RESUMEN
In this paper, the synthesis of core-shell particles (i.e. temperature-sensitive ferrite (TSF) covered with silica) has been investigated. At first, TSF (mean diameter of 10 nm) was prepared by the coprecipitation method in an alkaline solution. Then, silica coating on the TSF surface was carried out by the controlled hydrolysis and condensation of tetraethyl orthosilicate (TEOS). The core-shell particles were formed by a surface precipitation procedure using TSF nanoparticles as a core material. The particles of silica were formed and these particles were then absorbed on the TSF nanoparticles. The coating procedure was described and explained by calculating the potential energies of interaction between the TSF and SiO(2) nanoparticles, according to the Derjarguin-Landau-Verwey-Overbeck (DLVO) theory. The coating process was found to be influenced by the pH and concentration of the TEOS precursor. The thickness of the silica layer on TSF cores was observed by means of transmission electron microscopy (TEM). The results showed that the optimum thickness of the SiO(2) layer on TSF core particles was obtained at pH 7.5, while the TEOS concentration was kept at 9 mM.
RESUMEN
In order to recycle bottom ash and use it as raw material for cement production, the removal of insoluble chloride was investigated by testing various washing techniques. The present work is also focused on investigating the properties of insoluble chlorides and determining the conditions for dissolving these compounds in order to reduce the chlorine content to the required level, i.e., less than 0.1 wt%. Within this framework, the effect of washing with water and CO2 bubbling was investigated, because the main insoluble chloride found in bottom ash, i.e., Friedel's salt, can be dissolved by CO2. Then, in order to better understand the removal of Cl, Friedel's salt was artificially synthesized by hydration and then the effect of CO2 bubbling was investigated. If all chlorides in the ash are converted into Friedel's salt by hydration, all chlorides can then be dissolved by CO2 bubbling. In addition, the effect of pH on removing the remaining insoluble chlorides was investigated by washing the ash with sulfuric acid solution. It was found that the most effective technique to reduce the Cl content to less than 1000 ppm was washing with sulfuric acid solution, while keeping the pH value at less than 4. By using this method, Friedel's salt and other insoluble chlorides were dissolved.
