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Aluminum-pillared montmorillonites are useful materials for their application as catalysts, adsorbents and ceramic composites. The precursor is a pillared montmorillonite that is not thermally stabilized. The precursor preparation methods, textural properties and catalytic activity have been extensively investigated, but comparatively, studies concerning their thermal transformations at high temperature are limited. In this work, precursors were prepared using two types of montmorillonites, Cheto (Ch) and Wyoming (W), and using two different OH–Al polymer sources: hydrolyzed (H) and commercial (C) solutions. Structural and thermal transformations of the precursors with heating up to 1200 °C were determined by X-ray diffraction and thermogravimetric analysis. Thermal analysis of these precursors below 600 °C revealed the influence of OH–Al polymers from the two solutions. The major phases developed at 1200 °C from the original montmorillonites were mullite for W and cordierite for Ch. The content of these phases depended on the aluminum in the octahedral sheet of the pristine montmorillonites. Amorphous phase, cristobalite, spinel, sapphirine and others phases were also found. The intercalation of OH–Al polymers in montmorillonites caused an increase in amorphous content after treatment at 1030 °C; however, it favored mullite development above 1100 °C. Although total aluminum content of both W and Ch precursors was similar, the transformation to mullite was directly related to the octahedral aluminum/magnesium ratio. The phase composition of the products at 1200 °C was not dependent on the type of intercalated OH–Al polymers. The increase in mullite content of the thermally treated precursors contributes to its possible application as advanced ceramic products. Fil: Martinez, Juan Manuel. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Tecnología de Recursos Minerales y Cerámica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Tecnología de Recursos Minerales y Cerámica; Argentina Fil: Volzone, Cristina. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Tecnología de Recursos Minerales y Cerámica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Tecnología de Recursos Minerales y Cerámica; Argentina Fil: Garrido, Liliana Beatriz. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Tecnología de Recursos Minerales y Cerámica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Tecnología de Recursos Minerales y Cerámica; Argentina

A polymeric Al-modified bentonite (B-OHAl) obtained by intercalation of OH-Al species was used as precursor for mullite-containing coatings. Raw clay and B-OHAl were characterized by X-ray fluorescence (XRF), Infrared spectroscopy (FTIR), X-ray diffraction (XRD), thermogravimetric and differential thermal analysis (TG-DTA). Rheological and electrokinetic behavior of B-OHAl dispersions were optimized by the addition of sodium polyacrylate (NaPA) for its use in dip coating on ceramic substrates. Moderate densification and mullite development of B-OHAl by thermal treatment up to 1200 °C was observed by mercury intrusion porosimetry (MIP), XRD and scanning electron microscopy SEM. NaPA addition on dispersions and an increase in porosity values in substrate led to higher amounts of coating retained in dip coated composites sintered at 1200 °C. Fil: Martinez, Juan Manuel. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Tecnología de Recursos Minerales y Cerámica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Tecnología de Recursos Minerales y Cerámica; Argentina Fil: Volzone, Cristina. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Tecnología de Recursos Minerales y Cerámica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Tecnología de Recursos Minerales y Cerámica; Argentina Fil: Garrido, Liliana Beatriz. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas. Centro de Tecnología de Recursos Minerales y Cerámica. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Centro de Tecnología de Recursos Minerales y Cerámica; Argentina

The present paper presents the study of light green smectite clay, from Paraiba, Brazil, submitted to mild acid attack under moderated conditions. Usually, clays are subjected to treatment with strong inorganic acids at temperatures near the boiling point and at high acid concentrations and then, widely used as bleaching agents. The treatment occurred under bellow boiling temperature and at short times of reaction (90°C, reaction times of 1, 6, 12, 18 and 24 hours in close reactor, concentration of the aqueous solution of hydrochloric acid 1.5 M, clay/acid solution ratio of 1g/10mL). The purpose of these attacks is to reduce the concentration of impurities providing color, with minimal change in the clay minerals structure, aiming at use in products of high value such as cosmetics and polymer/clay nanocomposites. The raw clay and the attacked samples were characterized by X-ray diffraction (XRD), cation exchange capacity (CEC), stereomicroscopy, scanning electron microscopy (SEM) and energy dispersive X-ray detector (EDS).

