A PROCESS FOR RECOVERING METALS FROM RECYCLED RECHARGEABLE BATTERIES

Abstract

The invention relates to hydrometallurgical method for recovering lithium and one or more transition metals from spent lithium ion batteries, comprising: treating an electrode material of the batteries in an alkaline solution to dissolve lithium in said solution; separating from the alkaline solution a solid phase consisting of lithium-depleted electrode material; recovering lithium from said alkaline solution; leaching the lithium-depleted electrode material with an acid leach solution to dissolve one or more transition metals of the electrode material in the leach solution; separating insoluble material, if present, from the leach solution to obtain metal-bearing aqueous solution and isolating one or more transition metal(s) and optionally the remainder of the lithium from said metal-bearing aqueous solution.

Claims

1. A hydrometallurgical method for recovering lithium and one or more transition metals from spent lithium ion batteries, comprising: treating an electrode material of the batteries in an alkaline solution to dissolve lithium in said solution; separating from the alkaline solution a solid phase consisting of lithium-depleted electrode material; recovering lithium from said alkaline solution; leaching the lithium-depleted electrode material with an acid leach solution to dissolve one or more transition metals of the electrode material in the leach solution; separating insoluble material, if present, from the leach solution to obtain metal-bearing aqueous solution and isolating one or more transition metal(s) and optionally the remainder of the lithium from said metal-bearing aqueous solution.

2. A method according to claim 1, wherein the electrode material comprises a cathode material of spent lithium ion batteries selected from the group consisting of lithium cobalt oxide (LiCoO.sub.2), lithium manganese oxide (LiMn.sub.2O.sub.4) lithium manganese nickel oxide (Li.sub.2Mn.sub.3NiO.sub.8) and lithium nickel manganese cobalt oxide (LiNi.sub.xMn.sub.yCo.sub.zO.sub.2, where X:Y:Z is 1:1:1, 5:3:2, 6:2:2 or 8:1:1).

3. A method according to claim 1 or 2, further comprising a pretreatment step in which the electrode material is disrupted to increase its accessibility to the alkaline solution.

4. A method according to claim 3, wherein the pretreatment step comprises suspending the electrode material in an acidic environment.

5. A method according to claim 4, wherein the pretreatment step is followed by basification with the alkaline solution, or separation of the solid electrode material and its addition to the alkaline solution.

6. A method according to claim 1, wherein the alkaline solution is sodium hydroxide and the treatment temperature is from 30 to 70° C.

7. A method according to claim 1, wherein the alkaline solution is ammonium hydroxide and the treatment temperature is from 20 to 30° C.

8. A method according to claim 1, wherein lithium is recovered from the alkaline solution by precipitation of lithium carbonate.

9. A method according to claim 1, wherein the leach solution comprises hydrobromic acid.

10. A method according to claim 9, comprising reducing elemental bromine (Br.sub.2) formed during the leaching to generate HBr.

11. A method according to claim 10, comprising expelling the elemental bromine as vapors from the leach solution and absorbing said bromine vapors in an aqueous solution of a reducing agent.

12. A method according to claim 10, comprising adding a reducing agent to the leach solution.

13. A method according to claim 10, wherein the reducing agent is selected from the group consisting of hydrazine, elemental sulfur, bisulfite and sulfur dioxide, to generate HBr and optionally H.sub.2SO.sub.4.

14. A method according to claim 10, wherein upon completion of the leaching step, whereby metals-bearing aqueous solution is obtained, hydrobromic acid is recovered by distillation under reduced pressure from said metal-bearing aqueous solution in the presence of H.sub.2SO.sub.4.

15. A method according to claim 1, wherein the metals are isolated from the metal-bearing solution by precipitation, oxidative precipitation, electrodeposition, ion exchange or solvent extraction and their combination.

Description

[0021] FIG. 1 is a flowchart illustrating one preferred variant of the process that consists of three major blocks:

[0022] Block A: pre-leaching steps to recover lithium; Block B: leaching in hydrobromic acid and HBr regeneration; and Block C: recovery of metals from the leach solution.

[0023] In FIG. 1, dashed arrows indicate solid/liquid separation, with the downwardly directed arrow showing the solid phase or the filtrate that proceeds to the next step.

[0024] It is seen that Block A in FIG. 1 includes the pretreatment step of the black mass (e.g., in acidic environment, to alter and disrupt the mixed oxides in the black mass) and the subsequent alkaline treatment as described above. Next, lithium-depleted black mass is separated from the solution, e.g., by filtration, or by any other solid/liquid separation technique such as decantation, etc. (however, as noted above, the separation step is not essential and the NaOH or NH.sub.4OH solution may be fed to the black mass-containing acidic pretreatment solution directly). Lithium is conveniently isolated from the liquid phase, e.g., from the filtrate, by precipitation in the form of a water-soluble lithium carbonate. To this end, a precipitation reagent, namely, a carbonate source such as sodium carbonate is added to the solution. Another way is by bubbling CO.sub.2 into the lithium hydroxide solution to form an insoluble lithium carbonate precipitate. It is worthy to note that lithium carbonate exhibits an abnormal solubility curve (solubility of lithium carbonate in water decreases with increasing temperature), hence precipitation may take place at a temperature up to 100° C. The precipitate is usually collected by filtration, washed and dried to obtain lithium carbonate with an acceptable purity.

