NCNG - Raw Materials & Recycling

1. 1
II. RAW MATERIALS & RECYCLING
2010 Derived from NCNG course
Handbook for Glass Technologists

2. 2
BATCH
• The different ingredients/raw materials are mixed together in
the proper proportions. This mixture of raw materials is called
batch.
• Normally it is a powder batch. In some situations the powder
batch is compacted (into granules or pellets) before charging
into the furnace.
• A normal batch does not include pelletized materials or cullet.
However, today cullet recycling (internal and external – post-
consumer waste glass) is very common in the glass industry
• Especially in the glass wool and container glass industry,
external recycling provides the main raw material stream in
many cases.
• Many criteria have to be considered in the selection of the raw
materials. Following is a general survey.

3. 3
Raw material batch for glass production
• The glass and glass melt properties depend on the
chemical composition of the glass and temperature.
Therefore, the composition of the raw material mixture
(batch) and each raw material individually, including
impurities, will influence the glass (melt) properties.
• Not the composition of the raw materials only, but also
grain sizes of these materials are very important in the
melting process.
• The batch preparation, batch transport and melting
process need to deliver finally a homogeneous glass
with uniform properties.

4. 4
Important aspects of raw materials
• Chemical composition
• Stability
• Hygroscopic (clogging of hygroscopic compounds)
• Impurities
– Coloring oxides (e.g. iron oxides, chromium oxides,…)
– Heavy mineral (zircon, zirconia, chromite,…)
– Organic material  effect on redox & foaming
– Fluorides, chlorides, sulfur (in synthetic soda, cullet, clays, dolomite,
blast furnace slags, filter dust):  emissions
• Melting Characteristics
• Melting-in
• Melting enthalpy
• Mass losses
• Grain sizes
• Easy to melt form: clay, feldspars for Al2O3 in glass
• Costs (often determined by raw material production technology)

5. 5
Selection of raw materials
Mineral ingredient Chemical ingredient
less expensive
often contaminated
variable composition
limited process control
multiple sampling
delivery under certificate is often difficult
more expensive
higher purity
almost constant composition
process control available
singular sampling often sufficient
delivery under certificate possible
Table 1
Comparison mineral and chemical ingredients

6. 6
Survey of batch and glass components
• Network forming oxides
– SiO2, B2O3, P2O5, GeO2
– Non-oxide components: fluorides, halides, chalcogenides (As2S3, GeS2)
• Network modifying oxides
– Na2O, K2O, Li2O
– CaO, BaO, MgO, SrO
• Intermediate oxides
– Al2O3, PbO, ZnO, ZrO2
• Fining agents/redox active components
– Sulphates: Na2SO4, CaSO4
– Oxides: As2O3, Sb2O3, CeO2
– Chlorides: NaCl
– Nitrates: KNO3, NaNO3
– Carbon
• Fluxing agents
– CaF2, blast furnace slags/calumite, Spodumene (lithium raw material)
• Colouring agents
– Fe2O3, Cr2O3, CoO, Mn2O3, Se, Fe3+/S2-, rare earth oxides, sulfides, selenides
• Cullet (own and recycled)

7. 7
Sand or Quartz types
• SiO2 is available from natural sources as quartz sand (silica),
sandstone & quartzite. Only silica is sufficiently pure for most glass
productions.
• It occurs in primary and in secondary quartz deposits.
• Known examples of primary deposits are rock-crystal and gangue
quartz. Fine grain primary quartz deposits originate from leaching of
rock-formations. The grain size of this quartz may vary widely. Pure
deposits of quartz are found in Brazil, in the USA and in Portugal.
• Rock crystal may occur in nature as crystals of several hundreds of
kilograms.
• Secondary silica sand deposits are found in abundance all over the
world. They comprise of silica sand carried along by wind and water.
During this transport it has been classified on grain size. The grain
size distribution in such deposit is rather uniform. The purity may vary
widely. For grain sizes below 0.2 mm it is called silt, between 0.2 and
2 mm it is called sand and beyond 2 mm gravel.

