Immobilisation of heavy metal in cement-based solidification/stabilisation: a review

Heavy metal-bearing waste usually needs solidification/stabilization (s/s) prior to landfill to lower the leaching rate. Cement is the most adaptable binder currently available for the immobilisation of heavy metals. The selection of cements and operating parameters depends upon an understanding of chemistry of the system. This paper discusses interactions of heavy metals and cement phases in the solidification/stabilisation process. It provides a clarification of heavy metal effects on cement hydration. According to the decomposition rate of minerals, heavy metals accelerate the hydration of tricalcium silicate (C3S) and Portland cement, although they retard the precipitation of portlandite due to the reduction of pH resulted from hydrolyses of heavy metal ions. The chemical mechanism relevant to the accelerating effect of heavy metals is considered to be H+ attacks on cement phases and the precipitation of calcium heavy metal double hydroxides, which consumes calcium ions and then promotes the decomposition Of C3S. In this work, molecular models of calcium silicate hydrate gel are presented based on the examination of Si-29 solid-state magic angle spinning/nuclear magnetic resonance (MAS/NMR). This paper also reviews immobilisation mechanisms of heavy metals in hydrated cement matrices, focusing on the sorption, precipitation and chemical incorporation of cement hydration products. It is concluded that further research oil the phase development during cement hydration in the presence of heavy metals and thermodynamic modelling is needed to improve effectiveness of cement-based s/s and extend this waste management technique. (C) 2008 Elsevier Ltd. All rights reserved.

Metal oxide photoanodes for solar hydrogen production

The development of sustainable hydrogen production is a key target in the further facilitation of a hydrogen economy. Solar hydrogen generation through the photolytic splitting of water sensitised by semiconductor materials is attractive as it is both renewable and does not lead to problematic by-products, unlike current hydrogen sources such as natural gas. Consequently, the development of these semiconductor materials has undergone considerable research since their discovery over 30 years ago and it would seem prescient to review the more practical results of this research. Among the critical factors influencing the choice of semiconductor material for photoelectrolysis of water are the band-gap energies, flat band potentials and stability towards photocorrosion; the latter of these points directs us to focus on metal oxides. Careful design of thin films of photocatalyst material can eliminate potential routes of losses in performance, i.e., recombination at grain boundaries. Methods to overcome these problems are discussed such as coupling a photoanode for photolysis of water to a photovoltaic cell in a 'tandem cell' device.

Characterisation of products of tricalcium silicate hydration in the presence of heavy metals

The hydration of tricalcium silicate (C(3)S) in the presence of heavy metal is very important to cement-based solidification/stabilisation (s/s) of waste. In this work, tricalcium silicate pastes and aqueous suspensions doped with nitrate salts of Zn(2+), Pb(2+), Cu(2+) and Cr(3+) were examined at different ages by X-ray powder diffraction (XRD), thermal analysis (DTA/TG) and (29)Si solid-state magic angle spinning/nuclear magnetic resonance (MAS/NMR). It was found that heavy metal doping accelerated C(3)S hydration, even though Zn(2+) doping exhibited a severe retardation effect at an early period of time of C(3)S hydration. Heavy metals retarded the precipitation of portlandite due to the reduction of pH resulted from the hydrolysis of heavy metal ions during C(3)S hydration. The contents of portlandite in the control, Cr(3+)-doped, Cu(2+)-doped, Pb(2+)-doped and Zn(2+)-doped C(3)S pastes aged 28 days were 16.7, 5.5, 5.5, 5.5, and <0.7%, respectively. Heavy metals co-precipitated with calcium as double hydroxides such as (Ca(2)Cr(OH)(7).3H(2)O, Ca(2)(OH)(4)4Cu(OH)(2).2H(2)O and CaZn(2)(OH)(6).2H(2)O). These compounds were identified as crystalline phases in heavy metal doping C(3)S suspensions and amorphous phases in heavy metal doping C(3)S pastes. (29)Si NMR data confirmed that heavy metals promoted the polymerisation of C-S-H gel in 1-year-old of C(3)S pastes. The average numbers of Si in C-S-H gel for the Zn(2+)-doped, Cu(2+)-doped, Cr(3+)-doped, control, and Pb(2+)-doped C(3)S pastes were 5.86, 5.11, 3.66, 3.62, and 3.52. And the corresponding Ca/Si ratios were 1.36, 1.41, 1.56, 1.57 and 1.56, respectively. This study also revealed that the presence of heavy metal facilitated the formation of calcium carbonate during C(3)S hydration process in the presence of carbon dioxide.

