Showing papers on "Geopolymer published in 2008"
TL;DR: In this paper, the potential of one-part "just add water" geopolymer formulations is discussed, and the opportunities presented by the development of one part "Just Add Water" formulations are identified as exceeding their potential of the traditional two-part (solid plus alkaline activator solution) mix design.
Abstract: This paper presents a discussion of the ability to design raw materials for use in geopolymers. To provide a “green” material to complement existing cement binders, as well as in the interests of waste beneficiation, various potential means of tailoring geopolymer precursor chemistry and particle behavior are outlined. The opportunities presented by the development of one-part “just add water” geopolymer formulations are identified as exceeding the potential of the traditional two-part (solid plus alkaline activator solution) mix design. The key roles played by network-modifying (alkali and alkaline earth) cations and alumina in rendering glassy phases “ideal” for geopolymerization are discussed, and the potential value of ASTM Class C ashes in synthesis of high-performance geopolymers becomes evident. This provides a significant step toward the development of international standards for the application of geopolymer binders in the construction industry worldwide, and raises a number of important challenges for researchers in the field of geopolymer and cement technology.
482 citations
TL;DR: In this paper, the role of calcium in geopolymerisation was investigated and the effect of different calcium silicates on the performance of different matrices was found to depend most significantly on the crystallinity of the calcium silicate source and the alkalinity of activating solution used.
455 citations
TL;DR: In this paper, the authors present a study on geopolymers and aggregates made with class F fly ash and evaluate strength loss due to thermal damage, showing that the aggregates steadily expanded with temperature, reaching about 1.5-2.5% expansion at 800-°C.
Abstract: This paper presents a study on geopolymers and geopolymer/aggregate composites made with class F fly ash. Samples were heated up to 800 °C to evaluate strength loss due to thermal damage. The geopolymers exhibited strength increases of about 53% after temperature exposure. However, geopolymer/aggregate composites with identical geopolymer binder formulations decreased in strength by up to 65% after the same exposure. Test data from dilatometry measurements of geopolymers and aggregates provides an explanation for this behavior. The tests show that the aggregates steadily expanded with temperature, reaching about 1.5–2.5% expansion at 800 °C. Correspondingly, the geopolymer matrix undergoes contraction of about 1% between 200 °C and 300 °C and a further 0.6% between 700 °C and 800 °C. This apparent incompatibility is concluded to be the cause of the observed strength loss. This study presents the results of 15 different geopolymer combinations (i.e. mixture proportions, curing and age) and four different aggregates.
444 citations
TL;DR: It was found that synthesised geopolymer matrixes were only effective in the chemical immobilisation of a number of elements of environmental concern contained in fly ashes, reducing (especially for Ba), or maintaining their leachable contents after the geopolymisation process, but not for those elements present as oxyanions.
388 citations
TL;DR: The results of this work tentatively support a previous identification of Pb (3)SiO(5) as a potential candidate phase for hosting Pb(II) within the geopolymer structure, although the data are not entirely conclusive.
276 citations
TL;DR: The results have indicated that the systems under investigation are suited for the manufacture of pre-formed building blocks at room temperature.
270 citations
TL;DR: In this article, three repair materials were prepared using cement-based, geopolymeric and steel slag binders, and their mechanical performances such as compressive strength, bond strength and abrasion resistance were examined experimentally.
Abstract: Three repair materials were prepared using cement-based, geopolymeric, or geopolymeric containing steel slag binders. Their mechanical performances such as compressive strength, bond strength and abrasion resistance were examined experimentally. The test results showed that the geopolymeric materials had better repair characteristics than cement-based repair materials, and the addition of steel slag could improve significantly the abrasion resistance of geopolymeric repair. By means of scanning electron microscopy (SEM) it can also be concluded that the steel slag was almost fully absorbed to take part in the alkali-activated reaction and be immobilized into the amorphous aluminosilicate geopolymer matrix.
208 citations
TL;DR: In this article, the effects of geopolymer binder systems exposed to elevated temperatures are examined, and the results showed that Si/Al ratio has a significant influence on elevated temperature exposure deterioration.
