2. Assessment of the Egyptian Clayey Deposits for Ceramic Industries
Mohammed A. Serry
Department of Refractories, Ceramics and Building Materials, National Research Centre, Dokki, Cairo, Egypt

3. Aim of the Research work
Reviewing most of the studies published during the last 50 years on geology and assessment of the Egyptian clayey deposits for ceramic industries
Discussing the relationship between nature and ceramic properties of these clays and their chemical, mineral and particle-size composition
Colour, compactness and rate of slaking in water represent nature of the clays, whereas their ceramic properties are represented by plasticity as well as drying and firing behaviour
Accordingly, the Egyptian clayey deposits are classified into three main categories; namely, kaolinite- smectite- and illite rich clays.

4. What are Clayey Deposits?
Clayey Deposits are soft plastic sedimentary rocks, mainly compose of variable amounts of clay and non-clay minerals
Clay minerals are mainly:
Kaolinite, illite and smectite ( or montmorillonite)
Non-clay minerals are mainly:
Quartz, feldspars, micas, calcite, gypsum, goethite, limonite, alunite and others

5. Crystal Structure and properties of clay minerals:
Clay minerals are generally hydrated alumino-silicates with characteristic layer crystal structure (Figure 1), based on different combinations of SiO4-tetrahedral layers with AlO6-octahedral layers at their corners.
Such structure leads to formation of fine, platy and charged particles with variable rates of slaking in water and plasticity as well as drying and firing behaviour.

6. Figure 1: Crystal structure of the kaolinite, illite and smectite clay minerals

7. The physical properties of clay minerals are directly related to their crystal structure:
- Kaolinite clay mineral has high particle sizes (2-10 um), Al2O3 content (~40%) and vitrification range (>1400oC), with low cation-exchange capacity, impurity oxides (<5%), rate of slaking in water and plasticity as well as drying and firing shrinkage.

8. In contrast, smectite clay mineral has ultra-low particle sizes (<2 um), Al2O3 content (<20%) and vitrification range (<1000oC), with high cation-exchange capacity, impurity oxides (up to 20%), rate of slaking in water and plasticity as well as drying and firing shrinkage.
Meanwhile, illite clay mineral always shows intermediate levels of all physical properties between those of kaolinite and smectite

9. Summary of Previous Relevant
Research Work

10. Amer et al. (1970) have assessed the clayey deposits existing at some localities around the Nile Valley and Gulf of Suez for ceramic industries.
They have investigated geology, petrography and chemistry of these clays and generally summarized their suitability for ceramic industries.

11. In 1974, Hegab has studied in detail geology, petrography and mineralogy of many clay deposits exposed at the Nile Valley as well as Eastern and Western deserts.
He also outlined the prospective application fields of the studied clays according to their chemical and mineral composition.

12. Gindy (1983) has generally classified the Egyptian clays and marls into three major clay-mineral provinces as follows (Figure 2):
Kaolinite-rich clays, exposed south of Egypt and formed by chemical weathering and leaching of the Precambrian granite masses, during Paleozoic-Cretaceous times
Kaolinite-illite rich clays, exists around Gulf of Suez and formed due to effect of hydrothermal fluids associated the tectonic and volcanic activity, during Carboniferous time
The sedimentary smectite (or montmorillonite)-rich clays, covering most of Eastern and Western deserts and formed under marine conditions since Mid-Cretaceous time as well as by continental deposition from Mid-Eocene to Pliocene times and thereafter, the River Nile becomes the chief source up to the present time

13. Figure 2: Distribution of the three major clay-mineral provinces allover Egypt as given by Gindy, 1983

14. According to the clay mineral composition, previously characterized by many authors, for the Egyptian clayey deposits the following classification could be done as shown in Figure 3:
Kaolinite-rich clays, mainly exist around Suez Gulf and Aswan areas
Smectite-rich clays, existing around the Nile valley in most of Eastern and Western Deserts
Illite-rich clays, mainly occur in El-Bahariya Oasis, Western Desert

15. Figure 3: Location map of the Egyptian kaolinite-, smectite- and illite- rich clay deposits allover the country

16. Chemical and Mineral Composition of the Egyptian Clays in Relation to their Ceramic Properties

17. 1- Kaolinite-Rich Clays

18. Figure 4: DTA curves of the Gulf of Suez kaolinite-rich clays exposed at El-Tieh, Qiseib and Khaboba

19. Figure 5: DTA curves of Aswan kaolinite-rich clays exposed at Abu El-Riesh, Abu Sbera and Kalabsha

20. Table 1: Mean values of physical properties, particle- size distribution and major mineral composition of kaolinite rich clays representing Aswan and Gulf of Suez Provinces
Major mineral composition, (%)
Particle-size distribution,, (mm), (%)
Water of plasticity
(%)
Rate of slaking in water
Locality
Province
Quartz
Illite
Kaolinite
Clay
Silt
Sand 5 90 50 23
slow
El-Tieh
Gulf of Suez 10 85 48 40 12 21
Qiseib 20 15 65 2 28
Abu El-Riesh
Aswan -- 95 45
Kalabsha

