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1999 | Book

Natural Microporous Materials in Environmental Technology

Editors: P. Misaelides, F. Macášek, T. J. Pinnavaia, C. Colella

Publisher: Springer Netherlands

Book Series : NATO ASI Series

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Table of Contents

Frontmatter

Clay Minerals

Frontmatter
Structure and Chemical Characteristics of Modified Clays

Chemical modifications of various clay minerals from the smectite group are discussed. Acid activation, i.e., partial dissolution of smectites in inorganic acids, is a common treatment applied to produce laboratory samples as well as industrial materials, such as adsorbents, catalysts, etc. The reaction product of an acid dissolution of a clay is independent on the starting mineral used. It is a hydrous amorphous partly protonated high surface silica phase. Proton-saturated smectites, prepared either via mild acid treatment or using ion-exchangers, are unstable materials undergoing autotransformation to their (H,Al,Fe,Mg)-forms. Mildly acid-treated montmorillonites exhibit a high catalytic activity. Acid treatment of tetraalkylammonium cation exchanged smectites produces hybrid catalysts of increased catalytic activity because of the enhanced hydrophobicity of the organoclay. Acid attack of the clay structure occurs not only from the particle edges but also from the interlayers.The negative charge of the layers, arising from the partial non-equivalent substitution of the central atoms in the octahedral and/or tetrahedral sheets, is the most important feature of smectites. It can be chemically increased via structural FeIII reduction or decreased via Li+ fixation. Reduction of structural FeIII to FeII in smectites affects many properties of the clay. Over 90% of structural FeIII in smectites can be chemically reduced. The reduced clays are unstable and undergo reoxidation on air. Another method for modifying the layer charge and thus the properties of dioctahedral smectites is to heat the clay in the presence of Li+, causing the small Li+ ions to enter into the 2:1 layer structure, which decreases the layer charge. A partial stabilisation of FeII in chemically reduced smectites can be achieved via Li-saturation and heating of the reduced clay in an inert atmosphere.

P. Komadel
Pillared Clays: Chemistry and Prospects

Pillaring of smectites with Al consists of three processes: (i) ion exchange of the Al137+ Keggin ion; (ii) hydrolysis of the Keggin ion upon contact with the clay surface; (iii) precipitation of the Keggin ion on the clay particles. Conditions can be chosen to limit the pillaring to the first two processes. Smectites with Al in the tetrahedral layer are the preferred materials for pillaring. Thus, pillared saponite is an excellent acid catalyst. In other catalytic applications and in selective adsorption pillared clays perform well, but cannot yet compete successfully with the available microporous and mesoporous materials.

R. A. Schoonheydt, K. Y. Jacobs
Hg2+ Trapping by Thiol – Functionalised Mesoporous Silica Molecular Sieves

The covalent grafting of 3-mercaptopropylsilyl groups to the framework pore walls of mesoporous silica molecular sieves represents a promising new approach for trapping of Hg2+ and other heavy metals from dilute solution. Two framework structures were examined, namely, a calcined hexagonal silica prepared by electrostatic supramolecular assembly, and an uncalcined wormhole -like silica obtained through neutral surfactant assembly. Owing to the presence of a higher concentration of surface hydroxyl groups, the wormhole silica was far more effective for thiol fuctionalisation and heavy metal ion trapping.

L. Mercier, T. J. Pinnavaia
The Use of Clays as Sorbents and Catalysts

This paper attempts to show how the structural, physical and chemical properties of clay minerals relate to their laboratory, industrial and environmental uses as sorbents and catalysts. A brief review of the formulae, structures of clays and their relationship to their chemical and physical properties is given. Isomorphous substitution of layer cations generates layer charges, which are neutralised by the presence of exchangeable, compensating ions in the interlayer. Acid activation increases clay surface areas, acidity and sorption characteristics producing large volumes of acidic aluminium salt waste. Cationic clays often have high Brønsted and Lewis acidity, which enable the clays to be used as clean, often highly specific catalysts in organic and inorganic reactions or as supports for catalysts or reagents.Batch cation exchange experiments can be used in the comparison of the exchange sites available in intact and acid activated minerals, via Langmuir or Freundlich type isotherms and Rd plots. Industrially clays are used to form gels, in the removal of carotenoids and chlorophyll in the production of cooking oils and light coloured soaps, in cat litter and in carbonless copying paper. Singlet oxygen generated by these dyes in the latter case causes fading of the image, an autocatalytic effect in their own destruction. In the laboratory clays have been used extensively as acid catalysts, as selective supports in g.c. and as active supports for oxidants (e.g. clayfen and claycop) and Lewis acids (e.g. clayzic) and as regioselective catalysts for Diels-Alder reactions and for the generation of reactive intermediates such as carbenes. The thermodynamically less favoured isomer can often be selected for if the transition state of formation is less bulky.In the environment, clay minerals are highly important in soils, as they swell and retain water, act as pH buffers and as slow release agents for essential minerals and adsorb crude oil and radionuclides from spills and leaks.

M. Caine, G. Dyer, J. V. Holder, B. N. Osborne, W. A. Matear, R. W. McCabe, D. Mobbs, S. Richardson, L. Wang
Contaminant Plume Management Utilising in Situ Organoclay Sorbent Zones

An in situ subsurface remediation technology, based on the chemical conversion of native clays to organoclays, is being developed. The approach involves in situ injections of cationic surfactant solutions into the subsurface to create organoclay sorbent zones, that can intercept and immobilise contaminant plumes. Contaminants trapped in the sorbent zone can be treated by bioremediation.

