Geopolymer Structure Research Articles

Curing process and pore structure of metakaolin-based geopolymers: Liquid-state 1H NMR investigation

Geopolymers are emerging construction materials with lower carbon dioxide emissions compared to the conventional cementitious materials. The knowledge of the curing process and the related pore structures are important for optimizing the properties of these materials for different applications. The curing process and final pore structure are sensitive to the amount of used water, however the specifics are unclear. The curing process and pore structures of metakaolin-based geopolymers with a narrow water-to-solid (w/s) ratio (0.59–0.66) were monitored by nuclear magnetic resonance (NMR) relaxometry and cryoporometry. The 14-day curing process was investigated by monitoring the change of T2 and T1 relaxation times and water signal intensity. After the curing, the pore structures were characterized by 2D T1-T2 correlation and T2-T2 exchange measurements of absorbed water. The pore size distributions (PSDs) were measured with NMR cryoporometry and compared to nitrogen physisorption and mercury intrusion porosimetry (MIP) results. We found that the relaxation times decreased as the pore structure of the geopolymers matured during the curing while the dissolution and the condensation periods of the curing were distinguished by the changes in signal amplitude reflecting the proton density. After the curing, three distinct pore sizes and connectivity between pores were identified from T1-T2 and T2-T2 spectra. Their PSDs were measured, and they were found to correspond to two different pore sizes originating from the arrangement of clusters and defective pores. In the narrow w/s ratio (0.59–0.66), the curing times were the same for all samples when cured at 24 °C while the pore sizes were observed to increase as a function of the w/s ratio.

Mechanochemically activated bottom ash-fly ash geopolymer

A source of sub-bituminous coal bottom ash was mechanochemically activated by co-grinding fly ash and a sodium silicate powder for use in a geopolymer application. A total of nine different mixes were considered to study the effects of the mechanochemical treatment, mixing procedure, and bottom ash loading. The compressive strength, reactivity, rate of geo-polymerization and morphology were investigated using isothermal calorimetry, nano-indentation, optical and scanning electron microscopy, and Fourier-transform infrared spectroscopy. The solid-state mechanochemical activation attacks the fly and bottom ash particles producing small sheet-like activated agglomerates. The activation enhances the dispersion of the activated particle, alters the sodium silicate and aluminosilicate reaction kinetics and intensifies the interconnectivity of geopolymer structure, decreases pore size, and significantly increases compressive strength (between 60% and 80%). When treated in this manner, the bottom ash serves as an effective extender to fly ash in geopolymer systems up to 50% replacement of fly ash without significant reduction in mechanical strength or significant alteration to the microstructure.

Phosphoric acid based geopolymerization: Effect of the mechanochemical and the thermal activation of the kaolin

The purpose of this work was to study the effect of the mechanical activation of kaolin on the mechanical properties, the microstructure and the structure of the phosphate-based geopolymers and to compare these properties to those of the same materials but obtained from the thermally treated kaolin. Several experimental techniques, such as powder X-ray diffraction (XRD), 27Al, 29Si and 31P Magic angle spinning nuclear magnetic resonance (MAS-NMR), infrared spectroscopy (FTIR), scanning electron microscopy (SEM), as well as the determination of the specific surface and the particle size distribution were adopted to characterize the raw materials and then the obtained geopolymeric materials. The Brazilian tests were used to measure the materials mechanical resistance.The main findings of this work were that the two types of treatment allowed to obtain reactive kaolin for the synthesis of phosphate-based geopolymers. However, some fundamental structural differences were observed between the mechanically activated and the thermally activated kaolins. Indeed, the mechanically activated kaolin (MA) seemed to be more reactive than the thermally activated Kaolin (TA). Hence, the kinetic of the geopolymerization reaction would be more accelerated in the mechanically activated kaolin (MA) and phosphoric acid mixture. Consequently, the obtained phosphate-based geopolymer (GMA) would be denser and of better mechanical properties than those based on thermally activated kaolin (GTA) regardless of the curing time.

Effect of Si/Al molar ratio on the immobilization of selenium and arsenic oxyanions in geopolymer.

