Acid-based Geopolymers Research Articles

Valorization of ceramic sanitary waste into Resilient phosphoric acid-based geopolymers for sustainable construction: Thermal, mechanical, and microstructural properties

The construction industry's heavy reliance on conventional cement production contributes significantly to global carbon dioxide emissions, prompting the need for eco-friendly building materials. Geopolymers, synthesized from natural materials like clay and fly ash, offer a sustainable alternative to traditional cement. This paper investigates the development of phosphoric acid-activated geopolymers with sanitary ware waste (SWW) as aggregates, aiming to create high-performance, environmentally friendly building materials. Various particle sizes of SWW were incorporated into the geopolymer matrix, revealing a strong relationship between particle size and compressive strength. The inclusion of SWW improved compressive strength, with a notable 83 % increase at 30 % SWW content. Fourier transform infrared spectroscopy (FTIR) and X-ray diffraction (XRD) analyses highlighted the formation of new bonds in the geopolymeric gel, while scanning electron microscopy (SEM) showed microcracks and good adhesion between SWW particles and the geopolymer matrix. Thermal resistance tests demonstrated that SWW-reinforced geopolymers exhibited improved resistance to high temperatures compared to the reference geopolymer. XRD analysis of thermally treated geopolymers revealed the transformation of amorphous phases into stable crystalline phases. SEM/EDX mapping confirmed the presence of silica-rich phases, contributing to the materials' mechanical properties and thermal resistance. This study underscores the potential of SWW-based geopolymers as sustainable, high-performance building materials.

Enhancing thermal insulation with phosphate washing sludge waste as an inorganic foaming agent in porous acid-based geopolymers: Formulation and processing optimization

This study explores the potential utilization of phosphate washing sludge (PWS), a calcium carbonate-rich by-product of phosphate mining, as an inorganic foaming agent in the production of porous acid-based geopolymers. The investigation focused on evaluating the impact of various factors, including phosphoric acid concentration (ranging from 8 M to 12 M), liquid/solid (L/S) ratio (0.8 to 1.2), and the amount of PWS added (ranging from 0 wt% to 50 wt%), on the properties of the resulting geopolymers, such as porosity, density, thermal conductivity, and compressive strength. To optimize the formulation and processing parameters of porous acid-based geopolymers, a surface response methodology using statistical modeling was employed. This approach facilitated a systematic examination of the different factors influencing the properties of geopolymers. The raw materials involved in the study, namely kaolinitic clay, PWS, and the produced geopolymers, were characterized using various techniques such as X-ray Diffraction (XRD), X-ray Fluorescence (XRF), Scanning Electron Microscope coupled with Energy Dispersive X-Ray (SEM/EDX), laser particle size analysis, and mapping. The results revealed that the combination of a phosphoric acid concentration of 10 M, a L/S ratio of 0.88, and the addition of 16 wt% PWS yielded the best performance in terms of porosity, compressive strength, and thermal conductivity, with values of 29.4 %, 13.8 MPa, and 0.0931 W/m.K, respectively. Additionally, a mathematical model was developed to predict optimal parameter combinations for desired performance characteristics. This research holds promise for the development of cost-effective thermal insulation materials for building applications.

Wheat straw fibre based semi-IPN composite: Preparation and evaluation as a matrix for water and fertilizer release and in slope reinforcement

To improve the utilization rate of fertilizer and reduce environmental pollution, the effective management of water and fertilizer is extremely significant for the development of modern agriculture. Herein, using agricultural wastes (wheat straw fibre, WS) and phosphoric acid-based geopolymers (PGs) as eco-friendly materials, a novel wheat straw fibre composited polymer/PGs (WS-Po/PGs), was prepared by in-situ graft polymerization strategy, and a kind of nutrient-water carrier with semi-IPN was formed. Its structure and morphology were revealed by XRD, FT-IR, BET and SEM. Its water-retaining and controlled release behavior, and the nutrient release model were studied, while the effects on plant growth and loess slope of WS-Po/PGs were further investigated. The results illustrated that the obtained nutrient-water carrier had excellent water absorption (270.27 g/g) and salt tolerance (131.58 g/g) as straw fibres were mixed into polymer networks and formed semi-interpenetrating structures (semi-IPN). Comparing with controls, the WS-Po/PGs significantly improved the water retention capacity and N release longevity (30 d, 66.2%). Its nutrient release fitted the Fickian diffusion model (n < 0.5). Furthermore, the WS-Po/PGs could remarkably enhance the erosion resistance and stability of the loess slope, regulate the pH of the soil, and promote the germination rate of slope vegetation. In summary, by using agricultural wastes straw and loess as resources, the obtained WS-Po/PGs presented excellent slow-release behavior, salt tolerance and slope reinforcement function, and this kind of semi-IPN nutrient-water carrier could provide an insight for agriculture and slope protection.

