Lithium is an essential component of electric vehicle batteries which occurs abundantly in the Earth’s crust in many different forms, roughly classified as pegmatites (“hard rock”), brines, and sedimentary deposits (which you may sometimes hear erroneously generalized as “clays”)
America’s Lithium Valley
Do you think driving a Tesla or plugging-in to solar power are environmentally-conscious choices? Then you should know it’s almost certain the batteries in those systems traveled around the world two or three times before they were even installed. That’s not very “green,” is it? Lithium-ion batteries, found in so many things we use every day, often have a rather costly carbon footprint. That could soon change with a discovery that’s just a couple hours north of Tesla’s Gigafactory. A Canadian mining company, LithiumAmericas, identified what’s one of the world’s largest lithium deposits inside the footprint of an ancient volcano. NBCLX Storyteller Chase Cain takes us to the ancient volcano in Nevada that could hold the future of a green energy boom in the West.
Currently, only pegmatite and brine resources are used to produce lithium chemical products commercially.
But a host of new players aiming to produce lithium using sedimentary deposits in Western North America and around the world are coming on the scene.
The sedimentary deposit projects claim to take advantage of favorable chemistry of processing the sediments, sometimes described as the “best of both worlds” when compared to pegmatites and brines. In this article, I will share what are some of the most promising features of sedimentary deposit projects, who’s working on developing these deposits, and why investors and mainstream capital markets should take them seriously as future sources of lithium chemical products. It will be helpful to understand some of the pros and cons of processing pegmatites and brines into lithium chemical products to understand the “best of both worlds” argument for the sedimentary deposits.
In pegmatites, lithium is strongly bound in crystal structures like aluminosilicates (Al, Si oxides) and because the lithium is so tightly bound in the structure, the mineral requires aggressive processing to remove it to make lithium chemicals.
Spodumene [(LiAl(SiO3)2] is the most widely mined lithium-bearing pegmatite, and has been successfully developed into a significant source of lithium commercially (representing around half of global supply in 2019). It is first dug up and crushed to smaller pieces. The crushed material is then “upgraded” to remove waste materials from the mine that are not spodumene and don’t contain lithium. Once upgraded, calcination (heating to ~1,000°C) is used to convert the crystal to a different structure that is more amenable to removing the lithium.
These high temperatures are typically generated using coal or natural gas, meaning the carbon footprint of roasting pegmatites is typically higher than processing of other lithium resources.
The roasting is a fundamental aspect of extraction of lithium from spodumene because of their crystal structure, and it is difficult to get around this. Some other pegmatites may not require this roasting step however.
Lithium Mining in Nevada
This calcination process is followed by a chemical treatment to extract the lithium. This gives a mostly pure lithium concentrate (called the leachate) which can be refined into lithium chemical products with a relatively simple technological approach involving addition of chemicals.
Pegmatites are a good source of lithium because they are easy to manipulate from a mining engineering perspective, and the leachate obtained from the chemical treatment isn’t heavily contaminated with elements with similar chemical characteristics to lithium (ex. alkali/alkaline earths like Na, K, Mg, Ca, Sr), meaning the impurities are easy to remove from the leachate. The waste produced from spodumene operations can be simply put aside or used for other applications like concrete manufacturing and other applications.
Lithium can be produced from other minerals like lepidolite and zinnwaldite using similar flowsheets to spodumene, but some modifications are required depending on the unique mineralogy.
Brine resources are very different from pegmatites from a lithium extraction and processing perspective.
Brines are high concentration salty reservoirs in which salts are dissolved (ex. Li, Na, K, Mg, Ca, Sr are common cations, or positively charged species, while Cl, SO4, BO3, and CO3 are common anions, or negatively charged species, in these resources). The minerals in brines start off as volcanic materials but over millions of years, rain and geochemical phenomena cause them to dissolve in water and concentrate in basins. Brines can be as high as 20-40% salt by mass, meaning that if you were to evaporate away the water from the brine, around 20-40% of the mass would be left behind as white or clear crystals.