[0025] The lithium-depleted black mass that was separated from the alkaline solution now proceeds to Block B, i.e., to the leaching step in an acidic leach solution. Hydrochloric acid and sulfuric acid can serve for this purpose, provided that a reducing agent such as hydrogen peroxide is also present in the leach solution. However, the most preferred acidic leach solution according to the invention comprises hydrobromic acid, because its action is achieved absent an added reductant. As explained above, bromide reduces trivalent transition metal cations such as Co.sup.3+ and Mn.sup.3+/Mn.sup.4+ to generate the divalent cations, which demonstrate higher water solubility and move from the black mass to the leachate. The bromide is simultaneously oxidized to elemental bromine. The present invention further provides a process design to enable recycling of elemental bromine evolved during the leaching back to the leaching reactor in the form of HBr, as explained in more detail below.

[0026] The leach solution used in the process therefore preferably consists of aqueous hydrobromic acid with HBr concentration varying in the range from 10 to ˜48 wt %, for example, from 15 to 48 wt %, e.g. 15-35 wt %. The loading of the black mass in the leach solution may be up to 35% wt %, e.g., from 7-35 wt %.

[0027] The solid collected after the alkaline treatment of Block A and the hydrobromic acid are introduced into a leaching reactor and a slurry is formed. For example, the solid can be first suspended in deionized water (about 1:1 weight ratio) and then hydrobromic acid is gradually added to the slurry. A suitable solid/liquid ratio, namely, the proportion between the leachable solid electrode material and the aqueous hydrobromic acid leach solution added to the leaching reactor is from 1/99 to 30/70; in case of a black mass, which contains a significant fraction of carbon, a lesser amount of leach solution is needed and the workable ratio is from 10/90 to 30/70. The reactor is equipped with agitation systems (e.g., mechanical) to enable continuous mixing of the slurry. Another requirement is that the reactor design includes a means for removal and absorption of the evaporated co-product, i.e., elemental bromine vapors.

[0028] The cathode material (e.g., LiCoO.sub.2, LiMn.sub.2O.sub.4, Li.sub.2Mn.sub.3NiO.sub.8, LiNi.sub.xMn.sub.yCo.sub.zO.sub.2, where X:Y:Z can be 1:1:1, 5:3:2, 6:2:2, or 8:1:1) dissolves gradually, usually with concomitant generation of elemental bromine. The dissolution time of the electrode material in the leach reactor increases with increasing solid/liquid ratio and decreases with increasing temperature and acid concentration. It is possible to achieve good leaching efficiencies for a variety of cathode materials during a reasonable time at room temperature, but it is generally preferred to perform the leaching under heating, e.g. from 40 to 90° C. For example, the temperature at the leaching reactor can be maintained at about 45 to 65° C., i.e., around the boiling point of elemental bromine. For example, the hydrobromic acid leach solution could be first heated to about 35-45° C., following which the slow addition of the black mass begins (or vice versa, acid is slowly added to the black mass/water slurry). On a laboratory scale, the addition time of the black mass lasts not less than 10 minutes. On completion of the addition the reaction mixture is heated to about 55° C.-60° C. Under these conditions, the leaching advances effectively and formation of Br.sub.2 vapors is manageable. Br.sub.2 is recyclable through reduction to HBr, e.g., with the aid of a reducing agent such N.sub.2H.sub.4, sulfur, NaHSO.sub.3 and SO.sub.2, either ex-situ following removal of bromine vapors from the leach reactor into an absorption medium, or in-situ in the leach reactor. Thus, the process of the invention comprises reducing the elemental bromine (Br.sub.2) formed during the leaching, to generate HBr.

[0029] For example, the slurry in the leaching reactor is stripped with a suitable purge gas such as air or nitrogen; bromine vapors are discharged from the reactor by the outgoing gas stream. Vaporizing and expelling the free bromine is preferably achieved by blowing out with a current of air, such that bromine vapors are led to a suitable absorption medium. In one process variant illustrated in FIG. 1, the absorption medium consists of an aqueous solution of a reducing agent, to convert Br.sub.2 into aqueous HBr, which is returned to the leach reactor.

[0030] Another way to recycle bromine formed during the leaching is through direct addition of a reducing agent to the leach reactor. For example, while hydrobromic acid is slowly added to the black mass/water slurry, a reducing agent is added under oxidation-reduction potential (ORP) control. The in-situ bromine evolving is manageable and its reduction to HBr proceeds efficiently.

