Vol. 10(11), pp. 415 -431, November 2016 [620418]

Vol. 10(11), pp. 415 -431, November 2016
DOI: 10.5897/AJEST2016.2184
Article Number: 6A3AD9C61105
ISSN 1996 -0786
Copyright © 2016
Author(s) retain the copyright of this article
http://www.academicjournals.org/AJEST African Journal of Environmental Science and
Technology

Full Length Research Paper

Characterization and classification of clay minerals for
potential applications in Rugi Ward, Kenya

Ochieng Ombaka

Department of Physical Sciences, Chuka University, Kenya .

Received 8 August, 2016; Accepted 2 9 September, 2016

The applica tions of various clayey mineral s are related to their structural , physical and chemical
characteristics. The physical and chemical properties of the clayey minerals dictate th eir utilization in
the process industries and bene ficiation required before usage. The study aimed at establishing the
potentiality of clayey minerals from the study area , and the possibility of exploring and exploiting them
in order to spur industrial development and promote economic self reliance of Ken ya as a nation. The
plasticity, particle size, surface area, chemi cal and mineralogy composition, morphological, thermal
analysis and other physical properties were studied using various techniques. T he clay samples
composed of albi te (5-16.7%), kaolinite (11.4 -36.2%), micro cline (15.2 -35.3%), quartz (24.3 -68.1%),
hornblend e (7.6% in samples from Ngamw a only) , and other mineral i mpurities in small amount s.
Ngamwa clayey material s consist of high impurities of chemical oxide s such as TiO 2, MnO, MgO and
Fe2O3. Generally, q uartz and iron were the major impurities present in the samples from the concerned
sites . The findings shows that clayey minerals from the study area can be exploited for commercial
production of ceramic products after beneficiation using low cost and environmental friendly
techniques in order to reduce the levels of iron, quartz, and other impurities to acceptable levels .

Key words : Kaolin, Impurity m inerals, shrinkage, plasticity index, surface area, quartz.

INTRODUCTION

Clay is a natu rally occurring material composed of
layered structures of fine -grained minerals which exhibit
the property of plasticity at appropriate water content but
becomes perma nently hard when fired (Heckroodt , 1991 ;
Njoka et al ., 2015). The clay material is forme d from
chemical weathering processes on the earth’s surface ,
and contributes about 40% of the fine grained sedi –
mentary rocks (mudrocks ) which includes mud stones, clay stones and shales. Clay minerals are generally
composed of aluminum silicates which are formed by
tetrahedral and octahedral sheets that are linked tog ether
through sharing of apical oxygen atoms (Madejova,
2003). The formation of clay minerals is dependent on
physicochemical conditions of the immediate weathering
environment, nature of the starting materi als and other
related external environmental factors (Wilson, 1999),

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416 Afr. J. Environ. Sci. Technol.

thus resulting into vari ous types of clay material s.
Consequently, the application potent ial of any clay
mineral type in nature will depend on its chemical
composition, structure and other inherent properties
(Landoulsi , 2013). On this regard, clay minerals are
classified into different groups as follows; Kaolinite,
Smectite, Vermiculite Illite and Chlorites .
Kaolinite group which includes clay minerals like
kaolinite, hallosite, nacrite and dick ite, is a 1:1 type clay
mineral . It is composed of one layer of silica and one
layer of alumina , which is formed under acidic conditions
through advanc ed weathering processes or hydrothermal
changes of feldspars and other alluminosilicates
(Miranda -Trevino , 2003). The chemical formula of
kaolinite is Al 2O3.2SiO 2.2H 2O (39% Al 2O3, 46.5% SiO 2
and 14.0% H 2O) and its structure possesses strong
binding forces between the layers which resists
expansion when wetted (Miranda -Trevino, 2003 ;
Trickova, 2004). The cation exchange capacity (CEC) of
kaolinite is less than that of montmorillonite due to its low
surface area and low isomorphous substitution that result
from its high molecular stability ( Aroke, 2013 ; Murray,
1999) and this contributes to its low plasticity, cohesion,
shrinkage and swelling . However, the material can
adsorb small molecular substances such as lecithin,
quinolone, paraquat, diaquat polyacrylon itrite, some
proteins, bacteria and vir uses (Williams and
Environmental , 2005). Industrial uses of Kaoline includes;
manufacture of paper, paint, rubber, ceramic, plastic and
pharmaceutical products , catalyst for petroleum cracking
and auto exhaust emissio n catalyst control devices ,
cosmetics base and pigments (O laremu, 2015).
Furthermore, kaolin is incorporated as an anti -cracking
agent in the manufacture of fertilizer prills, as a carrier for
pesticides, manufacture of white cement where it
contributes al umina without iron, and in the production of
glass fiber as a low -iron and low alkali source of alumina.
On pharmaceutical applications for example , Kaopectate
and Rolaids are used as the main ingredients for the
original formulation of anti-diarrhea medic ation . Kaolin
can be used to decontaminate aflatoxins, plant secondary
metabolites, pathogenic microorganisms, heavy metals
and other poisons in the animal diets which could be
harmfu l to the digestive system through firm and selective
binding of these noxious agents (Trckova, 2004).
However, long term exposure to kaolin causes
developm ent of radiologically diagnosed pneumoconiosis .
Kaolin that is heavily stained with ferric iron results to red
or deep red colouration that is evenly widespread on
ceramic bo dies upon firing in an oxidizing environment.
These iron stained clays can be used for coloured clay
products but have no potential in high -grade ceramic
applications. Therefore, brightness i s the critical property
in most high-value applications o f kaolin (Chandrasekhar,
2006). Naturally, k aolin may be accompanied by other
mineral impurities such as feldspar and mica, quartz,

