Sodium Silicate Research Articles

Influence of anionic silica forms in clear sodium silicate precursors on metakaolin geopolymerisation via 29Si and 27Al MAS-NMR and microstructural studies

A number of synthesis parameters directly influence the degree of reticulation/geopolymerisation of metakaolin exposed to alkaline solutions of sodium hydroxide and/or sodium silicate. In the latter case, a sodium silicate solution can be depolymerised by the introduction of an appropriate amount of NaOH. The effects of the ageing of the activator solution on the reticulation of metakaolin-based geopolymers are quantified for the first time in this work. We studied the anionic species of the sodium silicate solution with the addition of NaOH made just before the preparation of the paste, 24 h or 7 days before. These three ageing periods cause a significant difference in the Si-bearing species in solution, as demonstrated by nuclear magnetic resonance on 29Si. The effect of these anionic species on the reticulation/polymerisation of metakaolin at room temperature was demonstrated by solid-state 27Al and 29Si MAS-NMR, the chemical stability in various solutions (deionised water, HCl, HNO3, H2SO4), and X-ray diffraction on geopolymer powders before and after immersion in acids. Compressive strength before and after the immersion in acidic media was an additional measurement to assess the overall structural stability of the 3D polymerised network of the final dense ceramic-like product. Ageing of the activator solution affected the chemical stability of the hardened geopolymers accompanied by a slight to severe reduction in strength after leaching in HNO3 or HCl and in H2SO4, respectively. The quantitative MAS-NMR description of the Si and Al coordination in the geopolymers was correlated with the chemical stability where the formulations with the higher number of Q4(0Al) and Q4(1Al) for the silicon species were more resistant (lower number of Na+ compensating for Al+3 to be exchanged with H+). The formulations with higher Al content in the structure, i.e. higher number of Q4(3Al) silicon species showed higher mechanical stability. These results show that the timing of the preparation of the alkaline activator is essential for a correct mix design.

Effect of Polypropylene Fiber on the Strength Properties of Geopolymer Concrete Activated with Water Glass

Effect of Polypropylene Fiber on the Strength Properties of Geopolymer Concrete Activated with Water Glass

Effect of inorganic salt impurities on seeded precipitation of silica hydrate from sodium silicate solution

To clarify the precipitation of silica hydrate from the real desilication solutions of aluminosilicate solid wastes by adding seeds and improve integrated waste utilization, the seeded precipitation was studied using synthesized sodium silicate solution containing different inorganic salt impurities. The results show that sodium chloride, sodium sulfate, sodium carbonate, or calcium chloride can change the siloxy group structure. The number of high-polymeric siloxy groups decreases with increasing sodium chloride or sodium sulfate concentration, which is detrimental to seeded precipitation. Calcium chloride favors the polymerization of silicate ions, and even the chain groups precipitate with the precipitation of high-polymeric sheet and cage-like siloxy groups. The introduced sodium cations in sodium carbonate render a more open network structure of high-polymeric siloxy groups, although the carbonate ions favor the polymerization of siloxy groups. No matter how the four impurities affect the siloxy group structure, the precipitates are always amorphous opal-A silica hydrate.

Progress in Researching the Ability of Geopolymer Concrete to Withstand a Penetration of Chloride Ions

