Sodium is made for use in the manufacture of indigo, the dye used for blue jeans,
pharmaceutical products such as the painkiller ibuprofen,
and for making petrol additives although this market is declining.
Sodium manufacturing uses a cell with a graphite anode and a steel cathode.
The molten sodium chloride produces chlorine gas at the anode
and molten sodium metal at the cathode.
On this site, salt, sodium chloride, arrives here by road.
This is the cell hall, which has room for up to 100 electrolysis cells.
Cells are rebuilt in this workshop.
The sodium which is produced is loaded for transport here
and this is the chlorine liquefaction plant.
Solid salt arrives five or six times a day.
The salt is thoroughly dried to a moisture content of less than 0.05%
in these gas heated rotary driers.
Water and hot sodium do not go together.
Electrolysis takes place in these cells, called Downs cells.
This is the raw material. Dry salt running into the electrolysis cell.
Each cell has four sets of electrodes arranged in two rows.
The graphite anodes are surrounded by steel cathodes.
Between them is a mesh diaphragm.
Chlorine collects at the anode.
Molten sodium metal collects at the cathode and rises into a storage tank.
The diaphragm prevents the sodium and chlorine from reacting.
This is how each set of electrodes is arranged.
Outside is a steel cathode, then a diaphragm,
and the graphite anode in the centre.
These are the four sets of electrodes before the diaphragms have been fitted.
The cells are made from steel, lined on the inside with heat-resistant brick.
Each cell is rebuilt every 36 months.
These are the steel diaphragms that surround the anodes.
The cells drop below the floor level of the cell room.
An electric current of around 40,000 Amps flows through the cells.
Large electrical connectors called bus bars carry electricity to the cells.
The cells are filled with a mixture of calcium chloride, barium chloride and sodium chloride,
kept molten by the flow of electricity.
The mixture is used because its melting point is six hundred degrees Celsius
compared with eight hundred degrees Celsius of the sodium chloride alone.
At eight hundred degrees Celsius hot sodium and chlorine
would attack the materials of the cell.
As electrolysis proceeds chlorine is sucked from the anode into the chlorine main.
Molten sodium floats to the top of the cell
and is stored in a two-hour tank.
A little solid calcium is also produced at the cathode.
It's cleared from the riser pipe and placed back in the electrolysis cell by a process called tickling.
Then the sodium is emptied into a larger 24-hour storage tank.
Each day the 24-hour tanks are disconnected from the cell and taken to be emptied.
The gas flame under the tank keeps the sodium molten.
The sodium is stored, still molten, in warmed tanks.
Some sodium is sold in blocks.
The liquid sodium cools and solidifies in the trays.
Blocks of the metal are cut to size, and packed into airtight drums.
The chlorine is liquefied.