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Inorganic polymers (geopolymers) were synthesized by alkali activation of water treatment residue, a waste material containing aluminosilicates and a significant concentration of iron in the form of a ferric nanoparticle oxide gel. The effect on the structures of these geopolymers of incorporating the heavy metals chromium, zinc and iron, as occur in industrial wastewaters, was studied by their addition at the geopolymer synthesis stage, both as the pre-prepared hydroxides and as 1 M nitrate solutions. The heavy metals form several new crystalline phases, but the geopolymers display typical solid-state 27Al and 29Si MAS NMR characteristics. The 28-day strengths of the geopolymers without the metals (up to 11.2 MPa) were significantly degraded by the presence of the heavy metals, particularly 1 M zinc nitrate solution. The deleterious effect of the heavy metals on the strength may arise from their presence as the hydroxides rather than their incorporation as charge-balancing cations in the geopolymer structure. Leaching tests in simulated acid rain indicate that the geopolymers with molar ratios of SiO2/Al2O3 = 1.78 are capable of immobilizing all three metals to within safe leachate levels. The geopolymers are sufficiently strong to withstand handling and transportation and are capable of immobilizing wastes containing these heavy metals for storage or disposal.

Novel photoactive composites of cubic Cu2O nanoparticles with aluminosilicate geopolymers were prepared and their structure was shown by SEM/EDS and TEM. XRD, FTIR, 27Al and 29Si MAS NMR to consist of a well-reacted geopolymer matrix containing homogeneously dispersed Cu2O nanoparticles. Under dark conditions, both the geopolymer matrix and the composites were shown to adsorb a model organic compound (methylene blue, chosen for its colour stability at high pH) by a process which follows pseudo-first-order kinetics and can be described by Langmuir-type isotherms. At concentrations >20 wt%, the oxide decreases the adsorption rate by blocking the active adsorption sites of the geopolymer. Under UV radiation, the composites remove the methylene blue by a combination of adsorption and photodegradation, without deterioration of the geopolymer structure or the photoactive Cu2O component, as evidenced by 63Cu NQR spectroscopy, suggesting that these geopolymer composites should function as useful new materials for the removal of organic pollutants from water or the atmosphere.

Attempts to synthesise magnesium-containing analogues of aluminosilicate geopolymers from the 1:1 and 2:1 layer magnesiosilicate minerals chrysotile and talc, as well as the magnesium mineral sepiolite are reported. The effect of pre-treating these starting minerals by grinding and/or dehydroxylation was also investigated by XRD, 29Si and natural-abundance 25Mg solid-state magic angle spinning (MAS) NMR spectroscopy. The products from sepiolite most closely resembled an aluminosilicate geopolymer, setting at 40 °C to an X-ray amorphous product containing a broad characteristic 29Si MAS NMR resonance at −90 ppm. The 25Mg MAS NMR spectrum of this product also showed evidence that some of the Mg was located in tetrahedral sites, as expected for a conventional geopolymer. A similar 25Mg MAS NMR result was obtained for chrysotile, but talc proved to be extremely resistant to geopolymer synthesis, requiring treatment at 120 °C for 3 days to set to a friable material retaining the XRD and NMR characteristics of the original talc or its crystalline dehydroxylation products. This lack of reactivity may be related to the 2:1 layer-lattice talc structure, or to the fact that a suitably reactive amorphous product is not formed upon dehydroxylation.

Lithium aluminosilicate inorganic polymers were synthesised from dehydroxylated kaolin-type clay (halloysite) by the conventional method under highly alkaline conditions with lithium hydroxide or lithium silicate solutions of two different Li2O/SiO2 molar ratios. Variants were also developed of a solid-state synthesis method involving the thermal reaction of dehydroxylated halloysite with LiOH followed by hydration of the product. The molar compositions of the materials prepared by all three methods (SiO2/Al2O3 = 2.41–3.27, Li2O/SiO2 = 0.30–0.61, and H2O/Li2O = 9.33–10.40) fall within the range of compositions previously reported to produce viable geopolymers. Curing at 40 °C produces solid samples of varying viability depending on the amount of synthesis water. The cured materials are not characteristically X-ray amorphous, but contain the lithium zeolites Li-ABW and fibrous Li-EDI, the latter in the materials synthesised by solid-state reaction. The 27Al and 29Si MAS NMR spectra of the cured materials contain narrow resonances more characteristic of zeolites than of inorganic polymers. Heating the synthesised products at