Geopolymer concrete is an innovative environmentally friendly construction material, and the transportation of chloride ions plays a crucial role in determining its durability. This study provides a summary of the characteristics and limitations of the test techniques used to measure the resistance of geopolymer concrete to the permeability of chloride ions, based on the introduction of the chloride ion transport mechanism in geopolymer concrete. This text provides an overview of the features and constraints of the test techniques used to assess the resistance of geopolymer concrete to chloride ion permeability. It also explores the connections between the mechanism of chloride ion transport and the resistance of geopolymer concrete to chloride ion permeability. This paper provides a concise overview of the properties and constraints of the test methods used to measure the resistance of geopolymer concrete to chloride ion permeability. It also discusses the factors that can affect the chloride ion permeability resistance of geopolymer concrete and presents a comparison between different methods. The article continues by highlighting that the chloride transport model of geopolymer concrete is complex. The essay continues by highlighting the chloride transport model of geopolymer concrete, specifically focusing on the impact of individual parameters such as high temperature, freezing-thaw cycles, and the resistance of geopolymer concrete to chloride ion permeability. The study investigates the impact of freeze-thaw cycles, alkali admixture, and water glass modulus on the resistance of geopolymer concrete to chloride penetration. The infiltration of chloride, as well as the precision of determining the concentration border of chloride ions for colour rendering, require further in-depth investigation.

Surface Texturing of Silicon Wafers by Two-step Ag-assisted Etching Process with New NSR Solution

Abstract: Solar cells made of monocrystalline silicon can convert more solar energy into electrical energy if the cells can absorb greater amounts of light. Recently, it has been observed that metal-assisted catalyzed etching (MACE) is a good technology for manufacturing micro and nanostructures on silicon substrates. In this work, we use silver as a catalyst in a two-step metal-assisted etching process followed by a rebuilding nanostructure (NSR). We study the effect of changing the parameters of the second step in the MACE process (concentrations of etching solution materials, temperature, and reaction time), where black silicon was obtained with a reduced reflection of 3% without the NSR process. We tested the effect of two types of alkaline solutions in the NSR process on the surface structure of silicon. After performing an NSR operation with sodium hydroxide solution, the field emission scanning electron microscopy (FESEM) image shows a surface with upright pyramidal structures intertwined with deep cavities, and with a reflectance of 10.74%. However, after performing the NSR process with a solution of sodium silicate, the FESEM image shows a rough surface with non-overlapping pores of small cross-sections, achieving a reflectance of 8.65% within the wavelength range of 550-850nm. Keywords: Texturing, Monocrystalline silicon, Ag-assistance chemical etching, Black silicon, Reflectance.

Permeability and self-healing behavior of alkali activated geopolymers for well cementing applications

Geopolymers, also identified as alkali-activated materials (AAM), are alternative well-cementing materials with a lower carbon footprint than traditional ordinary Portland cement (OPC). Geopolymers are formed by combining an aluminosilicate precursor, such as fly ash (FA), with an alkaline activator solution. Among their merits is an ability to self-heal after becoming damaged, which can be exploited to restore permeability, sealing ability, zonal isolation, and well integrity in wells that suffer from cracking, fracturing, or debonding in their annular cement sheaths and abandonment plugs.This study investigates the self-healing ability of various alkali-activated Class F fly ash-based geopolymers. Liquid sodium hydroxide (LSH), liquid sodium silicate (LSS), and solid sodium silicate (SSS) were used as activators for the preparation of geopolymer specimens, while Class H OPC was used as the control material. Permeability was characterized using pressure transmission tests (PTT). The tested samples were of different compositions, curing ages (7-day and 28-day), damage stages (pristine, damaged after freeze-thaw cycling, self-healed after post-damage curing), and damage severity (low, medium, and high). Fourier-transform infrared-spectroscopy (FTIR) and loss on ignition (LOI) tests were performed to examine the geopolymer reaction over time, in an attempt to relate the various permeability results to the geopolymerization process. The experimental results show that geopolymers possess low permeability, comparable to – or lower than – OPC, and that effective permeability restoration occurs in geopolymers, even after high degrees of damage. The implication of this work is that geopolymers are promising alternative barrier materials to OPC with a superior ability to guarantee low barrier permeability and appropriate zonal isolation, keys to wellbore integrity over the entire lifecycle of wells, even if those wells suffer from damage.

