Joe B. Dixon

Preparation and application of organo-minerals as sorbents of phenol, benzene and toluene

Abstract Nonionic organic contaminants (NOCs) such as benzene, phenol, and toluene from contaminated wastewater can be effectively sorbed by organo-modified minerals. Organo-minerals were prepared from Na-montmorillonite, sericite, and zeolite by exchanging quaternary ammonium cations with various molecular weights such as Benzyldimethyltetradecylammonium (BDTDA), Hyamine 1622®, and Benzyltrimethylammonium (BTMA). The adsorption capacity of these organic cations onto these minerals is in the order of montmorillonite>zeolite>sericite, which is mainly dependent on the Ca/Mg cation exchange capacity (CEC) of each mineral. The interlayer expansion of the basal spacings of BDTDA- and Hyamine-montmorillonite increases from 12.5 to 30.8 A as the amount of interlayer organic cation increases. BTMA-montmorillonite is characterized by less interlayer expansion. The aliphatic tale on the BDTDA ion apparently contributes to the multiple interlayer sorption in BDTDA in contrast to BTMAs reluctance to sorb a second interlayer. The exchange capacity of organic cations onto montmorillonite and the interlayer expansion of organo-montmorillonite correlate with the sorption of phenol, benzene, and toluene. BDTDA-, Hyamine-, and BTMA-montmorillonite complexes include benzyl functional groups and are effective sorbents for NOCs such as phenol, benzene, and toluene in aqueous solutions and may have practical applications in wastewater purification. The BTMA-zeolite complexes have potential for application as a sorbent for phenol. Organo-sericite complexes were the least effective sorbents of the three minerals tested. Comparison of the three NOCs with activated carbon indicates that these organo-mineral complexes all fall short of sorbing as did the activated carbon. BDTDA-montmorillonite stands out as the best performing product and it improved with each addition of surfactant to about 70% of the activated carbon sorption of benzene and 66% of toluene. BTMA-zeolite sorption was 65% of the sorption of the activated carbon for benzene and about 50% of the activated carbon sorption of toluene. Phenol was sorbed little on the untreated zeolite or sericite surfaces and poorly on the organo-mineral phases except that the BDTDA- and BTMA-montmorillonite sorbed about 35% as much phenol as sorption by activated carbon.

QUANTITATIVE DETERMINATION OF CLINOPTILOLITE IN SOILS BY A CATION-EXCHANGE CAPACITY METHOD

A cation-exchange capacity (CEC) method based on ion-sieving properties was developed for the quantitative determination of clinoptilolite in soils. In this method, both zeolitic and non-zeolitic exchange sites in the soil sample are saturated with Na+. The CEC of the non-zeolitic exchange sites is determined by replacing the Na− in these sites with tert-butylammonium ions. The tert-butylammonium ion cannot be exchanged into the zeolitic exchange sites because it is too large to pass through the channels in the clinoptilolite structure. The sample is next washed with NH4OAc to replace the Na+ in the zeolitic exchange sites. The amount of soil zeolite is then estimated by comparing the CEC of zeolitic exchange sites to the total zeolite CEC (175 meq/100 g for pure clinoptilolite). Prior to the CEC analyses, carbonates and organic matter must be removed to minimize interference with the exchange process. A high correlation (r2 = .96) was observed between the abundance of clinoptilolite estimated using the CEC method and the abundance estimated by semiquantitative X-ray powder diffraction analysis.The CEC procedure was used to quantify clinoptilolite in an Aridic Calciustoll soil from south Texas. About 2–5% clinoptilolite occurs in the A and B horizons, and concentrations progressively increase with soil depth to as much as 20% in the CBk2 horizon.