S. A. Boyd, G. Sheng
Atomistic Computer Modelling of Chiral Pillared Clays

Lattice energy minimisation techniques have been used to study the 2D molecular organisation of [Ru(bpy)3]2+ and [Ru(phen)3]2+ confined in the interlamellar space of low charged smectites with respect to the stereochemistry of the pillars and the charge distribution within the host. With racemic pillars, favourable π-stackings lead to clustering of pillars even with homogeneously charged smectites. Long range and/or short range ordering of the isomorphous substitution within the silicate layer strongly influences the interlayer structure, since host-guest interactions are dominated by electrostatics.

J. Breu, N. Raj, C. Richard, A. Catlow
Natural Microporous Materials of Central Slovakia

Reserves of natural microporous materials are situated in the region of Central Slovakian Neovolcanites, which is characterised by its stratovolcanic structure. The characteristics of deposits of clay minerals and zeolites of four stratovolcanoes present in this area, Kremnica, Banská Štiavnica, Javorie and Pol’ana, are presented in this paper.

V. Šucha, I. Kraus
Sorption and Leaching Properties of the Composites and Complexes of Natural Microporous Materials

This contribution deals with those aspects of the application of natural microporous materials (NMM), which are projected for a millennial horizon of environmental protection. Though the NMM possess excellent sorption properties, their natural physico-mechanical form usually limits their application in technological processes, such as packed-bed columns. However, due to their thermal and radiation stability, compressive strength, steadiness towards the freezing/ thawing and wetting/ drying cycles, they have received increasing interest in the long-term hazardous waste treatment both in situ and plant performance. To improve mechanical properties of crystals, solid carriers such as cellulose and carbon, or binders such as organic polymers, are applied. Artificial formation of composites and both inorganic and organic complexes of NMM is applied for: (1) field barriers (mortars and grouts), (2) reagents and organic coating supports, (3) granules, pellets and column packings, (4) additives to cementitious fixation matrices, and (5) ceramics and glass formulations.In natural conditions, by application of NMM engineering barriers, the complexes of NMM with natural organic components, namely humic substances, play an important role in the modification of their sorption properties and the immobilisation of pollutants. NMM have a marked superiority over commercially available cation exchange organic resins, due to high cation exchange capability, thermal and radiolytic stability, the possibility of transformation to stable ceramics and their compatibility with cement. Glass-bonded NMM are being developed as a potential ceramic waste form for the disposition of radionuclides. An overview of the various problems to be solved is presented and selected papers in the field from the last two decades are reviewed and indexed comprehensively.

F. Macášek
Experimental Study on the Formation of Heavy Metal Sulphides Using Layer Silicates: Environmental Aspects

Clay minerals saturated with metal ions (Cu, Pb, Cd, Zn, Tl, Ag, Hg) were treated by aqueous H2S solutions under controlled Eh and pH conditions. The heavy metal ions were released and precipitated at 80 °C as sulphides and in most cases appeared to be crystalline. They often formed coatings or crystals overgrown on clay minerals or formed tight intergrowths with clay particles. After 5 days, well crystallised sulphides were formed; covellite (CuS), galena (PbS) and sphalerite (ZnS) were identified by X-ray. The microscopic observations revealed some other Cu-Fe-minerals, like chalcopyrite (CuFeS2), idaite, and bornite. Native copper and pyrite were also observed. Cadmium formed hawleyite (CdS), whereas the greenockite crystals were rarely found in the reaction products. Mercury reacted very quickly with S2 ions and in the heavy fraction of the reaction products the metacinnabar (HgS) was determined. Several thallium sulphides were obtained: T1S, T12S (carlinite), T12S5, T14S3 and TlFeS2 (raquinite), Cu3Tl2S5, Cu2TlS3, AgTlS, Ag4Tl2S3 and AgTlS2.

E. Helios Rybicka, A. Piestrzynski, S. Th. Schmidt
Diffusion of Radionuclides in Clay-Based Ceramics

The diffusion coefficients of 22Na, 90Sr and 134Cs in clay-based ceramics were determined by the integral residual activity method. It was established that the diffusion coefficients of radionuclides decreased, at the investigated temperature range, in the following order: 22Na > 134Cs > 90Sr. The migration of 134Cs, in comparison with the migration of 22Na, was characterised by essentially the lowest values of the preexponential factor and of the activation energy of the diffusion process. It was shown that, in the case of a ceramic material containing 89% (w/w) of Cambrian clay and 11% (w/w) of perlite, increasing the relative moisture content from 0.05% to 0.3% resulted in a considerable (2–3 orders of magnitude) increase of the diffusion coefficients of radionuclides. A further increase of the relative moisture content did not influence appreciably their diffusion mobility.