The effect of Si/Al molar ratio of geopolymer on the immobilization of Se and As oxyanions was studied through leaching test and solid characterizations including XRD, FTIR, TG, NMR, XAFS, and N2 adsorption-desorption isotherm. As a whole, the leaching percentages of Se and As oxyanions increased with the increase of the Si/Al molar ratio of geopolymer. Linear combination fitting confirmed that most of selenite, selenate and arsenate ions existed in geopolymers through electrostatic interaction. Thus, Al tetrahedrons in geopolymer structure control the charge stability for these oxyanions to a large extent. Differently, as for arsenate ions, they were recrystallized into an arsenate compound (Na3.25(OH)0.25(H2O)12)(AsO4) in geopolymers. The additive of these pollutants has an adverse effect on the compactness of geopolymer, then influencing the leaching performance in turn. However, the changes in leaching results did not follow the variation trend of specific surface areas and pore volumes of geopolymers with different Si/Al ratios. The number and distribution of Al tetrahedron and compactness of geopolymer have a synergistic effect on the immobilization of these oxyanions. Besides, the compressive strengths of geopolymer samples are always higher than 20MPa, which meets the requirement of safe disposal of hazardous waste.

Effect of high temperatures on mechanical, radiation attenuation and microstructure properties of heavyweight geopolymer concrete

Heavyweight geopolymer concrete (HWGC) is a new concrete type that combines the benefits of geopolymer concrete (GC) and heavyweight concrete. HWGC can be used to produce particular properties such as high radiation shielding, and mass concrete elements. HWGC based on fly ash and ground granulated blast furnace slag, using electric arc furnace steel slag (EAFSS), barite and ilmenite coarse aggregates can substantially have higher specific gravities than concrete made with crushed dolomite. In the experimental work carried out on four main groups, 13 GC mixes are prepared by using heavyweight coarse aggregates (HWCAs) at volume ratios of 0%, 25%, 50%, 75% and 100%. Fresh and mechanical properties, compressive and tensile strengths, and influence of high temperature on radiation are investigated for specimens subjected to high temperatures of up to 900oC for 1, 2 and 3 hours. Moreover, the internal structure of geopolymer is analyzed using scanning electron microscope and energy-dispersive X-ray. Results show a good effect of HWCAs on the properties, radiation shielding and unit weight. The density of heavyweight geopolymer mixes ranges between 2,415 and 3,480 kg/m3, and HWCA ratios contribute to an increase in all properties of GC mixtures using up to 75% of NWCAs. Heavier coarse aggregate of ilmenite dampens the effect of higher temperatures on GC strength compared with lighter aggregates. In addition, replacing crushed dolomite with heavyweight aggregates of EAFSS, barite and ilmenite increases the attenuation rate to 27%, 21% and 13%, respectively. This finding confirms that the type of aggregate used in the production of GC is important for reducing the permeability of X-ray.

Rietveld analysis of geopolymer prepared from amorphous rice husk silica with different thermal treatment

The work aims to study the temperature effect on the geopolymer’s crystal structure prepared from amorphous silica rice husk. The samples were prepared via the sol-gel method and then subjected to thermal at a temperature of 250-650 °C. EDS identified the element and compound composition on the surface of the sample. The crystal structure of samples identified by Rietveld refinement of XRD. The sample was dominated by the gibbsite phase at relatively low temperatures (250 °C). The boehmite phase dominates at a temperature of 350-450 °C. The amorphous structure of the geopolymer was formed at a temperature of 550-650 °C. The geopolymer mainly formed from the reaction of boehmite and silica. This study shows a significant effect of temperature on the formation of the geopolymer structure.

Comparative Study Between Geopolymer and Cement Waste Forms for Solidification of Corrosive Sludge

Two waste forms, namely cement and geopolymer, were investigated and tested in this study to solidify the corrosive sludge generated from the surface and precipitates of the tubes of steam generators in nuclear power plants. The compressive strength of the cement waste form cured for 28 days was inversely proportional to waste loading (24.4 MPa for 0wt% to 2.7 MPa for 60wt%). The corrosive sludge absorbed the free water in the hydration reaction to decrease the cementation reaction. When the corrosive sludge waste loading increased to 60wt%, the cement waste form showed decreased compressive strength (2.7 MPa), which did not satisfy the acceptance criteria of the repository (3.45 MPa). Meanwhile, the compressive strength of the geopolymer waste form cured for 7 days was proportional to waste loading (23.6 MPa for 0wt% to 31.9 MPa for 40wt%). The corrosive sludge absorbed the free water in the geopolymer when the water content decreased, such that a compact geopolymer structure could be obtained. Consequently, the geopolymer waste forms generally showed higher compressive strengths than cement waste forms.

