Recycling of Alkaline Batteries Via a Carbothermal Reduction Process

batteries

Article Recycling of Alkaline Batteries via a Carbothermal Reduction Process

Selçuk Ye¸siltepe 1,* , Mehmet Bu˘gdaycı 2 , Onuralp Yücel 1 and Mustafa Kelami ¸Se¸sen 1

1 Department of Metallurgical and Materials Engineering, Faculty of Chemical and Metallurgical Engineering, Istanbul Technical University, Istanbul 34469, Turkey; [email protected] (O.Y.); [email protected] (M.K.¸S.) 2 Department of Chemical and Process Engineering, Faculty of Engineering, Yalova University, Yalova 77100, Turkey; [email protected] * Correspondence: [email protected]

Received: 12 December 2018; Accepted: 8 March 2019; Published: 19 March 2019

Abstract: Primary battery recycling has important environmental and economic beneﬁts. According to battery sales worldwide, the most used battery type is alkaline batteries with 75% of market share due to having a higher performance than other primary batteries such as Zn–MnO2. In this study, carbothermal reduction for zinc oxide from battery waste was completed for both vacuum and Ar atmospheres. Thermodynamic data are evaluated for vacuum and Ar atmosphere reduction reactions and results for Zn reduction/evaporation are compared via the FactSage program. Zn vapor and manganese oxide were obtained as products. Zn vapor was re-oxidized in end products; manganese monoxide and steel container of batteries are evaluated as ferromanganese raw material. Effects of carbon source, vacuum, temperature and time were studied. The results show a recovery of 95.1% Zn by implementing a product at 1150 ◦C for 1 h without using the vacuum. The residues were characterized by Atomic Absorption Spectrometer (AAS) and X-ray Diffraction (XRD) methods.

Keywords: alkaline battery; battery recycling; Carbothermal process

1. Introduction In many countries, the recycling of batteries is an important issue because of environmental sanctions that regulate the disposal of these products. Research has been conducted in various laboratories to develop new recycling processes for used batteries or to develop new solutions to ensure safe ﬁnal disposal in certain situations [1]. This situation requires a new approach in the management of these devices when they exhaust. In this case, the use of recycled metals instead of primary sources in battery production will have a positive environmental impact by reducing energy consumption and minimizing pollution [2]. Using recycled materials for new battery production will conserve exhausting primary resources. Alkaline batteries include many components which can be recycled using various methods. Veloso et al. investigated this kind of battery and analyzed its components. Table1 presents alkaline battery ingredients [3]. Primary batteries work according to irreversible chemical reactions (Equation (1)).

3MnO2 + 2Zn → Mn3O4 + 2ZnO (1)

This process has some valuable ingredients such as are ZnO, Mn3O4 and KOH. There are some investigations about Zn recovery from ZnO in literature. Xiong et al., published a paper about the carbothermal reduction of ZnO and achieved 95% Zn yield at 900 ◦C under vacuum in 50 min with C/ZnTotal 2.5 ratio [4].

Batteries 2019, 5, 35; doi:10.3390/batteries5010035 www.mdpi.com/journal/batteries Batteries 2019, 5, 35 2 of 13

Table 1. Alkaline batteries paste analysis [3].

Element Weight, % Zn 12–21 Mn 26–33 K 5.5–7.3 Fe 0.17 Pb 0.005 Cd - Hg -

As Xiong’s study states, ZnO recycling is an important process. With the expansion of the scope of Zn-based applications, the consumption of Zn is rapidly increasing, resulting in a gradual decrease of the amount of zinc sulphide. Zn has the highest amount of consumption, just after steel, aluminum, and copper [5]. Zn has good corrosion resistance and thus has wide use in the protective coating of metallic structures. [6]. Almost 35–50% of total Zn consumption is used in galvanizing, 20% is used in brass production, 15% in casting, 8% in zinc oxide production and 7% in semi-fabricated products [7]. In particular, Zn’s particulate form is a useful anti-corrosion pigment in paints, cathode materials for battery technologies, and has been receiving increasing interest as a catalyst for chemical reactions [8–12]. The recycling of Zn is a difficult process not only because of the difficulty of finding suitable waste sources, but also because of technological constraints. Alternatively, the black mass of alkali and zinc-carbon (Zn-C) batteries can be an important secondary source for the recovery of 20,000 t/year for Zn, as well as a similar quantity of manganese [13]. Therefore, how to develop and use zinc oxide effectively from waste has become an increasingly important issue [14]. There are two basic processes to evaluate the zinc oxide as a zinc raw material. The first one is the hydrometallurgical method. In this method, acid leaching, alkaline leaching and ammonia leaching are applied [15]. Hydrometallurgical processes have many advantages, but also have many disadvantages, such as impurities in the leach liquor due to difficulties in the treatment process, and the difficulties in solid-liquid separation [4]. However, alkaline battery wastes are melted at 1500 ◦C to produce iron based alloys (steel and FeMn) via pyrometallurgical processes. During this process, the Zn can be recovered by evaporation and condensation in the form of oxide powder. However, it is usually found as waste in steel production powder [16–18]. Although various hydrometallurgical and pyrometallurgical methods have been developed for the recycling of batteries, the existing processes are not economically suitable for the widespread recycling of these batteries [19]. The main purification methods for Zn are electrolytic purification, vacuum distillation, zone melting and so on. The vacuum technology used in metallurgy is an environmentally friendly and resource-saving method that shortens metal recovery processes. The low melting point and vaporization temperature of Zn permits technologically applicable vacuum processes [20–22]. In this study, the possibility of Zn recycling from alkaline and Zn-carbon battery waste were investigated via carbothermal and vacuum aided carbothermal reduction. Results are evaluated with thermodynamic data and a suitable way of recycling waste alkaline batteries is suggested.

