**2. Features of Zn-MnO2 batteries**

For these reasons in several countries, collecting batteries is becoming mandatory, and so is recycling those containing toxic materials. Recycling may also be applied to recovering

There are basically two types of household batteries: primary batteries that after becoming worn are discarded and the secondary batteries that can be recharged [12, 13]. Within the wide range of commercially available batteries zinc-carbon batteries (also known as Leclenché or dry cells) and alkaline batteries are the most consumed because of its low cost. In Europe, from the total of batteries sold in 2003, 30.5% and 60.3%, were Zn-C batteries and alkaline batteries, respectively. In China are produced annually more than 15 billion of these devices and in Brazil

The disposal of these batteries is a serious problem, because in their composition there are metals considered dangerous to the environment [13]. The cost for the safe disposal of these materials is quite high due to the large amount of dangerous waste generated and due to the fact that the storage capacity in landfills or dumps is running out. A policy adopted in 2006 by the European Union (EU) banned incineration and disposal of batteries in landfills. This regulation applies to all types of batteries regardless of shape, volume, weight, composition or use. Through this new policy it is expected to mobilize the EU countries member for the collection, recovery and recycling of metals present in these power devices [15]. In Brazil, according to the resolution 401/2008 of the *Brazilian National Council of the Environment* (CONAMA in Portuguese) [16], after consumption, household batteries must be collected and sent to the manufacturers, to be recycled, treated or disposed of an environmentally safe way, but until 1999 they could be disposed of in household waste since meet the limits of heavy metals in its composition. Although required, this resolution proved to be insufficient to solve the problem of environmental contamination by means of this waste since there is a large annual consumption of these batteries. A factor to be noted is that in spite of Zn and Mn match most of the composition of cells Zn-MnO2, the limits of contamination of these metals are not established by law. Another aggravating factor is the use of irregular cells entering the Brazilian market. Frequently these products do not meet manufacturing standards. The heavy metal content of these cells is seven times greater than that limited established by the CON‐ AMA. Thus, the contamination starts by improper disposal of these devices in landfills or dumps, which is the destination of the majority of household solid waste in Brazil [13,16, 17].

Industrial recycling of batteries is generally focused on two processes: the pyrometallurgical and/or the hydrometallurgical. The pyrometallurgical method is based on the difference of volatilization of different metals at high temperatures followed by condensation. The hydro‐ metallurgical method is based on the dissolution of metals in acidic or alkaline solutions. The advantage of the first method is the absence of the necessity of dismantlement of the devices. However, it is an expensive process, since it requires high temperatures and is not efficient selectively, for example, to obtain pure zinc from Zn-MnO2 batteries, Ni-Cd batteries cannot be treated simultaneously because the Zn and Cd are not selectively volatized in the oven, so sorting steps are required in advance of the materials recycling. Another drawback is related to the production of dust and gas emission into the atmosphere during the recycling process. The hydrometallurgical route is usually more economical and efficient than the pyrometal‐

estimating a consumption of six batteries per inhabitant per year [7, 8, 14].

valuable materials to be reutilized [11].

210 Modern Surface Engineering Treatments

Zn-C (also known as Leclanché or Zn-MnO2 Batteries) batteries and alkaline batteries are basically composed by potassium, manganese and zinc as metal species. The stack of Zn-C was invented in 1860 by George Leclanché and the devices currently used are very similar to the original version.

A schematic view of this type of batteries is showed in Figure 1. In these batteries the anode consists of a zinc metal cylinder used, usually in the form of plate to procedure the outside structure of the cell. The cathode consists of a graphite rod surrounded by a powder mixture of graphite and manganese dioxide. The electrolyte is a mixture of ammonium chloride and zinc chloride. During the Zn-C and alkaline batteries discharge, basically the following reactions are observed:

Zinc oxidation at anode:

$$\text{Zn} + 2\text{NH}\_4\text{Cl} + 2\text{OH}^\cdot \rightarrow \text{Zn} \text{(NH}\_3\text{)}\_2\text{Cl}\_2 + 2\text{H}\_2\text{O} + 2\text{ e}^\cdot \tag{1}$$

Manganese reduction at cathode:

$$2\text{MnO}\_2 + 2\text{H}\_2\text{O} + 2\text{e}^\cdot \rightarrow 2\text{OH}^\cdot + 2\text{MnOOH} \tag{2}$$

Resulting in the overall reaction:

$$\text{Zn} + 2\text{MnO}\_2 + 2\text{NH}\_4\text{Cl} \rightarrow \text{Zn} \left(\text{NH}\_3\right)\_2\text{Cl}\_2 + 2\text{MnOOH} \tag{3}$$

In this kind of batteries, during storage and in rest periods while operating some parallel reactions can occur, causing leaks and loss of efficiency. In this way, some metals such as Cd,

**Figure 1.** Schematic View of the Zn-MnO2 Battery (Leclanché Device)

Cr, Hg and Pb are added to these devices to improve their performance and to avoid these parallel reactions.

