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Organic compounds such as humic substances in the natural environment, especially in aquatic environments, are source of environmental problems. The stability of humic compounds in the soil is due to their adsorption on colloid surfaces through reactions with cations to form organ- mineral complexes. Many parameters such as pH, ionic strength. can affect the adsorption of humic substance on mineral surfaces. This study was initiated to investigate the use of a natural geo-material such as laterite for recovery and environmental application through batch adsorption tests. Since this system is a closed and agitated system, it makes it possible to obtain the maximum conditions for adsorption. Lateritic soil are abundant in tropical soil and exhibits some specificities that could promote humic acids-soil interactions. So, the analysis of pH influence on humic acid-laterite interactions is monitores through batch adsorption tests of a commercial humic acid at different pH (4.5; 6.5 and 8.5). The adsorption kinetic yield (R) is followed at each pH. Prior to the adsoption test, the raw laterite was analysed using infrared spectroscopy. The results of the kinetics of humic acid adsorption yield at different pH (4.5; 6.5 and 8.5) showed that the adsorption yield was inversely proportional to the increase of pH. The highest yield is obtained at pH 4.5 (94.56 %). Infrared analyzes of the laterite before and after adsorption shows that the surface of the laterite has undergone modifications associated to humic acid presence in the complexe after adsorption test. However, the media most affected by adsorption were observed at pH 8.5 and pH 4.5. The changes observed are due to the interactions between the aluminum oxides of gibbsite-AH (Al(OH)2–O–R) and kaolinite-AH (Si2O5Al2(OH)3–OH–R present on the surface of materials and the bonds of carboxylic, aromatic, phenolic, etc. groups confirms the adsorption reaction between humic acid and laterite.

The aim of this work was to identify parameters that could influence the conversion of kaolinite into metakaolinite. To this end, the dehydroxylation of four kaolinites, using controlled rate thermal analysis (CRTA) and thermogravimetric analysis (TGA), was investigated. X-ray diffraction (XRD) and Fourier transform infra-red (FTIR) were used to confirm the kaolinitic nature of the samples. Their crystallinity was evaluated using the Hinckley index from the XRD patterns and transmission electron microscopy (TEM) was used for morphological observation of the clay platelets. The thermal analyses of the samples indicate, for all samples, low defects as revealed by the low amount of adsorbed water on the clay surface. The dehydroxylation temperature from both techniques was influenced by the sample crystallinity and particle size. It was observed from both techniques that increase crystallinity resulted in highdehydroxylation temperature. Also, the influence of the clay platelets size on the dehydroxylation temperature, is proposed. All the results indicate that crystallinity and particle size are parameters that could be used to control the temperature for the conversion of kaolinite to metakaolinite. Keywords: Kaolinite; Crystallinity, Dehydroxylation; Thermal analysis

Ciprofloxacin (CFX) was loaded on Bana clay (Cameroon) and CFX loadedclays have been evaluated as drug delivery system. Raw clays and CFX loaded compounds have been characterized by some physico-chemicals methods. In vitro release studies have been done in gastric and phosphate buffer experimental mediums; bacteriological studies have been made up on Escherichia coli and Staphylococcus aureus. X-ray diffractometry patterns of loaded compounds show a basal spacing increasing due to CFX intercalation. On Fourier-Transformed Infrared spectrometry spectra, appearance of CFX characteristic bands and shifting of certain bands already presents on clay confirmed CFX intercalation. After 96 h of CFX released from release mediums, prolonged and continue profiles have been observed. Diffusion tests displayed an inhibition radius of ~2 cm on gelose seeded with Escherichia coli and Staphylococcus aureus due to CFX. The overall results show a modified release of ciprofloxacin with an effective antibacterial activity, giving the way for a new ciprofloxacin drug delivery system using Bana clay as carrier.