Correlation Mineral Water Consumption and Hemoglobin Levels in Adolescent Girls

Anemia is a global health issue that affects people of all ages, particularly adolescent girls. Adolescent girls require nutritional intake, both from food and water. According to the balanced nutrition guidelines, people (particularly adolescents and adults) require 2000 liters (or eight glasses) of water daily. Most adolescent girls barely consider their water consumption. A lack of water in the body affects the balance of minerals (salt and sugar), disrupting regular metabolic processes such as hemoglobin (Hb) level regulation. This study investigates the correlation between adolescent girls' water consumption and hemoglobin levels. This quantitative study uses a cross-sectional design to collect variable data at a certain time. The study used blood with anti-coagulants EDTA from 30 adolescent girls from Universitas Muhammadiyah Semarang. The primary data for this study are water consumption and hemoglobin levels. Results of the research show that adolescent girls' water consumption was adequate (66.7%) and low (33.3%). The average Hb level among adolescent girls was 12.4 g/dL. Adequate water consumption resulted in 3 respondents with low Hb levels and 7 with normal Hb levels. In contrast, low water consumption resulted in 2 respondents with low Hb levels and 18 with normal Hb levels. The Rank-Spearman correlation test showed sig 0.177 (p>0.05). The study concluded that there was no correlation between adolescent girl water consumption and hemoglobin levels. Food fluid intake can compensate for a lack of water consumption.

Manganese metal ion removal from aqueous solution using industrial wastes derived geopolymer

Heavy metal pollutants, highly toxic and invisible, have garnered attention due to bioaccumulation. Increased manganese production from steel industries is expected to lead to harmful concentrations in water, adversely affecting the environment and public health. The sustainable approach of utilizing industrial by-products to synthesize geopolymers for the immobilization of heavy metal ions has gained research interest. The current study aims to verify the feasibility of Paper sludge ash (PSA) in conventional geopolymer (CGP) to immobilize manganese (Mn) heavy metal ions from aqueous solutions. CGP was prepared using Fly ash (FA) as resource material, which was replaced by PSA at a level of 30 %, by weight. The precursors were treated with alkali solutions, namely sodium hydroxide and sodium silicate, incorporating ambient curing. The characterization studies of precursors and CGP were investigated using XRD, XRF, SEM, EDS, FTIR, and Brunauer-Emmett-Teller surface area (BET) analysis techniques to outline the crystal structure, morphology, and pore parameters. Additionally, the experimental investigation comprehensively examined the impact of various pH levels, dosages, contact times, and initial concentrations on the removal efficiency of Mn heavy metal ions. The difference in concentration of Mn heavy metal ions quantified by atomic absorption spectrometry. The Langmuir models effectively explained the removal of Mn ions by CGP due to high fitting coefficients. The highest value of uptake capacity was found to be 28 mg/g at 30 °C with pH value of 4. Therefore, blending industrial wastes improves the potential of decontamination agents in removing heavy metals from wastewater, promoting environmental sustainability.

Synergistic strengthening mechanism of Ca2+-sodium silicate to selective separation of feldspar and quartz

Synergistic strengthening mechanism of Ca2+-sodium silicate to selective separation of feldspar and quartz

Potensi Ketahanan Pangan sebagai Perekonomian Desa Sababilah dalam Mendukung Ketersediaan Pangan Kabupaten Barito Selatan

Sababilah Village in Dusun Selatan District, South Barito Regency, has great potential to increase food security through optimal resource management. With lowland topography and a tropical climate, this village has fertile soil that is ideal for various plants. The 2024 Real Work Lecture Program (KKN-T) from Palangka Raya University focuses on developing food security by planting various plants using innovative planting media containers such as drinking water glasses and providing technical assistance in watermelon harvesting. The results of the activity show that this agricultural technique is effective in utilizing local resources and increasing crop yields. To increase success, it is recommended that villages expand modern agricultural training, involve communities more actively, and develop local markets for agricultural products. Regular evaluation is also important to ensure the program's sustainability and positive impact.

