Synthesis of Lithium Fluoride from Spent Lithium Ion Batteries

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 Co3O4 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(Si4O10)] and lepidolite [K(Li,Al,Rb)4O10], 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 www.mdpi.com/journal/minerals Minerals 2017, 7, 81 2 of 13 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, H2SO4, HCl, HNO3,H2SO3, and H3PO4, 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 (H2O2) on the dissolution of LiCoO2 (from LIBs) with the inorganic acids, such as HNO3,H3PO4, and H2SO4, were studied in other investigations [17–25]. Lee and Rhee reported extraction values over 93% for cobalt and lithium, when working with HNO3-H2O2 [18], whereas Dorella and Mansur used H2SO4 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 H3PO4/H2O2 [17]. Zhang et al. studied the use of chemical agents that produce leaching and reduction at the same time and, working with H2SO3, 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 Na2CO3(s) or CO2(g) as the precipitating agent to obtain, in both cases, Li2CO3(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 6Li isotopes [34,35]. The industrial process to manufacture LiF is carried out by preparing a concentrated solution of a lithium salt, e.g., Li2CO3, 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 Minerals 2017, 7, 81 3 of 13

Co3O4 and LiF. Furthermore, a new process for their synthesis was developed, taking into account environmental and economic benefits. Minerals 2017, 7, 81 3 of 13 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 was obtained from the cathodes of spent lithium ion batteries from mobile A sample of LiCoO2 2 was obtained from the cathodes of spent lithium ion batteries from mobile phonesphones of different of different brands. brands. These These batteries batteries were were dismantled dismantled manually, manually, the thecathode cathode waswas separated, and the LiCoOand the2 wasLiCoO removed2 was removed from the from aluminum the aluminum film film by scraping. by scraping. CharacterizationCharacterization of theof the sample sample was was performed performed by by X-ray X-ray diffraction diffraction (XRD) (XRD) with with a Rigaku a Rigaku D-Max D-Max III C diffractometerIII C diffractometer (Osaka, (Osaka, Japan), Japan), operated operated at 35at 35 kV kV and and 30 30 mA mA using using K αKαradiation radiation ofof CuCu andand NiNi filter at λ =filter 0.15418 at λ nm.= 0.15418 Morphological nm. Morphological analysis analysis was done was by do SEMne by in SEM a LEO in 1450a LEO VP 1450 (Zeiss, VP (Zeiss, Jena, Germany).Jena, TheGermany). XRD and SEM characterization of the cathode material are shown in Figure1a,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 cathodea hollow lamp cathode (analytical lamp error(analytical 1.5%). error The 1.5%). quantitative The quantitative composition composition of the of sample the sample was was 6.7% 6.7% Li and 40.1%Li Co, and expressed 40.1% Co, expressed in mass percentage. 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- The075-0532). diffractogram The micrograph in Figure of Figure1a shows 1b shows thatthe that cathode LiCoO2 containsparticles have lithium irregular cobalt shapes oxide with (JCPDS 01-075-0532).rounded edges. The micrograph of Figure1b shows that LiCoO 2 particles have irregular shapes with rounded edges. 2.1. Leaching Assays 2.1. LeachingThe Assaysleaching tests were performed in a closed vessel of 500 mL capacity, constructed of polyvinyl Thechloride leaching (PVC), tests immersed were performed in a thermostatic in a closed bath, vesselfitted with of 500 a mechanical mL capacity, stirrer constructed and temperature of polyvinyl chloridecontrol. (PVC), The immersedoperational invariables a thermostatic studied were bath, te ﬁttedmperature, with areaction mechanical time, stirring stirrer andspeed, temperature solid- 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: − mm0 r X (%) =×100 (1) m −m m X(%) = 0 0 r × 100 (1) m0 where X is the conversion; m0 is the initial mass of LiCoO2, and mr is the mass of LiCoO2 unreacted whereafterX is the the reaction conversion; [17,34].m0 isEach the initialexperiment mass ofwas LiCoO replicated2, and threemr is thetimes. mass The of average LiCoO2 conversionunreacted after the reactionefficiency [17 is, 34presented]. Each experimentin the experimental was replicated results. three times. The average conversion efﬁciency is presented in the experimental results. 2.2. Recovery Assays

