Clay – a natural earthTo a clay mineralogist:

is a layer silicate mineral (called phyllosilicate) or other mineral which imparts plasticity and hardens upon drying or firing (Guggenheim and Martin, 1995)

could be referred to as a particle size in a soil or sediment of a diameter < 0.002 mm or 2 microns)

composed of silica (SiO2), Alumina (Al2O3) and water (H2O) plus appreciable concentrations of oxides of iron, alkali and alkaline earth.

Clay - classification As smectite, vermiculite, kaolinite, illite, chlorite, allophane,

hematite, geothite, ferrihydrite, and lepidocrocite.

Of interest in this study is the kaolinites, which are classified based on their physical properties, mode of formation and resistance to high temperature.

Further classifications in relation to high temperature resistance are as:

refractories, high melting clays and low-melting clays.

Kaolinitic Clay Deposit in South-west Nigeria

South-West Nigeria**

An estimated reserve of 3 billion tonnes of good kaolinitic clay has been identified in many locations in Nigeria (south-west) ready for massive development and exploitation.

PurposeTo improve the thermal and physical

properties of kaolinitic clay (south-western Nigeria deposits) for industrial application as insulators .

Approach Wood particles (sawdust)

Clay samples were collected from Ibule, Ikeji-Arakeji and Ikere-Ekiti deposits in Ondo, Osun and Ekiti states respectively.

Clay samples were crushed to 150 µm and proportions needed for different analyses were weighed.

Classical chemical analysis (Wet Analysis Technique) was used to determine the chemical composition(Beeley,1990).

Approach –Physical properties

Physical properties such as: - bulk density, - porosity, - shrinkage, - sintering temperature, - spalling resistance, - cold crushing and strength and - thermal conductivity were determined using

standard methods of the American Foundrymen’s Society (AFS, 1993).

Approach Ikere-Ekiti / Ikeji-Arakeji clay in ratios 50:50, 60:40 and 70:30 by

mass.

Each blend was soaked separately in a basin for 3days.

Mixing and wet sieving was performed to remove deleterious particles followed by sun drying, crushing, grinding to fine particles to obtain 50 µm.

Sawdust was mixed with the clay blends in varying percentages of 5, 10, 20 and 30%.

Cubical, cylindrical, spherical and rectangular shapes were obtained from the blends and then thermo- physical properties determined using AFS (1993) method.

Results – Characterization Ikere-Ekiti Clay was an Alumino-Silicate clay (fire-clays) which consists

essentially of Al2O3 and SiO2 associated with impurity oxides such as Fe2O3, TiO2, MgO, Na2O and K2O of about 13%.

The ratio of aluminium oxide to silicon oxide of Ikeji-Arakeji (19.67:48.24) confirms the clay deposit as a bentonite-montmorillonite.

Chemical composition in wt %Oxide Ikeji-Arakeji Ikere-Ekiti Fire- clay ((Omotoyinbo &

Oluwole, 2008)

Al2O3 19.67 30.82 23 -34

SiO2 48.24 47.14 48-60

Fe2O3 10.81 2.00 2-4

MgO 1.33 0.32TiO2 1.51 0.50

CaO 0.55 0.25Na2O 0.87 0.80

K2O 3.00 1.90

Ignition loss 9.74 7.98 7-11Others 4.78 1.09Total 100.00 100.00

Chemical composition of selected samples

Results and Discussion

Properties Ikeji-Arakeji

Ikere-Ekiti

Ikere-Ekiti/Ikeji-

Arakeji70/30

Ikere-Ekiti/Ikeji-

Arakeji60/40

Ikere-Ekiti/Ikeji-

Arakeji50/50

Fire clay accepted standard

range (Omotoyinbo & Oluwole, 2008)

Bulk density (g/cm3)

1.56 1.51 1.518 1.522 1.528 1.5-2.1

Volume fraction of open porosity

0.28 0.56 0.37 0.46 0.43 0.25-0.4

Shrinkage on firing (%)

4 2 2.47 2.63 2.91 3-7

Thermal conductivity (W/mK)

0.64 0.14 0.342 0.392 0.529 0.1-0.5

Sintering temperature (oC)

1200 1400 1430 1350 1300 1500-1750

Spalling resistance (cycles)

10 15 10 11 11 30+

Cold crushing strength (kN/m2)

4870 3610 3880 4090 4510 5000+

Thermal and physical properties of selected clays and clay blends

Results and Discussion

Results and Discussion

050

100150200250300350400450500

0.37 0.39 0.43 0.48 0.57 0.61

CCS x

10

(Kn/

m2)

Volume fraction of open porosityFig. 4 Effect of porosity on cold crushing strength of clay blends

70/30

60/40

50/50

Results and Discussion

Results and Discussion

Results and Discussion

Conclusion

Clay blends - low sintering temperature, spalling resistance and cold crushing strength as compared to standard values of 1500 0C – 1700 0C; 30+ cycles and 5000+ kN/m2 respectively.

The effect of sawdust addition on Ikere Ekiti and Ikeji Arakeji clay blends of 50:50, 60:40 and 70:30 showed that important properties such as, bulk density, porosity, shrinkage and thermal conductivity, improved, thus making the blends fit as fire clay.

However, the addition of sawdust has no effect on sintering temperature, spalling resistance and cold crushing strength.

A 10 % sawdust addition to 70:30 Ikere Ekiti / Ikeji Arakeji clay blend, makes the blend fit as a fire clay.