Geopolymer Synthesis Research Articles

Reuse of iron ore tailing to potassium silicate synthesis and to the production of geopolymers

This work involves reusing iron mining tailings to synthesize potassium silicate and further produce geopolymer, a sustainable substitute for Portland cement. The one-part geopolymer synthesis provided the best results of compressive strength.

Feasibility of geopolymer synthesis using soda ash in copper slag blended fly ash-based geopolymer

This study presents the strength development of geopolymer synthesized from class F-type fly ash blended with copper slag in 0–50 % variation using soda ash as the alkaline activator. Physical and chemical characterization of precursors was carried out with particle size analysis, X-ray diffraction, scanning electron microscopy and X-ray fluorescence analysis. The geopolymer paste mixtures were prepared with an activator to binder ratio of 0.32, liquid to solid ratio of 0.3, and cast in 50 mm cubes. The paste cubes were subjected to ambient and heat curing of 80 °C for 3 days and thereafter tested for compressive strength at 3, 7, and 28 days. The results showed varied performance within the sample mix types to curing condition. Ambient curing was most effective in geopolymer pastes with 100 % fly ash composition which developed early strength of 6.79 MPa at 3 days higher than other copper slag blended variations. While geopolymer pastes with 40 % slag mix developed significant strength with heat curing. Overall, the obtained optimum strength at the synthesis parameters with soda ash was 17 MPa.

Obtaining a Refractory Geopolymer Based on Clays and Seashells

AbstractThe synthesis of a refractory geopolymer with excellent thermal and mechanical properties to develop materials that resist temperatures above 1000 °C has become a challenge in recent years. The production of a refractory material involves the combination of clays and alkaline substances, whose formulation produces an improvement in the final properties of the refractory material. In this work, we report a Taguchi L18 design to synthesize a refractory geopolymer that exhibits the highest compressive strength, based on two natural clays from Mexico, seashells, sodium silicate and water. The prepared mixture was molded to form mini bricks, which were cured for 24 hours at room temperature. Subsequently, the bricks were dried for 4 days, and we evaluated the effect of temperature at 40 °C, 60 °C and 80 °C. Subsequently, the samples were subjected to calcination between 900 °C and 1200 °C to determine the resistance to both thermal and mechanical fracture via compression. The highest thermal resistance and compressive strength were obtained with a geopolymer formulated with 7.5 % seashells, 38.2 % Tepozán‐Bauwer clay, 30.0 % Kaolin clay, 20 % commercial sodium silicate and 4.3 % water, which was dried at 40 °C. The compressive strength was 7.28 MPa (74.2 kgf /cm2), and the thermal resistance was up to 1200 °C. In the FTIR analysis of the geopolymers calcined at 1200 °C, the influence of calcium was observed by the bands of the 800–1200 cm−1 region, where there was a greater distribution since the Si−O− bond was added. Ca was found at 950 cm−1. By adding CaCO3 in the form of seashells, the presence of the anorthite mineral phase (CaAl2Si2O8) can be identified, which originates from the degradation of calcium carbonate crystals (calcite, vaterite and aragonite) of the identified seashells using XRD. The synthesized geopolymer has potential use in the refractory and ceramic materials industry.

Use of glass waste in the production of metakaolin-based geopolymer submitted to room temperature and thermal curing

Abstract Metakaolinis the principal raw material utilized in the synthesis of geopolymers, although its ratio of silica and alumina contents is not ideal. Normally, the SiO2 content is adjusted with the use of silicates present in the activating solution. An eco-efficient alternative would be the use of glass waste as an additional source of silica.This work evaluates the efficiency of the alkaline activation of metakaolin, using potassium hydroxide and silicate, with and without the substitution of 12.5% of metakaolin by microparticles of glass. The efficiency of the alkaline activation was evaluated by X ray diffractometry, spectroscopy in the infrared region with the Fourier transform, nuclear magnetic resonance spectroscopy of 27Al and 29Si, specific mass and compressive strength. The results indicate the occurrence of geopolymerization with and without the use of glass waste. It was observed that the substitution of 12.5% favors the mechanical performance of the compounds at 28 days, with increases by 37% and 47% in the mechanical strength of the material with thermal curing and ambient temperature curing, respectively.