titanoferous, illite, montmorillonite, ilmenite, anastase,
haematite, bauxite, zircon, rutile, sil liminate, graphite,
attapugite, halloysite and carbonaceous materials
(Ramaswamy and Raghavan, 2011) , thus reducing its
industrial usefulness . On this regard , mineralogical
analysis coupled with visual assessment of the colour is
crucial when sampling for kaolinites, and then comple –
mented by beneficiation trials and product evaluation .
However, the late r processes are both exp ensive and
time consuming. P reliminary characterization stage
ensures that inferior sampl es are screened out so that
resources can be di rected towards in vestigation of
samples with most commer cial potential. This stage also
enable s the quantification of toxic elements and/or
micronutrients ( Fe, Sb, As , Cd, Co, Cu, Pb, Hg, Ni, S e,
Te and Zn) wh ose levels depend on their geological
history .
Smectite, which i ncludes montmorrilonite, beidellite,
nantronite, saponite and hectorite, are 2:1 layer clay
minerals formed from the weathering of soils, rocks
(mainly bentonite) or volcanic ash and belongs to a group
of hydrox yl alumino -silicate (Erdogan , 2015). The
variation of physical and chemical properties of bentonites
within and between deposits is caused by differences in
the degree of chemical substitution within the smectite
structure, the nature of the exchangeable cations
present, type and the amount of impuri ties present
(Christidis and W arren, 2009). Minerals associated with
smectites in clude quartz, cristobalite, feldspars, zeolites,
calcite, volcanic glass and other clay minerals such as
kaolinite (Abdou, 2013). The groups of smectit e clays are
distinguishe d by differences in the chemical composition
pertaining substitutions of Al3+ or Fe3+ for Si4+ in the
tetrahedral cation sites and Fe2+, Mg2+ or Mn2+ for Al3+
in the octahedral cation sites. Smectites have very thin
layers and small particle sizes which co ntributes to high
surface area and hence a high degree of absorbency of
many materials s uch as oil, water and other chemicals
(Marek, 2010 ; Amel, 2013) . Additionally, smectites have
higher cation exchange capacities, swelling and
shrinkage properties than other clays . The variable net
negative charge on smectites structural layers attracts
water molecules into the interlayer area thus causing
expansion, and the amount of swelling is related to the
type of interlayer cation present. For example, the sodium
rich smectite clays expand more than those containing
calcium ions (Odom, 1984). Na-montmorillonites contai n
one water layer in the interlayer position and C a-
montmorillonites consists of two water layers which
account for the basal spacing o n the x -ray dif fraction
pattern of 15.4 Å for Ca-montmorillonite and 12.6 Å for
Na-montmorillonite (Murray, 1999). S oils dominated by
these types of minerals form a wide range of cracks upon
drying up and the resultant dry aggregates are very hard
hence making the soil difficult to till (El -Maarry, 2013).
These soils are stable in arid, semi -arid or temperature

climate and they form smooth gels when mixed with the
right amount of liquids . Smectites are valuable minerals
for industrial applications due to their h igh cation
exchange capacities, high surface area, surface reactivity,
adsorptive capacity and catalytic activity (Odom, 1984).
This group of clays has found applications in bonding
foundry san ds, drilling fluids, iron ore pelletizing ,
agriculture (as carrier material for pesticides, fertilizers
and for coati ng seeds), paper making, paints, pharma –
ceuticals, cosmetics, plastics, adhesives, decolorization
and ceramics ( Christidis , 1998). The material is also used
as clarifying agents for oils and fats, chemical barriers,
liquid barriers and catalysts ( Abubakar, 2014).
Preparation of some high technology materials such as
pillared clays, organoclays and polymer/smectite -nano
ccomposites i nvolves purification and physico chemical
modifications of pure smectite (Ray and Okamoto , 2003).
However, t he commercial bentonites should contain not
less than 60% smectite.
Vermiculite is a hydrated magnesium aluminium -iron
silicate which possesses 2:1 type of clay minerals (Tang,
2012). It has a layer charge of 0.9 -0.6 per form ula unit ,
and contains hydrated exchangeable cations primarily
Ca, and Mg in the interlayer (Schulze, 2005). The high
charge per formula unit gives vermiculite a high cation
exchange capacity and c auses this clay type to have a
high affinity of weakly hydr ated cations such as K+, NH 4+
and Cs+. Upon rapid heating at a temperature of 900 °C or
higher, the water in raw flakes vermiculite flashes into
steam and the flakes expand into accordion -like particles
(Hillier, 2013), a phenomenon known as exfoliat ion
(Belhouideg and Lagache 2014). The expanded or
exfoliated material is low in density, chemically inert and
adsorbent has excellent thermal and acoustic insulatio n
properties, is fire resistant and odourless . The common
applications of exfoliated vermiculite i nclude making of
friction light weight aggregate s, thermal insulator , brake
linings, various construction products, animal feeds and
in horticulture (Chad and Stachowiak, 2004; Ucgul and
Girgin , 2002; Lescano, 2013). Incorporation of vermiculite
in fertili zers makes them more efficient in releasing
nutrients and hence making the fertilizers more
economical to the consumer s (Abdel -Fattah and Merwad
2015). The layered structure and the surface
characteristics of vermiculite enable them to be used in
products such as intumescent coatings and gaskets ,
treatment of toxic waste and air -freight. The expansion of
vermiculite on heating generates sufficient internal
pressure which can be utilized to break hard rock during
tunneling work ( Ahn and Jong, 2015). Vermicul ite ores
contain variable a mounts of other minerals such as
feldspars, pyroxenes, amphiboles, carbonates and quartz
that are formed along with vermi culite in the rock and
occur as major components, as well as minor components
such as phosphates, iron oxide s, titanium oxides and
zircon (Lescano, 2013). Some impurities like asbestiform Ombaka 417

