Chemical and mineralogical characterization and ceramic suitability of raw feldspathic materials from Dschang (Cameroon)

The chemical and mineralogical characterization of raw feldspathic materials from Dschang (Cameroon) was realized by means of X-ray diffraction, differential thermal analyses, optical and scanning electron microscopies, and analytical techniques. It was found that these materials consist of albite (43 ± 3 wt.%), microcline (41 and 26 wt.%), quartz (14.5 ± 1.5 wt.%), plagioclase (oligoclase type) (6 and 12 wt.%) and a minor content of biotite. The amount of fluxing oxides is about 12 wt.% and those of pigments are quasi-null. The ceramic suitability of these materials was assessed in the light of the obtained chemical data and physical characteristics (fusibility, viscosity, colour). The results showed that these raw materials are convenient, as fluxing compounds, for manufacturing white ceramic.KEY WORDS: Raw feldspathic materials, Mineralogy, Chemical composition, Ceramic suitability, Cameroon   Bull. Chem. Soc. Ethiop. 2010, 24(1), 39-46

CARACTÉRISTIQUES MORPHOLOGIQUES ET GÉOCHIMIQUES DES MANTEAUX D’ALTÉRATION DÉVELOPPÉS SUR GRANITOÏDES DANS LA RÉGION DE L’ADAMAOUA (CAMEROUN)

Seven samples of rocks, including three parent rock and four weathered rock from Wack (Vina division, Adamawa Region, Cameroon) have been studied. According to chemical analysis and chemical weathering indices calculated, weathering rocks conserve the structure of parent rocks. During weathering and the influence of the steep slope, the chemical elements are completely disorganized. The quantitative determination of the degree of chemical weathering of these rocks based on whole rock chemistry was performed. The slope of the straight regression absolute value is closed to 1. These various chemical weathering indices calculated has shown that they are significantly related

CARACTÉRISTIQUES MORPHOLOGIQUES ET GÉOCHIMIQUES DES MANTEAUX D’ALTÉRATION DÉVELOPPÉS SUR GRANITOÏDES DANS LA RÉGION DE L’ADAMAOUA (CAMEROUN)

Seven samples of rocks, including three parent rock and four weathered rock from Wack (Vina division, Adamawa Region, Cameroon) have been studied. According to chemical analysis and chemical weathering indices calculated, weathering rocks conserve the structure of parent rocks. During weathering and the influence of the steep slope, the chemical elements are completely disorganized. The quantitative determination of the degree of chemical weathering of these rocks based on whole rock chemistry was performed. The slope of the straight regression absolute value is closed to 1. These various chemical weathering indices calculated has shown that they are significantly related

Mechanical properties and durability of volcanic ash based geopolymer mortars

The mechanical properties and durability of volcanic ash based geopolymer mortars synthesized at 27 degrees C and 80 degrees C were evaluated. The water absorption and apparent porosity increase up to 28 days, then become almost constant with time. The bulk density of specimens cured at 27 degrees C decreases continuously with time, whereas it doesn't change considerably with time for specimens cured at 80 degrees C. Geopolymer specimens cured at 27 degrees C achieved the compressive strength of 20.5 MPa after 28 days and it no longer increases significantly with time. While a maximum strength of 37.9 MPa is reached at 90 days for specimens cured at 80 degrees C. Specimens performed well in wetting and drying conditions. Geopolymer specimens obtained at 27 degrees C developed a better resistance to 5% sulfuric acid than the ones cured at 80 degrees C. The microstructure of geopolymer specimens after acid exposure revealed the formation of gypsum as a secondary phase due to the reaction between sulfuric acid and calcium from geopolymer gel. The presence of Na-rich gel in specimen cured at 27 degrees C enhances its acid resistance. The pore structure and permeability are the key factors affecting the durability of volcanic ash based geopolymer mortars. (C) 2016 Elsevier Ltd.. All rights reserved

New Low-Cost Ceramic Microfiltration Membranes for Bacteria Removal

International audienceSafe water provision in low-income countries is constrained by limited financial resources, and the problem is worsened during natural disasters. Thus, there is a need to develop efficient low-cost technologies for point-of-use water treatment. This work reports on the development of new ceramic microfiltration membranes made from mixtures of inexpensive raw materials available locally (kaolin, bentonite and limestone) and their efficiency in rejecting bacteria such as Escherichia coli and Staphylococcus aureus. Thermogravimetric analysis, differential scanning calorimetry, Fourier-transform infrared spectroscopy, X-ray diffraction, mercury intrusion porosimetry, flexural strength and water uptake were used to characterize the raw materials and membranes. The addition of limestone in the membrane fabrication increased the pore size, the porosity and, thus, the permeability of the membranes but at the expense of the rejection performance. Among the different compositions studied, the membrane made of 83% kaolin, 10% bentonite and 7% limestone showed the best performance compromise with water permeability of 566 L·h−1·m−2·bar−1 and 100% rejection of both Escherichia coli and Staphylococcus aureus. These new low-cost microfiltration membranes are expected to have potential applications in water treatment and household applications. © 2022 by the authors. Licensee MDPI, Basel, Switzerland