For industrial use, the smectite clays are usually treated with inorganic acid of high concentration at temperatures under boiling point, which provide the bentonite´s bleaching power. In the present paper, a sample of brown smectite from Paraiba, Brazil, was submitted to treatment under moderate conditions (90°C, reaction times of 1, 6, 12, 18 and 24hours in close reactor, concentration of the aqueous solution of hydrochloric acid 1.5M, clay/acid solution ratio of 1g/10mL), aiming to reduce impurities, responsible for the color of the clay, without causing significant changes in their structure. The samples were characterized by scanning electron microscopy (SEM), energy dispersive X-ray detector (EDS), stereomicroscopy, Cation Exchange Capacity (CEC), Thermal Analysis (TG/DTA), and X-ray diffraction (XRD). It was observed a bleaching in samples with time of 12h to 18h. With the DRX was possible to monitor the peak intensity of the clay structure and the sample with 12 hours of treatment was not significantly altered its crystalline structure, maintaining the peak clay at d(001). The most pronounced changes in the bleaching occurred within the first 12 hours of acid treatment. Thus, clay can be used in products with high added value.

Montmorillonites, before and after being saturated with Na+, K+, H+, Ca2+ and Al3+ ions, were studied to analyse their O2, N2, CO, CH4, C2H2 and CO2 gas retentions at 25 °C and 0.1 MPa, previously degassed at 100 °C. The homoionic-montmorillonites were characterized by interlayer spacing measurements and BET surface area. The levels of gas adsorptions for C2H2 (0.184–0.218 mmolg−1) and CO2 (0.170–0.208 mmolg−1) by original and homoionic montmorillonites were higher than those for N2 (0.068–0.074 mmolg−1), O2 (0.070-0.076 mmolg−1), CO (0.070–0.080 mmolg−1) and CH4 (0.082–0.086 mmolg−1). The C2H2 and CO2 gas adsorptions by different cation-exchanged forms of montmorillonite follows the following order: H- > K- > Ca- > Al- > Na-montmorillonite. The ionic radius of the exchangeable cations, the interlayer separation and surface area of the montmorillonite influenced the gas adsorption.

In this work, a bentonite clay from Mendoza, Argentina was activated with H2SO4 (4 and 8 N) at 90oC for 2 and 3.5 hours. Under these conditions several cations were removed from the octahedral sheet (Mg, Al, and Fe) and the DTA-TGA curves of the solids obtained after treatment were modified. Treatment time and acid concentration increased the degree of destruction of the bentonite structure. Activated samples were tested in order to verify their capacity to bleach soybean oil and were compared to a standard commercial bleaching clay. Treated samples are more efficient in bleaching than the standard.

Retention of chromium (III) from a tanning wastewater by modified Al-bentonites was studied. One bentonite from San Juan province, Argentina, was used. Al-bentonite was prepared by contact of bentonite with hydrolyzed OH-Al solutions (0.10 M in Al) for 24 hours. The modified Al-bentonites were obtained by: a) treatment with 0.5 M sodium chloride; b) with 0.5 M sodium chloride adjusted at pH 8; and c) treatment with an hexametaphosphate solution after sodium addition. Then, the samples were dried at 100 °C and heated at 500 °C. The chromium (III) retention by samples was carried out in batch system putting in contact the material with a 2000 ppm Cr tannery waste at different times. The retained chromium was characterized by analyzing the supernatant using UV-visible spectroscopy. The different chromium retention was correlated with structural characteristics of the solids.Foi estudada a retenção de cromo (III) de águas residuais por meio de Al-bentonitas modificadas. Foi usada uma bentonita da província de San Juan, Argentina. As bentonitas-Al forma preparadas colocando-as em contato com soluções (0,10 M Al) hydrolizadas de OH-Al durante 24 horas. As bentonitas-Al modidicadas foram obtidas por meio de: a) tratamento com cloreto de sódio 0,5 M; b) com cloreto de sódio 0,5 M sodium com pH ajustado para 8; e c) tratamento com uma solução de hexametafosfato após a adição de sódio. As amostras foram então secas a 100 °C e aquecidas a 500 °C. A retenção do cromo (III) pelas amostras foi feita em lotes colocando o material em contato em diferentes tempos com um resíduo contendo 2000 ppm de cromo. O cromo retido foi caracterizado por meio de análise do sobrenadante usando espectroscopia UV-visível. As diferentes retenções de cromo foram correlacionadas com características estruturais dos sólidos.

