la producción de polvo de zinc electrolítico de zinc carcasa del Ánodo de pilas secas gastados

7/26/2019 La Produccin de Polvo de Zinc Electroltico de Zinc Carcasa Del nodo de Pilas Secas Gastados

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Production of electrolytic zinc powder from zinc anode casing of spentdry cell batteries

Ashour Owais a,, Mohamed Abdel Hady Gepreel b, Essam Ahmed a

a Department of Metallurgical and Materials Engineering, Faculty of Petroleum and Mining Engineering, Suez University, 43721 Suez, Egyptb Department of Materials Science and Engineering, EgyptJapan University of Science and Technology (EJUST), 21934 Alexandria, Egypt

a b s t r a c ta r t i c l e i n f o

Article history:

Received 11 April 2015Received in revised form 21 July 2015

Accepted 22 July 2015

Available online 30 July 2015

Keywords:

Zinccarbon batteries

Zinc anode casing

Packed bed electrolysis

Electrolytic zinc powder

Thispaper aimsto study experimentally the packed bed electrolysis of anode particles obtained fromzinc casing

of spent secondary batteries, by which electrolytic zinc powder can be produced. Zinc casings of the exhaustedzinccarbon type dry cell batteries were separated from both the internal carbon rods and MnO2 paste materials

and from the external covers then fed into cuboids anode basket made from graphite or titanium. Two stainless

steel permanent cathode sheets together with the anode basket were immersed in a basic solution containing

230 g/L NaOH. Electrolytic zincpowders in the form of nanorods, dendritic and/or a dispersed shape with a purity

of about 99.8% Zn and with an apparent density of 1203.1 to 2085.2 kg/m3 were obtained. The results indicated

that, the graphite basket is better than the titanium one for all studied parameters except for the specic energy

demand factor.The deposited zincpowders are contaminated with about 0.0053% Ti when using titanium basket.

The process was enhanced with increasing current density, electrolyte temperature, electrolyte stirring rate, and

the use of an old electrolyte. The electrolysis process was carried out with cathodic current efciency up to

94.85%, anodic current efciency up to 98.97% and specic energy demand in the range between 0.808 and

2.518 kWh/kg Zn with powder productivity up to 1.150 g/A.h.

2015 Elsevier B.V. All rights reserved.

1. Introduction

Zinccarbon type dry cell batteries are the oldest and most used type

batteries inthe world(Khan andKurny,2011). Inthese batteries,anode ma-

terial is zinc and thecathode is a mixture of manganese dioxide and carbon

(Fig. 1) (Shin et al., 2009). A very large quantity of these batteries is used in

ourdaily life, buttheir lives arelimited.They arenon-rechargeable (primary

cells)which means once discharged, theybecomeuseless andarediscarded

(Belardi et al., 2011; Rayovac Corp, 2014). The landlling disposal of the

spent batteries, along withother municipal waste, causes not onlyenviron-

mental hazards but also leadsto thelossof thesevaluable metallic elements

and materials (Belardi et al., 2014; Li and Xi, 2005).

Spent zinccarbon type batteries are considered very useful second-

ary resources of zinc recovery as zinc constitutes almost 22% of the total

weight of these type batteries. However, the zinc anode alone consti-

tutes the maximum portion of zinc in these batteries (Gallegos et al.,

2013; Ma et al., 2014; Nan et al., 2006).

The recovery of zinc from the spent dry cell batteries has been investi-

gated by both pyrometallurgical (Salgado et al., 2003; Xiao et al., 2009)

and hydrometallurgical (Belardi et al., 2011; Buzatu et al., 2013, 2014;

Rcz and Ilea, 2013) processing. A thorough comparison between the

two methodologies is reported in previous works (Espinosa et al., 2004;

Sayilgan et al., 2009).Baba et al. (2009)proposed a combined pyro- and

hydro-metallurgical process. However, using the pyrometallurgical pro-

cessing or the use of critical treatment conditions for Zn recovery has

bad effects on the environment by means of emissions, secondary waste

streams and hazardous work environments. Therefore, the development

of intensied hydrometallurgical, zero-waste (Toro et al., 2006) treatment

routes is highly recommended. The hydrometallurgical process generally

includes; dissolving the zinc anode in sulfuric or hydrochloric acid

media, sometimes with prior water washing treatment and recovering

the zinc from solution by electrowinning technique(Sayilgan et al., 2009).

