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

3.5.9.5 Graphite and activated Activated carbon from the treatment of
gaseous streams: (See Section 4.2.1.1)
Chapter 3
Solid waste results when process exhausts or hydrogen is treated with iodised or sulphurised
activated carbon or with metals on a carrier. Mercury adsorbed on activated carbon or metals
may be recovered by distillation or disposed of [ 3, Euro Chlor 2011 ], [ 87, Euro Chlor 2006 ].
3.5.9.6 Graphite from decomposer packing
The packing within the decomposers (the reactors where the mercury/sodium amalgam is
converted to caustic soda and hydrogen) is usually composed of graphite balls or granules. In
During normal use, there is an attrition of the graphite and approximately every 10 years
decomposers will need repacking. The graphite, typically containing 1 – 10 wt-% mercury, can
be retorted. The quantity of graphite is approximately 1 – 2 g/t annual chlorine capacity [ 75,
COM 2001 ]. tonnes for each 100 000 tonnes of Cl2 capacity.
3.5.9.7 Residues from retorts
The retorting or distillation process can be applied to most materials containing metallic
mercury, such as caustic filter media and decomposer graphite, stock tank sludges, etc. The
distilled mercury is recovered. However, not all contaminated wastes can be retorted because
some produce volatile mercury compounds which are difficult to remove from the process
exhaust. The solid residue is landfilled or stored underground (mines) [ 87, Euro Chlor 2006 ],
[ 94, Euro Chlor 2009 ]. The residue typically contains from < 10 – 200 mg Hg/kg waste. The
final solids typically contain from less than 10 up to 200 mg mercury/kg waste. In some cases,
particularly concerning materials having very fine pore sizes, this may increase to
approximately about 1000 mg Hgmercury/kg waste. Under normal circumstances, the quantity
of retort residues will be determined by the volume of caustic filtration solids and is typically
about 5 g/t annual chlorine capacity. , say 5 tonnes per 100 000 tonnes of Cl2 capacity.
However, retorts are frequently worked in campaigns and the quantity may be highly augmented
by special activities such as stock tank recoveries or sump cleaning [ 75, COM 2001 ].
3.5.9.8 Wastes from maintenance and renewal and demolition
By their nature, both the quantity and character of these wastes is highly variable. Materials
include personal protective equipment, process equipment and construction materials. Materials
can range from protective gloves to thousands of tonnes of bricks from demolished cell rooms.
3.5.9.9 Reported waste Waste generation levels
Most of the mercury which leaves an installation is contained in waste. In 2010, mercury in
waste disposed of by chlor-alkali plants in EU-27 and EFTA countries ranged from
WORKING DRAFT IN PROGRESS
0 – 98 g/t annual chlorine capacity, the median being 5.0 g/t annual chlorine capacity (Table
3.23). In general, the amount of waste disposed of varies considerably from one year to the next
depending on the type of maintenance work which is done and other factors, such as the time
during which waste is temporarily stored on site. Table 3.30 and Table 3.31 provide examples
of waste types, amounts, applied treatments and mercury contents from two mercury cell
chlor-alkali plants in Sweden.
To give an idea of what types and amounts of waste that are generated, Table 3.4 and Table 3.5
presents the yearly waste generation and treatment for AkzoNobel in Bohus and Hydro
Polymers AB in Stenungsund (both plants in Sweden). The production is based on vacuum salt
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