I. A. Ivanov, V. I. Tsvetkov, A. N. Gulin, V. M. Shatkov

Natural Zeolites

Frontmatter
Zeoponic Substrates for Space Applications: Advances in the Use of Natural Zeolites for Plant Growth

Natural zeolites have unique physical and chemical properties, which make them attractive for use in slow-release fertilisation for plants, zeoponic plant growth substrates, and soil conditioning and remediation. Zeoponic substrates are defined as artificial soils in which zeolites are a major component. Over the past 10 years, the National Aeronautics and Space Administration (NASA) has been developing a zeoponic substrate for plant growth in space. The primary zeolite used in these substrates is clinoptilolite, because of its selectivity for K+ and NH4+ and its stability in soil-based systems. In addition to NH4- and K-exchanged clinoptilolite, substrates developed by NASA contain either natural or synthetic apatite. Slow-release fertilisation has been achieved in this system by dissolution of either natural or synthetic apatite and cation exchange reactions of clinoptilolite. The synthetic apatites are hydroxyapatites in which Mg, S, and the micronutrients have been substituted into its structure for either Ca and PO4. Hence, these substrates have the capability of supplying all of the essential plant growth nutrients with only the addition of water.In several NASA studies, wheat grown in zeoponic substrates produced greater total dry matter as compared to wheat grown in control substrates watered with nutrient solutions. In another study, however, significantly less wheat grain was produced by plant grown in zeoponic substrates compared to plants grown in control substrates, and this was attributed to reduced seed set caused by the NH4-N source from clinoptilolite exchange. In a subsequent study, the addition of nitrifying bacteria and dolomite to zeoponic substrates produced higher wheat seed yields than control substrates, suggesting that the nitrifying bacteria converted NH4-N to NO3-N, which is more likely to enhance seed set. In a recent plant-growth chamber study, wheat seed production from plant grown in a hydroponic system slightly out performed a zeoponics system; however, the seed production from plants grown in the zeoponics substrate was equivalent to approximately 200 bushels/acre, substantially higher than yields obtained in the field.Wheat and brassica have been grown in zeoponic substrates on the U.S.A. Space Shuttle. During an 8-day flight the growth and development of both plant species on orbit appeared normal and similar to those of plants grown in ground controls. Zeoponic substrates may be used for long-term, plant growth experiments on the International Space Station.Several companies in the United States are marketing zeoponic or zeolite-based products, primarily for the golf industry. One company has developed a zeoponic substrate called “ZeoPro™”, which is being used as a slow-release fertiliser on golf greens. Because of the recent progress made in the development of zeoponic substrates, we anticipate that the application of zeoponic substrates in the horticultural, agricultural, and turfgrass industries will significantly increase over the next few years. It is likely that these products will be used to improve fertiliser-use efficiency and in environmental protection. With continued sound scientific research, it is likely that zeolites will be used extensively in the plant growth industry during the first part of 21st century.

D. W. Ming, E. R. Allen
Natural Zeolites and Nuclear-Waste Management: The Case of Yucca Mountain, Nevada, USA

The most important radionuclide migration issues at Yucca Mountain concern not 137Cs and 90Sr but anionic species and long-lived actinides that often form large, complex aqueous species. Zeolites do not interact strongly with such species, illustrating their limitations in real-world applications. Emplacement of radioactive waste will heat large volumes of rock, and zeolites will be important sources and sinks of water and thermal energy during heating and cooling in the vadose zone. In addition, dehydration/hydration reactions are accompanied by volumetric changes. Longer-term reactions, e.g., of clinoptilolite to analcime, will give rise to larger volume reductions and production of water and silica. These studies of Yucca Mountain show that the importance of zeolites extends far beyond cation exchange by zeolites to phenomena affecting the entire thermohydrologic system.

D. L. Bish
Interaction of Actinides with Natural Microporous Materials

This contribution contains a concise review of the existing literature on the interaction of actinides with natural microporous aluminosilicate minerals and metal oxides, hydroxides, oxyhydroxides). The interaction includes several types of chemical processes (absorption / ion-exchange, adsorption / surface sorption, surface precipitation, complexation, formation of colloidal / pseudocolloidal systems) controlling the transport of the actinides in the biosphere (environmental geochemistry of the actinides) and determining the suitability of these materials for the treatment, immobilisation and disposal of nuclear industry wastes. The contribution also includes some new data on the interaction of U and Th with granitic biotite and todorokite as well as on the sorption of Pu and Am by Greek and Slovak zeolites and clays.

P. Misaelides, A. Godelitsas
Environmental Applications of Natural Zeolitic Materials Based on Their Ion Exchange Properties

Present and potential use of natural zeolites as cation exchangers in environmental protection is reviewed. Siliceous zeolites, such as chabazite, clinoptilolite, mordenite and phillipsite, exhibit good selectivities for cations with low charge density, e.g., Cs+ and NH4+, and for cations with low hydration energy, such as Pb2+. Zeolitised tuffs, containing the mentioned zeolites, may therefore be utilised for removing the above and other cations from wastewaters before discharge.Continuous processes with fixed beds are usually employed for water purification, such as those in service in the USA and in other countries around the world for ammonium removal from municipal sewage. Direct addition of the ion exchanger is needed when the pollutant, e.g., radionuclide, must be removed from soil and trapped in the zeolite framework, such as in the case of the Chernobyl nuclear accident.Removal of heavy metals from wastewaters is made difficult by the complexity of the effluents to be treated, e.g., by the presence of several cationic pollutants for which zeolite does not exhibit comparably high selectivities.Discontinuous processes (addition of zeolite to the waste solution) are also possible, and recommended in the case of low process efficiency, provided that the zeolitic sludge, resulting from removal of polluting cations, is stabilised-solidified in a cement matrix before disposal or re-use.

