Recycling of Photovoltaic (PV) Batteries

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Batteries are used whenever electrical energy is needed, but there is neither a align="left">direct connection to the public electricity</div>

grid nor a generator-based stand-alone
supply. Batteries store electrical energy as
chemical energy. During discharge, the
chemical energy is re-converted into
electrical energy. Depending on the
battery system, this process is either
irreversible or reversible. There are two
types of batteries: 'primary batteries' and
'secondary batteries'.
Lead-acid batteries are called .secondary
batteries. or accumulators since they are
rechargeable. They again can be divided
into starter and industrial batteries. Starter
and industrial batteries are used to provide
large quantities of energy (e.g. to start a
car, operate electric vehicles, as energy
storage medium for solar applications, as
short-term emergency power source, etc.).
Units generally weigh from a few
kilograms to one ton.
In the lead-acid battery sector, starter
batteries have by far the largest share. In
1995, approx. 96 million units were
produced worldwide (source: Battery
Council International). An annual
production growth rate of < 2% is
expected. Especially in developing
countries, where the number of cars is
growing over-proportionately, high growth
rates in the use of lead-acid batteries are
to be expected. Studies carried out in
Botswana indicate that the number of
batteries used in the automobile sector will
grow by 40-50% over the period from 1995
to 2005 (source: GTZ waste management
project). If we consider China alone, the
most populous country of the world, which
currently starts to introduce private car
transport, it is obvious that high growth
rates in the consumption of starter
batteries must be expected in the future,
especially in developing countries.
Returning used lead batteries to the
recycling loop has a long tradition. Thanks
to the compactness of a battery, its high
lead proportion (>95%) and relatively high
metal prices, it has been worth while for
consumers to return their own or collected
car batteries to the scrap trade or
secondary smelters. The return rate of
spent batteries was thus already high in
times when catchwords such as resource
conservation and environmental
protection, recycling, closed-loop materials
management etc. did not yet play a role.
Even today, the success of lead battery
recycling in developing countries
continues to be determined largely by the
potential earnings of scrap collectors and
traders. In industrialised countries,
statutory requirements to take back spent
batteries have compensated for the loss of
economic incentives in spent battery
return.
In most European countries, battery
retailers are under obligation to take back
spent batteries. Lead batteries also come
from repair workshops, the reprocessing of
scrap car bodies and at municipal
collection centres. In Germany, for
example, this well functioning and effective
collection system has led to a return rate
of more than 95% for starter batteries and
almost 100% for industrial batteries. In
developing countries, too, return rates of
up to 80% can be achieved where buyingup
structures for spent batteries are in
place. In Zimbabwe (source: Central
African Batteries) for example, the entire
demand for local battery production is
covered by recycling of used batteries.
1. Battery scrap – raw material for
recycling
The major source of raw material for lead
recycling are starter batteries from motor
vehicles. Modern car batteries consist of a
PP (polypropylen)-casing, plates (grids
and paste), connectors/poles and bridges,
and PP-separators as insulators between
the plates (Fig 1). Paste consists of Pb,
PbO
reactions which take place during charge
and discharge of a lead acid battery are:
charging:
2PbSO
2and PbSO4. The electro-chemical4+ 2H2OPbO2+ Pb + H2SO4
discharging:
PbO
2+ Pb + H2SO42PbSO4+ 2H2O
Older types of batteries have a hard
rubber casing and PVC (polyvinylchloride)-
separators instead of casings and
separators from PP. In some developing
countries (e.g. Zimbabwe) these types of
batteries are still produced and in use.
Therefore, recyclers have to be aware that
batteries in hard rubber casing and PVCseparator
will come in with battery scrap.
Depending on the type of battery, its size
and design, the material composition of a
starter battery varies. Table 1 compares
an old type of battery in hard rubber
casing with a modern type of battery. The
lead-bearing components of a battery are:
Tab. 2: Approximate composition of Pbbearing
components of a starter
battery
The grids of old types of batteries have a
higher Sb (antimony)-content (~4%) than
the modern maintenance-free batteries
(~2%), which instead add Ca(calcium)
<0,5% to their grid alloy.
2. Recycling of lead-acid batteries
2.1 General considerations
As already mentioned, lead-acid battery
recycling has a long tradition, especially in
industrialised countries. The battery and
scrap trade takes back spent batteries free
of charge or even pays the metal value.
Because the metallic fraction of a battery
consists largely of lead, metallurgical
reprocessing of battery scrap was never a
serious problem. Recently it has been
rather the stricter environmental
requirements that have caused problems
for secondary lead smelters and made
lead recycling less economically viable.
Lead recovery from spent accumulators
can take two basic routes. Either the
components of an accumulators like lead,
plastics, acids, etc. are at first separated
and then processed individually, or the
acid is extracted first and the batteries are
processed as a whole. In the first case,
recycling materials are recovered from all
components of a battery. In the second
case, only lead is recovered (partially also
residual battery acid), whereby organic
components are consigned to energy
recycling. In view of the high pollution
control standards implemented in
secondary lead smelters of industrialised
countries, modern lead recycling does not
pose a significant health hazard to the
local population or the environment.
In developing countries spent lead
batteries are recycled both in industrial
facilities and by informal small enterprises.
Industrial recycling smelters use both the
grid metal and the lead-containing paste to
produce secondary lead. The informal
sector, in contrast, often only uses the
metallic parts of old batteries (grids,
terminals, bridges) to produce articles
such as solders or weights for fishing nets.
