Recovery of Cobalt from Spent Lithium-Ion Mobile Phone Batteries Using Liquid–Liquid Extraction

batteries

Article Recovery of Cobalt from Spent Lithium-Ion Mobile Phone Batteries Using Liquid–Liquid Extraction

Daniel Quintero-Almanza 1, Zeferino Gamiño-Arroyo 1,*, Lorena Eugenia Sánchez-Cadena 2 , Fernando Israel Gómez-Castro 1, Agustín Ramón Uribe-Ramírez 1, Alberto Florentino Aguilera-Alvarado 1 and Luz Marina Ocampo Carmona 3

1 Departamento de Ingeniería Química, Universidad de Guanajuato, Campus Guanajuato, Noria Alta s/n, Col. Noria Alta, Guanajuato 36050, Mexico; [email protected] (D.Q.-A.); [email protected] (F.I.G.-C.); [email protected] (A.R.U.-R.); [email protected] (A.F.A.-A.) 2 Departamento de Ingeniería Civil, Universidad de Guanajuato, Campus Guanajuato, Avenida Juárez No. 77, Col. Centro, Guanajuato 36050, Mexico; [email protected] 3 Departamento de Materiales y Minerales, Universidad Nacional de Colombia, Sede Medellín, Calle 75 N. 79 A 51 Bloque M17 of 407-05, Medellín 050034, Colombia; [email protected] * Correspondence: [email protected]; Tel.: +52-473-7320006 (ext. 8140)

Received: 25 March 2019; Accepted: 18 April 2019; Published: 6 May 2019

Abstract: The aim of this paper was to propose and test a continuous cobalt recovery process from waste mobile phone batteries. The procedure started with dismantling, crushing, and classifying the materials. A study on leaching with sulfuric acid and hydrogen peroxide was carried out with subsequent selective separation of cobalt by means of liquid–liquid extraction. The best extraction conditions were determined based on a sequence of experiments that consisted of selecting the best extractant for cobalt, then assessing the impact of extractant concentration, pH, and contact time on the extraction yield. With these conditions, an extraction isotherm was obtained and correlated with a mathematical model to define the number of extraction stages for a countercurrent process using the McCabe–Thiele method. Then, a similar study was done for stripping conditions and, as a last step, cobalt electroplating was performed. The proposed process offers a solution for the treatment of these batteries, avoiding potential problems of contamination and risk for living beings, as well as offering an opportunity to recover valuable metal.

Keywords: cobalt; spent lithium batteries; recovery

1. Introduction In recent decades, the use of lithium-ion batteries (LiBs) in a large number of portable devices, such as mobile phones, laptops, tablets, toys, medical equipment, and tools, has increased. This consumption has generated a large number of spent batteries. The Global E-waste Monitor [1] classiﬁes this e-waste within the category “small IT and telecommunication equipment”, with an estimated generation of 3.9 million metric tons in 2016 [1]. In a mobile phone, the battery represents 21.12% of the total weight, together with other materials such as plastics (25.75 wt%), printed circuit boards (PCBs) (17.67 wt%), metals (17.30 wt%), and displays (8.37 wt%) [2]. Worldwide, there are around 780,000 metric tons of spent LiBs, and for China alone, there is an estimated increase to 500,000 metric tons for 2020 [3]. There are two main reasons to recycle batteries: to recover valuable materials, especially if their supply is limited, and to comply with any government regulations on the disposal of this type of spent battery [4]. LiBs are composed of an anode, a cathode, a separator, and an electrolyte. The average composition of the materials in LiBs is presented in Table1[5].

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Table 1. Material percentage %(w/w) in lithium-ion batteries (LiBs) [5].

Anode Cathode Plastic Electrolyte Case Loss 18 35 6 11 26 4

In more than half of these batteries, the cathode contains any of the following compounds: LiCoO2 and LiNi0.33Co0.33Mn0.33O2 [6]. As previously mentioned, cobalt accounts for around 20 wt% of spent LiBs. These residues also contain lithium, nickel, copper, and aluminum; however, there is a higher composition of cobalt than the other metals, which is why it is important to recover [5,7]. Due to the complicated assembly of the batteries and the composition of the electrodes, recycling LiBs requires physical and chemical processes. Physical processes include pretreatments, such as dismantling, crushing, screening, magnetic separation, washing, and thermal pretreatment. Chemical processes include acid leaching, bioleaching, ultrasonic-assisted separation, solvent extraction, chemical precipitation, and electrochemical processes [6,8,9]. Many articles have focused on the stage of leaching with minerals acid [4,7,10,11], bioleaching [5], and organics acids [12–15]. Other proposed processes include precipitation [16,17], thermal treatment [18], reduction roasting [19], and mechanical separation [20]. While solvent extraction has industrial applications in the recovery and purification of metals from lixiviation liquors and residues of materials [21], few works have proposed solvent extraction to recover cobalt [22,23], copper [24], and other metals of spent batteries [25]. This work focused on the recovery of cobalt by solvent extraction, measuring the effect of parameters such as time, pH, and concentration of the extractant. Liquid–liquid extraction was used because of its flexibility, high selectivity, and lower energy requirements in comparison with pyrometallurgic methods [26]. The number of extraction and stripping stages required to perform the separation in a continuous scheme was estimated using the McCabe–Thiele method. After stripping, it was possible to achieve the electrodeposition of cobalt in sulfate medium [27], and it may be possible even with the presence of organic impurities [28]. With this last stage, the process of cobalt recovery was complete and could be used at the industrial level. The electrodeposition of cobalt was also studied in this work.