C. Colella
Zeolitised Materials of the Mediterranean Area as Adsorbents for Environmental Protection

An investigation on the adsorption properties of zeolite-rich rocks, coming from deposits located around the Mediterranean basin, has been carried out, in view of their possible utilisation in the field of environmental protection. Samples investigated contained chabazite, phillipsite, clinoptilolite, mordenite and faujasite and came from different formations in central Italy, north-eastern Greece and north-eastern Jordan.After a careful chemical and mineralogical characterisation of the samples, adsorption isotherms of H2O, CO2, SO2 and NH3 at 25 °C have been obtained.Experimental data have been processed according to the Langmuir, Freundlich and Dubinin-Astakhov theoretical models. Results have been interpreted considering an adsorption mechanism based on monomolecular layer coverage.

D. Caputo, B. de Gennaro, M. Pansini, C. Colella
Distribution of Industrial Minerals in Sardinia (Italy): Clinoptilolite Bearing Rocks of the Logudoro Region

Volcaniclastic products of Northern Sardinia (Italy) turned out to be affected by diffuse zeolitisation processes. About 130 samples, representative of the identified formations (pyroclastic flows and epiclastic deposits), were collected in order to evaluate the distribution of zeolitic phases. Clinoptilolite was the most widespread zeolite, whereas mordenite and chabazite rarely occured. A quantitative evaluation performed by the Reference Intensity Ratio (RIR) and Rietveld methods indicated that about 30% and 44% of samples from pyroclastic flows and epiclastic deposits, respectively, have a zeolite content higher than 50%.

A. Langella, P. Cappelletti, G. Cerri, D. L. Bish, M. de’ Gennaro
Application of Microporous Materials for the Recovery of Nutrients From Wastewaters

The RIM-NUT® process is based on ion-exchange precipitation operations for the abatement of the eutrophication potential present in biologically oxidised municipal, zootechnical and industrial wastewaters. A natural zeolite (clinoptilolite) and a commercial macroporous strong-base anion exchanger selectively remove nutrient species (i.e., NH4+; H2PO4=/HPO4), which are quantitatively precipitated and recovered in the form of a premium-quality, slow-release fertiliser (MgNH4PO46H2O) from the exchangers spent regeneration eluates. Demonstration campaigns carried out in Italy and the United States on a 240 m3/d mobile plant proved the technical feasibility of the process whose economical proficiency must still be assessed.

L. Liberti, G. Boghetich, A. Lopez, D. Petruzzelli
Transition Metal Complexes Supported on Natural Zeolitic Materials: An Overview

The literature concerning transition metal complexes supported on natural zeolitic materials is reviewed and the relevant experimental methods, along with the characterisation techniques, are presented. In contrast to synthetic zeolites, the research already performed using naturally occurring species is not extensive and mainly refers to HEU-type zeolites, as well as, to natural analogues of explicit synthetic products (FAU-type zeolites). Different intrazeolite and surface complexes of several metals (Mn, Fe, Co, Ni, Cu and Ag) have been investigated and potential applications of the obtained composite materials have been proposed. The utilisation of these materials in environmental technology has particularly been pointed out (e.g. specific sorbents/ catalysts, environment-friendly pesticides/insecticides, innovative pharmaceuticals/ nutrients). The future perspectives of this subject could include the investigation of supported complexes of Pt-group elements, and the study of specific complexes of transition metals with increased biological interest (e.g. Fe, Mn). The latter will also contribute to the understanding of problems related to the geochemistry and biogeochemistry of the microporous tectosilicate minerals.

A. Godelitsas
Heterogeneous Catalysis at Supercritical Conditions Using Microporous Materials. Environmental Advantages

Supercritical fluids possess unique properties that make them attractive as media for chemical reactions. Densities of supercritical fluids are comparable to those of liquids and therefore their dissolving power is high. On the other side diffusion coefficients of components in supercritical fluids are much higher than in liquids. Therefore processes that are mass transfer limited in the liquid phase, like the majority of heterogeneous catalysed reactions on microporous materials, become faster at supercritical conditions. Supercritical fluids have the potential to replace toxic organic solvents and make reaction processes environmentally friendly. This paper discusses some environmental applications of catalytic reaction processes at supercritical conditions.The enhanced maintenance of catalytic activity of zeolites and other microporous catalysts, that could enable them to overcome the obstacle of strong deactivation and replace liquid acids, that are used now and are very toxic, corrosive and pose high safety risk. A second example is the Fischer-Tropsch synthesis of liquid hydrocarbons, a process that would enable the production of liquid fuels from huge reserves of natural gas. That would make more economical and environmentally friendly use of natural gas than now. Hydrogenation over microporous catalysts containing precious metals is another only recently studied process. Hydrogenation in supercritical CO2 enhances dramatically the process safety, reduces the reactor size and increases the reaction rate too, due to enhanced solubility of H2 in supercritical CO2 compared to conventional solvents. Finally a novel wastewater treatment, catalytic supercritical water oxidation, takes advantage of the dramatic change of supercritical water properties compared to liquid water.

