The overall goal of this study is to characterize and to evaluate the potential uses of clay mined in the Nzaou locality. The Mou sample is argillaceous texture and medium plasticity (Ip = 28.9). Kaolinite is dominant clay species (44.41%). It is associated with illite (9%). Quartz and rutile are the main non clay minerals. The CEC is 8.66 cmol+/kg. Organic matter is low (0.839%). Total shrinkage obtained by dilatometry at 1200 °C is 9.26%. The chemical and mineralogical compositions have allowed using the ternary diagrams of Fabbri and Fiori that the MOU clay is favorable for glazed white stoneware (GWS) and for the production of clinker (KLK). Dondi typologies of ceramic tiles according to body color (mostly depending on the iron oxide content) and compactness (expressed by water absorption) have confirmed the use for the manufacture of the GWS and clinker. Classification always according to Dondi taking into account the rate of kaolinite, the fine fraction (<2 μm) and plasticity index gives MOU clay to be considered as medium ball clays (BC1). The absorption rate indicates that the body fired at 1200 °C will be vitrified. Flexural strength at 1200 °C (16 MPa) does not correspond to the requirements of GWS or a clinker.
Clays are used as raw materials in many industrial fields (ceramic, paper, paint, oil industry, clarification of various effluents, catalysis.) [
The objective of this study is to carry out mineralogical, physical and chemical characterization and determine the technological properties of the Nzaou clay (MOU).
So, we will try to define the possibilities of use of Nzaou clay (MOU).
The sampling site is located in the Department of Bouenza (Republic of Congo), in the district of Mouyondzi precisely to the Nkengue village about 10 km from Mouyondzi locality (
The valley of Niari in which the department of Bouenza is situated, presents soils, the mother rock of which consists in schisto-limestones represented by pink and grey dolomites, clayey limestones, built limestones and crystalline limestones, stony sands, sandy and siliceous limestones and finally by grey dolomites on oolitic levels [
eases (gastric problems, wounds). About 1 meter deep holes were dug to collect clay. It is at this depth that the samples have been collected and air-dried in the laboratory.
The plasticity was measured by the Atterberg indices: Liquid Limit (LL), Plastic Limit (PL) and Plastic Index (PI) according to the norm NF P 94-051 [
The XRD of sample powder was performed using a Philips model diffractometer operating by reflection under the Cu-Kα radiation for 2θ angle ranging from 5˚ to 60˚.
Diffuse Reflectance Infra-red Fourier Transform Spectroscopy (DRIFTS) was performed over a wave number domain between 600 and 4000 per cm using a Bruker IFS 55 spectrometer equipped with a broad band detector of the type MCT (Mercury and Cadmium Tellurium) cooled with 77 K and with an accessory of diffuse reflection (Harrick Corporation). The powdered sample was diluted in KBr (50 mg of sample in 350 mg of KBr). The spectra were recorded by accumulating 200 scans at 2.0 per cm resolution.
The Differential Thermal Analysis (DTA) and Thermo Gravimetry (TGA) were carried out with a device coupled with a thermobalance and a mass spectrometer THERMOSTAR. The speed of heating was 10˚C/mn. The dilatometric analysis was performed using a NETZSCH 402 ED horizontal differential dilatometer-internal Code: DI 1 with, for reference, a bar in dense alumina (purity 99.5%). The unit is equipped with the PROTEUS analysis and treatment software. The test specimen was obtained by application an vertical axial pressure of 20 kN into a 5 × 5 × 50 mm stainless mould on a manual hydraulic press (Pmax = 230 kN). Then pressed piece is cut for a vial of test size: (section 5 × 5 mm, length: 5 mm measured with caliper with 0.01 mm accuracy) the thermal cycle is: 5˚C/min up to 1200˚C, level of 2 hours and cool down lies at 5˚C/min
The chemical analysis of the major elements was carried out in the Center of Petrographic and Geological Research (CRPG) Nancy according to Carignan et al. [
Organic matter: the total organic carbon and total nitrogen have been determined by method described by the norms NF ISO 10694 and 13878 [
Cationic exchange capacity is measured by Metson method NF X 31-130 [
1) Preparation and firing of the test samples: 10 g and 45 g of clay powder were mixed respectively with 10 and 5 mL of distilled water in a porcelain mortar and then put respectively in cylindrical and parallelepiped steel mould. An axial vertical pressure of 342 MPa was applied to obtain two types of test specimens:
・ Discs of 4 mm diameter and 6 mm in thickness in order to measure the physical properties (open porosity, gross density and water absorption)
・ Parallelepiped test specimens for the determination of linear firing shrinkage and flexural strength
The test specimens obtained were first dried at 110˚C for 24 h and then fired at 1000˚C, 1050˚C, 1100˚C and 1150˚C, 1200˚C and 1250˚C in a NABERTHERM model kiln with a heating rate of 5˚C/mn and a 2 h evaluation time.