8. 8
Table 2
Sources for SiO2
and B2O3 for the
European glass
industry

9. 9
It is important from an economic perspective that the properties of
the raw sand, still unprocessed, are not too far from the desired
glass grade parameters:
• The grain size and mineralogical parameters/compositions/low level
impurities of glass sands are stringent, it is rare for a glass sand
deposit to satisfy these parameters without some processing.
• The preferred grain size distribution of glass sand is predominantly
between 0.125 mm and 0.500 mm and high percentages of finer or
coarser material in the sand may result in unacceptable processing
losses.
• The location and percentage of iron in the sand is important, as is
the effectiveness of the sand refining processes in reducing or
removing the iron.
• Humic or organic acids in the depositional environment often play
an important role in dissolving and removing iron from the sand and
naturally improving the quality.
• The content of heavy or non-meltable (hardly soluble in silicate
melt) refractory minerals is also an important factor.

10. 10
Network modifying oxides
(Na2O, K2O, Li2O, CaO, MgO, BaO)
• Alkaline and alkaline earth oxides are added to the
glass in order to increase the melting rate, to decrease the
viscosity of the molten glass and to obtain a good
processing performance during forming. The alkali oxides
are effective in improving the fusibility (“fluxing agent”).
• Alkali carbonates react with earth alkali oxides (or earth
alkali carbonates) or with silica sand far below the SiO2
melting point. Alkali silicates or alkali-earth alkali
silicates are formed during batch melting.
• However, the chemical durability of the glass decreases
by the alkali oxides. Replacing part of the alkali oxides by
earth alkali oxides will increase chemical durability.

11. 11
Table 4
Sources for
network
modifying oxides
Compo-
nent
Name Chemical
composition
Main origins Impurities
(mass %)
Na2O Soda ash
- light soda ash
- heavy soda ash
Na2CO3 From natural soda
ash: USA (Trona)
Synthetic,
Solvay process
Synthetic,
Solvay process
very low impurity
level
0.0013 F
0.1 Cl
0.0013 F
0.1 Cl
Sodium feldspar
(Albite)
Na2O·Al2O3· 6SiO2 Europe 0.004 F
0.04 Cl
Nepheline syenite (Na2O+K2O)·Al2O3·
4SiO2
Norway, Canada 0.004 F
0.01 Cl
Plus CaO, MgO,
FeO/Fe2O3
Borax decahydrate
or pentahydrate
Na2B4O7·10H2O
Na2B4O7-5H2O
USA, Turkey
K2O Potash K2CO3 Synthetic
Potassium nitrate KNO3 Synthetic 0.02 F
0.1 Cl
Potassium
feldspar
(Orthoclase)
K2O·Al2O3· 6SiO2 Europe 0.004 F
0.04 Cl
0.1-0.4 Fe2O3
Li2O Spodumene Li2O·Al2O3·4SiO2 Africa, Australia 0.01-0.04 Fe2O3
Lithium
carbonate
Li2CO3 Synthetic
CaO Limestone CaCO3 Europe 0.05 Fe2O3
0.006 F
0.008 Cl
Dolomite MgCO3·CaCO3 Southern Europe 0.10 Fe2O3
0.02 F
0.03 Cl
Colemanite Ca2B6O11·5H2O USA, Turkey 0.02 F
0.02 Cl
MgO Magnesite MgCO3
Magnesium
carbonate
MgCO3 Waste product
alkali industry
Dolomite MgCO3·CaCO3 Southern Europe 0.10 Fe2O3
0.02 F
0.03 Cl
Basic MgCO3 4MgCO3·Mg(OH)2·4
H2O
Synthetic
BaO Barium carbonate BaCO3 Synthetic ±0.05 SO3
SrO Strontium
carbonate
SrCO3 Synthetic ±0.05 SO3

12. 12
Soda (Na2O supplier)
• In Europe, mainly synthetic soda ash (Na2CO3) is used as sodium oxide
supplier.
• For this synthesis, the Solvay-process is used, in which NaCl or brine is used
as the raw material. Brine (sodium chloride solution) reacts with CO2 (from
limestone burning) using ammonia for intermediate reactions, the ammonia
can be re-used. Reaction product is sodium carbonate (soda ash) and
calcium chloride.
• Therefore synthetic soda always contains some residual NaCl as an impurity
(NaCl-content 0.09 - 0.3 mass %, dense soda qualities with 0.09-0.15 mass
% NaCl are on the market). Today, qualities with less than 0.15 mass %
NaCl are used in the Western-European glass industry.
• The soda derived from natural trona soda sources generally contains only
about 0.05 mass % NaCl.

