Introduction. Certain technology metals [1-5] hold promise of being key players in meeting one of society’s most pressing long-term goals — providing a reliable means of reducing our dependence on fossil fuels for future energy needs. This article focuses on Li, Co, and Ni, key components of rechargeable lithium-ion batteries (LIBs). Electric vehicles employing LIBs are seen as prime candidates for future reduction of the use of fossil fuels. Unlike fossil fuels, these metals are not consumed in energy production processes. Rather, if properly recycled, they provide the means to harness free, unlimited sunlight for continual energy production. An important feature of their use is that they are conserved in the process and can be recovered in pure form for unlimited use. Unfortunately, the recycling rate for Li, the metal most needed for LIB function is <1%. [2]
Increased high technology demand for Li, Co, and Ni in the past few decades has brought into focus several challenges associated with their production and use. Mining and processing these metals result in serious environmental and negative externality issues. High technology products containing them eventually come to an end of their useful lives and are discarded, usually in landfill. Contained metals, discarded with these products are unrecoverable with present technology. Recycling rates for these metals from end-of-life high technology products are low necessitating increased mine production in order to meet increasing market demand. Low recycling rates mean that the metal usually has a single use before being discarded with the product. Legacy separation methods, such as solvent extraction (SX), ion exchange (IX), and/or precipitation presently used for separation, recovery, and purification of the metals, both in production and recycling of end-of-life products are inefficient and are not environmentally friendly. These legacy methods have low metal selectivity resulting in large capital and operating expenses, generate large amounts of waste, and use large quantities of energy and water [3-6].
This article will focus on the necessity of developing green chemistry methods for the separation, recovery, and purification steps involved in commercial production of high purity Li, Co, and Ni both during ore processing and in recycling of spent LIBs. Other metals present and involved in the separations are also considered. Molecular Recognition Technology (MRT) is a tested, green chemistry procedure for these separations, as will be described. Use of MRT offers promise of marked improvement in separation and recovery of Li, Co, and Ni from spent LIBs, which is necessary if these metals are to reach their potential in clean energy devices.
Replacement of Fossil Fuels by Clean Energy Technologies. Critics of the use of fossil fuels to meet society’s energy needs point out that mining and processing of these fuels generate enormous amounts of waste [3,7]. Combustion of fossil fuels to produce electricity and power our modes of transportation increases carbon dioxide and other pollutant levels with dire environmental and societal results. It is important to realize that so-called clean energy devices such as electric-powered vehicles, and wind turbines require specialty metals for their operation. These metals are obtained by mining virgin ore containing them, usually as a by-product. Processing these ores using legacy methods leaves a trail of environmental and negative externality effects, as indicated earlier. Single use of the metals followed by discard of the spent product containing them is reminiscent of single use of fossil fuels. However, metals can be recycled, but fossil fuels cannot and the recycled metal can be used repeatedly without loss of function. The preferred scenario is to minimize generation of waste by using clean energy devices that make use of free, unlimited solar and wind sources, but incorporate green chemistry processes into the production of the metals required for these devices and increase the effectiveness of recycling to reduce the need for mining of new ore to replace metals lost to the commons. The ultimate goal would be to conserve our metal supply both in production and recycling. Achievement of this goal is possible with metals using green chemistry, high metal-selective technologies, such as MRT.
Seba [7] takes the extreme, but intriguing view that in the near future use of fossil fuels will become obsolete, with these fuels being largely replaced by free solar energy. He argues that bit-based and electron-based technologies will replace atom-based technologies in use today. Evidence that this transformation is in progress, according to Seba, is the recent exponential cost and performance improvement of technologies that convert, manage, store, and share clean energy. Lithium, Co, and Ni are essential components of devices used in high technology products, such as rechargeable batteries. Rechargeable batteries are central to the change from fossil fuel to solar sources as the means to generate needed energy since they are able to store solar energy and release it in a controlled way, as is done in hybrid electric vehicles and many tools employing these batteries. Efficient separation and recovery of metals from spent products can form a closed cycle allowing repeated use of metals with little loss [8].