amphibole minerals found in vermiculite have toxicity
impact on human health as they lead to development of
diseases such as malignant mesothelioma, a sbestosis or
lung c ancer ; hence, characterization of clay s is important
in order to identify such impurities.
Illite clay mineral group is also called clay micas. Mica
is a group of phyllosilicate minerals with crystalline
structure that can be split or de laminated into thin sheets
that are platy, flexible, clean, elastic, tr ansparent to
opaque, resilient, reflective, refractive, dielectric,
chemically inert, insulating, light weight and hydrophilic
(Unal and Mimaroglu, 2012) . The atoms of mica minerals
are bonded together into flat sheets which allow a perfect
cleavage of the mineral s to produce tough sheets that
occur in a variety of colours including brown, green ,
black, violet or colourless and often with a vitreous to
pearly luster ( Amrita et al., 2011) . Studies have shown
that t here are over 30 members of mica group, but six
forms that are found in nature and commonly used in
microscopy and other analytical applications consist of
muscovite, biotite, phlogopite, lepidolite, fuchsite and
zinnwaldite (Orl ando, 2002) .Three me mbers (illite group)
which includes illite, glau conite and muscovite are
referred to as clay minerals because they exhibit
characteristic properties of clay, with illite mineral being
the most common. Illite is formed from weathering of
potassium and aluminum rich rocks like muscovite and
feldspar under alkaline conditions. Illite group is a 2:1
layer silicate clay mineral which is non expansive
because the space between the crystals of individual clay
particles is filled by poorly hydra ted potassium cations or
calcium and magnesium ions which hinder water
molecules f rom entering the clay structure . The cation
exchange capacity of I llite ranges between 20 -40 meq
per 100 g. The colour of the mineral s ranges from grey
white, silvery white t o greenish grey . The illites find
application in structural clay industry and in agro minerals
due to high potassium content (Njoka et al ., 2015; Van,
2002). Mica clay ores contain a variety of impurities
which includes quartz, feldspar, kaolin and pyroxen e
(Capedri et al., 2004). Presence of these minerals in mica
ores will impact upon the industrial value of these
deposits and the process ing complexity thus reducing or
increasing its value depending on the applications
(Gaafar , 2014).
Chlorites are hydrou s aluminosilicates that are
arranged in a 2:1 structure with an interlayer (Wiewiora,
1990). They incorporate primarily Mg, Al and Fe cations
and to a less extent Cr, Ni, Mn, V, Cu and Li cations in
the octahedral sheet within the 2:1 layer and in the
interlayer hydroxide sheet . They also exhibit a large
substitution of Si by Al cations in the tetrahedral sheet
(Ako, 2015). The colour of chlorites varies from white to
almost black or brown with a tint of green where these
optical properties are coupled to the chemical
composition of chlorite (Saggerson, 1982). Knowledge of

418 Afr. J. Environ. Sci. Technol.

Figure 1. Locally made clay products.

the chemical composition of chlorite is important in the
study of phase relationships in low and middle grade
metamorphic rock ( Albee , 1962).
Considering the diversity of clay mineral groups in
nature, the initial mineralogical and chemical examination
of clay ores can be used to indicate the suitability of the
material for different applications. In Kenya , there are
several industries which can utilize the readily available
and cheap clay raw materials after beneficiation in order
to support industrial growth and relieve the government
off the burden of importing such products. The improved
indust rial utilization of clay minerals in the country will
depend mainly on the quality and durability of the
material, and for this to be realized, there is need for
rigorous studies on this resource . Unfortunately, v ery little
attention has been given to clay characterization and
mineralogy in Kenya despite the growing demand for clay
products and the possibility of creating jobs through
cottage industries. Currently , the local communities in
Kenya are relying on the indigenous knowledge to make
some clay prod ucts whose quality is hard to determine
and neither does it meet the export standards as shown
in Figure 1.
The objective of this study was to carry out the
mineralogical, physical a nd chemical characterization of
Rugi clay deposits in order to highlight i ts potential
application and encourage more studies on this
unexploited field.

MATERIALS AND METHODS

Study area

The ceramic clays occur in Tabaya -Karundu Valley in Rugi ward

which is lowland in Nyeri County. The valley has a west -east
orientation a nd covers an area of about 38 h a. The region
experiences average temperatures ranges of 12 – 27°C with low
temperatures in the month of June and July and highest
temperatures in the months January -March and September –
October. The average rainfall lies betw een 500 mm and 1500 mm
per annum with bimodal rainfall pattern where long rains occur
between March and May and short rains between October and
December. Within the valley, there are two major excavation sites
for ceramic clay that are close to each other but fall in different
administrative units namely, Mweru and Karundu. The former site
(Mweru) lies in Mweru sub location at an altitude of 1441 m above
sea level on latitude 0 ° 36.474’ S and longitude 37 ° 6.828’ E, whose
soil appear ance is black/brown (Fig ure 2).
Karundu lies in Karundu sub location at an altitude of 1445 m
above sea level, latitude 0 ° 36.400’ S and longitude 37 ° 6.799, and
the soil appearan ce is grayish white (Figure 3).
The two sites are located less than 200 m off the Nairobi –
Mukurwe -ini highway, and both lie on a swampy ground. The soils
within the sites are typically waterlogged with the water bearing
viscous appearance and issuing a smell characteristically indicative
of the presence of humic acids. Phagmites ( Typha spp.) are the
domin ant vegetation on the sites, and in areas where excavation
was abandoned, the local community grows a thriving crop of
arrowroots. A third excavation site locally known as Ngamwa lies a
little lower than Mweru and Karundu sites. Ngamwa lies at an
altitude of 1427 m above sea level on latitude 0 ° 36.504’ S and
longitude 37 ° 7.913 E, with soils bearing a light brown coloration
and coarse texture. This site is farther (2 km) off the highway than
the first two sites, it is impassable and inaccessible due to the poor
terrain, and there was virtually no evidence of recent excavation
activity compared to the other sites.

Sampling techniques

Three sites namely, Karundu, Mweru and Ngamwa were chosen
using purposive sampling technique to collect samples. The
collec tion and preparation of clayey samples was carried out as
described by Njoka et al. (2015). The quality and resolution of the
obtained results was improved by performing pretreatment of the
samples in order to remove the organic matter and other unwanted
materials. Spectroscopic grade chemicals were used in the present
investigation.