2. Experimental Studies In the experimental step, raw materials were collected from battery collection locations. Collected raw materials were classified manually for alkaline and Zn-C batteries. Alkaline batteries were dismantled by hand. The steel covering and battery paste that contains anode and cathode with electrolyte, were separated via sieving. 1.5 kg of alkaline battery paste was washed in water with 1/10 solid/liquid ratio for 72 h. The obtained solution is analyzed with AAS (Perkin Elmer Analyst 800) for chemical analysis. Washed and filtered battery paste was used for Zn recovery experiments. Washed and filtered battery paste was analyzed by using chemical analysis and AAS (Perkin Elmer Analyst 800) techniques. Aqua regia leaching method was employed for preparing AAS samples. 0.30 g of the Batteries 2019, 5, x FOR PEER REVIEW 3 of 13 were dismantled by hand. The steel covering and battery paste that contains anode and cathode with electrolyte, were separated via sieving. 1.5 kg of alkaline battery paste was washed in water with 1/10 solid/liquid ratio for 72 h. The obtained solution is analyzed with AAS (Perkin Elmer Analyst 800) for chemical analysis. Washed and filtered battery paste was used for Zn recovery experiments. Batteries 2019, 5, 35 3 of 13 Washed and filtered battery paste was analyzed by using chemical analysis and AAS (Perkin Elmer Analyst 800) techniques. Aqua regia leaching method was employed for preparing AAS samples. 0.30sample g of was the dissolved sample inwas a borosilcate dissolved beakerin a borosilc on a hotplateate beaker at 110 on◦C a forhotplate 30 min. at Afterward, 110 °C for the 30 cooled min. Afterward,sample was the diluted cooled in 100sample ml ofwas 5% diluted HNO3. in The 100 samples ml of 5% were HNO analyzed3. The forsamples zinc and were other analyzed elements for zincby AAS and (Perkinother elements Elmer AAnalyst by AAS (Perkin 800, USA) Elmer using AAnalyst a standard 800, protocol.USA) using XRD a standard pattern ofprotocol. the reduced XRD patternresidue of obtained the reduced by PANalytical residue obtained PW 3040/60 by PANalytical (Panalytical PW B.V., 3040/60 Almelo, (Panalytical The Netherland) B.V., Almelo, (Cu The Kα, Netherland)λ = 0.154 nm ).(Cu Xpert Kα, λ highscore = 0.154 nm). software Xpert highscore was used software in order was to collect used in data. order During to collect the data. experiment, During thetwo experiment, different retorts two weredifferent used. retorts The argonwere used. aided Th experimentse argon aided were experiments carried out were in a 9carried L 304 stainlessout in a 9steel L 304 retort stainless with a steel cylindrical retort shapewith a of cylindrical 20 cm height shape and of a 1220 cmcm radius.height Thisand retorta 12 cm has radius. high temperature This retort hasresistance, high temperature gas tightness, resistance, a sufficient gas reactiontightness, chamber a sufficient and reaction a gas cleaning chamber unit. and In a the gas second cleaning type unit. of Inexperimental the second set,type another of experimental retort were set, used another which retort was coherent were used with which vacuum. was This coherent retort with was producedvacuum. Thisby centrifugal retort was casting produced method by centrifugal because of casting its vacuum method tightness because properties. of its vacuum It is also tightness 304 stainless properties. steel, Itand is hasalso the 304 same stainless properties steel, asand the has first the retort. same On properties the other as hand, the first this retortretort. also On hasthe aother cooling hand, zone this in retortorder toalso obtain has a crystalized cooling zone metallic in order particles. to obtain crystalized metallic particles. In the experiments two types of productionproduction techniquestechniques were used:used: the vacuum aided method and the Ar flowingflowing carbothermal reduction method.method. Experiments without vacuum were conducted in a stainless steel retort with a volume of 9 L,L, underunder ArAr flowingflowing conditions.conditions. Ar gas was supplied to retort with a flowingflowing rate of 11 L/min.L/min. We We produced produced reaction reaction gases gases and and purged Ar to keep the retort atmosphere in reducing conditions while also carryingcarrying gas for Zn vapor.vapor. Zn evaporated after the oxide reduction occurred andand waswas carriedcarried outout ofof thethe retortretort viavia ArAr gas.gas. CO2 gasgas re-oxidizes re-oxidizes Zn at lower temperatures, thus Zn was obtained as ZnO in fume dust. Coke used as a carbon source in order to reduce the ZnO. Experiments were done on a stainlessstainless steel plate with 150%150% excess carbon without considering the initial carbon of battery paste. The flowchart flowchart of the experimental studies is given in Figure1 1..