13. 13
CaO
• Limestone (CaCO3) is by far the most important mineral used for supplying
CaO. The grain size can be as large as 3 mm (or even larger).
• Main impurities are alumina containing compounds, quartz and iron oxide;
alumina and quartz, are hardly being considered as harmful as long as the
concentration is reasonably stable and alumina particles are not too large.
• For glasses that may not contain high iron contents (tableware, ultra-clear glass
for solar PV modules (photovoltaic), flint glass), quality & purity of limestone is
very important.
• For the manufacturing of E-glass, colemanite is used as a CaO-carrier apart
from also supplying boric oxide. Quick lime (CaO) instead of limestone
(CaCO3) in the raw material batch will give significant energy savings during
melting, because decomposition of calcium carbonate is a strongly endothermic
process.
• Dolomite (MgCO3CaCO3) will be used when besides CaO also MgO is
desired in the glass composition (float glass, sometimes container glass,
lighting bulbs glasses).
• Quick lime (CaO) or hydrated lime (Ca(OH)2) are sometimes used in glass
manufacturing. However, production of CaO or Ca(OH)2 from limestone are
energy intensive processes.
• Lime rich filter dust are produced by scrubbers and filters applied to control
emissions from glass furnaces

14. 14
MgO
• CaO can be replaced partly by MgO e.g. in soda-lime-silica glasses or E-glass.
• Addition of MgO decreases the tendency to crystallize (decrease of the
liquidus temperature). The optimal concentration is 3 to 4 mass %, also being
favourable for the chemical resistance. At concentrations exceeding 5 mass %
the risk for crystallization increases again.
• MgO makes the glass “longer” compared to CaO.
• The main MgO carrying raw material is dolomite (MgCO3CaCO3). Dolomite
often contains chlorides and fluorides as impurities.
• Other MgO containing raw materials are magnesium carbonate (MgCO3), as
a mineral often contaminated with Fe2O3, or reasonably pure MgCO3
generated as a waste product in the alkali industry. Often being used is the
synthetic basic magnesium carbonate (4MgCO3Mg(OH)24H2O).
• Dolomite is prone to decrepitation. During heating of dolomite grains,
decomposition will takes place above a certain temperature. This
decomposition will release CO2 gas. Within the dolomite grains, this evolved
CO2 gas builds up a pressure and the grain can burst by this pressure.
• Magnesium containing raw materials should be properly checked on the
composition because the MgO content and impurity levels may vary in these
raw materials.

15. 15
Intermediate Oxides
• The intermediate oxides give the glass more stability.
• They decrease the tendency to crystallize, increase
the chemical resistance and with Al2O3 a favourable
influence on the tensile strength has been observed.

16. 16
Compo-
nent
Name Chemical
composition
Main sources Impurities
(weight %)
Al2O3 Kaolin
(china clay)
Al2O3·2 SiO2·2 H2O Europe < 0.04 F
Cl and oxides of
Fe and Ti variable
Nepheline
syenite
±Na2O·Al2O3·4SiO2 Norway,
Canada
Little F, Cl with
some FeO/Fe2O3,
MgO, CaO
Feldspar R2O·Al2O3·6 SiO2 Europe Little F, Cl
Phonolite ±4R2O·(CaO+MgO)·
4Al2O3·Fe2O3·20SiO2
0.12 F
0.3 Cl
Blast furnace
slag
(calumite,
ecomelt)
A slag based on SiO2,
CaO, Al2O3 and sulphur,
partly in sulfide form:
xSiO2·yAl2O3·zCaO·S2-
Waste product
from iron/steel
production: blast
furnace slags
< 0.05 F
< 0.01 Cl
PbO Red lead Pb3O4 Synthesis from
minerals
Lead
carbonate
PbCO3
Lead silicate PbO·SiO2
Table 3.5 Intermediate oxides