Eight kaolinitic materials from the Lokoundje River at Kribi were sampled and investigated for their physical, chemical, mineralogical and thermal characteristics in order to evaluate their potential suitability as raw materials in ceramics. The Lokoundje kaolinitic materials are clayey to silty clayey and are predominantly composed of kaolinite and quartz. The alkali (Na2O + K2O) content ranges between 1 and 2.5 wt.%, these low values do not favor vitrification of the ceramics but may be improved through flux amendment. The presence of goethite in some samples limits their utilization in white ceramics. The minerals content, color, metallic sound, cohesion, linear shrinkage, flexural strength, bulk density, water absorption and microstructure were determined. The XRD data reveal that kaolinite and goethite were transformed, respectively, into mullite and hematite. The colors of the fired products are characteristic of their mineral assemblage. The metallic sound is indicative of low vitrification which is confirmed by the presence of cracks due to low flux contents. The cohesion is good to very good, due to the abundance of kaolinite. The physicomechanical properties increase with temperature as well as densification. The geochemical data show that the Lokoundje alluvial clays are suitable for the manufacture of white stoneware tiles.

International audience; The surface properties of five kaolinites of various origins were analyzed using potentiometric titration, electrokinetic measurements and low-pressure gas adsorption associated to derivative isotherm summation (DIS) modeling. The data show that sample structure is important in determining the surface properties. The combined analytical results clearly shows the existence of a permanent negative layer charge for all the samples. The general features that could be observed for the five kaolinites are: the titration curves are shifted to lower pH with increasing ionic strength due to the layer charge; the amount of consumed proton is influenced by the permanent layer charge; although low, the permanent charge determines the electrokinetic behavior. The shape anisotropy and the charge distribution on the basal and edge surfaces are crucial parameters to understand the behavior of kaolinite particles in aqueous media. The Cameroonian sample of the set exhibits a significant permanent charge together with large specific surface area associated to fine particle size and considerable shape anisotropy.

This study focused on the deintercalation of dimethyl sulfoxide (DMSO) from a kaolinite–DMSO complex in various solvents. The use of kaolinite as filler in polymer–clay composite generally faced the difficulty of kaolinite dispersion due to its high cohesion. For improved dispersion of kaolinite within a given matrix, previous intercalation of small polar molecules is usually done prior to its displacement during composite-making. The influence of the solvent polarity on the deintercalation in analyzed here to understand its role during the deintercalation process. The intercalation of the DMSO was done by solution-mixing and its displacement was done in distilled water, ethyl acetate, and acetone. The products of deintercalation were analyzed using Fourier transform infra-red (FTIR), powder X-ray diffraction (XRD), and differential scanning calorimetry (DSC). The weakening of the kaolinite cohesion after DMSO intercalation is demonstrated through the broadening of the diffraction peak associated with the kaolinite on XRD patterns. From FTIR spectra, the weakening is associated with the displacement to low wavenumbers of the Si–O or Al–O vibration bands within the kaolinite–DMSO complex. The kaolinite dehydroxylation temperatures from DSC show that the rate of DMSO displacement affects the ordering of the recovered kaolinite. The crystallite size of the kaolinite is reduced from the raw to the recovered kaolinite after DMSO displacement, indicating an exfoliation of the kaolinite. From these results, it is found that the removal of the DMSO from the kaolinite–DMSO complex is influenced by solvent polarity. The higher the polarity, the greater the removal of the DMSO from the complex. Solvent polarity affects the rate of DMSO displacement, which influences the ordering of the recovered kaolinite. It is suggested that solvent polarity can be used to control the removal rate of DMSO, which may be key to the dispersion of the kaolinite platelets.