[0031] For example, reduction of elemental bromine to HBr may be achieved with the aid of hydrazine. Hydrazine is a powerful reductant, which reacts with bromine according to the equation:

N.sub.2H.sub.4+2Br.sub.2.fwdarw.N.sub.2+4HBr  (2)

[0032] Hydrazine is commercially available in an aqueous form, e.g., solution strength of 35%. For the purposes of this invention, 5 to 20% by weight aqueous hydrazine solutions can be used. The rate of hydrazine feeding to the leach reactor (during the gradual addition of HBr) is controlled by oxidation-reduction potential (ORP) measurements. We have found that adjusting the hydrazine addition rate to the leach reactor to maintain oxidizing environment in the range of +500 to +800 mV, e.g., 700 to 800 mV (ORP measured by platinum as the working electrode and Ag/AgCl as the reference electrode), enables the advancement of the leaching while effectively suppressing the escape of bromine vapors. Experimental results reported below indicate that operating within the ORP range mentioned above, hydrazine reduces Br.sub.2 back to HBr while hydrazine itself has no negative effect on the leachability of the transition metals. The leaching may be carried out in a stirred reactor fitted with a dosage pump which delivers hydrazine to the reactor based on the ORP set point. Drop of redox values indicates the cessation of in-situ bromine formation and hence that the leaching process of the metal is close to an end.

[0033] Another example of a suitable reducing agent is sulfur, which reduces bromine in water. The reaction equation is:

3Br.sub.2+1/8S.sub.8+4H.sub.2O.fwdarw.6HBr+H.sub.2SO.sub.4  (3)

[0034] More information about the preparation of hydrobromic acid from bromine and sulfur can be found, e.g., in U.S. Pat. No. 2,342,465. For example, sulfur may be supplied to the reaction as such, or by first preparing a solution of sulfur in elemental bromine and feeding the solution to the leach reactor.

[0035] Bisulfite, e.g., NaHSO.sub.3 (SBS) can also be used to regenerate HBr in the leach reactor:

Br.sub.2+NaHSO.sub.3+H.sub.2O.fwdarw.NaBr+HBr+H.sub.2SO.sub.4  (4)

[0036] As shown in the experimental work below, bisulfite can be added under ORP control, without altering the leaching efficiency.

[0037] Another way to reduce bromine to hydrobromic acid is by the reaction of bromine with sulfur dioxide and water. Sulfur dioxide, SO.sub.2, may be bubbled through the aqueous absorption medium to react with the bromine vapors that were expelled from the leach reactor:

Br.sub.2SO.sub.22H.sub.2O.fwdarw.2HBr+H.sub.2SO.sub.4  (5)

[0038] As pointed out earlier, the feedstock may be a mixture consisting of a cathode and anode (carbon). The latter remains as a solid residue in the leach solution. Cessation of the evolution of elemental bromine (with its characteristic red color) may indicate that the leaching reaction has reached completion or is about to end. But the progress of the leaching can also be determined by withdrawing samples from the leach solution to measure the concentration of the progressively dissolving metals and assess the leaching yield, for example, by inductively coupled plasma mass spectroscopy (ICP-MS).

[0039] Upon completion of the leaching operation, the content of the leaching reactor undergoes solid/liquid separation to remove insoluble material (graphite anode material and perhaps a remnant of the cathode material) and collect the filtrate, as shown in FIG. 1, Block B. The filtrate constitutes the metal-bearing solution, from which the precious metals (e.g., nickel, cobalt, manganese and the remainder of lithium) are isolable by a variety of methods.

[0040] However, prior to the separation of the metals, aqueous hydrobromic acid is recovered from the filtrate—see the last step in FIG. 1, Block B. That is, a step of HBr recovery from the HBr/H.sub.2SO.sub.4 aqueous mixture. Hydrobromic acid is separable from the HBr/H.sub.2SO.sub.4 mixture through distillation, see for example U.S. Pat. No. 2,342,465 and US 2019/0119111. The use of elemental sulfur, bisulfite or sulfur dioxide to reduce bromine results in the formation of an aqueous solution of hydrobromic acid and sulfuric acid, from which hydrobromic acid can be recovered (after adjustment of H.sub.2SO.sub.4 concentration as explained below). When Br.sub.2 formed in the leaching step is reduced with hydrazine, sulfuric acid is not coproduced and H.sub.2SO.sub.4 is added in its entirety to the filtrate collected following the leaching. The composition of the solution subjected to distillation is such that the HBr concentration varies in the range from 10 to 48%, and the molar ratio HBr:H.sub.2SO.sub.4 is adjusted in the range from 1:0.5-1.5, e.g., 1: 0.7-1.3. For example, commercially available sulfuric acid solutions with strength varying from 20 to 96 w/w % could be used to adjust the composition of the HBr/H.sub.2SO.sub.4 mixture undergoing distillation.

[0041] Efficient recovery of aqueous hydrobromic acid with acceptable purity is achieved by distillation under reduced pressure (vacuum distillation), say, in the range from about 50-400 mmHg.

