Heated blends of phosphate waste: Microstructure characterization, effects of processing factors and use as a phosphorus source for alfalfa growth

International audienceMicrostructure of expandable lightweight aggregates (LWAs), which was composed of phosphate waste (PW), cement kiln dust (CKD) and raw clay (RC) was investigated, and the effects of processing factors (temperature, waste content, soaking time) on their physical properties were quantified by using response surface methodology (RSM). The potential use of LWAs as a phosphorus source was assessed through the use of seeds of alfalfa. It was found that the main minerals of the waste, namely carbonates and fluorapatite, were involved in the formation of labradorite/anorthite and melt respectively. Stability of mullite- the main constituent of CKD- was sensitive to the melt content. The assemblage of the identified phases was discussed based on the CaO-SiO2-Al2O3 phase diagram. The results of RSM showed that the change of compressive strength, firing shrinkage and water absorption of LWAs versus processing factors was well described with a polynomial model and the weights of the effects of the factors increased in the following order: sintering temperature > waste content (in the case of PW-RC) > soaking time. On the other hand, it was found that due to the release of phosphorus by soil-embedded pellets, the growth of alfalfa plants improved, and the rate enhanced in this order: PW-RC > PW-CKD > PW-CKD-RC. The absorbed quantity of phosphorus (0.12%) was still lower than the common uptake amount. (C) 2016 Elsevier Ltd. All rights reserved

Heated blends of clay and phosphate sludge: Microstructure and physical properties

International audienceBlends of a naturally occurring clay (0-30 wt.%) and phosphate sludge were heated at different temperatures and times and their microstructures were investigated using impedance spectroscopy, dilatometry, X-ray diffraction and scanning electron microscope. The weights of the effects of the change of temperature, soaking time and clay addition on some physical ceramic properties (shrinkage, water absorption and compressive strength) were assessed. For the latter purpose, the response surface methodology was used. The results showed that the sintering process was effective between 750 and 1000 degrees C and occurred by melt flow. It was accompanied with low activation energy for ionic conduction (0.20-0.35 eV). Due to the quantitative formation of gehlenite (the unique neoformed phase), the ionic conduction regressed and the melt formation was limited. Also, it was shown that the effects of the experimental factors on physical properties of the blends were well described with the adopted polynomial models, and the weights of the effects of the factors followed the order: temperature > clay content > soaking time. The effects of the interactions between the factors on the properties studied were evaluated and discussed in relation to the microstructure change. (C) 2015 The Ceramic Society of Japan and the Korean Ceramic Society. Production and hosting by Elsevier B.V. All rights reserved

Cordierite containing ceramic membranes from smectetic clay using natural organic wastes as pore-forming agents

International audienceCordierite ceramic membranes were manufactured from natural clay, oxides and organic wastes as pore forming agents. Mixtures aforementioned materials with the pore-forming agents (up to 10 wt.%) were investigated in the range 1000-1200 degrees C using thermal analysis, X-ray diffraction, scanning electron microscopy, mercury porosimetry and filtration tests. Physical properties (density, water absorption and bending strength) were correlated to the processing factors (pore-forming agent addition, firing temperature and soaking time). The results showed that cordierite together with spinel, diopside and clinoenstatite neoformed. SEM analysis revealed heterogeneous aspects. The results of the response surface methodology showed that the variations of physical properties versus processing parameters were well described by the used polynomial model. The addition of pore forming agent and temperature were the most influential factors. Filtration tests were performed on the best performing sample. The results allowed to testify that these membranes could be used in waste water treatment. (C) 2017 The Ceramic Society of Japan and the Korean Ceramic Society. Production and hosting by Elsevier B.V. This is an open access article under the CC BY-NC-ND license

Structural properties of phosphate-washing waste based geopolymeric mortars

The phosphate ore extraction activities often generate serious environmental problems, particularly those engendered by the phosphate washing waste. The waste was characterized by X ray fluorescence. The powder was calcined at 700 °C. The calcined and uncalcined samples were then investigated by means of X-ray powder diffraction (XRD). The calcined PWW was activated with sodium hydroxide and sodium silicate to produce geopolymeric materials. The reached results prove to reveal that the present phases in the powder appeared to have a remarkable effect on the result of compressive strength

Evaluation of porosity, mechanical and thermal properties of self-ignition coal gangue-based foams via fast microwave foaming

Recently, the large-scale stock and pollution of solid waste has become a serious environmental and economic problem. Upcycling the solid waste to produce porous materials is a value-added waste management method. Self-ignition coal gangue-based alkali-activated foams were successfully produced via a fast microwave foaming method within a few minutes. The effect of alkali concentration on pore structure, porosity, mechanical and thermal properties of alkali-activated foams was explored. Alkali-activated foams with low bulk density (0.41–0.81 g/cm3), high total porosity (65.6–83.5 vol%), acceptable compressive strength (0.92–4.42 MPa), and low thermal conductivity (0.11–0.14 W/mK) were obtained by a fast microwave foaming method. The foams showed excellent high temperature performance. The compressive strength showed an increasing trend after heat treatment from 500 to 1100 °C. Simultaneously, a low high-temperature volume shrinkage (4.0–4.1%) was achieved. The obtained foams can be used as high-performance proppant materials, thermal insulation building materials, and in fire-resistant applications

Use of chalky algae in the manufacturing of clayey ceramic membranes: Microstructural and dielectric behavior for electrochemical applications

International audienceNovel ceramic membrane filters were manufactured from kaolino-illitic clays and calcareous algae (up to 20 wt.%) as porogenic agent. The produced membranes were investigated using X-ray diffraction, thermogravimetric analysis, scanning electron microscope, impedance spectroscopy, and Fourier-transform infrared spectroscopy. All of the filtration suitability, electrical properties, and dielectric behavior were assessed and interrelated to the microstructure. It was found that the original clay minerals were involved in the mineralization development while the inclusion of large pores (8–12 μm) was observed at high magnification alongside porosity increase (up to 70%) due to the addition of the bio-based pore-former. Both electric and dielectric measurements revealed that the sintering process was governed by the densification phenomenon and was accompanied with lower activation energy. The order of magnitude of the values taken by electrical impedance was close to average Mega-Ohms suggesting the suitability of the produced ceramic membranes as an electrical insulator for typical electrochemical devices. The tests of filtration have shown that the ceramic membranes produced operate normally in the microfiltration range for a period of 50 min without clogging and at pressures up to 0.12 bar. Conclusively, the developed ceramic membranes could be considered for applications in industrial wastewater treatment and electrochemical media.In addition to this, a perspective has been proposed on the improvement paths or designs for ceramic membrane filters with good performance in wastewater treatment present in some electrochemical environments as well as methods to cope with the challenges regarding the performance of such materials