ARTICLE

Received 26 Mar 2013 | Accepted 19 Jun 2013 | Published 19 Jul 2013

A green lead hydrometallurgical process based ona hydrogen-lead oxide fuel cellJunqing Pan1,2, Yanzhi Sun3, Wei Li2, James Knight2 & Arumugam Manthiram2

The automobile industry consumed 9 million metric tons of lead in 2012 for lead-acid

batteries. Recycling lead from spent lead-acid batteries is not only related to the sustainable

development of the lead industry, but also to the reduction of lead pollution in the

environment. The existing lead pyrometallurgical processes have two main issues, toxic lead

emission into the environment and high energy consumption; the developing hydro-

metallurgical processes have the disadvantages of high electricity consumption, use of toxic

chemicals and severe corrosion of metallic components. Here we demonstrate a new green

hydrometallurgical process to recover lead based on a hydrogen-lead oxide fuel cell. High-

purity lead, along with electricity, is produced with only water as the by-product. It has

a 499.5% lead yield, which is higher than that of the existing pyrometallurgical processes

(95–97%). This greatly reduces lead pollution to the environment.

DOI: 10.1038/ncomms3178

1 State Key Laboratory of Chemical Resource Engineering, Beijing University of Chemical Technology, Beijing 100029, China. 2 Electrochemical EnergyLaboratory, Materials Science and Engineering Program, The University of Texas at Austin, Austin, Texas 78712, USA. 3 National Fundamental ResearchLaboratory of New Hazardous Chemicals Assessment and Accident Analysis, Beijing University of Chemical Technology, Beijing 100029, China.Correspondence and requests for materials should be addressed to J.P. (email: jqpan@mail.buct.edu.cn) or to A.M. (email: rmanth@mail.utexas.edu).

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With the rapid developments in the automobile industry,the production of lead (Pb)-acid batteries as theautomotive ignition power source has experienced

enormous growth during the past few decades1. In 2012, 9 millionmetric tons of refined Pb, which is about 85% of annual Pbproduction, was consumed globally for manufacturing Pb-acidbatteries for vehicles (http://www.ilzsg.org/static/statistics.aspx?from=1). Moreover, due to their low cost, Pb-acid batteries arealso a strong contender for grid storage of electricity produced byrenewable energies such as solar and wind. An annual growth rateof 46% is anticipated for the production of refined Pb. Althoughthere is no Pb pollution from using Pb-acid batteries, theirwidespread use has caused a severe environmental problem dueto toxic Pb emission and high energy consumption of the existingPb pyrometallurgical processes for preparing metallic Pb2.

The raw materials (lead compounds) of the existing Pbpyrometallurgical processes are mainly obtained by extractionfrom natural lead oxide ores and pre-roasting oxidation of galena(lead sulphide (PbS)-lead oxide (PbO)). As Pb-acid batterieshave been used worldwide in vehicles for decades, the rawmaterials are now mainly attained by recovering from waste Pb-acid batteries via the desulfurization process of lead sulphate(PbSO4)3,4 and the redox reaction of Pb and lead dioxide(PbO2)5,6. The pyrometallurgical processes employ coke orcarbon monoxide to reduce lead compounds at hightemperature (about 1,000 �C) to gain the crude Pb with therelease of CO2 gas7. Pb vapour/dust is also produced owing to itslow melting point and escapes along with the exhaust gases intothe atmosphere, known as Pb pollution7–9. High-purity Pb(99.99%) is then obtained by refining the crude Pb usingelectrolytic refining or fire refining8. The whole process has ayield of 95–97% (refs 7,9,10).

Hydrometallurgical processes were proposed to eradicate the Pbpollution problem and obtain high-purity Pb (99.99%) without therefining step8,11–20. These processes do not emit Pb vapour/dust tothe environment due to their low operating temperature and lackof vapour production8,11; however, there are still manydisadvantages, such as high electricity consumption, use of highlytoxic hexafluorosilicic acid electrolyte and severe corrosion ofmetallic components12–21. As a result, these processes have not yetbeen adopted by the industry. It is an urgent requirement todevelop a new green lead recovery process with lower energyconsumption and without the use of toxic chemicals.