2.2. RecoveryIn the Assays 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 LiCoO studied were pH, temperature, and reaction time, with and without stirring. 2 with HF,The using recovery the best of Li leaching from the conditions resulting solution, determined after the in precipitation Section 3.1. of The Co, operatingcan be carried parameters out studiedby several were pH, known temperature, methods. In and this reaction case, lithium time, withwas precipitated and without as stirring.LiF, evaporating the solvents

Minerals 2017, 7, 81 4 of 13 Minerals 2017, 7, 81 4 of 13 aboveThe the recovery solubility of product Li from theconstant resulting (Ksp) solution, of LiF after[30,36,37]. the precipitation Finally, the of resulting Co, can be solutions carried outwere by − storedseveral to known eliminate methods. the content In this of case, F ions. lithium was precipitated as LiF, evaporating the solvents above the solubilityLithium and product cobalt constant were analyzed (Ksp) of by LiF atomic [30,36 ,absorption37]. Finally, spectroscopy the resulting to solutions calculate were the recovery stored to percentageeliminate the in contentall of the of experiments: F− ions. Lithium and cobalt were analyzed by atomicE absorption spectroscopy to calculate the recovery R (%) =×s 100 E (2) percentage in all of the experiments: m Es where Em is the initial amount of each elementR(%) in = the sample× 100 and Es is the quantity of each element (2)in 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 3.the Results leach liquor obtained after precipitation. 3. Results 3.1. Dissolution of LiCoO2 with HF

3.1. DissolutionThe following of LiCoO reaction2 with was HF proposed as the most probable for the dissolution of LiCoO2 with

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) (3) 4 LiCoO2(s) + 12 HF(aq) → 4 LiF(aq) + 4 CoF2(aq) + 6 H2O + O2(g) (3)

3.1.1.3.1.1. Effect Effect of of the the Leaching Leaching Temperature Temperature

FigureFigure 22 showsshows thethe effecteffect ofof temperaturetemperature onon thethe dissolutiondissolution ofof LiCoOLiCoO2 withwith HF HF at at a a concentration concentration ofof 15% 15% ( v/vv),), a a solid-liquid solid-liquid ratio ratio 2% 2% ( (ww//v),v), reaction reaction time time of of 120 120 min, min, and and a a stirring stirring speed speed of of 330 330 rpm. rpm. TheThe temperature range tested was between 25 °C◦C and 95 °C◦C..

2 FigureFigure 2. Effect 2. Effect of of temperature temperature on thethe dissolutiondissolution of of LiCoO LiCoO2. .

Figure 2 indicates that the dissolution of LiCoO2 increases while increasing the temperature, Figure2 indicates that the dissolution of LiCoO increases while increasing the temperature, which agrees with the known fact that, in solid–liquid heterogeneous2 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 LiCoO dissolution was obtained at 95 °C, but 75 °C was selected as the best for studying other operational2 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.

Minerals 2017, 7, 81 5 of 13 Minerals 2017, 7, 81 5 of 13 Minerals 2017, 7, 81 5 of 13 3.1.2. Effect of HF Concentration 3.1.2.3.1.2. EffectEffect ofof HFHF ConcentrationConcentration Tested HF concentrations were 5%, 10%, 15%, 20%, and 25% (v/v) with the other variables held TestedTested HF HF concentrations concentrations were were 5%, 5%, 10%, 10%, 15%, 15%, 20%, 20%, and and 25% 25% ( v(/v/vv)) withwith thethe otherother variablesvariables heldheld constant: temperature, 75 °C;◦ reaction time, 120 min; solid-liquid ratio, 2% (w/v); stirring speed, 330 constant:constant: temperature, 75 75 °C;C; reaction reaction time time,, 120 120 min; min; solid-liquid solid-liquid ratio, ratio, 2% 2% (w (/vw);/ vstirring); stirring speed, speed, 330 rpm. Figure 3 shows the dissolution values obtained. 330rpm. rpm. Figure Figure 3 shows3 shows the the dissolution dissolution values values obtained. obtained.