17. 17
Alumina
• Aluminum oxide also called alumina or corundum (Al2O3)
is by far the most frequently used intermediate oxide in the
glass composition.
• Pure alumina poweder / grains are dissolving very slowly in
the glass melt
• Often Al2O3 is added by raw materials such as kaolin,
feldspar or nepheline syenite. Nowadays also the much
more expensive synthetic ingredient aluminum oxide is
being used.
• Aluminum oxide occurs also in blast furnace slags (10 - 15
mass%) and as an impurity in sand and dolomite (0 - 0.3
mass%).

18. 18
Fining and Fluxing Agents
• In the industrial manufacture of glass, so called fining
agents are added to a maximum of ±1.0 mass-%.
• Fining agents are additives to enhance the removal of
dissolved gases and gas bubbles (e.g. seeds of typically
0.05 – 0.5 mm diameter) from the melt in order to get
seed-free glass.
• Fining agents release gases above the so-called fining
onset temperature
• Examples
– Sodium sulfate (Na2SO4)
– Antimonate or Arsenate (Sb2O5, As2O5)
– Sodium chloride (NaCl)

19. 19
• The best known fining agent is sodium sulfate (salt cake) especially used
for soda lime silica glass, E-glass .
• Sulfates in the melt may decompose at high temperatures spontaneously.
• In oxidized soda-lime-silica glass melts, this process needs temperatures
above 1400 oC. During the fining process, gaseous sulfur oxides, and in
case of oxidizing melts also oxygen gas are released from the melt as fining
gases.
• Sometimes Na2SO4 is used, combined with a reducing agent (carbon) in
order to start the fining (decomposition of sodium sulfate will start at lower
temperatures under reducing conditions) at lower temperatures.
Adding cokes to a sodium or calcium sulfate containing raw material batch
will cause reactions between sulfate and a reducing component, such as
cokes or CO gas formed from the cokes. This will result in sulfide formation.
After further heating of the batch, the sulfide reacts with sulfate (still
remaining) and forms SO2 gas. Typically this gas evolution takes place
between 1100 and 1350 oC.
This SO2 gas will be released by bubbles ascending in the molten glass.
Fining and Fluxing Agents

20. 20
Additive Fining action
Sulfate
in most soda-lime-silica
glass melts
Na2SO4
CaSO4
BaSO4
Formation of
SO2 and O2 gases
Sulfide (+ sulfate)
amber (soda-lime-silica)
glass melts.
blast furnace slags:
often used for all kinds
of glass melts
BaS
ZnS
Blast furnace slag:
SiO2·Al2O3·CaO·S
2-
Formation of
SO2 and O2 or S2
/ H2S gases or
other sulfur gas
species
Multivalent oxides:
in most crystal and TV
(panel/funnel) & glass-
ceramic melts
Arsenic
Antimony
Cerium in
melts for optical
glasses, special glasses
As2O3 (+ nitrates) As2O5
Sb2O3 (+ nitrates) Sb2O5
NaSbO3·3 H2O (+ nitrates)
CeO2
As2O5  As2O3 + O2 gas
Sb2O5  Sb2O3 + O2 gas
3CeO2 Ce3O4+ O2 gas
Tin oxide for fining of
LCD glass or glass
ceramics
SnO + (nitrates) SnO2 2SnO2  2SnO+O2 gas
Fluoride
E-glass melts (as flux)
Fluorspar
CaF2
Na2SiF6
Formation of
volatile SiF4
Chloride
in borosilicate glass
melts
NaCl Evaporation of NaCl
and HCl
(disadvantage: high
HCl emissions)
Oxidizing agent: Saltpeter
oxidant in lead glass
melts, TV glass melts (in
combination with
antimony or arsenic
oxides), special glass
melts or in glass wool
melts to oxidize
reducing material
KNO3
NaNO3
Ba(NO3)2
Ca(NO3)2
Oxidizing agent for
example for arsenic or
antimony oxide
Reducing agent: Carbon
amber glass melts,
feuille morte glass melts,
lowering fining
temperatures for sulfate
fining
C Reducing agent for
sulfates, leading to SO2
or S2 (or other sulfur
gases) gas formation <
1350
o
C.
Table 3.6
Fining agents and
oxidants/reductors:
survey of raw
materials and main
fining mechanisms/
reactions