A ativação ácida de uma argila tem por finalidade aumentar as suas propriedades adsortivas e catalíticas. Nesse estudo, uma amostra de argila bentonítica, proveniente da Província de Mendoza (Argentina), foi ativada com diferentes concentrações (4 e 8 N) por ácido sulfúrico e clorídrico. Para verificar a influência das concentrações e do tipo de ácido usado na ativação da argila, utilizou-se técnicas de difração de raios X, análise térmica diferencial e termogravimétrica e análise química. Os resultados mostraram que houve modificação na estrutura do material argiloso após o ataque ácido. O tratamento com ácido sulfúrico e clorídrico sobre uma mesma bentonita originou produtos com diferentes características estruturais. The clay acid activation has the purpose of increasing its adsorbent and catalytic properties. In this study, a bentonite clay sample from Mendoza (Argentine) was activated in different concentrations (4 N and 8 N) through the use of sulphuric and hydrochloric acid. To verify the influence of concentrations and the kind of acid utilized in the clay activation, it was utilized techniques of X-ray diffraction, thermogravimetric and differential thermal analysis and chemical analysis. The results have shown that the clay structure was modified after acid attack. Sulphuric and hydrochloric acid treatment in the same bentonite originated products with different structural characteristics.

A ativação ácida de uma argila tem por finalidade aumentar as suas propriedades adsortivas e catalíticas. Nesse estudo, uma amostra de argila bentonítica, proveniente da Província de Mendoza (Argentina), foi ativada com diferentes concentrações (4 e 8 N) por ácido sulfúrico e clorídrico. Para verificar a influência das concentrações e do tipo de ácido usado na ativação da argila, utilizou-se técnicas de difração de raios X, análise térmica diferencial e termogravimétrica e análise química. Os resultados mostraram que houve modificação na estrutura do material argiloso após o ataque ácido. O tratamento com ácido sulfúrico e clorídrico sobre uma mesma bentonita originou produtos com diferentes características estruturais.The clay acid activation has the purpose of increasing its adsorbent and catalytic properties. In this study, a bentonite clay sample from Mendoza (Argentine) was activated in different concentrations (4 N and 8 N) through the use of sulphuric and hydrochloric acid. To verify the influence of concentrations and the kind of acid utilized in the clay activation, it was utilized techniques of X-ray diffraction, thermogravimetric and differential thermal analysis and chemical analysis. The results have shown that the clay structure was modified after acid attack. Sulphuric and hydrochloric acid treatment in the same bentonite originated products with different structural characteristics.

