Cristina Volzone

Modified bentonitic clay minerals as adsorbents of CO, CO2 and SO2 gases

The adsorptions of CO, CO2 and SO2 gases by two bentonitic clay minerals from Patagonia, Argentina, in their natural state and after acid treatments, were analyzed. The clay minerals (bulk and <2 μm size fraction) were modified with 3.0 and 6.0 N HCl solutions at boiling temperature during 3 h. The samples were characterized by chemical analysis, X-ray diffraction and by N2 adsorption–desorption isotherms. Equilibrium adsorption of the gas was measured at 25 °C and 1 kg/cm2. Gas adsorptions by bentonitic clay minerals increased after acid treatments and the values were analyzed as a function of structural and textural changes. The retention values of the SO2 (0.636–1.232 mmol/g) by clay minerals were higher than CO2 (0.218–0.516 mmol/g) and CO (0.075–0.119 mmol/g). A high smectitic component in the original clay mineral, an increase in BET surface and micropore volume and an increase of the Si/(Al+Fe+Mg+Ti) ratio of the materials after acid treatments influenced to get a larger retention of the CO2 and SO2 gases.

Selective gas adsorption by amorphous clay mineral derivatives

Amorphous derivates prepared by aqueous reaction of various aluminosilicate clay minerals with concentrated KF solution at 80–110°C were studied for their gas adsorption properties. The four clay minerals studied are halloysite, a well-crystallized kaolinite, a poorly crystallized kaolinite, and a montmorillonite. The gases tested are N2, O2, CH4, CO, CO2, and C2H2. The kaolin-group mineral derivatives are characterized by substantial reduction in particle size, high specific surface, and significant selectivity towards CO2 and C2H2 relative to the other gases. The montmorillonite derivative shows no increase in adsorption over the starting material, however, for all the materials high adsorption of CO2 and C2H2 was observed. Levels of gas adsorption and gas adsorption ratios are comparable to pillared clays.

Selective gas adsorption by metal exchanged amorphous kaolinite derivatives

Metal exchanged amorphous kaolinite derivates are studied for their gas adsorption properties. The kaolinite derivatives were prepared by aqueous reaction of the clay with concentrated KF solution at 80–110°C. The K+ ions were then exchanged by Cs+, Sr2+, La3+, Fe3+ or Cu2+. Fe(II)- and Cu(I)-containing derivatives were prepared by reduction under H2. The gases tested were N2, O2, CH4, CO, CO2, and C2H2. Correlations between gas retention and various physical and chemical variables are investigated. Gas retention levels normalised against BET surface show that level of adsorption is at least partly determined by surface chemical composition. The highest gas retention levels per unit area are achieved for alkali metal exchanged derivatives or alternately for exchange cations with the largest ionic radius.

Effect of induced structural modifications on the physicochemical behavior of bentonite

Abstract The effect of impact and friction milling on the structure and texture of a bentonite, in its natural and in several monoionic forms (H + , Na + , Ca 2+ , Al 3+ ), is studied. An increase of treatment time shows progressive damage to the crystalline structure. The presence of different exchangeable ions does not exert a great influence on the behavior of the mineral. The physicochemical and structural alterations are studied by XRD, DTA, TGA, IR, CEC and swelling index.

SO2 gas adsorption by modified kaolin clays: Influence of previous heating and time acid treatments

Modified kaolin clays were used as adsorbents for SO(2) gas adsorptions. The clays were heated up to 900 °C previous to acid treatments with 0.5 N sulfuric acid solutions at boiling temperature during different times up to 1440 min. Equilibrium adsorption at 25 °C and 0.1 MPa was carried out by using a volumetric apparatus. The samples were characterized by chemical analysis, X-ray diffraction and infrared analysis. The heating of the clays followed by acid treatment improved the adsorption capacity of the kaolin clays. The presence of amorphous silica and hydroxyl in the final products improved SO(2) adsorption capacity. Better properties for SO(2) adsorption were found in kaolin rich in not well ordered kaolinite clay mineral.