2) Determinations of technological properties: The linear shrinkage, open porosity, bulk density and water absorption were measured according to the protocol P18-554 of the French norms [
The use of USDA texture triangle [
The positioning of the MOU clay in the Winkler triangle [
The grain-size distribution of MOU is not favorable for the manufacture of structural ceramics (tiles, bricks, hollow with thin walls, bricks with vertical perforation and full bricks).
The Atterberg limits values of MOU lead us to set MOU sample at the limit between the medium plastic inorganic clay and the high plastic inorganic clay in the Casgrande abacus [
Located between the areas of montmorillonite and illite in the diagram of Holtz and Kovacs [
Granulométrie | Argiles ˂ 2 µm | Limons fins (2/20µm) | Limons grossiers (20/50µm) | Sables fins (50/200µm) | Sables grossiers (200/2000µm) | ||
---|---|---|---|---|---|---|---|
65% | 20.9% | 8.1% | 3.6% | 2.4% | |||
Limites d’Atterberg | Limite de Liquidité | Limite de Plasticité | Indice de plasticité | ||||
51.2 | 22.3 | 28.9 | |||||
MOU clay would present optimal properties of moulding and a relatively weak shrinkage in considering its positioning in the workability chart of Bain and Highly [
X-ray diffraction pattern of MOU is shown in the
The analysis of this XRD pattern enabled to detect the presence of the following key minerals: illite, kaolinite and quartz [
We see the disappearance of the peaks of kaolinite and the persistence of the peaks at 10.03 Å, 5.01 Å and 4.47 Å characteristics of the illite.
The relatively high intensity of quartz indicates a significant presence of free silica even if the particle size analysis indicates only 6% of sand. This suggests that the sand is very fine and maybe a part is found in the silt fraction.
The reflection at 3.51 Å indicates the presence of anatase. The peak at 3.24 Å can be associated to rutile.
In the XRD pattern of an ordered kaolinite, the interval ranging from 19˚ to 23˚ presents usually three distinct peaks while the increase in disorder makes that the sequence of 02l, 11l reflections in the range 20˚ - 33˚ becomes increasingly blurred until with halloysite only a smooth diffraction band with the superimposed 002 basal reflection is obtained [
Considering the heights of characteristic peaks of kaolinite and the muscovite, kaolinite is the most abundant clay mineral.
2-2 Infra-red spectroscopy
The IR of MOU spectrum is represented on
The crystalline structure of kaolinite is constituted of two sheets tetrahedral and octahedral forming a layer [
The range of frequencies from 3700 cm−1 to 3100 cm−1 corresponds to stretching modes of OH groups [
So, kaolinite in MOU sample is considered as poorly crystalline. This observation corroborates the XRD pattern of MOU. The range from 1200 cm−1 to 600 cm−1 contains frequencies related to modes of deformation of groups OH [
mode appears as a shoulder near 1080 cm−1 [
The intense bands at 3420 and 1631 cm−1 are due to the molecular water molecules [
The presence of quartz in the sample is manifested by bands at 798 cm−1 (Si- O stretching mode) and 696 cm−1 (deformation mode Si ? O) [
Thermo-gravimetric and thermal differential analysis curves are given in
The following observations are made on the thermo-gravimetric and differential thermal analysis curve data:
・ An endothermic peak between 100˚C and 200˚C, with maximum at approximately 125˚C, corresponding to a loss of mass from 1.257%.
・ An endothermic peak important 547˚C, accompanied by a mass loss of 8.18%.
・ An exothermic peak around 967˚C.
The peak around 125˚C corresponds to the departure of water physically adsorbed to the surface of the particles [
The second endothermic peak observed around 547˚C corresponds to the dehydroxylation of kaolinite where structure water was eliminated following a broadcast mechanism resulting in the formation of amorphous material (metakaolin) [
The exothermic peak at 967˚C corresponds to the structural reorganization of the metakaolin that turns into mullite. And this temperature is very close to that indicated in cases of presence of iron (980˚C) [
During cooling, the ATD curve shows an exothermic lump of low amplitude at 567.2˚C corresponding to the reversible quartz β-quartz α transition and confirms the presence of quartz. This transition was not observed during heating. This could be explained by an high abundance of kaolinite.