The alkaline battery is a modified version of the stack of Zn-C. It features the same electrodes (anode and cathode), however, the electrolyte is a concentrated potassium hydroxide folder containing zinc oxide. Another difference is that its outer part is made on steel plate for assuring better seal. The reactions that occur in the cathode during discharge are the same that occurs in the Zn-C batteries, but the anodic reactions are different:

Zinc oxidation at alkaline batteries anode:

$$\text{Zn} + 2\text{OH}^{\cdot} \rightarrow \text{Zn}(\text{OH})\_2 + 2\text{e}^{\cdot} \tag{4}$$

saved and the pollution is also reduced as the chemical treatment of primary metals is not needed. Manganese and zinc are important metals in many fields. Zinc is the most important nonferrous metal after copper and aluminum [23] and of the total zinc consumption, 55% is used to cover other metals to prevent oxidation, 21% in zinc-based alloys, 16% in brass and bronze. The increase of zinc demand in 2010 was due to a revival of the consumption in Europe (24%) and also to the consolidated economic growth of the emerging economies like Brazil, India and most notably China where the consumption increased 11% respect to 2009. Most of consumption of manganese is related to steel production, directly in pig iron manufacture and in the ferroalloy industry. Manganese resources are large but irregularly widespread in the world and South Africa and Ukraine account for about 75% and 10 % of the word´s identified

*Zn-C* [23] *and*<sup>d</sup>*Zn-C* [21].

**A2b** *% in weight\**

Zn 21 20,56 5 5,05 Mn 45 26,60 23-30 29,04 Fe 0,36 0,15 0,2-10 0,18 Hg 1 (ppm) 0,0012 - - Cd 0,06(ppm) 0,0007 - 0,0002 Pb 0,03 0,005 - - Ni - 0,008 0,007 0,006 K 4,7 7,3 - -

Electrodeposition of Alloys Coatings from Electrolytic Baths Prepared by Recovery of Exhausted Batteries for…

**B1c** *% in weight\**

**B2d** *% in weight\** 213

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Due to the growing interest in global environmental issues, recycling of Zn–Mn batteries carried more attentions and was reviewed in detail recently [15]. As the most widely used hydrometallurgical process, acid leaching was frequently used to release both Zn and Mn from the spent Zn–Mn batteries in the presence of strong acid solution such as H2SO4, HCl, HNO3 and so on. In most cases, acid leaching produce nearly 100% of Zn extraction from the spent batteries, but Mn dissolution was rather poor due to insoluble MnO2; moreover, the heavy consumption of various strong acids endowed the leaching process with high cost, strict requirements of equipment and potentially safe risk. The reductive acidic leaching could greatly improve extraction yield of Mn by adding inorganic reductants such as H2O2 and SO2 or organic ones such as glucose, sucrose, lactose, oxalic acid, citric acid, tartaric acid, formic acid and triethanolamine, but higher safety risk and greater operation cost occurred [15]. So, developing the environmentally-friendly and cost-effective recycling methods for the spent Zn–Mn batteries are encouraged. At present, biohydrometallurgical processes (bioleaching-

manganese resources respectively [24].

**Metal**

a

**A1a** *% in weight\**

\* (% in weight of the electrolytic paste)

**Table 1.** Composition of Zn-MnO2 and Alkaline Cells.

*Alkaline* [23]; b*Alkaline* [22]; c

Resulting in the overall reaction:

$$\text{Zn} + 2\text{MnO}\_2 + 2\text{H}\_2\text{O} \rightarrow \text{Zn(OH)}\_2 + 2\text{MnOOH} \tag{5}$$

The advantage of the alkaline batteries is that they do not have parallel reactions and can be stored for up to four years keeping more than 80% of their original capacity, additionally its lifetime is up to ten times higher, however they are on average five times more expensive. Alkaline batteries are placed on the market as "mercury-free", however the literature reports that in several works on recycling of batteries were found heavy metals in these devices, including mercury [19-23]. The composition of some alkaline batteries and Zn-C are given in Table 1.