Abstract: The effects of geopolymer binder systems exposed to elevated temperatures are examined. Geopolymers investigated were synthesized from metakaolin, activated by combinations of sodium/potassium silicate and sodium/potassium hydroxide. The specimens were then exposed to temperatures of 800 °C. The factors studied were: (1) calcining temperatures of kaolin; (2) Si/Al ratio of the geopolymer; (3) activator/metakaolin ratio; (4) curing temperature; and (5) alkali cation type. Altogether 30 geopolymer formulations were studied. The samples were subjected to compressive strength, thermogravimetry, and scanning electron microscopy tests. Results showed that Si/Al ratio has a significant influence on elevated temperature exposure deterioration. Lesser strength loss due to elevated temperature exposures were observed in geopolymer with high Si/Al ratios (>1.5). The geopolymer binders activated by potassium-based activators showed an enhanced post-elevated temperature exposure performance compared to sodium-based systems. The optimum calcining temperature of kaolin and curing temperatures for improved temperature performance are also reported.
202 citations
TL;DR: In this article, the effects of water content, high early silica, and high early alumina in the formation of one-part mix geopolymers are investigated, and it is shown that the formulation with less water has an unexpected greater extent of crystallinity.
Abstract: In geopolymer technology, silicate solutions are frequently used as alkali activators to dissolve the solid aluminosilicate precursor and aid in binder formation. These corrosive and often viscous solutions are not user-friendly and would be difficult to use for bulk production. Developing geopolymers as a one-part mixture (“just add water”), similar to Portland cement, increases their commercial viability. Here, for the first time, the geopolymer system consisting of geothermal silica and solid sodium aluminate (providing the solid silica, alkali, and alumina sources) is studied. The effects of water content, high early silica, and high early alumina in the formation of one-part mix geopolymers are also investigated. This system demonstrates that making geopolymers from solid sources by “just adding water” is possible. XRD shows that the formulation with less water has an unexpected greater extent of crystallinity. It is also observed that a high early Al concentration inhibits geopolymerization, while a...
198 citations
TL;DR: In this article, the catalytic effects of the seed particles on gel phase formation and separation are explained mechanistically in terms of catalytic effect of seed particles in the formation of phase-separated gels.
TL;DR: A PVA short fiber reinforced fly ash-geopolymer composites manufactured by extrusion technique (SFRGC) is developed in this paper, where the effects of fly ash content and fiber volume fraction on the rheological and impact behaviors of SFRGC are systemically investigated.
TL;DR: In this paper, the influence of various parameters on the short term engineering properties of fresh and hardened low-calcium fly ash-based Geopolymer mortar were studied, and the obtained compressive strength was in the range of 1.6MPa -20MPa.
Abstract: Geopolymer is a novel binding material produced from the reaction of fly ash with an alkaline solution. In Geopolymer mortar, Portland cement is not utilized at all. In this research, the influence of various parameters on the short term engineering properties of fresh and hardened low-calcium fly ash-based Geopolymer mortar were studied. Tests were carried out on 50 x 50 x 50mm cube Geopolymer mortar specimens. The test results revealed that as the concentration of alkaline activator increases, the compressive strength of Geopolymer mortar also increases. Specimens cured at temperature of 65 o C for 1 day showed the highest 28 days compressive strength. The mass ratio of activator/fly ash of 0.4 produced the highest 28 days compressive strength for the specimen. The obtained compressive strength was in the range of 1.6MPa – 20MPa.
15 Dec 2008-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, a sheet-like carbon fiber preform was developed using short fibers (2, 7 and 12mm, respectively) as starting materials and used to strengthen a geopolymer.
Abstract: A kind of sheet-like carbon fiber preform was developed using short fibers (2, 7 and 12 mm, respectively) as starting materials and used to strengthen a geopolymer. Mechanical properties, fracture behavior, microstructure and toughening mechanisms of the as-prepared composites were investigated by three-point bending test, optical microscope and scanning electron microscopy. The results show that the short carbon fibers disperse uniformly in geopolymer matrix. The Cf/geopolymer composites exhibit apparently improved mechanical properties and an obvious noncatastrophic failure behavior. The composite reinforced by the carbon fibers of 7 mm in length shows a maximum flexural strength as well as the highest work of facture, which are nearly 5 times and more than 2 orders higher than that of the geopolymer matrix, respectively. The predominant strengthening and toughening mechanisms are attributed to the apparent fiber bridging and pulling-out effect based on the weak fiber/matrix interface as well as the sheet-like carbon fiber preform.