New Insights into the Depressive Mechanism of Sodium Silicate on Bastnaesite, Parisite, and Fluorite: Experimental and DFT Study

The surface properties of bastnaesite and parisite are similar to their associated gangue mineral, fluorite, which makes the flotation separation of these two rare earth minerals from fluorite one of the industry’s most significant challenges. This study systematically investigates the inhibitory effects and mechanisms of sodium silicate (SS) on bastnaesite, parisite, and fluorite in an octyl hydroxamic acid (OHA) collector system through flotation experiments, various modern analytical methods, and DFT simulations. The flotation test results indicate that the inhibition effects of SS on the three minerals are in the order: fluorite > parisite > bastnaesite. Detection and analysis results indicate that SS forms hydrophilic complexes with Ca atoms on the surfaces of fluorite and parisite, enhancing surface hydrophilicity and inhibiting OHA adsorption, but its impact on bastnaesite is relatively minor. DFT simulation results show that OHA forms covalent bonds with metal ions on mineral surfaces, favoring five-membered hydroxamic-(O-O)-Ce/Ca complexes, and reacts more strongly with Ce atoms than Ca atoms. SS primarily forms covalent bonds with metal atoms on mineral surfaces via the SiO(OH)3− component, and OHA and SS compete for adsorption on the mineral surfaces. OHA has a stronger affinity for bastnaesite, whereas SS shows the highest affinity for fluorite, followed by parisite, and the weakest affinity for bastnaesite.

Halloysite-derived hierarchical cobalt silicate hydroxide hollow nanorods assembled by nanosheets for highly efficient electrocatalytic oxygen evolution reaction

The oxygen evolution reaction (OER) is regarded as the bottleneck of electrolytic water splitting. Thus, developing robust earth-abundant electrocatalysts for efficient OER has received a great deal of attention and it is an ongoing scientific challenge. Herein, hierarchical hollow nanorods assembled with ultrathin mesoporous cobalt silicate hydroxide nanosheets (denoted as CoSi) were successfully fabricated, using the silica nanotube derived from halloysite as a sacrificial template, via a simple hydrothermal method. The resulting cobalt silicate hydroxide nanosheets stack with thicknesses ∼10 nm, as confirmed by transmission electron microscopy. The elaborated nanoarchitecture possesses a high specific surface area (SSA) allowing good exposure to the cobalt active centers exhibiting superior catalytic activity vs analogs synthesized using sodium silicate. Among all as-prepared CoSi samples, those synthesized at 150 °C (CoSi-150) exhibited the minimum overpotential of ∼347 mV at a current density of 10 mA cm–2. In addition, CoSi-150 also exhibited superior performance against typical cobalt-based catalysts, and its surface hydroxyl groups were beneficial for the enhancement of OER performance. Furthermore, the CoSi-150 showed excellent durability and stability after the 105 s chronopotentiometry test in 1 M KOH. This design concept provides a new strategy for the low-cost preparation of high-quality cobalt water splitting electrocatalysts.

Optimization and Evaluation of Alkali Activated Fly Ash for Lightweight Aggregate Production

