Aluminosilicate Solids Research Articles

Dissolution processes, hydrolysis and condensation reactions during geopolymer synthesis: Part I—Low Si/Al ratio systems

Initial geopolymeric reaction processes governing dissolution of solid aluminosilicate particles in alkali solutions have been investigated using conventional experimental techniques, and the data analysed by speciation predictions of the partial charge model (PCM). For metakaolin powders activated with 5.0 M NaOH, solid-state nuclear magnetic resonance (NMR) spectra disclose the existence of monomeric [Al(OH)4]− species after two hours of dissolution, consistent with PCM predictions. However, no equivalent monomeric silicate species were observed for 5.0–10.0 M NaOH activator solutions characteristic of systems with nominal Si/Al ≤ 1. The apparent absence of monomeric silicate species suggest rapid condensation of silicate units with [Al(OH)4]− to generate aluminosilicate species, as indicated by the evolution of the shoulder at around −87 ppm in the 29Si NMR spectra. Of the two possible stable silicate species [SiO2(OH)2]2− and [SiO(OH)3]−, the latter appears most likely to condense with [Al(OH)4]− to produce aluminosilicate oligomers, from which larger oligomers subsequently form through further condensation with [Al(OH)4]− leading to a gradual build up of aluminosilicate networks and a lowering of system alkalinity. This dissolution and hydrolysis sequence at the early stages of synthesis suggests a reaction path wholly consistent with predictions of the partial charge model.

Reactions between sodium and kaolin during gasification of a low-rank coal

The experimental results from the reactions between a low-rank coal containing sodium either in the form of ion-exchanged carboxylate or physical impregnation with NaCl, with kaolin during pyrolysis in nitrogen and gasification with steam or carbon dioxide in conditions corresponding to atmospheric FBG are presented. Sodium and kaolin react to form sodium aluminosilicates. Thermodynamic equilibrium predictions have indicated the formation of either a solid sodium aluminosilicate nepheline, Na 2O·Al 2O 3·2SiO 2 or liquid albite, Na 2O·Al 2O 3·6SiO 2 during coal gasification. The reaction between kaolin and either forms of sodium present in the coal is more effective in steam than in nitrogen or carbon dioxide. This results principally in the preservation of meta-kaolinite hexagonal crystal structure and the formation of a high melting point sodium aluminosilicate nepheline, Na 2O·Al 2O 3·2SiO 2 or its polymorph carnegietite. It appears that the catalytic effect of carboxylate sodium has been reduced by the binding of sodium readily through the reaction with kaolin, resulting in lower char conversion. During gasification with steam at least 20 wt.% of sodium present in coal as sodium chloride reacted into insoluble aluminosilicates. No sodium silicate or liquid albite formation was detected in any of the samples. It can be expected that during gasification of coal containing sodium in the presence of kaolin, the formation of solid aluminosilicates, principally nepheline, should help to avoid the formation of liquid silicates and the problems associated with agglomeration and potentially defluidisation of a fluidised bed.

Synthesis and Photochemical Properties of Poly(2,5-dimethoxy-p-phenylenevinylene) Hosted in the Intergallery Spaces of Montmorillonite

Poly(2,5-dimethoxy-p-phenylenevinylene) (dMeOPPV) has been formed in the intergallery spacing of a montmorillonite by introducing the (2,5-dimethoxy-1,4-phenylene)bis(methylene-S-tetrahydrothiophenium) monomer by ion exchange, increasing the basicity of the solid aluminosilicate with Cs(+) and subsequent heating at 200 degrees C. dMeOPPV@montmorillonite was characterized by optical spectroscopy, FT-IR spectroscopy, solid-state (13)C NMR, photoluminescence, and chemical analysis. All the data are compatible with that reported in the literature for pure dMeOPPV. The dMeOPPV polymer incorporated inside montmorillonite exhibits a green light emission which makes the organic polymer very attractive for its application in polymer light-emitting diodes (PLEDs). The new polymeric material can be submitted to laser irradiation (laser power, 10 mJ pulse(-1)) under oxygen without decomposition.