G. Manos
Properties of NaOH-Treated Slovak Zeolitic Tuff and Its Sorption Ability Towards Some Cations

The treatment of Slovak zeolitic tuff with different concentrations of NaOH solution creates modified forms of it. These forms exhibit an increased uptake of multivalent cations. The sorption ability of Cs+, Co2+, Cd2+, Fe3+ and Cr3+ cations was studied by gradual radioactive labelled ion-exchange and AAS methods. The influence of NaOH solutions on the structure and the surface of zeolite were studied by chemical analysis, XRD — analysis and by the measurement of the surface area of the material. DTA, TG and ETA methods were used for the studying of the influence of temperature on the natural and chemically modified zeolite. The leachability of loaded zeolitic material was also studied. Completely new matrices based on blast furnace slag were used for solidification of loaded zeolitic material.

M. Főldesová, P. Dillinger, P. Lukáč
Zeolites in Aquacultural Primary Production

Our studies in aquacultural systems began with the ammonium-ion elimination. They were continued with the investigation of the influence of zeolites in other marine biological processes such as the culture of marine micro-algae, this is, the primary production of marine phytoplancton by products of zeolitic nature (PZNs).The PZNs were prepared in our laboratory in various ways depending on the type of base material used for their synthesis. Especially significant was the positive influence they exerted over the growth of marine micro-algae. The presence of PZNs, which increased the cellular yields in the primary production of phytoplancton, showed a dependence on the dose and on the product used.

J. L. López-Ruiz
Sorption of Cadmium(II) and Nickel(II) on a Natural Zeolite Rich in Clinoptilolite

A natural zeolitic material from Argentina was used to study Cd(II) and Ni(II) sorption from different ionic media. Both metals were sorbed by the zeolite, the removal capacity being higher for the Cd(II) cations than for the Ni(II) cations. Equilibrium data have been found to fit the Freundlich adsorption isotherm.

M. Martínez, L. Duro, M. Rovira, J. de Pablo
Environmental Applications of Modified Natural Zeolites

Various chemical methods for the modification of zeolites, the properties of modified zeolites and their applications for environmental protection are discussed. Experimental data on obtaining organozeolites for water decontamination and ferritised zeolites for soil remediation are presented.

V. A. Nikashina, B. F. Myasoedov
Romanian Volcanic Tuffs Exploitation in Environmental Protection

The work presents data concerning genesis and occurrences of Romanian volcanic zeolitic tuffs, specifying a higher frequency of the following zeolitic types: stilbite, laumontite, clinoptilolite, heulandite, natrolite and mesolite. The volcanic tuff from Marsid — county Salaj - is one of the representative species of the volcanic tuff in Romania, having a clinoptilolite content ranging from 60% to 70%. The aim of this paper is the survey of our work on the use of volcanic tuffs from Marsid in environmental protection, which is mainly concentrated in the following areas: increase of the zeolite ion-exchange capacity; the advanced purification of some metallurgical wastewaters; the use of spent zeolites containing metallic cations for obtaining fertilisers of high agrochemical quality containing trace elements; the improvement of the water coagulation process; the improvement of the filtering of drinking water; the use of organoclinoptilolite for wastewater pollution abatement. The obtained results, as well as the availability and low cost of clinoptilolite tuffs, make these materials excellent candidates for environmental protection.

E. Popovici, G. Burtica, R. Pode, I. Bedelean, I. Calb
Sorption of Heavy Metals and Radionuclides on Zeolites and Clays

The sorption of zinc, strontium, technetium, cadmium, caesium, mercury, lead, plutonium and americium from their aqueous solutions by natural zeolitic materials from Metaxades (Greece), Nižný Hrabovec (Slovakia), synthetic zeolites Nalsit and Ysit (VURUP, Slovakia) and bentonites from Melos Island (Greece) and Jelsový Potok (Slovakia) was investigated using a batch-type procedure and radiotracer techniques. The metal uptake and the distribution coefficient (Kd) values determined for the materials of different origin were correlated with their mineralogical composition and their gross cation exchange capacity (CEC). The identification of specific uptake sites was attempted on the basis of the sorption isotherms and the exchangeable cation content. The experimental results provide information on the suitability of the individual materials for the treatment of radioactive waste and their application as a backfill in potential nuclear waste repositories. It was found, that the zeolites (natural and synthetic) are very efficient sorbents for caesium. The removal of lead from aqueous solutions by the investigated natural zeolites was almost as effective as the removal of caesium, whereas the materials were less effective for the removal of other heavy metal ions. The sorption of radionuclides (239Pu, 241Am, 90Sr, 99Tc, 137Cs) on zeolites and bentonites was correlated with their Gross Annual Stopping Power (GASP). The comparison of the obtained data indicated, that the Slovak synthetic zeolite NaY shows the best sorption characteristics among the studied materials.

P. Rajec, F. Macášek, P. Misaelides
A Preliminary Study of Mercury Uptake by a Greek Zeoliferous Rock

The mercury uptake from aqueous solutions by a mordenite rich tuff from Samos island, Greece, was studied as a function of ionic strength at an initial pH of 5.0±0.2, using 203Hg as a radiotracer. The total mercury concentration was varied from 5.0×10-4 to 5.0×l0-7 mol L-1. The adsorption was described quantitatively by fitting the data to a Langmuir isotherm, while the estimated Kd values ranged from 950 to 1600 mL g-1. The dependence of mercury adsorption on the solution ionic strength, suggested a predominantly electrostatic interaction of the adsorbate with the mineral surface.