The results of the chemical analysis are reported in
The SiO2/Al2O3 ratio is equal to 2.93. This ratio much higher than in kaolinite indicates a relatively abundant presence of quartz in the clay soil. The Fe2O3 content is relatively low.
The Fe content having reacted with the Mehra-Jackson reagent (free iron) corresponds to 0.098%. Therefore Fe2O3 represents 0.14%. Then about 1.36% of
SiO2 | Al2O3 | Fe2O3 | MnO | MgO | CaO | Na2O | K2O | TiO2 | P2O5 | P.F. | |||
---|---|---|---|---|---|---|---|---|---|---|---|---|---|
61.45 | 20.96 | 1.5 | 0 | 0.59 | 0.31 | 0.05 | 1.15 | 2.36 | 10.5 | ||||
Matière organique | Carbone organique | Azote total | Matière organique | ||||||||||
0.485% | 0.047% | 0.839% | |||||||||||
CEC | 8.66 cmol+/kg | ||||||||||||
Fe Tamm | Al Tamm | Fe Mehra-Jackson | Al Mehra-Jackson | ||||||||||
0.05% | 0.059% | 0.098% | 0.085% | ||||||||||
Fe2O3 comes from structural iron. Soro indicates that the iron not reacting to corresponds to structural iron [
Indeed many works indicated the substitution of the Al3+ by Fe3+ in kaolinite [
The structural Fe is considered as proof of the disorder. The presence of structural iron in MOU would be so related to low crystallinity of kaolinite.
The coloring oxides (Fe and Ti) rate (3.86%) suggests a colored fired body. The percentage of potassium (1.15%) could come from the presence of the illite. The alkaline earth metal with the total content of 0.9% may match these carbonates.
The mineralogical composition deduced from chemical analysis and XRD by using the follow formula [
T ( a ) = ∑ i M i P i ( a ) (1)
with:
T ( a ) = mass percent of the element oxyde “a” in the sample.
M i = mass percent of the mineral “i” in the studied material.
P i ( a ) = massic amount of the oxyde of the “a” element in the mineral “i”.
deduced from the ideal formula of the minéral “i”.
Considering the results of Mehra-Jackson Fe, we have neglected the oxides of iron.
The first estimation of mineralogical composition based on the results of the chemical analysis leads 6.21% of indeterminate (
The weight loss associated with the dehydroxylation of kaolinite is 8.16%. Therefore from ATG, the rate of kaolinite is estimated at 52.62%. By integrating the kaolinite rate deducted from the ATG, we greatly reduce the rate of the indeterminate (1.15%) (
The dilatometric curve of MOU sample is given in the
Echant | kaolinite | illite | talc | quartz | anatase | Hématite | Σm | indéter |
---|---|---|---|---|---|---|---|---|
Mou | 44.41 | 9.58 | 36.26 | 2.36 | 92.61 | 6.21 | ||
Mou | 52.62 | 9.58 | 33.21 | 2.36 | 97.77 | 1.15 |
The analysis of this curve reveals:
・ A light (low) dilatation until 570˚C.
・ A shrinkage between 550˚C and 600˚C.
・ An increasing shrinkage from 600˚C to near 900˚C.
・ A shrinkage between 900˚C and 1000˚C linked at an exothermic phenomenon.
・ An intense shrinkage from 1000˚C until 1200˚C.
・ On the cooling curve, a peak at 575˚C associated at the reversible transformation of quartz.
The shrinkage between 550˚C and 600˚C corresponds to the dehydroxylation of kaolinite for giving metakaolin. The diffusion of hydroxyl groups trends to bring together the plaques. That leads to an overall shrinkage.
The dilatometric curve from ambient temperature to 700˚C is given on the
There is a low shrinkage to almost 100˚C which was attributed to the departure of hygroscopic water. We observe a dilatation from 150˚C to 487˚C and from 490˚C to 564˚C shrinkage occurs. This last shrinkage is associated in the ATD curve at the dehydroxylation of kaolinite. Light withdrawal is induced by the dehydroxylation of the clay minerals mostly kaolinite. The dilation from ordinary temperature until near 600˚C, disturbed by some shrinkage, corresponds to the transformation quartz α-quartzβ. Quartz can reach an expansion of more than 1.7% at 580˚C [
behavior is dominated by kaolinite. Indeed it was not observed dilatation of the network of the muscovite at temperatures below 1000˚C. This suggests that the illite has a composition that is less than 10%, confirming the results of the mineralogical balance.