Fossil fuels are atom-based technologies that result in the transformation of the fuels into water, carbon dioxide and nitrogen products [7]. These fuels are not regenerable and require constant replenishment from virgin sources. Controlled combustion of coal, natural gas, and oil has powered our planet into the 21st century. Negative environmental, health, and climate effects resulting from this combustion have become increasingly important and, often, controversial global legislative issues. Digital (bit-based) and clean energy (electron-based) technologies based on the distinctive chemical properties of certain metals are disruptive and are becoming more important in the market place daily [9,10]. In principle, metals necessary for these digital and electron-based technologies can be used repeatedly without loss of function provided they are recovered and purified.
What is a Lithium-ion Battery?
Shuva and Kurny [11] describe the composition of LIBs as follows: “A LIB comprises a cathode, an anode, organic electrolyte, and a separator. The cathode is a thin aluminum foil coated with a mixture of active cathode material, electric conductor, binder, and adhesives. Most lithium systems use a material like LiMA
2 at the positive electrode. Some materials used at the cathode include LiCoO
2, LiNiO
2, and LiMn
2O
4 and the electrolyte is an organic liquid with dissolved substances like LiClO
4, LiBF
4 and LiPF
6. The anode is a thin copper foil coated with a mixture of carbon graphite, conductor, binder and adhesives. The heavy metals, organic chemicals and plastics are in the proportions of 5-20% cobalt, 5-10% nickel, 5-7% lithium, 15% organic chemicals, and 7% plastics, the composition varying slightly with different manufacturers.” This description indicates that a number of metals are present in functioning LIBs. Lithium is a constant in LIBs, but a number of other metals may be used depending on the manufacturer. Always, the goal is to achieve high energy density. Lightest of the metals, Li has the greatest electric potential, (3.7 eV) and provides the largest energy density for weight. Weight is of particular importance in hybrid and electric automobiles, but is also a consideration in other applications, such as alloys of Li with Al and Mg. A detailed listing of various components of LIBs with their properties and merits is given by Meshram, et al. [12].
Lithium Production and Use. Meshram, et al. [12] have reviewed the extraction of Li from primary and secondary sources. Lithium extraction from mined ores and minerals, such as spodumene, employs roasting followed by leaching. Extraction from brines includes evaporation, precipitation, adsorption, and IX. Production costs associated with Li extraction from brines is 30-50% less than that from mined ores. Evaporative concentration and refining of brines may require over a year to accomplish. This evaporation process from brine lakes is time consuming and suffers from low recovery efficiency. In addition, large negative environmental effects result due to waste generation and substantial water consumption. Recovery of Li from brines at high purities is complicated by the presence of large amounts of Na and Mg, whose chemical properties are similar to those of Li. [13]. Extensive precipitation, solvent extraction (SX) and ion exchange (IX) procedures are required to obtain pure Li. [12]. Magnesium is also a metal of value that may be recovered in these processes.
In secondary recovery from spent products, Li is extracted from LIBs by leaching followed by precipitation, IX, or SX and electrolysis. Meshram, et al. [12] estimate from literature data that 250 tonnes of ore (spodumene), or 750 tonnes of brine or 28 tons of LIBs from mobile phones and laptops, or 256 LIBs from electric vehicles (EV) are required to produce one tonne of Li. These estimates show several advantages of recycling from an urban mine over mining or extraction from brines as a source of Li. Izatt and Hagelüken [8] have enumerated advantages of recovering metals from urban mines compared to virgin ore deposits. These advantages include knowledge in urban mines of the elemental composition of the collected spent products, avoidance of need to remove large amounts of gangue material, elimination of the environmental burden and impact of mining, extending the lifetime of valuable metal resources, contribution to supply security of the metals, and improved demand-supply balance by broadening the supply base. In the case of Li, an additional benefit is the absence of Mg and Na in the spent product.