ION EXCHANGE, THERMAL TRANSFORMATIONS, AND OXIDIZING PROPERTIES OF BIRNESSITE

Synthetic sodium bimessite, having a cation-exchange capacity (CEC) of 240 meq/100 g (cmol/kg) was transformed into Li, K, Mg, Ca, Sr, Ni, and Mn2+ cationic forms by ion exchange in an aqueous medium. Competitive adsorption studies of Ni and Ba vs. Mg showed a strong preference for Ni and Ba by bimessite. The product of Mg2+-exchange was buserite, which showed a basal spacing of 9.6 Å (22°C, relative humidity (RH) = 54%), which on drying at 105°C under vacuum collapsed to 7 Å. Of the cation- saturated bimessites with 7-Å basal spacing, only Li-, Na-, Mg-, and Ca-bimessites showed cation exchange.Heating bimessite saturated with cations other than K produced a disordered phase between 200° and 400°C, which transformed to well-crystallized phases at 600°C. K-exchanged bimessite did not transform to a disordered phase; rather a topotactic transformation to cryptomelane was observed. Generally the larger cations, K, Ba, and Sr, gave rise to hollandite-type structures. Mn- and Ni-bimessite transformed to bixbyite-type products, and Mg-bimessite (buserite) transformed to a hausmannite-type product. Li-bimessite transformed to cryptomelane and at higher temperature converted to hausmannite. The hollandite-type products retained the morphology of the parent bimessite. The mineralogy of final products were controlled by the saturating cation. Products obtained by heating natural bimessite were similar to those obtained by heating bimessite saturated with transition elements.

Transformation of birnessite to buserite, todorokite, and manganite under mild hydrothermal treatment

Investigations were conducted to determine the hydrothermal transformations of synthetic birnessite exchanged with different metal ions. Autoclaving in a Teflon-lined stainless steel pressure vessel at 155°C for 24 hr of Mg-, Ca-, La-, and Co-saturated birnessite yielded manganese minerals having 10-Å X-ray powder diffraction (XRD) spacings. The autoclaved Mg-birnessite yielded a mineral identical to natural todorokite in its infrared (IR) spectrum and XRD patterns. High-resolution transmission electron microscopy (HRTEM) provided images having 10-, 12.5-, 15-, and 20-Å wide fringes indicating heterogeneous channel widths in the crystallographic a direction, and IR spectroscopy produced bands at 757, 635, 552, 515, 460, and 435 cm’1, confirming the product obtained by autoclaving Mg-birnessite to be todorokite. Prolonged autoclaving of Mg-birnessite yielded manganite (λ-MnOOH) as a by-product; manganite did not form when the autoclaving time was shortened to 8 hr. Also, when Ca-saturated samples were autoclaved, the product gave d-values of 10 Å, but the XRD lines were broad and heterogeneity of the channel sizes was evident from HRTEM observations. The Ca-derivative had an IR spectrum similar to that of natural todorokite. Images showing 10-Å lattice fringes were observed by HRTEM for the Ni-saturated sample, which also produced an XRD pattern similar to that of the Mg-saturated sample. Co- and Lasaturated samples did not form todorokite, although HRTEM of La-saturated samples indicated some 10-Å lattice fringes that were unstable in the electron beam. Birnessite saturated with Na, K, NH4, Cs, Ba, or Mn(II) gave products having 7-Å spacings upon autoclaving.

Overview of vertisols: characteristics and impacts on society.

Publisher Summary Vertisols are clayey soils that shrink and swell extensively upon changing soil moisture conditions. They occur globally under various parent material and environmental conditions. Vertisols exhibit unique morphological properties such as the presence of slickensides, wedge-shaped aggregates, diapir (mukkara), and gilgai. Shrink-swell phenomena are the dominant pedogenic processes in vertisols and are attributed to changes in interparticle and intraparticle porosity with changes in moisture content. This is in contrast to the commonly invoked process of clay interlayer hydration-dehydration to explain shrink-swell phenomena. However, models proposed to explain the genesis of vertisol features have not received universal agreement. Because of their clay content, vertisols are global resources that are resilient to degradation compared to other soils. Degradation of vertisols has occurred and has been reported worldwide regardless of the parent material, environmental conditions, and level of cultural input. Vertisols are significant global resources that serve as the lifeline in subsistence agriculture because of their high productivity. Efforts toward comprehension and successful utilization are imperative for continued productivity and long-term sustainability of these resources for current and future civilizations. This chapter is based on the literature published about vertisols and includes recent developments and concepts concerning vertisols with regard to their distribution, formation, pedogenesis, and classification; their morphological, mineralogical, chemical, biological, and physical properties; and their management as a soil resource in the world.