This study investigates the utilization of solid waste, specifically fly ash, and other materials to produce aggregates through geopolymerisation. The research aims to explore the properties of fly ash aggregates and assess their viability in concrete production. The objectives of the study encompass the preparation of aggregates using different proportions of fly ash and alkali activator such as sodium hydroxide and sodium silicate, alongside the casting of concrete cubes utilizing the artificial aggregate. The methodology employed involves the preparation of alkali activator, mix proportioning, and the subsequent processes of mixing, casting, crushing, and curing. Various ratios of fly ash to activator (2.5:1, 3:1, and 3.5:1) were investigated, with corresponding results obtained for properties such as abrasion value, impact value, bulk specific gravity, and water absorption. The findings reveal that the properties of the fly ash aggregates vary with different ratios, with notable differences observed in abrasion value, impact value, bulk specific gravity, and water absorption. For 2.5:1 abrasion value is 26.02%, impact value is 19.32%, bulk specific gravity 1.821 and water absorption 9.61%.For 3:1 abrasion value is 37.14%, impact value is 25.15%, bulk specific gravity 1.78 and water absorption 10.58%.For 3.5:1 abrasion value is 46.5%, imapct value is 32.87%, bulk specific gravity 1.648 and water absorption 12.83%. Casting cude using ratio 2.5:1, 28 day strength is 20.46 N/mm2.. This research project offers an eco-friendly solution for utilizing fly ash in the production of high-performance aggregates, contributing to sustainable construction practices. The implications of the findings include reduced environmental impact, enhanced resource efficiency, and the potential for resilient and environmentally conscious built environments. Further research and development in this area could lead to broader adoption of geopolymerized fly ash aggregates in the construction industry, paving the way for a more sustainable and Greener future.

Selective conversion of spent cracking catalyst to faujasite-structured zeolites

Current recycling strategies for spent catalyst in Fluid Catalytic Cracking (FCC) focus on valuable rare-earth elements (REE) and sometimes include a reuse of spent materials by down-cycling, which hinders a circular economy. Herein, a new procedure for the selective conversion of spent FCC catalysts to FAU-type zeolite without secondary crystalline phases such as sodalite, zeolite P or zeolite A is reported. The steps include a leaching process of REE, followed by thermal activation with sodium hydroxide and acid treatment to get an aluminum-rich feed. The synthesis of FAU-type zeolites with varying Si/Al ratios uses the aluminum-rich catalyst feed and commercial water glass. The experiments show that incorporation of silicate from water glass into the zeolite structure is limited to zeolite products with Si/Al ratio ≤ 2.0. It indicates a flocculation of silicates in higher concentration in competition to the crystallization process of FAU-type zeolites. This is reinforced by the resulting crystals, covered and surrounded with small particles with morphology of silica. Moreover, a clear differentiation between zeolite Y and zeolite X is possible from materials properties with the definite evidence of a mixed phase. The kinetics of feed dissolution and incorporation of impurities, alumina and silica are controlled by the pre-treatment temperature, duration and silicon source. This enables flexible adjustment of the aluminum re-use from spent FCC catalyst, the amount of foreign elements (Fe, Ni, V), phase purity, Si/Al ratio, specific surface area and thermal stability of the final zeolite product. Structural and textural data of the resulting zeolites reveals high crystallinity > 80 %, Si/Al ratios of 1.6–2.0, and specific surface areas up to 780 m2/g.

Variability of lead-zinc sulfide ore slurry rheological properties and its influence on flotation conditions

We investigated how the rheological characteristics of a flotation slurry change in response to variations in mineral species, slurry concentration, and particle size; slurry pH; and trap and rheological control reagent concentrations using slurries containing galena, sphalerite, quartz, and kaolinite. The results indicate that reducing particle size and increasing slurry concentration leads to varying degrees of increase in apparent viscosity and yield stress. At the same particle size, the slurry exhibits the following order of apparent viscosity and yield stress: kaolinite > galena > sphalerite > quartz. In addition, as the slurry’s apparent viscosity and yield stress increase, the rheology decreases, creating progressively unfavorable conditions for the flotation of lead, zinc, and other target minerals. Furthermore, changes in pH have no significant effect on the slurry’s rheology when the slurry is comprised of vein minerals. Moreover, galena and sphalerite depict particle agglomeration in the slurry. Ultimately, the addition of sodium silicate as a rheological control reagent substantially enhances the slurry’s rheological properties. This results in a system where problematic minerals like kaolinite are more effectively dispersed, thereby promoting efficient lead-zinc mineral flotation. Regarding the flotation of lead sulfide and zinc minerals, the addition of kaolinite raises the apparent viscosity of the mixed slurry, hindering the flotation of the target minerals. Conversely, quartz lowers the apparent viscosity aiding the flotation separation process. Understanding the relationship between flotation conditions and the pulp’s rheological properties can provide valuable guidance for subsequent flotation tests.