Figure 3. Effect of HF concentration on the dissolution of LiCoO2. FigureFigure 3. 3.EffectEffect of of HF HF concentration concentration on on the the dissolution dissolution ofLiCoO of LiCoO2. 2. The results in Figure 3 show that when leaching agent concentration (HF solution) increases so TheThe resultsresults inin FigureFigure3 3show show that that when when leaching leaching agent agent concentration concentration (HF (HF solution) solution) increases increases so so does the dissolution of the mixed oxide up to a HF concentration of 15% (v/v); after that, a plateau is doesdoes thethe dissolutiondissolution ofof thethe mixedmixed oxide oxide up up to to a a HF HF concentration concentration of of 15% 15% ( v(/v/vv);); afterafter that,that, aa plateauplateau isis observed in the dissolution value. This is because increasing the leaching agent concentration gives observedobserved in in the the dissolution dissolution value. value. This This is becauseis becaus increasinge increasing the the leaching leaching agent agent concentration concentration gives gives rise − + rise to a larger amount− of F and+ H ions, available to react with LiCoO2. From these results, the torise a largerto a larger amount amount of F andof F H− andions, H+ available ions, available to react to with react LiCoO with. FromLiCoO these2. From results, these the results, optimum the optimum HF concentration was selected to be 15% (v/v), which was2 used for the rest of the assays, HFoptimum concentration HF concentration was selected was to beselected 15% (v to/v ),be which 15% ( wasv/v), usedwhich for was the restused of for the the assays, rest of although the assays, the although the maximum dissolution value for the oxide (61%) was achieved by working with HF 25% maximumalthough the dissolution maximum value dissolution for the oxidevalue (61%)for the was oxide achieved (61%) was by working achieved with by working HF 25% (withv/v). HF 25% (v/v). (v/v). 3.1.3. Effect of Reaction Time 3.1.3. Effect of Reaction Time 3.1.3.Figure Effect4 ofshows Reaction the Time dissolution values obtained at 75 ◦C, a HF concentration of 15% (v/v), Figure 4 shows the dissolution values obtained at 75 °C, a HF concentration of 15% (v/v), a solid- a solid-liquidFigure 4 shows ratio of the 2% dissolution (w/v) and values stirring obtain speeded of at 33075 °C, rpm. a HF The concentration reaction time of range15% (v tested/v), a solid- was liquid ratio of 2% (w/v) and stirring speed of 330 rpm. The reaction time range tested was 5–240 min. 5–240liquid min. ratio of 2% (w/v) and stirring speed of 330 rpm. The reaction time range tested was 5–240 min.

FigureFigure 4. Effect 4. Effect of of reaction reaction time time on thethedissolution dissolution of of LiCoO LiCoO2. 2. Figure 4. Effect of reaction time on the dissolution of LiCoO2.

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InIn FigureFigure4 4it it 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 dissolution of the LiCoO2. 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 increaseincrease in in the the dissolutiondissolution of of the the solid, solid, which which is is consistentconsistent with with the the literature literature [ [38,39].38,39]. ItIt isis worthworth notingnoting that after 120 min of reaction, the LiCoO2 dissolution remained constant (plateau of the figure), which that after 120 min of reaction, the LiCoO2 dissolution remained constant (plateau of the ﬁgure), which isis whywhy thisthis valuevalue waswas selectedselected forfor the the study study ofof thethe otherother operationaloperational parameters. parameters.

3.1.4.3.1.4. EffectEffect ofof StirringStirring SpeedSpeed

TheThe effecteffect ofof thethe stirringstirring speedspeed onon thethe dissolutiondissolution ofof LiCoOLiCoO22 waswas testedtested betweenbetween 110110 rpmrpm andand 550550 rpm, and the the other other variables variables were were kept kept constant constant:: temperature, temperature, 25 °C; 25 reaction◦C; reaction time, time,120 min; 120 solid- min; solid-liquidliquid ratio, ratio,2% (w 2%/v), ( wand/v), HF and concentration, HF concentration, 15% ( 15%v/v). (Figurev/v). Figure5 shows5 shows the dissolution the dissolution values valuesobtained. obtained.

FigureFigure 5. 5.EffectEffect of of stirring stirring speed on on the the dissolution dissolution of LiCoOof LiCoO2. 2.