Another efcient method to recover metal powders from spent raw

materials without application of both leaching and electrowinning tech-

niques is the packed bed electrolysis process (Owais, 2012, 2015; Owais

and Friedrich, 2003; Owais and Gepreel, 2013). By applying this method,

high-quality electrolytic metal powders can be produced through the di-

rect electrolytic rening of exhausted materials. This technique combines

the leaching step and the metal recovery by electrowinning in one pro-

cess. This process depends on utilizing anode particles which are put in

a basket made from titanium to collect the particles and to conduct the

electricity to them. One of the main advantages of this technique is the

continuous feeding of the anode particles into the basket, also there is

no need for adding an external source of metal ions to the electrolytic

cell as usually done in the case of electrowinning technique.

The current efciency of an electrolytic process can be expressed as

the ratio of the amount of material actually deposited on the electrode

Hydrometallurgy 157 (2015) 6071

Corresponding author.

E-mail address: [email protected](A. Owais).

http://dx.doi.org/10.1016/j.hydromet.2015.07.014

0304-386X/ 2015 Elsevier B.V. All rights reserved.

Contents lists available at ScienceDirect

Hydrometallurgy

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to that which should have deposited on the basis of Faraday's law, by

the passage of the same charge, assuming that no side reactions take

place at the electrode. In general, the current efciency depends on

many factors such as the current density, the presence of additives

and/or impurities in the electrolyte, the composition and the properties

of the electrolyte, the electrolysis temperature, and the nature of the

electrodes andof theelectrodeposit. Thecurrent efciency also depends

on the presence of additives and/or of impurities which may co-deposit

or may inuence the electrochemical reaction or may affect the over-

voltages of the desirable and the undesirable reactions (Gupta, 2003).

The produced zinc powder can be employed in both chemical indus-

tries such as preparation of benzidine, hydrosulphite and rongalite, and

also in metallurgical industries such as production of precious metals

e.g., gold and silver by application of cementation process, in addition

to purifying zinc electrolytic baths. Moreover, it can be used for the pro-duction of amalgam alloy which is used in dental llings. It can be used

in differentapplicationsin electronic industriesas well. Zinc powdercan

be also used as paint for a heavy-duty coating for large-scale structures

such as offshore oil rigs, seacontainers andother marineequipment and

bridges. Besides, it is used in alkaline batteries, rocketfuel and cosmetics

(Shariet al., 2009).

The main aim of this research work is to study, experimentally, theef-

fect of different parameters on the packed bed electrolysis of the zinc

anode casing of the spent dry cell secondary batteries to produce electro-

lytic zinc powders (see owchart inFig. 2). The studied parameters are

electrolyte temperature, electrolyte stirring rate, current density, the ma-

terial of anode basket (graphite or titanium), and the state of the electro-

lyte (new or old). To accomplish this target, the zinc anode casing of the

spent batteries was separated from both internal cathode materials (car-bon and MnO2) and from the external plastic covers. Zinc casing sheets

were placed in an anode basket, which acts as the carrier and the current

feeder to the anode particles in the employed electrolytic cell. Two stain-

less steel sheets used as starting cathodes together with anode basket

were put in an electrolytic cell containing 230 g/L NaOH as a basic electro-

lytic solution. Theused materialsandtheproduced powderswere charac-

terized using XRD, XRF, and SEM analyzers.

2. Experimental details

2.1. Materials

Spent zinc batteries were broken and separated from the external

papers and non-zinc metal protecting covers. Zinc anode casing sheet

was separated from the internal paste material in the battery, cut to

smaller sizes by shredder and washed with distilled water. Zinc sheets

in the size range of 2030 mm length, 1020 mm width and 1 mm

Fig. 1. Schematic diagramof a typicalzinccarbonbattery cross section(Shin etal.,2009).

Fig. 2. Flowchart of production of electrolytic zincpowder from spent secondary batteries.

Fig. 3.Casing of secondary batteries as zinc anode sheets.

