In a typical configuration; the heavy metal removal step of the
wet FGD waste water treatment process is initiated by increasing
the pH-value of the purge from the hydrocyclone by the addition
of Ca(OH)2 or NaOH. Under these conditions, numerous heavy metals
precipitate in the form of solid metal hydroxides [10]. However,
Hg2+ does not precipitate sufficiently. For meeting strict effluent
limit values, the subsequent addition of precipitating and agents,
such as organosulfides in a second step is necessary, leading to
the formation of solid metal sulfides