Mecanismes d'adsorció de oxyaniones d'as i b per aplicacions de remediació d'aigües. Síntesi de adsorbents i caracterització mitjançant espectroscòpia d'absorció de rajos x
- Autores: Xiangyang Lou
- Directores de la Tesis: Roberto Boada Romero (dir. tes.), Manuel Valiente Malmagro (codir. tes.)
- Lectura: En la Universitat Autònoma de Barcelona ( España ) en 2021
- Idioma: catalán
- Tribunal Calificador de la Tesis: Alfonso Mazuelos Rojas (presid.), Montserrat López Mesas (secret.)
- Programa de doctorado: Programa de Doctorado en Química por la Universidad Autónoma de Barcelona
- Materias:
- Enlaces
- Tesis en acceso abierto en: TDX
- Resumen
The research carried out in the present thesis concerns with the development of new adsorption materials and procedures to improve the removal efficiency of contaminants oxyanions from polluted waters, particularly arsenic (As) and boron (B), in order to implement procedures to accomplish the actual water regulations.
For As removal, a commercial cube-shaped open-celled cellulose sponge adsorbent was modified by in-situ co-precipitation of superparamagnetic iron oxide nanoparticles (SPION) and used to remove As from aqueous solutions. XAS measurements at the Fe K-edge and TEM identified maghemite as the main iron phase of the SPION nanoparticles (average size ~13 nm).
Batch adsorption experiments of As(V) at 800 mg·L-1 showed a ~63% increase of adsorption capacity when loading 2.6 wt.% SPION in the cube-sponge. Experimental determination of the adsorption thermodynamic parameters indicated that the adsorption is a spontaneous and exothermic process. XAS results confirmed that the adsorption enhancement on the composite was due to the nanoparticles presence. In addition, adsorbed As(V) kept its oxidation state and formed a binuclear corner-sharing complex with SPION. The composite adsorbent also showed a good regeneration property.
Batch adsorption experiments of As(III) showed that the 2.6 wt.% of SPION loaded in the sponge outperforms the adsorption of the unsupported SPION, with the adsorption capacity of the composite being ~14 times larger than the one of the unsupported SPION, thus revealing the SPION aggregation drop when loaded at the sponge with consequent enhanced surface contact. The adsorption was best described by the Temkin isotherm model and the pseudo-second order kinetic model which indicates that chemisorption is controlling the speed of the adsorption process. Experimental determination of thermodynamic parameters indicated that As(III) adsorption was spontaneous and endothermic, as the already observed As(III) adsorption on the unsupported SPION. XAS results revealed that the adsorbed As(III) was partially oxidized to less toxic As(V) by hydroxyl free radical (•OH) generated from Fe(III) and hydroxyl groups. Besides, the oxidation of adsorbed As(III) on the composite was more favorable at lower temperatures and no difference was found as a function of the cube depth.
For As removal on fixed-bed column experiments, several parameters of the breakthrough experiments such as initial concentration and the adsorbent material (sponge and sponge-loaded SPION) had a greater effect than the flow rate and/or the temperature. The results obtained for sponge loaded SPION indicated that loading SPION on the commercial cube sponge results in a 96% and 97% increment in the number of bed volumes and adsorption capacity at breakthrough point, respectively, respect to sponge. For low concentrated As solutions (1 mg·L-1), the maximum desorption concentrations obtained for both systems were higher than 100 mg·g-1. Hence, we were able to concentrate the inlet solution by 100 times which is rather relevant for industrial applications.
For B removal, hierarchical alumina microspheres (HAM) were successfully synthesized by microwave-assisted co-precipitation method and used to remove boron from aqueous solutions. SEM, TEM and XRD analysis showed that synthesized HAM is hollow γ-Al2O3 particles with a fluffy and porous dandelion shape and an average size of 1.5 μm. Adsorption data were fitted well to the Langmuir isotherm, indicating a single-layer homogeneous adsorption, and Pseudo-second order model, suggesting a chemical adsorption to control the related adsorption rate. The theoretical maximum capacity calculated by Langmuir was 138.50 mg·g-1, which is, to our knowledge, higher than the adsorption capacities previously reported. Experimental determination of the adsorption thermodynamic parameters indicated the adsorption is an exothermic and non-spontaneous process. HAM also showed high adsorption affinity and excellent selectivity towards boron in an aqueous solution, even in the presence of competitive salt ions, metal ions, anions and high ion strength.
