Synthesis of Lithium Fluoride from Spent Lithium Ion Batteries - MDPI

minerals Article

Synthesis of Lithium Fluoride from Spent Lithium Ion Batteries Daniela S. Suarez, Eliana G. Pinna, Gustavo D. Rosales and Mario H. Rodriguez * Laboratorio de Metalurgia Extractiva y Síntesis de Materiales (MESiMat), Facultad de Ciencias Exactas y Naturales, Universidad Nacional de Cuyo, Mendoza 5500, Argentina; [email protected] (D.S.S.); [email protected] (E.G.P.); [email protected] (G.D.R.) * Correspondence: [email protected]; Tel.: +54-9261-337-9329 Academic Editor: William Skinner Received: 23 February 2017; Accepted: 11 May 2017; Published: 17 May 2017

Abstract: Lithium (Li) is considered a strategic element whose use has significantly expanded. Its current high demand is due to its use in lithium ion batteries for portable electronic devices, whose manufacture and market are extensively growing every day. These days there is a great concern about the final disposal of these batteries. Therefore, the possibility of developing new methodologies to recycle their components is of great importance, both commercially and environmentally. This paper presents results regarding important operational variables for the dissolution of the lithium and cobalt mixed-oxide (LiCoO2 ) cathodes from spent lithium ion batteries (LIBs) with hydrofluoric acid. The recovery and synthesis of Co and Li compounds were also investigated. The dissolution parameters studied were: temperature, reaction time, solid-liquid ratio, stirring speed, and concentration of HF. The investigated recovery parameters included: pH, temperature, and time with and without stirring. The final precipitation of lithium fluoride was also examined. The results indicate that an increase in the HF concentration, temperature, and reaction time favors the leaching reaction of the LiCoO2 . Dissolutions were close to 60%, at 75 ◦ C and 120 min with a HF concentration of 25% (v/v). The recovery of Co and Li were 98% and 80%, respectively, with purities higher than 94%. Co and Li compounds, such as Co3 O4 and LiF, were synthesized. Furthermore, it was possible to almost completely eliminate the F− ions as CaF2 . Keywords: LiF; cobalt; lithium; lithium ion batteries; LIBs

1. Introduction Cobalt is widely dispersed in nature, however, commercially important sources are cobalt arsenides, oxides, and sulfides. There are several methods to extract cobalt, usually to separate it from copper and nickel. One traditional method produces a concentrate from cobalt ore. After roasting, the metal concentrates are converted to sulfate, removing the copper, aluminum, nickel, zinc, and iron via chemical precipitation. Finally, cobalt metal can also be recovered by electrowinning. Cobalt is a metal used in numerous commercial, industrial, and military applications. For example, superalloys are employed to make parts for gas turbine engines, cemented carbides, and diamond tools. Additionally, cobalt is used for manufacturing animal feed additives; producing catalysts for chemical, petroleum, and other industries; drying agents for inks, paints, and varnishes; dyes and pigments; glass decolorizers; ground coats for porcelain enamels; humidity indicators; magnetic recording media; rubber adhesion promoters for steel-belted radial tires; and vitamin B12 [1,2]. Lithium is present in many minerals, spring waters, and especially in salars. Spodumene [LiAl(SiO3 )2 ] is the main source of Li, but since the exploitation of salars to extract the metal grows, other minerals, such as petalite [LiAl(Si4 O10 )] and lepidolite [K(Li,Al,Rb)4 O10 ], are being used [1,3]. Industrially, Li is obtained by electrolysis of molten LiCl (with a melting point of 613 ◦ C) or from Minerals 2017, 7, 81; doi:10.3390/min7050081

