In contrast to co-processing, dedicated pyrometallurgical processes for LIB recycling are specifically developed for the treatment of LIBs. The processes enable the enrichment of Li in the slag, and the furnaces are designed to handle the highly corrosive feed material. Furthermore, the off-gas treatment is dimensioned to capture the high amounts of halogenic and organic compounds. Nevertheless, also in dedicated processes, LIBs are often co-processed with other feed materials in order to meet a suitable energy and mass balance as well as to enable sufficient plant utilization in this emerging market.
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One of the most prominent examples is Umicore SA (Belgium), which operates a semi-industrial furnace at Hoboken (Belgium) with a capacity of 7000 t/year [ 52 ]. Umicore announced an increase of its recycling capacity by a factor of approximately 10 by the mid-2020s [ 53 ]. During the last 15 years, Umicore has published several patents regarding LIB recycling. Although little is known about the exact current direction, the history of patents indicates various changes regarding process design as well as furnace technology. In principal, all process options produce one or two alloys containing Co, Cu, and Ni, a Li-bearing slag, and a fly ash phase. Regarding process design, two principal flow sheets were published in the patents, which are shown in Figure 6
According to the patent history, the first approach was to produce a Co/Cu/Ni alloy and a Li-bearing slag using a single-furnace process ( Figure 6 , left). The first patents, e.g., [ 54 55 ], describe the use of a shaft furnace, in which Co/Ni-bearing batteries (LIB and NiMH batteries) and other materials are fed together with slag formers, mainly CaO and SiO, and coke as a reductant. A shaft furnace was chosen in order to take advantage of the temperature gradient over the packed bed. The temperature of the batteries is slowly increased by the rising counter current gas generated in the smelting and reducing zone. Therefore, the electrolyte is slowly evaporated in the upper part of the bed (pre-heating zone), which lowers the risk of battery explosions. The furnace is operated at a comparatively high bath temperature of about 1450 °C, which is necessary to keep the viscosity of the Al-rich slag system sufficiently low.
According to [ 56 ], the drawbacks of the process are a very high coke consumption, which is necessary to carry out the reduction and to keep the packed bed sufficiently porous. Furthermore, the occurrence of size segregation in the shaft leads to an increased pressure drop over the packed bed, and large quantities of fines are carried over with gases, resulting in problems at the bag house. In order to solve these problems, [ 56 ] suggests the use of a bath smelting process instead of a shaft furnace. Due to the rapid heating of the battery cells in the molten bath, the batteries are susceptible to violent explosions, which can damage the lining. Therefore, and as protection against chemical attack, the bath smelter is equipped with freeze lining at the bath level. The operating temperature is again about 1450 °C, and SiOand CaO are added to the feed in order to flux the Al.
The latest patent family indicates a change in direction ( Figure 6 , right). Instead of a fully dedicated process for Co/Ni-containing batteries, [ 57 ] suggests the processing of Co-bearing batteries and their scraps in a converter furnace together with Cu or Cu/Ni matte in order to produce a crude Cu/Ni alloy and a Co- and Li-bearing slag. Co can be recovered from the slag either by hydrometallurgy or by deep reduction, producing a crude Co metal phase and a Li-bearing slag.
The advantages of this approach are the ability to treat variable amounts of battery scrap in large-scale installations, an increased flexibility to meet a suitable energy and mass balance, as well as the pyrometallurgical separation of Co from Ni, which probably allows the hydrometallurgical refining of Co in existing plants designed for the refining of cobalt hydroxide produced from the African Cu/Co belt.
The further hydrometallurgical processing of the Co-, Cu-, and Ni-containing alloy is conducted in plants similar to those described in Section 3.2.1 . Umicore produces a variety of Co and Ni products, including battery grade chemicals and cathode materials for LIBs [ 52 58 ].
