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Αξιολόγηση μαγνησίτη από τη Β. Εύβοια για την παραγωγή καυστικής μαγνησίας

Papageorgiou Ioanna

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Summary

This Diploma Thesis aims at evaluating the cryptocrystalline magnesite of North Evia for the production of caustic calcined magnesia. Evaluation of magnesite was performed via the construction of a Time-Temperature-Transformation (TTT) diagram of cryptocrystalline magnesite. The magnesite samples were heated in a laboratory furnace at 500oC, 550oC, 600oC, 700oC, 800oC, 900oC and 1000oC. At each temperature the samples were soaked for 1, 2, 3, 4 and 6 hours. The caustic calcined samples were examined by X-ray Diffraction (XRD). Qualitative and quantitative analysis of the samples was performed with the Eva and Autoquan© version 2.80 software respectively. The mineralogical phases identified were magnesite, periclase, calcite, dolomite and lime.The Autoquan© software was used to determine the crystal size of the periclase and the abundance of the various phases. Based on the results of the qualitative analysis, the TTT diagram was created, which determined the temperatures and firing times at which the phase of magnesite disappeared and the periclase appeared. It was found that at lower temperatures (500oC) the decomposition of magnesite to periclase is slowly while at higher temperatures the decomposition takes place at a fast rate.The activity of all caustic calcined magnesia samples was determined with a standard solution of critic acid with a concentration of 0.4M. Citric acid reacted with the periclase to form magnesium citrate and water. The reaction was completed when the color of the solution changed from transparent to red, and the time required for the reaction to take place was recorded. The sorter the reaction time, the more active the material. The reaction time, and therefore the activity of the caustic magnesia, depended on the crystal size of the periclase. The smaller the crystal size of the periclase, the faster its reaction with citric acid and thus the more active the caustic calcined magnesia. Finally, the samples which were periclase-free or contained small amounts of periclase were inactive.The results showed that high activity caustic magnesia may be produced at 550oC and 3 to 6 hours soaking time and at 600oC and 2 to 6 hours soaking time. Finally, medium quality products may be prepared oner a wider range of temperatures and times from 700oC to 1000oC for soaking times 1 to 6 hours.

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