  Spintronics---the all-electrical control of the electron spin for quantum or
classical information storage and processing---is one of the most promising
applications of the two-dimensional material graphene. Although pristine
graphene has negligible spin-orbit coupling (SOC), both theory and experiment
suggest that SOC in graphene can be substantially enhanced by extrinsic means,
such as functionalization by adatom impurities. We present a theory of
transport in graphene that accounts for the full spin-coherent dynamics of the
carriers, including hitherto-neglected spin precession processes during
resonant scattering with dilute impurities. We identify a novel "anisotropic
spin precession scattering" process, specific to two dimensions and extrinsic
SOC, which contributes to a large current-induced spin polarization in
graphene. The theory also yields a comprehensive description of the spin
relaxation mechanisms in impurity-decorated graphene: the Elliot-Yafet and
Dyakonov-Perel relaxation rates are both present, and we find that the latter
can dominate for some choices of carrier density and impurity strength. This
provides theoretical foundations for designing future graphene-based integrated
spintronic devices.
