Volcanic rocks have been used for building activity by the inhabitants of important cities located on the slopes of Mt. Etna, Italy. In this paper, the potential use of volcanic residues (code 20 03 03—“Municipal waste” residues from road cleaning in the European Waste Catalogue (EWC)) for the production of alkali activated material, especially devoted to the restoration of buildings belonging to the Baroque Sicilian architecture, was investigated. In particular, large volcanic pyroclastic deposits of recent eruptions considered waste materials were studied and a volcanic paleo-soil, locally named ghiara, widely used for mortars and plaster production in XVII–XVIII century with good pozzolanic features, was also considered. Both volcanic materials were activated using different mixtures of NaOH and Na2SiO3. Furthermore, formulations with different amount of metakaolin addition (10–25 wt%) were prepared due to low reactivity of volcanic materials and to allow the activation at room temperature. X ray diffraction revealed the formation of small quantities of zeolites as a result of the alkali activation process. The mechanical-physical results evidenced that the mechanical strength is strongly dependent on the metakaolin amount (10–38 MPa); accessible porosity average 25% and an average pore diameter of 0.06 µm; water absorption range 9–15%, eluates conductivity in the range 20–350 µS/m. These results confirm the occurring of alkali activation and the good potential for these pyroclastic wastes for valorization in the restoration field.
Graphic Abstract
The treatment of tannery wastewaters is a complex task due to the complexity of the waste: a mixture of several pollutants, both anionic and cationic as well as organic macromolecules which are very hard to treat for disposal all together. Geopolymers are a class of inorganic binders obtained by alkali activation of aluminosilicate powders at room temperature. Such activation process leads to a cement like matrix that drastically decreases mobility of several components via entrapment. This process taking place in the matrix can be hypothesized to be the in-situ formation of zeolite structures. In this work we use a metakaolin based geopolymer to tackle the problem directly in an actual industrial environment. To obtain a geopolymer, the metakaolin was mixed with 10 wt% of wastewater added with sodium hydroxide and sodium silicate as activating solutions. This process allowed a rapid consolidation at room temperature, the average compressive strength was between 14 and 43 MPa. Leaching tests performed at different aging times confirm a high immobilization efficiency close to 100%. In particular, only the 0.008 and 2.31% of Chromium and Chlorides respectively are released in the leaching test after 7 months of aging.
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