From Mine to Mind and Mobiles: Society’s Increasing Dependence on Lithium

Lithium is everywhere. If you have a mobile phone or a laptop, you are taking advantage of one of the technological revolutions of the last 30 years: lithium-ion batteries. Lithium has long been used in pharmaceuticals and in the manufacture of grease, ceramics, and glass, but has now become the symbolic element of the current energy revolution. Lithium is ubiquitous in our society and plays a role in our lives that could not have been previously imagined. From its mining to its applications in advanced battery materials and pharmaceuticals, welcome to the lithium decade. Electric mobility will become the new normal.

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Classification and Characteristics of Natural Lithium Resources

There are three broad types of economic lithium deposit: 1) peralkaline and peraluminous pegmatite deposits and their associated metasomatic rocks; 2) Li-rich hectorite clays derived from volcanic deposits; 3) salar evaporites and geothermal deposits. Spodumene-bearing pegmatites are the most important and easily exploitable Li deposits, typically containing 0.5 Mt Li. Salar deposits hold the largest Li reserves, can reach up to 7 Mt Li, but are more difficult to exploit. Allowing for recycling, the current predicted demand up to the year 2100 is 20 Mt Li; world resources are currently estimated at more than 62 Mt Li. Thus, abundant resources exist, and no long-term shortage is predicted.

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Lithium and Lithium Isotopes in Earth’s Surface Cycles

Lithium and its isotopes can provide information on continental silicate weathering, which is the primary natural drawdown process of atmospheric CO2 and a major control on climate. Lithium isotopes themselves can help our understanding of weathering, via globally important processes such as clay formation and cation retention. Both these processes occur as part of weathering in modern surface environments, such as rivers, soil pore waters, and groundwaters, but Li isotopes can also be used to track weathering changes across major climate-change events. Lithium isotope evidence from several past climatic warming and cooling episodes shows that weathering processes respond rapidly to changes in temperature, meaning that weathering is capable of bringing climate back under control within a few tens of thousands of years.

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High-Temperature Processes: Is it Time for Lithium Isotopes?

The field of high-temperature Li isotope geochemistry has been rattled by major paradigm changes. The idea that Li isotopes could be used to trace the sources of fluids, rocks, and magmas had to be largely abandoned, because Li diffusion causes its isotopes to fractionate at metamorphic and magmatic temperatures. However, diffusive fractionation of Li isotopes can be used to determine timescales of geologic processes using arrested diffusion profiles. High diffusivity and strong kinetic isotope fractionation favors Li isotopes as a tool to constrain the durations of fast processes in the crust and mantle, where other geochronometers fall short. Time may be the parameter that high-temperature Li isotope studies will be able to shed much light on.

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The Cosmic Lithium Story

Lithium’s story spans the history of the universe and is one that links to all its largest-scale processes: big bang nucleosyntheses, the evolution of stars, and galactic chemical evolution. Lithium was the only metal produced in the big bang, alongside the gases H and He. Stars destroy both stable isotopes of Li easily, yet we still have Li today, even after generations of stars have come and gone. Ongoing production of Li by galactic cosmic rays and by a limited number of Li-producing nuclear reactions and transport processes in some rare types of stars keeps lithium present in the universe.

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The Minerals of Lithium

Lithium is rare in the cosmos, but the formation of continental crust has concentrated lithium into economic deposits. The 124 recognized Li mineral species occur largely in four geologic environments: (1) lithium–cesium–tantalum (LCT) granitic pegmatites and associated metasomatic rocks; (2) highly peralkaline pegmatites; (3) metasomatic rocks not directly associated with pegmatites; (4) manganese deposits. The geologically oldest Li minerals are reported from LCT pegmatites and date to 3,000–3,100 Ma, a critical period in the evolution of the continental crust and the rate of its generation. This suggests a link between the earliest appearance of LCT-family pegmatites and the onset of plate tectonics, consistent with the correlation between the observed abundance of LCT-family pegmatites and supercontinent assembly.

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Biogeochemical Controls on the Redox Evolution of Earth’s Oceans and Atmosphere

Download Article (PDF) June 2020 Issue Table of Contents Editorial A Symphony of ElectronsFrom the EditorsMeet the AuthorsThematic ArticlesSociety NewsBook Review Thermodynamics in Earth and Planetary Sciences 2nd Ed.CalendarCosmoElements Primitive Meteorite Contains Cometary SurpriseDigital Edition The redox state of Earth’s atmosphere has undergone a dramatic shift over geologic time from reducing to strongly oxidizing, and…

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Electron Transfer Drives Metal Cycling in the Critical Zone

Electron transfer in the critical zone is driven by biotic and abiotic mechanisms and controls the fate of inorganic and organic contaminants, whether redox-sensitive or not. In these environments, Fe- and Mn-bearing minerals, as well as organic matter, are key compounds. They interact with each other and constitute important electron shuttles. As a result, not only their solubility but also their structure controls the mobility of many essential and toxic elements. In addition, microorganisms that form hot spots and are widespread in environmental systems are also primordial players in electron transfer processes by acting as a catalyst between an electron donor and an acceptor, and through their contaminant detoxification metabolism.

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Volcanic and Geothermal Redox Engines

The redox (reduction–oxidation) potential is an essential variable that controls the chemical reactions of fluids in magmatic and associated geothermal systems. However, the evolution of the redox potential is difficult to trace from a magma’s source at depth to the surface. The key is knowing that electron transfer is the twin face of the acid–base exchanges that drive charge transfer in the many reactions that occur in multiphase and chemically complex systems. The deduced redox reactivity can reveal many features about the evolution of a system’s composition and the external factors that control it. As such, redox potential analysis is an important geochemical tool by which to monitor volcanoes and to explore geothermal systems.

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Magmas are the Largest Repositories and Carriers of Earth’s Redox Processes

Magma is the most important chemical transport agent throughout our planet. This paper provides an overview of the interplay between magma redox, major element chemistry, and crystal and volatile content, and of the influence of redox on the factors that drive igneous system dynamics. Given the almost infinite combinations of temperature, pressure, and chemical compositions relevant to igneous petrology, we focus on the concepts and methods that redox geochemistry provides to understand magma formation, ascent, evolution and crystallization. Particular attention is paid to the strong and complex interplay between melt structure and chemistry, and to the influence that redox conditions have on melt properties, crystallization mechanisms and the solubility of volatile components.

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