Figure 1. Flowchart of the Ar aided experimental studies.

During vacuum aided experiments, a 1 L cylindrical retort which was made of stainless steel was used. The retort was placed in an oven with a DC1010 temperature control unit, which can reach up to 1400 °C. The Zn metal was vaporized and the residue was placed in the retort inside an Batteries 2019, 5, 35 4 of 13 aluminate crucible (Height: 15 mm, Width: 25 mm, Length: 153 mm with 1700 °C stabilization capacity). In order to obtain the vacuum atmosphere inside the retort, a dual-stage Edwards 8 E2M8 rotaryrotary vane mechanical mechanical vacuum vacuum pump pump was was used, used, whic whichh can can hold hold a a final ﬁnal pressure pressure of of 10 10 Pa Pa (0.1 (0.1 mbar) mbar) (Edwards High Vacuum, Vacuum, Crawley, UK). The retort was externally heated by using a SiC resistance furnace.furnace. Figure Figure 22 presentspresents aa detaileddetailed vacuumvacuum reductionreduction system.system.

Figure 2. SchematicSchematic sketch sketch of of experimental experimental setup: setup: ( (AA)) vacuum vacuum pump; pump; ( (BB)) water water inlet-outlet; inlet-outlet; ( (CC)) retort retort cap;cap; ( D)) crown crown Zn; ( E) radiation shield; ( F) furnace wall.

InIn all all experiments, experiments, 20 20 g g samples samples were were weighted, weighted, mixed mixed via via Turbula Turbula mixer and charged charged in to the ◦ retorts.retorts. The The retorts retorts were externally heated with 10 °C/minC/min heating heating rate rate from from room room temperature temperature to to the the desired temperature underunder ArAr oror vacuumvacuum conditions. conditions. At At the the end end of of the the reduction, reduction, the the retort retort was was left left in inthe the furnace furnace at theat the same same vacuum vacuum values values and and it was it was cooled cooled to room to room temperature. temperature. Then, Then, the coverthe cover was wasopened, opened, and theand residue the residue left in left the in boat the was boat weighted was weighted and analyzed. and analyzed. The degree The ofdegree Zn metal of Zn recovery metal recoverywas calculated was calculated from the residuefrom the by resi usingdue theby using formula the given formula below. given below.

Zn recovery%Zn recovery% (from (from residue) residue) = {[(Zn = {[(Zn0% ×0%W ×0 )W−0)(Zn − (Zn1%1%× ×W W1)]/(Zn1)]/(Zn00% × WW00)})} ×× 100100 (2) where W0 is the weight of battery waste, Zn0% is the weight percentage of Zn in battery waste, W1 is where W0 is the weight of battery waste, Zn0% is the weight percentage of Zn in battery waste, the weight of residue, and Zn1% is the weight percentage of Zn in residue. The residues were W1 is the weight of residue, and Zn1% is the weight percentage of Zn in residue. The residues were characterized via the AAS and XRD techniques.

3. Results Results and and Discussion Discussion

3.1. Thermodynamic Thermodynamic Background Background FactSage is is a a powerful powerful self-teaching self-teaching aid. aid. With With regular regular program program usage, usage, one one can can rapidly rapidly acquire acquire a practicala practical understanding understanding of of the the principles principles of of thermo thermochemistry,chemistry, especially especially these these relating relating to to complex phase equilibria. The The program program has has a a built-in built-in database database of of chemical compounds and calculates the equilibrium conditions of of given reac reactions.tions. Starting Starting or or final ﬁnal conditions of of reaction can be determined at the start and results could be obtained as a tabletable oror aa ﬁgurefigure [[23].23]. This study’s thermodynamic calculation was realized via FactSage 7.1. database. The change of reaction productsproducts withwith increasingincreasing reactionreactiontemperature temperature is is given given in in Figure Figure3 with3 with a avacuum vacuum of of 10 10 Pa Pa for for the the reduction reduction of of ZnO ZnO from from battery battery residues residues by by using using carbon carbon as aas reductant a reductant in the in thevacuum vacuum and and an Aran purgedAr purged scenario scenario in Figure in Figure4 without 4 without a vacuum. a vacuum. Figure3 clearly shows that after reaching 500 ◦C, ZnO amount reduced dramatically and 1 mole Zn is the stable phase beyond 700 ◦C. According to these calculations, ZnO reduction starts at 500 ◦C ◦ and it reaches to maximum recovery values after 700 C. On the other hand, C and CO2 are the Batteries 2019, 5, x FOR PEER REVIEW 5 of 13