Herein we report a new green hydrometallurgical process forproducing high-purity metallic Pb based on a specially designedH2–PbO fuel cell. The PbO serves as the Pb source and is pre-refined in a hot sodium hydroxide (NaOH) aqueous solution.This and the hydrogen gas undergo electro-reduction at thecathode and electro-oxidation at the anode in the fuel cell,respectively. The new process is energy-efficient and toxic-free(except for PbO and Pb), and it produces only Pb, water andelectricity. It also does not involve Pb emission due to the lowoperating temperature of 60–100 �C. The NaOH concentration,temperature, PbO concentration and current density have beenoptimized to synthesize a dense, high-purity Pb (99.9992%),qualified for Pb-acid batteries with a high yield of 99.5–99.8%,which is higher than that of existing pyrometallurgical processes(95–97%), and greatly reduces lead pollution to the environment.

ResultsH2–PbO fuel cell. Figure 1 illustrates the schematic of the newgreen hydrometallurgical process using the proposed H2–PbOfuel cell. Hydrogen gas is fed into the anode, where it undergoeselectro-oxidation with the OH� ions to form water and releaseselectrons. The electrons pass through the external circuit, carryout electric work, and then arrive at the cathode. The refined PbOdissolved in heated aqueous NaOH forms HPbO2

� ions, whichare then pumped into the cathode, where the HPbO2

� ionscombine with the electrons from the anode and water to producemetallic Pb and OH� ions. The produced OH� ions combinewith the Naþ ions migrating from the anolyte through thesodium-ion exchange membrane to form NaOH. The involvedreactions including the complexation dissolution of PbO inNaOH are given below:

Anode: H2þ 2OH�-2H2Oþ 2e� (electro-oxidation, E�¼� 0.828 V)

Cathode: PbO(s)þOH�-HPbO2� (complexation reaction)

HPbO2� þ 2e� þH2O-Pb(s)þ 3OH� (electro-reduction,

E�¼ � 0.531 V)The overall reaction of the fuel cell isH2þPbO(s)-H2OþPb(s) (E�¼ � 0.531� (� 0.828)¼ 0.297 V)The positive standard potential of 0.297 V means that the

reaction between H2 and PbO occurs spontaneously to producePb, water and electricity. The experimental results show that theopen-circuit voltage at room temperature is 0.226 V, which is a

NaHPbO2+NaOH NaOH

Na+

2OH–

2H2O

NaOH H2

H2H2

H2

H2O

HPbO2–

R

Pb3OH–

+2e– –2e–

e– e–

H2

NaOHNaHPbO2 + NaOH

Catholyte supply Fuel cell Anolyte and H2 supplies

Nafion 2030 membrane

Graphite H2 flow plateGas difusion layer

Deposited Pb LayerCopper plates

Catalyst layer

+ –

NaOHHPbO2

–

Figure 1 | Schematic of the H2–PbO fuel cell. The Nafion 2030 membrane (DuPont) is an ion-selective, reinforced composite membrane designed to

transport sodium ions and water while blocking OH� and HPbO2� ions. The diffusion layer is a carbon paper (TGP-H-060, Toray) coated with carbon black

(Vulcan 72 R, Cabot). The catalyst is carbon black-supported platinum nanoparticles (40 wt% Pt/C, Johnson Matthey).

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little lower than the standard potential due to the non-standardconditions such as temperature, concentration and smallpolarization losses.

The complexation dissolution of PbO in a hot aqueous NaOHsolution has a key role in making this process feasible. AlthoughPbO is generally considered a basic metal oxide, it has a highsolubility in concentrated aqueous NaOH solutions22. As shownin Fig. 2, the solubility of PbO strongly depends on temperaturewhen the NaOH concentration is above 15%. This characteristicof its solubility makes it possible to obtain a high concentration ofhigh-purity PbO by a recrystallization process, which produceshigh-purity Pb at a fast reaction rate.

PbO recovery and purification. The PbO in this study wasrecovered from the spent lead paste (Zhejiang Huitong Group)from used Pb-acid batteries by a desulfurization process of lead

sulphate and a redox reaction of Pb and PbO2 with a catalyst6.The actual recovery efficiency of PbO reaches 99.7%.

The recovered PbO was purified by a recrystallization process,which is based on the strong temperature dependence of PbOsolubility in a concentrated aqueous NaOH solution. The highpurity of the obtained PbO ensures the quality of the electrolyteand the Pb synthesized by a H2–PbO fuel cell. Figure 3 comparesthe XRD patterns of the PbO samples purified by recrystallizationin different concentrations of NaOH. The location of the {001}peak was used to identify the polymorph of the PbO phase, thatis, massicot or litharge. It was found that the PbO obtained from alow concentration of NaOH (15%) is massicot (PDF no. 00-005-0570) and from a high concentration (30%) is litharge (PDF no.00-005-0561). The PbO obtained from NaOH concentrations of15–30% is a mixture of massicot and litharge. It was also foundthat the PbO obtained in 30% NaOH has the main peak located atabout 35.7�, which means that the crystalline PbO prefers to growalong with o0024 direction.