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a mixture of LiCl and KCl 45–55% (with a melting point at 450 ◦ C) [4]. This metal has a wide variety of industrial applications, such as in the production of lubricants and special alloys, manufacture of glass and ceramic materials, and in the development of psychiatric medications, among others. Today, the main industrial applications of Li together with Co are as components of batteries in mobile phones, laptops, watches, pacemakers, etc., as well as in electric and hybrid cars [3,4]. Taking into account that the average life of lithium ion batteries (LIB) is about two years, and that their market is rapidly growing, it is easy to predict that they will soon become a serious environmental problem unless proper actions are taken, regarding the disposal of electronic waste [5,6]. Therefore, we believe that the recycling of spent lithium ion batteries (LIBs) is a matter of major importance, not only because of the presence of flammable and toxic elements in them, but also due to the possibility of economic and environmental benefits which can be achieved from the recovery of their main components [7,8]. The technical literature contains many papers related to the recycling of the materials that compose batteries, either by using physical or chemical methods [9]. Physical treatments are generally used to separate the LiCoO2 which adheres to the cathode surface. Later, oxides are subjected to a chemical procedure that allows the recovery of the components. Among the physical processes used, mechanical and thermal separation may be included, as well as the dissolution of the adhesive which joins the oxide to the film. The chemical processes, as mentioned above, are used to solubilize and/or to recover metals contained in the LiCoO2 . These methods can be pyro- and/or hydrometallurgical [9]. Regarding the latter, LiCoO2 leaching of spent batteries has been done by using both organic and inorganic acids, such as citric acid, malic acid, aspartic acid, H2 SO4 , HCl, HNO3 , H2 SO3 , and H3 PO4 , as leaching agents. Experimental results have indicated that most Co dissolution is achieved with HCl. Moreover, increasing the temperatures and concentrations of the leaching agent promote the recoveries of Li and/or Co independently of the acid [10–17]. In addition, the effect of the reducing agent (H2 O2 ) on the dissolution of LiCoO2 (from LIBs) with the inorganic acids, such as HNO3 , H3 PO4 , and H2 SO4 , were studied in other investigations [17–25]. Lee and Rhee reported extraction values over 93% for cobalt and lithium, when working with HNO3 -H2 O2 [18], whereas Dorella and Mansur used H2 SO4 and obtained leaching values of around 95% for lithium and 80% for cobalt [23]. Pinna et al. obtained dissolutions of the mixed lithium cobalt oxide of nearly 100% working with H3 PO4 /H2 O2 [17]. Zhang et al. studied the use of chemical agents that produce leaching and reduction at the same time and, working with H2 SO3 , achieved lithium and cobalt dissolutions of about 60% [14], while when working with HCl, the dissolution of both metals were close to 99%. In the literature, there are several studies in which the Co is precipitated as hydroxide, using sodium or ammonium hydroxide [8,10,20,26], and as cobalt oxalate, employing sodium or ammonium oxalate [17,21,27,28]. In addition, some studies report the recovery of Li from LIBs as carbonate [8,14,21,29] using Na2 CO3(s) or CO2(g) as the precipitating agent to obtain, in both cases, Li2 CO3(s) [30,31]. One of the most commonly used lithium salts is LiF, which is utilized as a flux in ceramics and glass industry, as well as in light metal welding [4,32]. It is also used in the manufacture of optical components for analytical equipment (IR and UV spectroscopy). More recently, it has been employed in the fabrication of new cathodes for Li batteries, e.g., LiF-Fe [33]. A potentially important use of LiF is represented by atomic fusion, where it would be employed as a source of 6 Li isotopes [34,35]. The industrial process to manufacture LiF is carried out by preparing a concentrated solution of a lithium salt, e.g., Li2 CO3 , obtained from brines or rock deposits through well-known industrial processes [4,12,21]. This lithium-containing solution is then treated with fluorine salts or HF to obtain LiF as the final product. In order to avoid the reprocessing of Li salts when obtaining LiF, research was carried out through a direct process using LIBs as a raw material. The objectives of this work were to study the influence of operational parameters on the dissolution of LiCoO2 with HF (in a closed vessel) and to synthesize


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Co3 O4 and LiF. Furthermore, a new process for their synthesis was developed, taking into account environmental and economic benefits. Minerals 2017, 7, 81

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2. Materials and Methods

2. Materials and Methods

The leaching reagent used was analytical-grade HF. The leaching reagent used was analytical-grade HF. A sample of LiCoO obtained from the cathodes of spent lithium ion batteries from mobile 2 was A sample of LiCoO 2 was obtained from the cathodes of spent lithium ion batteries from mobile phones of different brands. These batteries were dismantled phones of different brands. These batteries were dismantledmanually, manually,the thecathode cathode was was separated, separated, and the LiCoO was removed from the aluminum film by scraping. and the LiCoO 2 was removed from the aluminum film by scraping. 2 Characterization of the samplewas wasperformed performed by (XRD) with a Rigaku D-Max Characterization of the sample byX-ray X-raydiffraction diffraction (XRD) with a Rigaku D-Max III C diffractometer (Osaka, Japan), operated at 35 and mA using Kαradiation radiation of of Cu Cu and and Ni Ni filter III C diffractometer (Osaka, Japan), operated at 35 kVkV and 30 30 mA using Kα at λ nm. = 0.15418 nm. Morphological was in 1450 a LEO 1450 VP (Zeiss, Jena, at λ =filter 0.15418 Morphological analysis analysis was done bydone SEMby inSEM a LEO VP (Zeiss, Jena, Germany). Germany). The XRD and SEM characterization of the cathode material are shown in Figure 1a,b, respectively. The XRD and SEM characterization of the cathode material are shown in Figure 1a,b, Determination of cobalt and lithium content in the LIBs was performed by atomic absorption respectively. Determination of cobalt and lithium content in the LIBs was performed by atomic spectroscopy (AAS) using a Varian SpectrAA 55 spectrometer (Palo Alto, CA, USA) with a hollow absorption spectroscopy (AAS) using a Varian SpectrAA 55 spectrometer (Palo Alto, CA, USA) with cathode lampcathode (analytical 1.5%). The quantitative composition of theofsample waswas 6.7% Li and a hollow lamp error (analytical error 1.5%). The quantitative composition the sample 6.7% 40.1%LiCo, expressed in mass percentage. and 40.1% Co, expressed in mass percentage.