TL;DR: In this article, the effect of adding calcite and dolomite to metakaolin-based geopolymers was investigated by compressive strength testing, X-ray diffractometry and electron microscopy, with the aim of better understanding the role played by calcium ions, carbonate ions and mineral surfaces.
Abstract: The effect of adding significant percentages of alkaline earth carbonate minerals (calcite and dolomite) to metakaolin-based geopolymers is investigated by compressive strength testing, X-ray diffractometry and electron microscopy, with the aim of better understanding the role played by calcium ions, carbonate ions and mineral surfaces in geopolymers. Addition of around 20% calcite or dolomite is seen to improve the compressive strength of the geopolymeric material, although does induce additional shrinkage during the first 90 days of aging. More than 20% mineral additive has a deleterious effect on strength due to significant disruption of the geopolymer gel network and the reduced reactive aluminosilicate content. No distinct calcium silicate hydrate phase formation is observed in any of the systems studied. Some dissolution of the mineral particles is observed, however this is not a major effect in most instances. The mineral particles interact with the geopolymer gel predominantly via surface binding, which appears to be somewhat stronger in the case of calcite than dolomite.
TL;DR: The phase evolution and microstructural development of a series of geopolymer mixtures comprising SiO2, Al2O3, Na2O and H2O prepared by alkali reaction of metakaolin, have been studied in this article.
TL;DR: In this article, a pozzolanic material-based geo-polymer was synthesized from pozzolana material under activation of NaOH 10 M or slurry of NaAlO2 in NaO 10 M solution, and the effect of the two activation methods on the properties of the geopolymer was investigated by means of X-ray diffraction, scanning electron microscopy (SEM), FTIR spectroscopy, nuclear magnetic resonance (27Al and 29Si NMR) and uniaxial compression tests.
Abstract: Pozzolanic material-based geopolymer has been proposed as a solving methodology to the geohazards, due to pozzolanic collapsible soils widely present in the South Italy. The geopolymer was synthesized from pozzolana material under activation of NaOH 10 M or slurry of NaAlO2 in NaOH 10 M solution. The specimens were cured at 25 °C and 100% RH for different ageing times. The effect of the two activation methods on the properties of the geopolymer was investigated by means of X-ray diffraction, scanning electron microscopy (SEM), FTIR spectroscopy, nuclear magnetic resonance (27Al and 29Si NMR) and uniaxial compression tests. XRD, NMR and IR analysis indicate the geopolymer is generated by the dissolution of the silico-aluminate phases present in the pozzolana and the successive re-organization in amorphous and crystalline neo-formed phases. The spectroscopic evidences confirm that the 4-coordinated Al atoms present in the neat pozzolana and in the NaAlO2 change their coordination state splitting between 6- and 4-coordinated atoms, modifying the traditional chemistry of polysialate formation. SEM results show the synthesized geo-polymer maintained the granular morphology of the pozzolana and the geo-polymeric reactions occurred mainly at the surface of pozzolana particulates. Furthermore, uniaxial strength data increase gradually upon the curing time, until 40 MPa for the specimens activated with the slurry system.
TL;DR: In this paper, the atomic pair distribution function (PDF) was used to study the structure of cesium aluminosilicate geopolymer (Cs2O·Al2O3·4SiO2·xH2O, with x ∼ 11).
Abstract: The atomic pair distribution function (PDF) method was used to study the structure of cesium aluminosilicate geopolymer (Cs2O·Al2O3·4SiO2·xH2O, with x ∼ 11). The geopolymer was prepared by reacting metakaolin with cesium silicate solution followed by curing at 50 °C for 24 h in a sealed container. Heating of Cs-geopolymer above 1000 °C resulted in formation of crystalline pollucite (CsAlSi2O6). PDF refinement of the pollucite phase formed displayed an excellent fit over the 10−30 A range when compared with a cubic pollucite model. A poorer fit was attained from 1−10 A due to an additional amorphous phase present in the heated geopolymer. On the basis of PDF analysis, unheated Cs-geopolymer displayed structural ordering similar to pollucite up to a length scale of ∼9 A, despite some differences. Our results suggest that hydrated Cs+ ions were an integral part of the Cs-geopolymer structure and that most of the water present was not associated with Al-OH or Si-OH bonds.