Mechanisms controlling acid neutralization and metal mobility within a Ni-rich tailings impoundment

Low-quality pore waters containing high concentrations of dissolved H +, SO 4, and metals have been generated in the East Tailings Management Area at Lynn Lake, Manitoba, as a result of sulfide-mineral oxidation. To assess the abundance, distribution, and solid-phase associations of S, Fe, and trace metals, the tailings pore water was analyzed, and investigations of the geochemical and mineralogical characteristics of the tailings solids were completed. The results were used to delineate the mechanisms that control acid neutralization, metal release, and metal attenuation. Migration of the low-pH conditions through the vadose zone is limited by acid-neutralization reactions, resulting in the development of distinct pore-water pH zones at depth; the neutralization reactions involve carbonate (pH ⩾ 5.7), Al-hydroxide (pH ⩾ 4.0), and aluminosilicate solids. As the zone of low-pH pore water expands, the pH will then be primarily controlled by less soluble solids, such as Fe(III) oxyhydroxides (pH < 3.5) and the relatively more recalcitrant aluminosilicates (pH ⩾ 1.3). Precipitation/dissolution reactions involving secondary Fe(III) oxyhydroxides and hydroxysulfates control the concentrations of dissolved Fe(III). Concentrations of dissolved SO 4 are principally controlled by the formation of gypsum and jarosite. Geochemical extractions indicate that the solid-phase concentrations of Ni, Co, and Zn are associated predominantly with reducible and acid-soluble fractions. The concentrations of dissolved trace metals are therefore primarily controlled by adsorption/complexation and (or) co-precipitation/dissolution reactions involving secondary Fe(III) oxyhydroxide and hydroxysulfate minerals. Concentrations of dissolved metals with relatively low mobility, such as Cu, are also controlled by the precipitation of discrete minerals. Because the major proportion of metals is sequestered through adsorption and (or) co-precipitation, the metals are susceptible to remobilization if low-pH or reducing conditions develop within the tailings.

Reaction mechanisms in the geopolymeric conversion of inorganic waste to useful products

High-performance materials for construction, waste immobilisation and an ever-growing range of niche applications are produced by the reaction sequence known as ‘geopolymerisation’. In this process, an alkaline activating solution reacts with a solid aluminosilicate source, with solidification possible within minutes and very rapid early strength development. Geopolymers have been observed to display remarkable chemical and thermal stability, but due to their largely X-ray amorphous nature have only recently been accurately characterised. It has previously been shown that both fly ash and ground granulated blast furnace slag are highly effective as solid constituents of geopolymer reaction slurries, providing readily soluble alumina and silica that undergo a dissolution–reorientation–solidification process to form a geopolymeric material. Here a conceptual model for geopolymerisation is presented, allowing elucidation of the individual mechanistic steps involved in this complex and rapid process. The model is based on the reactions known to occur in the weathering of aluminosilicate minerals under alkaline conditions, which occur in a highly accelerated manner under the conditions required for geopolymerisation. Transformation of the waste materials to the mixture of gel and nanocrystalline/semicrystalline phases comprising the geopolymeric product is described. Presence of calcium in the solid waste materials affects the process of geopolymerisation by providing extra nucleation sites for precipitation of dissolved species, which may be used to tailor setting times and material properties if desired. Application of geopolymer technology in remediation of toxic or radioactive contaminants will depend on the ability to analyse and predict long-term durability and stability based on initial mix formulation. The model presented here provides a framework by which this will be made possible.

Uranium Sorption on Solid Aluminosilicate Phases under Caustic Conditions

:The formation of aluminosilicate scales in the High Level Waste Evaporators at the Savannah River Site led to curtailed operation and an expensive cleaning evolution due in part to the presence of enriched uranium in the scale. Therefore, the sorption behavior of uranium species and sodium aluminosilicate (NAS) solid phases in nitrate/nitrite-rich sodium aluminosilicate solutions were studied under well-defined conditions at 22°C and agitation rate of 400 rpm. The NAS solids comprised four well-characterized phases of amorphous, zeolite A, sodalite, and cancrinite. Pure, synthetic sodium diuranate (Na2U2O7) crystals were precipitated and used as the base/reference U-containing compound.The studies of the sorption behavior of U-containing species on NAS solid phases were conducted under conditions where no detectable dissolution, precipitation, or crystallographic phase transformation of the NAS adsorbent phases were observed over a 6h test period. The uranium sorption capacities were reached typically within 3h. The uranium capacities were measured 6.36 to 9.3mgUkg−1 NAS solid for the Zeolite A and cancrinite phase. The amorphous and sodalite phase had higher uranium loading that measured between 19 and 58mgUkg−l NAS solid.

Novel concept of cleansing liquid steel of solid oxide inclusions by cullet injection in ladle

Disclosure is made of a novel process of steel refining in the ladle with cored wire injection of soda lime cullets to cleanse the steel of solid oxide, aluminosilicate and sulphide inclusions. This refining process is expected to improve steel castability, minimise surface defects in the casting, improve many metallurgical properties of steels for various applications and improve the machinability rating of resulphurised, free machining steel for continuous casting.