Figure 1. (a) XRD and (b) SEM of LiCoO2 from cathodes of LIBs. Figure 1. (a) XRD and (b) SEM of LiCoO2 from cathodes of LIBs. The diffractogram in Figure 1a shows that the cathode contains lithium cobalt oxide (JCPDS 01-

The diffractogram in Figure 1a shows that the containshave lithium cobalt oxidewith (JCPDS 075-0532). The micrograph of Figure 1b shows thatcathode LiCoO2 particles irregular shapes rounded edges. 01-075-0532). The micrograph of Figure 1b shows that LiCoO2 particles have irregular shapes with rounded edges. 2.1. Leaching Assays

2.1. Leaching The Assays leaching tests were performed in a closed vessel of 500 mL capacity, constructed of polyvinyl chloride (PVC), immersed in a thermostatic bath, vessel fitted with a mechanical stirrer and temperature The leaching tests were performed in a closed of 500 mL capacity, constructed of polyvinyl control. The operational variables studied were temperature, reaction time, stirring speed, solidchloride (PVC), immersed in a thermostatic bath, fitted with a mechanical stirrer and temperature liquid ratio and leaching agent concentration. The dissolution reaction was calculated by the control. The operational variables studied were temperature, reaction time, stirring speed, solid-liquid expression: ratio and leaching agent concentration. The dissolution reaction was calculated by the expression: X (%) =

m0 − mr

× 100

m0 − m0 mr X (%) = × 100 m0

(1)

(1)

where X is the conversion; m0 is the initial mass of LiCoO2, and mr is the mass of LiCoO2 unreacted after [17,34]. experiment was replicated times. Theofaverage where X isthe the reaction conversion; m0 isEach the initial mass of LiCoO mr is the mass LiCoO2 conversion unreacted after 2 , andthree efficiency is presented in the experimental results. the reaction [17,34]. Each experiment was replicated three times. The average conversion efficiency is

presented in the experimental results. 2.2. Recovery Assays

2.2. Recovery Assays In the tests of separation and synthesis, the cobalt solution was prepared by dissolving LiCoO2 with HF, using the best leaching conditions determined in Section 3.1. The operating parameters

In the tests of separation and synthesis, the cobalt solution was prepared by dissolving LiCoO2 studied were pH, temperature, and reaction time, with and without stirring. with HF, The using the best leaching determined in precipitation Section 3.1. ofThe parameters recovery of Li from theconditions resulting solution, after the Co,operating can be carried out studied were pH, temperature, and reaction time, with and without stirring. by several known methods. In this case, lithium was precipitated as LiF, evaporating the solvents

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aboveThe therecovery solubility constant (Ksp) of LiFafter [30,36,37]. Finally, the were of product Li from the resulting solution, the precipitation of resulting Co, can besolutions carried out by − ions. stored to eliminate the content of F several known methods. In this case, lithium was precipitated as LiF, evaporating the solvents above Lithium and cobalt were analyzed absorption calculatewere the recovery the solubility product constant (Ksp) of by LiFatomic [30,36,37]. Finally,spectroscopy the resultingto solutions stored to percentage in all of the experiments: − eliminate the content of F ions. Lithium and cobalt were analyzed by atomic Eabsorption spectroscopy to calculate the recovery R (%) = s × 100 (2) E percentage in all of the experiments: m Es R(%)in =the sample × 100 and Es is the quantity of each element (2) in where Em is the initial amount of each element Em the leach liquor obtained after precipitation. where Em is the initial amount of each element in the sample and Es is the quantity of each element in the leach liquor obtained after precipitation. 3. Results 3. Results 3.1. Dissolution of LiCoO2 with HF 3.1. Dissolution of LiCoO HFproposed as the most probable for the dissolution of LiCoO2 with 2 with The following reaction was HF: The following reaction was proposed as the most probable for the dissolution of LiCoO2 with HF:

4 LiCoO2(s) + 12 HF(aq) → 4 LiF(aq) + 4 CoF2(aq) + 6 H2O + O2(g) 4 LiCoO2(s) + 12 HF(aq) → 4 LiF(aq) + 4 CoF2(aq) + 6 H2 O + O2(g)

(3) (3)

3.1.1. 3.1.1. Effect Effect of of the the Leaching Leaching Temperature Temperature Figure Figure 22 shows shows the the effect effect of of temperature temperature on the dissolution of LiCoO22 with with HF HF at at aaconcentration concentration of 15% (v/v), a solid-liquid ratio 2% (w/v), reaction time of 120 min, and a stirring speed of 15% (v/v), a solid-liquid ratio 2% (w/v), reaction time of 120 min, and a stirring speedof of330 330rpm. rpm. ◦ ◦ The The temperature range tested was between 25 °C C and 95 °C C..

Figure 2. Effect ofoftemperature thedissolution dissolution LiCoO 2. Figure 2. Effect temperature on on the ofof LiCoO 2. Figure 2 indicates that the dissolution of LiCoO2 increases while increasing the temperature, Figure 2 indicates that the dissolution of LiCoO2 increases while increasing the temperature, which agrees with the known fact that, in solid–liquid heterogeneous reactions, a rise in temperature which agrees with the known fact that, in solid–liquid heterogeneous reactions, a rise in temperature causes an increase in the reactivity of the solids [38,39]. The maximum value of LiCoO2 dissolution causes an increase in the reactivity of the solids [38,39]. The maximum value of LiCoO2 dissolution was obtained at 95 °C, but 75 °C was selected as the best for studying other operational parameters. was obtained at 95 ◦ C, but 75 ◦ C was selected as the best for studying other operational parameters. In addition, in this working range, a plateau was verified in the dissolution of the oxide between ◦75 In addition, in this working range, a plateau was verified in the dissolution of the oxide between 75 C °C and 95 °C. and 95 ◦ C.