Instrument s used and procedures

The following instruments were used in the present work. PG -990
Atomic absorption spectrophotometer, Analytikjena model contra
700, IRAffinity-1 FTIR Spectrophotometer, Shimadzu, Perkin Elmer
Model TGA7, Thermal gravity analyzer, Transmission Electron
Microscope JOEL.JEM -1210 (120KV, MULTISCAN CAMERA),
Bruker AXS D8 Advance diffractometer, Quantachrome NOVA 1200
Gas sorption analyzer . The proce dures used by Njoka et al . (2015)
and El -Geundi et al . (2014) were adopted in the present study, and
the Atterberg limits were determined as described by Melo et al.
(2012).

RESULTS AND DISCUSSION

Table 1 presents the consistency limits and physical
properties of clayey raw materials from Rugi ward. The
consistency limits were determined in order to identify,

Ombaka 419

Figure 2. Mweru site.

Figure 3. Karundu site.

classify and predict the fine -grained soil behavior. Liquid
limit, plastic limit, plastic index and linear shrinkage of the
clayey raw materials collected varied from 40.00 -64.00,
19.00 -36.00, 18.00 -29.00 and 9.00-14.00 respectively. These results showed that the collected clayey materials
were inorganic clays except the samples from Karundu
site at the depth of 0 -20 cm which was inorganic silt. The
average values of the plastic index of the samples from

420 Afr. J. Environ. Sci. Technol.

Table 1. Physical properties of clay samples.

Sample site Depth
(cm) Atterberg limits (%) Texture classes of clay
Liquid
limit Plastic
limit Plastic
index Linear
shrinkage Inferences %
Clay %
Silt %
Sand %
Gravel Plasticity
ratio LL/PL Inferences
Karundu 0-20 40.0 19 21 11 Inorganic silt 4 21 60 15 2.11 Silty sand
20-40 44 26 18 9 Inorganic clays 33 17 48 2 1.69 Clayey sand
40-60 44.5 25 19.5 9.28 Inorganic clays 49 17 33 1 1.78 Clayey sand

Mweru 0-20 44 25 19 10 Inorganic clay 28 15 55 2 1.76 Clayey sand
20-40 53 26 27 12 Inorga nic clays 25 11 49 15 2.04 Clayey sand
40-60 53 31 22 10 Inorganic clays 31 20 41 8 1.70 Clayey sand

Ngamwa 0-20 63 32 31 13 Inorganic clay 49 19 29 3 1.97 Sandy clay
20-40 64 36 28 14 Inorganic clays 56 18 23 3 1.78 Clayey sand
40-60 60 31 29 14 Inorganic clays 55 17 26 2 1.93 Clayey sand

Karundu, Mweru and Ngamwa were 18.8, 22.7,
and 29.33 % respectively. The results revealed
that clayey raw material from Karundu have
medium plasticity while those from Mweru and
Ngamwa poss ess high plasticity. Furthermore,
results from Ngamwa indicated that the clay soil
has a finer (more clayer) texture as revealed by its
higher value of plasticity index in comparison to
the clayey materials from Karundu and Mweru.
The high plasticity claye y materials from Ngamwa
might be due to high levels of mineral oxide
impurities such as TiO 2, MnO, MgO and Fe 2O3.
Clay identification chart using plastic limit and
plasticity index parameters was used to identify
the type of clayey minerals present in the
samples. According to the clay chart, the results
obtained in all sampling points were slightly lower
in kaolinite tha n for pure kaolinite clays. The
difference might be contributed by the presence of
sand and silt in the samples. The plasticity ratio of
5.9, 2.16 and 1.59 indicates montmorillonite, illite and kaolinite respectively. Results obtained in the
present investigation are very close to what is
expected for kaolinite clays except those from
Karundu samples at the depth of 0 -20 cm and
Mweru at t he depth of 20 -40 cm which were close
to that of illite clay. However, the obtained results
are suggestive of the presence of both kaolinite
and illite clayey minerals in the samples in
question. The values of linear shrinkage ranged
between 9.00 -11.00, 10 .00-12.00 and 13.00 -14.00
for Karundu, Mweru and Ngamwa respectively.
High linear shrinkage value in clayey samples
from Ngamwa was attributed to the amount of
available clay minerals in the samples whereas
the slightly low shrinkage values obtained from
Mweru and Karundu samples was associated with
the presence of high amount of quartz which
tends to decrease the magnitude of shrinkage.
Clayey mineral samples from the study area
consist of 4 -56, 11 -21, 23 -60 and 2 -15% of clay,
silt, sand and gravel respectively. The clayey mineral samples which were collected at Karundu
(0-20 cm) and Ngamwa (0 -20 cm) were silty sand
and sandy clay respectively. The high level of
gravel from Karundu (0 -20 cm), Mweru (20 -40 cm)
indicated high level of quartz.
The oxid es analysis results using XRF and AAS
are presented in Table 2. The data obtained for
Al2O3, SiO 2, CaO, TiO 2 and Fe 2O3 were used to
determine whether XRF and AAS analytical
methods produced comparable results. Analysis
was done using statistical programme for social
sciences (SPSS) version 20 at p= 0.05, and
confirmed using excel and manual approaches.
The correlation values obtained were as follows;
Al2O3 (R = -0.16, p=0.968), SiO 2 (R= 0.824,
p=0.006), CaO (R= 0.446, p= 0.229), TiO 2(R=
0.173, p=0.655) and Fe2O3 (R= 0.609, p=0.081),
while the standard errors of the estimates for
Al2O3, SiO 2, CaO, TiO 2 and Fe 2O3 were 4.63,
8.58, 0.18, 2.07 and 5.88 respectively. These
results revealed that there was no significant

Ombaka 421

Table 2. Chemical composition of clay samples using XRF and AAS (%). Please provide the respective depths