Figure 5 shows that, below 300 rpm, the stirring speed affects the dissolution rate of the LiCoO2, Figure5 shows that, below 300 rpm, the stirring speed affects the dissolution rate of the LiCoO 2, thesethese resultsresults areare moremore remarkableremarkable atat higherhigher temperatures,temperatures, whichwhich wouldwould indicateindicate thatthat thethe reactionreaction hashas diffusiondiffusion control.control. AboveAbove 300300 rpm,rpm, thethe stirringstirring speedspeed slightlyslightly affectsaffects thethe leachingleaching rate.rate. TheThe latterlatter isis becausebecause thethe filmfilm thicknessthickness aroundaround thethe solid,solid, throughthrough whichwhich thethe HFHF mustmust flowflow inin orderorder forfor thethe solidsolid toto makemake contactcontact and react, react, does does not not change change when when in increasingcreasing the the stirring stirring speed. speed. This This suggests suggests that that HF HFtransfers transfers from from the the bulk bulk of ofthe the solu solutiontion to to the the solid, solid, through through the the bo boundaryundary layer, layer, and plateaus atat aa maximummaximum stirringstirring speed.speed. Therefore,Therefore, thethe filmfilm thicknessthickness isis minimal.minimal. TheseThese resultsresults wouldwould indicateindicate thatthat therethere isis notnot aa diffusivediffusive controlcontrol overover thethe globalglobal dissolutiondissolution raterate ofof thethe processprocess duedue toto thethe filmfilm thickness.

3.1.5.3.1.5. EffectEffect ofof Solid-LiquidSolid-Liquid RatioRatio FigureFigure6 6shows shows the the dissolution dissolution values values obtained obtained at at 75 75◦ C,°C, HF HF concentration concentration of of 15% 15% ( v(/v/vv),), stirringstirring speedspeed ofof 330330 rpm,rpm, andand aa reactionreaction timetime 120120 min.min. TheThe solid–liquidsolid–liquid ratioratio rangerange testedtested waswas betweenbetween 1%1% andand 5%5% ((ww//v).

Minerals 2017, 7, 81 7 of 13 Minerals 2017, 7, 81 7 of 13

Figure 6. Effect of solid-liquid ratio on the dissolution of LiCoO2. Figure 6. Effect of solid-liquid ratio on the dissolution of LiCoO2.

Figure 66 shows that that a a decrease decrease in in the the solid-liquid solid-liquid ratio ratio led ledto an to increase an increase in the in dissolution the dissolution of the LiCoOof the LiCoO2. Data2 .obtained Data obtained from this from figure this ﬁguredisplays displays that, for that, the for solid-liquid the solid-liquid ratio ratioof 1% of ( 1%w/v (),w /thev), dissolutionthe dissolution of LiCoO of LiCoO2 is 2high,is high, and and it begins it begins to todecrease decrease with with the the further further increase increase in in the the solid-liquid solid-liquid ratio. This This is is due due to the fact that, for a fixed ﬁxed concentration of HF acid, there is more acid available to react with the LiCoO2 atat a lower solid-liquid ratio.

3.2. Recovery of Co and Li 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(aq)(aq)+ + CoF CoF2(aq)2(aq)+ + 22 Na(OH)Na(OH) →→ Co(OH)Co(OH)2(s)2(s) + LiF LiF(aq)(aq) + +2 2NaF NaF(aq)(aq) (4)(4)

The effectseffects ofof pH, pH, temperature, temperature, and and reaction reaction time time on the on precipitation the precipitation reaction reaction of Cowere of Co studied. were Afterstudied. reaching After thereaching desired the agitation desired value,agitation the stirringvalue, the was stirring stopped, was and stopped, the obtained and the solid obtained was ﬁltered. solid wasIn the filtered. resulting In the solutions, resulting cobalt solutions, concentrations cobalt concentrations were determined, were determined, and then the and solid then was the dried solid in was an driedoven atin 120an oven◦C for at 2 120 h for °C further for 2 h characterization.for further characterization.

Effect of pH Several aliquots of 25 mL were taken from the solutionsolution 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 showsshows thethe resultsresults ofof thethe effecteffect ofof pHpH changeschanges onon thethe precipitation reaction of Co, indicating that the increase in pH led to an increase in the formation of Co(OH)2(s)2(s), ,which which agrees agrees with with the the literature literature that that reports reports the the formation formation of of such such solids solids at at an alkaline pH. The maximum recovery value ofof Co(OH)Co(OH)2(s)2(s) occurredoccurred at at pH pH = = 9 9 and and 10 10 with with and 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 acce accelerateslerates the mixing of the reactants and, thus, the precipitation of Co(OH)2..