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3.1.2. Effect of HF Concentration 3.1.2. 3.1.2.Effect Effectof ofHF HFConcentration Concentration Tested HF concentrations were 5%, 5%, 10%, 15%, 15%, 20%, and and 25% (v/v) (v/v) with the other variables held Tested TestedHF HFconcentrations concentrationswere were 5%,10%, 10%, 15%,20%, 20%, and25% 25% (v/v)with withthe theother othervariables variablesheld held constant: temperature, 75 °C; reaction time, 120 min; solid-liquid ratio, 2% ( w / v ); stirring speed, 330 ◦ constant: temperature, 75 C; reaction time, 120 min; solid-liquid ratio, 2% (w/v); stirring speed, constant: 75 °C; reaction time, 120 min; solid-liquid ratio, 2% (w/v); stirring speed, 330 rpm. Figure 3 shows the dissolution values obtained. 330 rpm. Figure 3 shows dissolution values obtained. rpm. Figure 3 shows the the dissolution values obtained.

Figure 3. Effect of HF concentration onthe thedissolution dissolution of LiCoO 2. Figure EffectofofHF HF concentration concentration on of LiCoO 2. Figure 3. 3.Effect on the dissolution of LiCoO 2. The results in Figure 3 show that when leaching agent concentration (HF solution) increases so The Theresults resultsin inFigure Figure33show showthat thatwhen whenleaching leachingagent agentconcentration concentration(HF (HFsolution) solution)increases increasesso so does the dissolution of the mixed oxide up to a HF concentration of 15% (v/v); after that, a plateau is does doesthe thedissolution dissolutionof ofthe themixed mixedoxide oxideup uptotoaaHF HFconcentration concentrationofof15% 15%(v/v); (v/v);after afterthat, that,aaplateau plateauisis observed in the dissolution value. This is because increasing the leaching agent concentration gives observed value. This is because increasing the the leaching agent concentration givesgives rise observedininthe thedissolution dissolution value. This is because increasing leaching agent concentration rise to a larger amount of F− −and H+ +ions, available to react with LiCoO2. From these results, the − + to a larger amount of F and ions, to react to with LiCoO results, theresults, optimum rise to a larger amount of FH and H available ions, available react with LiCoOthese 2. From these the 2 . From optimum HF concentration was selected to be 15% (v/v), which was used for the rest of the assays, HF concentration was selectedwas to be 15% (v/v), forwas the rest thethe assays, although the optimum HF concentration selected to bewhich 15% (was v/v),used which usedoffor rest of the assays, although the maximum dissolution value for the oxide (61%) was achieved by working with HF 25% maximum dissolution value for the oxide achieved by working HF 25% (v/v). although the maximum dissolution value(61%) for thewas oxide (61%) was achievedwith by working with HF 25% (v/v). (v/v). 3.1.3. Effect of Reaction Time 3.1.3. Effect of Reaction Time 3.1.3.Figure Effect 4ofshows Reaction theTime dissolution values obtained at 75 ◦ C, a HF concentration of 15% (v/v), Figure 4 shows the2% dissolution obtained 75 °C, a HFThe concentration of 15% (v/v), a solida solid-liquid ratio of (w/v) andvalues stirring speed at of rpm. reaction time was Figure 4 shows the dissolution values obtained at330 75 °C, a HF concentration of range 15% (vtested /v), a solidliquid ratio of 2% ( w / v ) and stirring speed of 330 rpm. The reaction time range tested was 5–240 min. 5–240 min. liquid ratio of 2% (w/v) and stirring speed of 330 rpm. The reaction time range tested was 5–240 min.

Figure 4. Effect ofofreaction thedissolution dissolution LiCoO Figure 4. Effect reactiontime time on on the of of LiCoO 2 . 2. Figure 4. Effect of reaction time on the dissolution of LiCoO 2.


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In Figure Figure 44 itit can can be be observed observed that that an an increase increase in in the the reaction reaction time time led led to to an an increase increase in in the the In dissolution of the LiCoO 2. That is, the increase in the contact time between the reactants led to an dissolution of the LiCoO2 . That is, the increase in the contact time between the reactants led to an increasein inthe thedissolution dissolutionof ofthe thesolid, solid,which whichisisconsistent consistentwith withthe theliterature literature[38,39]. [38,39].ItItisisworth worthnoting noting increase that after 120 min of reaction, the LiCoO 2 dissolution remained constant (plateau of the figure), which that after 120 min of reaction, the LiCoO2 dissolution remained constant (plateau of the figure), which whythis thisvalue valuewas wasselected selectedfor forthe thestudy studyof ofthe theother otheroperational operationalparameters. parameters. isiswhy 3.1.4. Effect Effectof ofStirring StirringSpeed Speed 3.1.4. The effect effectof ofthe thestirring stirringspeed speedon onthe thedissolution dissolutionof ofLiCoO LiCoO22 was was tested tested between between 110 110 rpm rpm and and The ◦ 550 rpm, and the other variables were kept constant: temperature, 25 °C; reaction time, 120 min; solid550 and the other variables were kept constant: temperature, 25 C; reaction time, 120 min; liquid ratio,ratio, 2% (w /v),(w/v), and HF 15% (15% v/v). (v/v). Figure Figure 5 shows the dissolution values solid-liquid 2% andconcentration, HF concentration, 5 shows the dissolution obtained. values obtained.

