BBC News Magazine
Where does road salt come from?
De-icing or gritting salt is nothing like the white
grains we use to season food. Made from crushed
rock salt carved out of underground mines, it is
brownish in colour and resembles gravel.
The salt used to melt ice and add traction on the
UK's snow-covered byways comes not from the sea
but from three main mines - the Salt Union's
Winsford Rock Salt Mine in Cheshire, Cleveland
Potash in Teesside and the Irish Salt Mining and
From here, beneath the ground
in Winsford, Cheshire...
Exploration Company in County Antrim.
These deposits were formed millions of years ago when the UK and Ireland were
covered by inland seas. Over time, the seawater evaporated, leaving vast salty
deposits that were gradually covered over. Some are 100m deep, others well over
1.6km - a mile - underground.
Today rock salt is extracted by machines known
THE ANSWER
as continuous miners fitted with rotating steel
cutting picks which grind salt from the walls of
these vast cathedral-like spaces.
"The salt is then carried away from the cutting
surface by conveyor belts to be crushed and
treated further," says Salt Union spokeswoman
Katie Moffat.
It is treated with anti-caking agent, then put into
storage to await transportation to gritting depots
by lorry or rail.
Those who work the salt mines are trained
engineers who keep the machinery running - a far
cry from the pickaxes and buckets used in the
mines' early days in the 1800s, when rock salt
was primarily used for salt licks - blocks of salt -
Salt now used instead of
traditional grit made of sand
and small stones
De-icing salt is rock salt carved
from mines deep underground
Mine deposits formed as ancient
bodies of salt water dried up
for animals.
Rock salt is now used for winter highway maintenance as salt lowers the freezing
point of water to below zero Celsius - how low depends on the concentration of salt to
water.
This means when salt is spread over a road or a
footpath, it either melts the snow and ice as it
dissolves, or helps prevent ice forming.
After heavy snow throughout this week and more
forecast to fall, de-icing salt has been in such
demand that council stocks are running low. And to
restock when the roads are slick with ice can be
problematic, so supplies are being rationed.
Meanwhile, production has been stepped up at Salt
... to the gritting lorries
Union's mine which has been working 24 hours a day since the beginning of January.
But as well as drilling salt for the nation's byways, Salt Union has also found a use for
the spaces left over by mining - storing important documents.
"A salt mine is clean and dry, with huge caverns carved over time, leaving giant
pillars of rock salt for stability," says Ms Moffat. "With low humidity, no water and no
UV light, it's perfect for archive document storage."
As well as storage rooms, the spaces formed by extraction also form road-sized
pathways for the miners and mining equipment to move around between cutting
surfaces.
The Salt Association, the trade body for producers, estimates the UK's salt mines to
have about 225km (140 miles) of tunnels - almost as long as the M5 motorway.
Reference
BBC (2009) where does rock salt come from? ‘http://www.bbc.co.uk accessed 25/10/2013