2. Materials and Methods

2.1. Materials The ﬁrst step of this research was to gather mobile phone batteries from collection centers, mobile phone repair shops, and friends and relatives. To dissolve the spent battery material, sulfuric acid (Karal) and hydrogen peroxide (Karal) were used. For the recovery of cobalt, the selected extractant was Cyanex 272 (bis-(2,4,4-tri-methyl-pentyl) phosphinic acid), which was supplied by Cytec Solvay and used without further puriﬁcation. The organic phase was prepared by diluting the extractant in kerosene (Reasol, technical grade). All other chemical products were of analytical reagent grade.

2.2. Experimental Procedure The experimental procedure is illustrated in Figure1, and it indicates the components that were removed at each stage. BatteriesBatteries2019 2019, 5,, 44 5, x FOR PEER REVIEW 3 of3 of13 13

Al, Cu, Fe, Spent Libs Discharge Dismantling Crushin Sieving plastics g

Co Electrodeposition Stripping Liquid–liquid extraction Acid leaching

FigureFigure 1. 1.Experimental Experimental procedureprocedure for recovery of of cobalt. cobalt.

EachEach step step is describedis described below. below. Collection.Collection.After After collecting collecting about about 4040 batteriesbatteries of didifferentfferent brands, brands, they they were were classified classified into into two two groupsgroups by by weight: weight: batteries batteries of of 20–30 20–30 g g and and those those ofof 30–4030–40 g. Discharge.Discharge.To To discharge discharge the the residual residual energy, energy, each each batterybattery was connected to to a alamp lamp until until its its ener energygy waswas minimal. minimal. This This was was measured measured with with a a multimeter multimeter modelmodel MP9600-MITZU.MP9600-MITZU. DismantlingDismantling and and crushing crushing. Each. Each battery battery was was cut cut into into three three or four or four parts parts with with the help the help of metal-cutting of metal- cutting scissors, which were then crushed with a 500-W blender. scissors, which were then crushed with a 500-W blender. Sieving and classification. After crushing, a sieve was applied for 1 min, which consisted of four Sieving and classification. After crushing, a sieve was applied for 1 min, which consisted of four meshes corresponding to mesh 18, 35, 60, and 140 with openings of 1 mm, 0.50 mm, 0.25 mm, and meshes corresponding to mesh 18, 35, 60, and 140 with openings of 1 mm, 0.50 mm, 0.25 mm, and 0.105 mm, respectively. Then, each mesh was taken apart to weigh its contents. 0.105 mm, respectively. Then, each mesh was taken apart to weigh its contents. Leaching. The leaching process was carried out using a sulfuric acid and hydrogen peroxide solutionLeaching to. dissolve The leaching the components process was of the carried batteries out containing using a sulfuric cobalt and acid lithium, and hydrogen using a solid peroxide-to- solutionliquid to ratio dissolve of 1:10, the components with controlled of the temperature batteries containing and time. cobalt Cobalt and concen lithium,tration using in a solution solid-to-liquid was ratiodetected of 1:10, by with stoichiometry. controlled temperatureCorresponding and dilutions time. Cobalt were prepared concentration and defined in solution by AAS was using detected a byPerkin stoichiometry. Elmer AAnalyst Corresponding 200. dilutions were prepared and defined by AAS using a Perkin Elmer AAnalystLiquid 200.–liquid extraction. In order to define the extraction operation conditions, batch experimentationLiquid–liquid extraction was perfo. Inrmed order in to a define30-mL thebeaker extraction using an operation aqueous conditions,-to-organic batch-phase experimentation ratio of 10:10 wasmL. performed The phases in a were 30-mL in beaker contact using with anconstant aqueous-to-organic-phase stirring at 700 rpm ratiofor 30 of min, 10:10 which mL. The was phases sufficient were in contacttime to withreach constant equilibrium. stirring Once at 700the rpmextraction for 30 time min, was which over, was the su ffiphasescient timewere toseparate reach equilibrium.d and the Onceconcentration the extraction of metal time wasin the over, aqueous the phases phase were([Co]aq separated) was determined and the concentrationby AAS, and in of the metal organic in the aqueousphase, phase([Co]org ([Co]) wasaq determined) was determined by mass by balance. AAS, and Every in thepoint organic of the phase,pH range ([Co] betweenorg) was 2 and determined 7 was byevaluated mass balance. with unitary Every pointsteps, ofadjusting the pH the range pH betweenby using 2concentrated and 7 was evaluatedalkaline or withacid solutions. unitary steps, A adjustingHanna Digital the pH pH by usingmeter model concentrated HI2209 alkalinewith a combined or acid solutions. glass electrode A Hanna was used Digital to measure pH meter the model pH HI2209of the with aqueous a combined solutions. glass Every electrode point of was the usedproposed to measure extractant the concentration pH of the aqueous range solutions.was evaluated Every pointbetween of the 0.1proposed mol/L extractantand 0.5 mol/L, concentration with steps range of 0.1 was mol/L. evaluated A contact between time 0.1 test mol was/L and performed, 0.5 mol/ L, monitoring the extraction yield for each time interval. All of these experiments were performed at 22 with steps of 0.1 mol/L. A contact time test was performed, monitoring the extraction yield for each ± 1 °C. The cobalt extraction rate was: time interval. All of these experiments were performed at 22 1 C. The cobalt extraction rate was: ± ◦ Cobalt Extraction % = 100 [Co]org/([Co]org + [Co]aq) (1) Cobalt Extraction % = 100 [Co] /([Co] + [Co] ) (1) Isotherms of extraction and continuous process. To obtainorg the orgisotherms,aq the parameters found by the experimental procedures were used at different rates of the aqueous phase in relation to the Isotherms of extraction and continuous process. To obtain the isotherms, the parameters found by the organic phase (A/O). The concentration of cobalt in the organic phase was calculated as follows: experimental procedures were used at different rates of the aqueous phase in relation to the organic phase (A/O). The concentration of cobalt[Co]org in = theA/O organic ([Co]aq initial phase − [Co] wasaq) calculated as follows: (2)