61A. Owais et al. / Hydrometallurgy 157 (2015) 6071


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thickness (Fig. 3) were put in an anodebasket made from graphite or ti-

tanium and employed as the anode in the electrolytic cell. The different

components contained in the casing sheets before the experiments

were examined by X-ray uorescence (XRF) (Rigaku XRF-NEXCG,

Japan) and illustrated inTable 1. The phases which exist in these zinc

sheets were examined by X-ray diffractometer (XRD-6100, Shimadzu,

Japan) and are presented inFig. 4. A sodium hydroxide salt was dis-

solved in a distilled water to give 230 g/L and used as an electrolyte in

the electrolytic cell (Calusaru, 1979).

2.2. Experimental apparatus and procedure

The sketch of the bench scale experimental setup used for the elec-

trolysis experiments is shown inFig. 5, while the actual view of the dif-

ferent applied devices is illustrated inFig. 6-a. Zinc anode sheets were

put in a graphite or a titanium basket, which has the dimension of

100 mm width, 100 mm active height, and 50 or 30 mm thickness re-

spectively with 5 mm net openings average size (Fig. 6-b and -c). Two

stainless steel sheets with the dimensions of 100 mm width, 100 mm

active height and 3 mm thickness were used as permanent cathodes.

Both anode baskets lled with zinc sheets and stainless steel cathode

sheets were inserted in a 5 L beaker glass, which was lled with the pre-

viously prepared NaOH basic electrolyte. The alkaline electrolytes aremore appropriate than acidic electrolytes. The energy consumption of

an acid process is about 35% of the cost of zinc powder production

(Habashi, 1991; Shariet al., 2009), whereas the alkaline process con-

sumes less energy due to the lower overpotential. Alkaline processes

are also friendlier to the environment because they avoid the problem

of iron dissolution and removal as jarosite in the acid processes (Lee

and Piron, 1997). The electrodes were suspended in the cell with an

anode/cathodeseparating distance of 25 mm. A hot plate with magnetic

stirrer (KRH basic IKA LABORTECHNIK, Germany) was used for

heating up and stirring the electrolyte. The direct current was supplied

to the electrodes by a power supply (GW Instek, DC Power supply

sps-1820, Taiwan). The output cell voltage was directly recorded to

the computer using digital multimeter VA18B with PC-Link computer

software.

The electrodeposited powders were extensively washed in distilled

water, dried in a vacuum drying oven (JSR, JSVO-30T, Korea) in an

argon gas as inert atmosphere to avoid the oxidation of the produced

powder, then weighed, and nally characterized using XRF, XRD, scan-

ning electron microscopy (SEM) (JEOL JSM-6360LA, Japan) and particle

size analyzer (Malvern mastersizer 2000, UK) equipped with Hydro

2000SM unit.

Table 1

XRF analysis of zinc anode casing.

Components Zn Pb Cd Fe Cu Sn Hg Ni Tc

Wt.% 99.000 0.7960 0.0597 0.0274 0.0166 0.0111 0.0198 0.0119 0.0170

Fig. 4.XRD analysis of zinc casing anode sheets.

Fig. 5.Sketch of bench scale experimental setup. 1 Hot plate with magnetic stirrer, 2

rotating sh, 3 stainless steel sheet 1 (), 4 anode basketlledwith zinccasing(+),

5 stand & cell cover, 6 thermometer, and 7 stainless steel sheet 2 ().

62 A. Owais et al. / Hydrometallurgy 157 (2015) 6071


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3. Results and discussion

Differentfactors were extensively studied to show their effecton the

electrolysis of zinc anode casing of spent secondary batteries to obtain

electrolytic zinc powder using a basic electrolyte solution containing

230 g/L NaOH. The main factors studied are electrolyte temperature

(3050 C), electrolyte stirring rate (250350 rpm), current density

(5001000 A/m2), the material of the anode basket (graphite or titani-

um), and the state of the electrolyte (old or new). Fresh (new) electro-

lyte solutions were used in all experiments (Sections 3.13.4) while old

and fresh (new) solutions were used when the state of the electrolyte

(old or fresh) was investigated (Section 3.5).