Figure 5.5.Effect speedon onthe thedissolution dissolution of LiCoO Figure Effectof ofstirring stirring speed of LiCoO 2 . 2. Figure55shows showsthat, that,below below300 300rpm, rpm,the thestirring stirringspeed speedaffects affectsthe thedissolution dissolutionrate rateof ofthe theLiCoO LiCoO2,, Figure 2 theseresults resultsare aremore moreremarkable remarkableat athigher highertemperatures, temperatures,which whichwould wouldindicate indicatethat thatthe thereaction reactionhas has these diffusion control. control. Above Above 300 300 rpm, rpm, the the stirring stirring speed speed slightly slightly affects affects the theleaching leachingrate. rate. The The latter latter isis diffusion because the the film film thickness thickness around around the the solid, solid, through through which which the the HF HF must must flow flow in in order order for forthe thesolid solid because to make contact and react, does not change when increasing the stirring speed. This suggests that HF to make contact and react, does not change when increasing the stirring speed. This suggests that transfers from the bulk of the solution to the solid, through the boundary layer, and plateaus at HF transfers from the bulk of the solution to the solid, through the boundary layer, and plateaus at aa maximumstirring stirringspeed. speed. Therefore, Therefore, the thefilm filmthickness thicknessisisminimal. minimal. These These results resultswould wouldindicate indicatethat that maximum there is not a diffusive control over the global dissolution rate of the process due to the film thickness. there is not a diffusive control over the global dissolution rate of the process due to the film thickness. 3.1.5. Effect Effectof ofSolid-Liquid Solid-LiquidRatio Ratio 3.1.5. Figure66shows showsthe thedissolution dissolutionvalues valuesobtained obtainedatat75 75◦ C, °C,HF HFconcentration concentrationofof15% 15%(v/v), (v/v),stirring stirring Figure speed of of330 330rpm, rpm,and andaareaction reactiontime time120 120min. min.The Thesolid–liquid solid–liquid ratio ratio range range tested tested was was between between 1% 1% speed and 5% ( w / v ). and 5% (w/v).


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Figure 6. Effect of solid-liquid ratio on the dissolution of LiCoO .

2 Figure 6. Effect of solid-liquid ratio on the dissolution of LiCoO 2.

Figure 66shows showsthat thata adecrease decrease solid-liquid ratio ledantoincrease an increase the dissolution Figure in in thethe solid-liquid ratio led to in thein dissolution of the of the LiCoO . Data obtained from this figure displays that, for the solid-liquid ratio of 1% (w/v), 2 LiCoO2. Data obtained from this figure displays that, for the solid-liquid ratio of 1% (w/v), the the dissolution of LiCoO is high, it begins decreasewith withthe thefurther furtherincrease increasein in the the solid-liquid solid-liquid dissolution of LiCoO 2 is2high, andand it begins to to decrease ratio. This This is is due due to to the the fact fact that, that, for for aa fixed fixed concentration concentration of of HF HF acid, acid, there there is is more more acid acid available available to to ratio. react with the LiCoO at a lower solid-liquid ratio. react with the LiCoO22 at a lower solid-liquid ratio. 3.2. Recovery Recovery of of Co Co and and Li Li 3.2. 3.2.1. Recovery of Co 3.2.1. Recovery of Co The following reaction was proposed as the most probable for the precipitation of Co(OH)2 : The following reaction was proposed as the most probable for the precipitation of Co(OH)2: LiFLiF + +CoF + LiF LiF(aq) NaF CoF 2(aq)++22Na(OH) Na(OH)→ → Co(OH) Co(OH)2(s) 2(s) + (aq) (aq)(aq) 2(aq) (aq)++2 2NaF (aq)

(4) (4)

The effectsofofpH, pH,temperature, temperature, reaction onprecipitation the precipitation reaction of Co were The effects andand reaction timetime on the reaction of Co were studied. studied. After reaching the desired agitation value, the stirring was stopped, and the obtained solid After reaching the desired agitation value, the stirring was stopped, and the obtained solid was filtered. was filtered. In the resulting solutions, cobalt concentrations were determined, then the solidinwas In the resulting solutions, cobalt concentrations were determined, and then theand solid was dried an ◦ dried in an oven at 120 °C for 2 h for further characterization. oven at 120 C for 2 h for further characterization. Effect of pH Several aliquots of 25 mL were taken from the solution and were kept with constant stirring at 110 rpm and without stirring, for two minutes of reaction time. The pH range studied was between 2 and 12 using 2 M NaOH solution. Figure Figure 77 shows shows the the results results of of the effect of pH changes on the precipitation reaction of Co, indicating that the increase in pH led to an increase in the formation of Co(OH)2(s) whichagrees agreeswith withthe the literature literature that that reports reports the the formation formation of of such such solids solids at an alkaline 2(s), ,which pH. The maximum recovery recovery value value of of Co(OH) Co(OH)2(s) 2(s) occurred at pH = 9 and 10 with and occurred at pH = 9 and 10 with and without without stirring, stirring, respectively. This slight difference between the pH values at which the maximum recovery of Co is obtained could be due to the agitation, which accelerates the mixing of the reactants and, thus, the precipitation of Co(OH)22.


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Figure Figure 7. 7. Effect Effect of of pH pH on on the the recovery recovery of of Co. Co. Effect of Temperature

Figure 7. Effect of pH on the recovery of Co.