where [Co]aq initial is the initial cobalt concentration before extraction, [Co]aq is the final silver [Co]org = A/O ([Co] [Co]aq) (2) concentration after extraction, while A and O areaq the initial volumes− of aqueous and organic phases, respectively. Aiming for industrial application, the number of stages required for a continuous where [Co] is the initial cobalt concentration before extraction, [Co] is the ﬁnal silver process wasaq initial computed by using the McCabe–Thiele method [21]. Figure 2 showsaq the experimental concentration after extraction, while A and O are the volumes of aqueous and organic phases, mixer-settler with a size of 3.8 × 23.3 × 6.5 cm and a stirring section of 3.8 × 3.8 × 6.5 cm. Stirring was respectively. Aiming for industrial application, the number of stages required for a continuous process performed with a magnetic stirrer, and to control flows, pumps and valves were used. was computed by using the McCabe–Thiele method [21]. Figure2 shows the experimental mixer-settler with a size of 3.8 23.3 6.5 cm and a stirring section of 3.8 3.8 6.5 cm. Stirring was performed × × × × with a magnetic stirrer, and to control ﬂows, pumps and valves were used. Batteries 2019, 5, 44 4 of 13

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Figure 2 2... MixerMixer-settler--settler for for continuous continuous process. process.

Electrodeposition. TheThe strippingstripping solutionsolution ofof cobaltcobalt was was treated treated in in a a system system with with a a lead lead anode anode and and a 2 2 astainless-steel stainless--steel cathode, cathode, both both with with an an area area of of 0.00499 0.00499 m m.2.. TheTheThe electrodeselectrodeselectrodes werewerewere cleanedcleanedcleaned andandand polishedpolished and thethe temperaturetemperature waswas controlled.controlled. TheThe systemsystem forfor electrodeposition electrodeposition is is shown shown in in the the Figure Figure3 with3 with a aregulated regulated DC DC power power supply. supply. The The effect effect of the of currentthe current over theover cobalt the cobalt deposition deposition was studied was studied by testing by testingfivetesting values five five for values values current for for (0.25 current current A, 0.5 (0.25 (0.25 A, 0.75A, A, 0.5 0.5 A, A, A,1 A, 0.75 0.75 and A, A, 1.5 1 1 A). A, A, Theand and current 1.5 1.5 A A).). e The Thefficiency current current was efficien efficien computedcy was as: computed as: Current efficiency = (deposited mass/theoretical deposition mass) 100 (3) Current efficiency = (deposited mass/theoretical deposition mass)*100∗ ((3))

Figure 3. System for electrodeposition of cobalt. Figure 3.3. System for electrodeposition of cobalt.

33... Results Results

33.1..1..1. Collection, Collection, Discharge, Dismantling, Drushing, and Sieving Commercial LiBs LiBs of of different different brands brands were were collected collected from from numerous numerous sources sources such such as markets as markets and stores.and stores. For safe For handling, safe handling, they theywerewere discharged, discharged, and the and remaining the remaining voltage voltage was less was than less 0.2 than V. 0.2 The V. Thebatteries batteries were were discharged discharged at a at controlled a controlled rate rate to toavoid avoid overdischarge overdischarge-related--related phenomena, phenomena, such such as tthosethose reported byby Ouyang etet al. [[29].29]. In the the first first step step of of dismantling, dismantling, the plastic or metallic cases were removed, and the batteriesbatteries were crushedcrushed with a blenderblender atat 500500 WW forfor 55 min.min. TheThe batteriesbatteries collectedcollected were classifiedclassified into two groups: batteries batteries between between 15 15 g g and and 30 30 g, g, and and those those between between 30 30 g g and and 40 40 g. g. Table2 2 presents presents the the fractions fractions obtained obtained from from the the batteries batteries after after the the classification. classification..

w w Table 2.2. Material percentage % ( (w//w)) presentpresent ininin LiBs.LiBs.LiBs.

