Over the past several decades, kaolin has been intensively used in ceramics formulation by the indigene of Erusu Akoko, in south western Nigeria. Kaolin is a clay mineral with wide technological applications in the industry. It finds applications in fiberglass, paper, rubber, tires, ceramics, cements, latex, paint, printing inks, catalysts for petroleum refining, medicines, water treatment, cosmetics and others. In the present work, we studied the mineralogy of Erusu clay that had been in use for several generations without understanding the physico-chemical properties. Samples of the material were pre-treated and subjected to analysis. From our results, Akoko clay exhibited decompositional water loss of 13.23% and 13.14% in air and argon respectively at 1000°C. The Brunanuer-Emmett-Teller (BET) analysis showed that the kaolin clay was majorly a mesoporous material and the isotherm was of the type iv. The micropore surface area obtained from t-plot is 9.06 m2/g indicating that the materials also contain micropore with size and volume of 15.611 ? and 0.265 cc/g respectively. The XRD, IR and TEM analysis confirmed the presence of Kaolin and Quarts as the major constituents of Akoko clay.
Kaolin is a fine clay mineral cream to dark brown, colored by iron oxides/hydroxides (and/or rutile/anatase). Its major constituent is kaolinite (Al2O3∙2SiO2∙2H2O), a hydrous aluminum silicate with a single silica tetra hedral layer linked through oxygen atoms to a single alumina octa hedral layer.
The common ancillary minerals occurring with kaolin include parent rocks like Feldspar and mica, quartz, ferruginous, titanoferrous, and carbonaceous materials [
The most deleterious impurities in kaolin are iron minerals which impart color to the white kaolin. Iron exists as oxides, hydroxides, oxy hydroxide, sulphides and carbonates along with iron stained quartz/anatase and mica in kaolin [
Extensive research has been carried out on the nature of iron impurities present in kaolin, which leads to the conclusion that iron is present as a part of the kaolinite or ancillary mineral (mica or titania) structure, which can be termed as “structural iron” or as independent iron minerals such as oxides, hydroxides, oxy-hydroxides, sulphides and carbonates, which can be termed as “free iron” [
Beneficiation of kaolin removes deleterious mineral phases and improves the critical properties of the product clay (such as chemical composition, particle size distribution, and brightness) destined for different uses. Size classification using a set of hydrocyclones leads to enrichment of finer clay fractions and the removal of iron and titanium minerals in coarse size ranges [
The kaolin wet beneficiation process consists mainly of degritting fractionation by centrifuge, high gradient magnetic separation, selective flocculation, chemical bleaching, filtering and drying [
The aim of the present study is to characterize kaolin from relatively unknown town in southwest Nigeria that has been known for quality ceramics production for ages focusing on the material characterization to identify the crystalline product and compares its properties to those of standards. X-ray diffraction analysis (XRD) is a traditional tool for mineral identification; FT-IR is used to identify the nature of iron present (free or structural), crystal defects, oxidation state of iron and other functional groups present. Transmission electron microscopy (TEM) pictures give the morphology and size of the particles.
The clay used was mined from Erusu village, near the ancient city of Ajowa Akoko in Akoko Northwest Local Government Area of Ondo state, southwest Nigeria. To avoid contamination from other sources de-ionized water was used for the present study.
The removal of somatic impurities from raw clay was first done by physical separation of dirt, followed by the wet/soaking process according to the procedures reported by Aroke et al. [
The sample was prepared, distilled and finally titrated as describe elsewhere [
Measuring the number of N2 molecules adsorbed at monolayer coverage, gives information needed for calculating the surface areas, which was calculated by the instrument. 0.3 g approx. of the sample was weigh and loaded in to the BET glass sample tube, the weight of the tube before and after loading was recorded. The samples were degassed at 473 K for 3 h by connecting the tube to micromeritics flow prep 060 linked with Nitrogen gas to remove physically adsorbed water molecules. Degassed sample was reweighed and the analysis was carried out in micromeritics Tristar 3000 V4.02 under liquid nitrogen temperature where BET surface area and pore volume/size of the samples were automatically calculated by the instrument using N2 isotherm and the results were recorded on the computer attached to the instrument.
Qualitative and quantitative determination of the nature of the phases and the amount of the phases that is present in the sample were determined by Panalytical X’Pert Pro diffractometer, employing Cu Kα monochromatic radiation. All the patterns were collected at room temperature with steps of 0.02˚ using a range of 5˚ - 80˚. The measurements were taken at room temperature (298 K), with scan rate of 2˚ min−1 and 0.02 steps and the patterns were recorded by the Broker-D8software.
Raman spectroscopy was used because its detection limits are below the 4 nm (approx.) cut-off of crystallite size for XRD and its ability to show bands that cannot be detected using FTIR. The Raman spectra were recorded with Renishaw spectrometer equipped with invia Raman microscope RE 02, 514 nm laser was employed as the exciting source and the measuring parameter were set as follow; accumulation 10, exposure time 20 minutes and laser power between 75%.
The infrared spectra of the sample were collected using attenuated total reflection (ATR) module with a Nicolet model 360 FTIR at 0.5 cm−1 nominal resolution. The spectra were recorded in the region of 4000 - 400 cm−1.