All purified PbO samples show irregular shapes with sizes inthe range of 10–15 mm (Supplementary Fig. S1). Compared withthe desulfurized PbO from the spent lead-acid batteries, theinductively coupled plasma (ICP) analysis shows that the purifiedPbO samples have much lower impurities of other metals(Table 1). These high-purity PbO samples are suitable for thesynthesis of high-quality Pb.

Synthesis of metallic Pb. The first trial to obtain Pb was carriedout with an anolyte of 20% NaOH and a catholyte of 20%NaOHþ 0.1 mol l� 1 PbO at a current density of 5 mA cm� 2 atroom temperature. The XRD pattern in Fig. 4a confirms that theobtained grey material on the copper cathode is metallic Pb withsome PbO impurities. The sample is made of loose particles asshown in the field emission-scanning electron microscopy (FE-SEM) image in Fig. 4b. Compared with bulk dense Pb, thisparticulate Pb has a larger surface area and is thus easier tooxidize in air in storage and in the melting process to make leadingots. This is why some PbO co-exists as shown by the XRDpattern in Fig. 4a. The product is also porous with a large volume,which is not desirable for transport and storage.

To obtain high-purity Pb with a dense structure, fast reactionrate and high yield, three factors, the NaOH concentration (sameat the anode and cathode before operation, 15–35%), temperature(30–105 �C) and PbO concentration (0.05–0.4 mol l� 1), weresystematically investigated. The details are presented in Supple-mentary Notes 1,2,3, respectively. A brief description is given asfollows. A low NaOH concentration is favourable to theformation of a dense structure (Supplementary Fig. S2) and thekinetics of the electro-reduction reaction of Pb2þ (Supplement-ary Fig. S3). As for the temperature effects, an intermediatetemperature is helpful to form a dense structure (SupplementaryFig. S4). A high temperature increases the kinetics of the electro-reduction reaction of Pb2þ (Supplementary Fig. S5) and thehydrogen electro-oxidation reaction (Supplementary Fig. S6). Acomparison between the kinetics of both reactions (Supplement-ary Fig. S7) reveals that the H2–PbO fuel cell performance islimited by the Pb2þ electro-reduction. Similar to the temperature

353025

CN

aOH (%

)

20

1520 40

Temperature (°C)

PbO

sol

ubili

ty (

g l–1

)

Sol

ubili

ty (

g l–1

)

60 80 100 12020

40

60

80

100

120

130

115

100

85

70

55

40

25

10

Figure 2 | Solubility of PbO versus temperature and NaOH

concentration. The solubility is determined by a complexometric titration

with EDTA.

10

Inte

nsity

(ar

bitr

ary

unit)

20 30 40

2� (°)50 60 70

{001

}

15% NaOH20% NaOH25% NaOH30% NaOH{1

01}

{002

}

{102

}{2

00}

{112

}

{211

}{2

02}

{103

}

{113

}{2

20}{110

}

Figure 3 | XRD patterns of the PbO samples. The purified PbO samples

were obtained from different concentrations of NaOH solutions: 15, 20, 25

and 30%.

Table 1 | ICP analysis results of the PbO samples.

PbO Ag, % Cu, % Bi, % As, % Sb, % Sn, % Zn, % Fe, %

a 0.0006 0.0022 0.0016 0.0007 0.0035 0.0019 0.0002 0.0045b 0.0002 0.0001 0.0003 0.00009 0.0006 0.0003 0.00005 0.0003

a, before recrystallization; b, after recrystallization in 25% NaOH; ICP, inductively coupled plasma.

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effect, an intermediate PbO concentration helps form a densestructure (Supplementary Fig. S8) and a high PbO concentrationpromotes the kinetics of the electro-reduction reaction of Pb2þ

(Supplementary Fig. S9). All three factors do not significantlyaffect the current efficiencies of the Pb electro-deposition, asshown in Supplementary Tables S1,S2,S3, respectively. Consider-ing the morphology of the produced Pb (dense structure), thekinetics of the Pb electro-deposition reaction (low overpotentialand fast reaction) and the current efficiency, the optimized NaOHconcentration, temperature and PbO concentration were deter-mined to be 20%, 85 �C and 0.3 mol l� 1, respectively.