CoverCover Plastic, Paper CuCu Al CoCo Li Li Powder Powder BatteryBattery Group Group (g) (g)(g) AverageAverage Weight Weight (g) (g)(g) (%(%(%w w//w/w))) (%(% w//w)) (%(% w//w)) (%(%(% ww//w/w)) ) 15–3015–30 21.2021.20 24.5224.52 24.16 8.84 8.84 41.90 41.90 30–4030–40 34.2334.23 21.7321.73 4.83 15.97 15.97 57.40 57.40 Batteries 2019, 5, 44 5 of 13 BatteriesBatteries 20192019,, 55,, xx FORFOR PEERPEER REVIEWREVIEW 55 ofof 1313

FigureFigure4 44 shows showsshows the thethe fractions fractionsfractions obtained obtainedobtained in inin this thisthis study. study.study. Figure FigureFigure4 c44cc shows showsshows the thethe copper coppercopper and andand aluminum aluminumaluminum fractionsfractions with with with a a a particle particle particle size size size greater greater greater than than than 0.25 0.25 0.25 mm, mm, mm, while while while Figure Figure Figure4d presents 44dd presents presents the cobalt–lithium the the cobalt cobalt–– powderlithiumlithium withpowderpowder a particle withwith aa size particleparticle smaller sizesize than smallersmaller 0.105 thanthan mm. 0.1050.105 mm.mm.

((aa)) CoverCover materialmaterial ((bb)) PlasticPlastic andand paperpaper ((cc)) CuCu––AlAl ((dd)) CoCo––LiLi powderpowder Figure 4. Fractions obtained from the crushing and sieving of batteries. FigureFigure 4.4. Fractions obtained from the crushing andand sievingsieving ofof batteries.batteries.

3.2.3.2. Leaching Leaching Leaching was performed in sulfuric acid (2 mol/L) and hydrogen peroxide (6 vol%) at a LeachingLeaching waswas performedperformed inin sulfuricsulfuric acidacid (2(2 mol/L)mol/L) andand hydrogenhydrogen peroxideperoxide (6(6 vol%)vol%) atat aa solidsolid-- solid-to-liquid ratio of 1/10 and a temperature of 75 ◦C for 90 min; the system is shown in Figure5. toto--liquidliquid ratio ratio of of 1/10 1/10 and and a a temperature temperature of of 75 75 °C °C for for 90 90 min; min; the the system system i iss shown shown in in Figure Figure 5. 5. Operating conditions were taken from a preliminary work, which reported that such leaching conditions OperatingOperating conditions conditions were were taken taken from from a a preliminary preliminary work, work, which which reported reported that that such such leaching leaching allow for obtaining the highest eﬃciency [30]. conditionsconditions allowallow forfor obtainingobtaining thethe highesthighest efficiencyefficiency [30].[30].

FigureFigure 5.5. ExperimentalExperimental setup setup for for acid acid leaching.leaching.

ItIt hashas beenbeen reported reported thatthat thethe addi additionadditiontion ofof hydrogen hydrogen peroxideperoxide helpshelps toto dissolvedissolve cobaltcobalt andand lithiumlithium oxidesoxides [[[101010].].]. AfterAfterAfter the thethe leaching leachingleaching step, step,step, the thethe product productproduct solution sosolutionlution was waswas ﬁltered, filtered,filtered, and andand the the cobaltthe cobaltcobalt concentration concentrationconcentration was analyzedwaswas analyzedanalyzed by atomic byby atomicatomic absorption absorptionabsorption spectrometry spectrometryspectrometry (AAS) (AAS)(AAS) using usingusing a Perkin aa PerkinPerkin Elmer ElmerElmer AAnalyst AAnalystAAnalyst 200. 200.200. With WithWith this process,thisthis process,process, an average anan averageaverage concentration concentrationconcentration of 10–12 ofof 1010––12 g12/L g/Lg/L for forfor cobalt cobaltcobalt was waswas obtained. obtained.obtained. The TheThe Co–Li CoCo––LiLi powder powderpowder beforebefore leachingleaching andandand residue residueresidue after afterafter leaching leachingleaching were werewere characterized characterizedcharacterized using usingusing a D8aa D8D8 Bruker BrukerBruker X-ray XX--rayray diﬀ diffractometer,diffractometer,ractometer, and andand the thethe resultsresults areare shownshown inin FigureFigure 6.6. FigureFigure 6a6a showsshows thethe presencepresence ofof differentdifferent cobaltcobalt––lithiumlithium oxidesoxides andand aluminum,aluminum, copper,copper, andand graphite.graphite. FigureFigure 6b6b confirmsconfirms thatthat thethe decreadecreasese ofof thesethese metalmetal oxideoxide peakspeaks waswas Batteries 2019, 5, 44 6 of 13

resultsBatteries are 2019 shown, 5, x FOR in PEER Figure REVIEW6. Figure 6a shows the presence of di ﬀerent cobalt–lithium oxides6 of 13 and aluminum, copper, and graphite. Figure6b conﬁrms that the decrease of these metal oxide peaks was observedobserved only only in in the the presence presence of of carbon carbon peaks peaks in in the the residue. residue. The The graphite graphite peakspeaks reportedreported toto appearappear in thein 2 θtherange 2θ range were were at 25–28 at 25◦–,28°, 43–46 43◦–,46°, and and 54–56 54–◦56°[7, 10[7,].10].

