(BAT) Reference Document for the Production of Chlor-alkali ...

{A list of techniques used on full scale can be found in Section 4.5.4.1.}
3.8.2 Mercury
Chapter 3
The contamination of soil with mercury is due to the atmospheric deposition as well as to the
historical disposal of graphite sludges from the use of graphite anodes and of other wastes on
and around the site. The mercury may leach from the soil and end up in the run-off water and
the groundwater. Mercury is mostly present in elemental form, but dissolved inorganic and
organically-bound mercury are also present. The redox potential of the soil determines the
direction of conversion [ 245, Euro Chlor 2009 ], [ 246, Wanga et al. 2004 ], [ 247, Orica
2011 ].
The soil beneath the production units can be contaminated with mercury up to several metres
depth, especially the areas beneath the cell room and the retorting unit where concentrations can
be as high as some g/kg of dry soil [ 245, Euro Chlor 2009 ].
As far as contamination through atmospheric deposition is concerned, experience has shown
that mercury concentrations in the topsoil (~ 30 cm) could vary from some Zg/kg up to some
hundreds of mg/kg within the first kilometres downwind from the cell room. The prevailing
wind direction has, not suprisingly, a major influence on the deposition rates and hence the
topsoil contamination levels [ 245, Euro Chlor 2009 ], [ 249, Biester et al. 2002 ], [ 250, Maserti
and Ferrara 1991 ]. However, most of the metallic mercury directly or indirectly released to air
from the plant is subject to atmospheric long-range transport [ 249, Biester et al. 2002 ]. In some
cases, the concentrations in soils due to deposition were reported to reach background levels at a
relative short distance (4 – 5 km from the plant) [ 250, Maserti and Ferrara 1991 ], while in
other cases this distance was reported to be as high as 100 km [ 251, Lodenius and Tulisalo
1984 ]. When soluble mercury is bound to organic matter, the contamination reached down to
approximately 20 – 50 cm in the soil. On the contrary, in sandy soils lacking organic matter,
contamination was restricted to the upper 5 cm. This means that reactive mercury forms are
effectively retained through sorption on mineral surfaces [ 248, Biester et al. 2002 ].
At some sites, discharge of mercury-containing waste water led to contamination of river
sediments [ 265, Hissler and Probst 2006 ].
Table 3.34 contains an estimation of the total number of mercury-contaminated chlor-alkali sites
in EU-27 and EFTA countries with estimated contamination levels. The estimate of the total
amount of mercury present at contaminated sites varies largely from 3 – 19 kt, the median being
estimated to be approximately 10 kt [ 241, COWI 2008 ].
Table 3.34: Estimation of total number of mercury-contaminated chlor-alkali sites in EU-27
and EFTA countries and contamination levels
Number of sites
Contamination level
in t of mercury per site
Total contamination level
in t of mercury
11 – 19 5 – 30 56 – 555
22 – 37 30 – 100 666 – 3 700
22 – 37 100 – 400 2 220 – 14 800
Total 56 – 93 NA 2 942 – 19 055
NB: NA = not applicable.
Source: [ 241, COWI 2008 ]
WORKING DRAFT IN PROGRESS
Table 3.35 shows examples of mercury-contaminated chlor-alkali sites in EU-27 and EFTA
countries.
TB/EIPPCB/CAK_Draft_1 December 2011 137