Transmission electron microscopy (TEM) images were recorded on a JEOL JEM-2011 high resolution (HR) TEM (JEOL Ltd., Tokyo, Japan). The electrons were produced by a LaB6 crystal and accelerated up to 200 kV. The TEM is capable of producing a beam diameter as small as 0.5 nm, with 0.19 nm resolution. Images were recorded on a Gatan 794 CCD camera (Gatan Inc., Pleasanton, California, USA). A very small amount of the clay was dissolved in isopropanol and loaded into a carbon coated metal grid which gives preferred orientation and allows observation of clay flakes and examination. Various magnifications were used to obtain suitable micrographs of clay minerals.
TGA is a technique in which the weight of a given sample is monitored continuously as a function of time and/or temperature, while under flowing air or nitrogen. TGA was used to probe the decomposition route of the sample and the thermal stability of the clay. The heating rate was set at 283 K/min from 298 to 1273 K in air stream (100 ml/min).
The CEC of kaolinite minerals range from about 3 - 15 meq/100 g [
The dispersion forces between the adsorptive molecules and the surface atom or ions of the adsorbing solid are described by the Lennard-Jones potential [
BET developed a model describing the adsorption on surfaces describing multi-layers [
Basically, BET is an extension of the Langmuir treatment to multilayer adsorption on a homogeneous, flat surface. It is useful for gas-solid systems in which condensation is approached. It takes no account of porosity [
The result obtained from N2 adsorption-desorption studies of kaolin clay at liquid nitrogen temperature (77 K) is given in
The BJH method was originally developed for relatively coarse porous adsorbents having a wide range of pore sizes.
However, the procedure proved to be applicable to almost all types of porous materials.
The distribution of pore volume with respect to pore size is called a pore size distribution. It is generally accepted that the desorption isotherm is more appropriate than the adsorption isotherm for evaluating the pore size distribution of an adsorbent. The surface properties of the material are given in
The diffraction pattern from xrd is shown in
Parameter | Surface area (m2/g) | Pore volume (cc/g) | Pore size (Å) |
---|---|---|---|
Multi point BET | 57.18 | ||
Langmuir | 78.10 | ||
BJH cumulative adsorption | 61.28 | 0.265 | 17.304 |
BJH cumulative desorption | 67.80 | 0.265 | 15.611 |
t-plot micropore | 9.06 | 0.004 | |
Single point p/po | 0.1998 | 0.249 |
To determine if there are any band in the clay that is Raman active, Raman spectroscopy study was conducted on the sample and it was observed that the material was not Raman active. The spectral obtain is given in
The ir methods are still less widespread for quantitative determination of clay and other minerals. The absorbing bands for most clay minerals and associated minerals are given by farmer (1974) [
Absorption bands of some clay minerals, data Farmer (1974, Gadsden (1975) [
Mineral: Absorption bands (cm−1).
Kaolinite: 3695, 3660, 3625, 1035, 1020, 915.
Halloysite: 3696, 3624, 3414, 1035, 1005, 910.
Montmorillonite: 3635, 3400, 1640, 1130, 1020, 920.
Chlorite: 3586, 3560, 3436, 1004, 980.
The spectral can be divided into two regions as shown in
The bands placed between 3744.64 and 3620.97 cm−1 region corresponds to -OH stretching. The 3620.97 cm−1 frequency band corresponds to the inner layer OH(Al-O―H) stretching which falls close to 3623 and 3622 cm−1 obtained by Burhan and Emin, 2009, and Yleana, 2005 [
Transmission electron microscopic analysis (TEM) was used to directly image nanoparticles of the raw clay at scales approaching a single atom and the result is presented in
Upon heating in air and under inert condition kaolin starts to lose water at approximately 400˚C, and the dehydration approaches completeness at approximately 525˚C [
In the present study, the physic-chemical characterization of Akoko Kaolin was attempted using different analytical tools such as cation exchange capacity, BET surface area and BJH pore size/volume, X-ray diffraction (XRD), laser Raman spectroscopy, infrared spectroscopy, transmission electron microscopic analysis and thermo-gravimetric-mass spectroscopy (TG-MS). The Brunanuer-Emmett-Teller (BET) analysis showed that the kaolin clay was majorly a mesoporous material and the isotherm was of the type iv. The micropore surface area
obtained from t-plot is 9.06 m2/g indicating that the materials also contain micropore with size and volume of 15.611 Å and 0.265 cc/g respectively. The XRD, IR and TEM analysis confirmed the presence of Kaolin and Quarts as the major constituents of Akoko clay. The result obtained when kaolin was heated in air and under argon atmosphere conditions indicated three decomposition routes, the first steps was due to losses of physically adsorbed water at 100˚C - 200˚C, the second at 450˚C - 500˚C which was due to loss of structural water while the third was at 600˚C - 850˚C which may lead to complete disintegration of kaolin. Finally, Akoko clay exhibited decompositional water loss of 13.23% and 13.14% in air and argon respectively at 1000˚C.
The author wants to appreciate the technologists Mr. Adeyemo, Mr. Bamidele and other laboratory staff of the Department of Chemical Sciences, Adekunle Ajasin University Akungba Akoko for their support during the research. Mr. Olatundun Stephen aka Mr. Clay for preparing the sample for this work. Mr. Oloye Femi Francis for his contributions in making this work successful.
Abimbola GeorgeOlaremu, (2015) Physico-Chemical Characterization of Akoko Mined Kaolin Clay. Journal of Minerals and Materials Characterization and Engineering,03,353-361. doi: 10.4236/jmmce.2015.35038