Synthesis and properties of poorly crystalline hydrated aluminous goethites

Al-substituted goethites were prepared by rapid oxidation of mixed FeCl2-AlCl3 solutions at pH 6.8 in the presence of CO2 at 25°C. A combination of Al substitution and adsorption of CO2 reduced crystal size (except for an increase at small additions of Al) and produced unusual thin, porous particles. Product goethites had surface areas up to 283 m2/g and unit-cell expansions induced by hydration. Substitution of Al for Fe reduced the 111 spacing and increased infrared OH-bending vibrational frequencies. Al substitution split the goethite dehydroxylation endotherm during differential thermal analysis into a doublet and increased the temperature of all reactions. Both cold and hot alkali solutions dissolved Al from the goethite structure.After drying the product in vacuo at 110°C. X-ray powder diffraction data indicated minimal deviation from Vegard’s law for the goethite-diaspore solid solution up to about 30 mole % Al substitution. Goethite prepared in the presence of 40 mole % Al had a 111 spacing of 2.403 Å corresponding to 36 mole % structural Al if Vegard’s law was obeyed. Rapid oxidation of mixed FeCl2-AlCl3 solutions appears to be conducive to a higher degree of Al substitution in goethite than alkaline aging of hydroxy-Fe(III)-Al coprecipitates.РезюмеАl-замещенные гетиты были приготовлены путем быстрого окисления смешанных растворов FeCl2-AlCl3 при рН = 6,8 в присутствии СO2 при температуре 25°С. Сочетание замещения А1 и адсорбции СO2 уменьшало разиер кристаллов (исключая их увеличение при малых добавках Аl) и производило необычно тонкие, пористые частицы. Полученные гетиты имели площади поверхности до 283 M2/г и расширение элементарных ячеек, вызванное гидрацией. Замещение алюминия ферритом уменьшило 111 параметр решётки и увеличило инфракрасные ОН-изгибающие колебательные частоты. Замещение Аl расщепило эндотермальные кривые дегидроксилации гетита во время дифференциального термического анализа в дуплет и увеличило температуру всех реакций. Оба, холодный и горячий щелочные растворы вытесняли Аl из структуры гетита. После высушения продукта в вакууме при 110°С, данные по рентгеновской порошковой дифракции показали минимальное отклонение от закона Вегарда для твёрдых растворов гетита-диаспора до около 30 молярных % замещения А1. Гетит, приготовленный в присутствии 40 молярных % Аl, имел 111 расстояние, равное 2,403 Å, что соответствует 36 молярных % структурного А1, если применить закон Вегарда. Быстрое окисление смешанных растворов FeCl2-AlCl3 может скорее привести к замещению А1 в гетите, чем щелочное старение совместных осадков гидрокси-Fe(III)-Al. [Е.С.]ResümeeAl-substituierte Goethite wurden durch schnelle Oxidation von FeCl2-AlCl3-Lösungsgemischen bei pH 6,8 und bei der Anwesenheit von CO2 bei 25°C hergestellt. Eine Kombination von Al-Substitution und CO2-Adsorption reduzierte die Kristallgröße (ausgenommen einer Vergrößerung der Kristalle bei geringer Al-Zugabe) und erzeugte ungewöhnlich dünne, poröse Partikel. Die erzeugten Goethite hatten eine Oberfläche bis zu 283 m2/g und zeigten Vergrößerungen der Einheitszelle aufgrund von Hydratation. Die Substitution von Al für Fe reduzierte den 111-Abstand und vergrößerte die OH-Deformations-schwingungsfrequenzen im Infrarot. Bei der Differentialthermoanalyse wurde die Dehydroxylierungs-Endotherme des Goethit dutch Al-Substitution in ein Dublett aufgespalten und erhöhte die Temperatur aller Reaktionen. Sowohl kalte als auch heiße Alkali-Lösungen lösten Aluminium aus der Goethitstruktur.Röntgenpulverdiffraktometer-Daten zeigten nach dem Trocknen des Produktes im Vakuum bei 110°C eine minimale Abweichung von Vegard’schen Gesetz für Goethit-Diaspor-Mischkristalle bis zu 30 Mol.−% Al-Substitution. Goethit, der in der Anwesenheit von 40 Mol.−% Al hergestellt wurde, hatte einen 111-Abstand von 2,403 Å, was bei Gültigkeit des Vegard’schen Gesetzes 36 Mol.−% Al in der Struktur entspräche. Die schnelle Oxidation von FeCl2-AlCl3-Lösungsgemischen scheint für eine höhergradige Al-Substitution im Goethit förderlicher zu sein als die Alterung dutch alkalische Lösungen von Hydroxy-Fe(III)-A1-Mischfällungen. [U.W.]RésuméDes goethites substituées à l’Al ont été préparées par oxidation rapide de solutions mélangées FeCl2-AlCl3 à un pH de 6,8 en présence de CO2 à 25°C. Une combinaison de substitution à Al et d’adsorbtion de CO2 a réduit la taille du cristal (sauf pour un agrandissement lors de l’addition de petites quantités d’Al) et a produit des particules rares, minces, et poreuses. Les goethites produites avaient des aires de surface jusqu’ à 283 m2/g et des expansions de maille induites par hydration. La substitution d’Al à Fe a réduit l’espacement (111) et a accru les fréquences vibrationelles pliant OH de l’infrarouge. La substitution d’Al a divisé I’endotherme de déshydroxylation de la goethite pendant l’analyse thermique différentielle en un doublet e t a accru la température de toutes les réactions. Des solutions chaudes et froides alkalines ont dissolu l’Al de la structure de la goethite.Après avoir seché le produit in vacuo à 110°C, des données de diffraction poudrée aux rayons-X ont indiqué une déviation minimale de la loi de Vegard pour la solution solide goethite-diaspore jusqu’à près de 30 mole % de substitution d’Al. La goethite préparée en présence de 40 mole % d’Al avait un espacement (111) de 2,403 Å correspondant à 36 mole % d’Al structural si la loi Vegard était suivie. L’oxidation rapide de solutions mélangées FeCl2-AlCl3 semble être plus favorable à un plus haut degré de substitution d’Al dans la goethite que le vieillisement alkalin de coprécipités hydroxy-Fe(III)-Al. [D.J.]

