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

3. Emptying of the cells and handling of metallic mercury
Chapter 4
In general, emissions of mercury can be reduced by minimising its handling. For this reason, it
is advantageous to carry out all recovery, cleaning and filling operations at the chlor-alkali plant
which, in addition, is likely to have an adequate infrastructure for this purpose [ 222, Euro Chlor
2007 ]. A suitable procedure for emptying of the cells and transferring metallic mercury to
containers includes [ 94, Euro Chlor 2009 ]:
keeping the system closed if possible, to reduce mercury emissions;
washing of mercury to remove residual sodium to avoid the risk of hydrogen formation
(e.g. by circulating the mercury of each individual cell with wash water until the exit
wash water stabilises at pH 7 ± 0.5 and the specific gravity at 1.0);
using gravity transfer if possible;
checking that the mercury is not contaminated and, when necessary, using filtration or
decantation to remove solid impurities such as rust and rubber particles;
avoiding the transfer of other liquids such as water into the mercury containers;
filling the containers to Q 80 % of their volumetric capacity to avoid overpressures;
hermetically sealing the containers after filling;
weighing and labelling the containers according to relevant legislation;
washing of the empty cells with an alkaline hydrogen peroxide solution and water
followed by filling with water to reduce mercury emissions until the cells are
dismantled.
4. Dismantling, demolition and decontamination
Techniques which have been recommended to reduce mercury emissions during dismantling,
demolition and decontamination include [ 94, Euro Chlor 2009 ], [ 274, Ancery 2011 ], [ 276,
French Ministry 2010 ]:
inclusion of some of the staff experienced in running the former plant;
replacement of hot cutting of equipment by cold cutting if possible;
taking precautions against the dispersion of mercury droplets if high pressure is used for
the cleaning of surfaces (e.g. confined areas with treatment of waste gases);
storage of contaminated equipment in suitable areas (e.g. steel can be highly
contaminated with mercury which can sweat out during storage);
frequent washing of the floor of the working area;
rapidly cleaning-up of mercury spills by using aspiration equipment with activated
carbon filters;
accounting of waste streams (origin, mass, volume, mercury concentration and
destination).
In general, mercury-contaminated waste is as much as possible separated from
non-contaminated waste. Decontamination aims at concentrating mercury into a smaller amount
of waste, preferentially as metallic mercury. The techniques used are the same as the ones used
in mercury cell plants in production but some adaptations may be required due to the much
higher quantities handled in a short period of time [ 94, Euro Chlor 2009 ].
WORKING DRAFT IN PROGRESS
Treatment techniques for solid waste include [ 87, Euro Chlor 2006 ], [ 94, Euro Chlor 2009 ]:
mechanical and physical treatments. These include washing with water (with or without
pressure), ultrasonic vibration and vacuum cleaners with appropriate adsorption or
condensation systems. Mechanical and physical treatments are suitable if significant
quantities of metallic mercury are present;
chemical treatment. This includes treatment with hypochlorite, chlorinated brine or
hydrogen peroxide. The liquid streams are treated as described below;
TB/EIPPCB/CAK_Draft_1 December 2011 163