A new synthesis method is described to produce aluminosilicate inorganic polymers by direct reaction of aluminium hydroxide with amorphous silica under alkaline conditions. XRD and 27Al and 29Si MAS NMR spectroscopy suggest that the reaction mechanism involves the dissolution of the aluminium hydroxide in the alkali. The best results are obtained with more reactive gibbsite of small particle size and X-ray amorphous ρ-alumina containing 5-fold coordinated Al, and with compositions in the previously reported optimum range (SiO2: Al2O3 = 3.0, M2O: SiO2 = 0.34, H2O: M2O = 9.4). Unreacted aluminium hydroxide occurs where there is insufficient silica for complete inorganic polymer formation but the reaction is less sensitive to variations in the K2O: Al2O3 and K2O: SiO2 ratios. Zeolite formation was not observed in any of the present samples. More complex alumina sources such as thermally activated hydrotalcite can also be used to form an inorganic polymer, but under the alkaline synthesis conditions the unused alumina reacts with the poorly crystalline MgO present to re-form hydrotalcite, presumably containing atmospheric carbonate as the interlayer anion. This synthesis method can also potentially be extended to hydroxides other than those of aluminium.

In vitro studies are reported of the behaviour of potassium aluminosilicate inorganic polymers containing 10 wt% Ca(OH)2, nanostructured calcium silicate and Ca3(PO4)2 exposed to simulated body fluid (SBF). Heating to 600 °C lowers the alkalinity of Ca3(PO4)2-containing samples, but their X-ray powder diffraction characteristics, 27Al, 29Si and 43Ca MAS NMR spectra are unchanged by heating. Exposure of the heated compounds to SBF usually results in the formation of the crystalline biomineral phases hydroxylapatite and hydroxycarbonate apatite in the samples containing Ca(OH)2 and Ca3(PO4)2, but scanning electron microscopy/energy dispersive spectroscopy suggests that all the samples in the present study form calcium phosphates on exposure to SBF. This conclusion is also consistent with the removal of P from the SBF by all the samples. The concentrations of Al leached from the samples containing nanostructured calcium silicate and Ca3(PO4)2 (0.05 and 0.47 ppm, respectively) are acceptable for biomaterials use, but apart from the Ca3(PO4)2-containing sample, which takes up Ca from the SBF, the levels of Ca released into the SBF by the other samples are well in excess of the published optimum amount for stimulation of new bone growth by gene transcription in osteoblasts. Only the calcium silicate-containing samples release Si into the SBF, but in a concentration that falls short of the optimum amount. The strength of all the present compounds after heating is probably adequate for applications as biomaterials, but the Ca3(PO4)2-containing compound shows slightly greater strength. Thus, on balance, the Ca3(PO4)2-containing compound appears to be the most promising as a bioactive material.

The DC electrical conductance of potassium aluminosilicate inorganic polymers (geopolymers) containing up to 6 wt% single-wall carbon nanotubes has been determined as a function of temperature up to 340 °C. After removal of the processing water during the first heating cycle, the conductance in subsequent heating cycles increases as a function of carbon nanotube content and temperature from 9.75 × 10−4 to 1.87 × 10−3 S m−1 in the composites containing 0 and 0.2 wt% carbon nanotubes, respectively, at 290 °C. By comparison, the electrical conductance of potassium inorganic polymer composites containing graphite was generally lower. The conductance activation energies of the carbon nanotube and graphite composites were similar, and decreased from about 55 to 5 kJ mole−1 with increasing carbon content. The tensile strengths of carbon nanotube and graphite-containing potassium geopolymer composites, determined by the Brazil method on 10–12 replicates, were about 2 MPa, and showed little change with increasing carbon nanotube content up to 0.3 wt%. By contrast, the tensile strengths of an analogous set of sodium composites were up to four times greater, possibly reflecting the necessity for less processing water in the synthesis of the sodium samples.