Intercalation and surface modification of smectite by two non-ionic surfactants

Non-ionic surfactants Brij 56 and Igepal CO 720, containing hydrophilic poly(ethylene oxide) (PEO) segments, expanded smectite from 1.5 nm to 1.7 nm at room temperature. The surfactant-smectite composites had larger layer spacings than Ca-smectite after heat treatment. The surfactant-smectite composites were solvated and expanded to 1.8–1.9 nm by polar solvents, glycerol and water, but were not affected by the non-polar or weakly polar solvents, toluene, hexane or octanol. The hydrophilic PEO segments of non-ionic surfactants would logically access the interlayer spaces of smectite whereas the hydrophobic segments extend away from the mineral. The molecular structure and solvation properties suggest that the surfactant molecules are probably concentrated in the margin area of the interlayer galleries forming an annular ring structure between two neighboring silicate sheets. Only two layers or less of the surfactants could access the interlayer galleries of smectite and layer spacings did not exceed 1.8 nm even where excess surfactant was introduced into the composites. The layer spacings of the surfactant-smectite composites were well preserved during water or electrolyte solution washings, indicating stability of most non-ionic surfactant molecules in the interlayer galleries even though ∼30% of the adsorbed Igepal CO 720 was desorbed by exhaustive washing. The non-ionic surfactant treatment preserved >80% of the CEC of the smectite. The interlayer cations of the resulting surfactant-smectite were exchangeable as in the untreated smectite. Therefore, the non-ionic surfactant-smectite was much more efficient at removing heavy metal ions than activated carbon or cationic surfactant-treated smectite. The surfactant-smectite composites effectively removed aromatic chlorophenols from a pH 4.9 acetate buffer solution while untreated smectite did not adsorb these molecules. The enhanced adsorption of the aromatic compounds is attributed to the aliphatic segments of the two surfactants.