Generally, the phosphoric acid-activated systems use aluminosilicates as raw material (e.g., metakaolin); and the addition of alkali metals (e.g., Mg or Ca) contributes to obtain best properties. Volcanic ash (Va) is an aluminosilicate globally available and contain these metal oxides, which makes it a suitable raw material to produce acid-activated cements. The research on the production of this type of cements using Va is relatively recent. The knowledge on some parameters that influence the activation process under acid conditions of Va can be of great value as a viable alternative to its industrial application in the foreseeable future. This study examines the reactivity of four samples of volcanic ashes with different chemical composition in phosphoric acid at ambient temperature (25 °C). Two concentrations of phosphoric acid were used (41.1% and 51.2% P2O5 by mass). The main parameter used in this study is the molar ratio R expressed as the relation (MgO + CaO)/P2O5. Properties such as setting time, paste temperature in fresh state and compressive strength at 28 days of curing were evaluated. The final products obtained via acid activation of the volcanic ashes were studied using the XRD and FTIR techniques. The results showed that the initial and final setting time and the compressive strength increases with the increase of the molar ratio R of the mix when the proportion of P2O5 is constant. This coincides with the decrease in the temperature of the pastes. The highest compressive strength at 28 days of curing (81.3 MPa) was obtained with a molar ratio R = 4.2 and 41.1% P2O5 using a volcanic ash with high calcium and magnesium content (13.1% and 9.9% respectively). This volcanic ash when is activated with phosphoric acid of 51.2% P2O5 (R = 3.0) reported lower strength (40%) and a significant increase in the setting time. The results obtained showed that the CaO and MgO content in the volcanic ash and the acid concentration used as activator are parameters that affect the final properties of the acid-activated cements. Also, the presence of amorphous phase hindered the reactivity. Based on the results, the volcanic ashes may be considered precursors in the production of phosphoric acid-activated cements for construction purposes.

The present study deals with the relation between crystalline order in kaolinites and their ability to intercalate DMSO. Raw clays and kaolinite&ndash, DMSO complexes are analyzed using FTIR, XRD powder diffraction and differential scanning calorimetry and thermogravimetric analysis (DSC-TGA). The crystallinity is accessed using the Hinckley index (HI) from the raw clays&rsquo, XRD patterns and the p2 factor from their FTIR spectra. The intercalation ratio is evaluated from XRD and compared among the samples. The thermal analyses show a decrease in the dehydroxylation temperature in the DMSO&ndash, kaolinite complexes, indicating a decrease in the interlayer cohesion that may be useful to improve the delamination of kaolinite. The analysis of the coherent scattering domain size in the raw and the DMSO-intercalated samples indicates that the ordering is not affected during the DMSO intercalation. From these results, it is deduced that DMSO intercalation is favored by an increased crystallinity, as revealed by the intercalation ratio from XRD and the DSMO release during DSC-TGA analysis.

Two geopolymer binders that did not exhibit efflorescence, even after partial immersion in water for more than 45 days were successfully obtained from a mixture of aluminosilicates (kaolin and bauxite) with talc, and a mixture solution of potassium hydroxide and potassium silicate. Leaching tests in water were not able to quantify the occurrence of free alkali metals in the surface. The identification of structural characteristics was by solid-state nuclear magnetic resonance spectroscopy, X-ray diffraction, fourier transform infrared spectroscopy and scanning electron microscopy. They showed the occurrence of a structural arrangement with K2O–MgO–Al2O3–SiO2 where K2O and MgO are additional components from usual geopolymers. The improved structural characteristics limit drastically the leakage of alkali metals and their diffusion toward the surface. In comparison to usual geopolymers-based solely on aluminosilicates, the linear shrinkage is reduced, and the mechanical strength is similar. The results turned the use of talc and potassium hydroxide and silicate as a promising way of achieving an improved durability that is required for ensuring the properties in use of geopolymers.

This study reports the effect of the incorporation of corn cob from Baleng (Cameroon) as pore forming agent in the production of porous ceramic brick. The bricks were prepared with addition of increasing amount of corn cob (0, 2, 5, 10, and 15 wt%) in the clay slurry. The samples were fired at different temperatures (900, 950, 1000, 1050, 1100 °C). Linear shrinkage, water absorption, porosity, apparent density and flexural strength of samples were measured and analyzed. It is observed that apparent density, flexural strength and linear shrinkage increase with temperature and decrease with increasing corn cob while the water absorption and the porosity decrease with higher temperature and increase with the amount of added corn cob. The obtained porous bricks could found uses as construction bricks or thermal/sound insulator parts.