Effect of Temperature

Figure 8 shows the effect of temperature on the precipitation of Co for several aliquots of 25 mL Effect of Temperature

Figure 8 showseach the one effect of temperature the(considered precipitation of Co Section for several aliquots of 25 mL of the solution, adjusted to pH = 9 on or 10 optimum, “Effect pH”) with Figure 8 shows the effect of temperature on the precipitation of Co for several aliquots of 25 mL of theand solution, one adjusted to pH 9 or 10 system (considered optimum, Section “Effect with and withouteach stirring, respectively. The=reaction was kept with constant stirring (atpH”) 110 rpm) of the solution, each one adjusted to pH = 9 or 10 (considered optimum, Section “Effect pH”) with without respectively. reaction systemtime. wasThe kepttested withtemperatures constant stirring (at 35, 11050, rpm) and stirring, without stirring, for twoThe minutes of reaction were 25, 60, and and without stirring, respectively. The reaction system was kept with constant stirring (at 110 rpm) and 75 °C during two minutes of time reaction. After each test, the obtained precipitate was filtered, without stirring, for two minutes of reaction time. The tested temperatures were 25, 35, 50, and without stirring, for two minutes of reaction time. The tested temperatures were 25, 35, 50, 60, 60, and ◦ and then in antwo oven. 75 C during two minutes of timeofreaction. AfterAfter eacheach test, the obtained was filtered, and and 75 dried °C during minutes time reaction. test, the obtained precipitate precipitate was filtered, and in then in an oven. then dried andried oven.

Figure Effect onthe the recoveryofofCo. Co. Figure8. Effect of of temperature temperature on Figure 8.8.Effect of temperature on therecovery recovery of Co. From thethe results that temperature temperaturechanges changesdodo not have a marked From resultsininFigure Figure8,8,ititcan can be be inferred inferred that not have a marked effect on the precipitation reaction of 2(s) given that theslight slightincrease increase the recovery of Co From the results in Figure 8, it can be inferred thatthat temperature changes do not have a marked effect on the precipitation reaction of Co(OH) Co(OH) 2(s), given the inin the recovery of Co when increasing temperature could be explained by taking into account that the solubility of when increasing temperature could be explained by taking into account that the solubility of effect on the precipitation reaction of Co(OH)2(s) , given that the slight increase in the recovery of −15at −15 Co(OH) ( K sp 1.6 × 10 at 25 °C) increases when the temperature decreases. This effect is less Co(OH) 2(s)2(s) ( K sp 1.6 × 10 25 °C) increases when the temperature decreases. This effect is less Co when increasing temperature could be explained by taking into account that the solubility of important when theexperiments experiments areagitated, agitated, since since the and, thereby, important when the the stirring stirringincreases increasesthe thesolubility solubility and, thereby, − 15 at 25 ◦are Co(OH) C) increases when the temperature decreases. This effect is less 2(s) (Ksp 1.6 × 10 decreases amountofofobtained obtainedsolid. solid. decreases thethe amount important when the experiments are agitated, since the stirring increases the solubility and, thereby, decreases the amount of obtained solid. Effect Reaction Time Effect of of Reaction Time The effect of reaction time on the precipitation of Co was studied using several aliquots of 25 mL of the solution, each of them adjusted to pH = 9 or 10 (considered optimum, with and without stirring,

The effectTime of reaction time on the precipitation of Co was studied using several aliquots of 25 mL Effect of Reaction of the solution, each of them adjusted to pH = 9 or 10 (considered optimum, with and without stirring,

The effect of reaction time on the precipitation of Co was studied using several aliquots of 25 mL of the solution, each of them adjusted to pH = 9 or 10 (considered optimum, with and without stirring, respectively). Stirring speed and temperature were kept constant at 110 rpm at 25 ◦ C and 75 ◦ C. These results are shown in Figure 9, for a time range between 1 min and 60 min.


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respectively). Stirring speed and temperature were kept constant at 110 rpm at 25 °C and 75 °C. These respectively). Stirring temperature kept1constant rpm at 25 °C and 75 °C. These results are shown in speed Figureand 9, for a time rangewere between min andat 60110 min.

results are shown in Figure 9, for a time range between 1 min and 60 min.

Figure Effect of Figure 9. 9. Effect of reaction reaction time time on on the the recovery recovery of of Co. Co.

As shown in Figure 9, high recoveries ofCo Co in intime every condition obtained. In addition, Figure 9.recoveries Effect of reaction ontested the recovery ofwere Co. As shown in Figure 9, high of every tested condition were obtained. In addition, the increase of the reaction time led to an increase in cobalt recovery, and this effect is more marked the increase of the reaction time led to an increase in cobalt recovery, and this effect is more marked at As 75 °C. For both temperatures, the maximum Co(OH) 2 is obtained a reaction of shown in Figure 9, high recoveries of Corecovery in every of tested condition were at obtained. In time addition, at 75 ◦ C. For both temperatures, the maximum recovery of Co(OH)2 is obtained at a reaction time of min. The were at increase 30 min and 60 minrecovery, with and without the30 increase ofbest the results reaction timeachieved led to an in cobalt and thisstirring, effect isrespectively, more marked 30 min. The best results were achieved at 30 min and 60 min with and without stirring, respectively, at at 75 Furthermore, increasing themaximum reaction time led to of theCo(OH) formation a solid that easiertime and of at 75 °C.°C. For both temperatures, the recovery 2 is of obtained at awas reaction 75 ◦ C.quicker Furthermore, increasing the reaction time led to the formation of a solid that was easier and to best filter.results 30 min. The were achieved at 30 min and 60 min with and without stirring, respectively, quicker to filter. at 75 °C. Furthermore, increasing the reaction time led to the formation of a solid that was easier and Synthesis of Co3O4 quicker to filter. Synthesis of Co O 3

