Open Access
Application of industrial wastes from chemically treated aluminum saline slags as adsorbents
(American Chemical Society, 2018) Gil Bravo, Antonio; Arrieta Chango, Ekhine; Vicente, Miguel Ángel; Korili, Sophia A.; Institute for Advanced Materials and Mathematics - INAMAT2
In this study, industrial wastes, which remain after aluminum extraction from saline slags, were used as adsorbents. The aluminum saline slags were treated under reflux with 2 mol/dm3 aqueous solutions of NaOH, H2SO4, and HCl for 2 h. After separation by filtration, aqueous solutions containing the extracted aluminum and residual wastes were obtained. The wastes were characterized by nitrogen adsorption at -196 °C, X-ray diffraction, scanning electron microscopy, and ammonia pulse chemisorption. The chemical treatment reduced the specific surface area, from 84 to 23 m2/g, and the pore volume, from 0.136 to 0.052 cm3/g, of the saline slag and increased the ammonia-adsorption capacity from 2.84 to 5.22 cm3/g, in the case of acid-treated solids. The materials were applied for the removal of Acid Orange 7 and Acid Blue 80 from aqueous solutions, considering both single and binary systems. The results showed interesting differences in the adsorption capacity between the samples. The saline slag treated with HCl rapidly adsorbed all of the dyes present in solution, whereas the other materials retained between 50 and 70% of the molecules present in solution. The amount of Acid Orange 7 removed by the nontreated material and by the material treated with NaOH increased in the presence of Acid Blue 80, which can be considered as a synergistic behavior. The CO2 adsorption of the solids at several temperatures up to 200 °C was also evaluated under dry conditions. The aluminum saline slag presented an adsorption capacity higher than the rest of treated samples, a behavior that can be explained by the specific sites of adsorption and the textural properties of the solids. The isosteric heats of CO2 adsorption, determined from the Clausius-Clapeyron equation, varied between 1.7 and 26.8 kJ/mol. The wastes should be used as adsorbents for the selective removal of organic contaminants in wastewater treatment.
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Surface tuning of a highly crystalline Ni/LaAlO3 perovskite catalyst obtained from aluminum saline slags using various synthesis methods for the dry reforming of methane
(Elsevier, 2025-03-01) Muñoz Alvear, Helir Joseph; Korili, Sophia A.; Gil Bravo, Antonio; Ciencias; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2
This research presents the first synthesis of nickel-modified lanthanum aluminate (Ni/LaAlO3) perovskite from aluminum (Al) saline slag waste involving acid extraction. Two methods were employed to extract Al: a 2 M HCl aqueous solution (AH) and various citric acid (CA) aqueous solutions (0.5, 1.0, or 2.0 M). Three preparation methods (Pechini, modified citrate, and metal–organic gel) were evaluated to obtain the pure lanthanum aluminate (LaAlO3) phase. This study also investigated the effects of several factors, with some variations being observed depending on the methodology used. The factors analyzed were: (i) preparation method; (ii) type of Al precursor solution (either extracted using HCl or CA); (iii) ligand/cations molar ratio (La3 + + Al3+), ranging from 0.3 to 3.0; (iv) CA concentration; (v) molar ratio (La/Al), between 0.5 and 1.0; (vi) calcination temperature; and (vii) acid etching of the final materials with aqueous dilute nitric acid (HNO3). The results indicated that it is possible to obtain LaAlO3 perovskite using all three methodologies and the Al extracted from saline slags. For the Pechini and metal–organic gel methods, ligand/cations molar ratios (La3+ + Al3+) of 3.0 and between 0.3 (with CA) and 1.5 (with AH), respectively, were obtained, while a CA concentration of 1.0 M was used for the modified citrate method. The optimal molar ratio (La/Al) for obtaining the perovskite was 1.0 in all three methods. The perovskite was synthesized at low temperatures, starting from 650 °C, and was obtained in a completely pure form at between 950 and 1050 °C. Treatment with aqueous dilute acid had a marked effect, especially on the materials obtained when using the initial solution extracted with 2.0 M HCl. This treatment was particularly beneficial for the material prepared using the Pechini method, which induced a 2.5-fold increase in the specific surface area and total pore volume without affecting the crystalline structure, and allowed the specificity of the nickel (Ni) active sites incorporated to be directed, particularly towards a higher proportion of β1 reducible species. This result improved the catalytic performance in the dry reforming of methane (DRM) reaction, achieving conversions of up to 73 % in CO2 and up to 70 % in CH4, with average selectivity of 0.93 after 20 h of reaction. These outcomes even surpassed the reference catalyst, which was entirely prepared using commercial-grade reagents. Factors such as the presence of other metals in the slag and the versatility of cationic substitution contributed to enhancing the physicochemical properties of the catalysts. Ultimately, all of this led to suppression of the formation of double-walled filamentous carbon deposits, which tend to deactivate the catalyst due to sintering and deformation of the active phase.

Gil Bravo, Antonio

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