Optimization of synthesis of geopolymer adsorbent for the effective removal of anionic surfactant from aqueous solution

This paper describes the optimization of synthesis of fly ash based geopolymer (FAGP) for removing the anionic surfactant sodium dodecylbenzene sulfonate (SDBS) using response surface methodology (RSM) by varying the synthesis parameters of silica to alumina (Si/Al), sodium to alumina (Na/Al) and water to solid (W/S) ratios with the adsorption capacity as the response. The geopolymer samples were designed, synthesized, characterized, used for removing SDBS surfactant, and regenerated. Surface area and pore size analysis, Fourier Transform Infrared Spectroscopy (FTIR) analysis, phase analysis, and microstructural analysis confirmed the synthesis of mesoporous and amorphous geopolymers with the presence of pores, cavities and rods in the geopolymer structure. Geopolymer sample synthesized with the composition of Si/Al-2.87, Na/Al-1.0 and W/S-0.35 (FAGP-2) achieved maximum surface area of 59.512 m2/g and displayed the highest adsorption capacity of 743.706 mg/g and removal efficiency of 84.5%. The ANOVA analysis showed a correlation coefficient (R2) of 0.952, F-value of 22.27, and p value of 0.05 which indicated the significance of the model and lack of fit was non-significant which showed good fitting of the experimental data to the quadratic model with 95% confidence level. The proposed geopolymer composition of Si/Al-2.353, Na/Al-1.056, and W/S-0.339 achieved adsorption capacity of 730.212 mg/g which is 99% similar to the predicted adsorption capacity. Thermal method successfully regenerated SDBS adsorbed geopolymer with only 13.8% loss of adsorption capacity after five cycles of regeneration. The adsorption capacity of optimized geopolymer is higher than other adsorbents such as cross-linked chitosan films, commercial activated carbon, surface functionalized mesoporous silica nanoparticles, multi-walled carbon nanotubes (MWCNTs), and others used for removing SDBS surfactant and only amino crosslinked chitosan microspheres (ACCMs) has higher adsorption capacity than geopolymer. This shows that geopolymer can also be effectively used to adsorb SDBS surfactant from wastewater.

Optimization of SiO2/Al2O3 Ratio in the Preparation of Geopolymer from High Calcium Fly Ash

High-calcium fly ash-based geopolymers have been successfully synthesized. The source of fly ash used in this study is fly ash from PT. IPMOMI, PT. Holcim and Paiton PLTU 9. The variation in the mole ratio of SiO2/Al2O3 carried out in this study was 3,0; 3,3; 3,6; 3,9 and 4,2. Compressive strength tests were carried out on geopolymers aged 7, 14, and 28 days. A geopolymer with a ratio of 3,6 has the best compressive strength. The compressive strength test results for IPMOMI, Holcim, and Paiton 9 geopolymers were 75,37; 50,95; and 39,25 MPa. The highest geopolymers with compressive strength were characterized using XRD and SEM. The results of the XRD showed that geopolymers had an amorphous phase and gibbsite mineral in the three geopolymers which indicated that there was still Al(OH)3 which had not reacted. Microstructure analysis using SEM shows the all of three solid structure of geopolymers. There is efflorescence on Holcim and Paiton 9 geopolymers which causes lower compressive strength than IPMOMI geopolymers.

Study on optical phonon vibration and gamma ray shielding properties of composite geopolymer fly ash-metal