The Pb prepared under the optimized conditions has a densestructure (FE-SEM image in Fig. 4c) and thus has no significantoxidation, as confirmed by the XRD pattern in Fig. 4a. The ICPanalysis in Table 2 indicates that the purity of the electro-deposited Pb is 99.9992%, which is much higher than the 1#standard Pb (GB/T 468-2005, Chinese standard, 99.994%) andPB990R grade Pb (EN 12659-1999, European standard, 99.99%).This ultra-high-purity Pb is a superior material for themanufacture of high-quality Pb-acid batteries with a longer cyclelife. In addition, all of the current efficiencies are greater than99.5%, indicating a very high selectivity of the Pb reductionreaction at the cathode.

Figure 5a shows the polarization curve and surface power curveof the H2–PbO fuel cell operated under the optimized conditions.The Pb samples prepared at 20, 40, 60 and 80 mA cm� 2 havedense structures as shown by the FE-SEM images (SupplementaryFig. S10), suggesting that the current density does not affect thesurface morphology of the Pb samples. Additionally, the currentdensity also does not affect the current efficiency (SupplementaryTable S4). Therefore, the fuel cell can operate at 40 mA cm� 2 toachieve a maximum electric surface power density of5.5 mW cm� 2 at 80 mA cm� 2 and a high production rate ofPb. As shown in Fig. 5b, the reduction of PbO can beaccomplished in 14.02, 7.02, 4.69 and 3.45 h at 20, 40, 60 and80 mA cm� 2, respectively. According to Faraday’s law, thereaction conversions of PbO to Pb were 99.6%, 99.8%, 99.7%and 99.3%. The catholyte thus had a very small amount ofunreacted PbO residue. This residual PbO can be further reducedby an ion exchange process or electrolysis until it does not affectthe recyclability of the reacted catholyte for preparing the anolyte.

DiscussionThis new green Pb hydrometallurgical process employing an H2–PbO fuel cell eliminates Pb pollution and significantly reducesenergy consumption, which are the two major issues for theexisting Pb pyrometallurgical processes and other developingpyrometallurgical and hydrometallurgical processes. A detailedcomparison is given in Table 3. Unlike the pyrometallurgicalprocesses, this new process has no Pb vapour or slag released tothe environment, leading to an annual reduction of 12,000–20,000 metric tons of Pb (vapor/dust and slag) emission to theenvironment for a plant with an annual output of 400,000 metrictons of Pb. Furthermore, compared with other hydrometallurgicalprocesses, this new process does not employ any toxic chemicals,

10

a

b

c

20 30

Pb from 1st trialPb from optimized operating conditions

40 50 60 70

2� (°)

Inte

nsity

(ar

bitr

ary

unit)

80 90

PbO impurity{111

}{2

00}

{220

}

{311

}{2

22}

{400

}

{331

}{4

20}

*

***

Figure 4 | Pb samples produced in the H2–PbO fuel cell. (a) X-ray

diffraction patterns of the Pb samples produced initially and under

optimized conditions later. (b) FE-SEM image of the Pb sample produced

initially. (c) FE-SEM image of the Pb produced under optimized conditions.

Scale bar, 100mm.

Table 2 | Comparison of Pb compositions.

Pb samples Composition (%)

Impurities, r� 10�4

Pb, Z Ag Cu Bi As Sb Sn Zn Fe Cd Ni

1# Pb 99.994 8 10 40 5 8 5 4 5 / /PB990R Pb 99.99 15 5 100 5 5 5 2 / 2 2Electro-deposited Pb 99.9992 1 0.8 2 0.5 1.5 1 0.3 0.4 0.2 0.1

The 1# standard Pb (GB/T 468-2005, Chinese standard), PB990R Pb (EN 12659-1999, European standard) and ICP analysis results of the Pb obtained under optimized operating conditions of 20%NaOH, 0.3 mol l� 1 PbO, 40 mA cm� 2 and 85 �C are listed.