Green, non-toxic and efficient adsorbent from hazardous ash waste for the recovery of valuable metals and heavy metal removal from waste streams

As compared to alkali-activated geopolymers with phosphoric acid which may be used in high concentrations resulting in disposal concerns, acid-based geopolymers may have superior properties. A novel green method of converting waste ash to a geopolymer for use in adsorption applications such as water treatment is presented here. We use methanesulfonic acid, a green chemical with high acid strength and biodegradability to form geopolymers from coal and wood fly ashes. The geopolymer is characterized for its physico-chemical properties and tested for heavy metal adsorption. The material specifically adsorbs iron and lead. The geopolymer is coupled to activated carbon forming a composite, which adsorbs silver (precious metal) and manganese (hazardous metal) significantly. The adsorption pattern complies with pseudo-second order kinetics and Langmuir isotherm. Toxicity studies show while activated carbon is highly toxic, the geopolymer and the carbon-geopolymer composite have relatively less toxicity concerns.

Mn release behaviors from electrolytic manganese residue-based slow-release fertilizer using acid/alkali-activated geopolymers as binders: A comparative study

In this study, acid/alkali-activated geopolymers and electrolytic manganese residue (EMR) were used as a binder and Mn source, respectively, to prepare EMR-based slow-release fertilizers (SRFs) and Mn release behaviors from SRFs were comparatively investigated. Mn release from SRFs prepared by acid/alkali-based geopolymers follows first-order kinetics and the Ritger-Peppas model. For alkali activator attack, the easily leachable manganese salt (MnSO4·H2O) in EMR is converted to stable fractions (such as MnO2, Mn4Si8O20, and Ca4Mn4Si8O24) in the SRFs. The K-(A)-S-H gel in SRFs prepared using alkali-based geopolymers (SRFs-alGo) restricts rapid Mn release through physical encapsulation and ion exchange. In contrast, SRFs prepared using acid-based geopolymers (SRFs-acGo) mainly limit Mn release through pediocratic NH4MnPO4·H2O formation and physical adsorption/encapsulation of phosphoric acid-activated geopolymer gel (Si–O–Si–O–P–O). Phosphoric acid attack did not significantly changed the proportion of the exchangeable fraction of Mn in SRFs, which was maintained at approximately 40%. Moreover, Mn in SRFs-alGo was uniformly distributed on the surface and bulk phases (SEM-EDS and XPS co-analysis), while most of the Mn in SRFs-acGo was distributed on the surface of particles, leading to readily released Mn and even higher Mn release concentrations of SRFs-acGo. This study provides a theoretical basis for strategically applying EMR-based SRFs to plants with different Mn requirements and guides subsequent field experiments.

