The feedstock is slaked lime (calcium hydroxide) and purified sea
water. These have to be produced from the raw materials, which are
limestone, fresh water and sea water. The limestone and fresh water
are used to produce the calcium hydroxide, which is then reacted
with the purified sea water to produce magnesium hydroxide.
About 1000 tonnes of limestone are used each day. The limestone is
very pure calcium carbonate (over 98%), and is crushed and washed
before being heated in a lime kiln to form quicklime (calcium
oxide):
CaCO3 → CaO + CO2
This reaction is carried out in a rotary kiln at 1500 o C. Fresh
water is then added to the quicklime to produce slaked lime
(calcium hydroxide):
CaO + H2O → Ca(OH)2
About 150 million litres of sea water is used each day. The sea
water is taken from the Boyne estuary for about 8 hours each day,
and is stored in a large reservoir, where sand and other solid
impurities settle out. It is then pumped through underground
pipelines to the Premier Periclase plant, four miles upstream.
In a similar manner as with the fresh water, the sea water is
acidified with sulfuric acid and passed downwards through a tower
against a rising current of air which strips off carbon dioxide.
The sea water then undergoes further clarification to remove excess
sand and other particles by a settling process.Rate and product
yield (temperature and pressure variables, catalysts etc.)
Catalysts, or pressures other than atmospheric pressure, are not
required for any of the reactions involved in the Premier Periclase
process. There are no reversible reactions involved, so no
compromises in relation to striking a balance between reaction
rates and product yields are needed. In the reaction of sea water
with calcium hydroxide:
The Physical Sciences Initiative
MgCl2 + Ca(OH)2 → CaCl2 + Mg(OH)2
conditions have to be chosen which will result in the production of
large crystals of magnesium hydroxide, which will settle and filter
more easily. To do this, the following is done:
• Dilution of the incoming sea water with spent sea water
• Seeding with a heavy slurry of magnesium hydroxide.
The reaction, which is a very rapid one, is carried out in large
tanks (circular, and about 30 metres in diamete