3.1. Effect of electrolyte temperature

From theresults shown in Figs. 7 and 8, it isobviousthat theincrease

of electrolyte temperature from 30 to 50 C has a positive effect on all

parameters of theelectrolysis process. Boththe anodicand cathodic cur-rent efciencies and powder productivity were increased from 88.88%

to 95.80% and from 78.21% to 89.98% and from 0.948 to 1.091 g/Ah re-

spectively, while the specic energy demand was decreased from 2.52

to 2.10 kWh/kg Zn. This can be due to the increase of dissolution rate

of zinc anode particles (Ren et al., 2010) which cause a good feeding

of the zinc ions to the electrolyte bulk solution (Zn Zn2+ + 2e)

and also due to theincrease of the diffusion rate of zinc ions in theelec-

trolyte bath, where the viscosity of the electrolyte is decreased with in-

creasing the electrolyte temperature (Owais, 2009; Sadiku-Agboola

et al., 2011). This is beside the enhancement of the reduction reac-

tion rate of zinc ions at the cathode surface to produce zinc metal

(Zn2+ + 2e Zn). Moreover, increasing the temperature has a

good effect on the electrolyte conductivity which decreases the

cell voltage and consequently decreases the specic energy demand.

This helps the electrolysis process to be more effective from the cost

point of view as well.

SEM micrographs of the electrodepositedzinc powderare illustrated

inFig. 9and indicated that the deposited powders are in a dispersive

shape while the ner particle size was obtained with powders which

electrodeposited at 30 C as shown inFig. 10. A low temperature is an-

ticipated to promote grain renement. A decrease in the temperature is

expected to result in a higher overpotential, which should increase the

nucleation rate (Youcai et al., 2013).

The apparent density of the deposited powders was increased with

increasing the temperature of the electrolyte as shown inFig. 11. Theapparent density is a function of particle shape, particle size distribu-

tion, particle arrangement and the degree of particles porosity (Angelo

and Subramanian, 2008). The apparent density decreases with decreas-

ing particle size and with increasing surface roughness. An increase in

the irregularity and porous texture of the powder grain decreases the

apparent density.

Fig. 6. Views of theused electrolytic cell(a),the Ti anode basketlledwithzinc sheets (b)and thegraphite anode basket(c).1 Hotplatewithmagnetic stirrer,2 a 5 L backerglasslled

with 3 L electrolyte, 3 Ti anode basket, 4 digital multimeter connected to laptop, 5 two stainless steel cathode sheets, and 6 DC supplier.

Fig. 7.Cell voltage against duration of the electrolysis of zinc anode casing of spent zinc

carbon type batteries in a graphite basket at different electrolyte temperatures, (1000 A/

m2

, 250 rpm). Fig. 8.Effect of electrolyte temperature on different electrolysis parameters.



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3.2. Effect of electrolyte stirring rate

As shown in Figs. 12 and 13, it is cleared that theincrease of electro-

lyte stirring rate has a good effect on both anodic and cathodic current

efciencies, and also powder productivity when the stirring rate is in-

creased from 250 to 300 rpm; while a further increase of the rate from

300 to 350 rpmhas a bad effect on all parameters instead of anodic cur-

rent efciency. The former case can be due to theincrease of both disso-

lution rate of zinc anode particlesand diffusionrate of zinc ions from the

anode surface to the cathode area; which consequently increase the

amount of the electrodeposited zinc metal. The latter case can be attrib-

uted to some zinc particles washed away from the stainless steel

cathodes because of turbulent ow in the bath (Bansal et al., 2011;

Ghorbani et al., 2001). So the moderate stirring rate of 300 rpm is the

best rate which can be used effectively. On the other side, the increasing

of electrolyte stirring rate causes a decrease in the specic energy de-

mand from 2.105 to 1.638 kWh/kg. This can be due to the decrease in

the average cell voltage from 2.333 V to 1.60 V which resulted from

the decrease of the electrical resistance of the electrolyte with increas-

ing the electrolyte stirring rate.

As shown from SEM micrographs in Fig. 14, the shape and sizeof the

deposited powders were strongly affected by the electrolyte stirring.