A eco-friendly acid fly ash geopolymer with a higher strength

Phosphoric acid (PA)-based geopolymer is usually prepared with PA as activator. However, the PA-based geopolymer using fly ash as raw material has not received much attention, and its strength is characterized by instability because excessive or insufficient PA will produce a negative impact on the strength. As the curing time prolongs, the compressive strength of geopolymer with Al/P molar ratio ≠ 1 reduces. In this work, the fly ash (FA) was used as raw material, the aluminum dihydrogen phosphate (ADP) were used as activators to develop a new acid-based geopolymers (ADP-based geopolymer) at room temperature. The geopolymers microstructure and mechanism were investigated by X-ray Diffraction, Infrared Spectroscopy, Scanning Electron Microscopy, Nuclear Magnetic Resonance, and Mercury intrusion analysis. The ADP-based geopolymer mechanical performance were investigated by unconfined compressive strength test. The geopolymer pH, electrical conductivity (EC), setting time, and fluidity were also studied. Additionally, the thermogravimetric characteristics of geopolymer were explored by thermogravimetry analysis. Results show that the ADP-based geopolymer had a higher strength than the PA-based geopolymer, the strength raised with the ADP concentration increasing, and the strength would not be weakened by excessive ADP activator. As the curing time prolonged, the compressive strength increased, and a higher ADP concentration caused a longer setting time. As the ADP concentration increased, the geopolymer pH decreased but the EC increased. However, as the curing time prolonged, an opposite trend was observed. Microcosmic analysis indicated that the ADP-based geopolymer matrix were mainly AlPO4, CaHPO4 crystalline phase and amorphous matrix composed of Si–O–Al–O–P, Al–O–P, Si–O–P, Si–O–Si, and Si–O–P–O–Si units.

Influence of alumina on the compressive strengths and microstructural properties of the acid-based geopolymers from calcined indurated laterite and metakaolin

The main objective of this work is to investigate the influence of alumina on the compressive strengths and microstructural properties of the acid-based geopolymers using calcined indurated laterite and metakaolin. These raw materials have been replaced by 0, 5, 10, 15 and 20 mass% of calcined bauxite. Phosphoric acid with molarity 10 M was used as a chemical reagent. The compressive strengths of the acid-based geopolymers increase with increasing the calcined bauxite content. Those from the substitution of calcined laterite by calcined bauxite are ranging from 21.45 to 47.95 MPa and higher compared to those from metakaolin (12.55 and 21.97 MPa). TG and DSC curves of all acid-based geopolymers indicate the decomposition of AlPO4.H2O at between 230 and 248 °C to an amorphous phase. In addition to this mineral, those from calcined laterite show the transformation of amorphous FePO4·2H2O at in the range 451–788 °C to the crystalline FePO4. The micrography images of the acid-based geopolymers indicate the formation of dense amorphous geopolymer matrices. It was found that the alumina incorporated in the acid-based geopolymers increases the compressive strengths. The presence of hematite in the calcined laterite leads to the formation of amorphous FePO4·2H2O which could contribute to enhancing exponentially the compressive strengths of the acid-based geopolymers.

The Coexistence of the Poly(phospho-siloxo) Networks and Calcium Phosphates on the Compressive Strengths of the Acid-Based Geopolymers Obtained at Room Temperature

This work aims to investigate the coexistence of the poly(phospho-siloxo) networks and calcium phosphates on the compressive strengths of the acid-based geopolymers obtained at room temperature. Waste fired brick and phosphoric acid were used as an aluminosilicate and chemical reagent, respectively. Calcium aluminate hydrate was prepared by mixing calcium hydroxide from the calcined eggshell and calcined bauxite. Calcium silicate hydrate was obtained by the mixture of rice husk ash and calcium hydroxide. The molar ratios CaO/Al2O3 and CaO/SiO2 in the calcium aluminate and calcium silicate hydrates are equals to 1.0. The X-ray patterns of the acid-based geopolymers indicate the broad hump structure between 18 and 38°(2θ). In addition to this broad band, those from the mixture of calcium sources show the reflection peaks of monetite and brushite. The compressive strength of the reference is 56.43 MPa. Those obtained with the addition of 10, 20, 40 and 50 g of calcined eggshell are 30.15, 22.85, 21.16 and 13.47 MPa, respectively. The ones from calcium aluminate hydrate are 32.62, 31.58, 17.83 and 16.33 MPa, respectively. Whereas those containing calcium silicate hydrate are 44.02, 42.71, 40.19 and 18.59 MPa, respectively. This work demonstrates that the formation of calcium phosphates in the structure of the acid-based geopolymers decreases the poly(phospho-siloxo) chains and therefore reduces their compressive strengths. The moderate addition of calcium silicate hydrate reduces slightly the compressive strengths of the acid-based geopolymers which can be comparable to the one of CEM II 42.5R.

