A. Macías-García

Adsorption of mercury, cadmium and lead from aqueous solution on heat-treated and sulphurized activated carbon

The adsorption of mercury, cadmium and lead from aqueous solutions on heat-treated and sulphurized activated carbon has been studied comparatively. The adsorption isotherms for the various metals were measured at 298 K, using adsorptive solutions at two pH values. The adsorption was much higher for mercury than for cadmium and lead for all adsorbents. The adsorption of mercury greatly increased for the samples of sulphurized carbon and also, though less, for the sample prepared in N2. The decrease of pH in the adsorptive solution to pH 2.0 drastically reduced the adsorption of mercury. The effect of pH change on the adsorption of Cd2+ and Pb2+ occurred with less adsorbents than for mercury.

Adsorption of Pb2+ by heat-treated and sulfurized activated carbon

Abstract Using activated carbon (AC) and samples obtained by heat and sulfurizing treatments of the material, the adsorption of Pb2+ from aqueous solution was studied at two pH values and at three temperatures in the range 25–45°C. Adsorbents were prepared either by heat treatment of AC from 30 to 900°C in N2 or H2S, or by treatment of the material first at 30°C successively in SO2 and H2S and then at 200°C in N2. Their characterization was in terms of textural properties and surface chemistry. Techniques used were gas adsorption (N2, −196°C), mercury porosimetry, density measurements (He, 30°C) and FT-IR spectroscopy. The treatments effected on AC originated a great increase in the adsorption of Pb2+, but only when it occurred from solutions of metallic ion at unchanged pH and at 25°C. Adsorption decreased strongly by pH and temperature variations, except for AC. The adsorption rate depended on the adsorbent, pH and temperature.

Adsorption of cadmium by sulphur dioxide treated activated carbon

Merck carbon (1.5 mm) was treated in three ways: heating from ambient temperature to 900 degrees C in SO(2); treatment at ambient temperature in SO(2); or successive treatments in SO(2) and H(2)S at ambient temperature. All samples were then characterised and tested as adsorbents of Cd(2+) from aqueous solution. The characterisation was in terms of composition by effecting ultimate and proximate analyses and also of textural properties by N(2) adsorption at -196 degrees C. Kinetics and extent of the adsorption process of Cd(2+) were studied at 25 and 45 degrees C at pH of the Cd(2+) solution (i.e., 6.2) and at 25 degrees C also at pH 2.0. The various treatments of the starting carbon had no significant effect on the kinetics of the adsorption of Cd(2+), but increased its adsorption capacity. The most effective treatment was heating to 900 degrees C, the adsorption in this case being 70.3% more than that of the starting carbon. The adsorption increased at 45 degrees C but decreased at pH 2.0 when compared to adsorption at 25 degrees C and pH 6.2, respectively.

Study of the adsorption and electroadsorption process of Cu (II) ions within thermally and chemically modified activated carbon

The aim of this work is to modify the porous texture and superficial groups of a commercial activated carbon through chemical and thermal treatment and subsequently study the kinetics of adsorption and electroadsorption of Cu (II) ion for these carbons. Samples of three activated carbons were used. These were a commercial activated carbon, commercial activated carbon modified thermically (C-N2-900) and finally commercial activated carbon modified chemically C-SO2-H2S-200. The activated carbons were characterized chemically and texturally and the electrical conductivity of them determined. Different kinetic models were applied. The kinetics of the adsorption and electroadsorption process of the Cu (II) ion fits a pseudo second order model and the most likely mechanism takes place in two stages. A first step through transfer of the metal mass through the boundary layer of the adsorbent and distribution of the Cu (II) on the external surface of the activated carbon and a second step that represents intraparticle diffusion and joining of the Cu (II) with the active centres of the activated carbon. Finally, the kinetics of the adsorption process are faster than the kinetics of the electroadsorption but the percentage of the Cu (II) ion retained is much higher in the electroadsorption process.

Preparation and characterization of activated carbons made up from different woods by chemical activation with H3PO4

There are many known methods for the preparation of activated carbons. They are often classified as chemical and physical activation methods, a division widely used in the scientific literature. In this paper we study the preparation of activated carbons from different woods (chestnut, cedarwood, walnut) by chemical activation with different concentrations of phosphoric acid (36 and 85 wt%). The prepared activated carbons were characterized by the following techniques: physical adsorption of gases, mercury porosimetry, chemical analysis and measurement of density by helium and mercury displacement. The main conclusion obtained was that chemical activation with 36 wt% H3PO4 yields activated carbons with better textural properties than those prepared with 85 wt% H3PO4. The effects of activation on the textural properties of the activated carbons improve when the concentration of phosphoric acid is reduced.There are many known methods for the preparation of activated carbons. They are often classified as chemical and physical activation methods, a division widely used in the scientific literature. In this paper we study the preparation of activated carbons from different woods (chestnut, cedarwood, walnut) by chemical activation with different concentrations of phosphoric acid (36 and 85?wt%). The prepared activated carbons were characterized by the following techniques: physical adsorption of gases, mercury porosimetry, chemical analysis and measurement of density by helium and mercury displacement. The main conclusion obtained was that chemical activation with 36?wt% H3PO4 yields activated carbons with better textural properties than those prepared with 85?wt% H3PO4. The effects of activation on the textural properties of the activated carbons improve when the concentration of phosphoric acid is reduced.