The most important use of Li is in rechargeable batteries for mobile phones, laptops, digital cameras, and electric vehicles. The top three producers (metric tons, 2014), are Australia (13,000), Chile (12,900), and China (5,000) [14]. The U.S. produced 870 metric tons in 2013. About 70% of global brine resources are found in four countries, the three above and Bolivia [15]. This level of resource concentration is exceptional and suggests that, for security reasons, efforts should be made to widen the search for other commercial deposits, either brines or mined ore and to pursue the development of a recycled source.
Growth in Li production parallels that of the rare earth elements (REE) and of other high-technology metals [1,3]. A few decades ago, little Li was mined, since there was no major use for it. The U.S. was the main source of mined Li at that time. The green chemistry revolution plus the development of rechargeable batteries have fueled the rapid growth in Li mining and production in the past few decades. Increased production of vehicles powered by LIBs will require especially large amounts of Li in the future. This surge of activity in Li production has largely taken place outside the U.S. and in 2016, as indicated earlier, top producers are Australia, Chile, and China. The largest undeveloped Li deposit is the Salar de Uyuni salt bed in Bolivia that is estimated to contain 10.2 million tonnes of Li or 27 % of the world’s in-situ Li resource [16]. The largest producing deposit of Li is the 3,000 km² Salar de Atacama bed in northern Chile. The concentration of Li in the Chile deposit is 0.14 %, the highest concentration of any producing brine deposits.
Cobalt and Nickel Use and Production
Cobalt and Ni are the metals of greatest value in LIBs. Cobalt is traditionally produced as a byproduct of mining another metal, such as Cu, Ni, or precious metals. In 2008, ~50% of refined Co production originated where Ni was the primary metal mined, ~35 % where Cu
was the primary commodity, and the remainder where Co was the principal product recovered from mining operations, metal scrap and slag [17]. Production of recoverable Co nearly tripled between 1995 and 2008
because of increased demand for Co use in rechargeable batteries and superalloys associated with aerospace and gas turbine operations. Projections are that need for Co use in LIBs will fuel large increases in production in the future suggesting that effective recycling operations could be beneficial in maintaining sustainability for this metal. Approximately 41% of global Co came from Congo (Kinshasa) in 2008 [17]. Effective recycling of Co from LIBs would reduce dependence on this volatile political region for this critical metal.
Recovery of Ni from LIBs is desirable, but not as urgent as that of Co. Nickel has a wider global production base and more diversified uses than Co [18]. Recycling of Ni from LIBs would provide a marketable product that would lower recycling costs.
Metal Recycling from Spent Batteries. Collection rates for EOL LIBs have improved over the years, but are still dismally low [19]. For example, only 0.5% of end-of-life LIBs were collected in the European Union in 2002. The number had improved to 2.7% by 2007, but only a few companies were processing them for recovery of the metals they contain. Metals commonly recovered from LIBs for recycling are Li, Co, and Ni. Precipitation and SX are the legacy methods used for these separations [19,20]. These methods have severe limitations in terms of capital and operating expenses, as have been discussed [4,21]. Limitations include lack of metal selectivity resulting in incomplete metal removal requiring additional downstream separations, decreasing ability to separate metals as concentrations decrease to the mg/L or lower levels, use of solvents and hazardous chemicals which later must be processed for disposal, slow kinetics, and large space requirements. These limitations add significantly to capital and operating costs.
As LIB recycling efforts expand to target this broad spectrum of metals, recycling technologies used must be optimized to achieve higher efficiencies and selectivities for target metals [19]. Legacy separation methods are not well designed for attacking this sort of problem, especially when the metals are present at low concentration levels [3,21]. The inefficiency of these methods may be responsible, in part, for the low recycling rates of the contained metals.
