an engineering geological characterisation of tropical clays - GBV

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The presence of BaO in the red and black soils is most likely a result of contributions in the
form of BaCO3 and/ or BaSO4 as contaminants from industrial effluents and/ or wastes.
Fertilizers and industrial water could also account for the presence of traces of P2O5 in both
types of soil.
Table 6.2. Results of chemical analyses of black clays obtained in this study.
Content SA2- SA2- SA41- SB1- SB1- SB41- SB41- SC17- SC41- SC41-
of (%): 70cm 105cm 50cm 50cm 70cm 30cm 50cm 50cm 30cm 50cm
SiO2 52,50 51,40 58,35 52,79 53,44 52,64 53,21 56,38 52,06 53,71
Al2O3 14,71 14,93 13,37 12,74 12,84 12,14 12,20 11,87 12,06 11,77
Fe2O3 8,66 8,85 6,98 6,90 6,96 6,67 6,75 6,20 6,49 6,10
FeO - - - - - - - - - -
BaO 0,052 0,052 0,031 0,062 0,062 0,064 0,062 0,085 0,123 0,104
MgO 1,25 1,22 1,13 1,16 1,23 1,43 1,42 1,28 1,34 1,31
CaO 1,28 4,29 1,28 1,54 2,01 2,61 2,32 1,47 1,64 1,48
Na2O 1,06 1,04 0,69 0,71 0,76 0,50 0,56 0,82 0,90 0,89
K2O 1,78 1,73 1,25 1,27 1,34 1,02 1,04 1,41 1,32 1,31
P2O5 0,026 0,024 0,037 0,032 0,038 0,038 0,038 0,047 0,036 0,04
ZrO2 0,092 0,091 0,085 0,091 0,092 0,078 0,078 0,072 0,073 0,072
TiO2 0,96 0,95 0,90 0,76 0,75 0,77 0,77 0,75 0,79 0,77
MnO 0,312 0,363 0,249 0,455 0,439 0,497 0,505 0,488 0,469 0,511
SO3 - - - - - - - 0,011 0,028 0,016
Cl 0,065 0,039 - - - - - - 0,015 0,015
F 0,262 0,362 0,247 0,294 0,325 0,281 0,267 0,311 0,300 0,293
Loss on - - - - - - - - - -
ignition
Total 83,01 85,34 84,60 78,80 80,29 78,74 79,22 81,19 77,64 78,39
SA2-70cm, SA2-105cm, SA41-50cm, SB1-50cm, SB1-70cm, SB41-30cm, SB41-50cm, SC17-50cm, SC41-
30cm and SC41-50cm are black clay samples.
The total sum of the various chemical components of the black clays add up to only 77,64 –
85,34% (Table 6.2), and not 100%. This is a relatively large difference which could be partly
accounted for by the presence in the soils of accessory amounts of heavy metal compounds,
light and noble elements; and partly by the loss on ignition of organic matter components. The
difference is comparatively small and negligible in the red soils (Table 6.1) in which the total
sum of the chemical components is virtually 100%, probably due to the relatively low and/ or
negligible organic content (Table 6.7).
6.3 X-ray diffraction (XRD) studies
6.3.1 Scope and method
X-ray diffraction studies and analyses were carried out in the present work to determine the
mineralogical composition of the black clays and red soils. Clay minerals present were
identified by their characteristic diffraction patterns.
A diffractometer (Type PW1710-Basis) was used to determine the presence of clay minerals
which include smectites ( montmorillonite), kaolinite and illite. This was done for selected
conditions of continuous scanning rate of 0,020 (° 2θ/second), chart speed 0,10 (mm/ second)
and using Cu-Kα radiation. The clay minerals were X-rayed from prepared clay fractions (