Diploma Thesis Defense by Mrs. Anastasia Rovithi
Thesis Title: «Conversion of coal fly ash into synthetic zeolite by hydrothermal treatment»
Friday 22 January 2021, at: 11:00 – 12:00 Link: https://tuc-gr.zoom.us/j/87962450121?pwd=UzFzbkxQaW5KcWR5ZlduY3BaZVphdz09
Examination Committee
- Assistant Professor Apostolos Giannis (advisor)
- Assistant Professor Alexandros Stefanakis
- Professor Elia Psillakis
Abstract
The purpose of this dissertation was to convert fly ash from lignite combustion into synthetic zeolite with hydrothermal treatment. Experiments were carried out using initial and washed fly ash with 5N hydrochloric acid. In the first phase, the fly ashes were treated only by a hydrothermal method in order to find the optimal conditions. The sequential process combustion-hydrothermal treatment and ultrasound-hydrothermal treatment, as well as their interactions in relation to zeolite synthesis, were studied. The samples were analyzed to measure moisture and ash content, particle-size distribution, chemical analysis using the X-ray fluorescence spectroscopy method (XRF) and mineralological analysis with X-ray powder diffraction (XRD). The first series of experiments studied the parameters of hydrothermal treatment such as time, temperature, silicon to aluminum ratio, solid to liquid ratio and calcium content. The results of the analyses showed a satisfactory performance since zeolite crystals were formed. In the second series of the experiments, the optimized values for zeolite formation were applied in two-stage processes instead of one stage because according to the literature the two-stage processes has good results for zeolite formation from fly coal ash. The results showed no significant improvement compared to the initial one-stage process. More specifically, the amorphous content was increased, resulting in lesser formation of zeolites. For this reason a third series of experiment was carried out, where ultrasound was used in combination to hydrothermal treatment at the optimal conditions and the results were very satisfactory. The amorphous content decreased significantly, the zeolite yield was satisfactory and most importantly, there was quite a large percentage of zeolite formation as units (single zeolite).In conclusion, the raw material showed the best result, i.e. the maximum zeolite yield, in the third set of experiments. The sample was treated with ultrasound for 30min and hydrothermal treatment for 6h at 150οC, using liquid sodium hydroxide, ratio S/L=1/4 and SiO2/Al2O3 ratio =6,3.