Phase formation in kaolinite heated at 1200°C in eight different reaction atmospheres in the presence and absence of carbon has been studied by solid-state magic angle spinning nuclear magnetic resonance (MAS NMR) and X-ray powder diffraction. Mullite (3Al2O3-2SiO2) and amorphous SiO2 are the principal products in all atmospheres. The amount of mullite formed is generally greater under vacuum and in reducing atmospheres, but the precise effect of the atmosphere is also modified by the presence of carbon. Vacuum and reducing atmospheres generally produce mullites of alumina: silica composition nearer 3∶2 than 2∶1 (estimated from unit cell measurements) and containing a higher proportion of Al*, i.e. tetrahedral aluminium associated with an oxygen defect (estimated by 27AlNMR measurements). The result of most significance to sialon formation is the detection by 29Si NMR of silicon oxynitride formation at 1200°C in systems containing either nitrogen or ammonia, in the presence of carbon. The preferential formation of Si-O-N bonds at such an early stage of the reaction under carbothermal conditions was confirmed by thermodynamic calculations, which also clarify other details of the complex interactions between the aluminosilicate, carbon, and the various gas atmospheres.

The room-temperature setting process in compacts of various silicate and non-silicate mineral particles bonded with sodium silicate was found to be markedly accelerated by treatment with the acidic gases CO2, S02 and H2S, but was unaffected by neutral or alkaline gases. Strength development increases with gassing time up to a maximum value which depends on the Si to Na ratio of the sodium silicate, the nature of the mineral matter and the gas used. Longer gassing times are needed to achieve ultimate strength with sodium silicates of higher pH and gases of lower solubility in water. The chemical species formed by reaction of CO2, S02 and H2S with sodium silicate were investigated by IR spectroscopy, X-ray diffraction and 29-Si solid state NMR spectroscopy.

Only very slight changes are observed in the29Si and27Al solid-sate magic-angle spinning NMR spectra of a montmorillonite containing almost equal numbers of octahedral aluminium and magnesium ions when its interlayer water is driven off by heating. The29Si NMR spectra are unaffected by dehydroxylation which begins at ∼ 450° C, but the27Al spectra show a decrease in total intensity, possibly due to the formation of 5-coordinated aluminium, with a slight increase in the intensity of the tetrahedral aluminium resonance. On the basis of these results, a structural model is proposed for the dehydroxylate phase and its formation mechanism is discussed. The destruction of the dehydroxylate X-ray pattern at ∼ 850° C and the subsequent recrystallization of the high-temperature products (β-quartz, enstatite and high-cordierite at ∼ 1100° C;β-cristobalite, enstatite and sapphirine at ∼ 1200° C) is accompanied by changes in the silicon and aluminium NMR spectra and in the57Fe Mbssbauer spectra which are fully consistent with the known structural features of these phases.

Studies of two muscovites of different iron contents, using solid-state NMR with magic-angle-spinning (MAS) combined with X-ray powder diffraction, thermal analysis and57Fe Mossbauer spectroscopy, suggest that dehydroxylation occurs by a homogeneous rather than an inhomogeneous mechanism, forming a dehydroxylate in which the aluminium is predominantly 5-coordinate. On further decomposition at about 1100° C, the tetrahedral layer and interlayer K+ form a feldspar-like phase similar to leucite (KAISi2O6), the remainder forming a spinel, which, contrary to previous suggestions, appears to contain little silicon. Further heating induces the formation of mullite (AI6Si2OP13), and, in the higher-iron sample, corundum (α-Al2O3), in addition to the feldspar-like phase. The presence of the iron impurity enhances the recrystallization reactions and promotes the conversion of mullite to corundum, which eventually becomes the sole aluminous product in the high-iron sample. In samples fired to higher temperatures, only the tetrahedral aluminium resonance is detectable by27AI NMR, probably because most of the iron is located in either the mullite or corundum phases, in which it broadens the octahedral aluminium resonance beyond detection.