Open Access
Removal of heavy metals from aqueous solutions by adsorption on zeolites synthesized from aluminum saline slags
(Elsevier, 2024-10-31) Jiménez, Alejandro; Trujillano, Raquel; Rives, Vicente; Vicente, Miguel Ángel; Gil Bravo, Antonio; Ciencias; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2
Three heavy metals (Cu2+, Cd2+ and Pb2+) were removed from aqueous solutions using zeolites prepared from saline slags, a very important waste generated during aluminum recycling. Zeolites were characterized by powder X-ray diffraction, thermal analysis, Fourier transform infrared spectroscopy, X-ray microfluorescence, element chemical analysis, nitrogen adsorption at -196 °C and electron microscopy. The textural and structural properties of X-type faujasite zeolite convert it in a promising adsorbent in aqueous streams. Removal of the heavy metals was evaluated in batch mode, studying the adsorbent dose, the initial concentration of the heavy metal, the selectivity of the solid in case of mixtures with various metal cations and the recyclability of the solid. The kinetic and equilibrium results were evaluated using both pseudo-first- and pseudo-second-order kinetics, and Langmuir, Freundlich and Toth equation isotherms for the equilibrium. The time needed to reach equilibrium was between 10 and 20 min. Faujasite was highly effective in removing Cu2+, Cd2+ and Pb2+ from aqueous solutions, much higher than analcime and pollucite, other two zeolites recently synthesized by us from aluminum slags, and used in this work for comparison purposes. The maximum adsorption capacity was 591 mg/g for Pb2+, 304 mg/g for Cu2+ and 279 mg/g for Cd2+.
Open Access
A comparative study of acid and alkaline aluminum extraction valorization procedure for aluminum saline slags
(Elsevier, 2022) Jiménez, Alejandro; Rives, Vicente; Vicente, Miguel Ángel; Gil Bravo, Antonio; Zientziak; Institute for Advanced Materials and Mathematics - INAMAT2; Ciencias
A management process for saline slags, one of the wastes from Secondary Aluminum Production, is proposed. The process begins with a grinding step, followed by washing with water, which removed the fluxing salts but provoking the hydrolysis of AlN, yielding Al(OH)3 and ammonia. Sieving of the solid generated an intermediate and a fine fraction. The first one was rich in metallic aluminum, and can also be returned to the Secondary Aluminum Production. The fine fraction was submitted to a extraction process in acid (HCl or HNO3) or alkaline (NaOH, KOH or CsOH) conditions, under reflux at 90 ºC, obtaining an Al(III) solution that can be used in the synthesis of aluminum-based solids. HCl (1-8 mol/L) and NaOH (1-4 mol/L) were used as reference solutions, HNO3, NaOH and KOH were used under specific conditions; the slag fraction:extraction solution solid:liquid ratio was also varied. The optimum extraction conditions were: extraction time 2 h, solid:liquid ratio 3:10, concentration 3 mol/L for the NaOH medium and 4 mol/L for the HCl medium. More than 30% of the aluminum present in the fraction smaller than 0.4 mm was recovered (the remaining aluminum was present as insoluble phases, corundum and spinel). Acid or basic media can be selected depending on the final use of Al(III) solutions, the basic medium leading to an Al(III) solution with a lower amount of impurities. The hazardousness of the solid obtained after the extraction process was greatly decreased, making possible the use of this solid residue in sectors such as construction.

Gil Bravo, Antonio

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