21. 21
Fluxing agents
Fluxing agents are additives for accelerating the batch melting
reactions. The action of these compounds may rely on several
principles:
- Lowering the temperature at which the first aggressive melt
phase occurs,
- Decreasing the surface tension of the batch melts, which
improves wetting of the sand particles by these reactive melts,
- Formation of low viscous eutectic melt phases,
- Some materials in the batch need less reaction enthalpy upon
melting compared to the raw materials that are replaced (e.g. cullet
replacing normal batch),
- Some raw material enhance the heat transfer into the batch
blanket

22. 22
Additive Chemical composition Action
Fluorspar
Lithium carbonate
Spodumene
Sodium sulfate
Potassium nitrate / Sodium nitrate
Blast furnace slag
Cullet
CaF2
Li2CO3
Li2O  Al2O3  4SiO2
Na2SO4
KNO3 / NaNO3
SiO2Al2O3  CaO  S2-
Glass composition
1, 3
2
2
1 , 3
2
2
4, 5
1 = decreasing viscosity of melt phase in batch
2 = formation of reactive melt phase in batch
3 = ”wetting” sand particles by reactive melts (lowering the
surface tension of these primary melts)
4 = low melting energy
5 = increasing heat transfer within the batch
Fluxing agents: review of raw materials and their action principles

23. 23
Processing of raw materials: routing of raw materials in
continuous glass production
Raw
materials

24. 24
Delivery of a raw material to glass production plant
Storage of raw materials for production of 4 to 5 days
recommended to avoid shortage during periods
that transport of materials is limited

25. 25
a several mixer types
b counter current fast mixers (dish or pan principle) - top views
Batch mixers in glass industry

26. 26
Pneumatic mixer
Gas jet mixer

27. 27
Mixing
• Typically 10 batches per hour are prepared by one mixer.
• The required mixing capacity and mixer volume depends
on the effective time per day (often 16 hours) for mixing
processes, the pull of the furnace and required mixing
time to obtain a well mixed batch.
• Water is added to the batch, preferably above 36 oC, to
avoid intense hydration of soda. Therefore water is often
added as steam. Hydration of soda by added water may
increase the batch temperature with 6 to 8 oC
• The added water is weighed before adding to the batch
(taking into account the water content of cullet and sand).

28. 28
Additions to batch
• The quantities of water addition to the batch need to be
limited: The evaporation of batch water in the glass
furnace requires a very high quantity of extra energy.
• Raw materials used in relatively small concentrations
in the batch formulation, like fining and fluxing agents
for example, are premixed separately together or with a
small amount of one of the other ingredients before
adding them to the large mixer.
• Cullet is added to the batch just before the end of the
mixing cycle or even afterwards during the emptying of
the mixer in order to prevent wear of the mixer.
Sometimes the day hoppers are filled alternately with
normal batch and cullet

29. 29
Doghouse
• The batch can be charged through the back wall of side-port-furnaces
or via a doghouse in one or both side walls of U-flame furnaces (end-
port-furnaces, horseshoe flame furnaces).
• The charging of batch may occur by means of screw conveyors or
vibrating plates but mostly scrapers are used.
• Sometimes, the batch charging can be applied at different angles
(alternating) to obtain a better coverage of batch on the glass melt
surface and to avoid piling up of the batch.
• In case of end-port fired furnaces, the doghouse (connected to the batch
charging mechanism) is generally located at the furnace sidewall, in the
vicinity of the back wall (wall with burner ports).
• The batch charging equipment for end-port fired furnaces is compact,
but charging rates of 300 tons batch per unit per day can be achieved.
• Batch from the day hopper is sinking to a plate that moves to bring a
blanket of batch into the glass furnace, pushing the batch on top of the
glass melt. The batch may also move by gravity on an almost horizontal
plate and a pusher moves the batch.

