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

Chapter 4
Sections 4.5.4.2 and 4.5.4.3 constitute specific examples of waste treatments relevant for
contaminated chlor-alkali sites.
Table 4.24 summarises potential techniques for the decontamination of mercury-contaminated
soils.
Table 4.24: Potential techniques for the decontamination of mercury-contaminated soils
Technique Description
Thermal desorption is an ex-situ physical technique to remove mercury from the
contaminated medium. Heat is supplied under reduced pressure to the contaminated
Thermal soil or waste, volatilising mercury. The off-gas is treated by condensation to
desorption generate liquid elemental mercury. The off-gas may require further treatment also
depending on the presence of other pollutants. The technique has been used at full
scale including chlor-alkali sites (see Section 4.5.4.2).
Vapour extraction is based on in-situ volatilisation of mercury by applying vacuum
Vapour
and heat followed by treatment of the exhaust gases. The technique has been used at
extraction
full scale, but not at chlor-alkali sites.
Soil washing is an ex-situ technique that takes advantage of the behavior of mercury
to preferentially adsorb onto fine particles. The contaminated soil is suspended in a
wash solution and the fine particles are separated from the suspension, thereby
Soil washing reducing the contaminant concentration in the remaining soil. The extraction of
and extraction mercury from the fine particles fraction can be based on desorption of adsorbed
species, oxidation of metallic mercury, complexation and dissolution (e.g. by using
acids). The technique has been used at full scale including chlor-alkali sites (see
Section 4.5.4.3).
Solidification and stabilisation are ex-situ techniques which reduce the mobility of
hazardous substances and contaminants in the environment through both physical
and chemical means. This technique physically binds or encloses contaminants
within a stabilised mass and chemically reduces the hazard potential by converting
Solidification
the contaminants into less soluble, mobile, or toxic forms. Amalgamation is
and stabilisation
typically used to immobilise elemental mercury and is often combined with
encapsulation to prevent volatisation of mercury from the amalgam. The technique
has been used at full scale including chlor-alkali sites. Soluble mercury may be
immobilised in-situ by precipitation as mercury sulphide.
Vitrification is a high-temperature treatment designed to immobilise contaminants
ex-situ or in-situ by incorporating them in the vitrified end product, which is
chemically durable and leach resistant. The primary residue generated by this
technique is typically glass cullet or aggregate. Secondary residues generated are air
Vitrification
emissions, scrubber liquor, carbon filters, and used hood panels. This technique
may also cause contaminants to volatilise or undergo thermal destruction, thereby
reducing their concentration in the soil. The technique has been used at full scale,
but not at chlor-alkali sites.
Source: [ 244, Hinton and Veiga 2001 ], [ 245, Euro Chlor 2009 ], [ 266, US EPA 2007 ]
Techniques for treating mercury-contaminated waste water arising during decontamination are
described in Section 4.1.3.1 and in the CWW and WT BREFs [ 124, COM 2011 ], [ 267, COM
2006 ]. Techniques for treating mercury-containing waste gases arising during decontamination
are described in Section 4.1.3.1 and in the WT and WI BREFs [ 267, COM 2006 ], [ 268, COM
2006 ].
WORKING DRAFT IN PROGRESS
4.5.4.2 Thermal desorption
Description
This technique consists in heating excavated soil (on site or off site) to volatilise mercury and
other organic compounds (e.g. PCDDs/PCDFs and halogenated organic compounds) with
subsequent treatment of the resulting waste gases.
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