[0042] When a satisfactory pressure is attained in the distillation apparatus, e.g., using a vacuum pump, the HBr/H.sub.2SO.sub.4 aqueous mixture is heated to a temperature in the range from 25-110° C. Owing to the reduced pressure, HBr—H.sub.2O evaporates over that temperature range. A first distillate is formed when the temperature reaches ˜70-80° C., the vapor phase is condensed and collected. Usually distillation is completed when the temperature reaches 100° C. The bromide-free distillation residue is cooled to about 40-50° C. (<1.0% by weight bromide is attainable) and water is added to the distillation residue, so that the aqueous solution formed can proceed to the metal separation step.

[0043] It should be noted that the variant illustrated in FIG. 1, Block B involves reduction of elemental bromine evolving at the leaching step to produce hydrobromic acid, and recycling of the hydrobromic acid for use as a leaching agent. As an alternative, bromine vapors can be absorbed in an alkaline solution, e.g., sodium hydroxide, to form bromide and bromate (BrO.sub.3.sup.−) according to the following reaction equation (5):

3Br.sub.2+6Na.sup.++60H.sup.−.fwdarw.5Br.sup.−+BrO.sub.3.sup.−+6Na.sup.++3H.sub.2O  (6)

[0044] The so-formed bromate is an effective precipitation reagent for divalent metals such as Mn.sup.2+ as discussed below.

[0045] Turning now to the separation of the metals from the filtrate collected after the leaching and HBr recovery, it should be noted that the metals can be isolated from the metals-bearing solution by a variety of techniques, namely, isolation by precipitation with the aid of added precipitation reagents optionally under pH adjustment (for example, alkali hydroxide, alkali carbonate, suitable complexing agents); oxidative precipitation (with the aid of an oxidizer such as bromate); or by electrodeposition, e.g., cathodic deposition. Other separation methods based on ion exchange resin with affinity towards specific metals and solvent extraction can also be employed to isolate the individual metals, e.g., separate between the transition metals and the lithium in the recycling of lithium ion batteries.

[0046] One major separation method consists of adding a precipitation reagent to the metals-bearing solution (i.e., the filtrate collected after the leaching step). A suitable precipitation reagent may be selected from the group consisting of alkali hydroxide (e.g., NaOH), alkali bicarbonate (e.g., NaHCO.sub.3), alkali carbonate (e.g., Na.sub.2CO.sub.3) and dimethylglyoxime. Under suitable pH adjustment of the metal-bearing solution, the aforementioned reagents were shown to be effective in separating the metals under consideration. The precipitation reagents may be added in a solid form or as aqueous solutions to induce precipitation. The precipitate is then separated by conventional techniques such as filtration, decantation and centrifugation, and the supernatant collected proceeds to the next separation step.

[0047] For example, manganese and lithium are separable from one another upon addition of alkali hydroxide (NaOH) or alkali carbonate (Na.sub.2CO.sub.3) to the metal bearing solution, at slightly alkaline pH (7.0≤pH≤9.0), whereby manganese selectively precipitates from the solution while lithium remains in a soluble form. Likewise, cobalt and lithium are separable from one another with the help of sodium hydroxide (e.g., at 7.5≤pH≤9.0); or sodium carbonate (e.g., at 7.5≤pH≤9.0, in particular around pH=8.0) or sodium bicarbonate (e.g., at 7.0≤pH≤8.0).

[0048] Some preferred methods for metal separation are described now in more detail in reference to FIG. 1, Block C. Such methods include (i) separation by precipitation with added reagents such as alkali hydroxide, alkali carbonate and complexation agents of the relevant transition metals (ii) separation by electrodeposition of the transition metal and (iii) separation by oxidative precipitation with added oxidizer. FIG. 1, Block C illustrates successive separation of three transition metals in a specific order (Ni.fwdarw.Co.fwdarw.Mn), followed by isolation of lithium. Commercial lithium batteries contain mixed lithium-metal oxide cathode with one transition metal [such as LiCoO.sub.2 (LCO) or lithium LiMn.sub.2O.sub.4 (LMO)], two transition metals [such as Li.sub.2Mn.sub.3NiO.sub.8 (LMNO)] and three transition metals [such as LiNiMnCoO.sub.2 (NMC)]. Accordingly, the separation methods shown in FIG. 1, Block C can be chosen to meet each specific case and the order of steps for the transition metals shown in FIG. 1 may be changed.

[0049] As shown in FIG. 1, Block C, separation by precipitation with a chelating agent is well-suited for nickel, e.g., by addition of dimethylglyoxime to the solution to form nickel bis(dimethylglyoximate).

[0050] As shown in FIG. 1, Block C, separation by electrodeposition is well-suited for cobalt. In general, electrodeposition of the transition metal (e.g., Co) in an elemental form onto an electrode can be achieved with conventional electrochemical techniques, e.g., (i) galvanostatic method, with constant current density set in the range from, for example, 4*10.sup.−4 to 2.5*10.sup.−3 A m.sup.2 (ii) potentiostatic method, at a constant potential set in the range between, for example, −1.5V and 1 V; and (iii) cyclic voltammetry, using either a two or three-electrodes cell configuration. The deposit is obtained in a highly pure form.