Effect of the use of waste glass (as precursor, and alkali activator) in the manufacture of geopolymer rendering mortars and architectural tiles

The environmental impact of construction demolition wastes (CDW) is high since it represents between 45 and 65 % of the solid wastes that reach landfills. These wastes can be concrete, bricks, ceramic, wood, glass, plastic, metals, and others. Specifically, the glass wastes are considered 100 % recyclable, nevertheless, in the United States it is estimated that the recycling rate is only 33.1 %, compared to the European average of 42.6 %. In this research, the use of waste glass in the synthesis of geopolymers from different precursors such as brick wastes (BW), ceramic tiles wastes (CW) and metakaolin (MK) was evaluated. Glass wastes were studied as: (i) precursor, (ii) alkaline activator and (iii) fine aggregate (FG). The results showed that, in the pastes, the best strength is reached when they are made with SS alkali activator, reaching compressive strength above 25 MPa; in pastes with 50 wt% glass as precursor reaches strength up to 15 MPa, but when using 100 wt% glass as solid activator the strength does not exceed 1 MPa. Calorimetry results showed that the use of glass (at 25 °C) does not release enough heat. The formation of hybrid reaction gels (N,CASH) were identified in the CW-SS activated pastes. However, in the mortars made with G and FG, an improvement in strength was found compared to their respective pastes, which is attributed to the fact that the microns G particles that did not react with the alkaline activation can act as fillers, allowing them to support higher loads. Finally, mortars with strengths of ∼10–15 MPa were successfully applied as render mortar and in the elaboration of architectonic tiles.

Geopolymer from tin mining tailings waste using Salacca leaves ash as activator for dyes and peat water adsorption

This research investigated preparation of geopolymer as adsorbent for dye-containing and peat water treatment. The green synthesis of geopolymer utilized tin mine tailings waste as source and Salacca leaves ash as activator. For the detail of study, effect of Salacca leaves ash amount to the physicochemical characteristics of the geopolymer was studied in comparison with the use of NaOH as common activator. Instrumental characterizations by using XRD, gas sorption analysis, SEM, and TEM analyses were employed. From the study, it is found that the Salaca leaves ash exhibits the capability to be activator in geopolymerization as identified by increasing specific surface area along with the surface morphologies appeared from SEM and TEM analysis as well as the structural analysis by XRD measurement. The geopolymers showed the capability to adsorb methylene blue and methyl orange in high capacity, and obey pseudo-second order kinetics. The maximum adsorption capacities for methylene blue and methyl orange are 30.31 mg/g and 3.06 mg/g by geopolymer synthesized with TW: TEOS: SLA: H2O of 5: 2: 1: 5. The Freundlich isotherm model was the most appropriate for both dyes. In addition, the geopolymer also shows capability to enhance peat water quality as shown by the removal of chemical oxygen demand and with COD and NOM removal of 100 and 92% by 90 min of batch adsorption system. The continuous adsorption system by all geopolymer samples to the COD of the peat water is in good agreement with Thomas model (R2 =0.99).

Synergistic gel formation in geopolymers of superior mechanical strength synthesized with volcanic ash and slag.

