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November 2018
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World Cement
incineration, and as a result of mining for mercury, gold,
and other metals. Once emitted, mercury settles or falls in
rain onto land or sea, where microorganisms convert it into
methylmercury, a highly toxic form that builds up in fish
and shellfish, as well as in the animals that eat these fish. As
a result, predatory, longer-living fish, such as tuna, contain
higher levels of methylmercury.
Mercury and its compounds have a range of severe
health impacts, including damage to the central nervous
system, thyroid, kidneys, lungs, immune system, eyes, gums,
and skin. Victims may suffer memory loss or language
impairment, and the damage to the brain cannot be
reversed. There is no known safe exposure level for
elemental mercury in humans; effects can be seen even at
very low levels. Foetuses, newborn babies, and children are
among the most vulnerable and sensitive to the adverse
effects of mercury.
Globally, average mercury emissions from cement kilns
has been estimated as 35 mg/t cement.
2
However, the
quantity of mercury emitted by different cement plants
varies significantly. It is reported that the cement industry
could contribute approximately 10% of all anthropogenic
mercury emissions.
3
Minimata Convention
Global initiatives to reduce mercury exposure have been
signed and ratified by 94 countries (as of July 2018) under
the Minimata Convention, which is a legally binding
agreement. Article 8 of the Convention stipulates that:
A Party with relevant sources shall take measures
to control emissions and may prepare a national
plan setting out the measures to be taken to control
emissions and its expected targets, goals, and outcomes.
For its new sources, each Party shall require the use
of best available techniques and best environmental
practices to control and, where feasible, reduce
emissions, as soon as practicable but no later than
five years after the date of entry into force of the
Convention for that Party. A Party may use emission
limit values that are consistent with the application of
best available techniques.
For its existing sources, each Party shall include in
any national plan, and shall implement, one or more
of the following measures, taking into account its
national circumstances, and the economic and technical
feasibility and affordability of the measures, as soon as
practicable but no more than ten years after the date of
entry into force of the Convention for it:
a.
A quantified goal for controlling and, where
feasible, reducing emissions from relevant sources.
b.
Emission limit values for controlling and, where
feasible, reducing emissions from relevant sources.
c.
The use of best available techniques and best
environmental practices to control emissions from
relevant sources.
d.
A multi-pollutant control strategy that would
deliver co-benefits for control of mercury emissions.
e.
Alternative measures to reduce emissions from
relevant sources.
4
One of the key strategies to reduce exposure to
mercury and its compounds is to lower emissions from
power plants, waste combustion plants, and cement plants.
Consequently, new regulations will often necessitate the
retrofit of mercury control technology. The success of these
mercury controls has to be measured accurately to check the
efficacy of abatement and to demonstrate compliance with
environmental targets and regulatory permits.
Mercury in the cement industry
Within the cement manufacturing process, mercury is
present in natural and waste-derived raw materials, as well
as in conventional and waste-derived fuels. As such, mercury
enters clinker production systems by all three principal
feeding points: raw materials, the main burner, and the
secondary firing system.
Almost all of the mercury and mercury compounds from
the raw materials and fuels are volatilised in the clinkering
process and exit the kiln system as a vapour. Therefore, the
mercury that enters the kiln system will be emitted through
the stack, unless a mercury removal system is in place.
In addition to abatement, there are other means by
which the cement industry can lower mercury emissions.
The mercury content of fuels and raw materials vary
considerably. For example, the concentration in coal can be
as low as 0.1 mg/kg but it varies up to 100 times that figure.
Similarly, limestone may contain concentrations as low as
0.005 mg/kg, but it also may contain levels up to 100 times
that amount. However, due to the fuel-to-raw-material
ratio, mercury intake through raw materials can be up
to tenfold higher than in fuels. An opportunity exists,
therefore, to minimise mercury emissions through the use of
raw materials and fuels with low mercury content. However,
limestone constitutes 75% – 100 % of the raw material used
to make clinker, so most plants are located at the limestone
source. It may not be economically viable to buy from
other sources – especially if the cement company owns the
limestone quarry.
Clearly, continuous and frequent mercury analysis of
fuels and raw material will be necessary if mercury inputs
are to be minimised. While costly and time-consuming,
this process would also assist with mercury mass balance
calculations.
Many cement plants employ dust shuttling as a mercury
emissions reduction tool.
5
This process relies on the ability
of mercury to adsorb on to the surface of particles, which
can then be removed. Once removed, the mercury-laden
dust can be re-fed into the kiln, but this can result in the
build-up of a mercury cycle within the plant. It is also
possible to remove this mercury from the process. Once
collected, it can be used as a mineral addition to the cement
or used in other products, such as certain mortar binders.
In the absence of another option, this mercury-laden
dust may become waste and should be disposed of