Part 1: Lithium Recovery: A Key Innovation Area in Mining

Introduction

Today, energy storage for electric and hybrid vehicles, as well as the transition to green energy sources such as solar, relies on lithium-ion batteries. Innovative lithium-air batteries currently being developed offer the potential for a much longer charge that could significantly expand the range of electric vehicles and facilitate larger electric transportation, like airplanes and shipping trucks [1]. To meet the increasing demand for lithium batteries for electric and hybrid vehicles and commercial and residential green energy storage, lithium availability must substantially increase. Some estimate that the vehicle industry alone requires a 20-fold increase in lithium availability. 

Lithium can be sourced from lithium-rich brines and hard rock ore (e.g., granitic pegmatites such as spodumene and petalite). Today, the majority of global lithium is extracted from lithium-rich brines or salt lakes in the form of lithium carbonate and lithium chloride[2]. Lithium extraction from brine, or brine mining, involves evaporation of large volumes of brine, leaving behind concentrated lithium and is a cost-effective method for lithium mining compared to ore mining [3]. Nevertheless, brine mining is a slow process that is chemical-intensive, utilizes large amounts of freshwater and land, and produces a lot of waste [2]. Brine mining strategies must also differ from site to site based on geological characteristics and climate, making it difficult to scale to meet lithium needs. In addition to demand concerns, utilizing an environmentally costly mining process to fuel the clean energy transition is not ideal. Advances in lithium mining and strategies for recycling lithium from spent batteries aim to address both the shortage and minimize the environmental impact of brine mining.

Direct Lithium Extraction

Traditional brine mining is a multistep process that involves pumping brine into shallow open-air ponds where water evaporates - fueled by solar radiation and wind - to concentrate lithium in the brine. The concentrated brine then undergoes chemical precipitation to extract other ions, purification steps to remove impurities, and extraction of Li2CO3 via the addition of Na2CO3. Though cost-effective, this process is very time-consuming, taking years. Direct lithium extraction (DLE) methods actively remove lithium from brine rather than relying on passive evaporation from solar radiation and wind. There are multiple DLE technologies that are used or proposed; some still require evaporation ponds, though these require less land than traditional brine mining. DLE methods include ion exchange, liquid-liquid extraction, electromembrane processes, nanofiltration, electrochemical ion pumping, selective precipitation of Li3PO4 via addition of Na3PO4 a, and thermal-assisted methods [4].

Ion exchange

Lithium-ion exchange involves the absorption of lithium using an ionic exchange resin that has a high affinity for Li+ cations, such as ceramic. The lithium is then eluted from the ceramic by acid or freshwater where a hydrogen ion from the acid is exchanged for lithium[4]. This process is quite harsh, and most ceramic materials can only be reused a few times. However, more durable ceramic materials have been developed to withstand many cycles of ion exchange [5].

Liquid-liquid extraction

In contrast to ion exchange described above using a solid material with a high affinity for Li+, liquid-liquid extraction, also known as solvent extraction, relies on a solvent with a high affinity for Li+. Organic solvents, including tri-n-butylphosphate and FeCl3, and ionic liquids, such as imidazole, have high affinities for Li+ and can be used for solvent extraction of lithium from brine [4].

Membrane-based methods

Electromembrane processes for brine mining may utilize Li+-selective membranes or membranes that are selective to anions or cations [6]. Nanofiltration involves forcing brine at high pressure through a filter with a typical pore size of 1nm to separate lithium from salt lake brine[7]. Current membrane-based approaches have proven to be highly efficient with high purity (>95%), though they are less efficient at higher lithium concentrations.

Electrochemical ion pumping

Like the ion exchange methods discussed above, electrochemical ion pumping uses materials that are highly specific for Li+ cations.  Li+ cations are selectively captured from brine by applying a current, and then the solution is replaced with a recovery solution, and the current is reversed to collect Li+ cations [8]. This process is rapid and does not require chemical input.

Selective precipitation

Selective precipitation is based on the poor aqueous solubility of lithium phosphate. Li3PO4 is recovered via the addition of a phosphate, such as Na3PO4, to the solution [4].

Thermal assisted

Thermal-assisted methods involve concentrating brine by promoting evaporation by applying heat or using an evaporator, distillation device, or membrane distillation [4].

Princeton’s String Method

Researchers at Princeton have developed an extraction technique that utilizes porous “strings” that are dipped in brine [9]. The water quickly evaporates, leaving the salt ions attached to the fibers, including lithium chloride. This process would decrease the amount of land and time needed for brine mining.

Next month, learn about the circular economy in lithium mining in part 2 of the article.

Sources:

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