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

Chapter 2
Table 2.4: Typical impurities with sources and effects on the membrane cell technique as well as typical brine specifications Example of brine specifications for the
membrane process operating at a current density up to 4 kA/m 2
Impurity Source
Ca 2+ + Mg 2+
Sr 2+
Ba 2+
Al 3+
Fe 3+
Hg 2+
Ni 2+
ClO3 -
I (e.g. H2IO6 3- )
Iodine
F -
SO4 2-
Salt 20 ppb
Salt
Upper limit of
brine
specification
0.1 – 4 ppm
0.04 ppm
Effects
Influence
Ca: CE
Mg: V
CE, V
Salt 0.05 – 0.5 ppm CE, V
Salt 0.1 ppm CE, V
Salt, pipework,
tank material,
anti-caking agent
Parallel
operation of
mercury cell
plant
0.05 – 0.1 ppm
( 1 )
1 ppm
0.2 ppm heavy
metals
10 ppm
V
Mechanism Remarks
Ca: Precipitation with various anions near cathode side of membrane, precipitation with silica and
iodine in the membrane
Mg: Fine precipitation with OH - near anode side of membrane, precipitation with silica in the
membrane
Precipitation with hydroxide on cathode side of membrane, precipitation with silica and iodine in
the membrane Sr and SiO2 seem to be co-precipitated within the membrane. (synergistic effect)
0.04 ppm in Sr content in purified brine is easily kept under normal operation of Chelating Resin
Tower.
If SiO2 content is kept less than 1 ppm, then Sr is allowable up to 0.1 ppm.
Very fine precipitation with iodine in the membrane, precipitation with silica in the membrane Ba
and Iodine seem to be co-precipitated within the membrane. (synergetic effect) When SO4 content
is kept 6 g/l, Ba content should be 0.05ppm or less.
Precipitation with silica in the membrane, precipitation of calcium/strontium aluminosilicates near
cathode side of membrane
Deposition on cathode, precipitation with hydroxide on anode side of membrane or in the
membrane (depending on pH of the brine)
V Deposition on cathode Mainly due to caustic user needs and risk of cathode damage
Salt, pipework, 0.2 ppm heavy
tank material, metals
V Deposition on cathode, absorption in membrane
cathode 0.01 ppm
Process side
reactions
10 g/l (as
NaClO3)
20 g/l
O Chlorination of ion-exchange resin
Salt
0.5 ppm
0.1 – 0.2 ppm
CE, V
Very fine precipitation with calcium, strontium or barium in the membrane, precipitation with
sodium on cathode side of membrane Iodine originates from underground salt and water. If solar
salt and ordinary surface water are used, Iodine content should be 0.1 ppm or less.
Salt 0.5 ppm V Destruction of anode coating
Salt,
dechlorination
with NaHSO3
< 4 – 8 g/l (as
Na2SO4)
6 g/l
CE
Precipitation with sodium near cathode side of membrane, anode coating with barium We are
evaluating to raise the upper limit to 8 g/l.
WORKING DRAFT IN PROGRESS
44 December 2011 TB/EIPPCB/CAK_Draft_1