Absorption properties of geopolymer from fly ash (FA) as a matrix, graphite and nickel or graphite and iron powder as a filler have been carried out by applying Cs-137 gamma ray source. Composite geopolymer was produced by the activating an alkaline solution and heated at 70 °C for 1 h. The optical phonon vibration determined from the quantitative analysis of Fourier transform infra-red (FTIR) spectra by using Krames Kronig (KK) relations. The difference between two optical phonon mode (LO-TO), longitudinal optical (LO) and transversal optical (TO) provided information of the stability bonding formation structure of composite geopolymer, for A-2 (graphite and nickel as a filler) shows the difference is 192 cm−1 and for A-3 (graphite and iron as a filler) shows the difference is 222 cm−1. The higher differences of optical phonon vibration mode is more stable bonding connection in composite compared with the lower differences. The TO mode was confirmed by the main peak position of imaginary dielectric function (ε2). The higher wavelength peak position of the LO for A-3 which confirmed by the energy loss function (ELF) (Im (−1/ε) compared with the A-2 due to the large of atomic radius of Fe (1.56 Å) compared with Ni (1.49 Å). The plasma frequency identified from the ELF is 1600 cm1 for A-2 and 1757 cm−1 for A-3. The absorption properties of sample A-3 by the attenuation coefficient 0.174 ± 0.008 cm−1 is higher and more effective than the sample A-2. The existence of large empty space on the sample A-2 is evidenced by its value of MFP which is higher than the sample A-3. In this study shows that the higher differences of two optical phonon vibration mode strongly influenced to the absorption properties which shows A-3 (graphite and iron) more effective than the A-2 (graphite and nickel) as a shield due to the strong bonding connection Al–Fe–Si formed in composite geopolymer.

Effect of kaolin and argillite mixtures on the dielectric properties of geopolymers

The use of geopolymer in radiofrequency applications and more precisely in antenna is innovative. The objective of this study is to highlight the impact of mixtures of kaolin and argillite on the structure and dielectric properties of geopolymers for antenna application. For this, six geopolymer formulations based on mixtures of kaolin and argillite with different proportions (33, 50 and 67%) and calcined at 600 and 750 ​°C were studied using mercury intrusion porosimetry, dielectric measurements and NMR spectroscopy. Low porosity values were obtained whatever the mixture. At 600 ​°C, the porosity increases with the increase of argillite content from 18 to 23%. At 750 ​°C, no impact of argillite content on the porosity (16%) was detected. However, the pore size increases with increasing the argillite content regardless of the calcination temperatures due to the unreacted secondary phases present in argillite. MAS-NMR experiments on geopolymer samples and calcined mixtures have evidenced a strong correlation between reactive aluminum resulting from dehydroxylation of kaolin and clay minerals of argillite and the geopolymerization rate. These structural variations influence the dielectric properties. Indeed, ε and tan ​δ values increase with the increase of argillite content and calcination temperature due to the increase in the number of moles of free alkali earth cations (Ca2+ and Mg2+).

Photocatalytic Nanocomposite Materials Based on Inorganic Polymers (Geopolymers): A Review

Geopolymers are ecologically-friendly inorganic materials which can be produced at low temperatures from industrial wastes such as fly ash, blast furnace slags or mining residues. Although to date their principal applications have been seen as alternatives to Portland cement building materials, their properties make them suitable for a number of more advanced applications, including as photocatalytic nanocomposites for removal of hazardous pollutants from waste water or the atmosphere. For this purpose, they can be combined with photocatalytic moieties such as metal oxides with suitable bandgaps to couple with UV or visible radiation, or with carbon nanotubes or graphene. In these composites the geopolymers act as supports for the photoactive components, but geopolymers formed from wastes containing oxides such as Fe2O3 show intrinsic photoactive behaviour. This review discusses the structure and formation chemistry of geopolymers and the principles required for their utilisation as photocatalysts. The literature on existing photocatalytic geopolymers is reviewed, suggesting that these materials have a promising potential as inexpensive, efficient and ecologically-friendly candidates for the remediation of toxic environmental pollutants and would repay further development.

Modified geopolymers as promising catalyst supports for abatement of dichloromethane

Geopolymers have not been extensively employed as catalytic materials despite of their zeolite-resembling Si–Al structure. Geopolymerization offers a novel way for preparation of catalysts and possibility to use waste or industrial side-stream derived raw material as a resource for catalyst manufacturing. This work concentrates on metakaolin-based geopolymer materials that were prepared, characterized and tested as alternative environmentally benign catalyst supports for the oxidation of dichloromethane. The geopolymers with the Si/Al ratio of 1.5 were modified with HCl to increase their specific surface area, which is important in catalytic applications. Significant increase in specific surface areas was achieved via leaching of Na and Al from the geopolymer structure. Highest specific surface areas achieved for calcined geopolymers were over 500 m2g-1. Use of acid concentrations higher than 1 M led to the dehydroxylation of the geopolymer. Dehydroxylation decreased the total acidity of geopolymer through the loss of the Brønsted acid sites, which are responsible for the adsorption of dichloromethane in the beginning of the catalytic reaction. Absence of Brønsted acid sites was observed by the formation of CH2O as the only reaction intermediate. The best result in the dichloromethane oxidation was found with the geopolymer treated with 1 M HCl. Without using any additional active sites, the maximum dichloromethane conversion of 90% was reached at 525 °C with the maximum HCl yield of 83%. This result indicates the good potential of modified geopolymers to be used as catalyst supports in environmental applications.