Sample site Depth
(cm) XRF AAS
MgO V2O5 Al2O3 SiO 2 CaO TiO 2 MnO Fe2O3 K2O Al2O3 SiO 2 CaO TiO 2 MnO Fe2O3 K2O MgO Na2O LOI Conductivity in Hs
Karundu 0-20 ND ND 25 71 0.29 1.3 ND 2.3 ND 15.38 78.33 0.28 0.02 0.07 2.30 4.40 0.20 0.28 4.17 28.8
20-40 ND 0.2 32 45 0.49 5.8 1.9 14.4 1.9 28.34 58.54 0.28 0.47 0.05 1.61 1.44 0.26 0.36 5.12 28.7
40-60 ND 0.08 40 54 0.51 2.2 ND 4.40 ND 17.18 60.61 0.47 2.28 0.08 6.40 1.66 0.33 0.65 8.97 27.8

Mweru 0-20 ND 0.1ND 27 41 0.53 5.5 0.2 24.40 1.8 20.13 71.02 0.82 2.25 0.10 9.80 2.80 0.60 1.02 8.08 108.8
20-40 ND 0.1 33 59 0.31 1.2 0.05 6.70 ND 13.50 84.27 0.24 2.62 0.06 2.56 0.76 0.22 0.19 4.08 105.2
40-60 ND 33 49 0.50 6.6 ND 9.57 1.1 21.64 54.37 0.54 3.10 0.07 4.05 1.10 0.56 0.42 9.63 111.0

Ngamwa 0-20 ND 0.1 34 33 0.1 4.2 ND 17.9 0.33 29.10 49.39 0.54 2.64 0.09 11.60 0.55 0.56 0.35 10.06 21.8
20-40 ND 0.1 30 30 0.1 3.4 ND 13.9 0.26 27.90 47.15 0.30 3.07 0.08 10.60 0.40 0.41 0.18 14.94 22.0
40-60 ND 0.08 30 29 0.09 3.2 ND 13.0 0.2 30.30 44.70 0.27 2.41 0.07 11.10 0.40 0.40 0.20 13.80 22.5

correlation for all the oxides since their p – values
were above critical value (0.05) except for SiO 2
which showed a strong positive correlation
(R=0.82) at p -value =0.006 (below critical value).
The F -value for SiO 2 was 14.81 at p=0.006 (less
than critical value) indicating that there was no
statistically significant differenc e in the precision
when the two methods are used. The t -value for
SiO 2 was 3.85 at p= 0.006 (less than critical value)
confirming that there was no statistically
significant difference in the silica results obtained
using the two methods. Also a close scru tiny of
the results revealed that several metal oxide were
not detected by the XRF analytical method in
some samples whereas they were detected in
those samples by the AAS method. AAS usually
exhibit superior sensitivi ty and low detection limit
than XRF spectroscopic method. Therefore, based
on above reasons, AAS results were used for
analysis.
The average percentage of Al 2O3 in clay mineral
samples from Karundu, Mweru and Ngamwa were
18.96, 18.42 and 29.10 respectively and those of Fe2O3 were 3.44, 5.47 and 11.10 respectively.
This revealed that the quantity of Al 2O3 was less
than 30% while that of Fe 2O3 was more than 1%
in all the samples studied. Clay with a composition
of 5% or more of Fe 2O3 are used as red firing
clays, those with between 1 – 5% Fe 2O3 are B tan
–burning clay and those containing less than 1%
Fe2O3 are used as white firing clays (Murray,
2007). Thus, these clays do not meet the
conditions necessary for refractory fired clays,
manufacture of high grade ceramic products such
as white porc elain and glossy papers and other
products that require clay with less than 1% iron
content and at least 30% Al 2O3. The presence of
other oxide impurities like CaO, MgO etc. might
also reduce the suitability of clayey mineral
samples for refractoriness. Th e average quantities
of Loss on Ignition (LOI) value obtained from
clayey minerals from Karund u, Mweru and
Ngamwa were 6.087, 7.263 and 12.933%
respec tively. Notably, there was high values of
LOI of clay samples from Ngamwa which might
imply that, they pos sess finer grains, high content of Al 2O3 and could be more compact compared to
those from Mweru and Karundu. The relatively
higher LOI values in clayey mineral samples from
Mweru compared to Karundu were associated
with high percentages of impurities, wat er and
organic matter in the samples. The low values of
alkaline oxides (K 2O, Na2O) in clay mineral
samples from Ngamwa in comparison to those
from Mweru and Karundu implies presence of low
percentage of flux minerals. Ngamwa clayey
minerals showed a high percentage of Fe 2O3
which might increase the action of alkaline flux
that results into a lower melting temperature and
an increase in the abundant liquid phases thus
making the material difficult to crystallize.
The results of inorganic elements present in
clay samples are summarized in Table 3. The
average concentration in mg/kg of various
elements obtained were; Karundu {Na (0.0243),
Ca (0.0229), K (0.0427), Mg (0.0228), Fe (2.207),
Mn (0.006), Zn (0.0016), Cu (0.0013), Cr (0.0094),
Pb (0.001)}; Mweru {Na (0.0353), Ca (0.0364),
K(0.0401), Mg (0.00364), Fe (1.25), Mn (0.0077),

422 Afr. J. Environ. Sci. Technol.

Table 3. Composition (mg/kg) of inorganic elements in the clay samples.