Minerals 2017, 7, 81 8 of 13 Minerals 2017, 7, 81 8 of 13

Minerals 2017, 7, 81 8 of 13

Figure 7. Effect of pH on the recovery of Co. Figure 7. Effect of pH on the recovery of Co. Effect of Temperature Figure 7. Effect of pH on the recovery of Co. Effect of Temperature EffectFigure of Temperature 8 shows the effect of temperature on the precipitation of Co for several aliquots of 25 mL Figureof the solution,8 shows each the effectone adjusted of temperature to pH = 9 onor the10 (considered precipitation optimum, of Co forSection several “Effect aliquots pH”) with of 25 mL Figure 8 shows the effect of temperature on the precipitation of Co for several aliquots of 25 mL of theand solution, without each stirring, one adjustedrespectively. to pHThe =reaction 9 or 10 syst (consideredem was kept optimum, with constant Section stirring “Effect (at pH”) 110 rpm) with and of the solution, each one adjusted to pH = 9 or 10 (considered optimum, Section “Effect pH”) with withoutand stirring,without stirring, respectively. for two The minutes reaction of reaction system time. was The kept tested with temperatures constant stirring were 25, (at 35, 110 50, rpm) 60, and and without stirring, respectively. The reaction system was kept with constant stirring (at 110 rpm) withoutandand stirring,75 without°C during for stirring, two minutes minutesfor two minutesof of time reaction reaction.of reaction time. Afte time. Ther each The tested test, tested the temperatures temperatures obtained precipitate were were 25, 25, was35, 35, 50, filtered, 50,60, 60, and ◦ 75 Cand duringand then 75 dried°C two during minutes in an two oven. minutes of time of reaction. time reaction. After Afte eachr each test, test, the the obtained obtained precipitate was was filtered, ﬁltered, and then driedand inthen an dried oven. in an oven.

Figure 8. Effect of temperature on the recovery of Co. FigureFigure 8.8. EffectEffect of temperature on on the the recovery recovery of of Co. Co.

FromFrom the the results results in in Figure Figure 8, 8, it it can can bebe inferred thatthat temperaturetemperature changes changes do do not not have have a marked a marked Fromeffecteffect on the on the resultsthe precipitation precipitation in Figure reaction reaction8, it can of of Co(OH) beCo(OH) inferred2(s), givengiven that thatthat temperature the the slight slight increase increase changes in in the do the recovery not recovery have of Co aof marked Co effectwhen onwhen the increasing increasing precipitation temperature temperature reaction couldcould of Co(OH)bebe explainedexplained2(s), given byby takingtaking that into theinto account slightaccount increasethat that the the solubility in solubility the recovery of of of Co whenCo(OH)Co(OH) increasing2(s) 2(s)(K (spKsp 1.6 temperature1.6 × ×10 10−15−15 at at 25 25 could °C)°C) increasesincreases be explained when thethe by temperaturetemperature taking into decreases. decreases. account This thatThis effect effect the is solubility lessis less of importantimportant when when the the experiments experiments−15 ◦are are agitated, agitated, since thethe stirringstirring increases increases the the solubility solubility and, and, thereby, thereby, Co(OH)2(s) (Ksp 1.6 × 10 at 25 C) increases when the temperature decreases. This effect is less decreasesdecreases the the amount amount of of obtained obtained solid. solid. important when the experiments are agitated, since the stirring increases the solubility and, thereby, decreasesEffectEffect theof ofReaction amount Reaction Time ofTime obtained solid. The effect of reaction time on the precipitation of Co was studied using several aliquots of 25 mL Effect of ReactionThe effect Timeof reaction time on the precipitation of Co was studied using several aliquots of 25 mL of theof the solution, solution, each each of of them them adjusted adjusted to to pHpH = 9 or 10 (considered(considered optimum, optimum, with with and and without without stirring, 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 Figure9, for a time range between 1 min and 60 min. Minerals 2017, 7, 81 9 of 13 Minerals 2017, 7, 81 9 of 13 Minerals 2017, 7, 81 9 of 13 respectively). Stirring speed and temperature were kept constant at 110 rpm at 25 °C and 75 °C. These respectively).results are shown Stirring in speedFigure and 9, for temperature a time range were between kept 1constant min and at 60 110 min. rpm at 25 °C and 75 °C. These results are shown in Figure 9, for a time range between 1 min and 60 min.

