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

Chapter 3
Especially relevant with regard to chlorate and bromate are plants that do not use the bleach
produced from the chlorine-containing waste gases but and destroy it the bleach by means of
heating to 70 ºC and acidifying it to pH 6 or 7. In this these cases, the free oxidants are
converted to decomposed into the less reactive chlorate and bromate. A value of 4 kg chlorate
per tonne of chlorine produced is reported for a plant applying thermal bleach destruction, while
bromate was in the range of 0.22 – 550 g per tonne of chlorine produced [ 17, Dutch Ministry
1998 ] [Dutch report, 1998].
Chlorate and bromate are less reactive than the free oxidants and have a lower acute toxicity for
aquatic biota. However, chlorate is classified as toxic to aquatic life with long-lasting effects
(chronic toxicity) and bromate is presumed to have carcinogenic potential for humans [ 76,
Regulation EC/1272/2008 2008 ].
3.4.2.3.6 Heavy metals Metals
Brine contains a certain amount of dissolved metals: such as nickel, zinc, iron, and copper,,
which originate from salt impurities and metallic equipment (see Table 2.4). depending on the
salt used. In some cases, the The addition of an anti-caking agent (ferrocyanides) to the solid
salt for transport, loading and unloading purposes provides an extra source of iron which is
mostly the case if vacuum salt is used. Dissolved heavy metals are unwanted compounds in the
process. In the case of the mercury cell technique, they can lead to the release of hydrogen in the
anode compartment (see Section 2.2.1) while in the case of the membrane cell technique, they
negatively affect the performance of the cells (see Table 2.4).
Part of this iron is Dissolved metals are partly removed by the bleed purge from brine treatment,
although the larger part majority is precipitated as hydroxides (e.g. iron hydroxide, Fe(OH)3)
and are removed during brine filtration. In the case of membrane cell plants, dissolved metals
are further removed from the brine during ion exchange and subsequently emitted during
regeneration. Reported values of iron releases are about 100 ppb from amalgam plants using
vacuum salt. A decomposition unit for to prevent iron complexes may be necessary for
membrane cell plants. After decomposition, releases of iron are about 30 to 40 ppb. {Data were
included in table.} Reported emission concentrations and factors are summarised in Table 3.15.
WORKING DRAFT IN PROGRESS
90 December 2011 TB/EIPPCB/CAK_Draft_1