C. Fernández-González

Adsorption of cadmium on carbonaceous adsorbents developed from used tire rubber

Carbonaceous adsorbents (CAs) are developed from used tire rubber (UTR) and tested as adsorbents of Cd(2+) in aqueous solution. In the preparation of the CAs, UTR was treated thermally at 400-900 °C for 2 h in N(2) and at 850 °C for 2 h in steam. Concentrated NaOH, HCl, H(2)SO(4), HNO(3) and H(2)O(2) solutions were also used. UTR and H900 (i.e. UTR pyrolyzed at 900 °C) were treated with O(3) at 25 °C for 1 h and with air at 250 °C for 1 and 24 h. CAs were characterized texturally by N(2) adsorption at -196 °C, mercury porosimetry, and density measurements. The surface groups were analyzed by FT-IR spectroscopy. Using the batch method, the adsorption process of Cd(2+) was studied mainly from the kinetic standpoint at various pH values of the adsorptive solution. Significant porosity developments are achieved only when UTR is heat-treated, in particular in steam. However, the variety and concentration of surface groups are low in CAs. This is so even for CAs prepared using oxidizing agents as strong as O(3) and H(2)O(2), which has been associated with a lack of available or accessible surface active sites for oxidation in UTR and H900, respectively. Thermal and thermal-chemical treatments are usually more effective than chemical treatments to increase the adsorption of Cd(2+) in aqueous solution. The adsorption process of Cd(2+) is first fast and then much slower. Adsorption-time data fit better to a pseudo-second order kinetic equation than to a pseudo-first order kinetic equation. The extent to which the adsorption process occurs is strongly dependent on the pH of the Cd(2+) solution, being larger at pH 4.6 or 7.0 according to the adsorbent.

On the use of a natural peat for the removal of Cr(VI) from aqueous solutions

A natural peat has been used as an adsorbent for the removal of hexavalent chromium from aqueous solution. The peat was firstly characterized in terms of particle size and chemical composition (ash content, pH of the point of zero charge, FT-IR and thermal analysis). Next, the kinetic and equilibrium aspects of the adsorption of Cr(VI) by this adsorbent were studied. The kinetic data were satisfactorily fitted to a kinetic law of partial order in C equal to one. The specific adsorption rates are around 10(-4)s(-1), increasing as temperature does. A noticeable influence of diffusion on the global adsorption process has been demonstrated. Finally, the equilibrium isotherms were satisfactorily fitted to a previously proposed model. The adsorption capacity of Cr(VI) was similar to some other previously reported and the affinity of Cr(VI) towards the active sites of the adsorbent increases as temperature rises.

Adsorption Isotherms of Methylene Blue in Aqueous Solution onto Activated Carbons Developed from Vine Shoots (Vitis Vinifera) by Physical and Chemical Methods

Carbonaceous adsorbents (CAs) developed from vine shoots (Vitis Vinifera, VS) and characterized texturally were used for the adsorption of Methylene Blue (MB) from aqueous solution. The CAs were prepared by physical activation in air, carbon dioxide and steam, and by chemical activation with H3PO4, ZnCl2 and KOH. One commercial activated carbon (CAC) was also used. The CAs were analyzed texturally by gas adsorption, mercury porosimetry and density measurements. Physical activation yielded mainly macroporous CAs, whereas chemical activation gave rise to mainly mesoporous CAs with high micro- and macro-pore contents. CAC was an essentially microporous carbon. The affinity of MB towards the CAs was usually low, except for the carbon prepared by activation of VS with KOH at 800 °C for 2 h. This AC exhibited a better behaviour in the adsorption of MB than CAC. The development of macroporosity in the KOH activation product was considerable.