Rheological changes were found in smectite (Wyoming- and Cheto-type montmorillonites) suspensions after structural modifications. The effect of the particle size and Na+ exchange on the flow curves of 6% wt/wt suspensions of smectites with and without Na2CO3 were examined. Mineralogical, structural and physicochemical characteristics were studied by X-ray diffraction (XRD), infrared spectroscopy (IR), cationic exchange capacity (CEC), Mg2+, Al3+ determinations, particle size distribution and swelling index (SI). Grinding in an oscillating mill modified the particle sizes. The montmorillonite grain size and the structural disorder increased after larger grinding times. The grinding treatment modified the apparent viscosity and the yield stress of the montmorillonite suspensions. The homoionic Na Cheto-type montmorillonite with fine particle size (obtained by grinding) increased the flow properties. Nevertheless, rheological properties were lower than those of suspensions of the Wyoming-type montmorillonite. Montmorillonite-types reacted differently with Na2CO3 additions and this behavior may be related to their structural composition. The Na2CO3 activation improved the flow properties of the original Wyoming-type montmorillonite and after 30 s grinding.Foram encontradas mudanças reológicas em suspensões de esmectitas (montmorillonitas tipos Wyoming e Cheto) após modificações estruturais. Foi examinado o efeito do tamanho de partícula e troca de Na+ nas curvas de escoamento de suspensões de esmectitas 6% peso com e sem Na2CO3. As características mineralógicas, estructurais e físico-químicas foram estudadas por difração de raios X (DRX), espectroscopia no infravermelho (IV), capacidade de troca catiônica (CTC), determinações de Mg2+ e Al3+, de distribuição de tamanho de partículas e de índice de expansão (swelling index - SI). Moagem em moinho oscilatório modificou o tamanho das partículas. O tamanho de grão da montmorillonita e a desordem estrutural aumentaram após maiores tempos de moagem. O tratamento por moagem modificou a viscosidade aparente e o limite de escoamento das suspensões de montmorillonita. A montmorillonita homoiônica de Na do tipo Cheto com pequeno tamanho de partícula (obtido por moagem) melhorou as propriedades de escoamento. Entretanto, as propriedades reológicas foram piores que as de suspensões de montmorillonita do tipo Wyoming. Os diferentes tipos de montmorillonitas reagiram de modo diferente com adições de Na2CO3 e este comportamento pode estar relacionado com suas composições estruturais. A ativação por Na2CO3 melhorou as propriedades de escoamento da montmorillonita tipo Wyoming original após moagem por 30 s.

Dioctahedral smectites (Cheto- and Wyoming-type montmorillonites and a beidellite) were treated with two hydrolysed OH-Al solutions (0.02 M in Al) containing different OH-Al complexes. The ratio of ∼3.25 mmol of Al per gram of smectite was used. The total Al and the presence of OH-Al species in solution before and after reaction with smectites were determined by the kinetics of Al-Ferron reaction colour development. The composition of the Al species retained by smectites was not the same as that present in the original solution added. The slow-reacting complexes present in the solution were preferentially adsorbed by dioctahedral smectites. Smectites prepared from slow-reacting polymer solutions showed changes in interlayer separation,b–dimension, order along thecaxis and spectroscopic properties, after storage at room temperature. The OH-Al Cheto-type montmorillonite prepared from both solutions showed more retention of Al, best stability at room temperature and after thermal treatment at 550°C than interlayered OH-Al Wyoming-type montmorillonite and OH-Al beidellite smectites.

Acid smectites in natural condition and after thermal treatment up to 900 °C were studied for their O2, CH4 and CO2 gas retentions at 25 °C and 1 kg/cm2. Two smectites, one dioctahedral and one trioctahedral, were treated with 5.0 N sulphuric acid solution for 15 and 60 min. The gas adsorptions by the smectites increased after acid treatments. The O2 (0.014–0.030 mmol/g) and CH4 (0.045–0.063 mmol/g) gas retention values were small whereas the values corresponding to CO2 (0.206–0.357 mmol/g) retentions were high for acid smectites. The acid trioctahedral smectite showed higher gas adsorption values than acid dioctahedral smectite. The CO2 gas adsorption values by acid smectites heated up to around 600 °C, decreased around 10% and 20% for acid trioctahedral and dioctahedral smectites, respectively. After that drastically decreased and at 900 °C both acid smectites showed very small adsorption values. The chemical composition, the structure and the texture of the smectites influenced the gas retention.

The adsorption of sulphuric acid on smectite from acidic aqueous solutions was studied. The amounts of cations dissolved in each equilibrium solution were determined by chemical analysis. Simultaneously, the original smectite and the smectite after each test were characterized by infrared, X-ray diffraction and swelling index. The results obtained permitted us to determine that the substitutions of the exchange cations and the chemical attack occurred at very different acid concentrations and treatment times. It was established that during the acid treatment of the smectite, a progressive damage of its crystalline structure was produced. Finally, the influences of the substitution of exchange cations and of the chemical attack in the swelling index were determined.A adsorção de ácido sulfúrico em esmectita de soluções aquosas ácidas é estudada. As concentrações de cátions dissolvidos em cada solução em equilíbrio foram determinadas por análise química. As esmectitas original e após cada teste foram simultaneamente caracterizadas por infravermelho, difração de raios X e índice de crescimento. Os resultados obtidos permitiram determinar que as substituições dos cátions de troca e o ataque químico ocorreram em diferentes concentrações de ácido e tempos de tratamento. Foi verificado que durante o tratamento em ácido da esmectita foi produzido um dano progressivo da sua estrutura cristalina. Finalmente foram determinadas as influências da substituição dos cátions de troca e do ataque químico no índice de crescimento.