The other parts of the battery are simply
dumped in the environment.
Even industrial recycling facilities in
developing countries employ many manual
techniques due to cheap labour. Batteries
are often broken up, emptied, separated
and charged to the furnaces by hand. The
lead extracted is refined and cast into
ingots manually. This creates a potential
hazard for the workers, the surrounding
population and the environment (soil,
ground, water resources, etc.) in general.
Some secondary smelters also buy up
pre-sorted battery fractions, e.g. grids and
lead paste without casings and separators,
in addition to complete batteries. The lead
smelters thus save several processing
stages and do not have to deal with casing
and separator wastes. They are therefore
willing to pay a higher price for the
material supplied. This practice is very
harmful in environmental terms. Through
the dispersed pre-sorting activities, lead-
Grid metal, poles, bridges
Pb 96-98%
Sb 2-4%
(Ca) <0,5%
Paste
PbSO
PbO (PbO
PB 21%
100%
4
gate
Phone: +49 (0)6196 / 79-3093, Fax: +49 (0)6196 / 79-7352, Email: gate-id@gtz.de, Internet: http://www.gtz.de/gate/
Fundamentals of the Recycling of Lead-Acid Batteries
containing residues and wastes arise in
many places and it becomes impossible to
control their proper disposal.
2.1 Metallurgical aspects of lead
recycling from battery scrap
As described before, the lead bearing raw
materials extracted from lead-acid battery
scrap are:
Pb(Sb)
and bridges
PbO (PbO
PbSO
paste
While the first component needs only
melting, the two other components have to
be converted by chemical/metallurgical
processes to obtain lead metal, which
takes place in the furnace.
The first type of chemical reaction
converts PbO (PbO
reduction process:
2 PbO + C
PbO
The second type converts PbSO
PbS, again through a reduction process:
PbSO4 + 2 C
Finally PbS is converted into Pb through
the following reactions:
PbS + Fe
or
PbS + 2 PbO
PbS + PbO
The above mentioned chemical reaction
are sum reaction. That means that there
are intermediate steps in between. The
reactions take place in the melting furnace
at high temperature (900-1200 °C) and
need additives, which are . carbon (in the
form of coal) and iron (in the form of iron
swarf). Impurities are collected in the slag
which requires for example soda ash as
liquidifying and slag forming constituent.
The product of the smelting operation is
crude lead, which needs subsequent
refining, and soda slag as residue. Since
soda slag is water soluble and therefore
hazardous when brought to landfills,
modern lead recycling plants use silica
slag (fayalite slag), which is water
insoluble. It requires, however, a much
higher furnace operation temperature of
approximately 1400°C.
The refining of crude lead takes place in a
refining kettle at temperatures between
400 and 550°C. If only battery scrap is
used for lead production, two subsequent
refining steps are required:
1. Removal of Cu which might have
entered the melts through copper
wires.
2. Removal of antimony originated from
the former grid metal to produce pure
lead
While the removal of Cu is done in adding
elementary sulphur, Sb can be removed
by selective oxidation or by adding sodium
nitrate (NaNO
stirred and a dross formed. The impurities
are now removed from the melt by
skimming of the dross formed. It is obvious
that the success of the refining has to be
controlled by chemical analysis. The
refined metal is cast into ingots for
shipment, sale or further manufacturing.
2.3 Technical steps in battery recycling
In developing countries lead-acid battery
scrap is normally processed in rotary drum
furnaces using liquid fuel as energy
source. Lead bearing feed materials are
either whole battery packs (grids and
paste) where the separators have been
removed or two separate fractions
a) grid metal only and b) paste and other
fines
The flow sheet in Fig. 2 shows a semimechanised
process option for small to
medium scale battery recycling in
developing countries. In this option grids
and paste are separated and individually
processed. Since the grids (2/5 of the total
material) are already in the metal stage,
metallurgical process of converting
they do not need to go through the whole
PbO/PbSO
need to be molten at some 500°C (low
temperature melt), refined and cast into
ingots. Thus, energy and time are saved.
2.3.1 Dismantling of battery cases
and feed preparation
Used batteries are emptied by hand and
the acid is collected in plastic barrels. If
the full barrels are kept motionless for
some time, solid impurities will settle at the
bottom of the barrels. This process of
sedimentation may be assisted by adding
some flocculent. The purified acid is then
decanted and packed for sale. Possible
customers for the recycled acid is the
mining and metallurgical industry which
uses acid in various leaching operations.
The remaining battery sludge is
neutralised with lime. After passing
through a filter press the filter cake may be
charged together with the fine fraction into
the melting and reduction furnace.
In a next step the tops of the acid-free
batteries are cut off by a guillotine shear
and the grid packs are removed from the
battery case. They are fed to a perforated
grinding drum, which rotates in a water
basin. By moving the feed in the drum an
autogenous grinding process starts which
separates the grids from the separators
and, more important, the paste from the
grids. At the same time the perforation of
the drum acts as a sieve. The fines are
separated and carried away by the water.
A bit of lime added to the water neutralises
the acidic solutions and prevents the drum
from massive corrosion.
Instead of this labour intensive method
whole batteries may be crushed in a
hammer mill (Fig. 3) and fed to a grinding/
washing drum for separation.
In both cases, the slurry is pumped
continuously or batchwise to
sedimentation tanks, where the solids
settle at the bottom. The clarified liquid is
returned back to the grinding operation,
while the sludge at the bottom of the tanks
passes a filter press or is left to sun-dry.
The filter or sun dried cake is the main
feed for the melting and reduction
operation which will produce almost pure
lead.
The second fraction . the coarse material
(basically grids and separators) . leaves
the grinding drum at its lower end.
Separators and grids are separated from
each other by hand sorting using a slow
moving transmission belt (Fig. 4). The
metal fraction is the main feed for the low
temperature melt producing a PbSb-alloy.