Four clay samples (Nt12, Nt11, Ab12 and Ab11) from the Ngog-Lituba alluvial deposits (Southern Cameroon) were investigated for their possible ceramic applications. X-ray diffraction (XRD), scanning electron microscopy (SEM), thermal and physico-mechanical analyses were used to assess the phase evolution and microstructure of the specimens fired between 850 and 1250 °C. The red color of the products at 850–1050 °C and the dark red at 1150–1250 °C are ascribed to the hematite formation and the disappearance of the organic matter. Mullite and glassy phase increase the mechanical strength and reduce the water absorption. Nt12 sample has the highest flexural strength and is suggested for porcelainized stoneware due to its low water absorption (0.51 vol%) around 1250 °C. According to the European Norm EN176, Ab11 and Ab12 samples (with respective water absorption of 1.32 and 2.38 vol%) are promising for the production of red-stoneware products, meanwhile Nt11, with water absorption of 4.48 wt%, is suitable for single fired bodies (earthenware).

This study reports the use of calcined talc for cementitious products making. The calcination is used to enhance the availability of magnesium from talc to react with phosphate for cement phase formation. It is shown that previous calcination of talc leads to products having enhanced mechanical performance due to the formation of more cement phase than in products based on raw talc. Talc fired at 900 °C was found to be the one in which magnesium release was maximal. Firing at temperature higher than 900 °C leads to the stabilization of enstatite, which decreased the magnesium availability. The cement phase is struvite, which was better detected on the X-ray patterns of the products involving fired talc. All the products have very rapid setting time and low shrinkage.

This study reports the physicochemical analysis of three alluvial clastic clays from the Ngaye River in northern Cameroon. X-ray diffraction, infra-red spectroscopy, scanning electron microscopy and thermal analysis are used to establish the mineralogical composition. It is found that the main clay minerals in these samples are kaolinite, muscovite-illite and smectite associated with quartz, goethite, feldspars and anatase. This mineralogical assemblage is in accordance with the chemical analysis which further confirmed the high quartz proportion. The low content in fluxing agent is indicated by the low contents in Na 2 O, K 2 O, MgO and CaO. The low content in fluxing agent and high sand proportion result in poor vitrification in ceramic testing brick obtained at 900 °C, 1000 °C and 1100 °C. For all the firing temperatures, linear shrinkage varied from 0.7% to 2.6%, weight loss varied from 3.5% to 7%, bulk density varied from 1.6 to 1.8 g/m 3 , water absorption decreased from 20.7% to 12.7%, and flexural strength ( σ ) varied from 0.60 to 2.07 MPa. The Ngaye alluvial clastic clays could be used in the fabrication of bricks (commons and perforated). However, an increase of fluxing agent and clays is needed to improve the mechanical performance of the ceramic products.

The thermal and mechanical properties of cassava starch films are analyzed in relation to the starch–kaolinite interactions. The kaolinite filler induces a lowering of the crystallinity in accordance with an increase plasticization of the starch matrix. The increase of plasticization induces a decrease of the elastic modulus and an increase of the elongation at break. A retardant effect to the starch matrix decomposition is observed. The filler–matrix interface at which the plasticizer infiltration is enhanced and the reduction of starch chain–chain interactions appears as keys of the observed properties changes. POLYM. COMPOS., 36:184–191, 2015. © 2014 Society of Plastics Engineers