TL;DR: In this paper, the short to medium range (∼1 nm) structural order of metakaolin-based KAlSi2O6·5.5H2O geopolymer was quantified and compared to zeolitic tetragonal leucite using the X-ray atomic pair distribution function technique.
Abstract: The atomic structure of geopolymers is often described as amorphous with a local structure that is equivalent to that of crystalline zeolites. However, this structural relationship has never been quantified beyond a first-nearest-neighbor bonding environment. In this study, the short to medium range (∼1 nm) structural order of metakaolin-based KAlSi2O6·5.5H2O geopolymer was quantified and compared to zeolitic tetragonal leucite (KAlSi2O6) using the X-ray atomic pair distribution function technique. Unheated KAlSi2O6·5.5H2O was found to be structurally similar to leucite out to a length of ∼8 A, but had increased medium range disorder over the 4.5 A 300 °C, changes in the short to medium range structure were observed due to dehydration and removal of chemically bound water. Crystallization of leucite occurred in samples heated beyond 1050 °C. Refinements of a leucite model against the PDF data for geopolymer heated to 1100 °C for 24 h yielded a good fit.
TL;DR: The use of binders such as phosphoric acid to consolidate aluminosilicates to form refractory products has been reported since the 1940s [1].
Abstract: The use of binders such as phosphoric acid to consolidate aluminosilicates to form refractory products has been reported since the 1940s [1]. Another class of materials formed by reacting concentrated alkaline silicate solutions with metakaolin (MK) has been termed geopolymers by Davidovits [2]. MK is made by heating (*750 C) of kaolin to render it X-ray amorphous and thus more reactive. In a geopolymer, the aluminosilicate is composed of cross-linked AlO4 and SiO4 tetrahedra, charge balanced with Na or K ions. It was shown by Cao et al. [3] that PO4 3can be incorporated in the geopolymer structure. Derrien et al. [4] added calcium phosphates to geopolymers, but they did not show whether the phosphate was part of the geopolymer structure. MacKenzie et al. [5] showed that the P occupied tetrahedral sites in the geopolymer with a different chemical shift from that of the aluminium phosphate reactants. Cao et al. [3] made nine compositions with Si/P molar ratios of 0.13–0.63 by adding H3PO4 to metakaolin and the maximum strength obtained was 55 MPa for the composition with Si/P = 0.21 molar ratio. Mackenzie et al. [5] made one composition of molar ratio of Si/P = 25 by adding a small amount of aluminium phosphate to an MK-based geopolymer, having molar ratios of Si/Al = 1.6 and Si/Na = 2.6. In the work reported here, the microstructure and the cold crushing strength (CCS) of the materials produced by alkaline-bonding and phosphoric acid-bonding of MK have been studied as a preliminary effort to develop these materials as replacements in some current uses and for future applications. Batches of 100 g of different compositions were made as listed in Table 1. The approximate chemical compositions of the nominal batch compositions based on the chemical analyses of the precursors from the suppliers resulted in molar ratios of Si/Al = 2 and Na/Al = 1 for MK-based geopolymers (MKGP). Similarly, the phosphoric acid-bonded MK (MKP) had molar ratios for Si/Al = 1 and Al/P = 1. MKGP (see Table 1) was prepared by adding MK to the sodium silicate solution. MKP was made by first mixing the deionised water (DIW) with 85 mass% H3PO4, then adding MK to the acid. Minimum amount of water was added to achieve the required workability, because any excess of water would increase the porosity and thus decrease strength. All the batches were mixed in a dental mixer (Renfert, Dental mixer, UK) for *5 min under vacuum at 300 rpm. To the MKGP and MKP batch compositions (see Table 1), 40 mass% sand was added before mixing (i.e. MKSGP and MKSP). Ordinary washed beach sand of size fractions, 81 mass% 250–500 lm, 17 mass% 125–250 lm and 2 mass%\125 lm, was used. Generally, sand is added in making mortar for building applications; hence, it was added for comparison with ordinary Portland cement mortar. The slurries produced in each instance were cast to form 25 mm dia 9 40 mm long cylindrical specimens in sealed polycarbonate containers for subsequent physical and mechanical testing. The cast items were kept at room temperature for 2 h before curing at 60 C for 24 h in an oven. After removing the seals, the samples were left at ambient temperature for 4 days before demoulding for MKGP. The MKP and MKSP samples were demoulded after 14 days when they were dry (they were still wet after D. S. Perera (&) J. V. Hanna J. Davis M. G. Blackford B. A. Latella Y. Sasaki E. R. Vance Australian Nuclear Science and Technology Organisation, PO Box 1, Menai, NSW 2234, Australia e-mail: pereradan@gmail.com; dsp@ansto.gov.au
TL;DR: In this paper, the microstructure and phase structure of the powders are investigated by SEM and XRD analysis, and the results show that the synthetic Al 2 O 3 -2SiO 2 powders have polycondensed property and their compressive strengthes are similar to that of nature metakaolin geopolymer materials.