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

As shownAs shown in Figure in Figure9Figure, high 9, high 9. recoveries Effectrecoveries of reaction of of Co Co in in time everyevery on tested tested the recovery condition condition of were Co. were obtained. obtained. In addition, In addition, the increasethe increase of the of the reaction reaction time time led led to to an an increase increase in cobalt cobalt recovery, recovery, and and this this effect effect is more is more marked marked at◦ As75 °C.shown For bothin Figure temperatures 9, high recoveries, the maximum of Co recovery in every oftested Co(OH) condition2 is obtained were atobtained. a reaction In timeaddition, of at 75 C. For both temperatures, the maximum recovery of Co(OH)2 is obtained at a reaction time of the30 increase min. The of best the resultsreaction were time achieved led to an at increase30 min and in cobalt60 min recovery, with and withoutand this stirring, effect is respectively, more marked 30 min. The best results were achieved at 30 min and 60 min with and without stirring, respectively, at at 75at 75°C. °C. For Furthermore, both temperatures increasing, the the maximum reaction time recovery led to ofthe Co(OH) formation2 is ofobtained a solid that at a was reaction easier time and of 75 ◦C. Furthermore, increasing the reaction time led to the formation of a solid that was easier and 30 quickermin. The to bestfilter. results 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 quickerSynthesis to filter. of Co 3O4 Synthesis of Co3O4 Synthesis was performed by accumulating the Co(OH)2(s) obtained in “Effect of pH” and “Effect SynthesisSynthesisof Temperature”. of Co was3O performed4 This solid was by accumulating washed five times the with Co(OH) 25 mL2(s) aliquotsobtained of hot in “Effect doubly-distilled of pH” and water “Effect of Temperature”.to remove residual This NaOH solid was and washedimpurities. five Then times the withpurified 25 mLCo(OH) aliquots2(s) was of dried hot doubly-distilledand calcined at 600 water Synthesis was performed by accumulating the Co(OH)2(s) obtained in “Effect of pH” and “Effect °C for 2 h. Co3O4 formation occurs through the following reaction: toof remove Temperature”. residual This NaOH solid and was impurities. washed five Then times the with purified 25 mL Co(OH)aliquots 2(s)of hotwas doubly-distilled dried and calcined water at ◦ 600to removeC for 2 h.residual Co3O 4NaOHformation and impurities. occurs6 Co(OH) through2(s) Then + O2 the → 2purified following Co3O4(s) +Co(OH) 6 reaction:H2O(g)2(s) was dried and calcined (5)at 600 °C for 2In h. Figure Co3O4 10formation the diffractogram occurs through and the the SEM following micrograph reaction: of the obtained solid after calcination 6 Co(OH)2(s) + O2 → 2 Co3O4(s)+ 6 H2O(g) (5) are shown. The XRD indicates the presence of Co3O4 (ICDD 01-080-1545) and SEM shows particles of 6 Co(OH)2(s) + O2 → 2 Co3O4(s)+ 6 H2O(g) (5) this oxide with sharp edges, and different shapes and sizes. InIn Figure Figure 10 10the the diffractogram diffractogram and and the the SEM SEM micrograph micrograph of of the the obtained obtained solid solid after after calcination calcination are shown.are shown. The XRD The indicatesXRD indicates the presence the presence of Co of3O Co4 3(ICDDO4 (ICDD 01-080-1545) 01-080-1545) and and SEM SEM shows shows particles particles of of this oxidethis withoxide sharp with sharp edges, edges, and different and different shapes shapes and sizes.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.

Minerals 2017, 7, 81 10 of 13

Minerals 2017, 7, 81 10 of 13 3.2.2.Minerals Recovery 2017, 7 of, 81 Li 10 of 13 3.2.2. Recovery of Li The3.2.2. liquor Recovery obtained of Li after the recovery of Co was evaporated (60 ◦C) until the appearance of The liquor obtained after the recovery of Co was evaporated (60 °C) until the appearance of a a gelatinous white precipitate. Figures 11 and 12 show the diffractogram and the SEM micrograph of gelatinousThe liquor white obtained precipitate. after Figures the recovery 11 and of12 Coshow wa sthe evaporated diffractogram (60 °C) and until the SEMthe appearance micrograph of of a the LiFthegelatinous precipitated,LiF precipitated, white respectively.precipitate. respectively. Figures 11 and 12 show the diffractogram and the SEM micrograph of the LiF precipitated, respectively.

Figure 11. XRD of the precipitated solid by evaporation. FigureFigure 11. 11.XRD XRD of of the theprecipitated precipitated solid solid by by evaporation. evaporation.