Adsorption of aqueous metal ions on oxygen and nitrogen functionalized nanoporous activated carbons

In this study, the adsorption characteristics of two series of oxygen and nitrogen functionalized activated carbons were investigated. These series were a low nitrogen content(similar to 1 wt % daf) carbon series derived from coconut shell and a high nitrogen content (similar to 8 wt % daf) carbon series derived from polyacrylonitrile. In both series, the oxygen contents were varied over the range similar to 2-22 wt % daf. The porous structures of the functionalized activated carbons were characterized using N-2 (77 K) and CO2 (273 K) adsorption. Only minor changes in the porous structure were observed in both series. This allowed the effect of changes in functional group concentrations on metal ion adsorption to be studied without major influences due to differences in porous structure characteristics. The surface group characteristics were examined by Fourier transform infrared (FTIR) spectroscopy, acid/base titrations, and measurement of the point of zero charge (pH(PZC)). The adsorption of aqueous metal ion species, M2+(aq), on acidic oxygen functional group sites mainly involves an ion exchange mechanism. The ratios of protons displaced to the amount of M2+(aq) metal species adsorbed have a linear relationship for the carbons with pH(PZC) <= 4.15. Hydrolysis of metal species in solution may affect the adsorption of metal ion species and displacement of protons. In the case of basic carbons, both protons and metal ions are adsorbed on the carbons. The complex nature of competitive adsorption between the proton and metal ion species and the amphoteric character of carbon surfaces are discussed in relation to the mechanism of adsorption.

From non-porous crystalline to amorphous microporous metal(IV) bisphosphonates

Porous layered hybrid materials have been prepared by the reaction of organo-bisphosphonate ligands, 4-(4'-phosphonophenoxy)phenylphosphonic, 4,4'-biphenylenbisphosphonic and phenylphosphonic acids, with metal(IV) cations (Zr and Sn). Crystalline Zr(IV) and Sn(IV) layered bisphosphonates were also prepared, which were non-porous. The amorphous M(IV) bisphosphonates showed variable compositions and textural properties ranging from mainly mesoporous to highly microporous solids with BET surface areas varying from 300 to 480 m(2) g(-1), micropore volumes ranging 0.10-0.20 cm(3)/g, and narrow porous size distributions for some materials. N-2 isotherms suggest that Sn(IV) derivatives show a comparatively higher micropore contribution than the Zr(IV) analogous at least for the ether-bisphosphonate hybrids. Sn(IV) bisphosphonates exhibit high microporosities without the need of using harmful DMSO as solvent. If ether-bisphosphonic acid is partially replaced by less expensive phenylphosphonic ligand, porous products are also obtained. P-31 and F-17 MAS NMR and XPS data revealed the presence of hydrogen-phosphonate groups and small (F-, Cl- and OH-) anions, which act as spacer ligands within the inorganic layers, in these hybrid materials. The complexity of the inorganic layers is higher for the Sn(IV) bisphosphonates likely due to the larger amount of small bridging anions including fluorides. It is suggested that the presence of these small inorganic ligands may be a key factor influencing both, the interaction of the inorganic layer with the bisphosphonate groups, which bridge the inorganic layers, and the generation of internal voids within a given inorganic layer. Preliminary studies of gases adsorption (H-2 and NO) have been carried out for selected Sn(IV) bisphosphonates. The H-2 adsorption capacity at 77 K and 1 bar was low, 0.26 wt%, but the NO adsorption capacity at similar to 1 bar and 298 K was relatively high, 4.2 wt%. Moreover, the hysteresis in the NO isotherms is indicative of partial strong irreversible adsorption of NO. (C) 2008 Elsevier Inc. All rights reserved.

Spatial patterns and autocorrelation in the response of microarthropods to soil pollutants: The example of oribatid mites in an abandoned mining and smelting area

Although exogenous factors such as pollutants can act on endogenous drivers (e.g. dispersion) of populations and create spatially autocorrelated distributions, most statistical techniques assume independence of error terms. As there are no studies on metal soil pollutants and microarthropods that explicitly analyse this key issue, we completed a field study of the correlation between Oribatida and metal concentrations in litter, organic matter and soil in an attempt to account for spatial patterns of both metals and mites. The 50-m wide study area had homogenous macroscopic features, steep Pb and Cu gradients and high levels of Zn and Cd. Spatial models failed to detect metal-oribatid relationships because the observed latitudinal and longitudinal gradients in oribatid assemblages were independent of the collinear gradients in the concentration of metals. It is therefore hypothesised that other spatially variable factors (e.g. fungi, reduced macrofauna) affect oribatid assemblages, which may be influenced by metals only indirectly. (C) 2009 Elsevier Ltd. All rights reserved.