Control of the alumino-silico-phosphate geopolymers properties and structures by the phosphorus concentration

Acid-based geopolymers are interesting materials, as they usually present higher mechanical and thermal properties than their alkali-based counterparts do, but they are difficult to use for complex shapes due to the high viscosity of their reactive mixture. This can be overcome by the addition of water in the formulation. In this study, geopolymers have been synthesized from metakaolin and phosphoric acid with variable [P] concentration (by a modification of either the water content or Al/P ratio). Measurements of the viscosity, density and consolidation times have been performed on reactive mixtures differentiated by their water content. Furthermore, a study of the geopolymers’ microstructure and mechanical properties confirmed their evolution with [P]. Finally, a characterization by thermal and structural analyzes of their structure (Fourier transform infrared spectroscopy and X-ray diffraction), have been carried out in order to assess the influence of the water content on the different amorphous networks. It appears that the addition of water influences the structure of the material, as it leads to the formation of new amorphous networks. More specifically, for Al/P = 1 and variable water amounts, the networks are mainly based on the coexistence of Al–O–P with an hydrated silica network, while for variable Al/P, the Al–O–P network coexists with the unreacted metakaolin. In addition, it seems that all the properties are governed by the parameter nP/nAl + nH2O.

Acid-based geopolymers using waste fired brick and different metakaolins as raw materials

Three metakaolins and waste fired brick were used to explore the effects of iron oxide, amorphous silica and quartz in the raw materials on the compressive strength and the microstructural properties of acid-based geopolymers cured at room temperature and 60 °C. Quartz content in the metakaolin from Dibamba is about 22.0 wt% and each other samples contain around 8.0 wt%. Waste fired brick and metakaolin from Bangoua contain nanocrystalline hematite and have higher amorphous silica content. The higher quartz content in the metakaolin from Dibamba could prevent the incorporation of PO4 units in the networks. The compressive strengths of the acid-based geopolymers cured at room temperature are higher (35.3–56.4 MPa) compared to those cured at 60 °C (17.8–32.9 MPa). The higher amorphous silica and nanocrystalline hematite content in the starting materials could accelerate the hardening process. It can be concluded that iron oxide, amorphous silica and quartz in the starting material could affect the compressive strengths of acid-based geopolymers.

The New Challenge of Acid-Based Geopolymers Synthesized with the Incorporation of Lithium Ions as Cathode Materials for Lithium-Ion Batteries

The central focus of this research work is upon the synthesis of Lix-geopolymers (where x = 0.5 and 0.75) performed with the integration of lithium ions, in order to be used as cathode materials for lithium ions batteries. The obtained results presenting the requirements for these types of materials, demonstrate that Li-geopolymers could stand for a new alternative. The geopolymers were prepared at ambient temperature. The identification phase was carried out by powders X-ray diffraction, after calcination at various temperatures. The thermal stability was investigated by differential thermal analysis up to 1400 °C. With increase of lithium ions insertion, the temperature relative to the evaporation of P2O5 groups increased accompanied by a decrease in the mass loss relative to this phenomenon. The electrical measurements of both samples, were elaborated in the frequency range of 1–106 Hz and at a temperature range of 75–725 °C. After heating at 300 °C, the electrical conductivity values in the Li0.5-geopolymer material, were in the range of 10−6 S cm−1 and 10−4 S cm−1. By increasing lithium ions, the electrical conductivity values of the Li0.75-geopolymer sample, went from 10−7 to 10−5 S cm−1.

Acid-based geopolymers: Understanding of the structural evolutions during consolidation and after thermal treatments

Materials such as ceramic matrix composites are developed for mechanical applications at high temperature, but their cost remains a limitation. Consequently, the use of acid-based geopolymer matrices may be an alternative to reduce costs.In this study, the sample was prepared from metakaolin and phosphoric acid. Fourier Transform InfraRed and Nuclear Magnetic Resonance spectroscopies, X-Ray Diffraction and thermal measurements were used to understand the structural evolution of acid-based geopolymers (binders) during consolidation and after thermal treatments.According to the results, the consolidation of the binder has been divided into four steps: the dissolution of the metakaolin, the polycondensation reactions forming AlPO4 entities and hydrated phases, the breakdown of SiOAl bonds with formation of various hydrated silica networks and finally the completion of the networks. After a thermal treatment at 1000 °C, the binder consists of AlPO4 phases, quartz and vitreous silica.