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 obtainedThe XRD particles, patterns whichin Figure have 11 apresent well-defined the structur crystale of structure, LiF (ICDD coinciding 01-089-361 with0). Figure the cubic 12 exhibits shape The XRD patterns in Figure 11 present the structure of LiF (ICDD 01-089-3610). Figure 12 exhibits ofthe LiF obtained particles particles, [36]. Gravimetric which have analysis a well-defined showed that crystal the recoverystructure, of coinciding Li as LiF was with close the tocubic 80%. shape EDS the obtained particles, which have a well-deﬁned crystal structure, coinciding with the cubic shape analysisof LiF particles indicated [36]. that Gravimetric the purity analysis of the LiFshowed prec ipitatethat the was recovery 98.4 wt of Li% as(see LiF Table was close1). These to 80%. results EDS of LiFsuggestanalysis particles that indicated [the36 ].solid Gravimetricthat LiF the obtained purity analysis byof thethis LiF route showed prec is ipitateof thathigh was thepurity. recovery98.4 wt % of(see Li Table as LiF 1). wasThese close results to 80%. EDS analysissuggest that indicated the solid that LiF theobtained purity by of this the route LiF precipitateis of high purity. was 98.4 wt % (see Table1). These results suggest that the solid LiF obtained by thisTable route 1. Purity is of high of LiF. purity. Table 1. Purity of LiF. Elemental Composition (wt %) Purity of LiF (wt %) Table 1. PurityElemental of LiF. Composition (wt %) Purity of LiF (wt %) Li F Na K Ca Al Others 98.4 26.5Li 71.9F 0.42 Na 0.26 K 0.08 Ca 0.05 Al Others0.78 98.4 26.5 71.9 Elemental0.42 Composition0.26 0.08 (wt0.05 %) 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 The precipitation98.4 of F− using 26.5 CaCO3 71.9 produces 0.42CaF2, which 0.26 can be used 0.08 for recycling: 0.05 0.78 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) − − + 3.3. Elimination of F Ion as4F CaF(aq)2 + 2CaCO3(s) + 4H (aq) → 2CaF2(s) + 2CO2(g) + 2H2O (6) − 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) Minerals 2017, 7, 81 11 of 13 Minerals 2017, 7, 81 11 of 13

ThisThis reaction reaction was was carried carried out out using using CaCO CaCO33; ;the the resulting resulting precipitate precipitate was was analyzed analyzed by by XRD XRD (see (see FigureFigure 13). 13). Figure Figure 13 13 shows shows that, that, with with the the addition addition of CaCO of CaCO3 (ICDD3 (ICDD 96-900-9669), 96-900-9669), precipitation precipitation of the of CaFthe2 CaF compound2 compound (ICDD (ICDD 96-900-9006) 96-900-9006) is achieved. is achieved. By Bycontrolling controlling the the reaction reaction time, time, most most of of the the remainingremaining F F−− fromfrom previous previous stages stages can can be be eliminated. eliminated.

FigureFigure 13. Diffractogram 13. Diffractogram ofof the the solid solid precipitated precipitatedby by the the addition addition of CaCOof CaCO3. 3.

4.4. Conclusions Conclusions

InIn this this work, work, the the effects effects of of the the operational operational parameters parameters on onthe the LiCoO LiCoO2 leaching2 leaching process process and andon the on recoverythe recovery of Co of were Co werestudied. studied. The obtained The obtained results showed results showedthat the thatincrease the of increase temperature, of temperature, reaction time,reaction and time,leaching and agent leaching concentration agent concentration (HF) favored (HF) the dissolution favored the reaction dissolution of LiCoO reaction2. The of optimum LiCoO2 . valueThe optimumof dissolution value ofwas dissolution 58%, which was was 58%, obtained which wasworking obtained under working the following under the conditions: following temperature,conditions: temperature, 75 °C; HF concentration, 75 ◦C; HF concentration, 15% (v/v); reaction 15% (v/ vtime,); reaction 120 min; time, solid-liquid 120 min; solid-liquid ratio, 2% ( ratio,w/v) and2% (stirringw/v) and speed, stirring 330 speed, rpm. The 330 rpm.recovery The of recovery Co and of Li Co as andCo3O Li4 asand Co LiF3O 4wereand LiF98% were (without 98% (withoutstirring atstirring 30 min at of 30 reaction min of reaction and pH and 9) and pH 9)80%, and respectively, 80%, respectively, with withpurities purities higher higher than than94%. 94%. Moreover, Moreover, F− − wasF was almost almost completely completely eliminated eliminated from from the effluent the efﬂuent with with the theaddition addition of CaCO of CaCO3. 3.