Empty battery cases and covers with the

attached poles, bridges and remaining grid

parts are charged to a wet hammer mill,

where metal parts and remaining paste

are separated from the plastic. The output


of the mill passes a perforated drum,
where solids and slurry are separated.
While the solids (metal and plastic parts)
are hand sorted, the slurry with the fines is
added to the slurry obtained from the
grinding drum. The solid metal parts
supplement the feed of the low
temperature melt.
The plastic residues of the dismantling
operation either have to be dumped (in the
case of PVC-separators) or can be used
as fuel (PP, cellulose, hard rubber) in
cement factories. In this case it is
important that no lead remains in the
plastic product.
2.3.2 Melting and reduction operation
of paste and battery fines
The filter or sun baked cake of paste is
charged to a short rotary drum furnace
(Fig. 5) where the charge is melted
together with slag forming constituents
(soda ash = Na
additives (Fe-swarf, coal). The ratio of the
feed materials Pb-fines : Fe-swarf : Soda
ash : coal is approximately 10:2:1:0,5. The
energy needed for the process is obtained
from the burning of the coal within the
furnace and by an additional burner
running on heavy fuel oil, paraffin,
diesel, waste engine oil, etc. To save
energy and to achieve a higher furnace
temperature the combustion air should be
preheated.
Depending on the temperature and the
amount of feed material in the furnace, the
reaction time will be 2-3 h. Due to the
difference in specific weight the molten
lead produced settles at the bottom part of
the furnace. When enough lead has
accumulated, it is tapped into a mobile
ladle and transported in liquid stage to the
refining kettle.
With less PbO/PbS in the slag and more
Pb-metal produced the viscosity of the
slag increases. This hampers the
separation of the small Pb-droplet from the
slag. To overcome this problem either
more soda ash has to be added or the
temperature in the furnace must be
increased. Both solutions have negative
effects. While the first measure increases
the amount of slag which finally needs to
be discarded, the second measure leads
to higher energy consumption and
evaporation of lead into the off-gas.
It is more advisable to tap the lead before
the optimum of recovery is achieved and
to leave the remaining lead-rich slag in the
furnace for a second or third cycle with
new feed material.
After a number of production cycles the
amount of slag in the furnace will be too
large to continue the operation. By adding
a bit more coal and fresh soda ash a slag
wiith a low Pb content (<9% Pb) can be
achieved which is then tapped from the
furnace together with the finally produced
lead. While the lead metal is forwarded for
refining the slag has to be dumped.
Off-gas and flue dust from the operation is
sucked of and treated in the off-gas
cleaning system.
2.3.3 Melting of grids, terminals and
bridges
The coarse fraction of the crushed battery
scrap is fed to a crucible furnace, melting
kettle or rotary drum furnace. By adding a
bit of soda ash the charge is melted and
stirred for some while. During this
operation insoluble impurities will settle on
top of the melt and join the soda ash slag,
which is skimmed off at the end of the
melting operation. Gases and flue dust
from the process are soaked away and
passed over to the gas cleaning system.
The melt is cast into ingots or transferred
in liquid stage to the refining kettle.
2.3.4 Refining of crude lead
First, the lead tapped from the furnace has
to be cleaned from residual oxides and
slag. For that purpose a bit of pitch and
saw dust is added. After stirring for a while
the impurities settle at the surface and are
skimmed off (Fig. 6).
Crude lead originating from battery scrap
is normally alloyed with copper and
antimony (with traces of Ca, Sn, As, Zn).
In order to remove the unwanted elements
two further refining operations have to be
carried out.
By adding sulphur to the lead melt and
after stirring for some time, a Pb/Cu
(and if present with minor parts of