Activated carbon from cherry stones by chemical activation. Influence of the impregnation method on porous structure

Cherry stones are utilized as a precursor for the preparation of activated carbons by chemical activation with phosphoric acid (H3PO4). The activation process typically consists of successive impregnation, carbonization, and washing stages. Here, several impregnation variables are comprehensively studied, including H3PO4 concentration, number of soaking steps, H3PO4 recycling, washing of the impregnated material, and previous semi-carbonization. The choice of a suitable impregnation methodology opens up additional possibilities for the preparation of a wide variety of activated carbons with high yields and tailored porous structures. Microporous activated carbons with specific surface areas of ∼800 m2 g−1 are produced, in which > 60% of the total pore volume is due to micropores. High surface areas of ∼1500 m2 g−1 can be also developed, with micropore volumes being a 26% of the total pore volume. Interestingly, using the same amount of H3PO4, either carbons with surface areas of 791 and 337 m2 g−1 or only one carbon with a surface area of 640 m2 g−1 can be prepared. The pore volumes range very widely between 0.07–0.55, 0.01–0.90, and 0.09–0.79 cm3 g−1 for micropores, mesopores, and macropores, respectively.

Monitoring of Zn(II) and Cd(II) adsorption on activated carbon from aqueous multicomponent solutions by differential pulse polarography (DPP)

The adsorption process of Zn(II) and Cd(II) from aqueous solution has been investigated from both kinetic and equilibrium standpoints, using differential pulse polarography (DPP) on a mercury dropping electrode as the analytical technique. With such an aim, adsorption experiments were performed using not only a single metal ion–Zn(II) or Cd(II) solution but also a multi-component ion metal–Zn(II), Cd(II) and Hg(II) solution. The influence of the pH change in the multi-component ion metal solution on the adsorption of Zn(II) and Cd(II) was also studied. The adsorption processes is relatively fast for Zn(II) and Cd(II). The presence of two foreign ions in the solution slightly speeds up the adsorption process for Zn(II) and significantly slows it down for Cd(II). The adsorption isotherms are similarly shaped for Zn(II) and Cd(II). The addition of the foreign ions has a more unfavourable effect on the adsorption for Cd(II) than for Zn(II). At pH 2, neither Zn(II) nor Cd(II) is adsorbed practically on the carbon. The voltammetric approach has proved to be a fast and efficient method that, at the same time, enables one to monitor the adsorption of Zn(II) and Cd(II) with potential on-line application, which could be useful in waste-water treatment.

Particle size distribution and morphological changes in activated carbon-metal oxide hybrid catalysts prepared under different heating conditions.

In catalysis processes, activated carbon (AC) and metal oxides (MOs) are widely used either as catalysts or as catalyst supports because of their unique properties. A combination of AC and a MO in a single hybrid material entails changes not only in the composition, microstructure and texture but also in the morphology, which may largely influence the catalytic behaviour of the resulting product. This work is aimed at investigating the modifications in the morphology and particle size distribution (PSD) for AC‐MO hybrid catalysts as a result of their preparation under markedly different heating conditions. From a commercial AC and six MO (Al2O3, Fe2O3, ZnO, SnO2, TiO2 and WO3) precursors, two series of such catalysts are prepared by wet impregnation, oven‐drying at 120ºC, and subsequent heat treatment at 200ºC or 850ºC in inert atmosphere. The resulting samples are characterized in terms of their morphology and PSD by scanning electron microscopy and ImageJ processing program. Obtained results indicate that the morphology, PSD and degree of dispersion of the supported catalysts are strongly dependent both on the MO precursor and the heat treatment temperature. With the temperature rise, trends are towards the improvement of crystallinity, the broadening of the PSD and the increase in the average particle size, thus suggesting the involvement of sintering mechanisms. Such effects are more pronounced for the Fe, Sn and W catalysts due to the reduction of the corresponding MOs by AC during the heat treatment at 850ºC.

Shock Resistance and Compression Analysis of Concrete in Expanded Polystyrene Formworks (EPSFWs)

Bench-scale and industrial expanded polystyrene formworks (EPSFWs) were prepared and tested in terms of shock resistance and compression analyses. The composition of the EPSFWs was varied and the influence of the substitution of calcium carbonate by granite, kaolin or slate on the mechanical properties of the EPSFWs was analyzed. Bench-scale samples were subjected to a previous selection based on the optimal mechanical behavior. Samples containing large grain sand and slate were chosen for the subsequent industrial scale preparation. The real EPSFWs were also tested from the shock resistance and compression standpoints. The results obtained suggest that the samples showing the best performance among all the tested EPSFWs are those in which calcium carbonate was substituted by slate. This fact is of special interest since large amounts of slate dust are obtained in the area of Spanish Extremadura from local mines. Thus, the preparation of formworks represents a good alternative for the valorization of this by-product.