M. Soupioni, B. Symeopoulos, J. Athanasiou, A. Gioulis, P. Koutsoukos, P. Tsolis-Katagas
Natural Sorbents as Barriers Against Migration of Radionuclides from Radioactive Waste Repositories

Sorption properties of natural occurring minerals (zeolites, clays and loess) of Bulgarian origin are studied in order to estimate their application as engineered and natural barriers, which retard the migration of radionuclides from radioactive waste repositories. A mineral rock, which contains clinoptilolite and celadonite, is proposed as a backfill for low- and intermediate-level waste repositories and as an in situ permeable barrier for the decontamination of radionuclide-contaminated groundwater.

I. G. Stefanova
Preparation of a Modified Adsorbent Based on Clinoptilolite and Its Application for The Removal of Iron and Manganese Ions from Artesian Water

A method is developed for the modification of the external surface of clinoptilolite grains by manganese dioxide. This modified clinoptilolite is shown to be an efficient material for the post-purification of artesian drinking water with respect to iron ions and the removal of Mn2+ ions from this water: 1 kg of adsorbent is capable for cleaning up to 600 dm3 of artesian water containing 1.2 - 1.4 mg/dm3 Mn2+ ions without regeneration. Optimum conditions for the regeneration of spent adsorbent by potassium permanganate are determined.Industrial testing was performed using pilot-scale equipment. These tests comprised the preparation of the modified adsorbent, its application for post-purification of water with respect to residual iron ions (following filtration combined with aeration through a layer of natural clinoptilolite grains) and purification with respect to Mn2+ ions, and also the spent-adsorbent regeneration stage.

Yu. I. Tarasevich

Natural Microporous Oxides

Frontmatter
Metal Detachments from (Hydr)Oxide Mineral Surfaces. A Molecular View

Geochemists strive to understand the reactions that occur in mineral micropores at a molecular scale so that predictions about rates and extents of reactions are possible over long periods of time. Our approach to understanding reactions at surfaces and micropores is to use the reactivity of dissolved species as a guide because analogues of many structural groups at the mineral surface can be found in well-chosen dissolved complexes. In this contribution, we discuss the ways in which the rates of dissociation of metal-oxygen bonds in these dissolved complexes are enhanced by protonations, ligand substitutions and deprotonations. Our approach is multifaceted in that we employ molecular-orbital calculations, NMR spectroscopy, and bulk dissolution experiments to try and constrain these classes of reactions and to understand how they can affect mineral surfaces. This work is relevant to microporous solids because so many of the geochemically important reactions that affect the rates of radioactive waste migration come down to a series of ligand exchanges where molecules in the innercoordination sphere of the dissolved contaminant are replaced by functional groups at the mineral surface. Even the dissolution of an oxide mineral can be viewed as a series of ligand exchanges where bridging oxygens and hydroxides that link a metal to the bulk mineral structure are replaced by terminal ligands, such as water molecules, at migrating monomolecular steps. In this chapter we examine how ligand substitutions can affect these rates and how the surface of a mineral can act as a ligand.

W. H. Casey, J. Nordin, B. L. Phillips, S. Nordin
Using Magnetites to Remediate Heavy Metal Wastewaters from Acid-Mine Drainage

The remediation of heavy metal wastewaters using magnetites, also known as ferrites, has been an area of investigation for many years. Early investigators used a synthetic procedure for the production of magnetites at 70 °C. Although quite effective, as demonstrated by remediation of small waste streams from universities in Japan, this method is too energy intensive for application to large volumes, such as found in acid mine drainage. Other researchers have investigated room temperature production of magnetites using thin film oxidation of ferrous ions or electrolytic oxidation of iron electrodes. Again, these methods have not been found to be easily applied to large scale applications. Recently we have discovered a catalytic method of production of magnetites at low temperatures using stoichiometric quantities of iron salts. In addition, we have found that the presence of organic chelators can dramatically enhance or inhibit the removal of heavy metals using this technique. Both of these avenues of investigation will be discussed in this lecture.Our work with magnetite synthesis at below room temperature was initiated to meet the demand from the US Bureau of Reclamation for the remediation of heavy metals from the Leadville Mine Drainage Tunnel (LMDT) effluent. This water comes from the tunnel at 9 °C year round. They presently use a typical high pH treatment process and generate large quantities of sludge that requires extensive dewatering. The Bureau is interested in new cost effective technologies that meet their discharge levels and reduce sludge and the plant footprint. In a combined effort between Los Alamos National Laboratory and New Mexico State University, we are attempting to meet this challenge.The current literature states that magnetite formation at temperature less than 70 °C is very slow and our preliminary work with the LMDT effluent agreed with this conclusion. Treatment times ranged between 24 and 48 hours to form magnetites for temperatures around 10 °C. This observation however is in contrast to studies done in deionised water. Under these conditions, magnetite formation was complete within a few minutes. In an attempt to determine the cause for this deceleration, we investigated the effects of several divalent metal ions several negative ions on the magnetite formation times. It was found that by themselves, none of these ions appreciably affected the magnetite formation. When combined however, the presence of both calcium and bicarbonate dramatically inhibited magnetite production. Although preliminary in nature, we feel that the formation of insoluble calcium carbonate, formed at the pH of these studies, interferes with the magnetite formation. Several experiments have been carried out to support this view.Although many attempts at removing or masking these ions were made, no suitable method was found to circumvent their effects. It was found however that the addition of pre-formed magnetites completely overcomes the presence of these ions and permits the subsequent rapid formation of magnetite in which entrapment of the heavy metals can take place. This represents a significant step toward the implementation of this technology in waste streams that are at ambient temperatures found in industry.Another aspect of our work is the examination of the effect of chelators on the removal of heavy metals from waters using an in-situ method of magnetite formation. Other researchers have used strong oxidants, such as permanganate, to chew up organics before forming magnetites. This was done in the belief that these chelators would inhibit the removal of heavy metals by tying them up and preventing their incorporation into the magnetite matrix. Although perfectly reasonable, in our attempts to quantify the extent of inhibition, we have found this premise to be somewhat simplistic!For example, with Pb2+, Cd2+ and Hg2+, we have found that the presence of chelators, such as EDTA or NTA, can either inhibit or enhance the removal efficiencies. In fact, with the appropriate selection of chelators we can chemically separate these three ions using magnetites. We have investigated this effect on several transition metal ions with a variety of chelators. The precise nature of this selectivity is under investigation in our laboratory.