[0051] For example, electrodeposition of Co.sup.(0) may be performed in a 3-electrode cell configuration, applying conditions similar to those reported by Freitas et al. (supra) where the working electrode to be coated was aluminum foil, platinum served as the counter electrode, and Ag/AgCl/NaCl as a reference electrode. The electrodes are immersed in the metal-bearing solution (pH may be adjusted) and a cathodic potential is applied on the working electrode for cobalt reduction, i.e., either a fixed voltage or variable voltage that is varied linearly with time.

[0052] Electrodeposition of the transition metal (e.g. cobalt) from the metal-bearing solution can also be achieved using a flow cell divided into cathodic and anodic compartments. With such configuration, the metal-bearing solution is recirculated through the cathodic side at a suitable rate while an electrolyte solution (e.g., sodium bromide solution) flows through the anodic side. An outline of a flow cell suitable for use in electrodeposition of metals, equipped with reservoirs for holding the respective plating solution and counter electrolyte solution and pumps for recirculating the solutions can be found in a paper by Arenas et al., Journal of The Electrochemical Society, 164 D57-D66 (2017). For example, experimental results reported below indicate that cobalt can be electrodeposited from ˜5.0 wt % Co-containing leachate onto the cathode in a three-electrode flow cell configuration under galvanostatic control where the working electrode (cathode) and anode consist of carbon felts supported onto current collectors in the form of carbon plates (reference electrode was Ag/AgCl), by applying 4*10{circumflex over ( )} (−4) to 2.5*10{circumflex over ( )} (−3) A m.sup.−2 for at least 60 minutes at room temperature. Electrodes other than carbon felts can also be coated by the electrodeposited cobalt.

[0053] As shown in FIG. 1, Block C, separation by oxidative precipitation is well-suited for the recovery of manganese. It can be accomplished with an oxidizing agent such as bromate, namely, a bromate-containing aqueous stream that is added to the metal-bearing solution. As mentioned above, absorbing bromine vapor evolving in the leaching in an alkaline solution leads to bromate formation (an indigenously generated bromate) which can be returned to the process to oxidize divalent manganese to form MnO.sub.2. The pH is adjusted to the preferred range, roughly 3.5≤pH≤5 owing to the alkalinity of the absorption basic solution. The bromate concentration in the returned aqueous stream may vary from 7 to 12 wt %. Hence about 1.1 moles of the indigenously generated bromate stream would be required to oxidize 3 moles of dissolved Mn.sup.2+. If needed, fresh bromate salts can be added to the indigenously generated bromate stream to meet precipitation requirements yet minimize the volumes of recycled streams. Alternatively, bromate can be supplied in its entirety to the metal-bearing solution in a solid form, i.e., by the addition of commercially available alkali bromate to the metal-bearing solution, or by injecting aqueous solutions made by dissolving commercial salts. The oxidative precipitation of manganese is not limited to the use of bromate and other oxidizing agents, e.g., potassium permanganate, can be used, as shown by reaction equation (7):

3Mn.sup.2++2MnO.sub.4−+2H2O5MnO.sub.2+4H.sup.+  (7)

[0054] Thus, the invention provides a method wherein the isolation of metals from the metal-bearing solution produced after the leaching step (e.g., leaching of particulate cathode material from industrially crushed spent lithium ion batteries) involves at least two, or at least three, or all of the following steps, which can be conducted in any order:

[0055] isolating nickel by precipitation, using a first precipitating reagent (especially chelating agent such as dimethylglyoxime); isolating cobalt by electrodeposition, and collecting cobalt from a plated cathode, e.g., carbon cathode;

[0056] isolating manganese by oxidative precipitation, using an oxidizer (preferably bromate as described above); and isolating the remainder of lithium by precipitation, using a second precipitating reagent (e.g., water soluble carbonate or carbon dioxide).

[0057] Preferably, nickel is the first metal to be isolated. Usually, the remainder of the lithium is the last metal to be isolated. One specific method consists of the following sequence of steps: adding chelating agent such as dimethylglyoxime to the metal-bearing solution to precipitate a nickel complex, e.g., nickel bis(dimethylglyoximate), recovering the nickel complex and collecting Ni-depleted metal bearing solution;

[0058] electrodepositing cobalt from the Ni-depleted metal bearing solution, to obtain cobalt deposit onto an electrode surface and collecting Ni, Co-depleted solution;

[0059] adding an oxidizer such as bromate to Ni, Co-depleted metal bearing solution to precipitate an oxide of manganese, separating said oxide of manganese and collecting Ni, Co and Mn-depleted metal bearing solution;

[0060] adding a second precipitation reagent to the Ni, Co and Mn-depleted metal bearing solution, for example, a water-soluble carbonate or carbon dioxide, to precipitate the remainder of the lithium as lithium carbonate.