30. 30
Example of compact batch charging system
(positioned below the day hopper) connected to doghouse of
glass melting tank (Zippe).

31. 31
Batch blanket
• Preferably a thin batch blanket is supplied on top of the
glass melt in a melting tank, in order to obtain a relatively
fast melting rate. A thick batch blanket on top of the
molten glass will limit the heating rate (~ 1/d2) of the inner
layers of this batch.
• Depending on the charging method, the batch can float
as a continuous blanket layer on the melt or may be
moving as islands (which is generally the case with
container glass furnaces) over the melt.
• When feeding at the back wall via an open doghouse the
batch dosed through a slit will float on the melt, generally
as a 10 to 25 cm thick blanket initially.

32. 32
Batch charging into glass furnace
Removable
vertical
wall
Batch charging into open doghouse
by a pusher mechanism
Batch charging into closed doghouse
using a screw charger

33. 33
Segregation by
Differences in:
• Grain size
• Density of the particles
• Shape of the particles
• Surface roughness
• Elasticity

34. 34
Types of segregation
• Trajectory segregation
– This type of segregation occurs during transfer and pouring
out of powders.

35. 35
Segregation by percolation
• When moving a powder pile, some holes /pores in the pile
may arise, into which particles from the higher layers can
fall; this is easier for fine particles (these fines can be
captured in the holes) than for coarse particles.
• Therefore eventually all fine particles will be found at the
bottom and the coarser particles at the top of the pile.
• When pouring out a batch of grains / powder on a pile (a
very important cause for segregation), the coarser particles
will roll along the slope (much more than fine particles). This
segregation will be intensified by the sieving (percolation)
effect mentioned and the large velocity gradient.

36. 36
Methods for preventing segregation
• All components of equal dimensions: impractical !
• Fine material, that is not free flowing: impractical !
• Wetting: usually effective
Added water
Standard deviation based on the
concentration of one of components
Size ratio

37. 37
Specifications of raw materials
• Composition of raw material
• Moisture content
• Purity with respect to colouring oxides
• Grain size distribution (0.1 – 0.3 mm)

38. 38
Fe2O3
maximum
level
Cr2O3
maximum
level
TiO2
maximum
level
Optical glass 0.002% 0.5-1.0 mass
ppm
Crystal glass/
Solar glass (PV)
< 0.01% 0.001%
Flint container glass 0.03-0.05% 0.001%
Clear tableware 0.01-0.025 0.001%
Green container glass 0.2-0.5% 0.2-0.4%
Float glass (clear) 0.05 - 0.1% 1 - 5 mass
ppm
0.03%
Tinted floatglass up to 1.5%
E-glass fibres (textile) 0.02% 0.06%
E-glass fibres (not textile) 0.04% in practice, 1 -
5 mass ppm
0.08%
Specification
colouring oxides

39. 39
Raw material Chemical
Composition (mass
%)
Tolerance
(mass %)
Grain size distribution
(example)
Quartz sand (for
flint glass)
SiO2 > 99.0
Fe2O3 < 0.030
Cr2O3 < 0.0002
Al2O3 < 0.3
± 0.2
± 0.01
± 0.05
> 0.84 mm - 0%
> 0.60 mm - 1% max
< 0.125 mm - 1% max
Nepheline
syenite
Al2O3 > 22.0
SiO2 < 62.0
Alkali > 13.0
Fe2O3 < 0.10
± 0.5
± 0.5
± 0.05
> 0.84 mm - 0%
> 0.50 mm -3.5% max
< 0.1 mm - 20% max
Limestone
and dolomite
CaO+MgO > 54.0*
Al2O3 < 0.3
Fe2O3 < 0.10
Rest is CO2
± 0.1
± 0.005
> 3.15 mm - 0%
> 2.0 mm - 10% max
< 0.1 mm - 20% max
Soda ash Na2CO3 > 99.0
NaCl 0.05-0.20
Fe2O3 <0.001
> 1.19 mm - 0%
> 0.59 mm - 3% max
< 0.074 mm -3% max
*Dolomite somewhat lower
Typical chemical and physical raw material specifications
for container glass manufacture