Synthesis of volcanic ash-based geopolymer mortars by fusion method: Effects of adding metakaolin to fused volcanic ash

International audienceThe 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

Mechanical activation of volcanic ash for geopolymer synthesis: effect on reaction kinetics, gel characteristics, physical and mechanical properties

This paper looks at the possibility of using low reactive volcanic ash for making geopolymer cement. The research is directed towards (a) alteration of the reactivity of volcanic ash by mechanical activation, and (b) use of mechanically activated volcanic ash for the synthesis of a geopolymer. The effect of mechanical activation was quite visible on particle size distribution and the degree of crystallinity. The disappearance of some anorthite peaks and appearance of quartz peaks in volcanic ashes milled for 120 min demonstrate the change in mineralogy. The appearance of an intense carbonate band with milling time could be related to sorption of atmospheric CO2 on the grains surface during mechanical activation. The manifestation of mechanical activation of volcanic ash was prominent on (a) the reaction kinetics, (b) microstructural development, and (c) physico-mechanical properties of the geopolymer product. The rate constant and extent of geopolymerization increased with milling time but decreased with curing temperature. This decrease is in non-conformity with other alumina-silicate materials used for geopolymerization such as metakaolin and fly ash. FEG-SEM and EDAX results revealed that the geopolymer gel obtained is mixture of poly(ferro-sialate-siloxo) and poly(ferro-sialate-disiloxo) binder type with a formula close to [Ca,Na,K,Mg]-[-Fe-O-](x)-[Si-O-Al-O-](1-x)-[-Si-O-](y). The physico-mechanical properties changed significantly. Setting time reduced by >95% in samples milled for 60 min or more. The compressive strength which was negligible for 0-30 min milled volcanic ash reached 29-54 MPa after 60-120 min of milling time. Heat curing influenced the early age (7 and 28 days) compressive strength but the 90 day compressive strength of both ambient and heat cured samples were comparable

Reactivity of volcanic ash in alkaline medium, microstructural and strength characteristics of resulting geopolymers under different synthesis conditions

The present paper investigated the reactivity of volcanic ash in alkaline medium and reported the effect of synthesis conditions on microstructural and mechanical properties of volcanic ash-based geopolymers. The reactivity of volcanic ash was carried out by leaching it under different NaOH concentrations (8, 10, and 12 M) and temperatures (27, 60, and 80 A degrees C), and chemical composition of the filtrate measured by ICP-OES. The influence of silica modulus (1.4, 1.5, and 1.66) and curing temperatures (27, 60, and 80 A degrees C) on microstructural characteristics of the resulting geopolymers was assessed by Calorimetry test, XRD, FTIR, Al-27 and Si-29 MAS-NMR, TGA, and FESEM-EDX. The dissolution behavior of Si is influenced by NaOH concentration, while Al is more sensitive to temperature. The low amount of dissolved species is correlated with the low amount of heat released. XRD, FTIR, Al-27 and Si-29 MAS-NMR, and TGA have shown the evidence of changes occurred during geopolymerization of volcanic ash and the extent of reaction with varying silica modulus and curing temperature. FESEM and EDX have shown that geopolymers obtained are poly(ferro-sialate-siloxo), poly(ferro-sialate-disiloxo), and poly(ferro-sialate-multisiloxo) binder types with Ca2+, Mg2+, and Na+ as charge-balancing cations. These structures are irrespective of silica modulus and curing temperature. The curing temperature is the main factor affecting the early compressive strength

Volcanic ash-based geopolymer cements/concretes: the current state of the art and perspectives

The progress achieved with the use of volcanic ash for geopolymer synthesis has been critically reviewed in this paper. This consists of an overview of mineralogy and chemistry of volcanic ash. The role of chemical composition and mineral contents of volcanic ash on their reactivity during geopolymerization reaction and, consequently, mechanical properties have been accessed. An attempt has been made to establish a relationship between synthesis factors and final properties. A critical assessment of some synthesis conditions has been addressed and some practical recommendations given along with suggestions of future works that have to be done. All this has shown that there are still many works such as durability tests (carbonation, freeze-thaw, resistance, etc.), life cycle analysis, etc. that need to be done in order to satisfy both suitability and sustainability criteria for a large-scale or industrial application