Figure 6. Spectra of X-ray diffraction analysis before (a) and after (b) leaching. Al2O3 PDF Card #00- Figure 6. Spectra of X-ray diﬀraction analysis before (a) and after (b) leaching. Al2O3 PDF Card 010-0173, Cu PDF Card #00-004-0836, C (graphite) PDF Card #00-026-1079, Li0.9Ni0.5Co0.5O2−x PDF Card #00-010-0173, Cu PDF Card #00-004-0836, C (graphite) PDF Card #00-026-1079, Li0.9Ni0.5Co0.5O2 x #00-050-0509, LiAlO2 PDF Card #00-044-0224, and LiCoO2 PDF Card #00-050-0653. PDF = Powder − PDF Card #00-050-0509, LiAlO PDF Card #00-044-0224, and LiCoO PDF Card #00-050-0653. PDF = Diffraction File. 2 2 Powder Diﬀraction File.

3.3.3.3. Eﬀ Effectect of of pH pH on on Extraction Extraction Based on preliminary tests, an evaluation pH range between 2 and 7 was used, with steps of 1 Based on preliminary tests, an evaluation pH range between 2 and 7 was used, with steps of 1 unit. unit. After sulfur acid leaching, the aqueous phase obtained a pH near 0. Then, in order to control After sulfur acid leaching, the aqueous phase obtained a pH near 0. Then, in order to control pH, pH, a sodium hydroxide concentrated solution was added. Figure 7 shows that the extraction a sodium hydroxide concentrated solution was added. Figure7 shows that the extraction percentage percentage increased as pH increased. For cobalt extraction, pH was a key factor. Within the increased as pH increased. For cobalt extraction, pH was a key factor. Within the evaluation range for evaluation range for pH values, there were low extraction percentages, starting from 7% to 12% for a pH values, there were low extraction percentages, starting from 7% to 12% for a pH range from 2 to 3, pH range from 2 to 3, up to yield values as high as 92% or 93% with pH values of 6 and 7. up to yieldThe valueseffect of as pH high on as extraction 92% or 93% can withbe explained pH values in ofterms 6 and of 7.the extraction mechanism, which occursThe ebyﬀ ectionic of exchange, pH on extraction as follows can [31]: be explained in terms of the extraction mechanism, which occurs by ionic exchange, as follows [31]: Co2+aq + 2(RH)2 org ↔ Co(R2H)2 org + 2H+aq (4) 2+ + Co aq + 2(RH) Co(R H) + 2H aq (4) where RH is the acid extractant Cyanex 2722 orgmolecule,↔ and2 2(RH)2 org 2 org is the organic complex formed in the organic phase. where RH is the acid extractant Cyanex 272 molecule, and 2(RH)2 org is the organic complex formed in the organic phase. Batteries 20192019,, 55,, 44x FOR PEER REVIEW 7 of 13 Batteries 2019, 5, x FOR PEER REVIEW 7 of 13

Figure 7. Effect of pH on extraction: aqueous-to-organic-phase ratio (A/O) = 1, initial concentration of Figure 7. Effect of pH on extraction: aqueous-to-organic-phase ratio (A/O) = 1, initial concentration of Figureaqueous 7. phaseEﬀect (Xi) of pH = 12 on g/L, extraction: [Cyanex aqueous-to-organic-phase 272] = 0.4 mol/L, time = 12 ratio min, (A and/O) temperature= 1, initial concentration = 22 ± 1 °C. of aqueousaqueous phase phase (Xi) (Xi) = =1212 g/L, g/L, [Cyanex [Cyanex 272] 272] = =0.40.4 mol/L, mol/L, time time = =1212 min, min, and and temperature temperature = 22= 22± 1 °C.1 C. ± ◦ 3.4. Effect of Extractant Concentration 3.4.3.4. Effect Eﬀect of of Extractant Extractant Concentration Concentration Cobalt was extracted using the extractant Cyanex 272 diluted in kerosene. The extractant CobaltCobalt was was extracted extracted using using the the extractant extractant Cyanex Cyanex 272 272 diluted diluted in in kerosene. kerosene. The The extractant extractant concentration was evaluated in the range between 0.1 mol/L and 0.5 mol/L, with 0.1-mol/L steps. concentrationconcentration was was evaluated evaluated in in the the range range between between 0.1 0.1 mol/L mol/ Land and 0.5 0.5 mol/L mol/,L, with with 0.1 0.1-mol-mol/L/ Lsteps. steps. Figure 8 shows that the extraction yield increased as the extractant concentration increased. Within FigureFigure 88 showsshows that that the the extraction extraction yield yield increased increased as as the the extractant extractant concentration concentration increased. increased. Within Within the evaluation range for concentration values, slightly low values around 27% were observed for a thethe evaluation evaluation range range for for concentration concentration values, values, slightly slightly low low values values around around 27% 27% were were observed observed for for a a 0.1-mol/L extractant concentration; on the other hand, values as high as 97% or 99% were obtained 0.10.1-mol-mol/L/L extractant extractant concentratio concentration;n; on the other hand,hand, valuesvaluesas as high high as as 97% 97% or or 99% 99% were were obtained obtained for for concentration values between 0.4 mol/L and 0.5 mol/L. forconcentration concentration values values between between 0.4 0.4 mol mol/L/L and and 0.5 0.5 mol mol/L./L.