Sample site Depth
(cm) Na Ca K Mg Fe Mn Zn Cu Cr Pb Al Sb Co Cd Conducti vity
(µs) pH
Karundu 0-20 0.0117 0.0210 0.0405 0.021 2.38 0.006 ND ND 0.0126 0.0002 0.752 ND ND ND 28.8 5.14
20-40 0.0499 0.0213 0.0508 0.0213 2.67 0.0120 0.0044 0.0044 0.0011 0.0011 1.798 ND ND ND 28.7 5.17
40-60 0.0114 0.0263 0.0368 0.0262 1.57 ND 0.0005 0.0005 0.0037 0.0017 1.613 ND ND ND 27.8 5.21

Mweru 0-20 0.0178 0.0298 0.0460 0.0298 1.23 0.0157 0.0039 0.0066 0.039 0.0008 1.705 ND ND ND 108.8 4.45
20-40 0.0386 0.0552 0.0258 0.0552 1.49 ND ND ND ND 0.0004 1.107 ND ND ND 105.2 4.32
40-60 0.0496 0.0241 0.0486 0.0241 1.03 0.0073 0.0058 0.0058 0.0058 0.0012 1.701 ND ND ND 111.0 4.35

Ngamwa 0-20 0.0140 0.0427 0.0262 0.0427 6.67 0.0146 0.0028 0.0030 0.0030 0.0014 1.942 ND ND ND 21.8 5.35
20-40 0.0076 0.0431 0.0282 0.0431 7.18 0.0162 0.0027 0.0047 0.0047 0.0012 1.93 ND ND ND 22.0 5.37
40-60 0.0162 0.0443 0.0347 0.0443 8.60 0.0181 0.0034 0.0034 0.0034 0.0024 2.84 ND ND ND 22.5 5.38

Zn (0.00393), Cu (0.0032), Cr (0.0095), Pb
(0.0008)], Na (0.02 43), Ca (0.0229), K (0.0427),
Mg (0.0228), Fe (2.207), Mn (0.006), Zn (0.0016),
Cu (0.0013), Cr (0.0094), Pb (0.001)}; Ngamwa
{Na (0.0126), Ca (0.0434), K (0.0297), Mg
(0.0434), Fe (7.483), Mn (0.0163), Zn (0.00297),
Cu (0.0037), Cr (0.00683), Pb (0.001667 )}. The
high levels of iron in all clay samples collected
might be associated with the black, brown or
grayish white colour that was observed in clay
mineral samples from the study area. This
colouration will have a negative eff ect on the
degree of brightn ess of the products manufactured
using clay minerals from the study area as shown
in Figure 1, hence reducing their quality. However,
the final product quality can be achieved by
reducing the levels of iron and other impurities
present to acceptable levels by employing low
cost and environmentally friendl y techniques. The
average pH of clay samples from Karundu, Mweru,
Ngamwa were 5.17, 4.37 and 5.36 respectively,
and all fall within the pH range of 4.0 to 9.0 f or
chemically inert kaolinites, implying that the kaolinites present in the studied clay samples are
chemically inert. The average conductivity of clay
samples from Karundu, Mweru, Ngamwa were
28.4, 108.3 and 22.1 µS respectively. The high
value of conductivity of clay samples from Mweru
is associated with low pH observed. However, the
electrical conductivity has a linear relationship
with cation exchange capacity, particle size
distribution, mineralogy, organic matter content,
porosity and water content of the soil sample.
High electrical c onductivity relates to clay minerals
like the smectite group that exhibits high cation
exchange capacity (CEC) thus, the low electrical
conductivity observed in the clay samples from
Kurundu and Ngamwa imply presence of clay
minerals with low CEC like the kaolinite group.
Low electrical conductivity can also be brought
about by high levels of quartz and low levels of
clay mineral content.
The average results of BET (Brunauer, Emmett
and Teller) surface area for Karundu, Mweru and
Ngamwa were; 35.222, 47.222 , and 34.222 m2/g
respect ively. The BET surface area for pure kaolinite ranges between 10 -20m2/g. The results
obtained in the present investigation suggest the
presence of kaolinite in the samples as was
observed in the physico -chemical propertie s
analysis. The high kaolinite values obtained
compared to those of pure clay is associated with
the levels of impurities like quartz, sodium,
magnesium ions in the samples. The high level of
very small size quartz which are smooth, uniform
and non -porous might be present in the region
thus contributing to high surface area. This is
supported by the high amount of quartz (Karundu,
31.3%, Mweru, 68.1% and Ngamwa, 24.3%)
which was present in the samples. Na+ and Mg2+
saturated systems can contribute to a high er
surface area compared to other elements. In the
present study, the average level of Na+ in the
samples from Karundu, Mweru and Ngamwa were;
0.0242, 0.0353 and 0.0126 respectively while
Mg2+ values were found to be 0.02283, 0.03636
and 0.04336 respective ly. The high values of
quartz, Na+ and Mg2+ in the samples from Mweru
could have contributed to the high surface area

Ombaka 423

Table 4. BET surface area results.

Sample site Depth (cm) BET surface area
(m2g)/ Pore volume cm3/g Pore size (A°) Nanoparticle size (A°)
Single point adsorption total pore volume of pores
less than 917.424 A° at PP/PO=0.97843255 Adsorption
average width Average particle size
Karundu 0-20 35.222 0.2.601 130.7983 1895.316
Mweru 20-40 47.222 0.11311 130.7 915 1890.176
Mweru 40-60 46.6703 0.167204 143.3070 1285.618
Ngamwa 0-20 31.722 0.10301 129.8985 1891.376
Ngamwa 40-60 34.222 0.40201 133.7981 1888.276