Removal of Metals by Natural and Modified Clays

This chapter describes removal of metals by natural and modified clays. Metallic elements are classified because of their physicochemical properties and these occupy three-quarters of the periodic table of elements. Growth in population and advances in science and technology have brought comfort, but a number of natural systems were altered and health and the environment have been affected as well. Heavy metals refer to high-density metallic elements such as mercury, cobalt, copper, chromium (III),and iron. However, some of these metals including manganese, molybdenum, vanadium, strontium, zinc, etc, are essential to human, animal and plant life. On the contrary, excessive levels of some of them may be toxic. Others that are harmful to health even in low concentration such as mercury, lead, cadmium, chromium (VI), arsenic, and antimony. Most often, cadmium occurs in small quantities associated with zinc ores but also with copper and lead ores. These may be carried out through different techniques: chemical precipitation, solvent extraction, ultrafiltration, ionic exchange, adsorption, biosorption, photocatalysis, reverse osmosis, evaporation, non-conventional flotation, etc.

OH-CR(III) in dioctahedral and trioctahedral smectites : texture and structure changes

Hydroxy-chromium smectites are of interest for use in catalysis and as adsorbents. This paper determines the influence of the OH-Cr species on the structure and texture of dioctahedral smectites (montmorillonite, beidellite and nontronite) and trioctahedral smectites (saponite and hectorite). Interlayers with larger spacing (approximately 2.05 nm), different specific areas and micropore volumes were obtained. Such behavior could be related to the different structural characteristics of the smectites.

Swelling of TMA(tetramethylammonium)- and HDP(hexadecylpyridinium)-montmorillonites in water and toluene media: influence of the type montmorillonites

Organo-clays were prepared by exchange cations of the montmorillonite with tetramethylammonium (TMA)- and hexadecylpyridinium (HDP)-chloride. Two different montmorillonite types were studied. Two amounts of each organic substances (1 and 4 cation exchange capacity times of montmorillonite) were contacted with each montmorillonite clay for 1 and 24 h. The solids were characterized by X-ray diffraction and swelling index. The swelling was measured in water and toluene media. The structural characteristics of montmorillonites changed after organo treatment and showed different behaviour in water and toluene media. The type of montmorillonite, the organic cation intercalates (TMA, HDP) and condition of treatment influenced in the different swelling in water and toluene media.

Influence of organobentonite structure on toluene adsorption from water solution

Due to increase water pollution by organic compound derived from hydrocarbons such as toluene, several alternative technologies for remediation of polluted water have been originated. In this work natural bentonites were modified with cetyltrimethylammonium (CTMA+) for obtaining organophilic bentonites. The obtained CTMA-bentonites would be suitable for use as adsorbents of toluene present in water. The influence of structural characteristics of CTMA-bentonites on their adsorption capacity was studied. It was shown that adsorption of toluene depended on homogeneous interlayer space associated with arrangements of CTMA+ paraffin-monolayer and bilayer models, accompanied by a high degree ordering of the carbon chain of organic cation in both arrangements. However, packing density would not have an evident influence on the retention capacity of these materials. The solids obtained were characterized by chemical analysis, X-ray diffractions and infrared spectroscopy. Toluene adsorption was measured by UV-visible spectrophotometer. Adsorption capacity was studied by determining adsorption isotherms and adsorption coefficient calculation. The adsorption isotherms were straight-line indicating a partition phenomenon of toluene between the aqueous and organic phase present in organophilic bentonites.

Hydration of α-pinene catalyzed by acid clays

AbstractThe hydration reaction of α-pinene in the presence of natural clays treated with monochloroacetic acid as catalyst to obtain oxygenated compounds was studied. Catalysts were characterized using X-ray diffraction, differential thermal analysis, programmed thermal desorption of adsorbed pyridine, and infrared spectroscopic analysis of adsorbed pyridine to determine Brønsted and Lewis acid sites. Catalytic tests revealed that treatment of the natural clay with the acid improved the catalytic activity and the selectivity toward oxygenated products by increasing the acidity of the catalyst. The selectivity toward oxygenated compounds increased with the augment of the α-pinene conversion because of greater contact between water molecules with the remaining α-pinene molecules. The natural clay without treatment produced compounds resulting from α-pinene isomerization, whereas the treated clays produced alcohols and other products in addition to isomerization compounds. After a certain time, the α-terpineol was isomerized into cineols. Studies of the reusability of the JAL catalyst were performed (clay treated with monochloroacetic acid). As the number of reuses increased, the percent conversion decreased; however, the selectivity toward oxygenated compounds increased.