100 100

80 80

60 60

40 Cobalt extraction % extraction Cobalt Cobalt extraction % extraction Cobalt 20 20

0 0 0 0.1 0.2 0.3 0.4 0.5 0.6 0 0.1 0.2 0.3 0.4 0.5 0.6 Extractant (mol/L) Extractant (mol/L)

Figure 8. EEffectﬀect ofof extractantextractant concentration:concentration: extraction atat AA/O/O == 1, Xi == 11 gg/L,/L, pH = 6, time = 1212 min, Figure 8. Effect of extractant concentration: extraction at A/O = 1, Xi = 11 g/L, pH = 6, time = 12 min, and temperature = 22 ± 11 °C.C. and temperature = 22 ± ±1 °C.◦

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3.5. Extraction Kinetics 3.5. Extraction Kinetics Contact time is a key parameter for defining an extraction process. Based on preliminary tests, Contact time is a key parameter for deﬁning an extraction process. Based on preliminary tests, an evaluation range for contact time between 2 min and 30 min was used. Figure 9 shows that an evaluation range for contact time between 2 min and 30 min was used. Figure9 shows that extraction percentage increased as the contact time increased. Within the evaluation range, there were extraction percentage increased as the contact time increased. Within the evaluation range, there were relatively high values in the extraction percentage that varied from 57% for a contact time of 2 min, relatively high values in the extraction percentage that varied from 57% for a contact time of 2 min, up to recovery values as high as 98% from 10 min of operation. up to recovery values as high as 98% from 10 min of operation.

FigureFigure 9. 9. ExtractionExtraction at AA/O/O = = 1,1, XiXi= =10.2 10.2 g /g/L,L, [Cyanex [Cyanex 272] 272]= 0.4 = 0.4 mol mol/L,/L, pH =pH6, and= 6, temperatureand temperature= 22 =1 22C. ± ◦ ± 1 °C. 3.6. Extraction Isotherm and Stages 3.6. ExtractionThe concentration Isotherm and experimental Stages data was obtained for each phase and is represented in graphical form,The with concentration the aqueous experimental phase in the data horizontal was obtained axis and for the each organic phase phase and in is the represented vertical axis. in graphicalThe correlation form, with between the aqueous the concentration phase in the of cobalthorizontal in the axis organic and the phase organic ([Co] phaseorg) and in the aqueousvertical phase ([Co] ) was deﬁned by Equation (4), with: a = 0.005634419 and b = 10198.184. Figure 10 shows axis. The correlationaq between the concentration of cobalt in the organic phase ([Co]org) and the the isotherm from experimental data for cobalt extraction. aqueous phase ([Co]aq) was defined by Equation (4), with: a = 0.005634419 and b = 10198.184. Figure

10 shows the isotherm from experimental data for cobalta[Co]aq extraction. [Co]org = b (1 e− ). (5) − [Co]org = b (1 − e−a[Co]aq). (5) Calculation of Theoretical Stages 3.6.1. CalculationBased on of the Theoretical proposed Stages isotherm model and the McCabe–Thiele method using iterative software, the extraction steps were calculated by performing parameter variations, such as the Based on the proposed isotherm model and the McCabe–Thiele method using iterative software, aqueous-to-organic-phase ratio (A/O) and the initial concentration of aqueous phase (Xi). This method the extraction steps were calculated by performing parameter variations, such as the aqueous-to- allowed for obtaining the concentration proﬁles through steps and a proper extraction process. For an organic-phase ratio (A/O) and the initial concentration of aqueous phase (Xi). This method allowed initial concentration of 10 g/L of cobalt in sulfate medium in the aqueous phase, two theoretical for obtaining the concentration profiles through steps and a proper extraction process. For an initial extraction stages were obtained. With a rate of A/O = 1.0 and a ﬁnal concentration of cobalt (Xf) of concentration of 10 g/L of cobalt in sulfate medium in the aqueous phase, two theoretical extraction 12.18 mg/L, the calculation of these steps is shown in Figure 10. stages were obtained. With a rate of A/O = 1.0 and a final concentration of cobalt (Xf) of 12.18 mg/L, the calculation of these steps is shown in Figure 10.

