Use of Zeolites in the Capture and Storage of Thermal Energy by Water Desorption-Adsorption Cycles.

In this work, four zeolite-bearing materials (three naturally occurring and one of synthetic origin) were considered for thermal energy capture and storage. Such materials can store thermal energy as heat of desorption of the water present therein, heat that is given back when water vapor is allowed to be re-adsorbed by zeolites. This study was carried out by determining the loss of water after different activation thermal treatments, the water adsorption kinetics and isotherm after an activation step of the zeolites, the intergranular and intragranular porosity, and the thermal conductivity of the zeolite-bearing materials. Moreover, the thermal stability of the framework of the zeolites of the four materials tested was investigated over a large number of thermal cycles. The results indicate that zeolite 13X was the most suitable material for thermal energy storage and suggest its use in the capture and storage of thermal energy that derives from thermal energy waste.

Thermodilatometric Study of the Decay of Zeolite-Bearing Building Materials.

Six zeolite-bearing rocks, often used as building materials, were analyzed by thermodilatometry, together with a rock not bearing zeolites and a plaster covering a containing wall made of zeolite-bearing dimension stones, up to 250 °C. The main results obtained were the following: (i) the zeolite-bearing rocks exhibited very small, if any, positive variation of ΔL/Lo (%) up to about 100 °C, whereas they more or less shrank in the temperature range 100-250 °C (final values ranging from -0.21 to -0.92%); (ii) the rock not bearing zeolites regularly expanded through the whole temperature range, attaining a final value of 0.19%; (iii) the plaster showed a thermodilatometric behavior strongly affected by its water content. Obtained results were interpreted based on plain thermal expansion, shrinkage by dehydration, cation migration and thermal collapse of the zeolitic structure. The decay of the zeolite-bearing building materials was essentially related to: (i) the large differences recorded in the thermodilatometric behavior of the various rocks and the plaster; (ii) the different minerogenetic processes that resulted in the deposition of the various zeolite-bearing rocks.

Structural concretes with waste-based lightweight aggregates: from landfill to engineered materials.

This research provides possible opportunities in the reuse of waste and particularly muds, coming from both ornamental stone (granite sludges from sawing and polishing operations) and ceramic production (porcelain stoneware tile polishing sludge), for the manufacture of lightweight aggregates. Lab simulation of the manufacturing cycle was performed by pelletizing and firing the waste mixes in a rotative furnace up to 1300 degrees C, and determining composition and physicomechanical properties of lightweight aggregates. The best formulation was used to produce and test lightweight structural concretes according to standard procedures. Both granite and porcelain stoneware polishing sludges exhibit a suitable firing behavior due to the occurrence of SiC (an abrasive component) which, by decomposing at high temperature with gas release, acts as a bloating promoter, resulting in aggregates with particle density < 1 Mg/m3. However, slight variations of mixture composition produce aggregates with rather different properties, going from values close to those of typical commercial expanded clays (particle density 0.68 Mg/m3; strength of particle 1.2 MPa) to products with high mechanical features (particle density 1.25 Mg/m3; strength of particle 6.9 MPa). The best formulation (50 wt.% porcelain stoneware polishing sludge +50 wt.% granite sawing sludge) was used to successfully manufacture lightweight structural concretes with suitable properties (compressive strength 28 days > 20 MPa, bulk density 1.4-2.0 Mg/m3).