The Li content of the slags is comparable to the Li content of spodumene concentrates, which are beside Li-containing brines the major commercial source for Li [ 59 ]. In addition, the chemical composition shows similarities; see Table 5 . Besides the listed oxides, minor amounts of Fe and Mn oxides occur. Therefore, an economic extraction might be feasible in comparison to slags with lower Li concentrations from co-processing plants.
The extraction of Li from different slag compositions was investigated in the research project Lithium-Ion Battery Initiative (LiBRi) [ 64 ] as well as by [ 58 ]. A general flow sheet of the developed process is given in Figure 7
2SO4 or HCl at 80 °C. Good Li yields are obtained with both media at a free acid concentration of approximately 10 g/L. In order to ensure good filtration, the leach solution is neutralized to obtain a solution at pH 5. Al, the main impurity in solution, is removed under these conditions. Several neutralization agents can be used. In a sulfate medium, CaO has the advantage that CaSO4 is formed, which reduces the salt load of the solution. In a chloride medium, NaOH is preferred over CaO because Ca is more difficult to separate from Li. Na2CO3 can be used as a neutralization agent in both media but could decrease the Li yield of the process if it is already used in this stage of the flowsheet. After the removal of Al by filtration, it is advantageous to increase the Li concentration in solution by using the filtrate again in the next leach operation a few times until the Li concentration is high enough for the next steps. When the desired Li concentration is reached, the leach solution can be essentially purified of other metals by precipitation between pH 9 and pH 10 with Na2CO3. This is an efficient way to remove Ca and Mg by forming their carbonate salts. Ca and Mg carbonate salts are less soluble than Li2CO3. Finally, pure Li2CO3 is precipitated at high temperature (between 80 and 100 °C) and pH > 10. The solubility of Li2CO3 decreases at higher temperature and higher Na2CO3 content. Moreover, the Li yield in this step increases at higher initial Li concentration. Therefore, the yield can be improved if water is removed from the solution prior to precipitation, e.g., by evaporation [In a first step, the slag is milled to obtain a micrometer-sized powder. Then, this powder is leached in HSOor HCl at 80 °C. Good Li yields are obtained with both media at a free acid concentration of approximately 10 g/L. In order to ensure good filtration, the leach solution is neutralized to obtain a solution at pH 5. Al, the main impurity in solution, is removed under these conditions. Several neutralization agents can be used. In a sulfate medium, CaO has the advantage that CaSOis formed, which reduces the salt load of the solution. In a chloride medium, NaOH is preferred over CaO because Ca is more difficult to separate from Li. NaCOcan be used as a neutralization agent in both media but could decrease the Li yield of the process if it is already used in this stage of the flowsheet. After the removal of Al by filtration, it is advantageous to increase the Li concentration in solution by using the filtrate again in the next leach operation a few times until the Li concentration is high enough for the next steps. When the desired Li concentration is reached, the leach solution can be essentially purified of other metals by precipitation between pH 9 and pH 10 with NaCO. This is an efficient way to remove Ca and Mg by forming their carbonate salts. Ca and Mg carbonate salts are less soluble than LiCO. Finally, pure LiCOis precipitated at high temperature (between 80 and 100 °C) and pH > 10. The solubility of LiCOdecreases at higher temperature and higher NaCOcontent. Moreover, the Li yield in this step increases at higher initial Li concentration. Therefore, the yield can be improved if water is removed from the solution prior to precipitation, e.g., by evaporation [ 58 64 ].
Investigations by [ 64 ] showed that silica management is of paramount importance. Under certain conditions, the dissolution of silica leads to gel formation, resulting in severe filtration problems and low yields. Overall Li yields under favorable conditions were reported to be between 60% and 70%.
Another critical issue is residue management. Due to the low Li content of the slags, the amount of residue from the leaching and precipitation of impurities is high. The disposal of such residues is restricted in Europe and is associated with high costs.