4

Synthesis was performed by accumulating the Co(OH)2(s) obtained in “Effect of pH” and “Effect Synthesis of Co 3Operformed 4 This solid was Synthesis was by accumulating the with Co(OH) obtained in “Effect of pH” and “Effect of Temperature”. washed five times 25 mL of hot doubly-distilled water 2(s)aliquots to remove residual NaOH and washed impurities. Then thewith purified Co(OH) 2(s) was dried and calcined at 600water of Temperature”. This solid was five times 25 mL aliquots of hot doubly-distilled Synthesis was performed by accumulating the Co(OH)2(s) obtained in “Effect of pH” and “Effect °C for residual 2 h. Co3O4NaOH formation throughThen the following reaction: to remove andoccurs impurities. the purified Co(OH)2(s) was dried and calcined at

of Temperature”. This solid was washed five times with 25 mL aliquots of hot doubly-distilled water 600to◦ remove C for 2 h. Co3 O4NaOH formation occurs through the following 6 Co(OH) 2(s) + O2the → 2purified Co3O4(s)+Co(OH) 6reaction: H2O(g)2(s) was dried and calcined (5) residual and impurities. Then at 600 °C for 2Inh.Figure Co3O4 10 formation occurs through the following reaction: the diffractogram and the SEM micrograph of the obtained solid after calcination 6 Co(OH)2(s) + O2 → 2 Co3 O4(s) + 6 H2 O(g) (5) are shown. The XRD indicates6the presence of Co3O4 (ICDD 01-080-1545) and SEM shows particles of Co(OH) 2(s) + O2 → 2 Co3O4(s)+ 6 H2O(g) (5) this oxide with sharp edges, and different shapes and sizes. In In Figure 10 10 thethe diffractogram and thethe SEM micrograph ofof the obtained Figure diffractogram and SEM micrograph the obtainedsolid solidafter aftercalcination calcinationare shown. The XRD the presence of Coof3 O 01-080-1545) andand SEM shows particles ofof this 4 3(ICDD are shown. The indicates XRD indicates the presence Co O4 (ICDD 01-080-1545) SEM shows particles oxide with sharp edges, and different shapes and sizes. this oxide with sharp edges, and different shapes and sizes.

Figure 10. (a) XRD and (b) SEM of the precipitated solid by the addition of NaOH.

Figure 10. (a) XRD and (b) SEM of the precipitated solid by the addition of NaOH. Figure 10. (a) XRD and (b) SEM of the precipitated solid by the addition of NaOH.


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10 of 13 10 of 13

3.2.2. Recovery of Li

3.2.2. Recovery of Li 3.2.2.liquor Recovery of Li after the recovery of Co was evaporated (60 ◦ C) until the appearance of The obtained The liquor obtained after the recovery of Co was evaporated (60 °C) until the appearance of a a gelatinous precipitate. Figures 11 and 12Co show the diffractogram and the micrograph of Thewhite liquor after the recovery wasthe evaporated (60 °C) the SEM appearance gelatinous whiteobtained precipitate. Figures 11 and of 12 show diffractogram anduntil the SEM micrographofofa the LiF precipitated, gelatinous white respectively. precipitate. Figures 11 and 12 show the diffractogram and the SEM micrograph of the LiF precipitated, respectively. the LiF precipitated, respectively.

Figure 11. XRD of the precipitated solid by evaporation.

Figure 11.11. XRD solidby byevaporation. evaporation. Figure XRDofofthe theprecipitated precipitated solid

Figure 12. SEM of the precipitated solid by evaporation. Figure 12. SEM of the precipitated solid by evaporation.

Figure 12. SEM of the precipitated solid by evaporation. The XRD patterns in Figure 11 present the structure of LiF (ICDD 01-089-3610). Figure 12 exhibits The XRDparticles, patterns which in Figure 11 apresent the structure LiF (ICDDcoinciding 01-089-3610). 12 exhibits the obtained have well-defined crystalofstructure, withFigure the cubic shape The XRD patterns in Figure 11 present the structure ofstructure, LiF (ICDD 01-089-3610). Figure 12 exhibits the obtained particles, which have a well-defined crystal coinciding with the cubic of LiF particles [36]. Gravimetric analysis showed that the recovery of Li as LiF was close to 80%.shape EDS the obtained particles, which haveanalysis a well-defined crystal structure, coinciding with the80%. cubic shape of LiF particles [36]. Gravimetric showed that the recovery of Li as LiF was close to EDS analysis indicated that the purity of the LiF precipitate was 98.4 wt % (see Table 1). These results analysis indicated that the purity of the LiF precipitate was 98.4 wt % (see Table 1). These results of LiF particles [36]. Gravimetric analysis showed that the recovery of Li as LiF was close to 80%. suggest that the solid LiF obtained by this route is of high purity. suggest that the solid LiF obtained by this route is of high purity. EDS analysis indicated that the purity of the LiF precipitate was 98.4 wt % (see Table 1). These results

Table 1. Purity of LiF. suggest that the solid LiF obtained by this route is of high purity. Table 1. Purity of LiF.

