no
clear tendency to power-law decay around the impurity and its magnitude
decreases strongly with lowering the adatom content in the supercell
calculations. This is in contrast to top and bridge position. We conclude our
study with a comparison to models of point-like vacancies and strong midgap
scatterers. The latter model gives rise to significantly higher momentum
relaxation rates than caused by single adatoms.