The present work studies gel evolution and microstructure of geopolymers synthesized with volcanic ash (VA) and blast furnace slag (BFS). The synthesis parameters such as BFS proportions on geopolymer formation were investigated. Gel evolution and microstructure of the geopolymers were studied by FTIR, X-ray diffraction (XRD), 29Si NMR spectroscopy and scanning electron microscopy measurements. Silicate gels (N-S-H) were mainly formed in VA-based geopolymers of low compressive strength (14.07MPa). While with VA and BFS each account for 50%, VA-BFS-based geopolymers possessed a compressive strength of 55.6MPa, as well as the homogeneous C-(A)-S-H and N-A-S-H gels were formed. The C-(A)-S-H and N-A-S-H gels show synergistic effects on the mechanical property of the geopolymers. This work provides a clue for the synthesis of geopolymers with superior mechanical properties in areas of architecture. Detailed characterization gel evolution and microstructure of geopolymers synthesized with volcanic ash (VA) and blast furnace slag (BFS) were studied. Silicate gels (N-S-H) were mainly formed in VA-based geopolymers of low compressive strength (14.07MPa). When VA and BFS each account for 50%, VA-BFS-based geopolymers possessed a compressive strength of 55.6MPa, as well as the homogeneous C-(A)-S-H and N-A-S-H gels formed. Synthesis protocol for VA-BFS-based geopolymers.

Influence of Mixing Order on the Synthesis of Geopolymer Concrete.

Geopolymers are high-performance, cost-effective materials made from industrial waste that ideally fit the needs of 3D printing technology used in construction. The novelty of the present work lies in the investigation of methods to mix geopolymer concrete from fly ash (FA) class F, ground granulated blast furnace slag (GGBS), and raw calcined kaolin clay (RCKC) to determine the mixing procedure which provides the best mechanical strength and structural integrity. The experimental results show that aluminosilicates with different reaction parameters when mixed one after another provide the optimal results while the geopolymer concrete possesses the highest compressive strength and the denser structure. The results demonstrated that the reactivity of GGBS, FA, and RCKC increased for different depolymerization speeds of the selected aluminosilicates. This research will provide results on how to improve the mixing order for geopolymer synthesis for 3D printing demands. The highest compressive strength and denser structure of geopolymer concrete is achieved when each type of aluminosilicate is mixed with an alkaline medium separately.

Synthesis of Geopolymer from a Novel Aluminosilicate-Based Natural Soil Precursor Using Electric Oven Curing for Improved Mechanical Strength.

Natural soil (NS)-based geopolymers (GPs) have shown promise as environmentally friendly construction materials. The production of ordinary Portland cement is known to release significant amounts of greenhouse gas (CO2) into the atmosphere. The main objective of this work is to synthesize a geopolymer (GP) from an uncommon aluminosilicate-based NS and a sodium silicate (SS) activating solution that would not only minimize the emission of harmful gases, but also offer improved mechanical strength. Samples of different compositions were produced by varying the wt.% of NS from 50% to 80% and adding a balancing amount of SS solution. The drying and curing of the samples were carried out in an electric oven at specific temperatures. The degree of geopolymerization in the samples was measured by Fourier transform infrared spectroscopy, and microstructural analysis was performed using a scanning electron microscope. Mechanical tests were conducted to evaluate the range of compressive strength values of the prepared GP samples. A minimum compressive strength of 10.93 MPa at a maximum porosity of 37.56% was observed in a sample with an NS to SS ratio of 1:1; while a ratio of 3:1 led to the maximum compressive strength of 26.39 MPa and the minimum porosity of 24.60%. The maximum strength (26.39 MPa) was found to be more than the reported strength values for similar systems. Moreover, an improvement in strength by a factor of three has been observed relative to previously developed NS-based GPs. It may be inferred from the findings that for the given NS, with almost 90% aluminosilicate content, the extent of geopolymerization increases significantly with its increasing proportions, yielding better mechanical strength.