Preparation of activated carbons from walnut wood: a study of microporosity and fractal dimension

Agricultural and forest residues constitute an extraordinarily important source of precursors for the manufacture of activated carbons. Activated carbons are well known as porous solids with a highly developed apparent surface area. In the present work, activated carbon has been prepared from forest residues of walnut tree wood (a raw material not studied until now) by physical activation. Raw material has been carbonized between 573 and 1073 K and afterwards activated in air at temperatures between 623 and 823 K. The apparent surface area, micropore volume, mesopore volume and fractal dimension of the samples prepared have been calculated.

Carbonization and demineralization of coals: A study by means of FT-IR spectroscopy

Coal basically consists of two parts—a crystalline, inorganic part, and an amorphous, organic part. Based on this, we intended to study the changes that occurred on the composition and on the chemical structure of coals after carbonization at 1000 or 900° C and demineralization treatments with hydrochloric and hydrofluoric acids. For this, four coals of different categories (or levels) were chosen: semianthracite (A-O) and high volatile bituminous coal (B-O), which are high level coals, and lignite (Li-O) and leonardite (Le-O), these being low level coals. The coals were first analysed in terms of their proximate and elemental compositions and then carbonized and demineralized. Also, the starting coals and the prepared samples were examined by infrared spectroscopy. In addition, a study of the optimization of the application of this technique for only A-O was carried out. For A-O and B-O, the spectra recorded intense absorption bands that are ascribable to vibration modes in mineral components as quartz and aluminosilicates, such as kaolinite. For Li-O and Le-O, the spectra displayed some other bands as well, also quite intense, which have been assigned to bond vibrations in functional groups and structures of their organic part. The carbonization of the coals resulted in significant changes in their inorganic part as the content of quartz increased and the content of aluminosilicates decreased. In addition, the thermal decomposition of mineral carbonates occurred. The carbonization greatly affects the organic part of the coals, especially in Li-O and Le-O, as most functional groups and structures are not thermally stable under heating conditions. With regard to demineralization, HF is a more effective agent than HCl, achieving products with higher organic content. The mass losses are higher in Li-O and Le-O than in A-O and B-O. So, the infrared spectroscopy allows the analysis of both inorganic and organic parts of the coals and of their carbonization and demineralization products. These processes facilitate subsequent analysis of the inorganic and organic parts of coals by infrared spectroscopy. In the application of this technique, both the coal: KBr ratio and the thickness for the disks should be controlled, owing to the influence on the infrared absorption.

Theoretical study of the molecular structure for zirconium complexes

Abstract This work constitutes a study guided to the design of the molecular geometry of ZrO 2 gels aided by computer-based calculations (Density-Functional Theory). The electronic and spectroscopic properties of two zirconium complexes, [Zr(OH) 6 ] 2− and [Zr(OH) 5 (OCH 2 CH 2 CH 3 )] 2− , are explored. Vibration frequencies and properties of nuclear magnetic resonance are theoretically studied.

Use of cork agglomerates as acoustic absorbents

Abstract Black agglomerate (BA) and composite agglomerate (CA) of cork were tested as acoustic absorbents. The energy absorption coefficient was studied as a function of the specimen thickness. For CA, the effects on the acoustic absorption of the particle size and the resin dosage used in its preparation were also analysed. The wave ratio n, the coefficient of acoustic absorption α and the coefficient of noise reduction (CNR) were calculated using an ASTM norm (C-384-56). Usually, regardless of the specimen thickness, for both BA and CA, α first increased with frequency and then decreased. The maximum of α shifted to a higher frequency with decreasing specimen thickness. In general, BA was the best acoustic absorbent at low and high frequencies, whereas CA was at intermediate frequencies. Particle size and resin dosage had a less important influence on the absorbent behaviour of CA.

Preparation of Micropore-Containing Adsorbents from Kenaf Fibers and Their Use in Mercury Removal from Aqueous Solution

Here, a number of activated carbon fibers (ACFs) prepared from kenaf natural fibers (KNFs) by chemical activation with KOH under different operation conditions have been used as adsorbents for the removal of mercury from aqueous solutions. Samples were characterized by N2 adsorption at 77 K, mercury porosimetry, scanning electronic microscopy (SEM), and FT-IR spectroscopy. The adsorption of mercury at 25°C without pH adjustment from an aqueous solution was evaluated from both kinetic and equilibrium standpoints. It was found that the activation conditions during the preparation of ACFs (i.e., impregnation ratios and activation temperatures) had a strong influence on the porosity of the resultant samples and, therefore, on their mercury adsorption capacity. The sample prepared at 800°C using an impregnation ratio of 3:1 (named K3-800) presented the maximum Langmuir adsorption capacity (10.53 mg/g). This sample showed a specific surface area of 881 m2/g, a micropore volume of 0.60 cm3/g, and the highest total pore volume (2.69 cm3/g).