observed. The lower BET surface area of the samples
from Ngamwa might be associated with high lev el of
weathering of kaoli nite in the surface soils or authige ic
formation of large kaolinite which could be as a result of
less inhibition of crystal growth by organic matter (Melo et
al., 2001). The average values of pore volume and pore
size for Karundu, Mweru and N gamwa were 0.20601,
0.167204, 0.40201 cm3/g and 130.7983, 143.307, 133.
7981 Ǻ respectively . The average particle size of n ano
particles for samples from Karundu, Mweru, N gamwa are
1895.316, 1285.618 and 1888.276 Ǻ respectively. The
high value of pore vol ume for samples collected from
Ngamwa could imply that, the clay from this reg ion have
a better crystalline kaolinite in comparison with the other
two sites studied (Table 4) .
The representative X -ray diffractogram for the clay
samples from K arundu site is shown in Figure 4. The d-
spacing reflections at; 4.18545, 3.53312, 2.59849,
2.50075, 2.32134, 2.21881, 2.11127, 1.96630, 1.78147,
1.66399, 1.56111 and 1.48185 revealed the presence of
kaolinite in the sample . The presence of albite, microcline
in the samples was revealed by d -spacing reflection at
3.21200, 3.23012 respectively. The reflection at 3.30796,
2.52836, 2.21881, 2.11127, 1.80485 and 1.66399
showed that qu artz was present in the sample. Generally,
the reflections of quartz were the strongest in comparison
with other peaks thus indicating dominance and high
crystallinity of this mineral in the samples compared with
other minerals. The peaks of illite and humi nic acid at d –
spacing 3.32000 to 3. 35000 and 3.33000 respectively
were not es tablished due to the fact that the principle
reflection of quartz (3.30796 Ǻ) occurs almost at the
same position.
Clay and non -clay minerals in the samples from Mweru
site were identified using XRD method and a
representative X-ray diffr actogram is shown in Figure 5.
The presence of kaolinite clay mineral was revealed by
reflect ion at d- values of 4.17788, 3.52252, 2.31 787,
2.21856, 2.10941, 1.96249, 1.66034, 1.5524 and
1.48023. The d -spacing at 3.20419 and 3.24103 re vealed
the availability of albi te and microcline respectively in the
sample. Quartz was identified by reflections at 3.30114, 21.21856, 2.10941, 1.96249, 1.80478, 1.66.95.
Figure 6 shows a representative X -ray diffractogram of
the clay sample from Ngamwa site. The availability of the
kaolinite in this sample was indicated by the reflection at
4.18303, 3.53124, 2.32 200, 2.21872, 2.11326, 2.50119,
1.98008, 1.65982, 1.54713 and 4.8144. The d -spacing at
reflection 3.21062 and 3.24012 indicated the presence of
albite and microline respectively in the sample. Quartz
was revealed by reflection at 3.30495, 2.54130, 2.22412,
2.111464, 1.97273, 1.81135 and 1.66119. The
percentage composition of the minerals in the clay
samples as revealed by XRD results is shown on Table
5.
The percentage composition of Albite was in the range
(5.3-16.7), Kaolinite (11.4 -36.2), Microcline (15. 2-35.3)
and Quartz (24.3 -68.1). Kaolinite was the only clay
mineral detected in the samples with appreciable
amounts for industrial applications (greater than 10%).
For kaolinite mineral to be utilized industrially , other
accessory minerals like albite, mi crocline and quartz
should be reduced to acceptable levels through
appropriate beneficiation techniques .
The identification of different types of clay minerals was
achieved by the use of absorption bands due to structural
OH and Si -O groups that were obtai ned from the FT -IR
spectrum. The types of cations that are linked directly to
the hydroxyls influences the OH absorption bands and
this is important for the determination of cation
distribution around hydroxyls. The interpretation of the
FT-IR spectrums in Figures 7 to 9 was done using the
available literature (Madejova, 2003; Vaculikova and
Plevo va, 2005; EmDadul, et al ., 2013). A close
examination of the obtained FT -IR spectrums revealed
the presence of kaolinite clay minerals in all the samples
that wer e investigated and this confirms the XRD results.
The four bands in the ranges, 3620.55 -3621.39, 3651.92 –
3653.75, 3670.01 -3670.85 and 3690.31 -3694.17cm-1
confirmed the presence of kaolinite in the samples. The
presence of sharp doublets at around 3620.55 -3621.39
and 3690.31 -3694.17 further revealed the presence of
kaolin group in the sample. The absorption bands at the
range of 3620.55 -3621.39 was assigned to the stretching

424 Afr. J. Environ. Sci. Technol.

16000

15000

14000

13000

12000

11000

10000

9000

8000

7000

6000

5000

4000

3000

2000

1000

0

15 20 30 40 50 60 70 80

2-Theta – Scale

Figure 4. X-ray diffractogram for the clay samples from Karundu site.

Ombaka 425

Figure 5. X-ray diffractogram for the clay samples from Mweru site.

vibration of internal surface OH groups whi ch is located
between the tetra hedral and octahedral surface of the
layers and it forms hydrogen b onds with the oxygen of
the Si -O-Si bonds on the lower surface of the next layer
which is weak. The strong band at around 3690.31 –
3694.17 cm-1 was attributed to the in -phase symmetric
stretching vibrations while the two weak bands a t around
3651.92 -3653.75 and 3670.01 -3670.85 cm-1 were due to
the out-of plane stretching vibrations. The b ands
observed at the range of 911.40 -914.30 cm-1 were either
due to vibrations of the inner surface or OH bending
groups which is common to kaolinit e containing samples,
while occurrence of bands at 936.48 -936.58 cm-1 are as a
result of surface OH groups . The bands at the ranges
691.15 -695.37 cm-1 and 752.27 -754.20 cm-1 are
attributed to the surface hydroxyls while the ones at
1006.89 -1113.94 cm-1 can be associated with Si -O
stretching vibrations of kaolinite. The bands occurring at
the ranges 3645.36 -3652.75 (OH stretching), 911.40 –
913.33 (shoulder), 780.24 -795.67 and 747.86 -753.23
(doublets) cm-1 indicate d the presence of illite in the
sample and the y represent Al-Mg-OH deformation. The strong stretching bands ranging between 909.06 -1112.97
and slightly less intense bending bands at 406.97 -794.95
cm-1 revealed the presence of Si -O bonds in all the
samples studied. The bands observed at 460.35 -4621. 87
and 522.96 -524.96 cm-1 (Si-O asymmetrical bending
vibrations), 692.47 -695.37 (Si -O symmetrical bending
vibrations) 780.24 -789.06 and 794.95 -795.67 cm-1
(symmetrical stretching vibrations) and 1081.15 -1099.47
cm-1 (Si-O symmetrical stretching vibrations due to Al for
Si substitution) indicated the presence of quartz in the
samples. The bands ranging from 590.92 -604.03 cm-1
can be attributed to O -Si-(Al)-O bending vibrations and
revealed the presence of microcline feldspar in the
samples which accords the results from XRD. The four
OH stretching bands (3669.00, 3656.00, 3642.00 and
3623.00cm-1) were associated with the presence of
hornblend in the sample. The bands observed at the
ranges of 3411.10 -3417.43, 2851.88 -2957.97, 1031.96 –
1102.37, 1633.59 -1650.36 and 1338.84 -1350.17 cm-1
indicated humic acid was present in the sample which is
in line with observation at the sampling sites. The bands
recorded at the range of 2852.88 -2957.97 was attributed

