Removal of emerging pollutants in water through adsorption and catalytic processes using pillared clays synthesized from aluminum saline slags

Abstract

In this work, the aluminum was extracted from the saline slags using both ways the alkaline and the acidic one. Those extracts were used as precursors in the synthesis of Pillared Clays (PILC) obtaining pillared structures from the acidic extract (Al-PILCAE) and from the alkaline one (Al-PILCBE). The parameters in the synthesis of those PILC were studied characterizing the solids obtained with the purpose to optimize the synthesis process and choose the solids with the better characteristics. The solids chosen were studied as adsorbents and catalytic supports for the removal of three emerging pollutants from water: 2,6-dichlorophenol (2,6-DCP), triclosan (TCS), and bisphenol A (BPA). The adsorptive and catalytic behavior was compared with both the raw clay used in their synthesis (montmorillonite – Mt) and with a PILC synthesized by the conventional method using an aluminum commercial salt as the precursor (Al-PILCCM). The first two sections of this thesis focus on the theory related to the subject. First Chapter (I) refers to PILC, their synthesis, the parameters involved in this, and their importance and impact on the properties of the solid obtained. This chapter collected the studies related to this field, trying to understand the formation of the polycations that make possible the synthesis of PILC. The Second Chapter (II) is related to water pollution and the techniques used to eliminate pollutants from the aquatic environment. This chapter focused on the use of the adsorption process, and the use of PILC as adsorbents for organic pollutants, collecting the studies which have used them for this purpose. The next four chapters (Chapter III to Chapter VI) are related to the results and analysis of the results of the experimental part developed in this work. The first two of them (Chapter III and Chapter IV) are related to the synthesis of the porous clay-based materials and their use as adsorbents, and the next two (Chapter V and Chapter VI) to their use in photocatalysis. Chapter Three (III) corresponds to the synthesis of PILC from the saline slag and their evaluation as adsorbents in batch mode. The parameters involved in the synthesis process were evaluated, characterizing every time the synthesized solids to confirm that the pillaring process was successful. The synthesis process which resulted in solids with better characteristics was chosen for every one of both extracts: alkaline (Al-PILCBE) and acidic (Al-PILCAE). Those PILC were evaluated as adsorbents to remove 2,6-DCP, BPA, and TCS from water, in batch mode. The resulting adsorption capacities were compared with Mt and Al-PILCCM. Additionally, the reuse of the intercalating agent sequentially to synthesize Al-PILC as the reuse of the initial Al-PILC synthesized as adsorbent also was studied. It is necessary to highlight that this is the first time that a porous material is synthesized from saline slag using both extracts, alkaline, and acid. The annex in this document is related to this part of the study. The results obtained in the optimization of the synthesis of PILC using saline slag gave, as a result, a methodology that synthesized PILC with improved textural characteristics compared with those prepared through the conventional method. This methodology was evaluated using a commercial salt as the precursor and the results confirmed that the solids obtained using this had improved textural properties than using the conventional methodology. For this reason, due to the novelty of the methodology found, the technical information about the invention was disclosed in a patent application (202130047) as can be seen in the annex section. Chapter Four (IV) corresponds to the study of the three Al-PILC (Al-PILCAE, Al-PILCBE, and Al-PILCCM) as adsorbents in fixed bed column systems for the removal of TCS. In addition to the breakthrough curves, the adsorption of TCS adsorption in this system was optimized for its use in Solid Phase Extraction (SPE) by Response Surface Methodology using a Box–Behnken Design (RSM-BBD). Fixed-bed column studies are usually carried out to consider the possible application of the adsorbents in water purification processes, however, those studies can be made on a small scale to propose new materials to improve methodologies and routinary techniques used in the laboratory, including the sample preparation methodologies such as SPE. This study, for the first time, used chemometric tools to optimize the adsorption of TCS in fixed bed column by Al-PILC to use it in SPE. This is another way to support the research related to water pollution with EP. The low concentrations of EP in water sources can be lower than the Limit of Detection (LOD) and Limit of Quantitation (LOQ) of the analytical techniques necessary to evaluate those. It makes necessary a pre-concentration step prior to their determination and quantification. For this reason, the study and proposal of new sorbents that can be used in preparation techniques such as SPE for the determination and quantification of EP in water are relevant. Chapter Five (V) corresponds to the use and comparison of Mt and the three Al-PILC as catalytic supports for the removal of 2,6-DCP, TCS, and BPA from water through photocatalytic degradation using both VIS and UV light irradiation. TiO2/catalysts were synthesized by wet impregnation through stirring followed by calcination. Different loads of titanium were studied, and the characterization of the solids was carried out by several techniques. Finally, the photoproducts present in the solutions at the end of the process were evaluated by High-Performance Liquid Chromatography-Mass Spectrometry (HPLC-MS). Additionally, since this chapter is the first related to catalysis, it complements the theoretical information shown in chapter two, listing those studies which have used clays and PILC in catalytic photodegradation processes. The novelty of this work lies in the use of Al-PILC synthesized from aluminum saline slags as catalytic supports and the evaluation of visible light irradiation for this process. Finally, Chapter Six (VI) corresponds to the use and comparison of Mt and the three Al-PILC as catalytic supports for the removal of 2,6-DCP, TCS, and BPA from water by Fenton and Photo-Fenton like processes. Fe(III)/TiO2/ catalysts with different titanium and iron loads were evaluated in single-component solutions and in an equimolar mixture. All catalysts were characterized by several techniques and the by-products for every pollutant were identified during the reactions by HPLC-MS. A degradation pathway was suggested for every pollutant based on the by-products identified during the reactions. The originality of this work is related to the fact of analyzing the process in both single and mixture components systems, using Al-PILC synthesized from aluminum saline slags as catalytic supports.