21. Table 2: Mean values of chemical constitution as well as vitrification range and linear drying & firing shrinkage of the kaolinite-rich clays representing Aswan and Gulf of Suez districts
Linear firing shrinkage after vitriication
(%)
Linear drying shrinkage (%)
Vitrification range, (0C)
from- to
Chemical constitution, (%)
locality
Area
K2O
Na2O
MgO
CaO
TiO2
Fe2O3
Al2O3
SiO2
12.30
3.5
0.40
0.20
0.30
2.30
0.80
36.90
45.60
El-Tieh
Gulf Of
Suez
4.90
2.3
0.50
0.10
1.90
35.20
48.80
Qiseib
8.50
4.8
1.70
4.20
27.10
55.30
Abu El- Riesh
Aswan
11.80
3.6
1250 – 1500
2.90
1.40
36.70
44.10
Kalabsha

22. Figure 6: XRD pattern and DTA curve of A Tushka kaolinite-rich clay exposed at Sinn El-Kaddab Plateau

23. 2- Smectite-Rich Clays

24. Figure 7: DTA curves of the Western Desert smectite-rich clays exposed at Wadi El-Natrun, El-Fayoum and El-Kharga

25. Water of plasticity, (%) Rate of slaking in water
Table 3: Mean values of physical properties, particle -size distribution and clay- mineral composition of smectite-rich clays of the Eastern and Western Deserts
Clay-mineral composition,
( %)
Particle size distribution, (mm)
Physical properties
Locality
Desert
smectite
Illite
Kaolinite
Clay
( )
Silt
( )
Sand
( )
Water of plasticity, (%)
Rate of slaking in water 63 12 25 27 32 41
V. Fast
El-Tebbin
Eastern Desert 66 7 45 30 42
El- Minia 72 5 23 74 20 6 65
Wadi El Natrun
Western Desert 75 57 11 55
El-Fayum

26. Chemical constitution, (%)
Table 4: Mean values of chemical constitution as well as vitrification range and total drying and firing shrinkage of smectite-rich clays of the Eastern and Western Deserts
Total
drying and firing shrinkage after vitrification,, (%)
at C
and (12500C)
Vitrification range,
(oC)
from - to
Chemical constitution, (%)
locality
Desert
K2O
Na2O
MgO
CaO
TiO2
Fe2O3
Al2O3
SiO2
11.2
(Bloated)
1.2
1.9
1.5
2.0
1.4
8.9
14.7
59.7
El-Tebbin
East
14.0
1.3
1.1
1.6
0.7
8.8
19.9
53.6
El-Minia
15.7
Bloated
1.8
2.7
2.2
4.4
17.8
56.2
Wadi El-Natrun
West
15.9
2.6
5.1
17.9
55.3
El-Fayum

27. Mechanism of bloating of the smectite-rich clays at 1000-1250oC:
Formation of excessive amount of viscous silicate liquid phase due to the fluxing effect of their high impurity oxide content (15-20%) on their high SiO2 (50-60%) and low Al2O3 (15-20%) contents.
Gradual reduction of Fe2O3 into FeO with the evolution of O2 gas, with simultaneous development of sufficient amount of the viscous silicate phase to trap the oxygen gas and formation of the black magnetite (FeO.Fe2O3 ) spinel.
This results to produce brown, rounded and lightweight bloated clay aggregate with variable sizes and very low bulk density (~0.5 g/cm3).
- These aggregates are greatly demanded for processing insulating building and refractory concretes for application up to 1000oC instead of the more expensive vermiculite, perlite and diatomite lightweight materials, currently imported for this purpose.
Figure 8 confirms the location of the chemical composition plots of all clays in terms of their SiO2 , Al2O3 and total fluxing oxides (TFO) content, on calcined basis, within the area of bloated clays as defined by Riley (1951).

28. Figure 8: Ternary Al2O3-SiO2-total fluxing oxides composition diagram showing the chemical constitution of Tushka as well as Eastern and Western Deserts Clays, on calcined basis plotted and existed within the bloated clays area [after Riley (1951)]

29. 3- Illite-Rich Clays

30. Figure 9: XRD paterrns of the raw illite-rich clays exposed at El-Gedida iron ore mine, El-Bahriya Oasis (a) and its vitrified product (b)

31. Table 5: Mean values of physical properties, particle-size distribution, clay-mineral composition, chemical constitution as well as vitrification range and total linear shrinkage after vitrification of El-Bahariya illite-rich clays.
Clay mineral composition, (%)
Particle- size distribution, (mm), (%)
Water of plasticity (%)
Rate of slaking in water
Sample
Smectite
Illite
Kaolinite
Clay
( )
Silt
( )
Sand
( ) - 65 35 32 33 37
Fast 1 84 16 58 10 38 2
Total linear shrinkage after vitrification (%)
Vitrification range
(oC)
from to
T.F.O
(%)
L.O.I.
Chemical constitution, (%)
Sample
K2O
Na2O
MgO
CaO
TiO2
Fe2O3
Al2O3
SiO2
14.00
24.30
10.50
4.30
1.70
1.50
0.50
0.40
16.00
52.00 1
15.50
25.30
6.10
1.80
1.60
0.10
0.20
15.60
15.00
48.40 2