TL;DR: In this paper, the authors used visible spectroscopy of Co2+ ions in a Co2-exchanged geopolymer to characterize the local geometry of the Co2 + ions and the regularity and shape of local structures accommodating these Co 2+ ions.
Abstract: Ion exchange of Na+ ions in a geopolymer by Cs+, NH4+, and Co2+ was used to characterize the accessibility of the inner volume of a Na-geopolymer (Si/Al 1.8) and the size of the rings controlling the mobility of cations in the geopolymer matrix. Ultraviolet (UV)—visible (vis) spectroscopy of Co2+ ions in the Co2+-exchanged geopolymer was used to characterize the local geometry of the Co2+ ions and the regularity and shape of local structures accommodating these Co2+ ions in the geopolymer matrix. Na-geopolymers exhibit ion-exchange properties similar to those of zeolites. All Na+ ions balancing Al atoms of the network of the as-prepared geopolymer could be replaced (ion-exchanged) by NH4+ or Co2+ ions. By analogy to zeolites, this indicates that all the Al atoms are accessible through rings containing at least eight Al and Si atoms. Co2+ ions in the geopolymer network are accommodated in two regular types of deformed six-membered or eight-membered rings. As indicated by the lower extent of Cs+ exchange, only one-half of the Al atoms are simultaneously accessible through 10-membered or larger rings. This indicates that neither regular alumosilicate six-membered rings nor the hexagonal prisms typical of some zeolitic structures are present in the geopolymer network.
28 Mar 2008
TL;DR: The semiamorphous three-dimensional networks of polymeric Na, K, Li, and Mg aluminosilicates of both poly(sialate) and poly(Sialate-siloxo) type, collectively known as geopolymers, harden at 20-120 C and are similar to thermoset resins, but are stable at up to 1200-1400 C without shrinkage as mentioned in this paper.
Abstract: The semiamorphous three-dimensional networks of polymeric Na, K, Li, and Mg aluminosilicates of both poly(sialate) and poly(sialate-siloxo) type, collectively known as geopolymers, harden at 20-120 C and are similar to thermoset resins, but are stable at up to 1200-1400 C without shrinkage A wide variety of alkaline-resistant inorganic reinforcements, notably SiC fibers, have been combined with geopolymer matrices to yield nonburning, nonsmoking high-temperature composites An SiC fiber-reinforced K-poly(sialate-siloxo) matrix, shaped and hardened at 70 C for 15 hr, develops flexural mean strengths of the order of 380 MPa that are retained after firing at up to 900 C 16 references
TL;DR: In this article, the authors used fluidized bed combustion bottom ash (FBC-BA) without any thermal activation as a partial or full replacement for kaolinitic raw material in geopolymerization.
TL;DR: In this article, a hydration mechanism for the formation of geopolymer by waterglass activation of granulated blast furnace slag is proposed in detail, and the results show that the network structures of glassy phases are disintegrated and there is not any new material phase formed in the early stage of hydration processes.
Abstract: The hydration mechanism and mineral phase structures by waterglass activation of granulated blast furnace slag (GBFS) are investigated in detail by means of XRD and FTIR. The results show that the network structures of glassy phases are disintegrated and there is not any new material phase formed in the early stage of hydration processes. With evolution of hydration, the polycondensation reaction takes place between [SiO4]4− and [AlO4]5− species and some new mineral phases are produced. A hydration mechanism for the formation of geopolymer by waterglass activation of GBFS is proposed in detail.
TL;DR: In this paper, alternating current impedance spectroscopy (ACIS) is used to monitor in situ the kinetics of geopolymer formation by alkali silicate activation of metakaolin at 40°C.