Mn2O3 + ZnO + 1.5 C Batteries 2019, 5, 35 C:\FactSageSA\Equi0.res 26Kas18 5 of 13

dominant carbon-based2.500 phases until 500 ◦C is reached. Bouduard reaction occurs at approximately ◦ 580 C, CO2 and C converts to CO [24]. MnO 2.000 CO2 + C → 2CO (Bouduard Reaction)

CO oxygen afﬁnity is higher than CO2 and C, so ZnO reduction exponentially increased after the Bouduard reaction1.500 was realized. Decreasing the vapor pressure of the chamber enhances Zn reduction Mole andBatteries Zn 2019 vaporization., 5, x FOR PEER Mn REVIEW2O3 dissociates toCO MnO through the vacuum effect. 5 of 13

ZnO 1.000 Mn2O3 + ZnO + 1.5 C ZnC:\FactSageSA\Equi0.res 26Kas18

C 0.500 2.500 CO2

0 MnO 2.000400 500 600 700 800 900 Temperature (C)

Figure 3. The change of reaction products with increasing process temperature for 10 Pa vacuum 1.500 conditions. Mole CO

ZnO Figure 3 clearly1.000 shows that after reaching 500 °C, ZnO amount reduced dramatically and 1 mole Zn is the stable phase beyond 700 °C. According to these calculations, ZnO reduction starts at 500 °C Zn and it reaches to maximum recovery values after 700 °C. On the other hand, C and CO2 are the C dominant carbon-based0.500 phases until 500 °C is reached. Bouduard reaction occurs at approximately CO2 580 °C, CO2 and C converts to CO [24].

2 → 0 CO +C 2CO (Bouduard Reaction) 400 500 600 700 800 900 CO oxygen affinity is higher than CO2 andTemperature C, so ZnO (C) reduction exponentially increased after the Bouduard reaction was realized. Decreasing the vapor pressure of the chamber enhances Zn Figure 3. The change of reaction products with increasing process temperature for 10 Pa reductionFigure and 3. TheZn vaporization.change of reaction Mn2 Oproducts3 dissociates with increasing to MnO through process temperaturethe vacuum for effect. 10 Pa vacuum vacuum conditions. conditions. Mn2O3 + ZnO + 1.5 C Figure 3 clearly shows that after reachingC:\FactSageSA\Equi0.res 500 °C, ZnO 26Kas18 amount reduced dramatically and 1 mole Zn is the stable phase beyond 700 °C. According to these calculations, ZnO reduction starts at 500 °C 2.500 and it reaches to maximum recovery values after 700 °C. On the other hand, C and CO2 are the dominant carbon-based phases until 500 °C is reached. Bouduard reaction occurs at approximately

2 MnO 580 °C, CO and C2.000 converts to CO [24].

CO2+C→2CO (Bouduard Reaction)

CO CO oxygen affinity1.500 is higher than CO2 and C, so ZnO reduction exponentially increased after

the Bouduard reactionMole was realized. Decreasing the vapor pressure of the chamber enhances Zn reduction and Zn vaporization. MnZnO 2O3 dissociates to MnO through the vacuum effect. 1.000

Mn2O3 + ZnZnO + 1.5 C C C:\FactSageSA\Equi0.res 26Kas18 0.500

2.500 CO2 0 700 800 900 1000 1100 1200 Temperature (C) MnO 2.000 FigureFigure 4. 4. TheThe change change of of reaction reaction produc productsts with with increasing increasing process process temperature for 1 atm condition.

CO 1.500 Mole

ZnO 1.000

Zn C 0.500

CO2 0 700 800 900 1000 1100 1200 Temperature (C) Figure 4. The change of reaction products with increasing process temperature for 1 atm condition. Batteries 2019, 5, 35 6 of 13

Figure4 shows reaction products in an Ar ﬂowed situation. ZnO reduction starts at 850 ◦C and ◦ the reaction is completed at 1150 C. MnO is produced by thermal dissociation of Mn2O3 at elevated temperatures and thus decreases the C content in the mixture. The reaction starts with direct reduction of ZnO by C then proceeds with indirect reduction by CO in the retort atmosphere and equilibrium observed at 1150 ◦C.

3.2. Carbothermal Reduction of Battery Wastes without Vacuum In the ﬁrst experimental set, carbothermal reduction conditions of zinc oxide are examined under Ar atmosphere. The produced reaction gases and purged Ar to keep the retort atmosphere in reducing conditions while also having the role of carrying gas for Zn vapor. Zn evaporated after the reduction from the oxide form and was carried out of the retort via Ar gas. CO2 gas re-oxidizes Zn at lower temperatures and thus Zn was obtained as ZnO in fume dust. Battery paste is washed and dried before reduction experiments. 65% of KOH is washed out in the washing process and a solution of KOH is obtained. Chemical analysis of the battery paste that is used for reduction experiments is given in Table2. The chemical composition of KOH solution obtained after washing is given in Table3.

Table 2. Battery paste analysis.