[0061] The order of steps may be reversed. For example, removal of manganese may take place before the recovery of cobalt, such that cobalt is electrodeposited from Ni, Mn-depleted bearing solution. Procedures illustrating the separation of the transition metals by the techniques described above can be found in WO 2020/031178.

[0062] It should be noted that the method described herein can be used for separating lithium and precious metals from mixtures in general, i.e., not only from lithium spent batteries, such as fly ash and catalysts.

EXAMPLES

[0063] Inductively coupled plasma (ICP) was used to determine the metal content in the feedstock and in solution; the ICP instrument was ICP VISTA AX, Varian Ltd or ICP 5110, Agilent Technologies. Recovery percentage (yield) was calculated, e.g., by [M] solution/[M] feedstock×100, where [M] indicates the measured amount of metal M in the solution and the feedstock, respectively.

Example 1

Treatment of Black Mass in an Alkaline Solution with Varying Sodium Hydroxide Concentration and Temperature

[0064] A series of tests were conducted to investigate the separability of Li from samples of black mass using sodium hydroxide solutions at different concentrations (5% by weight, 10% by weight or 20% by weight NaOH solution) at different temperatures (30° C., 60° C. and 80° C.). Each experiment consisted of gradual addition of 20 grams of the black mass, over a period of ten minutes, to 180 gr of sodium hydroxide solution in a 250 mL Erlenmeyer held at the test temperature, following which the reaction mixture was stirred for three hours at the abovementioned temperatures. After three hours the sample was filtered on a Buchner with 70 mm Whatman filter paper under vacuum conditions. Metal concentrations were analyzed using ICP. The conditions of each of the experiments and percentage yield of the metals are tabulated in Table 1.

TABLE-US-00001 TABLE 1 Solution pH Temperature Al % Li % Co % Mn % Ni % F  5% NaOH 13.58 30° C. 23.82 22.81 0.04 0.02 0.02 — 10% NaOH 13.68 30° C. 26.91 25.13 0.07 0.04 0.04 — 20% NaOH 13.60 30° C. 28.36 25.31 0.04 0.03 0.00 —  5% NaOH 13.64 60° C. 30.0 22.80 0.054 0.019 0.02 70.6 10% NaOH 13.61 60° C. 35.4 28.30 0.034 0.022 0.027 64.1 20% NaOH 13.6 60° C. 37.6 29.54 0.041 0.022 0.0045 56.8  5% NaOH — 80° C. 42.2 15.2 0.00 0.00 0.00 — 10% NaOH — 80° C. 40.0 17.6 0.00 0.00 0.00 — 20% NaOH — 80° C. 44.9 22.5 0.00 0.00 0.00 —

[0065] The results indicate that transition metals are not affected by the alkaline treatment: Co, Mn and Ni remained in the black mass and were not dissolved in the alkaline solution. In contrast, appreciable removal rates were measured for Al and Li. The trend shown in Table 1 is that Al removal generally increased with increasing temperature and alkali hydroxide concentration, whereas the separability of lithium from the black mass did not benefit from temperature elevation. Comparable Al and Li removal rates were achieved in sodium hydroxide solution under moderate heating.

[0066] The black mass contained fluoride compounds (F.sup.− may have originated from the LiPF.sub.6 electrolyte or from fluorinated ethylene carbonate). The presence of F.sup.− in the leaching step with hydrobromic acid is undesirable, because hydrofluoric acid (byproduct during bromide recovery at high temperatures) may damage the reactor system. It is seen that treating the black mass with an alkaline solution serves an additional goal: removal of fluoride ions [F.sup.− was measured potentiometrically with fluoride ion selective electrode (ISE)].

Example 2

Pretreatment of Black Mass in an Acidic Solution Followed by Treatment in an Alkaline Solution with Varying Sodium Hydroxide Concentration and Temperature

[0067] The series of tests of Example 1 were repeated, but each experiment was preceded by treating the black mass in 25 gr of 24% (% wt) hydrochloric acid solution at room temperature for a short period of time (20-30° C., 10-30 minutes). Next, the mixture was basified by addition of the alkaline solution and the experiment then proceeded as described in Example 1. The conditions of each of the experiments and percentage yield of the metals are tabulated in Table 2.

TABLE-US-00002 TABLE 2 Alkaline solution pH T Al % Li % Co % Mn % Ni %  5% NaOH — 30° C. 6.5 38.3 0.00 0.00 0.00 10% NaOH — 30° C. 6.7 41.8 0.00 0.10 0.00 20% NaOH — 30° C. 7.3 48.2 0.23 0.03 0.00  5% NaOH 13.20 60° C. 3.4 28.5 0.00 0.00 0.00 10% NaOH 13.44 60° C. 11.3 29.2 0.01 0.02 0.00 20% NaOH 13.40 60° C. 10.6 25.0 0.20 0.05 0.00  5% NaOH — 80° C. 4.83 22.0 0.00 0.00 0.00 10% NaOH — 80° C. 9.50 24.0 0.00 0.00 0.00 20% NaOH — 80° C. 19.3 24.8 0.05 0.11 0.00

[0068] The results demonstrate that it is possible to enhance Li removal from the black mass in an alkaline solution, if the black mass is pretreated in an acidic environment, and then transferred to the alkaline solution. The effect is unique to Li: the transition metals Co, Mn and Ni were resistant to the combined procedure, whereas Al rate removal was conversely reduced. That is, the combined procedure led to better selectivity towards lithium removal.