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FigureFigure 10. 10. Extraction Extraction stages stages at at AA/O /A/OO == 1,= 1, Xi Xi = 1010= 10 g/L, g/ g/L,L, Xf Xf = 12.18=12.18 12.18 mg/L, mg mg/L,/L, [Cyanex [Cyanex 272] 272] = 0.40.4= 0.4 mol/L, mol mol/L,/L, pH pH = 6,6,= 6, timetime= 10= 10 min, min, and and temperature temperature= =22 22 ±1 1 C.°C. time = 10 min, and temperature = 22 ±± 1 °C.◦

InIn the the extraction extraction study study in in the the continuous continuous mixer mixer-settler, mixer-settler,-settler, a flowa ﬂow flow of of 5.5 5.5 mLmL/min mL/min/min was was used used for for the the organicorganic phase phase and and a ﬂowflowa flow of of 5.5 5.5 mLmL/min mL/min/min was was used used for for the the aqueous aqueous phase phase (A(A/O (A/O/O == 1),= 1), obtaining obtaining yield yield of of globalglobal extraction extraction of of 99%, 99%, wh which whichich allowed allowed for for validation validation of of the the results results obtained obtained by by the the McCabe–ThieleMcCabe McCabe–Thiele–Thiele method.method. The The equipment equipment is isshown shown in in the the Figure Figure 11.11 11..

Figure 11. Extraction of cobalt in the continuous mixer-settler. Figure 11. ExtractionExtraction of of cobalt in the continuous mixer mixer-settler.-settler. In order to regenerate the extractant and obtain a cobalt electrolyte solution for subsequent In order to regenerate regenerate the extractant extractant and obtain a cobalt cobalt electrolyte electrolyte solution for subsequent electrodeposition, the correlation between the concentration of cobalt in the aqueous phase ([Co]aq) electrodeposition, the correlation between the concentration of cobalt in the aqueousaqueous phasephase ([Co]([Co]aqaq)) and the organic phase ([Co]org) was defined by Equation (6): and the organic phase ([Co]org)) was was defined deﬁned by by Equation Equation (6): (6): [Co]aq = 23.1338 [Co]org. (6) [Co]aq = 23.1338 [Co]org. (6) [Co]aq = 23.1338 [Co]org. (6) ForFor an an initial initial concentration concentration of of 9.630 9.630 g/L g/L of of cobalt cobalt in in the the organic organic phase, phase, two two theoretical theoretical extraction extraction stagesstagesFor were were an initialobtained, obtained, concentration with with a ratea rate of of 9.630of O/A O/A g=/ L1.5= of1.5 and cobalt and a finala in final the concentration concentration organic phase, of of twocobalt cobalt theoretical of of 37.87 37.87 mg/L. extraction mg/L. The The calculationstagescalculation were of obtained,of these these steps steps with is isshown a shown rate in of in Figure O Figure/A = 12.1.5 12. and a ﬁnal concentration of cobalt of 37.87 mg/L. The calculation of these steps is shown in Figure 12. Batteries 2019, 5, x FOR PEER REVIEW 10 of 13 BatteriesBatteries2019 2019, 5, ,5 44, x FOR PEER REVIEW 1010 of of 13 13

28 28 Isotherm 24 Isotherm 24 Experimental Experimental 20 20 stage 1 stage 1 16 16

12 [Co] aq (g/L) aq [Co]

[Co] aq (g/L) aq [Co] 8 8

4 4 stage 2 0 stage 2 0 0 4 8 12 16 0 4 8 12 16 [Co] org (g/L) [Co] org (g/L) Figure 12. Stripping stages at O/A = 1.5, Xi = 9630 mg/L, Xf = 37.87 mg/L, [H2SO4] = 1 mol/L, time = 4

Figuremin,Figure and 12.12. temperature StrippingStripping stages stages= 22 ± at1 at °C.O/A O /A = =1.5,1.5, Xi Xi= 9630= 9630 mg/L, mg Xf/L, = Xf37.87= 37.87mg/L, mg [H/2L,SO [H4] =2 SO1 mol/L,4] = 1 time mol /=L, 4 timemin,= and4 min, temperature and temperature = 22 ± 1 =°C.22 1 C. ± ◦ In the stripping operation in the continuous mixer-settler, a flow of 11.0 mL/min was used for the aqueousInIn the the stripping stripping phase and operation operation that of in 16.5in the the mL/min continuous continuous for mixer-settler,the mixer organic-settler, ph a ﬂowase a flow (O/A of 11.0of = 11.0 mL1.5), /mL/minmin obtaining was was used a yieldused for the forof aqueousglobalthe aqueous extraction phase phase and of that97%and ofusingthat 16.5 of a mL 16.5single/min mL/min extraction for the for organic stagethe organic phaseafter 40 (Oph min/aseA = of(O/A1.5), operation, obtaining= 1.5), obtainingas shown a yield ina of yield Figure global of extraction2.global extraction of 97% usingof 97% a using single a extraction single extraction stage after stage 40 after min of40 operation, min of operation, as shown as inshown Figure in2 .Figure 2. FigureFigure 1313 shows thethe UV–VISUV–VIS spectraspectra obtainedobtained inin thethe organic phase,phase, which shows that the organic solutionsolutionFigure couldcould 13 bebeshows regenerated.regenerated. the UV–VIS spectra obtained in the organic phase, which shows that the organic solution could be regenerated.

