However, HgCl2 does not precipitate sufficiently. For meeting strict effluent limit values, the subsequent
addition of organosulfides in a second step is necessary, leading to the formation of solid metal sulfides.
Finally, the insoluble compound HgS can be disposed safely due to its advantageous properties. However,
it has been reported in previous works that increasing the pH-value of HgCl2 containing slurries promotes
re-emissions of Hg0 [4]. This could result in uncontrolled desorption of Hg0 during the first stage of waste
water treatment, limiting the actual Hg-removal rate of the plant and causing unnoticed safety issues.
Thus, the approach of this study is to take advantage of the redox characteristics of HgCl2 and
intentionally enhance its desorption by aeration of the liquid during alkalization in a controlled process.
The resulting small gas flow with increased content in Hg0 is directed to a suitable adsorber.