Different dioctahedral and trioctahedral smectites were treated with OH–Cr solutions. OH–Cr smectites were analyzed after thermal treatment up to 1000°C. The OH–Cr solutions were prepared using 0.1 M chromium nitrate and 0.2 N NaOH hydrolyzed at 60°C for one day. The OH–Cr smectites were characterized by differential thermal analyses and X-ray diffraction. The Cr2O3 appeared at around 420°C and was present together with transformation smectite phases throughout all temperature ranges studied (up to 1000°C). Phases at high temperature owing to the exchangeable cations in original smectites were not present when smectites were treated with OH–Cr solutions.

The clay minerals, kaolin and montmorillonite, were compacted at different pressures up to 300 MPa. The textural characteristics (pore radius, surface area and porosity) of the clay minerals were measured after compaction and related to the particle size and the cation exchange capacity of these clays. Kaolins and montmorillonites with and without compaction were characterized by mercury intrusion using a porosimeter within the range 0.1 MPa to 200 MPa. A negative linear correlation was obtained between the mean pore radius of compacted clays and the cation exchange capacity. A larger percentage of fine particles originated compacts with small pore sizes. The pore radius and the porosity of the clay minerals diminished with increasing compaction pressure, whereas the surface area increased. Quecksilberintrusion von kompaktierten Tonmineralen Die Tonminerale Kaolinit und Montmorillonit wurden mit verschiedenen Drucken bis 300 MPa kompaktiert. Kennwerte der Textur und des Gefuges (Porenradius, Oberflache und Porositat) wurden nach der Kompaktion gemessen und mit der Teilchengrose und der Kationenaustauschkapazitat korreliert. Die Porengrosenverteilung wurde durch Quecksilberintrusion im Bereich 0.1 bis 200 MPa vor und nach der Verdichtung untersucht. Der durchschnittliche Porenradius kompaktierter Tone korreliert linear mit der Kationenaustauschkapazitat. Ein hoher Prozentgehalt kleiner Teilchen bewirkt ein stark kompaktiertes System mit kleinen Porengrosen. Mit zunehmenden mechanischen Drucken nehmen der Porenradius und die Porositat der Tonminerale ab, und die Oberflache vergrosert sich.

Different E samples were dispersed in distilled water (2% w/w) and the fresh hydroxy-chromium solutions were added slowly with stirring. After two hours in contact with continuous stirring, the solids were separated. The 0.5, 1.5, 3.5, 5, 10 and 20 mmol Cr/g samples were prepared (E-0.5, E-1.5, E-3.5, E-5, E-10 and E-20). The supernatants S-0.5, S-1.5, S-3.5, S-5, S-10 and S-20 corresponding to the different treatments with 0.5, 1.5, 3.5, 5, 10 and 20 mmolCr/g of sample respectively were analyzed by spectrophotometer. The solids were washed several times with distilled water in order to remove the electrolyte excess. The differential thermal analyses (DTA) diagrams were carried out with a Netzsch apparatus using ot-Al203 as a reference and a heating rate of 10*C/min.

Two bentonite clays with different mineralogical compositions from Mendoza, Argentine, were activated with H2SO4 solutions of 4 and 8 N at 90ºC for 3.5 hours. This treatment affected clay structural properties, as was shown by thermogravimetry, infrared spectrometry and chemical analysis. Bleaching efficiency for sunflower oil was strongly dependent on the acid concentration used for clay activation. The samples have bleaching capacity comparable to that observed with a commercial adsorbent standard. The mineralogical composition of natural clays influenced the properties of the activated clays.

