The bleaching of cottonseed oil by alumina-pillared (Al-pillared) acid-activated clays was investigated. Acid activation of a Ca-rich montmorillonite (CMS STx-1) following treatment with 1, 4, and 8 eq/L sulfuric-acid solutions, as well as subsequent pillaring with alumina, produces new materials. These materials have bleaching properties dependent upon the extent of activation of the clay prior to pillaring. The pillared acid-activated montmorillonites possessed higher bleaching efficiency compared to pillared products of the untreated clay. Mild activation of the montmorillonite matrix, pillaring with the Keggin ion [Al13O4(OH)24(H2O)12]7+, and calcination temperatures to 500°C produced materials with the best fractional degree of bleaching. Direct comparison to the performance of a commercial bleaching earth (Tonsil Optimum 214, Sud-Chemie AG. Moosburg, Germany) shows that the efficiency of the Al-pillared acid-activated montmorillonite may be improved. The optimization of the bleaching process is achieved via a judicious utilization of intermediate surface area, relatively high acidity, and enhanced pore volume.

A ferrous saponite (griffithite) from Griffith Park (California, USA) was treated with solutions of HCl (0.62, 1.25 and 2.5% by weight) at 25°C for 2, 6, 24 and 48 hours. The resulting solids were characterized by XRD, FT-IR spectroscopy, thermal analyses, SEM, TEM and nitrogen adsorption isotherms at 77 K, showing the destruction of silicate structure by the treatments. The free silica generated by these treatments was digested and determined in all samples. Several samples had specific surface areas up to 250 m2/g, with maximum values which are 10 times higher than the surface area of natural saponite (35 m2/g). A sudden decrease in specific surface areas was observed when free silica was digested, which indicates that free silica makes a very important contribution to the surface area of leached samples.

Bentonites are excellent materials for sequestering various metal cations because of the cation fixation ability of the constituent montmorillonite layers, but sometimes, such as in the case of Cu2+, the exact location of cation fixation with respect to the clay layers is difficult to determine. Na-montmorillonite was prepared from the <2 µm fraction of the bentonite Calcigel (from Bavaria, Germany) and exchanged by Cu2+ and Na+ or by Cu2+ and ${\text{NH}}_4^{+}$\$\end{document} cations. The resulting materials (bi-ionic Cu-Na and Cu-NH4 samples, respectively, as well as homo-ionic forms with Cu2+, Na+ and ${\text{NH}}_4^{+}$\$\end{document}) were heated for 24 h at temperatures of 300 and 450°C and the structural evolution characterized using X-ray diffraction (XRD) analysis, Fourier Transform Infrared (FTIR) spectroscopy, and differential scanning calorimetry (DSC) analysis.

The XRD patterns showed that the Cu sample and the Cu-Na sample have basal spacings of 12.5 Å. Upon heating at 300 and 450°C, the layers collapsed to 9.5 Å. In contrast, the d001 value in the NH4 sample and Cu-NH4 sample decreased to 10.0 Å and 10.2 Å, respectively, during the heat treatment. The Cu2+ ions migrated irreversibly into the montmorillonite structure.

For the NH4 and the Cu-NH4 samples, DSC analyses show that NH3 evolved at between 300 and 400°C though the octahedral sheet was not altered substantially by the H+ generated. Infrared spectra show that the bands of the Si-O and OH vibrations of all samples were changed upon heating due to the movement of the dehydrated cations into the hexagonal holes of the tetrahedral sheet. Apparently no Cu2+ was trapped in the octahedral sheet. In the case of the Cu-NH4 form, both Cu2+ fixation and de-ammonization occurred during the heat treatment. Other than maintaining the basal spacing, no effect of the presence of ${\text{NH}}_4^{+}$\$\end{document} on the Cu2+ fixation could be found for the montmorillonite studied.

The chemical and biological methods employed to date in the removal of free cyanide (CN−) and metal-cyanide complexes from aqueous fluids have proved expensive and problematic. A simpler and more economical approach was attempted in the present study using zeolite and sepiolite. The effectiveness of zeolite from Manisa-Gördes (Turkey) and of sepiolite Eskişehir-Sivrihisar (Turkey) at removing free and Cu-complexed cyanide, [Cu(CN)3]2− was investigated. For removal of CN−, the system performance was examined in terms of concentration, particle size, and retention time. Material with smaller particle sizes (<0.106 mm) performed better, particularly in the case of sepiolite. The maximum CN− removal capacities of zeolite and sepiolite were calculated as 571 and 695 meq/100 g for free CN adsorption, and 455 and 435 meq/100 g for Cu-complexed CN adsorption, respectively. The time to reach equilibrium was calculated as 1050 min. Acid activation, a simple cation adsorption removal method, did not improve the process, instead leading to reduced CN adsorption. Hydroxylated surfaces of metal oxides at the edges of zeolite develop charges and exchange with anions in water. Mg2+ ions located at the edges of the octahedral sheet can create complexes with CN− anions. Moreover, hydrogen bonding with anions (CN− in this case) and H+ of zeolitic water bonded to coordinated water molecules can also create complexes. These two complexes are considered to be effective mechanisms for sepiolite. The effects of both acid activation and CN adsorption were clearly observed in the Fourier-transform infrared spectra. Removal of CN was characterized by the Langmuir isotherm, indicating monolayer coverage with chemical bonding to the surface, which deteriorated during acid activation. The study indicated that zeolite and sepiolite can be used efficiently and easily for removal of free and Cu-complexed CN.

