  Black-hole (BH) accretion disks formed in compact-object mergers or
collapsars may be major sites of the rapid-neutron-capture (r-)process, but the
conditions determining the electron fraction (Y_e) remain uncertain given the
complexity of neutrino transfer and angular-momentum transport. After
discussing relevant weak-interaction regimes, we study the role of neutrino
absorption for shaping Y_e using an extensive set of simulations performed with
two-moment neutrino transport and again without neutrino absorption. We vary
the torus mass, BH mass and spin, and examine the impact of rest-mass and
weak-magnetism corrections in the neutrino rates. We also test the dependence
on the angular-momentum transport treatment by comparing axisymmetric models
using the standard alpha-viscosity with viscous models assuming constant
viscous length scales (l_t) and three-dimensional magnetohydrodynamic (MHD)
simulations. Finally, we discuss the nucleosynthesis yields and basic kilonova
properties. We find that absorption pushes Y_e towards ~0.5 outside the torus,
while inside increasing the equilibrium value Y_e^eq by ~0.05--0.2.
Correspondingly, a substantial ejecta fraction is pushed above Y_e=0.25,
leading to a reduced lanthanide fraction and a brighter, earlier, and bluer
kilonova than without absorption. More compact tori with higher neutrino
optical depth, tau, tend to have lower Y_e^eq up to tau~1-10, above which
absorption becomes strong enough to reverse this trend. Disk ejecta are less
(more) neutron-rich when employing an l_t=const. viscosity (MHD treatment). The
solar-like abundance pattern found for our MHD model marginally supports
collapsar disks as major r-process sites, although a strong r-process may be
limited to phases of high mass-infall rates, Mdot>~ 2 x 10^(-2) Msun/s.