3)2). A simplified spodumene processing flow sheet is given inA possible solution to this problem is the application of the slags as a neutralization agent instead of conventional Ca-based agents in spodumene processing as described in [ 65 ]. Furthermore, this bypasses the need to establish a specific process for comparatively low amounts of slag. Spodumene is a pyroxene mineral consisting of lithium aluminium inosilicate (LiAl(SiO). A simplified spodumene processing flow sheet is given in Figure 8
After spodumene ores have been mined, concentrated, and comminuted, the finely divided material is submitted to a first high-temperature treatment step during which α-spodumene is converted into β-spodumene. Following the phase transformation, the material is mixed with H2SO4 and submitted to a roasting step that aims to liberate the Li from the mineral. This step is performed at 250–300 °C with an excess of acid with respect to Li.
The roasted material is subsequently mixed with water, upon which the Li2SO4 dissolves, together with the free H2SO4. Next, a conventional neutralizing agent such as CaCO3, CaO, or Ca(OH)2 is added to neutralize the free acid and to precipitate a number of impurities.
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Typically, the neutralization step is performed at a pH of 5 to 6 to remove impurities such as Al, Si, and Fe from the solution. A solid–liquid separation step is applied to separate the crude Li2SO4 solution from the residue that mostly contains aluminum silicates, gypsum, and precipitated impurities. Then, further purification steps are applied for the removal of Ca, Mg, and other impurities before Li precipitation as carbonate or hydroxide.
In the described process, the Li-bearing metallurgical slag is used to substitute part of the conventional neutralizing agent. In this neutralization step, most of the Li in the slag is released and supplements the Li liberated from the spodumene. To ensure the optimum release of the Li from the slag, it is preferred to neutralize with Li-bearing slag up to a pH of less than 4. Above, it is recommended to proceed with a conventional neutralization agent to reach a pH between 5 and 7. So far, no information has been published about the industrial implementation. According to information published in the patent, overall Li yields around 90% from the slag are achievable, which is comparable to Li yields from spodumene concentrates [ 59 ].
Adding lead for machinability is not an argument anymore, because we have developed new alloys that can replace those which contain lead. Do you know how you can benefit from using these alloys?
Lead is used as an alloying element in aluminium for machining purposes, but it is generally forbidden in consumer products, and its exemption in aluminium will expire in a couple of years. This is why we have been developing lead-free alloys.
Do you know how much lead your aluminium suppliers use in the alloys they deliver for your products? How about the lead-free aluminium alloys that have been developed? These are questions you should consider when you look at using aluminium in your new product designs.
The issue with lead is not new, but the concerns are getting more important because exemption 6b in RoHS is going to expire in Europe in 2021. In particular, I’m talking about 6(b)-II under RoHS Annex 3, which refers to lead as an alloying element in aluminium for machining purposes with a lead content up to 0.4 percent by weight.
When an aluminium producer intentionally adds lead as an alloying element, they need to make sure that the alloys comply with European REACH and RoHS legislation. Stick with me here while I explain.
All RoHS-restricted substances also are on the REACH restricted list.
The RoHS requirement states that lead (Pb) content shall be below 1000 parts per million (ppm). Mercury content also shall be below 1000 ppm, while cadmium content has a maximum limit of 100 ppm.
Lead was – and still is, in other markets than the EU – intentionally added in some 6xxx-series aluminium alloys for achieving better machinability. In those cases, lead was regarded as an alloying element. The rules for the U.S. market have lead limits of 0.5 percent in aluminium alloys. These tend to be 6xxx-series alloys for improved machinability, such as the 6262 aluminium alloy.
As I mentioned, adding lead for machinability is not an argument anymore, because we have developed new alloys that can replace those which contain lead. This is a sustainable solution.
In fact, we have successful implementations where we replaced lead-containing alloys with lead-free variants. And these are truly lead-free, not ones that simply contain less than 0.1 percent lead.
My advice is that you double-check with your supplier when you ask them about their lead-free aluminium alloys. Are they completely lead-free? Maybe not. Be sure you get what you want.
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