426 Afr. J. Environ. Sci. Technol.

Figure 6. X-ray diffractogram for the clay samples from Ngamwa site.

Table 5. Percentage composition of clay and non-clay minerals in the sampled clays.

Site Albite Clinochlore Hornblende Hematite Kaolinite Magnetite Microcline Quartz
Karundu 16.7 – – – 16.6 – 35.3 31.3
Mweru 5.3 – – – 11.4 – 15.2 68.1
Ngamwa 11.4 – – – 36.2 – 20.4 24.3

to CH 2-CH 3 stretching, while those at 1633.59 -1650.36
and 1338.84 -1350.17 cm-1 indicated humic acid was
present in the sample. The bands which appeared at the
range of 2 851.88 -2957.97 was attributed to CH2 -CH3
stretching while those at 1633.59 -1650.36 and 1338.84 –
1350.17 cm-1 was attributed to COO – asymmetric and
symmetric stretching respectively. Presence of the humic
acid could contribute to the decrease in the amounts of Si and Al contents in the clay structure due to
decomposition of the Si -O-Si by acidolytic attacks.

Thermal analysis

The representative thermographic curves for the samples
studied are shown in Figures 10 and 11. These curves

Ombaka 427

102.9
100

95

90

85

80

75

70

65

60 100.0

95

90

85

80

75

70

65

60

55
%T 55
50

45

40

35

30

25

20

15

10.0
4000.0 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 380.0
cm-1 %T
50

45

40

35

30

25

20

15

10.0
4000.0 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 380.0
cm-1
Figure 7: FT-IR Spectrum (Karundu site) Figure 8: FT-IR Spectrum (Mweru site)

Figure 7. FT-IR Spectrum (Karundu site).

102.9
100

95

90

85

80

75

70

65

60 100.0

95

90

85

80

75

70

65

60

55
%T 55
50

45

40

35

30

25

20

15

10.0
4000.0 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 380.0
cm-1 %T
50

45

40

35

30

25

20

15

10.0
4000.0 3600 3200 2800 2400 2000 1800 1600 1400 1200 1000 800 600 380.0
cm-1
Figure 7: FT-IR Spectrum (Karundu site) Figure 8: FT-IR Spectrum (Mweru site)

Figure 8. FT-IR Spectrum (Mweru site).

428 Afr. J. Environ. Sci. Technol.

Figure 9. FT-IR Spectrum (Ngamwa site).

contain useful information regarding various temperature
range s which is indicative of where the processes of
dehydration, dehydroxyl ation and phase transformation of
various clay minerals studied takes place. A close
examination of the curve s revealed that o nly 3.125% of
free water, ad sorbed water and volatile product s are lost
between the temperature range s of 25-200°C. The loss in
weight of 10.625% between the temperature ranges of
200 to 500 °C was attributed to the loss of the products
resulting from organic reaction. The dehydroxylation
process which resulted to th e loss of 0. 875% of structural
water took p lace between the temperature range of 500
to 800 °C. About 0.625 of hydroxyl water was lost from
800 to 900 °C which completed dehydration process. A
combustion reaction between inorg anic oxygen and
organic carbon took place from 900 to 1000 °C. The
symmetrical and smooth thermal curve in the interval
from 400 to 800 °C suggested the presen ce of kaolinite in
the samples. The representative of SEM micrographs of
the clay minerals samples is presented in Figures 12 and
13. The presence of almost pseudo hexagonal shapes
and very small flattened platelets observed in these figures shows the presence of kaolinite. On further
examination of SEM micrographs, the larger clay mineral
particles seems to consist of much smaller platelets
which indicates that the clay sample is made up of very
fine particles. The presence of quartz was revealed by
almost rounded and also V -shaped platelets with brighter
luminescing and this confirms the results of XRD and FT –
IR.

Conclus ion

The clayey mineral samples are kaolinitic in nature,
having more than 10% kaolinite and contain different
types of impurities which make it less useful. The major
impurities species are quartz and iron with minor ancillary
cations such as Mn2+, Mg2+, Na+ and K+ etc. The
identification and quantification of impurities in the clay
samples from the study area makes it easier for future
researchers in the selection or modification, and
sequentialization of beneficiation process with the
objective of reducing impurity levels to acceptable limits

Ombaka 429

Figure 10. Representative thermographic curve A.

Figure 11. Representative thermographic curve B.

430 Afr. J. Environ. Sci. Technol.

Figure 12. SEM micrograph A.

Figure 13. SEM micrograph B.

hence rendering the raw materials useful for commercial
production of ceramic products and eventually
maximizing its potential utilization .

Conflict of interests

The authors have not declared any conflict of int erests. ACKNOWLEDGEMENTS

The author extends gratitude to the Vice Chancellor and
Chuka University management for availing facilities and
funding this project. More appreciation goes to the
Ministry of Mining, World Agro forestry Centre (WAC) in
Kenya and the department of Chemistry, Chuka and
Kwazulu Natal Universit ies. The author is grateful to Dr.

Munene Nderi , Felicity Kaari and the reviewers for their
comments which went a long way in improving the
document. Juliet Makau is also thanked for her te chnical
support.

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