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such as hydrofluoric acid. Regarding the energy consumption,this new process needs about 1/2 or 1/3 of the energy used for theexisting pyrometallurgical or other hydrometallurgical processes,respectively. This new process, as a fuel cell, also produceselectricity (5.3–45.5 W h per kg of Pb) depending on the currentdensity, and can also be applied for preparation of other metalssuch as copper, silver, antimony and nickel. To accomplish this,two main conditions need to be satisfied. First, the raw materialsshould dissolve in a basic solution. Second, the reductionpotential of the metal ions should be higher than that of thehydrogen ion.

MethodsGeneral procedure for recovery of PbO from the spent lead paste. The spentlead paste from used Pb-acid batteries was supplied by Zhejiang Huitong Group,China. Its main ingredients are 12.6% Pb, 15.3% PbO, 26.8% PbO2 and 44.2%PbSO4, and the remainder (1.1%) is H2O and H2SO4. The recovery of PbO fromthe spent lead paste employs four processes6: desulfurization , redox, synchronizingdissolution and crystallization. The involved chemical reactions and detaileddescriptions are given below.

Desulfurization process. PbSO4(s)þ 2NaOH(aq)¼PbO(s)þH2OþNa2SO4(s)(30 �C). The spent lead paste (100 g) was added to 10% NaOH (120 ml) for thedesulfurization process to convert PbSO4 to PbO. The reaction temperature wascontrolled at 30 �C and the paste was stirred at 150 r.p.m. for 10 min.

Redox process. Pb(s)þPbO2(s)þ 2NaOH(aq)¼ 2NaHPbO2(aq) (115 �C). Theobtained sample A (a mixture of Pb, PbO and PbO2) from the desulfurizationprocess was filtered with a Buchner funnel and washed with deionized water.Sample A was carefully transferred to the reactor containing 30% NaOH saturatedwith 30 g l� 1 PbO at room temperature. A calculated amount of Pb powder (10.6 g,120 mesh) was supplied as the reductant and Na3SbO3 (0.15 g) was added as thecatalyst for the redox reaction of Pb and PbO2. The reaction was controlled at115 �C and the reaction paste was stirred at 300 r.p.m. for 3 h.

Synchronizing dissolution process. PbO(s)þNaOH(aq)¼NaHPbO2(aq)(115 �C). During the redox process, the PbO of sample A was also synchronizationdissolved in the NaOH solution at 115 �C.

Crystallization process. NaHPbO2(aq)¼NaOH(aq)þ PbO(s) (25 �C). Thepreviously obtained NaHPbO2/NaOH solution was immediately filtered and slowlycooled to room temperature with continuous stirring. During the cooling process,kermesinus PbO slowly precipitates from the solution. It was filtered by a G-2sintered glass filter, washed with deionized water and dried at 60 �C. The finalrecovered PbO weighed 97.2 g, and thus the PbO recovery efficiency was 99.7%.

Determination of PbO solubility. The recovered PbO was purified by a recrys-tallization process. The solubility of the purified PbO in NaOH aqueous solutionswas determined by a complexometric titration with EDTA, described as follows.An excess of PbO was added to a NaOH solution, which was then stirred andheated to the temperature, at which the solubility will be determined. The solutionwas kept stirring at that temperature for 5 min and subsequently stayed still for10 min. An aliquot of this PbO/NaOH solution (0.10 ml) was quickly transferred toa stirring HNO3 solution (10 ml, 1 mol l� 1). After that, an extra amount (1.5�stoichiometric amount) hexamethylenetetramine was added to neutralize theHNO3. The solution was finally titrated by a standard EDTA solution(0.020 mol l� 1) with xylenol orange as the indicator.

H2–PbO fuel cell and synthesis of Pb. The H2–PbO fuel cell consisted of ananode of 2� 2 cm2 carbon paper (TGP-H-060, Toray) with a carbon black (Vulcan72R, Cabot) loading of 0.5 mg cm� 2 and a Pt catalyst loading of 1.0 mg cm� 2

(40 wt% Pt/C, Johnson Matthey)23, a cathode of 2� 2 cm2 high-purity copperplate, Nafion 2030 sodium ion-selective membrane (DuPont), anolyte of aqueousNaOH solution (15–35%, 60 ml min� 1) and catholyte of aqueous NaOH–PbO(15–35% NaOH and 0.05–0.4 mol l� 1 PbO, 60 ml min� 1) solution. The NaOHconcentrations at the anode and cathode were kept the same before operation. TheH2 flow rate was kept at about 5 ml min� 1 for 30 min to expel the air in the

0.25a

b

0.20

0.15

0.10

0.05

0.00

0 2 4 6 8 10 12 14 16

Vol

tage

(V

)

Sur

face

pow

er d

ensi

ty(m

W c

m–2

)

Vol

tage

(V

)

Time (h)

Current density (mA cm–2)

0

1

2

3

4

5

6

20 mA cm–2

40 mA cm–2

60 mA cm–2

80 mA cm–2

0 10 20 30 40 50 60 70 80 90

0.30

0.25

0.20

0.15

0.10

0.05

0.00

Figure 5 | Characterizations of the new lead hydrometallurgical process.

