A nonconventional aluminum source in the production of alumina-pillared clays for the removal of organic pollutants by adsorption

This study is the first to propose the use of aluminum saline slag as aluminum source in the synthesis of alumina pillared clays (Al-PILC). Aluminum was extracted from this waste using both alkaline and acid solutions and both were compared for preparation of the intercalation solutions used for the synthesis of Al-PILC. Variations in parameters such as [OH–]/[Al3+], Al/clay (mmol/g), clay/volume solution ratios and temperature were studied in the synthesis processes. The solids obtained were characterized by X-ray diffraction (XRD), N2 adsorption–desorption at −196 °C, transmission electron microscopy (TEM), scanning electron microscopy (SEM) and energy-dispersive X-ray spectrometry (EDX), which confirmed that the pillaring process was successful. PILC obtained from both acid (Al-PILCAE) and alkaline (Al-PILCBE) extracts were evaluated as adsorbents for three organic pollutants, namely bisphenol A (BPA), 2,6-dichlorophenol (2,6DCP) and triclosan (TCS), in batch mode. The resulting adsorption capacities were compared with montmorillonite (Mt) and an Al-PILC prepared by the conventional method, namely, dropwise addition of an NaOH solution into an aluminum chloride solution (Al-PILCCM). In all cases, the effect of factors such as pH, initial concentration of pollutant, adsorbent dosages and contact time was studied. The kinetic and equilibrium results obtained were evaluated using both pseudo-first- and pseudo-second-order kinetics, and Langmuir, Freundlich and Sips equation isotherms for the equilibrium. The kinetic study showed that the time needed to reach equilibrium was 30, 900 and 510 min for BPA, 2,6DCP and TCS, respectively. Moreover, adsorption data showed that the Al-PILCAE and Al-PILCBE synthesized have excellent potential as adsorbents for 2,6DCP and TCS, removing 98.46% and 98.47% of these compounds, respectively.