The adsorption and decomposition of cyanogen chloride by modified inorganic molecular sieves

Aluminosilicate and silicate porous solids have been evaluated as supports for triethylenediamine (TEDA) for the adsorption and decomposition of cyanogen chloride. A series of silica-gel supports has been used to study the effect of varying pore size. A series of faujasitic zeolites has been used to examine the effect of the cation exchange capacity of the support and the type of exchangeable cation. Results show that the activity of adsorbed TEDA towards cyanogen chloride appears to increase with increasing support pore diameter, and TEDA seems to be activated by basic adsorption sites on the support. Cesium-exchanged zeolite supports are particularly active. In general, zeolite supports appear to confer significantly higher activity to TEDA than traditional activated carbon supports. A series of mesoporous MCM-41 and AlMCM-41 supports has also been studied, but the activities of adsorbed TEDA are lower than expected. Significantly, the specific surface area of the inorganic supports does not seem to be a primary factor in controlling adsorbed TEDA activity.

Role of Aluminosilicate deposits in Lead and Copper Corrosion

Aluminosilicates frequently deposit onto plumbing materials in distribution systems. Such solids were previously believed to provide some degree of corrosion protection to pipes—although at the expense of increased head loss, reduced flow, and consumer complaints related to postprecipitation. However, this work demonstrates that new copper and lead pipe sections did not benefit from the deposition of aluminosilicate solids. In fact, in most situations the presence of solids actually caused the release of more metal to drinking water compared with solutions without solids. Final pH played a key role in determining the extent of copper corrosion, and the aluminum deposits prevented increases in pH during stagnation through a buffering action.

Low-temperature synthesized aluminosilicate glasses. Part III Influence of the composition of the silicate solution on production, structure and properties

The low-temperature reaction between an aqueous sodium or potassium silicate solution and metakaolinite yields a solid aluminosilicate. The influence of the molar ratios H2O/R2O (between 6.6 and 21.0) and SiO2/R2O (between 0.0 and 2.3) of the silicate solution (R=Na or K) on the aluminosilicate's production, on the reaction stoichiometry and on the aluminosilicate's molecular structure is studied with differential scanning calorimetry, 27Al and 29Si magic angle spinning nuclear magnetic resonance (MAS NMR), cross-polarization MAS NMR, Fourier transform infrared spectroscopy and X-ray diffractometry. The reaction stoichiometry is determined by a one to one ratio for R/Al. H2O/R2O has no influence on the molecular structure of the aluminosilicate. Aluminium in the aluminosilicate is four-fold coordinated for the whole range of silicate solutions investigated. Moreover, Si and Al are homogeneously distributed and the ratio Al/Si in the aluminosilicate is the same as in the reaction mixture if the stoichiometric one-to-one ratio for R/Al is used. If SiO2/R2O in the Na-silicate solution is equal to or higher than 0.8, the low-temperature reaction yields an amorphous aluminosilicate or “inorganic polymer glass”. For smaller values of SiO2/R2O the Na-aluminosilicates are partially crystalline. Thermomechanical analysis and dynamic mechanical analysis indicate that a variation in the composition of the amorphous aluminosilicates can shift the glass transition over a few hundreds of degrees, with a minimum value of 650°C.

Application of sol-gel process to H-zeolite synthesis over amorphous aluminosilicate materials

The impregnation preparation of H-zeolite over amorphous aluminosilicate solids (cracking catalysts) is compared with new synthesis procedures based on sol-gel process. The characterization results show that the H-zeolite reacts with the intermediates of the amorphous aluminosilicate.

Simultaneous condensation and reaction of metal compound vapors in porous solids

High-temperature interactions of metal compound vapors with solids are important in processes like coal conversion, waste incineration, catalyst poisoning, chemical vapor deposition, and chemical vapor infiltration. In this study, the interactions of alkali-metal vapors with porous aluminosilicate solids are investigated

Stability relationships between solid cesium aluminosilicates in aqueous solutions at 200 °C

Interconversion reactions among the solids SiO2 (quartz and fused), γ-AlOOH (boehmite), CsAlSiO4, CsAlSi2O6 (pollucite), and CsAlSi5O12, in contact with aqueous solutions at 200 °C, have been investigated. Results support earlier suggestions that CsAlSi5O12 is not stable with respect to CsAlSi2O6 + SiO2. CsAlSiO4 is only stable, if at all, when the activity product of dissolved Cs+ and OH−, with respect to unit molality standard states, exceeds about 10−2. CsAlSi2O6 is stable with respect to boehmite and quartz when the cesium hydroxide activity product exceeds 10−7.8±1.5. The significance of these results to the possible immobilization of radioactive cesium as a solid aluminosilicate is discussed. Based on a comparison with published estimates of enthalpies of formation, the following revised values are suggested:[Formula: see text]Keywords: cesium aluminosilicates, enthalpy of formation, hydrothermal reactions, pollucite, thermodynamic stability.