FigureFigure 13. 13. UV-VISUV-VIS spectra: spectra: (a ) (a Cyanex) Cyanex 272 272 in kerosene, in kerosene, (b) organic (b) organic phase phase after stripping, after stripping, and (c) organic and (c) phaseorganicFigure complex phase 13. UV complex cobalt–Cyanex-VIS spectra: cobalt (–a 272Cyanex) Cyanex after 272 extraction. 272 after in extraction. kerosene, (b) organic phase after stripping, and (c) organic phase complex cobalt–Cyanex 272 after extraction. Batteries 2019, 5, 44 11 of 13

Batteries 2019, 5, x FOR PEER REVIEW 11 of 13 3.7. Electroplating 2.7. Electroplating Cobalt was recovered from a cobalt solution with a concentration of 9 g/L using a lead anode and a stainless-steelCobalt was cathode.recovered In from Table a 3cobalt, the results solution of thewith current a concentration e fficiency of are 9 g/L shown. using As a lead the current anode andwas a increased, stainless-steel the current cathode. effi Inciency Table was3, the higher. results Thisof the implies current that efficiency high values are shown. of current As the allow current for wasobtaining increased, cobalt the deposition current efficiency closer to thewas theoretical higher. This deposition implies mass.that high values of current allow for obtaining cobalt deposition closer to the theoretical deposition mass. Table 3. Results of the electrodeposition of cobalt. Table 3. Results of the electrodeposition of cobalt. Current (A) Potential (V) Current Density (A/m2) Mass (g) Current Efficiency (%) Current (A) Potential (V) Current Density (A/m2) Mass (g) Current Efficiency (%) 0.25 2.71 50.1 1.1947 66.37 0.250.50 2.71 3.07 50.1 100.2 1.1947 1.5484 68.8266.37 0.500.75 3.07 4.02 100.2 150.3 1.5484 1.3698 76.1068.82 0.751.00 4.02 4.19 150.3 200.4 1.3698 1.3194 73.3076.10 1.001.50 4.19 5.51 200.4 300.6 1.3194 1.4410 80.0673.30 1.50 5.51 300.6 1.4410 80.06 The Figure 14 shows the cobalt layer deposited on the stainless-steel cathode after removing it fromThe the electrolyticFigure 14 shows cell. the cobalt layer deposited on the stainless-steel cathode after removing it from the electrolytic cell.

Figure 14. CobaltCobalt deposited in the cathode. 4. Conclusions 4. Conclusions A process for the recovery of cobalt from spent lithium-ion mobile phone batteries has been A process for the recovery of cobalt from spent lithium-ion mobile phone batteries has been proposed and analyzed. The process involved mechanical conditioning of the batteries, leaching, proposed and analyzed. The process involved mechanical conditioning of the batteries, leaching, liquid–liquid extraction, and electrodeposition. The best conditions for the selective separation of liquid–liquid extraction, and electrodeposition. The best conditions for the selective separation of cobalt from the leaching-based treatment step, using the commercial extractant Cyanex 272 dissolved cobalt from the leaching-based treatment step, using the commercial extractant Cyanex 272 dissolved in kerosene, were defined. It has been determined that the extraction yields were higher, in the range in kerosene, were defined. It has been determined that the extraction yields were higher, in the range 97–99%, for pH between 6 and 7 and concentration of extractant between 0.4 mol/L and 0.5 mol/L. It is 97–99%, for pH between 6 and 7 and concentration of extractant between 0.4 mol/L and 0.5 mol/L. It important to mention that the temperature was ambient; thus, no external energy input was required is important to mention that the temperature was ambient; thus, no external energy input was in this stage. required in this stage. A mathematical model to define the number of extraction and stripping steps for cobalt recovery A mathematical model to define the number of extraction and stripping steps for cobalt recovery was established, and its reliability was tested in a continuous process in an experimental mixer-settler was established, and its reliability was tested in a continuous process in an experimental mixer-settler system. The best conditions were established for the electrodeposition of cobalt. It has been determined system. The best conditions were established for the electrodeposition of cobalt. It has been that increasing the current also increases the current efficiency. determined that increasing the current also increases the current efficiency. The proposed process has proved to be efficient for the recovery of cobalt from spent lithium-ion The proposed process has proved to be efficient for the recovery of cobalt from spent lithium- mobile phone batteries and has the potential to be scaled to an industrial level, allowing the second ion mobile phone batteries and has the potential to be scaled to an industrial level, allowing the use of waste materials and the recovery of high-value metal. second use of waste materials and the recovery of high-value metal. Batteries 2019, 5, 44 12 of 13

Author Contributions: All the authors made significant contributions to the development of the experimental tests, the analysis of results, and the writing of this manuscript. Funding: The authors wish to thank to Direccción de Apoyo a la Investigación y Posgrado of Universidad de Guanajuato for the financial support given to this project, 1078/2016. Acknowledgments: To Enrique Villegas of Cytec Solvay for supplying the extractants. We thank Dra Marina Vega of the Institute of Geology of the UNAM and M.I.Q. Paloma Eloisa Ramírez of the Universidad de Guanajuato for their assistance in DRX analysis. Daniel Quintero Almanza thanks the National Council of Science and Technology (CONACYT, Mexico) for the scholarship granted for his Master degree studies. Conflicts of Interest: The authors declare no conflict of interest. The funders had no role in the design of the study; in the collection, analyses, or interpretation of data; in the writing of the manuscript; nor in the decision to publish the results.

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