M. D. Johnson, R. Wingo, M. Valdez
Wastewater Treatment Technology Based on Iron Oxides

Iron oxides have been used in a variety of forms for wastewater treatment. In most precipitation processes ferric ions are used to treat basic aqueous solutions by forming a ferric hydroxide floc to scavenge radioactive and heavy metal contaminants. In adsorption processes, a variety of iron containing minerals have been utilised. Since 1970, we have utilised ferrites and the mineral magnetite, iron ferrite (FeOFe2O3), for actinide and heavy metal removal from wastewater. Natural magnetite and ferrites, prepared in a variety of ways, were used in the batch mode to treat wastewaters. Magnetite was also supported and used in a column mode. In the presence of an external magnetic field, enhanced capacity was observed in using supported magnetite for removal of plutonium and americium from wastewater. This paper will review previous work on the use of ferrites and work in progress on supported magnetite (in a magnetic field) for wastewater treatment.

J. D. Navratil
Goethite Mineral as a Sorbent for Heavy Metal Ions

A toxic metal cation (cadmium) and an oxyanion (arsenic in III or V valence state) removed from dilute aqueous solutions by mineral goethite. The simultaneous removal of cations and anions is a great advantage of goethite as a sorbent material. The pure mineral sample was initially characterised by adsorption (and desorption) of nitrogen at liquid nitrogen temperature. The metal ion removal was strongly dependent on the solution pH. The modification of the mineral by potassium hydroxide was examined. Its removal capacity was compared to that of a synthetic goethite. The modelling of the sorption isotherm was discussed. An efficient solid/liquid separation technique, such as flotation preceded by flocculation, may be necessary downstream, when the material used is in an ultrafme state, as in the present study.

K. A. Matis, D. Zamboulis, A. I. Zouboulis, N. K. Lazaridis
Reversed Phase Column Extraction Studies Using a Standardised and Silanised Anatolian Perlite

This paper describes the preparation of an improved adsorbent from natural perlite and its properties for laboratory and environmental applications. The SiO2 content of mineral perlite, which is in the 70–75% range, was converted to soluble silicates with NaOH. The acidification of soluble silicates in the perlite formed hydrogels, which turned into xerogels upon drying. Several parameters — particle size, specific surface area, pore size and volume, and surface hydroxyl group density — were investigated for NaOH-standardised perlite. The standardised perlite was silanised and loaded with 20% (w/w) tributyl phosphate before being used as a reversed-phase column chromatography solid support. Furthermore, the sorption of UO22+ and Fe3+ from aqueous solutions by the modified perlite was investigated using batch techniques.

H. Akçay, S. Kýlýnç
Characterisation of Natural Microporous Manganese Oxides: The Case of Todorokite

A natural todorokite reference sample originating from the Montenegro mines, Cuba, was identified by powder X-ray diffraction, whereas details of its composition were investigated using, among others, advanced spectroscopic techniques such as X-ray photoelectron spectroscopy (XPS). The cation exchange capacity (CEC) of this Mn oxide, determined on the basis of the K+ ↔ Cs+ exchange method, was found to be rather low (ca. 15 meq / 100 g) compared to the corresponding values of other typical microporous minerals. According to the ζ-potential measurements, the material is negatively charged in aqueous solutions with pH > ca. 2.4 and able to sorb cations. At pH values < ca. 2.4, it is positively charged but considerable amounts of Mn are released from the building framework of the crystal structure. The thermal analyses of the mineral and the following FT-IR investigation showed that the water molecules, initially located into the tunnels, are irreversibly lost at temperatures up to ca. 450 °C resulting in dehydrated crystals. In accordance, the maximum specific surface area (SSA), measured at 350 °C by means of nitrogen sorption-desorption isotherms (59 m2/g), gave additional information on the porosity of the material. The maximum solid acidity determined by temperature programmed desorption (TPD) after thermal pretreatment at 350 °C, though low (0.5 mg of ammonia desorbed / g), provided evidence for the absence of strong active sites (such as extended OH groups) even in the dehydrated phase. The data obtained during the present work, based on a reference todorokite sample, indicate that the mineral does not possess especially interesting sorptive properties compared to other raw natural microporous materials. Therefore, additional research is necessary on certain chemically-modified forms which could exhibit potential favourable properties, suitable for technological and environmental applications.