Zn, Sb, As) is formed and skimmed off.
This de-copperisation step should be
carried out at least two times to secure the
refining result.
The de-copperised lead still contains a
large amount of antimony (and maybe
some Sn, As). All of these elements can
be removed by oxidation. For that purpose
air or oxygen-enriched air is blown into the
melt and stirred. The different oxides
formed settle at the surface and can be
skimmed off. The oxidising process is
completed when mainly lead oxide is
formed.
Instead of oxidising the impurities by
injecting air, sodium nitrate (NaNO
be added. Here again a dross containing
the impurities (and lead) is formed, which
is skimmed off afterwards. All refining by
byproduced
or residues should be processed
to recover lead and other valuables
components.
The refining processes and the purity of
the refined lead are monitored by chemical
analysis.
The off-gases of each of the processes
are collected and fed into the central gas
cleaning system of the plant.
2.3.5 Gas cleaning system
Due to the lack of environmental
legislation and monitoring, and due to lack
of funds industrial operations in developing
countries often have very poor emission
control and off-gas cleaning systems.
Because of the hazardous potential of the
majority of the elements and compounds
which are involved in lead smelting and
refining (Pb, Sb, As, SO
gas cleaning standard must be achieved
and should be compulsory.
Therefore, all fumes, gases and dusts
which are generated during the different
production steps should be collected and
treated in a central gas cleaning system. A
standard off-gas treatment system
normally consists at least of a hot dust
chamber and/or hot cyclone, a venturi
washer and a wet scrubber (Fig. 7).
From the furnace the hot gases pass
through a hot dust chamber and/or a hot
cyclone where most of the coarse dust
particles are separated from the gas
stream. From there the off-gas feed into a
wet gas cleaning system which consists of
a venturi washer and a wet scrubber.
The task of the venturi washer is the
collection of the fine dust particles. Water
and off-gas is mixed under high turbulence
and gas/water spray velocity, forming a
fine slurry, which is pumped to a
sedimentation tank.
The more or less dust free off-gas
afterwards enters a wet scrubber. Here,
the main task is the removal of the SO2-
gas of the off-gas. By adding lime to the
scrubber liquid, the SO2 in the off-gas will
react with the lime water forming gypsum.
The gypsum is insoluble in water and
precipitates. Again, the fine slurry of the
second scrubber is pumped into a
sedimentation tank. The clean gas leaves
the whole process via the main chimney.
In the sedimentation tank small amounts
of lime and flocculent neutralise the slurry
and assist the sedimentation of the fines.
The sludge passes a filter press producing
a filter cake. The extracted water is recirculated
to the scrubbers while the filter
cake is fed back into the melting and
reduction furnace.
3. Environmental considerations
As already mentioned, the potential health
and environmental risk involved when
processing battery scrap is very high.
Depending on the level of mechanisation
and environmental standards, the
following environmental hazards can arise:
acid spilled when batteries are emptied
battery scrap is stored without
protection
(e.g. lead-containing dust, soot, SO
chlorides, dioxins, etc.) when battery
scrap is smelted due to:
-
including its organic parts (casing,
PVC separators in older battery
types)
-
vapours during the smelting and
refining process
-
treatment
the corresponding landfill design that
would prevent leaching and dust
formation
refining process
such as battery casings and PVC
separators.
Workers, too, are exposed to raised levels
of harmful substances in such facilities.
This generates considerable health risks if
appropriate precautionary measures are
not taken (respiratory equipment, washing
facilities, separate eating and resting
rooms, regular examinations, etc.).








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