LIQUID MARBLES GRANULATED USING SUPER-HYDROPHOBIC METAL POWDERS

Superhydrophobic (SH) particles based on a copper substrate were prepared by a silver deposition technique of different particle sizes from 10µm to 425µm. Such SH particles were found to be pH-responsive and liquid marbles formed using the SH copper substrate destabilised under certain pH conditions. The exposure to high concentrations of acidic or basic gases caused immediate collapse of the liquid marble. However, low concentrations of acidic and basic gases could diffuse across the shell of liquid marbles without adversely affecting the structure. Liquid marbles formed with large SH particles (425
µm) did not fully form a mono-layer around the liquid droplet. This phenomenon, whereby SH particles slide down the surface of the water droplet until an equilibrium position is reached, was studied using a mathematical approach, which related the angle to the vertical axis of the SH particles at t
he equilibrium F, to the shape of liquid marble and the contact angle, ?.

Lipoxidation products as biomarkers of oxidative damage to proteins during lipid peroxidation reactions

Oxidative stress is implicated in the pathogenesis of numerous disease processes including diabetes mellitus, atherosclerosis, ischaemia reperfusion injury and rheumatoid arthritis. Chemical modification of amino acids in protein during lipid peroxidation results in the formation of lipoxidation products which may serve as indicators of oxidative stress in vivo. The focus of the studies described here was initially to identify chemical modifications of protein derived exclusively from lipids in order to assess the role of lipid peroxidative damage in the pathogenesis of disease. Malondialdehye (MDA) and 4-hydroxynonenal (HNE) are well characterized oxidation products of polyunsaturated fatty acids on low-density lipoprotein (LDL) and adducts of these compounds have been detected by immunological means in atherosclerotic plaque. Thus, we first developed gas chromatography-mass spectrometry assays for the Schiff base adduct of MDA to lysine, the lysine-MDA-lysine diimine cross-link and the Michael addition product of HNE to lysine. Using these assays, we showed that the concentrations of all three compounds increased significantly in LDL during metal-catalysed oxidation in vitro. The concentration of the advanced glycation end-product N epsilon-(carboxymethyl)lysine (CML) also increased during LDL oxidation, while that of its putative carbohydrate precursor the Amadori compound N epsilon-(1-deoxyfructose-1-yl)lysine did not change, demonstrating that CML is a marker of both glycoxidation and lipoxidation reactions. These results suggest that MDA and HNE adducts to lysine residues should serve as biomarkers of lipid modification resulting from lipid peroxidation reactions, while CML may serve as a biomarker of general oxidative stress resulting from both carbohydrate and lipid oxidation reactions.