40. 40
Batch composition calculations
determination batch recipe
• For each raw material, the concentration of the relevant oxides and
impurities (Cl, F, S, iron oxides) should be determined.
• Many raw materials contain carbonates and nitrates or water
(hydrated compounds / OH-groups). These components dissociate
at higher temperatures into oxides and volatile CO2, NO2 and H2O,
which evaporate from the batch. This is called melting loss.
• For container glass raw material batch, the amount of dry normal
batch is about 1170 to 1190 kg per 1000 kg molten glass.
• For soda-lime-silica float glass, about 1200 -1220 kg dry normal
batch is needed to melt 1000 kg glass. The difference is the loss by
batch gases.

41. 41
Take into account / correct for
• Moisture content of different raw materials
• Evaporation
Some components are volatile and will evaporate from the melt.
For this phenomenon, empirical retention factors (indicating the
retention of the added components in the glass) mostly are used,
especially for B2O3, PbO, As2O3, Sb2O3 and alkali oxides (Na2O,
K2O, Li2O).
• Carry-over
Fine particles may disperse preferentially during conveying,
charging and in the furnace itself. This depends on the
circumstances. It has to be determined empirically.
• Cullet
The chemical composition of the cullet may differ from the
composition of the glass to be produced.

42. 42
Example batch calculation
Example of batch calculation, assuming 50 % SO3 retention
Ingredient Amount
(gram)
Oxide
mass fraction
Mass
in glass (g)
Oxide in
glass
Sand
Soda ash
Sodium sulfate
Dolomite
Borax
Feldspar
1000
1000
370
4
200
30
55
0.98
0.00025
0.585
0.437
0.563
0.310
0.210
0.365
0.163
0.180
0.130
0.680
980
0.25
216.4
1.7
0.5 x 2.25*
62
42
10.9
4.9
9.9
7.1
37.4
SiO2
Fe2O3
Na2O
Na2O
SO3
CaO
MgO
B2O3
Na2O
Al2O3
K2O
SiO2
1659 g batch 1373.6 g glass
Melting loss 1659 g - 1373.6 g = 285.4 g = 17.2 % of the batch
Glass composition: 74.1 SiO2 ; 16.2 Na2O; 4.5 CaO; 3.1 MgO; 0.8 B2O3; 0.7
Al2O3; 0.52 K2O; 0.08 % SO3 0.02 % Fe2O3 (all in mass %)

43. Glass recycling

44. 44
Recycling of cullet/waste glass
• Use of recycled cullet/waste glass
– In container glass industry: up to > 90% of recycled cullet
– In float glass industry: 20 – 30% of (own) cullet, typically; trend to
recycle external cullet (after removal of PVB-foil, sealants, etc.)
– Fiber glass: scrap recyling (after pyrolysis of organic coatings)
• Quality aspects
– Impurities
– Colour composition
– Moisture content
– Cullet size
– Redox state

45. 45
Situation for container glass production:
• Often, 10-20 % of the cullet is own (internal) cullet and the
residual amount is mixed cullet (but not for flint glass) and/or
colour sorted cullet.
• Green glass furnaces: up to 90 % cullet in batch
• Amber glass: 70-80 % cullet
• Flint glass: 65 % cullet
• Very clear (ultra clear flint): only own cullet (10-15 %)

46. 46
Advantages
Apart from the advantages for the environment (diminishing
waste heaps), the use of cullet will also benefit the melting
process it self:
Cullet has a lower melting energy than the raw materials (it
has been melted previously and there is no endothermal
decomposition of carbonates when melting cullet).
Cullet can act as a fluxing agent and it decreases the
melting energy. The energy savings when 100 % cullet is
used is about 25-30 % compared to supplying 100 %
regular batch.