Element Weight, % Zn 27.1 Mn 38.12 K 6.47 Fe 1.35 Pb 0.0018 Loss of Ignition 20.21 Moisture 6.75

Table 3. KOH solution analysis.

Element mg/L K 6400 Zn 0.0147 Mn 0.0007

The experiments were done at 950, 1000, 1050, 1100 and 1150 ◦C. Zn reductions results are given in Figure5. It can be seen in Figure5 that a signiﬁcant change in Zn reduction occurred at 1050 ◦C. Above 1050 ◦C the Zn amount in the residue decreased to an acceptable level of reduction. The best result was seen at 1150 ◦C, with 1.32% weight Zn in the residue. This result means recovery of 95.1% of Zn in alkaline battery paste. Batteries 2019, 5, 35 7 of 13 Batteries 2019, 5, x FOR PEER REVIEW 7 of 13

FigureFigure 5. 5.( a()a Zinc) Zinc recovery recovery of ambientof ambien conditiont condition experiments, experiments, (b) Zn (b amount) Zn amount in the residuein the residue (1 h, various (1 h, temperature,various temperature, Ar ﬂow). Ar flow).

InIn the the second second experiment, experiment, the setthe effect set effect of time of was time investigated. was investigated. The experiments The experiments were conducted were ◦ 1100conductedC for 30,1100 60 °C and for 120 30, min 60 and of duration 120 min time.of duration Figure 6time. shows Figure that best6 shows result that has best been result detected has been for thedetected 60 min for experiment the 60 min with experiment 93.1% Zn with recovery. 93.1% In Zn parallel recovery with. thisIn parallel result, thewith lowest this result, amount the of lowest Zn in theamount residue of wasZn in determined the residue as was being determined 1.86% in as the being same 1.86% experiment. in the same experiment. Batteries 2019, 5, 35 8 of 13 Batteries 2019, 5, x FOR PEER REVIEW 8 of 13

Figure 6. (a) Zn recovery of ambient condition experiments, (b) Zn amount in the residue (1100 ◦C Figure 6. (a) Zn recovery of ambient condition experiments, (b) Zn amount in the residue (1100 °C various duration, Ar flow). various duration, Ar flow). 3.3. Vacuum Carbothermal Reduction of Battery Wastes 3.3. Vacuum Carbothermal Reduction of Battery Wastes In the third stage, vacuum applied experiments were done with two different carbon source types: coke andIn the lignite. third Cokestage,was vacuum used applied for its high experiments carbon content, were done yet lignite with two is the different more reactive carbon carbonsource source.types: coke In the and light lignite. of thermodynamic Coke was used calculations, for its high experimentscarbon content, were yet done lignite at loweris the temperatures.more reactive Incarbon the first source. two experimentalIn the light setof reactionsthermodynamic the temperature calculations, was aboveexperiments 1050 ◦ C,were in the done third at stage lower it changedtemperatures. from 500 In tothe 800 first◦C two with experimental 100 ◦C intervals. set re Duringactions experiments, the temperature samples was were above placed 1050 in °C, alumina in the cruciblethird stage then it chargedchanged infrom the 500 stainless to 800 steel °C with retort. 100 The °C intervals. retort was During vacuumed experiments, and heated samples to desired were valuesplaced at in the alumina same time. crucible After then the charged experiments in the were stainless finished, steel the retort. samples The cooled retort to was room vacuumed temperature and underheated vacuum to desired atmosphere. values at the Then same Zn recoveriestime. After were the experiments calculated from were residue finished, according the samples to Equation cooled (2)to forroom both temperature coke and lignite under used vacuum experiments. atmosphere. Results Then are Zn given recoveries in Figures were7 andcalculated8 respectively. from residue according to Equation (2) for both coke and lignite used experiments. Results are given in Figures 7 and 8 respectively. Batteries 2019, 5, x 35 FOR PEER REVIEW 99 of of 13

