Natural zeolite clinoptilolite was calcined at different temperatures (700–1000 °C) in order to increase its reactivity as geopolymer precursor. The clinoptilolite structure was completely destructed at 900 °C and the material was called “metazeolite”. Geopolymer pastes were prepared with different SiO₂/Al₂O₃ ratio by using silicate and aluminate activators, including alkaline waste solution from a Dutch aluminium anodizing industry. The prepared geopolymers were cured at 80 °C and were characterized by XRD, FTIR and SEM. The metazeolite based geopolymer activated with potassium silicate solution possessed the highest compressive strength (43 MPa ± 4 MPa). The silicate and hydroxide activated geopolymers showed relatively high shrinkage. On the other hand, by using aluminate solutions the shrinkage of geopolymers was significantly decreased. The aluminate activated geopolymer contained newly formed phillipsite and zeolite Na-P. However, there was no significant difference in geopolymer product when using chemical grade aluminate solutions and industrial waste aluminate solutions. The use of alkaline waste solutions is recommended because of economic and environmental benefits.

The rate of photocatalytic oxidation of contaminants in drinking water using an immobilized catalyst can be increased by properly designing the catalyst structure. By creating a solar reactor in which meshes coated with TiO₂ were stacked, we demonstrated that degradation of humic acids with four superimposed stainless steel meshes was up to 3.4 times faster than in a single plate flat-bed reactor. Incorporation of TiO₂ coated mesh structures resulted in a high specific photocatalytically active surface area with sufficient light penetration in the reactor, while the coated area for one mesh was 0.77 m² per m² projected area. This brought the photocatalytic efficiency of such reactors closer to that of dispersed-phase reactors, but without the complex separation of the very fine TiO₂ particles from the treated water.

Abstract: The increasing amount of fluidized bed combustion (FBC) ash is putting pressure on researchers to invent novel methods for utilizing the ash. The low reactivity and heavy metal content constrict the use of FBC ash in the same way as coal ash from pulverized combustion. Four FBC fly ashes from different power plants were granulated with sodium silicate solution in order to produce artificial aggregates. All aggregates matched the definition for lightweight aggregate according to the EN 13055-1 standard. The strongest aggregates were produced from fly ashes that had the highest X-ray amorphous material content and the highest amount of selectively soluble SiO₂ and Al₂O₃. However, the same leaching problem (leaching of the anionic species) as with coal fly ashes was observed with the FBC fly ashes. The simultaneous high shear granulation and alkali activation of FBC ashes showed that artificial aggregates with satisfactory physical properties, such as density and strength, can be obtained even from low-reactive fly ashes that contain heavy metals. Graphical Abstract: [Figure not available: see fulltext.]

The presence of water (H₂O) is essential for the adsorption of carbon dioxide (CO₂) on the serpentine particles. However, the use of H₂O in the slurry bed columns requires high energy inputs to maintain the temperature during operation above ambient temperatures. Moreover, the separation, drying, handling, and processing of the product stream will pose challenges and cost even more energy. Here, we show the proof of principle of CO₂ sequestration on mineral particles in a fluidized bed using a moist CO₂ stream. The setup allows wetting of the particles while maintaining fluidization. The results show 50% mineral conversion and 40% CO₂ conversion in 8 min at 1 bar and 90 °C.

Combined management of coal combustion fly ash and waste aluminium anodising etching solutions using geopolymerisation presents economic and environmental benefits. The possibility of using waste aluminium anodising etching solution (AES) as activator to produce fly ash geopolymers in place of the commonly used silicate solutions was explored in this study. Geopolymerisation capacities of five European fly ashes with AES and the leaching of elements from their corresponding geopolymers were studied. Conventional commercial potassium silicate activator-based geopolymers were used as a reference. The geopolymers produced were subjected to physical, mechanical and leaching tests. The leaching of elements was tested on 28 days cured and crushed geopolymers using NEN 12457-4, NEN 7375, SPLP and TCLP leaching tests. After 28 days ambient curing, the geopolymers based on the etching solution activator showed compressive strength values between 51 and 84 MPa, whereas the commercial potassium silicate based geopolymers gave compressive strength values between 89 and 115 MPa. Based on the regulatory limits currently associated with the used leaching tests, all except one of the produced geopolymers (with above threshold leaching of As and Se) passed the recommended limits. The AES-geopolymer geopolymers demonstrated excellent compressive strength, although less than geopolymers made from commercial activator. Additionally, they demonstrated low element leaching potentials and therefore can be suitable for use in construction works.