Research on diatomite from Polish deposits and the possibilities of its use

Diatomite from a deposit in Jawornik Ruski (Poland) has been selected as the material for study. The paper aimeds to show the possibility of using diatomite from the Carpathian Foothills as a sorbent of petroleum substances.Diatomite in the delivery condition (DC) and diatomite after calcination were used for this study. The material was calcined at 600, 650, 750, 850 and 1000°C. The diatomaceous earth was then granulated. The morphology of diatomite was observed using SEM. Particle size distribution was determined by Laser Particle Analyzer, chemical composition was determined by XRF, and mineralogical composition by XRD. Specific surface area, pore volume and pore size were determined. Thermal analysis (TG, DTA) was carried out. Absorption capacity tests were performed and the effect of diatomite addition on water absorption of concrete samples was determined.Within the framework of the study, it was shown that diatomite from the Jawornik deposit could be successfully used as a sorbent for petroleum substances. The absorption capacity of calcined at 1000°C diatomaceous earth was 77%. The obtained result exceeds the effectiveness of previously used absorbents, for which the sorption level is 60-70%. This allows commercial use of diatomite from deposits in Poland. In addition, water absorption tests have shown that diatomaceous earth can successfully replace cement used in concrete productione. The most favourablee effect on the reduction of water absorption is the addition of diatomite in the amount of 10%.The properties of diatomaceous earth from the Jawornik Ruski deposit indicate its high potential for use in the synthesis of geopolymers, which is important not only from an economic but also from an ecological point of view.The novelty of this work is the demonstration of the possibility of using diatomite as a sorbent of petroleum substances with high efficiency, exceeding the previously used sorbents.

Effect of Magnesite Addition and Mechanical Activation on the Synthesis of Fly Ash-Based Geopolymers

Ca/Mg carbonate minerals, such as calcite and dolomite, play an increasingly important role in the development of alkali-activated binders or geopolymers, which are regarded as promising sustainable cement materials. In contrast to studies on calcite and dolomite, the effect on geopolymer properties of the addition of natural magnesite (magnesium carbonate) to aluminosilicate raw materials has not been investigated. The aim of this study is to investigate the influence of mechanical activation (MA) and natural magnesite addition to fly ash (FA) on the compressive strength of geopolymers based on the natural magnesite–FA blend. Magnesite substitutes FA in amounts of up to 20 wt.%. Geopolymers were prepared using NaOH solution as an alkaline agent. XRD, FT-IR spectroscopy, thermogravimetry, SEM, and a dissolution test are used to investigate the geopolymerization process. The major reaction product was sodium-containing aluminosilicate hydrogel. Magnesite is found to transform, to a minor degree, to hydrotalcite. MA of the blend significantly improves geopolymer strength. For geopolymers based on (FA + magnesite) blends mechanically activated for 180 s, the strength is on average 8.0 ± 1.5, 3.0 ± 0.9, 1.5 ± 0.2, and 1.7 ± 0.5 times higher than that for the geopolymers based on the blends mechanically activated for 30 s at the age of 7, 28, 180, and 360 d, respectively. Although blending FA with magnesite does not increase geopolymer strength, for the mixtures containing 1%–10% magnesite, in general, the strength is either not reduced or it is reduced to a small degree compared to the geopolymers based on 100% FA. Using previously obtained data, for the first time, the effect of the addition of three Ca/Mg carbonate minerals to FA and MA on geopolymer performance is compared. Under similar conditions, geopolymer strength decreases in the order calcite > dolomite > magnesite. The main factors affecting the strength of geopolymers based on the mechanically activated blends of FA with magnesite including filler, dilution, and chemical effects are discussed.

Influence of GGBFS and silica fume on characteristics of alkali-activated Metakaolin-based concrete

Alkali-activated or geopolymer composites have been introduced as a promising green alternative to ordinary Portland cement concretes and mortars. Metakaolin (MK) is a common source material produced from the calcination of kaolin, which has been widely employed for geopolymer synthesis. The present study involves testing thirteen alkali-activated concrete mixes divided into two groups to investigate their fresh and mechanical properties. The two groups attempted to study the effect of partial replacement of MK by ground granulated blast furnace slag (GGBFS) and silica fume (SF) (ranging from 5% to 30% by MK weight). The effect of the water-to-solids ratio for MK-GGBFS and MK-SF concretes was also studied. The investigated fresh and mechanical properties were slump, density, compressive strength, compressive strength rate of development, splitting tensile strength, water absorption, abrasion resistance, and ultrasonic pulse velocity. The partial replacement of MK by GGBFS of up to 10% caused about 10% reduction in the compressive strength of geopolymer but enhanced early strength development. The conclusions derived from the study are supported by XRD analysis and SEM images. Models are proposed for estimating the mechanical properties of geopolymer concrete as a function of either the molar ratios and the aggregate content or compressive strength.