A. Godelitsas, P. Misaelides, T. Katranas, C. Triantafyllidis, H. Klewe-Nebenius, E. Pavlidou, I. Anousis
Modelling Sorption of Metals from Aqueous Solution onto Mineral Particles: The Case of Arsenic Ions and Goethite Ore

Several mineral particles were shown to act as sorbents for metal ions. Among them, goethite, an abundant iron mineral, was found to present the specific advantage of being able to remove both cations and oxyanions, such as arsenic. The modelling of the sorption process, using the diffuse double layer model, was attempted in this paper. A good agreement with experimental results was found; therefore, it proved to be a useful tool for such sorption applications. A brief review of this scientific area is critically presented.

K. A. Matis, M. Lehmann, A. I. Zouboulis
Preparation of Granular Forms of Powdered Materials for Their Application in Column Packed Beds

This contribution summarises the possibilities of the application of powdered materials for liquid waste treatment and evaluates the published procedures for the preparation of “engineered” (granular) forms of such materials with regard to their potential application in environmental technologies. The advantages and disadvantages of the procedures used for the granulation of powdered materials are discussed and compared with regard to the properties of an “ideal” granular absorber. The applicability of various groups of granular materials for the treatment of nuclear waste, mixed waste, toxic or hazardous wastes, separation of various contaminants from surface and ground water, or for water pollution control, are compared. In the last part, composite absorbers containing finely divided materials and granulated using a binding matrix based on modified polyacrylonitrile are briefly characterised and the universal character of the respective granulation procedure is demonstrated.

F. Šebesta
The Molecular Layering Method as a Basis of Chemical Nanotechnology

The molecular layering method (ML) is a technique for the modification of the silica surface by successive, repeated and alternate processing of the solid surface by an excess of appropriate reagents; this is followed by the removal of those reagents, that have not taken part in the reaction, and of any gaseous products formed in the various stages of the treatment. An essential feature of the ML method is the synthesis under conditions far from equilibrium.The present paper presents experimental results of the modification of SiO2 with volatile chlorides of V, Ti, P, Cr and vapours of H2O. Industrial silica gel SchSK (with a surface area of 250 m2/g, a mean porous diameter of 14 run, and a particle size of 0.5 mm — 1.0 mm) was used as a solid matrix. Modification of the matrix surface was carried out in a gas flow reactor under an inert dry atmosphere using vapours of VOC13, CrO2Cl2, POC13, TiCl4 and H2O.It was possible to form on the surface not only an oxide, but also other structures: a sulphide (using ZnCl2 and H2S) and a nitride structure (using vapours of TiCl4 and NH3) or their composites were synthesised on the silica surface. The main advantages of the chemical nanotechnology and the ML method over traditional surface processing methods are: strong (chemical) binding of sorbents on the substrate surface, homogenous distribution of heterocomponents over the surface, i.e., high uniformity of covering, and the possibility to control the surface layer composition down to the monomolecular layer, to deposit different atomic layers one by one and to form multicomponent regular structures.

A. A. Malygin

Other Natural Microporous Materials

Frontmatter
Natural Chitin Containing Materials for Colour Removal from Textile Wastewaters

The main objective of this work was to study the ability of some low-cost materials containing chitin namely, Squid (Loligo vulgaris) and Sepia (Sepia officinalis) pens, and Anodonta shells (Anodonta cygnea), for colour removal by adsorption from textile wastewaters. A reactive and a direct green dyestuff, the Cibacron green T3G-E (CI reactive green 12) and the Solophenyl green BLE 155% (CI direct green 26) from CIBA, respectively, were selected for this study. The physical and chemical properties of the adsorbents were briefly characterised. Isotherms at 20 °C were determined for all systems using two different grain sizes. The experimental results were well fitted by both Langmuir and Freundlich models. Isotherms using pure chitin and activated carbon in the same conditions were also determined. Continuous adsorption experiments were performed in a packed column at 20 °C for the six pairs adsorbent / dyestuff and compared with experiments using chitin and activated carbon. These results and the mathematical simulation of the column runs with the studied adsorbents led to the conclusion that a very large internal resistance is present. In order to allow a more efficient use of the larger diameter particles in packed columns (decreasing their internal resistance), the adsorbents were submitted to various chemical treatments, namely, a demineralisation, followed by a deproteinisation step, or only one of these steps. The results show that, for the natural adsorbents, the Squid pen has the largest adsorption capacity; this is probably due to its larger specific surface area (8.8 m2/g as compared with the Anodonta shell with 1.4 nrVg) with more meso and micropores. The tests also show that the effective adsorption capacities of these materials decrease when increasing particle diameter.

S. A. Figueiredo, R. A. Boaventura, J. M. Loureiro
Backmatter
Metadata
Title
Natural Microporous Materials in Environmental Technology
Editors
P. Misaelides
F. Macášek
T. J. Pinnavaia
C. Colella
Copyright Year
1999
Publisher
Springer Netherlands
Electronic ISBN
978-94-011-4499-5
Print ISBN
978-0-7923-5889-3
DOI
https://doi.org/10.1007/978-94-011-4499-5