Ancient organo-mineral geopolymer in South-American Monuments: Organic matter in andesite stone. SEM and petrographic evidence

Davidovits, Joseph; Huamán, Luis; Davidovits, Ralph

doi:10.1016/j.ceramint.2019.01.024

Cited by 33 publications

(23 citation statements)

References 2 publications

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“…The displacement of this dome towards large values of 2 θ reflects the depolymerization of MK‐MY3 and the polycondensation of dissolved species, 17 leading to the formation of a poly(phosphosiloxy) network 28,29 characteristic of geopolymeric types of cement in an acidic environment. The XRD pattern showed the formation of new crystalline phases (including Joint Committee on Powder Diffraction Standards (JCPDS) data) such as monetite (CaHPO 4 , JCPDS 1070‐0360) 30 (M), brushite (CaHPO 4 ⋅2H 2 O, JCPDS 00009‐0077) 30 (B) and berlinite or aluminium phosphate (AlPO4, JCPDS 10‐0423) 31 (AP) which are formed during geopolymerization. The presence of M and B was attributed to the reaction between phosphoric acid and calcite from eggshells.…”

Section: Resultsmentioning

confidence: 99%

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Removal of lead ions from aqueous solution using phosphate‐based geopolymer cement composite

Njimou

Pengou

Tchakouté

et al. 2021

J of Chemical Tech & Biotech

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BACKGROUND Water contaminated by heavy metals has many negative impacts on human health and the environment. According to the UN's sustainable development goals, preserving natural resources will have positive impacts on living conditions by reducing diseases. In this study, a novel adsorbent synthesized from phosphate‐based geopolymer cement composite material was developed and evaluated for lead removal from aqueous solutions. The developed adsorbent is made from natural resources using a facile protocol, and thus it is suitable for both developed and developing countries. RESULTS Analyses of mineralogical composition, pore‐size distribution and surface of the synthesized phosphate‐based geopolymer cement composite were performed. A microporous structure was observed from the microstructural characterization. Geopolymer cement was immobilized with sodium alginate to fabricate alginate–geopolymer cement beads (Alg/GES). The parameters influencing the adsorption process were investigated in batch mode. The obtained results showed that the adsorption capacity of Pb(II) ions increased with time and equilibrium was reached in 90 min. The optimum adsorption pH was 4.17. The experimental results showed that the adsorption equilibrium of Pb(II) on Alg/GES was well described by the Freundlich and Langmuir models whereas the adsorption rate was well fitted by the pseudo‐second‐order kinetics model. The maximum adsorption capacity obtained from the Langmuir isotherm was qmax = 0.38 mmol g−1. From the Dubinin–Radushkevitch isotherm model, the value of the free adsorption energy was 41 kJ mol−1. CONCLUSIONS Compared with other adsorbents, Alg/GES exhibited a greater adsorption capacity confirming that the phosphate‐based geopolymer cement can be suitable for removal of heavy metals from wastewaters. © 2021 Society of Chemical Industry

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Section: Resultsmentioning

confidence: 99%

“…This aluminium subsequently reacts. In brief, the synthesis mechanisms are detailed below 29,31,32 : Step 1: Preferential binding of the free oxygen atom of a siloxane group with a proton produced from the deprotonation of phosphoric acid in aqueous solution (Eqn (10)). …”

Section: Resultsmentioning

confidence: 99%

Removal of lead ions from aqueous solution using phosphate‐based geopolymer cement composite

Njimou

Pengou

Tchakouté

et al. 2021

J of Chemical Tech & Biotech

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“…Over the designated time span, the geopolymer stationary phase did not show any significant drift in retention times for the test analytes (Figure a). According to both the Davidovits and Barbosa geopolymer network model, the oxygen atoms are mainly bonded to other non-hydrogen atoms, thus limiting the number of free surface silanol groups. ,− Furthermore, geopolymers are known to have exceedingly low water solubility. , …”

Section: Resultsmentioning

confidence: 99%

Geopolymers as a New Class of High pH Stable Supports with Different Chromatographic Selectivity

et al. 2018

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Geopolymers belong to an interesting class of X-ray amorphous polycondensed aluminosilicate ceramic solids. The high mechanical strength, chemical stability in basic conditions, and water insolubility make geopolymers a unique solid support in separation science. This work describes a new straightforward synthetic procedure for making spherical porous geopolymer particles with high surface area which are amenable for chromatographic purposes. In-depth physicochemical evaluation of geopolymers is conducted via particle size distribution, porosity measurements, X-ray diffraction, pH titration, and energy-dispersive spectroscopy and compared with silica, titania, and zirconia. Chromatographic selectivity shows that the surface chemistry of geopolymers has strong hydrophilic and electrostatic character, which makes it different from 36 chromatographic columns. Hydrophilic interaction liquid chromatography in columns packed with geopolymer particles shows different selectivity than that in silica columns, with excellent peak shapes. Phosphate or fluoride additives are not required as they are for zirconia or titania phase.

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“…Recently, Davidovits developed research characterizing the material present in ancient monuments of pre-Columbian civilizations in South America, concluding that they were alkali-activated materials [11]. The studies carried out between 2016 and 2019 in the Tiahuanaco monuments (Tiwanaku/Pumapunku), Bolivia, and other monuments in Peru complement the studies carried out in the 70s and 80s and prove the durability of alkali-activated materials [12].…”

Section: Historical Aspectsmentioning

confidence: 92%

Reaction mechanisms of alkali-activated materials

Marvila

Azevedo

Vieira

2021

Rev. IBRACON Estrut. Mater.

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The Alkali-Activated Materials (AAM) are defined as materials obtained through the reaction between precursors and activators, and are separated into two classes depending on the products formed in the reaction, those rich in calcium, as the blast furnace slag, whose Ca/(Si+Al) ratio is higher than 1; and poor in calcium, which is the geopolymers subclass. In this review article, some bibliographical aspects were discussed regarding the discovery of these materials, through research conducted by Victor Glukhovsky and through the characterization of historical monuments by Davidovits, which began in the 50s and 60s and persist to the present day. The main products obtained in the alkaline activation reaction were also addressed, using the definition of polysialates and zeolites, in the case of geopolymers, and the tobermorite structure, in the case of materials rich in calcium. The main steps of the alkali-activated reaction, such as dissolution, condensation, polycondensation, crystallization, and hardening, were discussed. Some techniques for characterizing the AA reaction products were also examined, such as X-ray diffraction (XRD), nuclear magnetic resonance spectrometry (NMR), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy (SEM). Finally, the main factors that interfere in the kinetics of AA reactions were explored, in which the type of cure and the activating solution used in the alkali-activated materials production stands out.

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Ancient organo-mineral geopolymer in South-American Monuments: Organic matter in andesite stone. SEM and petrographic evidence

Cited by 33 publications

References 2 publications

Removal of lead ions from aqueous solution using phosphate‐based geopolymer cement composite

Removal of lead ions from aqueous solution using phosphate‐based geopolymer cement composite

Geopolymers as a New Class of High pH Stable Supports with Different Chromatographic Selectivity

Reaction mechanisms of alkali-activated materials

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