Experimental and thermodynamic investigating of carbonation behavior in Alkali-activated slag-calcined clay materials with different binder constituent

Alkali-activated materials (AAMs) have gained interest as sustainable alternatives to traditional Portland cement in recent years. However, concerns still exist regarding their durability against harsh environments such as carbonation. This study presents an experimental and thermodynamic investigation into the carbonation behavior of alkali-activated slag-calcined clay (AASCC) prepared with varying activator types (sodium hydroxide, sodium silicate, sodium carbonate), slag replacement levels with calcined clay (0 %, 10 %, 20 %), and alkali concentrations represented by the solid part of activator to base material ratio (SPA/B = 0.05, 0.075, 0.1). Furthermore, Portland cement mixtures were also prepared to compare the results with AASCC mixtures. Compressive strength, capillary water absorption, and accelerated carbonation testing were conducted on paste and concrete mixtures over 28–90 days. Thermodynamic modeling accurately predicted the experimental trends, demonstrating that this is a valuable tool for simulating complex processes in AAMs. Results illustrated that AASCC paste mixtures produced with sodium hydroxide demonstrated the best carbonation resistance due to higher pore solution pH (up to 13.74), sodium and alumino-substituted calcium silicate hydrate (CNASH) gels content, and layered double hydroxide phases (Mg-Al-LDH). Increasing alkali concentration further improved durability against the carbonation process by elevating pore solution pH and CNASH content. However, replacing slag with calcined clay reduced carbonation resistance regardless of activator type, attributed to lower pore solution pH, CNASH, and Mg-Al-LDH, although higher alkali concentrations alleviated this impact. In general, the study elucidates key chemical and physical factors regarding the carbonation of these novel materials by utilizing comparative experimental investigation and thermodynamic modeling.

Effects of different activators on autogenous shrinkage of alkali-activated slag cement

Despite the exceptional early strength of sodium silicate or sodium hydroxide-activated slags, much emphasis has always been drawn to the volume instability brought on by their autogenous shrinkage. In this study, a ternary composite activation system was developed by introducing sodium sulfate (Na2SO4), and the effect of Na2SO4-Na2O·1.5SiO2-NaOH ternary composite activators system on the autogenous shrinkage, setting time, and mechanical properties of alkali-activated slag (AAS) was investigated. The effect mechanism of different activator compositions on the autogenous shrinkage of AAS was discussed through the internal relative humidity (IRH), surface tension of pore solution, and microstructure analysis. According to experimental results, the surface tension of pore solution can be reduced and IRH increased by increasing Na2SO4 content in AAS. Additionally, the formation of crystals (anhydrite, ettringite, and thenardite) with specific expansion properties can effectively mitigate autogenous shrinkage in AAS with Na2SO4. The proportions of Na2O·1.5SiO2 and NaOH determine the extent to which Na2SO4 impact the autogenous shrinkage of AAS. An optimal composite activator composition for AAS was determined using a model analysis: When the content of Na2O·1.5SiO2 ranged from 5 % to 17 %, Na2SO4 content ranged from 40 % to 55 %, and NaOH content ranged from 33 % to 56 %, the AAS mortar exhibited a compressive strength exceeding 42.5 MPa at 28 days. Furthermore, the autogenous shrinkage strain of AAS paste remained below 1500 microstrain within 7 days, with an initial setting time surpassing 45 min and a final setting time under 390 min.