Figure 7. (a) Zn recovery, (b) Zn amount in residue with coke (1 h, 0.1 mbar vacuum, various temperature). Figure 7. (a) Zn recovery, (b) Zn amount in residue with coke (1 h, 0.1 mbar vacuum, various temperature).Zn residue is analyzed for both carbon sources, with lignite showing a higher Zn recovery rate under vacuum. Coke coal is known for high stability at high temperatures, therefore with the increasing temperature recovery rate of coke, the used vacuum reaction is decreased. The XRD result of residue is given in Figure9. The XRD pattern shows that residue contains ZnO, MnO and unreacted C. Therefore the vacuum dissociated Mn3O4 residue only had the MnO phase. Unreacted carbon could be the result of a lack of mixing. Results showed that the reduction and evaporation of Zn from alkaline battery paste is possible for all three reaction schemes: Ar purged carbothermal reduction, lignite and coke used vacuum reactions. However, ZnO reduction is found to be easier for the Ar purged condition. Reactions conducted under vacuum were ineffective for Zn reduction and evaporation. High temperature with Ar purged reaction for 1150 ◦C experiment was found to be the optimum and most effective reaction. Bouduard reaction is known for being essential to carbothermal reduction processes. Thermodynamic calculations showed that Zn reduction is easier for vacuum applied situations, yet vacuum pumped out reaction gases out of the retort. Thus from the kinetical point of view, the reaction could not be continued. The time needed for the reaction between ZnO and CO could not be provided due to high vacuum conditions. Ebin et al. Batteries 2019, 5, 35 10 of 13 investigated the recovery of Zn with pyrolysis and hydrogen reduction from battery waste [19]. Also Shuqing et al. studied pyrolysis of Zn battery waste and they obtained a 94% recovery rate at ◦ 950 C[25]. Belardi et al. studied the carbothermal reduction of spent batteries under N2, air and CO2 ◦ media. They obtained 99% Zn recovery at 1200 C-30 min. in N2 atmosphere [26]. As a result of the experiments carried out in the N2 atmosphere, they achieved 80% and 99.8% Zn recovery respectively at 950 ◦C[19,27]. Therefore, it’s clearly seen that hydrogen reduction is the most effective way recover Zn from battery waste. A vacuumed retort for ZnO reduction was studied by Xiong et al. and the results showed that under an effective vacuum, ZnO reduction needs at least 250% more carbon due to this carbothermal reduction of ZnO under vacuum [4]. In this study, alternative reduction techniques were studied for hydrogen reduction and pyrolysis. Ar gas purge for carbothermal ZnO reduction needs less carbon and offers more effective reduction. Ar gas decreases the partial pressure of CO developed by reduction reaction, while vacuum completely takes away reaction gases. Thus vacuum needs lower temperatures but higher carbon content for effective reduction. In order to reduce carbon Batteries 2019, 5, x FOR PEER REVIEW 10 of 13 foot prints, it is logical to use the high temperature Ar purged way to recycle alkaline batteries.

Figure 8.8.( a()a Zn) Zn recovery, recovery, (b) Zn(b) amount Zn amount in residue in residue with lignite with (1 lignite h, 10 Pa (1 vacuum, h, 10 Pa various vacuum, temperature) various. temperature).

Zn residue is analyzed for both carbon sources, with lignite showing a higher Zn recovery rate under vacuum. Coke coal is known for high stability at high temperatures, therefore with the increasing temperature recovery rate of coke, the used vacuum reaction is decreased. The XRD result of residue is given in Figure 9. The XRD pattern shows that residue contains ZnO, MnO and unreacted C. Therefore the vacuum dissociated Mn3O4 residue only had the MnO phase. Unreacted carbon could be the result of a lack of mixing. BatteriesBatteries2019 2019,,5 5,, 35 x FOR PEER REVIEW 1111 of 1313

