1. Introduction
The EU Directive on end of life battery treatment (2006/66/EC) established targets for collection and recycling rates in order to avoid improper disposal, but also to promote resource recovery. In particular, 50% recycling target is fixed for batteries not containing dangerous metals such as Cd and Pb. Nevertheless, the Directive does not include technical aspects concerning the way such end of life devices should be treated in recycling facilities, leaving to the different countries the promotion and adoption of proper collecting schemes and treatment processes. In the same way, no specific obligation was established concerning the target of collection of the different battery types or the recycling rate of specific components, which could be strategic elements or critical raw materials (such as lithium and graphite, respectively) but have little percentage weight in the batteries. Thus, the recycling target can be achieved by treating only certain kinds of batteries (the most abundant on the market) and recycling the components with the highest percentage weight in the wastes (for instance steel and heavy metals).
This has led to the adoption of treatment schemes in which only a partial fraction of the value contained in a battery is recycled and some types of battery with difficult treatment processes are just diluted with other solid charges to solve the problem of their end of life without real valorization of the components included. This means a “downcycling” of battery components, that is some values are lost and not properly valorized, while the virtuous approach should be “upcycling”, that is not merely recycling the materials, but hopefully giving them additional value (as an example let us consider the production of high value nanomaterials from end of life batteries) [
1].
Among the different battery types, Li(0) are primary non rechargeable batteries covering about 3% of primary batteries put on the market, which in turn represents 75% of portable batteries [
2]. This means that annually about 2000 ton of this type of battery are put on the market in the EU. Primary Li batteries still present many critical issues regarding recycling. In fact, the presence of highly reactive metallic lithium and flammable organic solvents entail safety risks during the recycling process. As a consequence, Li primary batteries are currently a cost for battery collectors, who after manual sorting of the different battery types, can have revenues from some types (Li-ion batteries), while having to pay for the disposal of some others (Li(0) types).
The most common adopted treatment for Li(0) primary batteries is a pyro-metallurgical one in which whole batteries, or some battery fractions, are smelted along with other solid feeds also from primary sources. This leads to the down-cycling of different battery components such as lithium and manganese, which are lost in the slag. In addition, pyro-metallurgical processes have huge environmental impacts for energy consumption and gas emissions; they can be operated only at large scale to exploit the law of economy of scale to have low production costs; this means that dangerous wastes such as batteries have to travel across EU countries to the few existing pyro-metallurgical plants able to down-cycle them. Apart from this, the pyro-metallurgical processes cannot be the right way to refurnish the battery manufacture system, which the EU is trying to promote with he dedicated initiative of the European Battery Alliance. In fact, in pyro-metallurgical processes. metals are recovered in the reduced metallic form, while metals as oxides are used are electrodic materials in the benchmark technology of batteries, i.e., Li-ion batteries dominating the market for portable electronics and for hybrid and electric vehicles. Using pyro-metallurgy as a treatment option for battery recycling would imply first reducing the metals present in end of life batteries as oxides (with high carbon consumption for such an aim) and then re-oxidizing them to obtain new products for battery manufacture.
Conventional pyro-metallurgical processes do not allow for Li and Mn recycling from Li(0)-MnO
2 batteries because both metals are lost in the slag. An innovative pyro-metallurgical approach has been presented aiming at Li recovery from Li batteries (both Li primary and Li–ion) [
3]: in this case, Li was reduced using carbon, volatilized and re-condensed, while Mn in the slag was recovered by leaching.
In the literature, only a few works have been reported regarding the hydrometallurgical treatment of primary lithium batteries and generally including a preliminary thermal treatment for Li oxidation followed by leaching [
4,
5]. A patent survey also denoted the combined hydro-pyro- metallurgical process of Toxco for Li recycling from Li(0) containing wastes including primary batteries [
6]. Nevertheless, to the Authors knowledge no process or plant is now operating in the EU for the dedicated hydrometallurgical treatment of Li(0) primary batteries.
In this context, the LIFE-LIBAT project [
7] aims at the demonstration of an innovative cryo-mechano-hydrometallurgical process for the treatment of end of life Li(0)-MnO
2 batteries without preliminary high temperature treatment.
The idea of the project is to demonstrate the technical and economic feasibility of a process able to recycle the different components in these batteries (steel scraps, Mn, and Li) designing and constructing prototypes, which can be used also for the treatment of other types of batteries such as Li-ion batteries [
1,
8]. The technical solution for the treatment of these batteries includes a cryo- mechanical treatment avoiding the fire and explosion risk due both to residual Li(0) (present in end of life primary batteries for uncomplete discharge) and flammable solvents. In this way, the safe liberation of battery components is achieved and the electrodic materials rich in Li and Mn can be fed to the hydrometallurgical section, where the oxidized products of Mn and Li can be recovered for the manufacture of new electrodic materials.
Environmental benefits generated from the adoption at large scale of hydrometallurgical processes instead of pyro-metallurgical ones will be in terms of the reduction of energy consumption (hydrometallurgical processes are performed in water at temperature lower than 100 °C), the reduction of greenhouse and toxic gas emissions, improved exploitation of resources avoiding down- cycling, and the reduction of potential impacts associated with the transport of dangerous wastes throughout the EU to pyro-metallurgical plants.
In the present work, economic feasibility of the proposed LIBAT process was assessed by process simulations and estimation of economic data.
