  We report the results from a 2011 Suzaku observation of the nearby
low-ionization BAL quasar/ULIRG Markarian 231. These data reveal that the X-ray
spectrum has undergone a large variation from the 2001 XMM-Newton and BeppoSAX
observations. We interpret this finding according to a scenario whereby the
X-ray continuum source is obscured by a two-component partial-covering absorber
with NH ~10^22 and ~10^24 cm^-2, respectively. The observed spectral change is
mostly explained by a progressive appearance of the primary continuum at <10
keV due to the decrease of the covering fraction of the denser absorption
component. The properties of the X-ray obscuration in Mrk 231 match well with
those of the X-ray shielding gas predicted by the theoretical models for an
efficient radiatively-driven acceleration of the BAL wind. In particular, the
X-ray absorber might be located at the extreme base of the outflow. We measure
a 2-10 keV luminosity of L(2-10) = 3.3 x 10^43 erg s^-1 for the 2011 data set,
i.e. an increase of 30% with respect to the 2001 value.
