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DELTARES, September 2016
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W
hen iron-rich groundwater
comes into contact with oxygen,
dams and nuggets with a rusty
brown colour form in the ground:
bog iron. In prehistoric times, our ancestors
made grateful use of it to produce cast iron.
By today's standards, the metal isn't pure
enough but researchers Wim de Lange, Jos
Vink, Rob Zwaan and Marco de Kleine have
thought of a modern application for bog iron.
Not by mining it but precisely by using a
smart method to inject it into the ground.
Iron injection
Bog iron is – at least in theory – an ideal
way of making underground sheet piling.
There is no digging and the approach is
environmentally friendly and invisible. ‘The
iron-rich liquid goes to where you want
the sheet and it only goes to work once it's
there,’ says project manager Wim de Lange.
In that sense, it resembles the existing
injection technology with sodium silicate or
water glass. Unfortunately, that technique
produces highly alkaline results and it isn't
environmentally friendly. ‘It's like injecting
ammonia into the soil,’ says Jos Vink, the
team's chemical expert. So bog iron is
preferable: it is something that is already
present in the ground. But how do you make
it, and how do you get it into the right place
in the right form?
Search
There is actually only one drawback to
the idea: it really is difficult to adjust the
interaction between the rate of the chemical
reactions, spreading the injection fluid and
blocking off the soil. And that process can
also be affected by local conditions,
as was seen during every step of the
search that began in the Deltares chemical
laboratory, Utrecht Castel, where Jos Vink
and his colleagues looked at a range of
mixtures to see how they blocked off the soil
and tested them at the centimetre scale.
A mixture was then tested in a glass
container measuring 2 m³ to see how it
worked in real soil. ‘You see the bog iron
forming as you watch,’ says researcher Rob
Zwaan in his laboratory. ‘It's a beautiful
process.’
Once this step was completed, the next
challenge was: how can you spread the
mixture evenly across a large surface area?
Wim de Lange: ‘We insert a large number of
lances – they're like big syringes – into the
soil. We induce groundwater flows between
two rows of lances and the groundwater
can only move in one direction between the
A natural phenomenon from the dawn of
time could well be the ultimate substitute
for standard sheet piling. A seal is
created within a few hours. This is the
story of bog iron.
BY JANNEKE IJMKER
IMAGE JANDERZEL