The effect of Na+ and H2O on structural and mechanical properties of coal gangue-based geopolymer: Molecular dynamics simulation and experimental study

The aim of this work is to study the impacts of Na+ and H2O on structural and mechanical properties of coal gangue-based geopolymer by experiment and molecular dynamics. Geopolymers were prepared by coal gangue and mixed solution of NaOH and water glass. Then X-ray fluorescence (XRF) and X-ray diffraction (XRD) were utilized to characterize the main chemical composition and crystalline phase of geopolymer after 28d curing. Moreover, Na2Si2O5 glass was firstly proposed to establish the molecular structure of geopolymers with different Na/Al and H2O/Al. Structural optimization and molecular dynamics simulation were implemented under the specific force field. Simulated XRD pattern, energy and temperature curves, radial distribution function (RDF), hydrogen bond, bond angle distribution, mean square displacement (MSD) and elastic modulus of geopolymer were calculated and analyzed. Results indicated that with the increase of Na+ and H2O content, structure of geopolymer became more stable and mechanical properties were improved significantly.

The Impact of the Amount of Water Used in Activation Solution and the Initial Temperature of Paste on the Rheological Behaviour and Structural Evolution of Metakaolin-Based Geopolymer Pastes

This study aimed to determine the impact of the initial temperature of the paste (from 5 °C to 35 °C) and the addition of water, which reflects a decrease in the molarity of activation solutions (AS) by diluting 10 M NaOH with distillate water, on the rheological properties of geopolymer pastes. Additionally, this resulted in changes to the physical–mechanical properties of geopolymers after curing. A higher amount of water in the AS composition and higher initial paste temperature led to an increase in the spread values up to 28% and decreases viscosity. A smaller amount of water in the AS composition and a higher initial paste temperature accelerated the speed of the geopolymer structure formation up to 1.5 times during the curing period, increased compressive strength and reduced apparent porosity and pore size. X-ray diffraction confirmed the compressive strength test results and revealed that the lower amount of water in the AS and the higher initial paste temperature for the geopolymer preparation significantly affected the mineral formation and physical and mechanical properties of the samples.

Formation of Geopolymers Using Sodium Silicate Solution and Aluminum Orthophosphate.

This paper reports the formation and structure of fast setting geopolymers activated by using three sodium silicate solutions with different modules (1.6, 2.0 and 2.4) and a berlinite-type aluminum orthophosphate. By varying the concentration of the aluminum orthophosphate, different Si/Al-ratios were established (6, 3 and 2). Reaction kinetics of binders were determined by isothermal calorimetric measurements at 20 °C. X-ray diffraction analysis as well as nuclear magnetic resonance (NMR) measurements were performed on binders to determine differences in structure by varying the alkalinity of the sodium silicate solutions and the Si/Al-ratio. The calorimetric results indicated that the higher the alkalinity of the sodium silicate solution, the higher the solubility and degree of conversion of the aluminum orthophosphate. The results of X-ray diffraction and Rietveldt analysis, as well as the NMR measurements, confirmed the assumption of the calorimetric experiments that first the aluminum orthophosphate was dissolved and then a polycondensation to an amorphous aluminosilicate network occurred. The different amounts of amorphous phases formed as a function of the alkalinity of the sodium silicate solution, indicate that tetrahydroxoaluminate species were formed during the dissolution of the aluminum orthophosphate, which reduce the pH value. This led to no further dissolution of the aluminum orthophosphate, which remained unreacted.