Degradation mechanism of cement–sodium silicate hardened grout bodies under ion erosion

Cement-sodium silicate (C-S) grout is extensively employed as a grouting material in shield tunnel synchronous grouting projects. However, in water-rich areas, its hardened grout bodies are vulnerable to erosion damage caused by various ions. In order to elucidate the degradation mechanism of C-S hardened grout bodies' strength under salt ion erosion. This study analyzed the influence of SO42- ions, Cl- ions, and SO42- and Cl- mixed ions at different concentrations on the compressive strength of C-S hardened grout bodies through laboratory experiments. Moreover, microscopic techniques (XRD, SEM-EDS) were employed to illustrate the phase characteristics and microstructure of ion-eroded C-S hardened grout bodies, and the distribution of surface calcium elements. Molecular dynamics (MD) simulation investigated the adsorption, diffusion degree, and energy change of erosive ions in C-S-H gel. The results show that the higher the concentration of erosion ions, the faster the erosion rate. A nonlinear spatiotemporal strength degradation prediction model was developed, assessing the deterioration degree of hardened grout bodies due to ions: SO42- > SO42-and Cl- mixture > Cl- > water. Additionally, microscopic observations reveal a tight correlation between the degradation level of C-S hardened grout bodies and the loss of Ca2+ ions inside. The more significant the loss of Ca2+ ions from hydration products, the more evident the strength degradation of C-S hardened grout bodies. MD simulations demonstrate that SO42- ions and Cl- ions occupy adsorption sites like SiOCa+ and SiOH, altering interatomic Coulomb forces and intermolecular van der Waals forces, changing system energy, thereby influencing the structure of C-S-H gel, leading to strength degradation in C-S hardened grout bodies.

Silver recovery into lead bullion from a lead concentrate by direct reduction with Na2CO3 and SiC reagents

ABSTRACT Silver has been recovered in lead bullion from a lead concentrate throughout a direct reduction process. The lead concentrate was obtained from a plant that processes polymetallic minerals located in the central mining area of Mexico. The direct reduction process has been tested through mixtures of Na2CO3 and SiC that were put in contact with the lead concentrate at 1000 °C for 60 min to produce lead bullion containing silver and slag. The produced lead bullion containing silver and the slag after direct reduction trials showed that it is possible to recover about 90% of lead and 86.5% of silver into the lead bullion, leading to a low silver content in the slag phase (<0.2 wt.%). The slag was constituted mainly by sodium silicate compounds such as Na2SiO3, Na4SiO4, and Na2Si2O5, when 50 wt. % of Na2CO3 and 10 wt. % of SiC regarding the initial charge of the lead concentrate was used. The proposed process has been assisted thermodynamically by the software FactSage 7.6, which allowed us to predict the main expected compounds and understand the process mechanism for silver recovery into a lead bullion using Na2CO3 and SiC reagents.

Advancing the Sustainability of Geopolymer Technology through the Development of Rice Husk Ash Based Solid Activators

Rice husk ash (RHA), an agricultural waste byproduct, has already been tested as a component in geopolymeric binders, typically as part of the precursor solid mix, alongside materials like fly ash (FA), slag, and cement. This study presents a novel approach where RHA is employed to create a solid activator, aimed at entirely replacing commercial sodium silicates. The synthesis process involves mixing RHA, NaOH (NH), and water by applying a SiO2/Na2O molar ratio equal to 1, followed by mild thermal treatment at 150 °C for 1 h, resulting in the production of a solid powder characterized by high Na2SiO3 content (60–76%). Additionally, microwave treatment (SiO2/Na2O = 1, 460 W for 5 min) increases the environmental and economical sustainability of alkali silicates production from RHA since this processing is 12 times faster than conventional thermal treatment reducing at the same time the final product’s embodied energy. The efficacy of this new material as a sole solid activator for the geopolymerization of Greek FA is investigated through various techniques (XRD, FTIR, SEM). One-part geopolymers prepared with RHA-based solid activators demonstrated mechanical performance comparable to those prepared with commercial products (~62 MPa at 7 days). This research contributes to the advancement of sustainable construction practices emphasizing the importance of local materials and reduced environmental impact in achieving long-term sustainability goals.