(a) Polarization curve and specific power curve of the H2–PbO fuel cell.

(b) Voltage versus time curves at different current densities of the H2–PbO

fuel cell.

Table 3 | Comparison of three Pb metallurgical processes.

Item Pyrometallurgical processes Hydrometallurgical processes H2–PbO fuel cell

Temperature, �C 700–1,100 20–100 20–100Yield, % 95 497 499.5Pb purity, % 97–99 99.99 99.9992Refining required Yes No NoRefining energy consumption,kW h per metric ton Pb

120–130 0 0

Pollution Pb vapour, dust and slag; HF from refining HF and so on NonePb production, kg 900 919 926Energy consumption per metric ton PbO 120–175 kg coal 650–930 kW h 9.2 kg H2

Energy price 0.28 US $ kgcoal� 1 , 0.12 US $ kW h� 1 0.12 US $ kW h� 1 3.1 US $ kgH2

� 1

Energy cost, US $ per metric ton PbO 47.3–63.8 78–112 28.5*

The raw material is PbO.*Not considering the 5.3–45.5 Wh kgPb

� 1 electricity generated by the H2–PbO fuel cell.

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hydrogen channel before operation. The valve at the hydrogen channel outlet wasclosed during the experiments. The pressure of H2 in the channel was 0.1 MPa. Toreduce the formation of Pb dendrites, DPE-3 (electroplating additive, WuhanYangtze Plating Additives Plant) was added as an additive into the catholyte with aconcentration of 6 ml l� 1. Two Hg/HgO reference electrodes were used to controlthe potentials of the anode and cathode. A battery test station (LAND 2001A,Wuhan LAND Electronics) was used to run the fuel cell in constant current mode.The electrochemical measurements of the fuel cell were performed on a CSU-300electrochemical workstation (Wuhan Corrtest Instrument).

Characterization of the synthesized Pb. For the characterization of the Pbproduct, the cathode with produced Pb plate was taken out from the system,washed with deionized water, vacuum dried at 60 �C for 3 h and then stored underargon to avoid oxidation in air. The mass of Pb was obtained by subtracting the Cucathode from the total mass of the Cu cathode with Pb. The Pb surface morphologywas examined by an FE-SEM (Hitachi S4700). The composition of the Pb wasmeasured with an ICP analyzer (Agilent 7700). The XRD patterns of the Pbsamples were recorded on a Rigaku D/max2500VB2þ /PC diffractometer with CuKa radiation (l¼ 0.15418 nm, 40 kV, 200 mA).

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AcknowledgementsThe work at Beijing University of Chemical Technology (BUCT, China) was supportedby the State Key Program of National Natural Science of China (no. 21236003) andNational Natural Science Foundation of China (no. 21006003). The work at theUniversity of Texas at Austin (UT-Austin) was supported by the US Department ofEnergy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineeringunder award number DE-SC0005397.

Author contributionsJ.P. proposed the concept, designed and performed the experiments, and supervised theresearch work at BUCT. Y.S. designed and performed the experiments at BUCT. W.L.contributed to the concept and designed and performed the preliminary experiments atUT-Austin. J.K. performed the preliminary experiments at UT. A.M. supervised theresearch work at UT-Austin. All five authors contributed to the writing of themanuscript. J.P. worked at UT during August 2010–September 2011.

Additional informationSupplementary Information accompanies this paper at http://www.nature.com/naturecommunications

Competing financial interests: The authors declare no competing financial interests.

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How to cite this article: Pan, J. et al. A green lead hydrometallurgical process based on ahydrogen-lead oxide fuel cell. Nat. Commun. 4:2178 doi: 10.1038/ncomms3178 (2013).

ARTICLE NATURE COMMUNICATIONS | DOI: 10.1038/ncomms3178

6 NATURE COMMUNICATIONS | 4:2178 | DOI: 10.1038/ncomms3178 | www.nature.com/naturecommunications

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