Lithium in Cornwall - The Full Story (Part 2)
Author: Zara Parkes (Geomechanics Specialist)
Lithium is set to become the latest in a long line of minerals to be extracted from Cornish ground in a tradition dating back thousands of years, as Cornish Lithium announced yesterday that it “plans to explore for, and to potentially develop, lithium contained in underground hot spring brines in Cornwall.” This is the second of a three part blog, and focuses on global sources of lithium, and the main methods used to extract it. It also describes some previously unexploited sources of lithium which are now being considered as global demand increases. This follows on from Part 1 which investigated the occurrence of lithium in Cornwall. The third part of the blog will explore the reasons behind the recent global upsurge in the demand for lithium.
Lithium is extracted from two main sources: brines and hard (igneous and metamorphic) pegmatite rocks. According to the USGS, 26% of worldwide lithium resources are reported to be within hard rock mineral deposits, and 59% within brine deposits. In 2015, global lithium production was split about 50-50 between the two. The largest producers of lithium in 2015 were Australia (13,400 tons) followed by Chile (11,700 tons) and Argentina (3,800 tons). In 2015, over 90% of global supply came from just four countries: Australia, Chile, Argentina and China.
Lithium from hard rock
Lithium minerals containing lithia (lithium oxide) such as spodumene, petalite and lepidolite are mined from pegmatite open cut & underground mines. The largest producer of lithium from hard rock mining is Australia, and the world’s largest operating lithium mine is near the town of Greenbushes in the southwestern corner of Australia 250km south of Perth. It has been producing lithium for over 30 years from large open pits. The lithium-rich zone is over 2km long and up to 300m wide, and the lithium bearing mineral spodumene often makes up 50% of the rock. The ore containing 3.0-4.5% lithium oxide is fed into the on-site processing plants, which use gravity, heavy media, flotation and magnetic processes to produce lithium concentrates for shipment.
Via Kim McDonald
Image source: https://www.mindat.org/loc-11514.html
Lithium from brines
There are three types of lithium brine deposits: salt lakes, geothermal and oil field. Of these, salt lakes are the major source of commercial lithium. These brines vary greatly in concentration depending on the extent to which they have been subject to solar evaporation. Highly concentrated deposits are found in the high altitude salt lakes and flats, known locally as salars, of Chile, Argentina and Bolivia in the Andes, and on the Tibetan Plateau in China. These comprise the major global source of brine lithium. The largest operations are at the Salar de Atacama dry lakebed in Chile, which in 2015 yielded about a third of the world’s lithium supply.
At approximately 3000km2, it is one of the largest salt lakes in the world, where the lithium concentration varies between 0.1 and 0.4%. It has a high evaporation rate (a pan evaporation rate of 3500mm per year), and very low annual rainfall (at 15mm per year it is one of the driest place on earth) (source: www.sqm.com). This makes it an ideal setting for lithium production through solar evaporation.
I, Luca Galuzzi [CC BY-SA 2.5 (http://creativecommons.org/licenses/by-sa/2.5)],
The lithium-containing brine is pumped from beneath the salar into evaporation ponds which cover approximately 2km squared. During the evaporation process through several ponds, the lithium concentration is increased from about 0.2% to 6% in the final brine in a process that takes up to 18 months. It is then transported to a nearby plant for further purification & processing. This YouTube clip shows some of the SQM-owned operations in Salar de Atacoma and gives a feel for the sheer size of the site and the space and conditions needed for this process to work.
Geothermal lithium brines have been found in several locations such as Wairakei, New Zealand, Reykanes Field, Iceland and El Tatio, Chile. Several projects are underway to find economic ways of extracting the lithium from these brines. In the Salton Sea geothermal field in California, Simbol Materials came the closest to a commercial operation, with reported lithium values of 0.01 – 0.02% in the brines (source: www.mineralsuk.com). According to the USGS, they planned to use a “unique reverse osmosis process” to extract high-purity lithium carbonate from the discharge brine of the geothermal power plants operating there, eliminating the need for solar evaporation. However, Simbol Materials ran out of money in 2015 before production could commence. The mantle has now been taken up by other Salton Sea companies such as EnergySource at the Featherstone geothermal plant, and Controlled Thermal Resources partnering with Alger Alternative Energy who plan to build a new geothermal energy plant with the sale of extracted lithium offsetting some of the cost.
Via Geo Thermal
Lithium brines can also be found in some deep oil reservoirs. Brine from the Smackover oilfield in Arkansas, USA has one of the highest concentrations of lithium at up to 0.05% from depths of 1800-4800m (source: www.mineralsuk.com). Companies are starting to look to commercialise these resources: last week MGX Minerals Inc. announced that it has formed a subsidiary company PetroLithium Corporation of America to acquire and explore oil field assets in lithium brine bearing areas in Colorado, Texas and Arkansas. In November MGX Minerals filed a patent application for the extraction of lithium and other valuable minerals from oil brine. Power Metals Corp. has also just announced the strategic acquisition of a 500,000+ acre lithium oilfield brine project portfolio in Alberta, Canada targeting the Leduc formation.
Lithium: other sources
Other sources of lithium in the early days of development include lithium clays (hectorite), and Jaderite a lithium-rich deposit so far only found in the Jadar Valley in Serbia. In 2015, Japanese researcher Tsuyoshi Hoshino published details of a technique to recover lithium from seawater using dialysis with a lithium ionic superconductor as a membrane which only the lithium ions can pass through. The lithium ratio increased from 0.000017% to approximately 7% after 72 hours.
Location of selected lithium deposits. Labels coloured orange are the sites known or believed to be producing lithium, as at May 2016 (Some locations shown on the map are in production but not for Lithium) after BGS.
Lithium extraction and geothermal energy in Cornwall
Cornish Lithium Ltd intends to extract the lithium bearing hot spring brines via wells drilled to depths in excess of 400m. The brines will be pumped to surface, and then be transferred to a treatment plant the size of a medium-sized supermarket where “recently developed technology allows lithium extraction from brine over a very short period of time yielding up to 99.9% purity (LUT).” Now they need to secure funding for a £5million exploration phase.
The Cornubian granite is a well-known for its high heat flow, and is therefore considered a good potential source of geothermal energy. Experimental work carried out by Camborne School of Mines’ world renowned ‘Hot Dry Rocks’ project at Rosemanowes Quarry in the 1980s, recorded a temperature of approximately 100°C at 2.5km depth. Cornish Lithium intends to explore the possibility of exploiting the geothermal energy from the thermal brines as part of the lithium extraction process.
Geothermal energy is still a hot topic in Cornwall today: at GeoScience Ltd we are working with our partners Geothermal Engineering Ltd to develop the first commercial geothermal power project in the UK at United Downs, near Redruth targeting depths of 4.5km. On a smaller scale, Geothermal Engineering Ltd are expected to start work in September 2017 to drill a geothermal well to a depth of 2km to supply heat to a section of the Art Deco Jubilee seawater pool in Penzance.
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Siame, E., R.D. Pascoe, 2011. Extraction of Lithium from Micaceous Waste from China Clay Production. Minerals Engineering, vol. 24. 1595-1602.