Nanorods from zinc powders appeared when high stirring rate of

350 rpm was applied (Fig. 14-d). The size of the deposited powders issignicantly inuenced by stirring rate as shown inFig. 15.The use of

bath stirring (300 rpm) is intended to improve the mass transport in

the electrolyte and therefore enhance the rate of deposition and nucle-

ation results inne particles. However, further increase of the stirring

rate (350 rpm) led to a reduction of the cathodic current efciency.

Since the main reactions at the cathode during electrodeposition is a

competition between zinc reduction and hydrogen evolution, as the

limiting current density is approached during zinc deposition, the zinc

ion concentration near the cathode is quickly depleted and the cathode

reaction shifts from zinc deposition to hydrogen evolution (Rajkumar

and Alagar, 2014; Tuaweri et al., 2013). An improvement in cathode cur-

rent efciency with stirring (at 300 rpm) helps to prevent the adsorp-

tion of evolved hydrogen, which regularly sits on the surface of the

cathode The deposition of a mixture of zinc and zinc hydroxide or zinc

oxide results in a pH increase in the vicinity of the cathode and also

the stirring could depolarize the hydrogen evolution reaction and possi-

bly reduce thenucleation rate of zinc on the surface of the cathode. This

means, stirring rate may have been inauspicious to the zinc nucleation

process conditions. The highest apparent density was obtained at

300 rpm as shown inFig. 16.

Fig. 9. SEM micrographsof the deposited zincpowders from electrolysis of zincanode casing of secondary batteries at 1000 A/m2 and 250rpm (magnication 200),(a) 30C, (b)40 C,

and (c) 50 C.

Fig. 10. Effect of electrolyte temperature on particle size distribution of the electrodeposited

zinc powder in a graphite basket.

Fig. 11.Effect of electrolyte temperature on the apparent density of the electrodeposited


Fig. 12.Cell voltage against duration of the electrolysis of zinc anode casing of spent

zinc carbon type batteries in a graphite basket at different electrolyte stirring rates,

(1000 A/m2

, 50 C).



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Fig. 13.Effect of electrolyte stirring rate on different electrolysis parameters.

Fig. 14.SEM micrographs of the deposited zinc powders from electrolysis of zinc anode casing of secondary batteries at 1000 A/m2 and 50 C, (a) 250 rpm, (b) 300 rpm, (c) 350 rpm at

magnication 200, and (d) 350 rpm at magnication 15000.

Fig. 15. Effect of electrolytestirring rate on particlesize distribution of the electrodeposit-

ed zinc powder in a graphite basket.

Fig. 16.Effect of electrolyte stirring rate on the apparent density of the electrodeposited




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3.3. Effect of current density

A sharp difference wasobserved between the cell voltages of the dif-ferent experiments carried out at different current densities (Fig. 17).

The lowest current density at 500 A/m2 showed a lower cell voltage

(0.710 V) while that at 1000 A/m2 showed a higher value of 1.990 V.

This can be interpreted from Ohm's law (V = I R), where a direct pro-

portional effect between voltage (V) & current (I) is taken place. From

Fig. 18, it is cleared that, the increase of current density from 500 to

1000 A/m2 hasa positive effecton cathodic current efciency (increased

from 74.23% to 94.85%), anodic current efciency (increased from 78.35%to 96.91%) and powder productivity (increased from 0.900 g/Ah to

1.150 g/Ah). These results are in agreement with those ofChaim

et al. (1994),Shariet al. (2009)and Diggle et al. (1973). This can


carbon type batteries in a graphite basket at different current densities, (300 rpm, 50 C).

Fig. 18.Effect of current density on different electrolysis parameters.

Fig. 20.Effect of current density on particle size distribution of the electrodeposited zinc

powder in a graphite basket: a) 500, b) 750 and c) 1000 A/m2.

Fig. 19. SEMmicrographs of thedeposited zinc powders from electrolysisof zinc anode casingof secondary batteriesat 300 rpm and50 C (magnication 200),(a) 500A/m2, (b) 750 A/m2,

and (c) 1000 A/m2

.



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be attributed to the increase of the deposition rate of zinc powder onthe cathode surface when the current density is higher, and no fear

from the passivation of zinc anode particles at the higher current

densities as happened in electrolysis of the other nonferrous metals,

like Cu which passivated strongly when a higher current density is

applied.