These portable batteries (alkaline and Zn–C) contain Mn and Zn in high concentrations. Considering that the production of these kind of power device are increasing it has become important the usage of recycled metals production instead of primary metals. Besides the positive impact on the environment, in the recuperation process of materials lot of energy is Electrodeposition of Alloys Coatings from Electrolytic Baths Prepared by Recovery of Exhausted Batteries for… http://dx.doi.org/10.5772/56438 213


**Table 1.** Composition of Zn-MnO2 and Alkaline Cells.

Cr, Hg and Pb are added to these devices to improve their performance and to avoid these

The alkaline battery is a modified version of the stack of Zn-C. It features the same electrodes (anode and cathode), however, the electrolyte is a concentrated potassium hydroxide folder containing zinc oxide. Another difference is that its outer part is made on steel plate for assuring better seal. The reactions that occur in the cathode during discharge are the same that

( ) - -

The advantage of the alkaline batteries is that they do not have parallel reactions and can be stored for up to four years keeping more than 80% of their original capacity, additionally its lifetime is up to ten times higher, however they are on average five times more expensive. Alkaline batteries are placed on the market as "mercury-free", however the literature reports that in several works on recycling of batteries were found heavy metals in these devices, including mercury [19-23]. The composition of some alkaline batteries and Zn-C are given in

These portable batteries (alkaline and Zn–C) contain Mn and Zn in high concentrations. Considering that the production of these kind of power device are increasing it has become important the usage of recycled metals production instead of primary metals. Besides the positive impact on the environment, in the recuperation process of materials lot of energy is

<sup>2</sup> Zn + 2OH Zn OH + 2e ® (4)

**Grafite Rod** 

**Electrolytic Paste** 

( ) 2 2 <sup>2</sup> Zn + 2MnO + 2H O Zn OH + 2MnOOH ® (5)

occurs in the Zn-C batteries, but the anodic reactions are different:

**Zinc Anode** 

**Figure 1.** Schematic View of the Zn-MnO2 Battery (Leclanché Device)

**Separator** 

Zinc oxidation at alkaline batteries anode:

Resulting in the overall reaction:

Table 1.

parallel reactions.

212 Modern Surface Engineering Treatments

saved and the pollution is also reduced as the chemical treatment of primary metals is not needed. Manganese and zinc are important metals in many fields. Zinc is the most important nonferrous metal after copper and aluminum [23] and of the total zinc consumption, 55% is used to cover other metals to prevent oxidation, 21% in zinc-based alloys, 16% in brass and bronze. The increase of zinc demand in 2010 was due to a revival of the consumption in Europe (24%) and also to the consolidated economic growth of the emerging economies like Brazil, India and most notably China where the consumption increased 11% respect to 2009. Most of consumption of manganese is related to steel production, directly in pig iron manufacture and in the ferroalloy industry. Manganese resources are large but irregularly widespread in the world and South Africa and Ukraine account for about 75% and 10 % of the word´s identified manganese resources respectively [24].

Due to the growing interest in global environmental issues, recycling of Zn–Mn batteries carried more attentions and was reviewed in detail recently [15]. As the most widely used hydrometallurgical process, acid leaching was frequently used to release both Zn and Mn from the spent Zn–Mn batteries in the presence of strong acid solution such as H2SO4, HCl, HNO3 and so on. In most cases, acid leaching produce nearly 100% of Zn extraction from the spent batteries, but Mn dissolution was rather poor due to insoluble MnO2; moreover, the heavy consumption of various strong acids endowed the leaching process with high cost, strict requirements of equipment and potentially safe risk. The reductive acidic leaching could greatly improve extraction yield of Mn by adding inorganic reductants such as H2O2 and SO2 or organic ones such as glucose, sucrose, lactose, oxalic acid, citric acid, tartaric acid, formic acid and triethanolamine, but higher safety risk and greater operation cost occurred [15]. So, developing the environmentally-friendly and cost-effective recycling methods for the spent Zn–Mn batteries are encouraged. At present, biohydrometallurgical processes (bioleachingtech) have been gradually replacing hydrometallurgical ones due to their higher efficiency, lower cost and few industrial requirements [25]. Bioleaching was characterized by efficient release of metals from solid phase into aqueous solution under the mild conditions of room temperature and pressure by contact and/or non-contact mechanisms in the presence of acidophilic sulfur-oxidizing and/or iron-oxidizing bacteria [26, 27].

concentration of the solution. Table 2 shows the typical composition obtained by an acid leaching with diluted HCl, of the carbon paste obtained from Zn-C spent batteries manufac‐ tured in Brazil [28]. This quantitative analysis of the metal content was performed by atomic absorption spectrometry and indicated that in addition to Zn2+ and Mn2+ traces of other species

Electrodeposition of Alloys Coatings from Electrolytic Baths Prepared by Recovery of Exhausted Batteries for…