Monochloroanilines and dichloroanilines are important reagents or chemical intermediates in the production of dyes, pharmaceuticals, and agricultural chemicals. These toxic compounds have a large tendency to accumulate in the environment and a low natural biodegradability, so improved methods to remove or sequester them are needed. Halloysite is used as an efficient adsorbent to remove toxic compounds, such as aniline, from aqueous solutions. The purpose of this study was to evaluate whether acid-activated halloysites from the “Dunino” (Poland) strip mine could be effective in the removal of not just aniline but also of its chloro-substituted forms from aqueous solutions. The composition, structure, and morphology of activated halloysites were characterized using the following methods: wavelength dispersive X-ray fluorescence analysis (WDXRF), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM), energy dispersive X-ray spectroscopy (EDX), Fourier-transform infrared spectroscopy (FTIR), and N2 adsorption-desorption analysis. The acidactivated halloysites had an increased ability to remove aniline and chloroanilines from aqueous solutions as the acid activation temperature was increased. This suggests that the acid activation temperature is an important factor that influences the ability of acid activated halloysites to adsorb aromatic amines (anilines) from water. The efficiency of aniline and chloroaniline removal by halloysite activated at 80°C reached maximum levels, especially for the removal of aniline and 4-chloroaniline. The adsorption isotherm data were best described by the Langmuir adsorption model. The values of the Langmuir adsorption constants were calculated using the inverse liquid chromatography method.

Acid activation was carried out by heating muds prepared from Ca-rich bentonite (CaB), sulfuric acid (H2SO4) and distilled water, yielding various bleaching earths (BEs). The roles of each of the process variables, namely mass fraction of H2SO4 (x) in the dried CaB and pure H2SO4 mixture, heating temperature (T) and contact time (t), in the activation were tested. The raw CaB and each BE were examined with X-ray diffraction, chemical analyses, N2 adsorption/desorption, pH-metry and tintometry. The BE contents in both the aqueous and oily suspensions were set to 2% by mass in order to measure the pH value and the bleaching power, respectively. The optimum conditions for the activation to obtain a BE having the same bleaching power (0.60) as Tonsil® Optimum Bleaching Earth for soybean oil were determined as x = 0.35, T = 100°C and t = 2 h. The bleaching power increased only marginally upon increasing the activation time from 2 h up to 10 h at a given x and T. After 10 h, significant changes did not take place in the bleaching power of the BE. The mass fraction of total structural metal oxide (y), pH value, specific pore volume (V), specific surface area (S) and mean internal diameter (D) of the mesopores for the optimized BE are y = 0.10, pH = 3.0, V = 0.31 cm3 g–1, S = 225 m2 g–1 and D = 7 nm. The pH and D values were more important for bleaching the alkaline refined soybean oil compared to the other parameters tested.

A Na-montmorillonite (Na-MMT) was activated with HNO3 (20 wt.%) solution at various temperatures and times to obtain acid-activated MMT (Acid-MMT). Zinc (4 wt.%) was supported on Acid-MMT via the impregnation method using Zn(NO3)2⋅6H2O as a precursor. The catalytic performance of the Zn/Acid-MMT for the aromatization of heptane was investigated. The amount and distribution of acidity of Acid-MMT, which could be adjusted by changing the acid activation time and temperature, significantly affected the heptane conversion and aromatics content. As a result, an efficient Zn/Acid-MMT catalyst for the aromatization reaction was obtained by optimizing the acid-treatment conditions of Na-MMT.