Example 3

Metal Removal from Black Mass in Ammonium Hydroxide Solution

[0069] The experimental procedure of Example 1 was repeated, but this time the alkaline environment was created by ammonium hydroxide. 12.5% by weight and 25.0% by weight NH.sub.4OH solutions were used at room temperature; amounts were as set out in Example 1. The conditions of each of the two experiments and percentage yield of the metals are tabulated in Table 3.

TABLE-US-00003 TABLE 3 Solution pH Temperature Al % Li % Co % Mn % Ni % 12.5% NH.sub.4OH 12.9 25° C. 5.54 21.6 0.92 0.00 0.84 25.0% NH.sub.4OH 13.3 25° C. 3.27 18.32 0.34 0.00 0.79

[0070] It is seen that ammonium hydroxide solution was especially selective towards Li removal from black mass. Moreover, the favorable effect was achieved at room temperature.

Example 4

Recovery of Lithium from Sodium Hydroxide Solution

[0071] Lithium was recovered from a filtrate obtained following the alkaline treatment and filtration of the black mass (for the alkaline treatment, 200 gr of 20% (% wt) sodium hydroxide solution was used to treat 22 gr of black mass (two samples: one without the acidic pretreatment step (4A) and the other following the acidic pretreatment step (4B), as described in Examples 1 and 2, respectively). The black mass was then separated by filtration from the alkaline aqueous phase.

[0072] The filtrate, which in each sample 4A and 4B contained 0.11% (% wt) Li, was treated to recover lithium in the form of Li.sub.2CO.sub.3. To this end, Na.sub.2CO.sub.3 (20 gr) was added to the filtrate, and the solution was heated to 100° C. and stirred for three hours.

[0073] After three hours the samples were filtered on a Buchner with 70 mm Whatman filter paper under vacuum. Lithium concentrations were analyzed using ICP. Lithium removal percentage measured for sample 4A (no acidic pretreatment) and 4B (including acidic pretreatment) were 41% and 45%, respectively.

Example 5 (of the Invention) and 6 (Comparative) Leaching with HBr (of the Invention) or H.SUB.2.SO.SUB.4 .(Comparative) of Black Mass after Treatment in Sodium Hydroxide Solution

[0074] Black mass sample (30 gr) was treated in 20% (% wt) sodium hydroxide solution at 60° C. as described in Example 1. The treatment was repeated twice. The black mass was then separated from the alkaline solution and added to a 250 mL Erlenmeyer that was previously charged with 120 gr of an acidic solution (either 48% wt HBr or 30 wt % H.sub.2SO.sub.4). The black mass was gradually added over 10 minutes. The temperature during the addition was 60° C.

[0075] After the addition was completed the suspension was stirred for three hours. Then the sample was filtered on a Buchner with 70 mm glass-microfiber discs (Sartorius stedim) under vacuum. Recovery % of the metals are tabulated in Table 4 below, indicating recovery % owing to the action of the acidic leach solution, and total recovery % (in parentheses) achieved by the alkaline treatment and the action of the acidic leach solution.

TABLE-US-00004 TABLE 4 Ex. leachate Al (%) Li (%) Co (%) Mn (%) Ni (%) 5 HBr 36.1 (93.5) 43.0 (85.0) 98.2 (98.5) 87.5 (87.6) 85.8 (85.9) 6 H.sub.2SO.sub.4 18.6 (75.9) 27.4 (69.7) 67.6 (67.9) 57.8 (57.9) 56.4 (56.5)

[0076] While transition metals were exclusively removed during the leaching step, lithium removal was roughly equally divided between the alkaline treatment and the leaching step. The results also demonstrated that leaching with HBr achieves high removal rates (85-95%) compared to sulfuric acid.

Example 7

Leaching of Black Mass with HBr, Ex-Situ Bromine Reduction and HBr Recovery by Distillation

[0077] The next example illustrates a leaching procedure of black mass using aqueous HBr 48%, enabling the conversion of elemental bromine (co-product evolving during leaching) back to aqueous HBr, and recovery of pure aqueous HBr by distillation, for further use in a next leaching cycle.

[0078] Step 1: Reduction of Elemental Bromine to Produce HBr

[0079] Assemble the reactor system, connect the heating system to the reactor jacket and the cooling system to the condenser. The condenser outlet should be connected to two traps.

[0080] The first trap is assembled as a back-flash trap.