Synthesis of new vegetable oil-based polymeric materials

A crescente procura de recursos fosseis a que se tem assistido nos ultimos anos, tem resultado num crescimento sem precedentes dos precos, com consequencias imprevisiveis e que levara, no espaco de decadas, ao seu inevitavel esgotamento. A procura de um modelo de desenvolvimento sustentavel, baseado em recursos renovaveis e o grande desafio que se coloca a civilizacao no seculo XXI. A biomassa vegetal, atraves das designadas gBio-refinarias h, e uma alternativa logica para a producao de produtos quimicos e de materiais mas tambem de combustiveis e energia. Os oleos vegetais constituem uma das fracoes da biomassa vegetal, cuja exploracao tem merecido redobrada atencao nos ultimos anos, como fonte de materiais e de combustiveis. Assim, a presente dissertacao tem por objetivo o desenvolvimento de novos materiais polimericos derivados de oleos vegetais, seguindo duas abordagens distintas, nomeadamente a preparacao de polimeros atraves de polimerizacao por etapas e polimerizacao em cadeia (Parte B e C, respetivamente). Em primeiro lugar, foram sintetizados poliesteres alifaticos de cadeia longa a partir de monomeros provenientes do oleo de colza (Capitulo III). A auto-metatese do acido erucico com catalisadores de rutenio, seguida de hidrogenacao da ligacao dupla, originou o acido 1,26-hexacosanodioico, que por sua vez foi convertido em hexacosano-1,26-diol. Subsequentemente, a policondensacao do acido ƒ¿,ƒÖ-dicarboxilico de cadeia longa com o hexacosano-1,26-diol originou o poliester 26,26. O diacido C26 foi tambem polimerizado com outros alcano-diois de cadeia curta, nomeadamente o dodecano-1,12-diol e o butano-1,2-diol, produzindo, respetivamente, os poliesteres 12,26 e 4,26. Estes poliesteres de fontes 100% renovaveis possuem valores de Mn na ordem dos 8-14 kDa e valores de PDI entre 2.1 e 2.7. As propriedades destes poliesteres alifaticos foram avaliadas atraves de varias tecnicas, revelando elevada cristalinidade (com uma estrutura cristalina como a do polietileno) e elevadas temperaturas de fusao (74-104 ‹C), cristalizacao (68-92 ‹C) e degradacao (323-386 ‹C). Em segundo lugar, foram sintetizados polimeros lineares termo-reversiveis a partir de derivados do oleo de ricinio (Capitulo IV). Para tal foram preparados monomeros que incorporam aneis furanicos inseridos atraves do acoplamento tiol-eno, e que posteriormente foram polimerizados pela reacao de Diels-Alder (DA) entre os grupos furano (dieno A) e estruturas complementares do tipo maleimida (dienofilo B). Para as polimerizacoes DA foram consideradas duas abordagens diferentes, nomeadamente (i) o uso de monomeros com dois aneis furanicos terminais em conjunto com uma bismaleimida (sistemas AA+BB) e (ii) a utilizacao de um monomero que incorpora ambos os grupos reativos, furano e maleimida, na sua estrutura (sistema AB). Este estudo demonstrou claramente que ambas as estratégias foram bem sucedidas embora com diferentes resultados em termos da natureza dos produtos obtidos. Estes polímeros lineares apresentam valores relativamente baixos de Tg (-40 to -2 °C) devido à natureza flexível dos grupos separadores das funções reativas, e de Mn (4.5-9.0 kDa) dada a observada tendência de ciclização associada a concentrações baixas de monómero. A aplicação da reação de retro-DA aos polímeros em causa confirmou o seu caráter reversível, ou seja, a possibilidade de promover, em condições controladas, a despolimerização com recuperação dos monómeros de partida. Esta particularidade abre caminhos para materiais macromoleculares originais com aplicações promissoras tais como auto-reparação e reciclabilidade. Em terceiro lugar, sintetizaram-se polímeros não-lineares termo-reversíveis a partir de derivados do óleo de ricínio (Capítulo V). Para tal foram preparados monómeros trifuncionais e posteriormente polimerizados através da reação de DA entre os grupos reativos complementares furano/maleimida. Foram consideradas três abordagens distintas para preparar estes polímeros não-lineares, nomeadamente através da utilização de (i) um monómero bisfurânico em combinação com uma trismaleimida (sistema A2+B3) e (ii) um monómero trisfurânico em conjunto com uma bismaleimida (sistema A3+B2) que originaram materiais ramificados ou reticulados, e ainda (iii) a utilização de monómeros assimetricamente substituídos do tipo A2B ou AB2 capazes de originar estruturas macromoleculares hiper-ramificadas. Todos os sistemas apresentaram valores de Tg perto de 0 °C, o que era de esperar para estes materiais não-lineares. A aplicação da reação de retro-DA comprovou mais uma vez o caráter termo-reversível das polimerizações em causa. Em quarto lugar e último lugar, foram preparados copolímeros de acetato de vinilo (VAc) com monómeros derivados de óleo de girassol (Capítulo VI). Ésteres vinílicos de ácidos gordos (FAVE) foram sintetizados por transvinilação dos ácidos oleico e linoleico com VAc catalisada por um complexo de irídio. Os monómeros vinílicos preparados foram caracterizados e posteriormente homopolimerizados e copolimerizados com VAc através do uso dos grupos vinílicos terminais como função inicial de polimerização. A variação do tipo e quantidade de monómero FAVE e da quantidade de iniciador radicalar originou copolímeros de VAc com valores de Mn na gama de 1.2-3.0 kDa e valores de Tg de -5 a 16 °C. Os copolímeros foram avaliados em testes de cura oxidativa através das insaturações nas suas cadeias alifáticas para formar materiais reticulados, e os resultados sugerem que eles podem ser sistemas efetivos de cura para aplicações como tintas, vernizes e outros tipos de revestimento. Todos os materiais poliméricos preparados ao longo deste trabalho constituem contribuições atrativas para a área dos polímeros oriundos de recursos renováveis e representam uma prova indiscutível de que os óleos vegetais são percursores promissores de materiais macromoleculares com potenciais aplicações.