Zeng, et al. [22] provide a critical review on recycling of spent LIBs. These authors point out that increasing consumer demand for electronic products (mobile phones, digital cameras, laptop computers) and, especially, for electric vehicles have resulted in increasing demand for Li and Co that strains available virgin ore resources. They suggest that recycling of these metals from spent LIB will be a necessity in the future to decrease energy consumption involved in mining, conserve rare metal resources, and eliminate pollution by hazardous chemicals used in the mining process. These authors review the current status of recycling LIBs from collection to separation of individual metals of value. Structure and components of LIBs are described together with batch mode operations associated with pretreatment, secondary treatment, and recovery of the metals of value. A combination of SX, precipitation, electrowinning, crystallization, and calcining is currently used to produce high purity metal products.
Unlike the high recycling rate of Pb from lead-acid batteries (>90%), recovery of metals of value from LIBs and other rechargeable batteries is very low [22]. For example, in China spent products are disposed of in landfills or piled in warehouses. It is estimated that 2% and 5% of waste batteries (LIBs, Ni-metal hydride, Ni-Cd) are recycled in China and Beijing, respectively. These authors [22] emphasize that it is essential for global legislative systems to take action for regulations or rules for disposal of spent LIBs, since these items are rapidly becoming a major portion of e-waste, which is the fastest growing waste stream globally [23].
The need for recycling of Li and other value metals from LIBs has been summarized by Hanisch, et al. [20]. These authors point out that demand for Co for the production of 20 million electric vehicle (EV) batteries per year, assuming averaged material composition, would be about equal to current world mine production of Co and would deplete Co reserves in less than 60 years. The Ni needed for production of 60 million EV batteries per year would be larger by 170 fold than today’s existing production capacity. These figures demonstrate a need for recycling Co and Ni from spent LIBs. Overall recycling rates for these metals is 25-50% [2,22], but rates from spent batteries is <1%. Recycling of spent products containing Ni and Co is beneficial in reduction of material production emissions like SOx that are produced during mining of virgin ore. Energy consumption during production of LIBs can be reduced through use of recycled materials. Also, in-production
recycling of these metals can result in substantial economic and ecological savings [20]. Present recycling processes are aimed at recycling Co and Ni, rather than Li from LIBs. This is consistent with the higher raw material costs of these metals compared with the costs of the less expensive Li. Hanisch, et al.[20] cite arguments that Li will be in critical supply in this century if EV batteries become used on a large scale or if the Li in these batteries is not recycled to high levels (~90%). Projections cited by these authors [20] agree that recycling of Li is desirable for long-term sustainability of this metal.
The number of LIBs produced is large. In 2000, global production was ~500 million cells [22]. In the period between 2000 and 2010, annual global production increased 800%. Zeng, et al. [22] estimate that by 2020 the quantity and weight of discarded LIBs could surpass 25 billion units and 500 thousand tonnes, respectively. These numbers indicate a large loss of valuable metal resources unless effective metal recycling is begun and maintained. The numbers also present a tremendous opportunity for separation and recovery of Li and Co from this urban mine. Mining and processing virgin ore for these metals is fraught with many challenges as indicated earlier.
Gruber, et al. [16] have reported a comprehensive study of global Li availability to sustain the need for Li in electric vehicles through the 21st century. They conclude that Li availability will not constrain the electrification of the automobile during the present century. Many factors are considered in arriving at this conclusion. One of these factors is that by the end of the century as much as half of the available Li will come from recycling. Assuming a 3% gross domestic product growth rate and recycling participation of 90%, they estimate that a total of 25.40 million tonnes of Li will be required for the period 2010-2100. Of this total, 12.65 million tonnes will come from recycled Li and 12.75 million tonnes from mined Li. Other recycling rate and growth rate scenarios give slightly different ratios of recycled and mined Li required. As mentioned earlier, the present recycling rate for Li is < 1% [2]. Methods based on SX and precipitation are presently used for separation and recovery of Li, Co, and Ni [11]. These methods suffer from slow kinetics, need for solid-liquid separations, high cost, and low purity making economic commercial separations problematic. The need for improved technologies for separation and recovery of Li from LIBs has been noted [12].