47. 47
Disadvantages
• When using own cullet, there are no specific
disadvantages, provided the cullet is stored clean and dry
and the cullet pieces are not too fine.
• Very fine cullet may lead to extra foaming and glass dust
carry-over.
• Application of foreign (external) cullet may bring some
risks (see also chapter 8 of this textbook):
• The composition of the cullet may vary.
• Impurities of concern (to be removed)
– Ceramics, Stones, China (Porcelain)
– Metals
• Ferro
• Non-Ferro (Aluminum, Nickel, Cupper, Lead,…
– Glass Ceramics
– Colored glass from flint cullet
– Organic components de-stabilizing redox state & color of to be
produced glass

48. 48
Impurities in recycled cullet from collection
banks
• Ceramics, stones, china: should be < 10 – 50 g/ton
• Ferro and non-ferro metals (Al, Pb): should be < 1 - 5
g/ton
• Special glass types (quartz, glass ceramic, lead crystal,
opal): very difficult to separate
• Organic waste: paper, plastic, food residues: affects
redox state !

49. 49
Use of mixed cullet for container glass
• For melting green: > 80%
• For melting amber: up to 60%
• For melting flint: only colour separated due to Fe- and
Cr-contents of mix
• Colour composition of mix will influence redox state
Table 1.6:
Typical Fe- and Cr-contents of different types of container glass

50. 50
Colour composition of mixed cullet
from collection bank: example
France Netherlands Germany
0
10
20
30
40
50
60
70
France Netherlands Germany
amber
green
flint

51. 51
Moisture content and cullet size
• Moisture content
– Usually 1 – 3 %
– Affects batch melting behaviour and energy usage !
• Cullet size
– Affects batch melting behaviour:
• Powdered and contaminated cullet: results in
excessive foaming
• Too large pieces: transportation and
homogenisation problems
– Preferably between 10 – 40 mm

52. 52
Cullet specifications acceptable cullet
(units in mass % or grams/ton cullet)
stones, ceramics, chinaware, pottery
excluding glass ceramics
glass ceramics
glass ceramic pieces
magnetic metals
non-magnetic metals
lead
aluminum
all metals
organic material
COD of washing water from cullet
plastics
moisture
paper/cork/wood
opal glass
grain size cullet
< 25 -35 g/ton
indicative < 25 g/ton
if present, size should be < 3-4 mm
< 5 g/ton
< 5 g/ton
< 1 g/ton
< 5 g/ton
< 7 g/ton
< 200 or 500 g/ton
< 1200 -1500 mg O2/liter
< 60 g/ton
< 2-3%
< 1500 g/ton
< 100 g/ton
no cullet pieces > 7 cm
cullet pieces < 0.5 cm: max. 12%
Typical cullet specifications for container glass production

53. 53
Savings on energy for glass melting with cullet
• Remelting of cullet requires no energy for
endothermic fusion reactions (see table)
• Higher melting kinetics: increase of furnace capacity
Table 1.7: Example of energy savings (in kJ/kg
glass) due to recycled cullet for container glass
production :
Specific melting energy q = 4800 – (1200.b)/100
in kJ/kg glass, with b = cullet% in batch

54. 54
Practical relation of specific energy use versus
cullet% from benchmarking studies

55. 55
Effects of recycling cullet on flue gas emissions
• Reduction of NOx: less energy, lower temperatures
• Reduction of CO2: less fuel and less carbonates in batch
• Reduction of fluorides and chlorides: lower temperatures
• Effect on SOx- and dust emissions depends on specific
situation
Table 1.8: Sources of flue gas emissions for container
glass furnace

56. 56
Advantages
- Reduce waste production
- Save natural raw materials
- Less CO2 emissions (direct & indirect)
- Energy profit ( ca. 2.5 % per 10 %)
- More pull from furnace
- Easy to recycle, from glass you can make glass
Disadvantages
- Inclusions in glass product
- Melting process and color less stable
- More production stops
- Lead (Pb) in the container glass (max 200 ppm)
Summary
Cullet input disadvantages versus benefits