◦ FigureFigure 9.9. XRD pattern of residueresidue afterafter vacuumvacuum appliedapplied processprocess withwith 800800 °CC andand 1010 PaPa vacuumvacuum conditionsconditions (lignite(lignite asas carboncarbon source).source). In metallurgical processes, process efficiency can be increased as furnace sizes increase. This is Results showed that the reduction and evaporation of Zn from alkaline battery paste is possible because heat losses occur from the furnace surface and the increasing furnace size decreases the unit for all three reaction schemes: Ar purged carbothermal reduction, lignite and coke used vacuum surface area where heat losses can occur. For this reason, it is expected that the process efficiency will reactions. However, ZnO reduction is found to be easier for the Ar purged condition. Reactions be increased at a larger scale. conducted under vacuum were ineffective for Zn reduction and evaporation. High temperature with 4.Ar Conclusions purged reaction for 1150 °C experiment was found to be the optimum and most effective reaction. Bouduard reaction is known for being essential to carbothermal reduction processes. ThermodynamicIn conclusion calculations the production showed of Zn that from Zn batteryreduction paste is easier is possible for vacuum via a carbothermal applied situations, reduction yet undervacuum Ar pumped atmosphere. out Duringreaction vacuum gases aidedout of experiments,the retort. Thus lignite from coal the is found kinetical to be point a better of reductantview, the thanreaction coke. could Lignite not isbe known continued. for having The time a higher needed reaction for the capabilityreaction between at lower ZnO temperatures and CO could than not coke be coal.provided On the due other to high hand, vacuum coke coal conditions. has better Ebin chemical et al. investigated stability at higher the recovery temperatures, of Zn with although pyrolysis is it foundand hydrogen to be an ineffectivereduction from reductant battery for waste ZnO under [19]. Also vacuum Shuqing conditions. et al. studied Both coal pyrolysis types are of ineffectiveZn battery inwaste vacuum and environmentsthey obtained againsta 94% recovery atmospheric rate conditions.at 950 °C [25]. Reaction Belardi gases et al. pumped studied outthe ofcarbothermal the system via vacuum show that an indirect reduction of ZnO by CO did not take place in the vacuum chamber. reduction of spent batteries under N2, air and CO2 media. They obtained 99% Zn recovery at 1200 °C- Thermodynamic results are based on stable reaction systems, however experimental conditions are 30 min. in N2 atmosphere [26]. As a result of the experiments carried out in the N2 atmosphere, they dynamicachieved and80% theand produced 99.8% Zn reactionrecovery gases respectively are pumped at 950 out °C [19,27]. of the system Therefore, by vacuum.it’s clearly Bouduard seen that reactionshydrogen could reduction not be is formedthe most in effective vacuum way conditions, recover thusZn from vacuum battery applied waste. systems A vacuumed are found retort to for be ineffectiveZnO reduction for recycling was studied the Zn by of Xiong alkaline et al. batteries. and the results showed that under an effective vacuum, ZnOThe reduction Ar supplied needs non-vacuum at least 250% system more carbon had the du beste to results this carbothermal for reduction reduction with 95.1% of Zn ZnO recovery. under COvacuum formation [4]. In wasthis study, found alternative to be essential reduction for the techniques reduction were and evaporationstudied for hydrogen of ZnO. Consequently,reduction and thepyrolysis. vacuumed Ar gassystem purge only for providedcarbothermal direct ZnO reduction reduction because needs the less produced carbon and CO offers was being more pumpedeffective outreduction. of the system, Ar gas resulting decreases in the lower partial Zn recovery pressure rates. of CO Bouduard developed reactions by reduction can take placereaction, under while Ar purgedvacuum situation, completely therefore, takes away both reaction direct and gases. indirect Thus reduction vacuum ofneeds ZnO lower by carbothermal temperatures technique but higher is foundcarbon to content be effective for effective way of recyclingreduction. ZnO In order in alkaline to reduce batteries. carbon Thermal foot prints, dissociation it is logical of Mn to3O use4 may the havehigh causedtemperature the use Ar of purged carbon way by oxygen to recycle dissociated alkaline frombatteries. Mn3 O4. ThermodynamicIn metallurgical calculationsprocesses, proces deviates efficiency from experimental can be increased results byas furnace higher reaction sizes increase. temperatures. This is Thisbecause can beheat explained losses occur by the from activation the furnace energy surface of reactions. and the Thermodynamic increasing furnace calculations size decreases show thatthe unit the reactionsurface area influences where the heat temperature, losses can occur. yet time For is this not reas takenon, into it is consideration.expected that the Experiments process efficiency showed thatwill be increased at a larger scale. Batteries 2019, 5, 35 12 of 13 reactions need longer time or higher temperatures in practice. Vacuum is found to be an ineffective technique to recycle ZnO from alkaline batteries because of its limited indirect or gas–solid reaction. The direct reduction effect is seen with higher reactivity lignite coal. The need for direct reduction causes the use of more carbon in the reduction process and therefore increases the carbon foot print of the recycling process.

Author Contributions: Conceptualization, S.Y.; Methodology, M.B.; Project administration, M.K.¸S.;Supervision, O.Y.; Writing—original draft, M.B. Funding: This research received no external funding. Conﬂicts of Interest: The authors declare no conﬂict of interest.

References

1. Espinosa, D.C.R.; Bernardes, A.M.; Tenorio, J.A.S. An overview on the current processes for the recycling of batteries. J. Power Sources 2004, 135, 311–319. [CrossRef] 2. Ferella, F.; Michelis, I.D.; Beolchini, B.; Innocenzi, V.; Veglio, F. Extraction of zinc and manganese from alkaline and zinc-carbon spent batteries by citric-sulphuric acid solution. Int. J. Chem. Eng. 2010, 2010, 659434. [CrossRef] 3. Veloso, L.R.S.; Rodrigues, L.E.O.C.; Ferreira, D.A.; Magalhaes, F.S.; Mansur, M.B. Development of a hydrometallurgical route for the recovery of zinc and manganese from spent alkaline batteries. J. Power Sources 2005, 152, 295–302. [CrossRef] 4. Xiong, L.Z.; Xiang, Y.H.; Wu, X.W.; He, Z.Q.; Yin, Z.L. Preparation of high purity zinc from zinc oxide ore by vacuum carbothermic reduction. Vacuum 2017, 146, 200–205. [CrossRef] 5. Habashi, F. Handbook of Extractive Metallurgy, Zinc; Wiley-VCH: Weinheim, Germany, 1997; Volume 2, pp. 641–682. 6. Mathewson, H.C. Zinc: The Metal, Its Alloys and Compounds in Physical Metallurgy of Zinc; Reinhold Publishing Corporation: New York, NY, USA, 1959; pp. 400–422. 7. Onem, K. Searching of Manufacturing Parameters Effecting Ductility of Zinc Wires for Thermal Spraying Application. Master’s Thesis, Istanbul Technical University, Istanbul, Turkey, 2002. 8. Yun, T.H.; Park, J.H.; Kim, J.-S.; Park, J.M. Effect of the surface modiﬁcation of zinc powders with organo silanes on the corrosion resistance of a zinc pigmented organic coating. Prog. Org. Coat. 2014, 77, 1780–1788. [CrossRef]