Acknowledgments:Acknowledgments: TheThe financial financial support support from from Universidad Universidad Nacional Nacional de de Cuyo, Cuyo, Secretaria Secretaria de de Ciencia, Ciencia, Técnica Técnica y Posgrado,y Posgrado, is isgratefully gratefully acknowledged. acknowledged. Four Four anonymous anonymous referees referees provided provided constructive constructive and and helpful helpful reviews, reviews, 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 Authorand designed Contributions: the experiments; Daniela DanielaS. Suarez, S. Suarez,Eliana G. Eliana Pinna, G. Gust Pinna,avo and D. MarioRosales, H. and Rodriguez Mario performedH. Rodriguez the conceivedexperiments and and designed analyzed the theexperiments; data; Mario Daniela H. Rodriguez S. Suarez, contributed Eliana G. Pinna, reagents, and materials, Mario H. andRodriguez analysis performed tools; and theDaniel experiments S. Suarez, and Eliana analyzed G. Pinna, the data; Gustavo Mario D. Rosales,H. Rodriguez and Mario contributed H. Rodriguez reagents, wrote materials, the paper. and analysis tools; andConflicts Daniel of S.Interest: Suarez, ElianaThe authors G. Pinna, declare Gustavo no conflict D. Rosales, of interest. and Mario H. Rodriguez wrote the paper. Conflicts of Interest: The authors declare no conflict of interest. References References 1. Habashi, F. Handbook of Extractive Metallurgy, 1st ed.; Wiley-VCH: Berlin, Germany, 1997; Volume II. 1.2. Habashi,USGS National F. Handbook Minerals of Extractive Information Metallurgy Center., 1st ed.;Cobalt Wiley-VCH: Statics Berlin and, Germany, Information. 1997; AvailableVolume II. online: 2. USGShttp//minerals.usgs.gov/minerals/pubs/commodity/cobalt/ National Minerals Information Center. Cobalt Statics (accessed and Information. on 14 April 2017). Available online: 3. http//minerals.usgs.gov/minerRa, D.; Han, K.S. Used lithiumals/pubs/commodity/cobalt/ ion rechargeable battery (accessed recycling on 14 using April 2017). Etoile-Rebatt technology. 3. Ra,J. Power D.; Han, Sources K.S.2006 Used, 163 lithium, 284–288. ion rechargeable [CrossRef] battery recycling using Etoile-Rebatt technology. J. Power 4. SourcesHabashi, 2006 F. ,Handbook 163, 284–288. of Extractive Metallurgy, 1st ed.; Wiley-VCH: Berlin, Germany, 1997; Volume IV. 4.5. Habashi,Nan, J.; Han, F. Handbook D.; Zuo, of X. Extractive Recovery Metallurgy of metal values, 1st ed.; from Wiley-VCH: spent lithium-ion Berlin, batteriesGermany, with 1997; chemical Volume deposition IV. 5. Nan,and solventJ.; Han, extraction. D.; Zuo, J.X. Power Recovery Sources of2005 metal, 152 valu, 278–284.es from [CrossRef spent ]lithium-ion batteries with chemical 6. depositionLi, L.; Ge, J.;and Chen, solvent R.; Wu,extraction. F.; Chen, J. Power S.; Zhang, Sources X. 2005 Environmental, 152, 278–284. friendly leaching reagent for cobalt and 6. Li,lithium L.; Ge, recovery J.; Chen, from R.; Wu, spent F.; lithium-ion Chen, S.; Zhang, batteries. X. EnvironmentalWaste Manag. 2010 friendly, 30, 2615–2621.leaching reagent [CrossRef for ][cobaltPubMed and] 7. lithiumConard, recovery B.R. The from role spent of hydrometallurgy lithium-ion batteries. in achieving Waste sustainable Manag. 2010 development., 30, 2615–2621.Hydrometallurgy 1992, 30, 7. Conard,1–28. [CrossRef B.R. The] role of hydrometallurgy in achieving sustainable development. Hydrometallurgy 1992, 30, 1–28. 8. Wang, R.C.; Lin, Y.C.; Wu, S.H. A novel recovery process of metal values from the cathode active materials of the lithium-ion secondary batteries. Hydrometallurgy 2009, 99, 194–201.

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