Various physical and analytical techniques (XRD, XRF, SEM, FTIR and EPR) have been used to investigate the effects of chemical and/or physical modification of Ranong kaolin, which has been proposed as a potential bleaching clay for vegetable oils. Acid treatment after grinding resulted in major changes compared with acid treatment of the original mineral sample or mechanical treatment alone. Previous work has shown that the combined treatments produce increases in surface area and new porous structures, and the present measurements show reductions in Al:Si ratios. These are accompanied by a major reduction in O–H stretching vibrations as a result of grinding, although acid treatment produced little subsequent effect on the O–H bands in the FTIR spectra. However, acid treatment resulted in a reduction in the Al–OH–Al bending vibrations and the appearance of Si–O bands associated with newly synthesized material; these effects were much greater with samples that had been ground prior to the acid treatment. There were appreciable qualitative differences in the way in which the EPR spectra of Fe and Mn were affected; the Fe signal was sensitive to mechanical treatment, but little subsequent change was induced by acid extraction, whereas the Mn peaks were sensitive to the both the pH and the chemical nature of the acid used. These results therefore indicate that the Fe and Mn are in different types of site in the kaolin structure. Little change was observed in the main oxygen-based free radical centre associated with Si atoms, but that associated with Al was lost as a result of the treatments. Such mineral characterization is of fundamental importance to understanding the modification of kaolins and their uses as adsorbents in the food and environmental sciences.

The effects of acid activation on the chemical composition, surface area and pore structure of palygorskite from Xuyi (Jiangsu, P.R. China) were investigated systematically using X-ray fluorescence (XRF) and BET techniques. The palygorskite samples were activated with HCl, H2SO4 and H3PO4 of various concentrations at 80ºC for 4 h. The influences of acid concentration and acid type on the chemical composition, adsorption-desorption isotherms at 77 K, pore-size distribution, surface area and pore volume were studied in detail. The contents of most components of palygorskite decrease with increasing acid concentration except for Si and Ti. HCl shows a greater activation activity and its effect on the dissolution of components of palygorskite is greater than that of H2SO4 and H3PO4. It was found that 3 mol l–1 H3PO4 is a more efficient activator for increasing the number of micropores in palygorskite, whereas 12 mol l–1 HCl is more suitable for use in enhancing the number of meso- and macropores. The acid concentration and acid type have a great influence on the surface area and pore volume. HCl is the most effective at enhancing the external surface area and mesopore volume of palygorskite, whereas, H3PO4 is more suitable for use in improving the micropore surface and volume.

Bentonite samples from Choushan treated at various acid concentrations were studied using chemical analysis, XRD, 29Si and 27Al MAS NMR to investigate the microstructure of the activated montmorillonites. Two types of structural units were formed during the activation: (1) (SiO)3SiOH, in which up to 15% of Si is bound; (2) Q4(0Al), a major building unit when the acid concentration is >10%. A significant 27Al signal at 55.0 ppm was recorded for both untreated montmorillonite and (to a much greater extent) in acid-treated montmorillonites. This was interpreted as arising from four-fold coordinated Al located in the ‘bulk’ octahedral sheet of montmorillonite. In the course of activation, the removal of one of a pair of octahedral Al ions from montmorillonite removes two hydroxyl groups and leaves the other Al of the pair in four-fold coordination.

The experimental data on adsorption of Fe and CN of a ferrocyanide complex onto raw and acid-activated clinoptilolite/sepiolite on the basis of detention time and particle size was modelled by a linear and a non-linear approach. The linearized best-fit isotherm selection method and non-linear error minimization was applied through Freundlich, Langmuir and Temkin isotherms. ERRSQ, MPSD, HYBRID and ARE error functions were minimized by a developed MATLAB script to determine the isotherm parameters in non-linear optimization. The complex was not adsorbed as whole anions but the Fe and CN were adsorbed separately. 0.65 mg Fe/L. min and 4.84 mg CN/L. min initial adsorption rates were achieved with acid activated clinoptilolite. The Fe adsorption was not as successful as CN. The adsorption of Fe and CN was described by Freundlich and Langmuir isotherms respectively. The differences between the predicted isotherm parameter sets of linear models and minimized error function models indicated that both the best-fit isotherm selection and the isotherm constant determinations can be performed properly by error minimization as well as by conventional linear best fit modelling approach.

The physicochemical properties of clays can be modified by acid treatment with inorganic acids. This treatment is usually referred to as ‘acid activation’, because it increases the specific surface area and the number of active sites of the solids. In the present study, the acid activation of saponite from Cerro del Aguila (Madrid, Spain) with HCl solutions was measured. Illite, quartz and small amounts of feldspar were found as impurities in the raw saponite.

Acid treatments were carried out with different concentrations of HCl solutions. The samples obtained were characterized by mineralogical and chemical analyses, XRD, FT-IR spectroscopy, N2 adsorption-desorption isotherms and TEM. The acid attack, under the conditions employed, produced a progressive destruction of the structure of saponite by partial dissolution of the octahedral Mg(II) cations. Amorphous silica coming from the tetrahedral sheet of saponite was generated. The specific surface area of the most intensely treated sample (2.5% for 24 h) was doubled with respect to that of natural saponite. This increase in the surface area is due to the increase in both the external and internal surface areas.