Decalcification effect on stabilization/solidification performance of Pb-containing geopolymers

Geopolymers have been widely applied to pretreat Pb-containing solid wastes due to low carbon footprint and superior stabilization/solidification (S/S) performance. However, the wastes may be exposed to rainwater or water flow during long-term landfill, leading to the decalcification of internal geopolymer structure. Here, the influence of decalcification on the S/S performance of Pb-containing geopolymers was investigated through combined inductively coupled plasma mass spectrometry (ICP-MS), X-ray diffraction (XRD), differential Thermogravimetry (DTG), X-ray photoelectron spectroscopy (XPS), nuclear magnetic resonance (NMR), and mercury intrusion porosimeter (MIP) tests. Results show that decalcification can increase the cumulative leaching concentration of Pb and degrade the S/S performance of geopolymers due to the release of [Pb(OH)4]2- ions from the end-of-chain silicates of calcium aluminosilicate hydrates and the dissolution of Pb(OH)2 precipitates. A leaching model further indicates that surface wash off, i.e., the dissolution of Pb(OH)2 precipitates from the surface, is the main factor controlling degradation. In addition, for evaluating potential hazards of Pb leakage, electrochemical impedance spectroscopy (EIS) test was proposed to precisely predict the cumulative leaching concentration of Pb. Overall, this study is an innovative attempt to reveal the changes of the S/S characteristics of geopolymers under decalcification and track the leaching behaviors of Pb in landfill sites.

Mechanical and microstructural properties of geopolymer mortars from meta-halloysite: effect of titanium dioxide TiO2 (anatase and rutile) content

This study aimed to investigate the effect of Titanium Dioxide TiO2 (anatase and rutile) on mechanical and microstructural properties of meta-halloysite based geopolymer mortars namely GMHA and GMHR series. Meta-halloysite received 2.5, 5.0, 7.5 and 10 wt% of anatase or rutile as addition before calcination and geopolymerization. The raw materials and the end products were characterized using XRD, FTIR, ESEM and MIP analyses. The flexural strength increases from 6.90 to 9.13 MPa and from 6.90 to 12.33 MPa for GMHA and GMHR series respectively. The cumulative pore volume decreases from 102.2 to 84.2 mm3 g−1 and from 102.2 to 51.3 mm3 g−1 for GMHA and GMHR products respectively. Both matrices present micrographs with very low capillaries pores and fractured surfaces that confirmed the enhancement of the mechanical properties. It was concluded that TiO2 in both forms is beneficial for the reduction of porosity and densification of geopolymer matrices. Rutile enabled more compact and denser geopolymer structure compared to anatase. The aforementioned results showed the efficiency of both fine TiO2 particles to improve the geopolymer network significant for its durability.

Optimization of geopolymer mortar incorporating heavy metals in producing dense hybrid composites

The aim of this study is to examine capability of geopolymer in immobilization and entrapping of heavy metals bearing materials; also, dose optimization that will be more efficiently affect the resultant geopolymer structure will be studied. The main binder used for mortar preparation was water cooled slag in addition to air cooed slag as fine aggregate passing sieve of one mm in equal ratio, whereas the used activator was 8 % wt sodium hydroxide. The studied heavy metals bearing materials were barium sulfate, lead phosphate, lead slag and electric arc furnace dust used as partial replacement of water-cooled slag. Physico-mechanical characterization of each set of samples was conducted using XRD, FT-IR, SEM, compressive strength and bulk density. Results demonstrated that barium sulfate can be efficiently used up to 2%, lead phosphate up to 1%, lead slag up to 5%, and electric arc furnace dust up to 10%.

An Analysis of the Formation Mechanism of Geopolymer Made from Obsidian Mineral and Its Potential Application as a Slow Release Fertilizer.

Geopolymer is the inorganic polymer commonly made from kaolin, clay, fly ash, or slag. Obsidian mineral is the new candidate material for geopolymer formation. Obsidian is a material that used in ancient eras, but nowadays, this function has been replaced by various metals. Obsidian consists of cristobalite and sodium aluminum silicate. Obsidian was reacted with disodium metasilicate (Na2SiO3) to form a mineral-based geopolymer. An analysis of the formation mechanism through X-ray diffraction and Fourier transform infrared spectroscopy showed that the geopolymer formation from obsidian takes place in two stages. The first stage is the formation of a geopolymer from a reaction among cristobalite, disodium metasilicate, and amorphous aluminum silicates, whereas the second stage is the incorporation of crystalline sodium aluminum silicate into the former geopolymer structure. Geopolymer is usually utilized to form brick or concrete for an infrastructure purpose, but in this research, the geopolymer is proposed to control the release rate of elements from fertilizer. The result of potassium release test shows that the geopolymer has a slow-release property.