**Metal Concentration (mg L-1) Metal Concentration (mg L-1)**

It could be seen from the Table above that the batteries used containing Pb as heavy metal in their composition, however this quantity found corresponds to 0.18% by weight of the battery electrolytic paste that was in agreement with the limits established by CONOMA (0.20%). To prepare the electrolytic bath from this solution the pH is adjusted to 5.0. During this step occurs the hydrolysis of some metallic ions forming a gelatinous brown material, possibly due to the formation of iron hydroxide that was removed by filtration. From this filtrated solution it was prepared four electrolytic baths used in obtaining the Zn-Mn alloy coatings. These baths were prepared to the addition of boric acid and different quantities of additives (ammonium

Zn 6,981.33 Pb 55 Mn 3,030.30 Cr 0 Cu 30.4 Ag 0 Fe 5.5 Ni 0

**Table 2.** Composition of the Electrolytic Bath Obtained from Recycling of Zn-C Batteries.

isocyanate - NH4SCN and polyethylene glycol – PEG10.000) as showed in Table 3.

S1 1 g L-1 - S2 - 6.5 mmol L-1 S3 1 g L-1 6.5 mmol L-1

0.10 mol L-1 0.06 mol L-1

**Bath Name Zn Mn PEG10.000 NH4SCN H3BO3**

**Table 3.** Composition of the Obtained Electrolytic Bath through Recycling of Cells Used to Obtain Mn-Zn Alloys.

The behavior of AISI 1018 carbon steel electrodes in the presence of the electrolytic baths prepared from recycled batteries could be investigated by measurements of cyclic voltamme‐ try. The Figure 2 shows the voltammetric curves obtained on 1018 carbon steel immersed in the proposed electrolytic baths (see Table 3). It could be seen from Figure 2a that with no additive on the bath the voltammogram showed two regions of reduction. The first region present a peak current with maximum current in -1.4 V and is related to the electrodeposition of zinc on the electrode. The second region present a continuous increase on reduction current starting on E = -1.5 V, this region can be related to the formation of Mn-Zn alloy, but tis increase


0.32 mol L-1

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215

such as Fe2+, Cu2+ and Pb2+ were present in solution.

S0

Another alternative method developed for Zn-Mn batteries recycling is the electrodeposition of Zn and Zn–Mn alloy coatings over different kinds of steel to corrosion protection [28, 29]. Electrodeposited coatings of zinc are extensively employed in the protection of steel against corrosion. However, this protective effect is not very effective under aggressive atmospheric conditions [30]. In recent years, several materials have been investigated to improve the durability of these coatings. Electrodeposited alloys of Zn, such as Zn–Ni, Zn–Co and Zn–Fe, present higher corrosion resistance than pure zinc coatings. Also, it has been reported in the literature that Zn–Mn alloys show even better corrosion resistance properties [31–34]. The high corrosion resistance of these alloys is likely due to the dual protective effect of manganese: on the one hand Mn dissolves first because it is thermodynamically less noble than Zn, thereby protecting Zn; and on the other hand Mn ensures the formation of compounds with a low solubility product over the galvanic coating. Depending on the aggressivity of the environment to which the Zn–Mn alloy is exposed, various compounds may be found in the passive layer, including oxides such as MnO, MnO2, Mn5O8 and *γ−*Mn2O3, or basic salts like Zn4(OH)6SO4.*x*H2O and Zn5(OH)8Cl.2H2O [31, 35, 36]. The protective effect of Zn–Mn is dependent on the Mn content of the alloy. Although it has been reported that among the Zn alloys those of Zn–Mn show the highest corrosion resistance, their deposition process presents some drawbacks related to the bath instability and current efficiency. Among the various electrolytic baths and additives proposed to obtain Zn–Mn alloys, the use of a chloride-based acid bath with polyethylene glycol (PEG) as the additive seems very promising [31–33].

The mainly practical application in produce a protective Zn-Mn layer over steel is related to the substitution of the primary painting process on metallic parts produced in foundries. Furthermore it is important to note that beside the great interest in recycling Zn-C batteries the use solution produced by the acidic leaching of these exhausted batteries to obtaining protective Zn-Mn films were described only in two papers[28,29].

Considering the concepts described above this chapter brings some highlighting on the development of a methodology to recover zinc and manganese present in exhausted zinc– carbon batteries through chloride acidic leaching of the solid material. The leaching solution is then used as an electrolytic bath for the electrodeposition of the galvanic coating on AISI 1018 steel. Polyethylene glycol is used as the additive in the bath to obtain both Zn and Zn– Mn alloys.