A bentonite from Milos, Greece, was activated with oxalic acid and the effect of acid activation conditions on bleaching of sunflower oil was investigated. The activation parameters studied were temperature, retention time and oxalic acid to bentonite mass ratio. The activated materials produced had good bleaching properties and were suitable for industrial use as bleaching earths. Optimum bleaching properties could be achieved using a variety of combinations of acid to bentonite ratios and activation times. Bleaching efficiency tests indicated that 24 h activation at 100°C with 1m oxalic acid and 25% pulp density (w/v) gave results equivalent to that of a commercial bleaching earth (Tonsil Optimum 210 FF). The combination that is likely to be more preferable on an industrial scale was 100°C, 25% pulp density (w/v), 1m initial oxalic acid concentration, 60% recycling of the oxalate solution (making up an acid to bentonite ratio 0.2 w/w) and 6 h activation time. The materials produced under these conditions have acceptable bleaching properties, corresponding to bleaching capacity greater than 78% compared to commercial Tonsil, and colour index (in red and yellow units) equal or even better than Tonsil.

A kaolin clay was activated with 1.0 M H2SO4 solution at minimum liquid to solid ratio (L/S) using microwave heating. The optimum experimental conditions for activation were L/S ratio 3.0 mL 1 M H2SO4 per gram kaolin, microwave input power 500–600 W, and heating time 5–10 min. Activation at L/S < 3.0 mL/g using 1.0 M H2SO4 was not efficient, indicating the influence of solvent for absorbing microwaves more intensively and thus improving activation. Significant physicochemical changes were observed by the proposed procedure with smaller volumes of activator compared to the conventional heating method. Microwave input power and heating time have a strong influence on the quality of the final material; activation at high input power (>700 W) and longer heating times (>10 min.) are not recommended since they cause dissolution of kaolinite structure. Microwave-heated kaolin manifested better adsorption for tartrazine dye due to improvements in textural and chemical properties of kaolinite. Moreover, irradiation of used kaolinite has significantly improved dye desorption, increasing the importance of microwaves in regeneration/recycling studies. Detailed dielectric measurements of kaolin-acid mixtures recorded at frequencies much lower than 2.45 GHz revealed that absorption of radiation is highly dependent on the activator solution in the mixture. For 3.0 mL/g mixtures, high dielectric constant ε’ 5223, dielectric loss factor ε” 5083, tangent loss tan d 1.30, penetration depth dp 0.57 cm at (103 Hz), and AC-conductivity σ 0.032 Om–1 were determined at 105 Hz. Filling the pores of kaolin by acid solution increased the microwave absorption and hence de-alumination of kaolinite.

The present study investigated the efficiency and mechanisms of aqueous Pb(II), Cd(II), Zn(II) and As(V) adsorption on natural (H), calcined (HC), and acid-activated halloysite (HA). The XRD and FTIR measurements indicated that the aluminosilicate framework was not affected by high-temperature treatment, in contrast to acid activation, which led to structural changes mainly in the tetrahedral sheet. The sorption of cations on H sample was low, though it was most effective for As(V). The X-ray photoelectron spectroscopy results suggested that removal of As(V) might be related to its reduction to As(III) involving oxidation of Fe(II) present in the mineral structure and/or iron minerals. The calcination enhanced halloysite sorption capacity for cations, while the As(V) sorption decreased. This was due to partial dehydroxylation and the subsequent formation of additional active sites. The acid treatment induced selective adsorption of Pb(II).

Smectitic clays from the Sabga and Bana areas, western Cameroon were treated with sulfuric-acid solutions of various concentrations – 0.5, 0.7, 1.0 and 4.0 N – at 80°C for 2 h. The mineralogical, physicochemical and morphological characteristics of the samples treated were analysed using several techniques. The sulfuric acid caused structural modification of the dioctahedral smectite. The accessory minerals such as cristobalite, quartz, feldspars and anatase remained unaltered by the acid attack. The supernatant solutions after acid treatment contain Mg, Ca, K, Na, Si, Al and Fe as a result of partial dissolution of octahedral and tetrahedral cations. The activated clay samples exhibited a smaller cation exchange capacity (CEC) and the specific surface area (SSA) increased with increasing concentration of sulfuric acid, ranging from 65 to 134 m2/g for the sample from Bana and from 74 to 84 m2/g for the sample from Sabga. The different SSAvalues were affected by the relative abundance of smectite and cristobalite (SiO2/Al2O3 = 2.2 and 6.5, respectively, from Bana and Sabga). The activated clays from Bana and Sabga displayed interesting physicochemical and textural properties and can be considered as promising adsorbents for the bleaching of vegetable oils.