The effect of increasing current density on the specic energy re-

quired for the electrolysis process showed that the highest value is

1.771 g/Ah when the highest current density at 1000 A/m2 is applied.

This can be attributed to the increase of cell voltage at higher current

density and consequently the increase of the calculated energydemand.

From the previous obtained results, it is concluded that the application

of higher current densities is favorable and higher values more than1000 A/m2 must be studied extensively to obtain the best current

density which give the best results of the process parameters.

SEM micrographs of the electrodeposited powders (Fig. 19) indicat-

ed that, zinc powders with dispersed shape were obtained at low and

high values of current density while at a moderate value (750 A/m2),

a dendritic shape was formed. Particle size distribution analysis was

performed to gain further knowledge of the dependence of ultrane

powder electrowinningon current density. The particle size distribution

depending on the current density was shown inFig. 20. The deposit

powder obtained during zinc electrowinning in NaOH solution de-

creases considerably the real current density as a consequence of the

large increase in surface area. As a result, the cathodic overpotential is

also decreased (St-Pierre and Piron 1990). In other words, the number

of smaller particles present in the mixture increased with increasing

current density. This observation may be explained by the easy forma-

tion of stable nuclei due to a large number of ions discharged in the

cathode. The hydrogen evolution overpotential on the cathode also is

high when the current density is high, favoring the discharge of the

zinc ions (Guillaume et al., 2007; Hewaidy et al., 1979; Youcai et al.,

2013). The apparent density of the deposited powders was increased

gradually with increasing current density as shown inFig. 21.

3.4. Effect of the material of anode basket

Asshown in Fig. 22, thecell voltage of theelectrolysis process carried

out in a titanium basket is lower than that which was carried out in a

graphite basket, because the electrical conductivity of the titanium

metal is better than that of graphite. Fig. 23 shows the effect of bothbas-

ket materials on the different process parameters and indicates that thegraphite basket is better than titanium for the all process parameters in-

stead of thespecic energy demand which is better when titanium bas-

ket was used. The big process problem when the titanium basket is

Fig. 21.Effect of current density on the apparent density of the electrodeposited zinc

powder in a graphite basket.


carbon type batteries in different anode basket materials, (1000 A/m2, 300 rpm, 50 C).

Fig. 23.Effect of anode basket material on different electrolysis parameters.



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utilized is its serious corrosion at the applied experimental conditions.

This of course will lower the age of the basket beside its bad effect on

thepurity of the electrolyte solution after a long period of the electroly-

sis process, due to the gradual accumulation of titanium ions in the so-

lution, which consequently will cause a contamination of the deposited

zinc powder due to its penetration in the deposited powders.

When graphite and/or titanium baskets were used, the electrode-

posited powders showed a dispersive shape as indicated from SEM mi-

crographs which presented inFig. 24with a somewhat ner particle

size when titanium basket was utilized as indicated from the size ana-

lyzer curves inFig. 25. The deposited powders have a higher apparent

density when graphite basket was used (Fig. 26).

3.5. Effect of the electrolyte state

To study the possibility of re-application of the pre-used electrolyte

in the electrolysis process or the reproducibility of the electrolyte, two

different age electrolytes (new and/or old) were tested and the resulted

electrolysis curves were illustrated inFig. 27. It was observed that, the

cell voltage of the electrolysis process is higher when a new electrolyte

is utilized in the electrolytic cell. The effect of the age of the electrolyte

solution on the different process parameters was illustrated inFig. 28and showed that the pre-used old electrolyte for 3 h is better for all pa-

rameters compared to the anodic current efciency which showed a

lower value. This can be due to the accumulation of zinc ions in the

pre-used electrolyte from the previous experiments and also due to

the change in the concentration of NaOH in the electrolyte solution.

The rise of anodic current efciency with new electrolyte may be due

to the utilization of a fresh solution which is empty from any previous

concentration of zinc ions and causes a good dissolution of anode parti-

cles, beside an effective diffusion of zinc ions in the electrolyte bulk so-

lution. Further experiments should be done extensively to show the

effect of the initial concentrations of both NaOH and zinc ions on the

electrolysis process.