The alkaline fusion method was used to enhance the reactivity of volcanic ash for geopolymer synthesis. To that end, different mixtures of fused soda–volcanic ash (fused volcanic ash) were used to assess reactivity for geopolymer synthesis. The amount of amorphous phase was determined both in the volcanic ash and the fused volcanic ash and X-ray diffraction analysis was used to evaluate effect of the alkaline fusion method. Different geopolymer mortars were prepared by alkaline activation of mixtures of powders of fused volcanic ash and metakaolin and river sand using sodium silicate as activator. Metakaolin was considered as consumer of excess of alkali contained in the fused volcanic ash. The geopolymer mortars were characterized by determination of setting time, linear shrinkage, compressive strength and scanning electron microscopy. The amount of amorphous phase and excess of fused soda content of the fused volcanic ash depended on molar ratio of Al 2 O 3 /Na 2 O and played a key role for geopolymer synthesis. The most convenient Al 2 O 3 /Na 2 O molar ratio of fused volcanic ash to produce effective geopolymer mortars ranged between 0.13 and 0.18. This study showed that volcanic ash can be used successfully as an alternative raw material for production of geopolymers via alkaline activation of fused volcanic ash.

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This research compares the properties of geopolymers made from metakaolin and volcanic ash and investigates the effect of addition Al 2 O 3 to metakaolin and volcanic ash-based geopolymers and synthesis at ambient temperature (24 ± 3 °C). FTIR, XRD, mechanical testing and SEM were used to characterize the geopolymer pastes. The results show that both metakaolin and volcanic ash can be utilized as source materials for the production of geopolymers. Metakaolin is a good source of Al 2 O 3 and SiO 2 and it is highly reactive with alkaline activators and produces a higher degree of geopolymerization in comparison with volcanic ash. The properties of volcanic ash-based geopolymer can be improved when alumina is used to compensate the deficiencies in Al 2 O 3 content in the volcanic ash. Addition of appropriate amount of Al 2 O 3 (such as 20% of Al 2 O 3 to MK and 40% of Al 2 O 3 to Vol) increased the geopolymerization extent resulting in the increase of the compressive strengths. It was typically found that 20% and 40% Al 2 O 3 lead to 18.1% and 32.4% increases of the compressive strengths respectively for the metakaolin and volcanic ash-based geopolymers.

Smectitic clays from the Sabga and Bana areas, western Cameroon were treated with sulfuric-acid solutions of various concentrations – 0.5, 0.7, 1.0 and 4.0 N – at 80°C for 2 h. The mineralogical, physicochemical and morphological characteristics of the samples treated were analysed using several techniques. The sulfuric acid caused structural modification of the dioctahedral smectite. The accessory minerals such as cristobalite, quartz, feldspars and anatase remained unaltered by the acid attack. The supernatant solutions after acid treatment contain Mg, Ca, K, Na, Si, Al and Fe as a result of partial dissolution of octahedral and tetrahedral cations. The activated clay samples exhibited a smaller cation exchange capacity (CEC) and the specific surface area (SSA) increased with increasing concentration of sulfuric acid, ranging from 65 to 134 m2/g for the sample from Bana and from 74 to 84 m2/g for the sample from Sabga. The different SSAvalues were affected by the relative abundance of smectite and cristobalite (SiO2/Al2O3 = 2.2 and 6.5, respectively, from Bana and Sabga). The activated clays from Bana and Sabga displayed interesting physicochemical and textural properties and can be considered as promising adsorbents for the bleaching of vegetable oils.

International audience; In this study, intercalation of dimethylsulphoxide (DMSO) in a Cameroonian kaolinite is used to achieve weakening of the interlayer hydrogen bonds, in the perspective of dispersion or even exfoliation of the clay within polymer composite materials. Displacement of intercalated DMSO by ethyl acetate and ammonium acetate is studied in order to simulate the interactions with the polymer matrix. The exfoliation of the kaolinite is well evidenced by X-ray diffraction and SEM observations. The disruption of the interlayer bonds is shown by the displacement of the FT-IR vibration modes of both Al–OH and Si–O functions, and by the decrease of the dehydroxylation temperature recorded by Controlled Rate Thermal Analysis. Complete displacement of DMSO by ethyl acetate is achieved and the crystalline structure is deeply disordered as a result of interlayer bonds weakening. The displacement of DMSO by ammonium acetate leads to a ternary composite of DMSO/ammonium acetate with respective intercalation ratio of 62.4% and 57.7%.

