Brine evaporation
Concentrating salt water in the sun until what is dissolved in it crystallises — the source of most of the world's lithium, bromine and iodine, and of solar salt.
Some elements were never in a rock. They are dissolved in seawater, in the brines trapped beneath salt flats, and in the water pumped out of oil wells, and the way to get them is to remove the water rather than to break open a mineral.
At its simplest this is a salt pan: seawater in a shallow pond, sun and wind, and salt left behind. At its most valuable it is a lithium operation in the Andes, where brine is pumped from beneath a salar into a sequence of ponds and spends a year or more evaporating from a few hundred parts per million of lithium to a few per cent.
Processing
The sequence is the same one that produced the evaporite rocks: salts crystallise in order of solubility, and each pond in a series is held at the concentration that drops out the salt you want to discard before moving the liquid on. A lithium operation spends most of its pond area precipitating sodium and potassium salts it does not want, and the lithium stays in solution to the end precisely because it is among the last things to come out.
What makes it economic is that the energy is free and the time is not. Evaporation rate is set by climate, which is why the industry is concentrated in a handful of high, dry, sunny places — the Atacama, the Argentine and Bolivian salars, the Qaidam basin — and why a lithium brine operation cannot simply be scaled up in response to price.
Bromine and iodine work differently at the end. Both are concentrated by the same evaporation and then displaced from solution chemically — bromine with chlorine, iodine from the caliche brines of northern Chile and from Japanese gas-field water — because both are wanted as elements rather than as salts.
Economic significance
Brine supplies the majority of the world's lithium and effectively all of its bromine and iodine, and it does so at a fraction of the energy cost of the hard-rock route. Spodumene mining answers price faster; brine is cheaper and slower.
The water is the argument. A salar brine is not fresh water and pumping it does not directly take drinking water, but salars sit in the driest places on Earth and the hydrology connecting brine to the freshwater aquifers around it is poorly understood and contested. The communities living on them have not generally been persuaded by that uncertainty, and lithium's environmental story is as much about hydrogeology as about carbon.
How we know: checked recently · only one source, so there is nothing to cross-check it against · stated directly by the source.
How this connects
Where a connection has been confirmed by an outside reference, that reference is named beside it.
produces
- Lithium — element · the majority of world supply, concentrated over a year or more in ponds on the Andean salars from a few hundred parts per million to a few per cent
- Bromine — element · concentrated by evaporation and then displaced from solution with chlorine, because bromine is wanted as the element
- Iodine — element · from the caliche brines of northern Chile and from Japanese gas-field water, which between them supply nearly all of it
- Magnesium — element · from seawater and from salt-lake brine, precipitated as the hydroxide before reduction — the ocean is an effectively unlimited magnesium resource
- Potassium — element · from potash brines, where the potassium salts are among the last to crystallise and so the last ponds in a series
- Salt — compound · in the solar route — the same process, read from the other end
was succeeded by
- Molten salt electrolysis — process · the concentrated salt still has to be reduced; evaporation delivers a compound, and electrolysis delivers the metal
Sources
- Material WorldOur own writing