9. Stamatiou, A.; Loutzenhiser, P.G.; Steinfeld, A. Syngas production from H2O and CO2 over Zn particles in a packed-bed reactor. AIChE J. 2012, 58, 625–631. [CrossRef] 10. Ebin, B.; Petranikova, M.; Steenari, B.-M.; Ekberg, C. Effects of gas flow rate on zinc recovery rate and particle properties by pyrolysis of alkaline and zinc carbon battery waste. J. Anal. Appl. Pyrolysis 2016, 121, 333–341. [CrossRef] 11. Ito, Y.; Nyce, M.; Plivelich, R.; Klein, M.; Steingart, D.; Banerjee, S. Zinc morphology in zinc-nickel flow assisted batteries and impact on performance. J. Power Sources 2011, 196, 2340–2345. [CrossRef] 12. Schaefer, K.; Miszczyk, A. Improvement of electrochemical action of zinc-rich paints by addition of nano particulate zinc. Corros. Sci. 2013, 66, 380–391. [CrossRef] 13. Gallegos, M.V.; Falco, L.R.; Peluso, M.A.; Sambeth, J.E.; Thomas, H.J. Recovery of manganese oxides from spent alkaline and zinc-carbon batteries: An application as catalysts for VOCs elimination. Waste Manag. 2013, 33, 1483–1490. [CrossRef] 14. Li, Y.J.; Yang, D.J. Study of leaching zinc from difficult dealt zinc oxide ore with high silicon in the alkaline. Adv. Mater. Res. 2015, 1120–1121, 105–109. [CrossRef]

15. El-Nadi, Y.A.; Daoud, J.A.; Aly, H.F. Leaching and separation of zinc from the black paste of spent MnO2-Zn dry cell batteries. J. Hazard. Mater. 2007, 143, 328–334. [CrossRef][PubMed] 16. Sayilgan, E.; Kukrer, T.; Civelekoglu, G.; Ferella, F.; Akcil, A.; Veglio, F.; Kitis, M. A review of technologies for the recovery of metals from spent alkaline andzinc-carbon batteries. Hydrometallurgy 2009, 97, 158–166. [CrossRef] 17. Bernardes, A.M.; Espinosa, D.C.R.; Tenório, J.A.S. Recycling of batteries: A review of current processes and technologies. J. Power Sources 2004, 130, 291–298. [CrossRef] Batteries 2019, 5, 35 13 of 13

18. Sun, Y.; Shen, X.; Zhai, Y. Thermodynamics and kinetics of extracting zinc from zinc oxide ore by the ammonium sulfate roasting method. Int. J. Miner. Metall. Mater. 2015, 22, 467–475. [CrossRef]

19. Morcali, M.H. Reductive atmospheric acid leaching of spent alkaline batteries in H2SO4/Na2SO3 solutions. Int. J. Miner. Metall. Mater. 2015, 22, 674–681. [CrossRef] 20. Ebin, B.; Petranikova, M.; Steenari, B.-M.; Ekberg, C. Investigation of zinc recovery by hydrogen reduction assisted pyrolysis of alkaline and zinc-carbon battery waste. Waste Manag. 2017, 68, 508–517. [CrossRef] [PubMed] 21. Han, L.; Yang, B.; Dai, Y.-N.; Liu, D.-C.; Yang, B.-Z. Applications of vacuum metallurgical technology in recovery of secondary zinc-based resources. Vacuum 2008, 45, 20–22. 22. Xiong, L.; Chen, Q.; Yin, Z.; Zhang, P.; Ding, Z.; Liu, Z. Preparation of metal zinc from hemimorphite by

vacuum carbothermic reduction with CaF2 as catalyst. Trans. Nonferrous Met. Soc. China 2011, 22, 694–699. [CrossRef] 23. Xiong, L.; He, Z.; Liu, Z.; Yin, Z. Study on vacuum carbothermic reduction kinetics of hemimorphite catalyzed by calcium ﬂuoride. Vacuum 2015, 119, 163–167. [CrossRef] 24. Yucel, O.; Demirci, F.; Turan, A.; Alkan, M. Determination of Direct Reduction Conditions of Mill Scale. High Temp. Mater. Process. 2013, 32, 405–412. [CrossRef] 25. Shuqing, Z.; Jie, Y.; Xu, Z.; Xingbin, S. One-step Pyrolysis Process for Recover Zinc and Mercury from Spent Zinc-manganese Batteries. Adv. Mater. Res. 2010, 113–116, 2224–2227. 26. Belardi, G.; Medici, F.; Piga, L. Inﬂuence of gaseous atmosphere during a thermal process for recovery of manganese and zinc from spent batteries. J. Power Sources 2014, 248, 1290–1298. [CrossRef] 27. Bale, C.W.; Chartran, P.; Degterov, S.A.; Eriksson, G.; Hack, K.; Mahfoud, R.B.; Melançon, J.; Pelton, A.D.; Petersen, S. FactSage “Thermochemical Software and Databases”. Calphad 2002, 26, 189–228. [CrossRef]

© 2019 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (http://creativecommons.org/licenses/by/4.0/).