Relation between working properties and structural properties from 27Al, 29Si and 31P NMR and XRD of acid-based geopolymers from 25 to 1000°C

Highlights: (maximum 85 characters, including spaces, per bullet point).  Acid-based geopolymers display different processing-dependent working properties.  Acid-based geopolymers are mostly composed of Al-O-P and Si(OH)4 networks.  The quantities of Al-O-P and unreacted metakaolin govern the thermal resistance.  The increase of the Young's modulus is related to a higher thermal resistance.  Ordered structures and low amounts of physisobed water lead to water resistance.

Composition and properties of phosphoric acid-based geopolymers

Two metakaolins exhibiting different reactivities were used to study geopolymers obtained via phosphoric acid activation. The study of consolidation of samples with various Si/Al and Al/P showed that the Al- and Si-rich and P-poor compositions were more likely to consolidate properly. The geopolymers formed at 20 or 70 °C kept the same crystalline impurities as the starting metakaolins, the samples remaining mostly amorphous. The microstructure of geopolymers formed with less reactive metakaolin was smooth and dense, while the geopolymers prepared from the most reactive one were more porous and rough. Finally, tests on water and fire resistances of all the samples were reported.

Effect of SiO2/Al2O3 Molar Ratio on Microstructure and Properties of Phosphoric Acid-based Metakaolin Geopolymerss

The phosphoric acid-based metakaolinite geopolymeric materials with different SiO2/Al2O3 molar ratios were prepared from metakaolinite, Al2O3 powder and phosphoric acid. X-ray diffraction (XRD), Thermogravimetry and Differential Scanning Calorimeter (TG-DSC), Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM) were used to determine the reaction process and phase formation. The results indicated that different SiO2/Al2O3 ratios raw materials can generate geopolymers composition of the amorphous phase and quartz crystalline phase. The still existed quartz peaks indicate that quartz from metakaolinite did not totally take part in the chemical reaction or dissolve into the gel phase of geopolymers. The best performance was observed in the geopolymeric material prepared with SiO2/Al2O3 molar ratio of 1.4 due to the proper obtained Si-O-Al-O-P-O- bonds in geopolymeric structures. The acid-based geopolymers were stable below 1450 °C. These geopolymers have a potential use in fireproofing materials, since they display important high temperature stability.

Surface decoration of polyimide fiber with carbon nanotubes and its application for mechanical enhancement of phosphoric acid-based geopolymers

A new methodology to decorate the surface of polyimide (PI) fiber with carbon nanotubes (CNTs) has been developed in this study. This surface decoration was carried out through a surface alkali treatment, a carboxylation modification, surface functionalization with acyl chloride groups and then with amino groups, and a surface graft of CNTs onto PI fiber. Fourier-transform infrared and X–ray photoelectron spectroscopic characterizations confirmed that CNTs were chemically grafted onto the surface of PI fiber, and scanning electron microscopic observation demonstrated the fiber surface was uniformly and densely covered with CNTs. The surface energy and wettability of PI fiber were improved in the presence of CNTs on the fiber surface, which made a contribution to enhance the interfacial adhesion of PI fiber with other inorganic matrices when used as a reinforcing fiber. The application of CNTs-decorated PI fiber for the reinforcement of phosphoric acid-based geopolymers was investigated, and the results indicated that the geopolymeric composites gained a noticeable reinforcement. Compared to unreinforced geopolymer, the geopolymeric composites achieved a remarkable increase in compressive strength by 120% and in flexural strength by 283%. Fractography investigation demonstrated that the interaction adhesion between the fibers and matrix was enhanced due to the surface decoration of PI fiber with CNTs, which contributed to an improvement in fracture-energy dissipation by fiber pullout and fiber debonding from the matrix. As a result, a significant reinforcement effect on geopolymeric composites was achieved through a fiber-bridging mechanism. This study provided an effective methodology to improve the interracial bonding force for PI fiber and also proves a highly efficient application of CNTs-decorated PI fiber for the mechanical enhancement of geopolymeric composites.