Optimization of coal fly ash-based porous geopolymer synthesis and application for zinc removal from water

Coal fly ash-based porous geopolymer (CFAPG) is a potential adsorbent for heavy metal-contaminated water remediation and can also mitigate the accumulation of coal fly ash from thermal power plants. Production parameters influence the physicochemical properties (e.g., adsorption capacity) of CFAPG. Ten potential factors involved in the CFAPG production process were examined using a Plackett-Burman design (PBD) and then an orthogonal experimental design (OED). The results show the alkali activator modulus (MS), alkali-ash mass ratio (AA), foaming agent-ash mass ratio (FAR), and sodium dodecyl sulfate-ash mass ratio (SDSA) were the most important factors influencing the Zn adsorption capacity of CFAPG. Ternary plots confirm the interaction between these four factors, with the role of FAR being easily masked by other factors and MS being the least influenced by other factors. Furthermore, Zn adsorption on the CFAPG created with optimal parameters was best described by the Bi_Langmuir model, indicating two different sorption site classes on the surface of CFAPG with a total maximum Zn adsorption capacity of 13.42 mg g−1. These results provide key parameters for the production of geopolymers as heavy metal adsorbents.

Synthesis and optimization of green one-part geopolymer from mine tailings and slag: Calcium carbide residue and soda residue as supplementary alkali sources

• Activated tailings acted as an alkaline activator for the one-part geopolymer production. • Waste treatment by waste: Calcium carbide residue was used as a supplementary alkali source. • Waste calcium carbide residue prompted the hydration reaction and increased the sample strength. • This study provides promising guidance for the rational and cost-effective utilization of tailings. The use of mine tailings (MTs) as the precursor for producing geopolymers is an effective way to reduce their storage and mitigate their negative effects on the environment. MTs were firstly activated through hydrothermal pretreatment in the presence of NaOH at 200 °C. Then one-part geopolymer (OPG) samples were synthesized from activated MTs and slag, and calcium carbide residue (CCR) and soda residue (SR), the solid industry wastes, were added as supplementary alkali sources to improve the strength of OPG samples. The effects of alkali sources on the setting time, fluidity, compressive strength, pH, hydration kinetics, hydration products, and microstructure of OPG samples were investigated. Both alkali sources shortened the setting time, decreased the fluidity, and increased the strength of OPG samples, and the CCR showed a more significant effect on these properties than SR. These clear differences in sample performances were associated with the pronounced mineralogical differences between SR and CCR. Compared to SR, CCR rich in Ca(OH) 2 produced a higher pH of the pore solution, which significantly promoted the slag dissolution, shortened the induction period, and accelerated the hydration process. Calcium–sodium aluminosilicate hydrate (C(N)-A S H) gel was the dominant reactant in all samples that enhanced the strength of OPG samples. More geopolymer gel was generated in CCR-doped samples and thus a much higher strength than SR-doped samples. However, the incorporation of excessive alkali sources induced the high carbonization degree of samples, and it was likely responsible for the reduction in strength.

RETRACTED: A review of the sustainable utilisation of red mud and fly ash for the production of geopolymer composites