Contributions of Isotope Research to the Knowledge of the Distribution Coefficients of Rare Earth Elements between Natural Aluminosilicates and their Molten Phases

The distribution coefficients D of yttrium and the lanthanides between solid and liquid natural aluminosilicates can be described in terms of an extension of Schuetze's [1] incremental method for calculating oxygen isotope effects in silicate systems: log D = k + S · ΔI, where , ΔI the difference of the 18O indices of the liquid and the solid phase and k and S coefficients to be determined empirically. The coefficient k accounts for the effect of the aggregational state, particularly the water content, S accounts for the effect of the degree of linking of the (Si, Al)O4 tetrahedrons in the phases being in equilibrium on the distribution coefficients. The dependence of D, k and S on the atomic number can be understood in terms of the radii of the hydrated and not hydrated lanthanide ions. The constraints on the structural properties of magmas are discussed.

Some Geochemical Applications of a Semi-Empirical Approach for Estimating Distribution Coefficients of a Series of Cations between Liquid Aluminosilicates and their Crystallization Products

The distribution coefficients of alkali, alkaline earth, rare earth and a series of other elements between solid and liquid natural aluminosilicate systems can be estimated by a semi-empirical equation which can be derived by extension of Schuetze's incremental method for calculating oxygen isotope effects in silicate systems. This equation is used for investigating the partial melting of mantle wedge and subducted oceanic crust as potential sources of magmas giving rise to continental growth and for evaluating the history of igneous rocks. A series of geochemical criteria are derived for attributing igneous rocks to common parent magmas and for contributing to the estimation of the length of intrusive pathways. Particular attention is devoted to the evaluation of the geochemical behaviour of the rare earth elements.

High-resolution solid-state 29Si and 27Al n.m.r. of aluminosilicate intermediates in zeolite A synthesis

Solid aluminosilicate gels formed as intermediates in zeolite A synthesis were studied by 29Si and 27Al magic angle spinning n.m.r. The spectra reveal that the initial gel consists mainly of tetrahedral Si(OAl) 4 and Al(OSi) 4 building units which form an amorphous structure with alternating Si,Al ordering. With increasing time of heating of the reaction mixture the transformation of the amorphous gel phase into highly crystalline zeolite Na-A can be followed by characteristic changes of the n.m.r. spectra. By comparison with previous studies it is concluded that the composition and structural properties of the initially formed gel may be highly dependent on the specific mode of preparation.

Detection of imogolite in soils using solid state 29Si NMR

High resolution solid state 29Si-NMR has recently been used to examine silicates, and synthetic and natural zeolites1–4. This has been possible through the use of dipolar decoupling, magicangle spinning and cross-polarization techniques which have enabled line narrowing and also considerable signal enhancement for 29Si nuclei in close proximity to protons. It has been found that isotropic 29Si chemical shifts in solids and solutions are generally similar and depend mainly on the degree of condensation of silicon–oxygen tetrahedra1 For silicates, increasing condensation from single (Q0, −66 to −72 p.p.m.) to double tetrahedra (Q1, −78 to −82 p.p.m.), to chains (Q2, −86 to −88 p.p.m.) and cyclic layered structures (Q3, −107 to −109 p.p.m.) leads to increasing diamagnetic shielding. In solid aluminosilicates, the 29Si chemical shift is sensitive to the substitution of aluminium. A further important point was that the 29Si linewidth in aluminosilicates is sensitive to the regularity of aluminium distribution in the lattice. Thus 29Si-NMR has obvious potential for the elucidation of the coordination of silicon in soils and mineral components. We report here the first 29Si-NMR study of the clay mineral imogolite, and show that 29Si-NMR is an excellent analytical technique for the identification of imogolite (or imogolite like materials, that is proto-imogolite) in clay fractions. The observed chemical shift of imogolite (−78 p.p.m.) is consistent with the proposal that imogolite is a tubular hydrated aluminosilicate in which silicon tetrahedra are isolated by coordination through oxygen with three aluminium atoms and one proton.