Water molecular dynamics of metakaolin and phosphoric acid-based geopolymers investigated by impedance spectroscopy and DSC/TGA

In this paper, thermal behavior and dielectric response of a series of metakaolin-phosphoric acid geopolymers with different amounts of H3PO4 were investigated. Two thermal phase transitions were detected in geopolymers by means of Differential Scanning Calorimetry (DSC) in a temperature range (−50°C; 175°C). These transitions were absent for metakaolin and were attributed to free and interstitial water evaporation. These results were confirmed with mass losses in geopolymers observed through Thermogravimetric analysis (TGA). In order to probe molecular mobility and dielectric relaxations, samples were characterized by dielectric spectroscopy in a board temperature range (−50°C–200°C) and in a frequency range of 0.1Hz to 1MHz. Results showed that in the case of metakaolin, only a percolation process was detected occurring as a result of the migration of protons and ions filling the porous space. For geopolymer materials, different dielectric processes were observed. In fact, an ice like water relaxation processes appeared at low temperatures followed with a percolation processes. At temperatures above 100°C, two new dielectric relaxations were detected and were attributed to the reorientations of free and interstitial water molecules, respectively. Besides, a conduction phenomenon noted for high temperatures occurring as a result of the carrier charges diffusion. All these processes showed a dependency on the amount of phosphoric acid added to the metakaolin. Indeed, activation energies and relaxation times calculated basing on Arrhenius law and Macedo and Litovitz laws as well as conduction process were to be found strongly dependent on the H3PO4 concentration.

Geopolymers Based on Phosphoric Acid and Illito-Kaolinitic Clay

New three-dimensional geopolymer materials based on illito-kaolinitic clay and phosphoric acid were synthesized. The effect of Si/P molar ratio on the geopolymers properties was studied. Raw, calcined clay, and geopolymers structures were investigated using XRD, IR spectroscopy, and SEM. The phosphoric acid-based geopolymers mechanical properties were evaluated by measuring the compressive strength. The Si/P molar ratio was found to increase with the increase of the compressive strength of the obtained geopolymers, which attained a maximum value at Si/P equal to 2.75. Beyond this ratio, the mechanical strength decreases. The XRD patterns of these geopolymers samples have proven that when the Si/P molar ratio decreases, the amorphous phase content increases. Besides, the structural analyses have revealed the presence of aluminum phosphate and Si-O-Al-O-P polymeric structure, whatever the Si/P molar ratio is (between 2.25 and 3.5). The obtained results have confirmed that the presence of the associated minerals such as hematite and quartz in the clay does not prevent the geopolymerization reaction, but the presence of illite mineral seems to have a modest contribution in the geopolymerization.

Structural, thermal and dielectric properties of phosphoric acid-based geopolymers with different amounts of H3PO4

Phosphoric acid-based geopolymers were synthesized using metakaolin (Al2O3–2SiO2) and different amounts of phosphoric acid (H3PO4) at an ambient temperature. Structural and thermal properties of geopolymers with different molar ratios SiO2/H3PO4 (Si/P =1.25, 1.5 and 1.75) were investigated to study the effect of the molar ratio SiO2/H3PO4 (Si/P=1.25, 1.5 and 1.75). The results showed that an increase in the amount of phosphoric acid leads to an augment in the amorphous nature of samples and to a change in their thermal behaviors. Dielectric measurements at a range frequency of 1–106Hz revealed that the permittivity, the dielectric loss and the electrical conductivity of geopolymers at room temperature were found to be strongly dependent on the H3PO4 concentration. In fact, the addition of phosphoric acid improved the ionic conduction resulting in a great change in the dielectric properties.

The phase evolution of phosphoric acid-based geopolymers at elevated temperatures

The Al 2O 3–2SiO 2 powders for sol–gel synthesis have good phosphoric acid activation properties. The phase evolution of phosphoric acid-based geopolymers at elevated temperatures is similar to that of alkali-based metakaolin geopolymers. The chemosynthetic phosphoric acid-based geopolymers have been found to possess extremely good thermal stability, with no sign of melting up to 1550 °C. The onset temperature of crystallization of the specimens occurred at 900 °C. The amount of quartz and berlinite crystal reached a maximum at approximately 1000 °C. Further exposure to 1150 °C showed that quartz and berlinite phases were converted to cristobalite and aluminum phosphate.