Roles of clays in soils

Abstract In soil science, the term clay refers to all particles less than 2 μm in diameter. Thus it includes layer silicates, oxides and other minerals. Clays are the source of many of the chemical and physical properties of soils that make them a useful medium for the growth of plants and for the less common uses such as a medium for the disposal of wastes. Clays add much of the diversity found in soils. The minerals in soil clays frequently differ from their counterparts in commercial deposits. Also, the behavior of soil clays is influenced by the associated minerals in the coarser fractions. Organic matter is an important reactant with clays of some soils, but it is beyond the scope of this review. The cation exchange properties of clays are among their most important properties in retaining plant nutrient ions (e.g., NH 4 + , K + , Ca 2+ , Mg 2+ , etc.). Cation selectivity of clays influences soils as a plant growth medium and as a disposal medium for wastes (e.g., radioactive and toxic metal ions). Native K in layer silicates of soils is the most important element provided to plants by illites and other micas. Clays contribute to the formation of soil structure by undergoing seasonal shrinking and swelling. Also, they are transported and form clay films that coat natural aggregates that characterize many friable soils. The dispersion and flocculation of clays are important reactions in the physical behavior of soils which in turn influence friability, water infiltration rate, erodibility and other behavioral properties. Vermiculite and smectite in soils frequently have Al 3+ or polymeric Al on the cation exchange sites. Thus the behavior of these minerals is different from structurally similar minerals in natural deposits. The Fe oxides in soils occur largely as goethite and hematite. Yet they contain Al substituted in their structures, consequently the crystals are smaller and less soluble than their ideal counterparts. Iron oxides contribute to the color, aggregation, and adsorptive properties of soils. Manganese oxides in soils contribute to the retention of trace metals (Co, Zn, Ba, Ni, etc.) and to the oxidation of Fe. Lithiophorite forms in acid soils thus marking another group of minerals that occurs in soils and that is influenced by Al in the structure or in interlayer positions as a result of weathering.

X-ray microspectroscopy and chemical reactions in soil microsites.

Soils provide long-term storage of environmental contaminants, which helps to protect water and air quality and diminishes negative impacts of contaminants on human and ecosystem health. Characterizing solid-phase chemical species in highly complex matrices is essential for developing principles that can be broadly applied to the wide range of notoriously heterogeneous soils occurring at the earths surface. In the context of historical developments in soil analytical techniques, we describe applications of bulk-sample and spatially resolved synchrotron X-ray absorption spectroscopy (XAS) for characterizing chemical species of contaminants in soils, and for determining the uniqueness of trace-element reactivity in different soil microsites. Spatially resolved X-ray techniques provide opportunities for following chemical changes within soil microsites that serve as highly localized chemical micro- (or nano-)reactors of unique composition. An example of this microreactor concept is shown for micro-X-ray absorption near edge structure analysis of metal sulfide oxidation in a contaminated soil. One research challenge is to use information and principles developed from microscale soil chemistry for predicting macroscale and field-scale behavior of soil contaminants.

Mineralogy of B horizons in alpine forest soils of Taiwan

The nature of minerals in the B horizons of alpine forest soils in subtropical and tropical areas remains to be identified. The objective of this study was to investigate the distribution of Fe-oxides and hydroxy-interlayered vermiculite (HIV) in typical alpine forest soils of Taiwan. Five pedons at roughly 2000 m elevation of Taiwan were selected as example for this study. High gradient magnetic separation (HGMS), conventional X-ray diffraction (XRD), differential X-ray diffraction (DXRD), and transmission electron microscopy (TEM) were employed to characterize the clay minerals. The content of crystalline Fe-oxides increased sharply from E to B horizons. Only Al-substituted lepidocrocite and goethite were identified by differential X-ray diffraction (DXRD) analysis in magnetic clay fractions of the B (or placic) horizons; no substantial hematite peaks appeared in the XRD patterns of any pedons. These observations are quite different from those of Spodosols or Spodosol-like soils developed in the temperate and frigid zones of North America. Hydroxy-interlayered vermiculite (HIV) was characterized by collapse of the 1.42-nm peak in the XRD diagrams toward 1.0 nm when the K-saturated clay samples were heated to 350°C. In the surface horizons, only vermiculite could be identified in the coarse clay fractions. The distribution patterns of acid ammonium oxalate extractable Fe and Al in these pedons indicate that Al and Fe were leached from the A horizons and accumulated in the B horizons when forming Al-substituted lepidocrocite, goethite, and HIV. This is attributed to the combined effect of organic acids, Al, and Fe in the pedogenic environments. The present findings are of fundamental significance in understanding the formation of Spodosol-like soils in alpine forest soils in the subtropics and tropics.