The physicochemical and mineralogical characterization of the 2, (13–16%) Al2O3and (2–7%) Fe2O3. Physico-chemical characterization of the clays showed that the cation exchange capacity (CEC) and the specific surface area range from 38 to 46 meq/100 g and from 33 to 90 m2/g respectively. The physical and chemical properties are fully compatible with potential uses in environmental applications. After purification and chemical modification, these materials could also be used in refining edible oil as adsorbent, waste water treatment and wine technology.

International audience; The present study aimed at improving the properties of geopolymer mortars obtained from volcanic ash as a source material. An alkali fusion process was used to promote the dissolution of Si and Al species from the volcanic ash and thus to enhance the reactivity of volcanic ash. Various amount of metakaolin (30%, 40%, 50% and 60% MK by weight) was used to consume the excess alkali needed for the fusion. The amount of amorphous phase was determined both in the volcanic ash and the fused volcanic ash and X-ray diffraction analysis was used to evaluate effect of the alkaline fusion method. Geopolymers were prepared by alkali activation of mixtures of powders of fused volcanic ash, various amount of metakaolin and river sand using a sodium silicate solution as activator. The geopolymer mortars were characterized by determination of setting time, linear shrinkage, scanning electron microscopy and compressive strength. The results of this study indicate that geopolymer mortars synthesized by the fusion method exhibit low setting time (7–15 min), low shrinkage (0–0.42%) and high compressive strength (41.5–68.8 MPa). This study showed that, by enhancing the reactivity of volcanic ash by alkali fusion and balancing the Na/Al ratio through the addition of metakaolin, all volcanic ashes can be recycled as an alternative source material for the production of geopolymers.

International audience; The influence of kaolinite content within a plasticized starch matrix on the glass transition and decomposition temperatures, water uptake, transparency and UV-vis blocking is reported. Exfoliation of the kaolinite clay within the composite is enhanced when previously intercalated with DMSO. The DMSO-intercalated kaolinite brings in advantages for the clay dispersion within the polymer matrix, the transparency and the water uptake. The transparency of the films is better preserved when DMSO intercalated kaolinite is used and a clay load between 2% and 6%, leads to a significant reduction of the UV light transmission.

The flocculation of kaolinite colloidal particles was carried out at pH = 6 in suspension of initial turbidity varying between 24 NTU and 102 NTU by a casein extracted from Cocos nucifera cream. During Jar-test essays, 90% to 99% of colloids were eliminated in the sediments. The optimal doses of casein used depend on the initial colloids concentrations of the suspension and were found to be 60 mg/L and 100 mg/L respectively for suspensions having turbidity of 24 NTU and 102 NTU. The corresponding residual turbidity are respectively 2.80 NTU and 10.22 NTU for clarified water. The structural analysis of the freeze-dried sediments by FTIR shows sharp adsorption bands at 1558 cm–1 and 1653 cm–1, indicating the presence of casein in the sediment. The flocculation process between the particles of kaolinite and the coconut casein is adsorption and bridging.

This study aimed at assessing the potential uses of alluvial clayey materials from Batouri. Their mineralogical, chemical and some physicomechanical characteristics are presented with some characteristics of fired bricks at 900, 950, 1000, 1050 and 1100 °C. The raw materials consisted of kaolinite, quartz, K-feldspars, anatase, and goethite. The phases formed during the firing process were mullite, quartz, hematite, and anatase. The linear shrinkage increased with firing temperature and remained

International audience; This study reports the characterization of a talc from Cameroon as a possible source material for cement formulation. To that end, the talc sample was characterized and mixed with a solution of sodium polyphosphate to formulate the cementitious products. Addition of magnesia (MgO) was done to analyze the effect of available MgO on the products. Fourier transform infrared, X-rays diffraction, linear shrinkage, compressive strength and scanning electron microscopy were used to analyze the products. The compressive strength increased with addition of MgO and the linear shrinkage decreased. All the analyses indicate that talc is a raw material of interest in cementitious products formulation; however, the inclusion of the MgO is a key factor for a better performance of the products.

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