Read More: US Lithium Mining May Get a Boost …
Brines are liquid, meaning that they need to be pumped to the surface for processing, not dug up and crushed like pegmatites are mined. This means that they do not require roasting or leaching operations to put the lithium into solution for further processing – the lithium is already dissolved. There are two ways to remove lithium from brines.
First, evaporation pond systems can be used to evaporate the water from the brine, leaving behind contaminant salts and an “end brine” of mostly lithium chloride which is processed into lithium carbonate by adding sodium carbonate. This process only works for high lithium concentration brines with low impurities in places with no rainfall, and there is concern that if brine is pumped out from too deep in the salar, freshwater may be sucked in, diluting the salar and destroying potable water resources used by humans.
Second, direct lithium extraction (DLE) processes can be used to remove lithium from the natural brine to produce a highly pure concentrate, leaving behind a “spent brine” containing all the original components of the natural brine but without the lithium. This spent brine needs to be reinjected and/or separated from the natural brine so that the two don’t mix, or else the natural lithium-bearing brine will be diluted by the spent brine containing no lithium, making it impossible to extract more lithium from the reservoir.
As mentioned above, sedimentary deposits are considered to share some of the positive attributes of both pegmatites and brines. Sedimentary deposits are created when lithium is washed out of volcanic materials into basins where the salts and minerals dry, creating chemical structures in which the lithium is bound up in a mineral, but much less strongly compared to pegmatite resources. They typically have the consistency of dirt, not hard rock, and often break up when placed in water. If the lithium was not bound in a mineral at all, it would wash out in water forming a brine (this is typically not observed).
A number of leading projects are proposing not using any roasting, meaning the lithium is bound in the mineral with an “intermediate” strength compared to pegmatites and brines. A chemical leach is used to extract the lithium from the sediment, after which the waste sediment can be stored in mounds or back-filled into an open pit.
The lack of requirement to roast the sediment is a positive asset for these resources because it means that natural gas pipelines may not necessarily need to be built to process the sediment. Some projects report requiring upgrading of the sediment ore to remove contaminants which would “unnecessarily” consume acid, and in October 2019, only one project is proposing to use a roasting step in their flowsheet. The benefit of processing a sediment containing “loosely bound” lithium is that the solid waste can be easily disposed of without diluting the original resource, similar to the waste materials from after removing lithium from pegmatites.
The sedimentary deposit projects have some promising attributes for a future of supplying lithium to the battery industry, but reagent inputs will need to be optimized thoroughly for each individual project. Every sediment is different and the flowsheets of the different projects may look quite different. The chemistry of the sediments varies significantly (which is also the case for brines), and each project will need to take this into account. Currently, most public pre-feasibility studies show that tens to hundreds of times excess of reagents are used to create the lithium leachates. This implies low lithium concentrations in the leachate compared to pegmatite-derived leachates, and high concentrations of impurities like Na, K, and Mg.
This explains why most projects currently propose by-product sales to reduce apparent OPEX (electricity, sulfuric acid, boric acid, potash, etc.) because these are likely high OPEX flowsheets if they were “pure play” lithium.
Further, the high porosity and low particle size of the sediments mean that they “hold on” to leachate during leaching, and solid/liquid separations will be key to extracting most of the lithium as leachate from the spent ore. When this is done poorly, the ore “gums up” and a significant amount of lithium is lost with the waste.
The “in between” strength of how lithium is chemically bound in sediments results in some of their “best of both world” characteristics when compared to brines and pegmatites, and these strengths should be taken advantage of in future flowsheet development. New leaching techniques and reagent management flowsheets may be helpful in unlocking these sedimentary materials to produce high lithium concentration, low impurity concentration leachates that can be more easily processed into battery quality lithium chemical products. The sedimentary deposit lithium projects are young, but I believe that some of them will be built in the near future.
The healthy mining jurisdiction of Western North America, proximity of the deposits to American battery manufacturers, and potential for low carbon intensity means that they have excellent potential for helping supply lithium for batteries in the near future, and that they should be followed closely.
A map of these projects is seen below.
Thanks to all those who influenced this article through including Anna Wall, Tom Benson, Gene Morgan, and Davd-Deak
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