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Fly ash from power plants is very toxic because it contains heavy metals. In this study fly ash was treated with a thermal plasma. Before their treatment, the fly ash was analyzed by many technics such as X-ray fluorescence, CHN elemental analysis, inductively coupled plasma atomic emission spectroscopy and scanning electron microscopy. With these technics, the composition, the chemical and physical proprieties of fly ash are determined. The results obtained by these analysis show that fly ash is mainly composed of carbon, and it contains also sulfur and metals such as V, Ca, Mg, Na, Fe, Ni, and Rh. The scanning electron microscopy analysis shows that fly ash particles are porous and have very irregular shapes with particle sizes of 20–50 μm. The treatment of fly ash was carried out in a plasma reactor and in two steps. In the first step, fly ash was treated in a pyrolysis/combustion plasma system to reduce the fraction of carbon. In the second step, the product obtained by the combustion of fly ash was vitrified in a plasma furnace. The leaching results show that the fly ash was detoxified by plasma vitrification and the produced slag is amorphous and glassy.

In this work, the main objective is to enhance the gas sensing capability through investigating the effect of Al and Mg doping on ZnO based sensors. ZnO, Mg1% doped ZnO, Al5% doped ZnO and (Al5%, Mg1%) co-doped ZnO nanoparticles (NPs) were synthesized by a modified sol-gel method. The structural characterization showed the hexagonal crystalline structure of the prepared samples. Morphological characterizations confirmed the nanometric sizes of the NPs (27–57 nm) and elemental composition investigation proved the existence of Al and Mg with low concentrations. The optical characterization showed the high absorbance of the synthesized samples in the UV range. The gas sensing performances of the synthesized samples, prepared in the form of thick films, were investigated. Sensing tests demonstrated the high influence of the Al and Mg on the sensing performances towards H2 and CO gas, respectively. The 5A1MZO-based sensor exhibits high sensitivity and low detection limits to H2 (<2 ppm) and CO (<1 ppm). It showed a response around 70 (at 250 °C) towards 2000 ppm H2 and 2 (at 250 °C) towards CO.

In this study, a two-dimensional numerical model was developed to simulate operation conditions in the non-transferred plasma torch, used to synthesis nanosilica powder. The turbulent magnetohydrodynamic model was presented to predict the nitrogen plasma flow and heat transfer characteristics inside and outside the plasma torch. The continuity, momentum, energy, current continuity equations, and the turbulence model were expressed in cylindrical coordinates and numerically solved by COMSOL Multiphysics software with a finite element method. The operation conditions of the mass flow rate of ionized gas ranging from 78 sccm to 240 sccm and the current varying between 50 A to 200 A were systematically analyzed. The variation in the electrothermal efficiency with the gas flow rate, the plasma current, and the enthalpy was also reported. The results revealed that the increase in working current lead to a raise in the effective electric power and then an increase in the distribution of plasma velocity and temperature. The efficiency of the torch was found to be between 36% and 75%. The plasma jet exited the nozzle torch with a larger fast and hot core diameter with increasing current. The numerical results showed good correlation and good trends with the experimental measurement. This study allowed us to obtain more efficient control of the process conditions and a better optimization of this process in terms of the production rate and primary particle size. X-ray diffraction (XRD) and transmission electron microscopy (TEM) were used to characterize the primary nanosilica powder that was experimentally collected. The arc plasma method enabled us to produce a spherical silicon ultra-fine powder of about 20 nm in diameter.

The phosphate industry generates a large amount of waste called phosphogypsum (PG). Generally, this waste is discharged without any treatment, and it causes considerable environmental problems. Hence, the objective of this study is the treatment of phosphate waste using thermal plasma technology. First, the waste is characterized using different techniques, such as X-ray fluorescence (XRF), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS), and inductively coupled plasma (ICP). Such characterization shows that the waste contains different toxic elements, such as heavy metals, fluorine, chlorine, sulfur, and phosphorus. For this reason, a plasma reactor is used to separate toxic elements from metals, such as silicon, aluminum, and magnesium, with a pyrolysis/combustion plasma system. In this work, the influence of different parameters, such as time of treatment and plasma current, on the volatility of toxic elements is studied. The obtained results show that after 40 min of treatment and at a plasma current of 160 A, the phosphogypsum completely melts, and the most toxic elements, namely Pb, Cd, V, Cr, and As, are completely vaporized.