[0081] Fill the second trap with 10% N.sub.2H.sub.4 solution. This trap is used to absorb bromine generated during the reaction and to transform it to HBr.

[0082] Add 150 gr HBr 48% (% wt) into a stirred vessel.

[0083] Heat the vessel content to 60° C.

[0084] When the temperature of the HBr in the vessel reaches 40° C., start adding 37.5 gr LCo based black mass into the reactor. The black mass addition should be slow (duration of about 30 min).

[0085] Agitate the vessel content for 3 hours at 60° C.

[0086] Bubble air into the reactor content to remove remaining bromine vapors (during 30 minutes).

[0087] Cool the mixture to 40° C.

[0088] Filter the reactor content upon a glass fiber filter to obtain a filtrate.

[0089] Wash the cake with 50 gr distilled water (DW), the wash water should be added to the filtrate.

[0090] Dry the filter cake in an oven, T=100° C., under vacuum conditions.

[0091] Step 2: Distillation of Aqueous Hydrobromic Acid from Leachate

[0092] Assemble the reactor system, connect the heating system to the reactor jacket and the cooling system to the condenser. In addition, connect a distillate receiver to the bottom of the condenser. Connect the condenser outlet to a vacuum pump.

[0093] Filtrate obtained by the procedure set out in the previous step (253 gr) was added to the stirred reactor, followed by addition of 40 wt % H.sub.2SO.sub.4 (164.3 gr).

[0094] The temperature of the reactor's jacket was raised to 100° C.

[0095] The reactor was under vacuum conditions (157 mbar).

[0096] When the reactor temperature reached 78° C., the first distillate started to exit the system. The HBr—H.sub.2O mixture was condensed in the distillation receiver. After about two hours the distillation ended, and the reactor temperature was cooled to 40° C. 152 gr of DW were added to the distillation residue.

TABLE-US-00005 TABLE 5 Fraction Br.sup.− , % wt Blank - the stock solution 23.5 1.sup.st distillate 9.3 2.sup.nd distillate 41.4 3.sup.rd distillate 39.8 Distillation residue 0.88 Total yield: 92%.

[0097] In the next set of examples (8A, 8B and 9), during gradual addition of HBr leaching solution to a slurry of the treated black mass in water, a reducing agent was supplied under ORP control to suppress escape of bromine vapors and recycle bromine. The reactor system was based on a stirred reactor fitted with an ORP control. When redox values exceeded a desired value, a solution of the reducing agent was added gradually into the reactor using a prominent dosage pump (Gamma/L).

Examples 8A and 8B Leaching of Black Mass with HBr and In-Situ Bromine Reduction with Hydrazine

[0098] 8A: A slurry of 70 gr black mass and 90 gr DW was prepared and added into a 0.5 L reactor. 396 gr 48% (% wt) HBr was slowly added to the slurry (addition time was 50 min). The HBr addition was performed while controlling the reaction ORP value at 780 mv, using 10% (% wt) N.sub.2H.sub.4. A total of 35 grams N.sub.2H.sub.4 solution was needed. ORP electrode used was Mettler Toledo Pt4805-DXK-S8/425. Removal rates are tabulated in Table 6.

TABLE-US-00006 TABLE 6 Ex. leachate Al (%) Li (%) Co (%) Mn (%) Ni (%) 5 HBr 96 78.2 100 100 100

[0099] The results show that the leaching efficiency was not affected by N.sub.2H.sub.4 addition to the leaching reactor.

[0100] 8B: The experiment was repeated, this time the HBr addition was performed while controlling the reaction ORP value at 750 mv, using 10% (% wt) N.sub.2H.sub.4 solution. A total of 63 grams N.sub.2H.sub.4 solution was needed. ORP electrode used was Pt4805-DPA-SC-S8/425 ORP electrode. Removal rates are tabulated in Table 7.

TABLE-US-00007 TABLE 7 leachate Al (%) Li (%) Co (%) Mn (%) Ni (%) HBr 94 78 100 96 100

[0101] The results show that the leaching efficiency was not affected by N.sub.2H.sub.4 addition to the leaching reactor.

Example 9

Leaching of Black Mass with HBr and In-Situ Bromine Reduction with Sodium Bisulfite

[0102] A slurry of 70.1 gr black mass and 90.6 gr DW was prepared and added into a 0.5 L reactor. 396 gr 48% (% wt) HBr was slowly added to the slurry (addition time was 60 min). The HBr addition was performed while controlling the reaction ORP value at 740 mv, using 15% (% wt) NaHSO.sub.3. A total of 341 grams NaHSO.sub.3 solution was needed. ORP electrode used was Mettler Toledo Pt4805-DXK-S8/425. Removal rates are tabulated in Table 8.

TABLE-US-00008 TABLE 8 leachate Al (%) Li (%) Co (%) Mn (%) Ni (%) HBr 95.1 75 100 100 100

[0103] The results show that the leaching efficiency was not affected by NaHSO.sub.3 addition to the leaching reactor.