Thermal and mechanical treatment effects on a raw smectite (E), its acid activated product (Ea) and a commercial activated smectite (F) were studied by X-ray diffraction (XRD) and isoelectric point (IEP) measurements using the transport number method. The samples were divided into two groups: samples of one group were heated between 350 and 950°C and those of the other group were ground for between 300 and 3600 s. Both treatments, on natural and activated smectites, shift the pH of the IEP to higher values. IEP values of activated smectites (Ea and F) were higher than that of natural samples (E), explained by a removal of structural cations and their superficial adsorption.

Hydroxy-chromium solutions were prepared from chromium nitrate solutions by adding NaOH with OH/Cr = 2. The solutions were treated at 20~ and 60~ The hydrolysis "times were from 1 to 100 days. Polymeric species in hydrolyzed chromium solutions were followed by visible absorption spectra within the range 325-800 nm and by pH measurement. OH-Cr-smectite with high d(001) spacing (2.07 nm) was obtained when hydroxy-chromium solution was prepared at 60~ and with 1-day hydrolysis. When this sample was heated up to 350~ the basal spacing collapsed at 1.8 nm. The samples were characterized by X-ray diffraction and N2 adsorption-desorption isotherms.

The effect of Na 2 CO 3 on several Argentine bentonites was studied. Mineralogical and physicochemical characteristics were studied by means of XRD, DTA, DTA-piperidine, CEC, exchangeable cations, surface area determination, particle size distribution, gelation and swelling indexes. It was observed that the increase of the apparent viscosity at 160 s −1 and the gel strength, are related to the beidellite/montmorillonite ratio, the percentage of particles ≤ 0.5 μm and the Na/Ca ratio.

The oxidation of Fe(II) produced by dry oscillating milling on natural magnetite was investigated by X-ray photoelectron spectroscopy (XPS), determinations of point of zero charge (PZC), and Mossbauer spectroscopy. Examinations of surface samples (original and milled at different times), by XPS, indicate an increase in Fe(III) content in milled samples evidenced by modifications in Fe 2p and O ls photopeaks. The deconvolution of O ls photopeaks agree with an increase of Fe(III)/Fe(II) relationship of 2.5 to 2.9 from original and sample milled at 40' respectively. Determinations of PZC let us infer the formation of an oxide mixture, by grinding, of Fe 3 O 4 and an iron oxide of higher PZC (that could be α-Fe 2 O 3 or γ-Fe 2 O 3 ). By Mossbauer spectroscopy the presence of γ-Fe 2 O 3 was revealed in amounts that increased with grinding time.

Rheological changes were found in smectite (Wyoming- and Cheto-type montmorillonites) suspensions after structural modifications. The effect of the particle size and Na+ exchange on the flow curves of 6% wt/wt suspensions of smectites with and without Na2CO3 were examined. Mineralogical, structural and physicochemical characteristics were studied by X-ray diffraction (XRD), infrared spectroscopy (IR), cationic exchange capacity (CEC), Mg2+, Al3+ determinations, particle size distribution and swelling index (SI). Grinding in an oscillating mill modified the particle sizes. The montmorillonite grain size and the structural disorder increased after larger grinding times. The grinding treatment modified the apparent viscosity and the yield stress of the montmorillonite suspensions. The homoionic Na Cheto-type montmorillonite with fine particle size (obtained by grinding) increased the flow properties. Nevertheless, rheological properties were lower than those of suspensions of the Wyoming-type montmorillonite. Montmorillonite-types reacted differently with Na2CO3 additions and this behavior may be related to their structural composition. The Na2CO3 activation improved the flow properties of the original Wyoming-type montmorillonite and after 30 s grinding., Foram encontradas mudanças reológicas em suspensões de esmectitas (montmorillonitas tipos Wyoming e Cheto) após modificações estruturais. Foi examinado o efeito do tamanho de partícula e troca de Na+ nas curvas de escoamento de suspensões de esmectitas 6% peso com e sem Na2CO3. As características mineralógicas, estructurais e físico-químicas foram estudadas por difração de raios X (DRX), espectroscopia no infravermelho (IV), capacidade de troca catiônica (CTC), determinações de Mg2+ e Al3+, de distribuição de tamanho de partículas e de índice de expansão (swelling index - SI). Moagem em moinho oscilatório modificou o tamanho das partículas. O tamanho de grão da montmorillonita e a desordem estrutural aumentaram após maiores tempos de moagem. O tratamento por moagem modificou a viscosidade aparente e o limite de escoamento das suspensões de montmorillonita. A montmorillonita homoiônica de Na do tipo Cheto com pequeno tamanho de partícula (obtido por moagem) melhorou as propriedades de escoamento. Entretanto, as propriedades reológicas foram piores que as de suspensões de montmorillonita do tipo Wyoming. Os diferentes tipos de montmorillonitas reagiram de modo diferente com adições de Na2CO3 e este comportamento pode estar relacionado com suas composições estruturais. A ativação por Na2CO3 melhorou as propriedades de escoamento da montmorillonita tipo Wyoming original após moagem por 30 s., Centro de Tecnología de Recursos Minerales y Cerámica