• This study progresses a state-of-the-art review of red mud and fly ash for the production of geopolymer composites. • The physical and chemical properties of RM-FAGPC is reviewed. • The fresh and hardened properties of RM-FAGPC is discussed. • The durability and microstructure properties of UHP-GPC is reviewed. • Recommendations and observations are advanced for future research. Cement manufacturing emits a lot of CO 2 , which adds to negative environmental effects, including global warming and climate change. These phenomena have reignited interest in using a range of industrial waste products to make geopolymer composites and alkali activated binders, with the goal of reducing the use of regular Portland cement in building construction. One of these toxic radioactive waste substances is red mud (RM), which is produced as a byproduct of Bayer's aluminium (Al) production process. The objective of this study is to undertake a state-of-the-art review of the literature on the usage of red mud and fly ash (FA) in the production of red mud-fly ash geopolymer composites (RM-FAGPC). The environmental and economic implications, physical and chemical characteristics, manufacturing, distribution, categorization, and prospective uses of red mud are all discussed. Furthermore, current advances in the use of red mud and FA for geopolymer synthesis in terms of physical, mechanical, durability, and microstructure characteristics are highlighted. Furthermore, this research aims to design a path toward a realistic valorisation that considers both actual and perceived problems, including leaching, radioactivity, and the life cycle evaluation of red mud geopolymer composites (RM-GPC). The potential usage of RM-FAGPC manufacturing highlights the need for more research into the combination and proportion of these two raw materials with other cement-based materials, which might lead to novel, cost-effective, and energy-saving construction processes and products. It is also suggested that investigative efforts be focused on ecological, economic, and life cycle analyses.

Synthesis and Characterization of Fly Ash-Based Geopolymers Activated with Spent Caustic.

The spent caustic with strong alkali first replaced the alkali activator to prepare the geopolymer. The influence of spent caustic to the geopolymer was characterized through compressive strength measurement, XRD, MIP analysis and NMR, and the immobilization efficiency of organic in geopolymer was evaluated through the measurement of total organic carbon (TOC). The results show that the spent caustic can partially replace the alkali activator to prepare the geopolymer, and it shows a better performance than that which was activated with pure NaOH solution when the alkalinity is between 4 mol and 14 mol. The organic matter in the spent alkali can be effectively fixed in the geopolymer, which will hinder the geopolymerization in the initial stage of the polymerization reaction but has little effect on the chemical structure and mechanical properties of the final product. With the degree of alkalinity increasing, the immobilization efficiency is improved, and the maximum can reach 84.5%. The organics in the spent caustic will hinder geopolymerization at the initial stage but has little effect on the chemical structure and mechanical property of the final product. This study proposes a new method for the recycling of spent caustic, which also reduces the preparation cost of geopolymers.

Mix design formulation range for metakaolin-based geopolymer synthesis

This article presents a range of mix design formulations to obtain metakaolin-based geopolymer synthesis. Geopolymer samples were synthesized from metakaolin, a 10 M sodium hydroxide solution, and alkaline sodium silicate. These three components were mixed in different proportions to form a paste which was molded in a cylindrical shape, set at room temperature for 24 hours, and demolded. The workability of the paste, the integrity of the samples, development of efflorescence, and the presence of undissolved metakaolin particles in the microstructure of the geopolymer matrix were observed. Since sodium and water play a vital role in the geopolymerization and were added at fixed proportions, a mix design was employed based on the molar proportions of aluminum, silicon, and sodium plus water. The simplex design plot was able to separate the regions of a mix of the components that showed different behaviors according to the observed responses. The dissolution of metakaolin, condensation of ortho-sialate and silicate species, which are expected to interact with each other according to the model of geopolymerization of Davidovits, can explain the observed results. “Good results” (no release of white powder, no efflorescence, no shrinkage, and no cracks) after 28 days of curing at room conditions were observed for the molar proportions 0.097 < Al < 0.112, 0.120 < Si < 0.178, and 0.711 < Na+H2O < 0.775 (Na/H2O = 0.185).