Purity of LiF (wt %) Purity of LiF (wt %) 98.4 98.4

Li Li 26.5 26.5

Elemental Composition (wt %) F Na K Ca Al F Na K Ca Al 71.9 0.42 0.26 0.08 0.05 71.9 Elemental 0.42 Composition 0.26 0.08 (wt0.05 %)

Table 1. Purity of LiF.Composition (wt %) Elemental

Others Others 0.78 0.78

Purity of LiF (wt %) 3.3. Elimination of F− Ion as CaF2 Li F Na K Ca Al Others 3.3. Elimination of F− Ion as CaF2 98.4 26.5CaCO371.9 0.26can be used 0.08 for recycling: 0.05 0.78 The precipitation of F− using produces0.42 CaF2, which The precipitation of F− using CaCO3 produces CaF2, which can be used for recycling: 4F−(aq) + 2CaCO3(s) + 4H+(aq) → 2CaF2(s) + 2CO2(g) + 2H2O (6) −(aq) + 2CaCO3(s) + 4H+(aq) → 2CaF2(s) + 2CO2(g) + 2H2O (6) 3.3. Elimination of F− Ion as4F CaF 2

The precipitation of F− using CaCO3 produces CaF2 , which can be used for recycling: 4F− (aq) + 2CaCO3(s) + 4H+ (aq) → 2CaF2(s) + 2CO2(g) + 2H2 O

(6)


11 of 13 11 of 13

Thisreaction reactionwas wascarried carriedout out using using CaCO CaCO33; ;the theresulting resultingprecipitate precipitatewas wasanalyzed analyzedby byXRD XRD(see (see This Figure13). 13).Figure Figure1313shows shows that, with addition of CaCO (ICDD 96-900-9669), precipitation of Figure that, with thethe addition of CaCO 3 (ICDD 96-900-9669), precipitation of the 3 the 2CaF (ICDD 96-900-9006) is achieved. controlling reactiontime, time,most mostofof the the CaF compound (ICDD 96-900-9006) is achieved. By By controlling thethe reaction 2 compound remainingFF−−from fromprevious previousstages stagescan canbebeeliminated. eliminated. remaining

Figure 13. Diffractogram ofofthe bythe theaddition addition of CaCO Figure 13. Diffractogram thesolid solidprecipitated precipitated by of CaCO 3 . 3. 4.4.Conclusions Conclusions In the operational parameters on on thethe LiCoO 2 leaching process and and on the Inthis thiswork, work,the theeffects effectsofof the operational parameters LiCoO process on 2 leaching recovery of Co were studied. The obtained results showed that the increase of temperature, reaction the recovery of Co were studied. The obtained results showed that the increase of temperature, time, and time, leaching concentration (HF) favored(HF) the dissolution of LiCoO 2. Theof optimum reaction andagent leaching agent concentration favored thereaction dissolution reaction LiCoO2 . value of dissolution was 58%, which was obtained working under the following conditions: The optimum value of dissolution was 58%, which was obtained working under the following temperature, 75 °C; HF concentration, 15% (v/v); reaction time, 120 min; solid-liquid ratio, 2% (w/v) conditions: temperature, 75 ◦ C; HF concentration, 15% (v/v); reaction time, 120 min; solid-liquid ratio, and stirring speed, 330speed, rpm. The recovery Co andofLiCo asand Co3O and were 98% (without stirring 2% (w/v) and stirring 330 rpm. The of recovery Li4 as CoLiF O and LiF were 98% (without 3 4 at 30 minatof and pHand 9) and 80%, with with purities higher thanthan 94%.94%. Moreover, F− stirring 30reaction min of reaction pH 9) andrespectively, 80%, respectively, purities higher Moreover, − was almost completely eliminated fromfrom the effluent withwith the the addition of CaCO 3. F was almost completely eliminated the effluent addition of CaCO 3. Acknowledgments:The Thefinancial financialsupport supportfrom fromUniversidad UniversidadNacional Nacionaldede Cuyo, Secretaria Ciencia, Técnica Acknowledgments: Cuyo, Secretaria dede Ciencia, Técnica y y Posgrado, gratefully acknowledged. Four anonymous refereesprovided providedconstructive constructiveand andhelpful helpfulreviews, reviews, Posgrado, is is gratefully acknowledged. Four anonymous referees corrections, and comments. Many thanks are due to the editorial staff of Minerals. corrections, and comments. Many thanks are due to the editorial staff of Minerals. Author Contributions: Daniela S. Suarez, Eliana G. Pinna, Gustavo D. Rosales, and Mario H. Rodriguez conceived Author Contributions: Daniela Daniela S. Suarez, Eliana G. Pinna, D. Mario Rosales, Mario performed H. Rodriguez and designed the experiments; S. Suarez, Eliana G. Gustavo Pinna, and H. and Rodriguez the conceived and designed the experiments; Daniela S. Suarez, Eliana G. Pinna, and Mario H. Rodriguez experiments and analyzed the data; Mario H. Rodriguez contributed reagents, materials, and analysisperformed tools; and Daniel S. Suarez,and Eliana G. Pinna, Gustavo D. Rosales, and Mario H. Rodriguez wrote the paper. the experiments analyzed the data; Mario H. Rodriguez contributed reagents, materials, and analysis tools; and Daniel S. Suarez, Eliana G. Pinna, Gustavo D. Rosales, and Mario H. Rodriguez wrote the paper. Conflicts of Interest: The authors declare no conflict of interest.

Conflicts of Interest: The authors declare no conflict of interest.

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