Metal speciation dynamics in colloidal ligand dispersions. Part 2: electrochemical lability

We investigate the dynamic nature of metal speciation in colloidal dispersions using a recently proposed theory [J.P. Pinheiro, M. Minor, H.P. Van Leeuwen, Langmuir, 21 (2005) 8635] for complexing ligands that are situated on the surface of the particles. The new approach effectively modifies the finite rates of association/dissociation of the colloidal metal complexes, thus invoking consideration of the two basic dynamic criteria: the association/dissociation kinetics of the volume complexation reaction (the ‘‘dynamic’’ criterion), and the interfacial flux of free metal to a macroscopic surface due to dissociation of complex species (the ‘‘lability’’ criterion). We demonstrate that the conventional approach for homogeneous systems that assume a smeared-out ligand distribution, overestimates both the dynamics and the lability of metal complexes when applied to colloidal ligands. It is also shown that the increase of lability with increasing particle radius, as expected for a homogeneous solution, is moderated for spherical microelectrodes and practically eliminated for planar electrodes.

DRIFT and DRUV spectroscopy methods for studying the interaction of metal compounds with native cellulose

Dissertação de mestrado, Qualidade em Análises, Faculdade de Ciências e Tecnologia, Universidade do Algarve, 2015

Reactions of polyhalogenated aromatic compounds and related ethers with metal/ammonia solutions

This work contains the results of a series of reduction studies on polyhalogenated aromatic compounds and related ethers using alkali metals in liquid ammonia. In general, polychlorobenzenes were reduced to t he parent aromatic hydrocarbon or to 1 ,4-cyc1ohexadiene, and dipheny1ethers were cleaved to the aroma tic hydrocarbon and a phenol. Chlorinated dipheny1ethers were r eductive1y dechlorinated in the process. For example, 4-chlorodipheny1- ether gave benzene and phenol. Pentach1orobenzene and certain tetrachlorobenzenes disproportionated to a fair degree during the reduction process if no added proton source was present. The disproportionation was attributed to a build-up of amide ion. Addition of ethanol completely suppressed the formation of any disproportionation products. In the reductions of certain dipheny1ethers , the reduction of one or both of the dipheny1ether rings occurred, along with the normal cleavage. This was more prevalent when lithium was the metal used . As a Sidelight, certain chloropheno1s were readily dechlorinated. In light of these results, the reductive detoxification of the chlorinated dibenzo-1,4-dioxins seems possible with alkali metals in l iquid ammonia.

Kinetic and product studies for the oxidtion of organic sulfides and sulfoxides in the presence of transition metal complexes

Rates and products of the oxidation of diphenyl sulfide, phenyl methyl sulfide, p-chlorophenyl methyl sulfide and diphenyl sulfoxide have been determined. Oxidants included t-Bu02H alone, t-Bu02H plus molybdenum or vanadium catalysts and the molybdenum peroxo complex Mo0(02)2*HMPT. Reactions were chiefly carried out in ethanol at temperatures ranging from 20° to 65°C. Oxidation of diphenyl sulfide by t-Bu02H in absolute ethanol at 65°C followed second-order kinetics with k2 = 5.61 x 10 G M~1s"1, and yielded only diphenyl sulfoxide. The Mo(C0)g-catalyzed reaction gave both the sulfoxide and the sulfone with consecutive third-order kinetics. Rate = k3[Mo][t-Bu02H][Ph2S] + k^[Mo][t-Bu02H][Ph2S0], where log k3 = 12.62 - 18500/RT, and log k^ = 10.73 - 17400/RT. In the absence of diphenyl sulfide, diphenyl sulfoxide did not react with t-Bu02H plus molybdenum catalysts, but was oxidized by t-Bu02H-V0(acac)2. The uncatalyzed oxidation of phenyl methyl sulfide by t-Bu02H in absolute ethanol at 65°C gave a second-order rate constant, k = 3.48 x 10~"5 M^s""1. With added Mo(C0)g, the product was mainly phenyl methyl sulfoxide; Rate = k3[Mo][t-Bu02H][PhSCH3] where log k3 = 22.0 - 44500/RT. Both diphenyl sulfide and diphenyl sulfoxide react readily with the molybdenum peroxy complex, Mo0(02)2'HMPT in absolute ethanol at 35°C, yielding diphenyl sulfone. The observed features are mainly in agreement with the literature on metal ion-catalyzed oxidations of organic compounds by hydroperoxides. These indicate the formation of an active catalyst and the complexation of t-Bu02H with the catalyst. However, the relatively large difference between the activation energies for diphenyl sulfide and phenyl methyl sulfide, and the non-reactivity of diphenyl sulfoxide suggest the involvement of sulfide in the production of an active species.