26 Mar 2008
TL;DR: In this article, the microstructure and chemical composition of the geopolymer bond as well as interface were studied with scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) in the SEM.
Abstract: Geopolymer cements (GPs) possess the ability to form high-strength, thermally-stable, and near-net shape structures at room temperature. It has been found that GPs can also be used to bond both metals and ceramics. Unlikeorganics, geopolymers can be heated to elevated temperatures and are easier to apply as compared to refractory adhesives. Many refractory adhesives require at least one, if not multiple curing steps, at elevated temperatures before they can be used in service. Geopolymers, however, need only be cured once at relatively low temperatures (40 - 80°C) to complete their curing process. Geopolymers contain no organic carriers often found in refractory adhesives, and can be processed from inexpensive and relatively non-toxic materials, i.e. watetglass and calcined aluminosilicate clays. This study details how geopolymer cements can be used to bond 6061-T6 aluminum alloy, 1008/1010 steel, alumina, and borosilicate glass at both ambient and elevated temperatures (25 - 430°C). Shear strength values of various samples were determined according to ASTM D1002-01 (single) and ASTM D3528-96 (double) shear lap tests. The microstructure and chemical composition of the geopolymer bond as well as interface were studied with scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) in the SEM.
TL;DR: In this article, the mechanical properties of four different types of geopolymers, but of the same composition, made using a combination of precursors, were determined, and the effect of adding sand (40 ¼wt%) on their mechanical properties was also determined.
Abstract: The mechanical properties of four different types of geopolymers, but of the same composition (Na/Al ≈ 1, Si/Al ≈ 2 molar ratio), made using a combination of precursors, were determined. The four types were: (i) sodium aluminate (NaAlO2/NaOH solution), Ludox (colloidal SiO2 solution) and metakaolin (MK), (SAGP), (ii) NaOH, fumed silica and MK (FSGP), (iii) Ludox, NaOH and MK (LGP) and (iv) commercial sodium silicate and MK (SGP). The highest crushing strength (CCS) value obtained was for SGP (70 MPa) and the lowest value was for SAGP (16 MPa). The highest modulus of rupture (MOR) value obtained was for LGP (9 MPa) and the lowest value was for SAGP (3 MPa). The fracture toughness (K1c) and Young’s modulus (E) showed the same trend. The effect of adding sand (40 wt%) on their mechanical properties was also determined. The K1c values increased up to 65% and E values increased up to 80% compared to samples free of sand. However, CCS and MOR values did not change much and gave mixed results. Overall, porosity is found to be the chief microstructural variable limiting the mechanical properties of the geopolymers. The properties of the geopolymers are compared with those of ordinary Portland cement.
TL;DR: In this paper, the authors demonstrate the important role of the aluminate species in the formation of aluminosilicate inorganic polymers, and demonstrate that severe mechanochemical processing (ball-milling for 60h or vibro-melting for 15min) leads to the formation four-, five-and sixfold coordinated Al as in metakaolinite, and enables viable polymers to be formed at 60°C which show the characteristic XRD, 27 Al and 29 Si MAS NMR spectra.
Abstract: Attempts to produce fully reacted aluminosilicate inorganic polymers (judged on the basis of their hardening at ambient temperatures, amorphous XRD patterns and their 27 Al and 29 Si NMR spectra) from the crystalline 2:1 layer lattice mineral pyrophyllite were unsuccessful. Although dehydroxylation of this pyrophyllite at 800 °C produces significant changes in the Al coordination, the dehydroxylate does not form a viable geopolymer, probably because of its retention of a crystalline 2:1 layer structure which encloses the Al–O sheet by Si–O sheets and prevents alkaline attack to form soluble aluminate species. Disruption of the crystalline 2:1 layer lattice structure by severe mechanochemical processing (ball-milling for 60 h or vibro-milling for 15 min) leads to the formation of four-, five- and sixfold coordinated Al as in metakaolinite, and enables viable inorganic polymers to be formed at 60 °C which show the characteristic XRD, 27 Al and 29 Si MAS NMR spectra. These results illustrate the important role of the aluminate species in the formation of aluminosilicate inorganic polymers.
TL;DR: In this article, the use of fly ash-based geopolymer binders to immobilize chromium is investigated in detail, with particular regard to the role of the sulfide ion as a reductant for Cr(VI) treatment.