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Αλκαλική ενεργοποίηση αργιλικών στείρων εκμεταλλεύσεων βιομηχανικών ορυκτών

Lallou Evangelia

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Summary

Alkali–activated materials (AAMs) are a promising alternative to conventional Portland cement building materials. Large quantities of secondary products rich in clay-silicate minerals such as fly ash, volcanic ash, clays, and slags can be exploited as well. The mining and metallurgical industry produces millions of tons of inert materials every year, which are left unattended in the environment and are not-valorized.The subject of the present diploma thesis is the alkaline activation of inert industrial clay mineral wastes. The aim is to investigate the behavior of geopolymers resulting from alkaline activation of clayey wastes. Specifically, inert clay materials (smectite and serpentine wastes) from the quarries of Geohellas in Knidi, Grevena, were used as raw material. The effect of various factors, such as the type and concentration of the alkaline activating solution, the mineralogy and particle size distribution of the raw materials, the curing temperature, and the aging period, on the compressive strength of the geopolymers was investigated.Also, in this study the possibility of co-utilisation of clayey wastes with metallurgical by-products such as LARCO’s ferronickel slag or commercial metakaolin, was exploited. The alkaline activators used consisted of sodium hydroxide (NaOH) or potassium hydroxide (KOH) and sodium silicate (Na2SiO3) solutions.For the synthesis of the geopolymers, the raw materials were mixed with the alkaline activator (KOH or NaOH, and Na2SiO3 solution). After continuous mechanical stirring, the formed geopolymer slurry was added into cubic molds. After being left for 48 h to sufficiently solidify, it was cured at 60 °C for 24 h. The aging period of the specimens was set at 7 and 28 days. They were then subjected to uniaxial compression testing. The molarities of the alkaline activators tested were 4 - 8M KOH or NaOH, while the percentages of slag and metakaolin additions were 15, 30 and 50 wt%. A reference (control) specimen, produced from alkaline activation of only clay wastes, was used as a guide for comparison.The highest compressive strength obtained from the experimental tests was 5.82 MPa, for the geopolymer produced from clayey wastes and metakaolin using a mass ratio of 70:30 after curing at 25 C and ageing for 28 days.

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