The origin of the waste water is the continuously operated FGD process. Very low total Sulfite
concentration in the waste water is indicated by the ORP of ~ 250 mV. After filtration, the liquid is
gradually alkalized by the addition of Ca(OH)2 solution to the constantly aerated reactor at a temperature
of 60 °C. The strong impact of pH on the reduction of Hg2+ and the subsequent re-emission of Hg0 to the
exhaust air becomes obvious by the results presented in Fig. 1a). Interestingly, the shapes of the resulting
curves for all Cl--concentrations can be qualitatively separated in two pH ranges (lower and higher than ~
pH 8) as illustrated by Fig. 1a). For pH < 8, the here proposed mechanism for the generation of Hg0 is the
reduction of aqueous Hg2+ by residual SO3
2- according to Eq1. Further evaluation indicates additional
evidence for the assumption for SO3
2- being the dominant reducing agent in the low pH region. Almost
identical dependency on pH of both Hg0 formation and share of SO3
2- on total Sulfites, calculated using