The purpose of the work was to obtain an improvement in the method, proposed by Greene-Kelly, to differentiate montmorillonite from other smectites using LiBr (substituting to LiCl) and plates of glass, Teflon or steel. For the test, montmorillonite Clay Spur and nontronite 33-a-Garfield Washington were used

The zero points of charge (ZPC) of a natural bentonite and those of its homoionic forms (Na, Ca and Al) were determined by the transport number method. The influence of the interlayer cation was observed in the different pH values of the ZPC obtained. No influence of the water contains was observed. Bestimmung des Ladungsnullpunktes monoionisch belegten Montmorillonits mit Hilfe der Transportzahlmethode Zur Bestimmung des Ladungsnullpunktes eines naturlichen Bentonites und seiner homoionischen (Na, Ca, Al) Formen wurde die Transportzahl-Methode angewendet. Aus dem unterschiedlichen pH-Wert des Ladungsnullpunkts last sich ein Einflus der verschiedenen Zwischenschichtkationen ableiten. Der Wassergehalt zeigte dagegen keinen Einflus.

The adsorption of sulphuric acid on smectite from acidic aqueous solutions was studied. The amounts of cations dissolved in each equilibrium solution were determined by chemical analysis. Simultaneously, the original smectite and the smectite after each test were characterized by infrared, X-ray diffraction and swelling index. The results obtained permitted us to determine that the substitutions of the exchange cations and the chemical attack occurred at very different acid concentrations and treatment times. It was established that during the acid treatment of the smectite, a progressive damage of its crystalline structure was produced. Finally, the influences of the substitution of exchange cations and of the chemical attack in the swelling index were determined. A adsorção de ácido sulfúrico em esmectita de soluções aquosas ácidas é estudada. As concentrações de cátions dissolvidos em cada solução em equilíbrio foram determinadas por análise química. As esmectitas original e após cada teste foram simultaneamente caracterizadas por infravermelho, difração de raios X e índice de crescimento. Os resultados obtidos permitiram determinar que as substituições dos cátions de troca e o ataque químico ocorreram em diferentes concentrações de ácido e tempos de tratamento. Foi verificado que durante o tratamento em ácido da esmectita foi produzido um dano progressivo da sua estrutura cristalina. Finalmente foram determinadas as influências da substituição dos cátions de troca e do ataque químico no índice de crescimento.

On etudie les correlations entre la composition chimique du kaolin, sa structure cristalline et son point de charge zero

Two montmorillonitic clays were put into contact with a solution containing inorganic OH-Al polymers and subsequently washed and dried. The obtained solid (i.e.the clays with the OH -Al species in the montmorillonite interlayer) which was called the precursor, was subjected to a thermal treatment up to 1000 i C using DTA-TG for analysis at low temperature. Additionally, the structural changes of the precursor by heating at 1030, 1100 and 1200 i C for 2 hours and that of the natural clays were examined. The crystallinity and formation of new phases was followed by x-ray diffraction analysis. Mullite and cordierite were originated depending on the different contents of aluminium and magnesium in the structure of natural montmorillonite, respectively, accompanied with other phases. The intercalated OH-Al species in both clays favored the increase in the mullite content in the final products. However, the transformation to this phase was directly related to the octahedral aluminium of the natural clay and thus mullite was found to be the dominant phase from montmorillomite containing higher octahedral Al.