The microstructure of the deposited zinc powders in an old or new

electrolyte is illustrated inFig. 29and indicated that dispersive zinc

powders were obtained in old electrolyte while nanorod shape powders

were obtained in new electrolyte with a ner particle size as shown

in Fig. 30. The apparent density of theproduced powders in an old elec-

trolyte is higher than that which obtained from a fresh electrolyte as

shown inFig. 31.

Fig. 24. SEM micrographsof thedeposited zincpowders from electrolysis of zincanode casing of secondary batteries at 1000 A/m2, 300 rpm and 50C (magnication 200),(a) graphite

basket, and (b) titanium basket.

Fig. 25. Effectof an anode basket material on theparticle size distributionof theelectrode-

posited zinc powder: a) graphite basket and b) titanium basket.

Fig. 26.Effect of anode basket material on the apparent density of the electrodeposited

zinc powder.


carbon type batteries in different electrolyte states in a titanium basket, (1000 A/m2,

300 rpm, 50 C).



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XRFanalyses of the electrodeposited zinc powders from both graph-

ite and/or titanium baskets are illustrated inTable 2and indicate that

zinc powders with an average composition of about 99.8% Zn were ob-

tained during the electrolysis process. The deposited powders were

contaminated with about 0.0053% Ti when the titanium anode basket

was utilized. The source of titanium in the produced powders can be

due to the serious corrosion of the basket and entrapment of the dis-

solvedTi ions to thedepositedzinc powders. This value canbe increased

over a long period of electrolysis process. The severe corrosion of the

Fig. 28.Effect of the electrolyte state on different electrolysis parameters.

Fig. 29. SEMmicrographsof the deposited zincpowders from electrolysis of zincanodecasingof secondary batteries in a titanium basket at 1000 A/m2, 300 rpm and 50C (magnication

15000), (a) old electrolyte, and (b) new electrolyte.

Fig. 30.Effect of the electrolyte state on the particle size distribution of the electrodepos-

ited zinc powder in a titanium basket: a) old electrolyte and b) new electrolyte.

Fig. 31.Effect of electrolyte state on the apparent density of the electrodeposited zinc

powder in a titanium basket.



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titanium basket causes also a rapid failure of the basket beside a lot of

money losses.The produced zinc phase appeared in XRD analysis as shown in

Fig. 32is in the metallic form without any zinc oxides. This can be due

to the utilization of an inert gas drying furnace for drying the produced

powders.

4. Conclusions

Packed bed electrolysis process was successfully applied on zinc

anode casing of secondary dry cell batteries to produce high quality

electrolytic zinc powders (about 99.8% Zn). The following conclusions

can be drawn from this investigation:

1. The produced zinc powders have different shapes (nanorods, den-

dritic and/or dispersive), different sizes and different densities(from 1203.1 to 2085.2 kg/m3) depending on the applied process

conditions.

2. The graphite basket was more efcient than titanium one in terms of

all the studied parameters including; cathodic and anodic current ef-

ciencies and powder productivity, except for the specic energy de-

mand due to the better electrical conductivity of the titanium basket.

3. The process is enhanced by increasing both the current density, elec-

trolyte temperature, electrolyte stirring rate (up to 300 rpm) and

when an old electrolyte was utilized.

4. The proposed electrolysis process is a promising recycling technique

since it was carried out withcathodic current efciency up to 94.85%,

anodic current efciency up to 98.97% and specic electrical energy

demand in the range from 0.808 to 2.518 kWh/kg Zn with powder

productivity up to 1.150 g/A.h.

Acknowledgments

The authors would like to thank Eng. Alaa Dardeir (Department of

Metallurgical and Materials Engineering, Faculty of Petroleum and

Mining Engineering, Suez University) for his assistance in conducting

the experimental work.

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Table 2

XRF analysis of the deposited Zn powder.

Component Zn Pb Cd Fe Sn Tc Ni Ti

Wt.%, in a graphite basket 99.8000 0.0895 0.0139 0.0460 0.0240 0.0142 0.0147

Wt.%, in a titanium basket 99.8000 0.0912 0.0073 0.0288 0.0235 0.0186 0.0151 0.0053

Fig. 32.XRD analysis of the electrodeposited Zn powder.

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la producción de polvo de zinc electrolítico de zinc carcasa del Ánodo de pilas secas gastados

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