2. Materials and Methods
Li(0)-MnO
2 batteries collected by SEVal Srl (Colico, Italy) were manually sorted according to the different types as reported in
Figure 1. Mechanical treatment was performed on a mixture of cylindrical and prismatic cells (type a and b in
Figure 1) and coin cell (type e in
Figure 1).
Cryo-crushing and hydrometallurgical treatment is performed in the prototypes (potentiality: 50 Kg/d) constructed at the SEVal site including a cryo-mechanical section, a sieving and separation section, a hydrometallurgical section, and a gas treatment section (
Figure 2).
In
Table 1, the main characteristic of the equipment included are reported.
During the preliminary activity of the LIBAT project, about 300 Kg of Li(0) batteries were thermally stabilized with liquid N
2, and then crushed in a vertical axis hammer mill. Crushed samples were then sieved obtaining two fractions identified as the coarse fraction (>1 mm) and fine fraction (≤1 mm). The coarse fraction was submitted to magnetic separation obtaining a magnetic coarse fraction (made of steel case) and a non-magnetic coarse fraction (made of internal separators of plastic and paper)
Figure 3.
The LIBAT process includes the hydrometallurgical treatment of solid fractions. In particular, Li extraction from the crushed fractions (fine fraction, magnetic coarse fraction, and non-magnetic coarse fraction) was performed in a mechanically stirred reactor using water at room temperature with a solid-to-liquid ratio equal to 1:5. After filtration, the liquid stream was recycled for subsequent washing operations of the same fractions thus increasing the Li concentration in solution. The resulting solution was heated at 95 °C and Na
2CO
3 added for the precipitation of Li
2CO
3 [
9]. After two hours, the obtained suspension was filtered and oven-dried overnight at 105 °C. The extraction of manganese from the electrodic powder was achieved by leaching for 3 h under stirring at 85 °C with 1:10 g/mL of solid/liquid ratio using 1.3 M sulfuric acid and 20%
v/
v hydrogen peroxide. A manganese-rich solution was recovered after the leachate filtration and used for Mn recovery according to the conditions optimized in [
10]: sodium hydroxide was added to the solution obtained from the leaching to increase the pH to around 10; after 2 h, the suspension obtained was filtered and the collected solid oven-dried at 105 °C overnight.
Solid and liquid samples were analyzed by Atomic Absorption Spectrophotometer (AAS, contrAA® 300—Analytik Jena AG) equipped with a Xenon short arc lamp as radiation source and with a flame atomizer fed with a mixture of C2H2 and air. Multi-standard solution (Merk Millipore 1000 mg/L HNO3 sol.) was used for calibration and each metal was determined according to a selected wavelength with three replicates for each measurement.
In
Figure 4 the block diagram of the process is reported.
At this stage, the hydrometallurgical section was built but not yet in operation. The mass balances for this section were obtained by laboratory scale tests on the solid fractions obtained by cryo-mechanical treatment and separation at pilot scale.
Quantified mass balances including the metal composition of each stream of the process were estimated from pilot scale tests for the cryo-mechanical treatment and fraction separation, and from lab scale tests for the hydrometallurgical section.
These balances were used for preliminary process simulations and the estimation of economic figures assuming the cost and price reported in
Table 2 which was fixed according to previous demonstration campaigns.
The cost of the LIFE-LIBAT prototype (€320,000) made up of the units reported in
Table 1 was used for estimating the plant costs for different potentiality in the process simulation according to a scale law with exponent 0.6.
4. Discussion
Preliminary process simulations performed using material balances from pilot and lab scale denoted that economic feasibility can be achieved in the range of potentiality of Li(0) batteries actually collected in Italy. Finalization of mass balances in the pilot scale and further process optimization will be performed during the next activities of the LIFE-LIBAT project.
The proposed process is an alternative to downcycling pyro-metallurgical plants allowing the recycling of potentially all materials included in these batteries. Preliminary tests at pilot scale demonstrate the technical feasibility of cryo-crushing giving the separation of directly recoverable steel from the external case and electrodic powder. This powder is then treated for Li and Mn recovery at lab scale and further tests are planned at pilot scale.
Some additional aspects should be considered regarding the flexibility of the proposed process and plant for treating other types of batteries. In particular, considering primary Li batteries, the Li-MnO2 type is about 50% of the total collected batteries of this specific type. The other 50% is mainly Li-SOCl2 presenting problems regarding the toxicity and corrosion of SOCl2 and its decomposition products (SO2). A campaign will be dedicated to Li-SOCl2 batteries in the demonstration activities of the LIFELIBAT project in order to assess the technical feasibility of the cryo-mechanical treatment and the gas treatment section for treating this specific type of Li(0).
More interestingly the proposed process (cryo-mechanical and hydrometallurgical treatment) will allow the treatment of Li-ion batteries, which are rechargeable batteries used in almost all electronic devices (laptop, smartphone, tables) and hybrid and electric vehicles. In addition during the project, a campaign dedicated to Li-ion batteries will be performed to assess the flexibility of the process for this type of battery. This could be a crucial aspect for further exploitation of the process. In fact, Li-ion batteries are largely diffused (about 75,000 t were put on the market in EU countries in 2015 [
11]) and contain also critical raw materials such as Co increasing the recoverable value from these wastes. Then, the possibility of treating Li-ion batteries according to the proposed route will dramatically change the scale of operation of the process and thus improve its economic feasibility.