Large earth moving equipment is used to extract rock
salt. This method of extraction leaves the salt with
insoluble impurities such as reddish clay. This kind of
salt is used to put on roads during freezing weather
and does not need to be pure.
Solution in water
when pure salt for industrial purposes is needed a different
method is used. Water is forced down a borehole into rock.
The salt dissolves making a solution of brine and this solution
is withdrawn to the surface and pumped to a purification plant.
Water is evaporated from the brine under a range of pressures
making the process more efficient. The salt crystallises and is
separated from any remaining brine by filtering or using a
centrifuge.
Environmental impact
Extracting salt in solution can create large
underground caverns. This can lead to bedrock
collapsing and as a consequence, cause the
lowering of the Earth’s surface. This is known as
subsidence. It can be avoided by sensibly spacing
out the holes created so the surface is supported
by a sufficient amount of rock underground.
Risk of salt
Salt (sodium chloride) is used in foods as a flavouring and
preservative. Humans need sodium in their diet to allow the body
to carry out essential functions. The main sources of salt in our
diet are processed meats and fish, cereal products and some dairy
products.
Studies have shown that eating too much salt can increase a
person’s blood pressure. Having high blood pressure increases the
risk of heart disease and having a stroke.
Government departments such as the Department of Health and the
Department for Environment, Food and Rural Affairs are involved in assessing
what level of risk is acceptable in foods. They may respond to concerns that
people are putting their health at risk by eating too much salt by carrying out
risk assessments on foods and advising the population.
Perceived and measured risk
People’s perception of a particular risk can often differ from the
statistically calculated risk. The risk of unfamiliar things (such as
skydiving) and things that have an invisible effect (like ionising
radiation) is often over-estimated by people. Attempts are frequently
made to assess the chance of something happening and the
consequences if it did.
Sometimes there is not enough evidence to say for certain how great
the risk is for an action. For example, the information offered by many
reports on the adverse effects of a high-sodium diet is challenged by
others who suggest there is no scientific proof for this, and that in fact
a low-sodium diet could be harmful.