Metakaolin/sludge based geopolymer adsorbent on high removal efficiency of Cu2+

Activated carbon (AC) has received a lot of interest from researchers for the removal of heavy metals from wastewater due to its abundant porous structure. However, it was found unable to meet the required adsorption capacity due to its amorphous structure which restricts the fundamental studies and structural optimization for improved removal performance. In addition, AC is not applicable in large scale wastewater treatment due its expensive synthesis and difficulty in regeneration. Thus, the researchers are paying more attention in synthesis of low cost geopolymer based adsorbent for heavy metal removal due its excellent immobilization effect. However, limited studies have focused on the synthesis of geopolymer based adsorbent for heavy metal adsorption by utilizing industrial sludge. Thus, the aim of this research was to develop metakaolin (MK) based geopolymer adsorbent with incorporation of two types of industrial sludge (S1 and S3) that could be employed as an adsorbent for removing copper (Cu2+) from aqueous solution through the adsorption process. The effects of varied solid to liquid ratio (S/L) on the synthesis of metakaolin/sludge based geopolymer adsorbent and the removal efficiency of Cu2+ by the synthesis adsorbent were studied. The raw materials and synthesized geopolymer were characterized by using x-ray fluorescence (XRF), x-ray diffraction (XRD), scanning electron microscope (SEM), fourier transform infrared spectroscopy (FTIR), Brunauer-Emmett-Teller (BET) and micro XRF. The concentration of Cu2+ before and after adsorption was determined by atomic absorption spectroscopy (AAS) and the removal efficiency was calculated. The experimental data indicated that the synthesized geopolymer at low S/L ratio has achieved the highest removal efficiency of Cu2+ about 99.62 % and 99.37 % at 25 %:75 % of MK/S1 and 25 %:75 % of MK/S3 respectively compared to pure MK based geopolymer with 98.56 %. The best S/L ratio for MK/S1 and MK/S3 is 0.6 at which the reaction between the alkaline activator and the aluminosilicate materials has improved and enhanced the geopolymerization process. Finally, this work clearly indicated that industrial sludge can be utilized in developing low-cost adsorbent with high removal efficiency.

Development of the geopolymer-based zeolite from powdery silica fume and its application in methanol to dimethyl ether

A large number of non-biodegradable powdery silica fume waste produced in industry increase the severity of environmental problems due to their potential harmfulness. The synthesis of geopolymers or zeolitic materials using powdery silica fume as silicon source has become an attractive sustainable solution to remedy this crisis. In this paper, a cost-effective porous ferrierite was synthesized by a facile hydrothermal strategy using silica fume-based geopolymer as precursor and applied to methyl dimethyl ether reaction (MTD). The specific surface area of geopolymer increased from 30.5 to 258.4 m2/g of ferrierite, and the methanol conversion rate correspondingly improved from 16.04 % to 78.5 %. Moreover, rare earth (RE) metal ions were introduced to optimize the performance, and the maximum conversions of RE-modified ferrierite were higher than 90 %. The superior catalytic performance of RE-modified ferrierite was related to the synergy of abundant porosity, acidic active sites and metal functions, which could be realized by regulating the crystallization degrees and ion exchange concentrations. Moreover, the abundant active amorphous silica in silica fume is conducive to the preparation of eco-friendly geopolymers and the further development of zeolite materials, realizing the high value-added utilization of solid wastes.

Physico-mechanical and durability properties of new eco-material based on blast furnace slag activated by Moroccan diatomite gel.

Natural diatomite, an amorphous siliceous rock, was used as a source of silica for the synthesis of a silicate gel to replace commercial sodium silicate gel in the synthesis of geopolymers from blast furnace slag at room temperature. Nine diatomite gels were synthesized by varying the diatomite content in the gel by 0, 10, and 15% and the NaOH molarity by 6M, 8M, and 10M. The chemico-mineralogical and microstructural characterization results of the elaborated geopolymers showed that the blast furnace slag activation by diatomite gel under optimal conditions (8M NaOH molarity and 10% diatomite) leads to a good dissolution and polycondensation of the precursor by forming amorphous gels of C-A-S-H type, as well as the mineral phase hydrotalcite, which are the same geopolymerization products detected in the case of the use of conventional silicate gel, and consequently, the obtaining of a geopolymer with interesting physical-mechanical characteristics: compressive strength of 42MPa, density of 1. 61g/cm3, ultrasonic pulse velocity of 3855m/s. Thus, this new approach used in this work proved to be successful in reducing the cost and environmental impact of geopolymers.