The comparison of the dilatometric curve of MOU with LOU’s which has lower quartz content is given in
Relatively low shrinkage in MOU compared that of LOU resulted in the highest rate of quartz in MOU. The abundant presence of quartz (33%), which, as long as it is not dissolved in the stream, form a rigid percolating skeleton that opposes the densification, thus justifying a weak shrinkage [
・ water absorption and the apparent density
・ open porosity, flexural strength and linear shrinkage
The rate of absorption and the open porosity curves have the same trends. They decrease quickly from 1000˚C to 1200˚C when they reach a minimum. The minimum absorption rate is 2.5% then the minimum value of the open porosity is 6.02%. These values are comparable with LOU. Despite the rate of quartz in MOUY, the gresification favored by the presence of fusible material allows significantly reduce the open porosity and rate of water absorption. The apparent density increases to a maximum at 1200˚C and decreases beyond this temperature. The linear shrinkage moves up a level from 1200˚C. the maximum is 5.5%. The flexural strength increases up to 1150˚C (15 MPa), with a slight drop at 1200˚C and dates back to 1250˚C (16 MPa)
Gresification parameters (water absorption, open porosity, linear shrinkage
and apparent density) indicate maximum densification around 1200˚C. The field of optimum sintering is reached when the open porosity reaches the minimum while the shrinkage its maximum. Beyond 1200˚C the sintered material knows expansion characterized by the decrease in density. Two causes for this phenomenon are proposed:
・ The presence of the cristobalite that appears at these temperatures [
・ This expansion can be explained also by the pressure of the gas in closed pores, which tends to expand the pores [
Sintering is defined as the consolidation under the action of heat from one medium dispersed without total melting of the material. This consolidation is often accompanied by an increase of the density which translates by shrinkage [
However, the water absorption is an indicator of classification of clayey materials: it allows defining the areas of use of materials. According to the Brazilian and Indian norms [
・ if water absorption > 25% Clay is suitable for the manufacture of refractories
・ if 25% > water absorption > 20%, the clay is indicated for the production of baked bricks
・ if water absorption ˂ 20%, the clay is suitable for the manufacture of the tiles
MOU clay would be suitable for the manufacture of the tiles.
Dondi et al. established the typology of ceramic tiles based on the water absorption and rate of iron oxides [
Considering the kaolinite estimated content (44.41%) and with a clayey fraction of 65%, MOU would be classified as Ball Clays. Plasticity index (28.9) indicates that MOU is medium ball clays (BC1). The content of kaolinite obtained from the loss of weight corresponding to kaolinite dehydroxylation would be higher than 50%. In this case MOU lies in the common area between BC and LK. (Low-grade Kaolins).
The objective of this work was to characterize clay extracted in Bouenza Department specifically in the locality of Nzaou in order to estimate in a first time its possibilities of use in the ceramic.
The illite and kaolinite were able to be highlighted as clay species. Quartz, anatase and rutile are the main impurities in the clay. The MOU clay is of medium plasticity and has a clay texture. The optimum temperature of sintering has been determined (1150˚C). The apparent density (2.6), the linear withdrawal to cooking (5.7), open porosity (6%), the rate of water absorption (2.6%) and the resistance to bending (16 MPa) have been achieved at the temperature of 1200˚C.
Clay proved to be used as glazed white stoneware (GWS) therefore for manufacturing the floor tiles and in the manufacture of clinkers. From the point of view of its plasticity, it can serve in the composition of ceramic pasta like medium ball clays.
We plan to improve the mechanical resistance. Indeed, as the flow obtained from illite which can play the role of flux is not enough for favor the densification, the influence of the addition of feldspar on the mechanical resistance and porosity open as well as the absorption rate will be studied for determining the conditions of improvement the densification therefore the mechanical resistance and studying the possibility to reduce the porosity at a value inferior to 1%.
The DRX, ATD and ATG were realized in The Institute of condensated matter chemistry at Bordeaux (France). The authors are grateful to Jean-Pierre Chaminade, Denux and members of this institute. We also thank the BCBTP officials who have allowed us to achieve limits d\’Atterberg.
Moutou, J.M., Foutou, P.M., Matini, L., Samba, V.B., Mpissi, Z.F.D. and Loubaki, R. (2018) Characterization and Evaluation of the Potential Uses of Mouyondzi Clay. Journal of Minerals and Materials Characterization and En- gineering, 6, 119-138. https://doi.org/10.4236/jmmce.2018.61010