Kang, et al. [24] have studied the potential environmental and human health impacts of rechargeable LIBs in small product units. Advantages of these batteries that have led to their widespread use are high energy density and product longevity. However, these authors [24] report that the small size of many LIBs, the high rate of turnover (two to four years) of products that contain them, and lack of uniform regulatory policies on their disposal mean that discarded batteries could contribute substantially to environmental pollution and adverse health impacts due to potentially toxic materials. Batteries from cell phones and smart phones were studied. Levels of metals found, reported as mg specific metal per kg of total battery material, were: Al (51,800 to 278,000 mg/kg), Co (58,000 to 278,000 mg/kg), Cu (54,100 to 152,000 mg/kg), Li (9,800 to 37,200 mg/kg), Ni (120 to 30,500 mg/kg), and Fe (254 to 24,500 mg/kg). Levels of other metals, including Cr, Tl, Ag, and Pb, were much lower and varied according to the material requirements of the phones. The results indicate that the environmental impact associated with resource depletion and human toxicity is mainly due to the presence of Co, Cu, Ni, Tl, and Ag. Contributions of Al and Li to human toxicity could not be estimated due to inadequate data. Kang et al [24] concluded that stronger government policies are needed at local, national, and international levels to encourage recovery, recycling, and reuse of battery materials. It is apparent that recycling efforts extend beyond Li and Co to other constituents of LIBs. Spent electronic devices are expected to contribute significantly to the increasing problem of electronic waste, which is the fastest growing segment of U.S. and global solid waste streams [23,24].
Molecular Recognition Technology – A Green Chemistry Method for Metal Recovery from Lithium-ion Batteries
Summarizing their review on Li mining and recovery from secondary sources, Meshram, et al. [12] observed that “there is a need to develop appropriate technology which can address the limitation of current processes for extraction of all valuable metals from its [Li] primary as well as secondary resources.” MRT meets these requirements with its proprietary SuperLig® products. These products are pre-designed, using principles of nanochemistry and supramolecular chemistry, for selective green chemistry separation and recovery of specific metals from primary ore sources as well as from spent products [4,25,26].
Lithium Separation and Recovery from an Industrial Brine Solution. A SuperLig® product has been used in column mode at laboratory scale to selectively separate and recover Li at the 99%+ level from an industrial brine solution containing high amounts of Na, K, Ca and Mg [25]. Concentrations of other metals, including Mn, Cr, Co, Fe, Ni, Cu, Zn, Cd, Al, Ga, and In, if present in the brine solution, were <1mgL
-¹ in the recovered Li solution, as determined using inductively coupled spectroscopy (ICP). The pure Li product is collected in dilute (1 M) hydrochloric acid solution.
Benefits of the green chemistry MRT process for separating and recovering Li from brine feed solutions are: (1) simplicity of the process requiring few steps, short time for separation, small equipment inventory, and small floor space to house apparatus, (2) use of few, relatively benign chemicals, (3) no organic solvents used, (4) selective removal and recovery of Li eliminating additional steps downstream to remove impurity metals, (5) separation of Li from Mg, which is difficult using conventional technologies, (6) short inventory time for Li, (7) rapid separation time, (8) separation and recovery of Li at the 99% or greater level, (9) generation of minimal waste, and perhaps of greatest importance, (10) accomplishment of the separation directly from brine without the necessity of long (up to a year) wait for evaporative concentration [12].
Lithium Separations from Spent LIBs. Separation and recovery of Li from spent LIBs should be easier than from brines because of the absence of Mg and Na.
Cobalt and Nickel Separations from Brines or Spent LIBs. MRT products are available for separations of Co and Ni from other matrix metals which may be present, such as Fe and Cu [25]. These MRT products are available for separations of these metals from brines or spent LIBs after proper treatment of the feed.
