Salton Sea - a place where we can extract geothermal energy and lithium at the same time

The Salton Sea is a real and very unique body of water located in California near the border with Mexico. It is also a possible solution to one of humanity’s greatest challenges: the transition to new energy sources.

The climate emergency is forcing us to rapidly abandon the use of fossil fuels. Luckily, we do have a solution: renewable energies. Until just recently, when talking about renewable energy sources, we had to limit ourselves basically to constructing reservoirs that allow us to take advantage of the power of water flow to generate electricity. Now, solar and wind energy are being hailed as the new kings of the energy sector for the next few years, since they can be installed anywhere and, more importantly, are the cheapest ways to produce electrical energy. However, there is another renewable energy source that until recently was considered far less and which is now coming into the spotlight: geothermal energy, which takes advantage of the heat inside our planet.

Where does this heat come from? The main bulk of this immense heat—which can reach up to 6,000 ºC (10,000º F), similar to what is found on the surface of the Sun—comes from the moment our planet was formed. Celestial bodies (some as big as the planet Mars) smashed into and then united with the Earth in the process of creation. These impacts released incredible amounts of energy (heat) that has been held within the interior of our planet ever since. Another source of this inner energy are the physical and chemical changes that happened as the Earth grew in size, due to the enormous pressures inside the planet, which generated heat. The most important source of heat is natural radioactivity. A small part of the atoms in the rocks inside the Earth are unstable and naturally split to transform into stable atoms. At the moment they break apart, they release heat, which then accumulates within the inside of our planet.

The end result of all of this is that if we are on the surface of the Earth and drill a hole, the temperature will progressively increase the deeper we go. This proportional increase is known as the geothermal gradient, and typically amounts to a value of 25-30 ºC (77-86º F) for each kilometer (0.62 miles) down we go. However, there are certain spots on the planet that are unusually hot close to the surface. These generally coincide with the edges of tectonic plates, which see a concentration of volcanism. The presence of magma near the surface, whose temperature ranges between 700 and 1,200 ºC (approx.1300-2200º F), means that without drilling particularly deep, we can rapidly reach rocks whose temperatures reach hundreds of degrees. The regions with these characteristics are the preferred choice for the construction of geothermal power plants to produce electrical energy.

This kind of power plant makes use of subterranean water in these areas that exceeds 100 ºC (212 ºF) and naturally turns into steam, which is then channeled by the perforations and used to spin turbines to create electricity. In order to affect the aquifers as little as possible, another option is to extract energy from the steam by using a heat exchanger, so that the water returns to liquid form and can be put back underground where it will heat up again and begin the cycle anew. In those areas where the water is near 100 ºC but does not become steam, the liquid can be pumped out to extract heat. If there is not enough underground water, it is possible to inject cold water (from a river for example) underground so that it is heated by the surrounding rocks and then carry out the same cycle as above.

The advantage of geothermal energy is that it remains constant throughout the day and the year. The disadvantage is that there are few places on our planet where we can access these high subterranean temperatures, so the supply is limited. That is why many countries choose solar and wind energy. But both of these options have a problem: they are intermittent. There is no sun at night, and there are times during the day that the wind does not blow. To solve this, we need to store electricity, and using lithium batteries is one of our best options. Furthermore, we need to replace the use of fossil fuels for vehicles and use renewable electricity more. This has led to a boom in the manufacturing of batteries, with lithium as a key element for an essential part of the energy transition.

Lithium is a very common element and there is plenty present on the planet. However, until recently, there was not much demand and we do not have enough mines to cover the new needs generated by the energy transition. This is why, with the boom in electric vehicles and renewable energy, we are searching for new deposits of this element around the world so that they can be mined. The greatest amount of lithium is in the sea, dissolved in the water. However, it is so diluted and in such quantities that enormous amounts of water would need to be treated (basically evaporated), and the cost would not be worth the yield. That is why the main areas of interest are those that contain brine: water that has higher salt content than normal marine saltwater. The most common origin of brine is the evaporation of salt water in areas that have been isolated from the ocean. With brine, nature has already done a large part of the evaporation work for us.

If all the water evaporates, solid salt deposits are formed. Geology calls these “evaporites”, precisely because they come from that process. The reverse process can also occur, when fresh water is added to these evaporites (e.g., a river or lake forms above them) and the deposits are dissolved and become brine again. In those cases where there are subterranean brine deposits, we can drill down and pump the brine out since they are liquid. For cases of semisolid or solid salts mixed with sediments and rocks, we can inject water into the perforations to dissolve the salts and then pump out that water, which has been transformed into brine. That is one of the new mechanisms that is now being used to obtain lithium, in addition to traditional methods such as mining solid evaporites and exploiting existing brine deposits.

An important property of water is that the hotter it is, the more dissolved salts it can hold. Therein lies the connection to geothermal heat. As we discussed above, very hot water can be pumped up and heat energy taken from it. If the geothermal power plant is located in an area with brine, we can take advantage of the water (which is brine) that is being pumped up to extract lithium as well as heat. Then the water is injected back underground so that it dissolves more evaporites and is heated by the earth again. The hotter the water gets, the greater quantity of lithium we can extract from each liter of brine. This yields a greater profit than if water is injected into sediments and rocks at a normal temperature. This win-win situation has brought geothermal power plants into the spotlight as a means to extract this valuable element. They take advantage of the heat inside the planet to create electrical power, and at the same time are a potential source of lithium.

The Salton Sea is unique because it brings together all of these elements. On one hand, we have the famous San Andreas Fault that separates the tectonic plates of the Pacific and North America. As at most of the edges of tectonic plates, the area of the Salton Sea, known as the Imperial Valley (which spans 155 miles), shows signs of volcanism and geothermal activity. This geothermal activity is taken advantage of by several power plants, both in the USA and in Mexico. Furthermore, because of its particular geological history, the Imperial Valley was an area in which sea water evaporated: Originally, millions of years ago, this area was part of the ocean. The progressive advance of the Colorado River from the north slowly isolated what would become a valley from the ocean, creating a new inland sea that progressively evaporated away. The river deposited sediments within the valley, which mixed with the brine that had formed there. Today, the area of the Salton Sea is below sea level, and there is a lake that formed there due to an accident in the early 20th Century. For two years, the Colorado River drained into the depression because of an irrigation canal that was not constructed with sufficient safety measures, and it took two full years for the engineers to rectify the problem so that the river mouth drained into the Gulf of California again.

This combination of events makes the area of the Salton Sea a great opportunity for the construction of geothermal power plants that can take advantage of the natural resources present. You can drill to get steam and hot water in an area of significant geothermal activity. On top of that, you can use that same hot water, which is indeed brine, to extract lithium and sell that as well as the electricity. Together, you will be able to completely avoid the use of fossil fuels and lead the energy transition towards a fully renewable future.

Marc Belzunces(Barcelona, 1976). Geologist with a bachelor’s degree from the Autonomous University of Barcelona and masters of Ocean Sciences from the Polytechnic University of Catalonia. He was a researcher in the Spanish National Research Council and a consultant on pollution for the Catalan Water Agency and the Spanish Ministry of Agriculture, Food, and the Environment.

Points of sale

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