Acid Treatment of Crushed Brick (from Central African Republic) and its Ability (After FeOOH Coating) to Adsorb Ferrous Ions from Aqueous Solutions

Abstract

Brick made by craftsmen in Central African Republic was treated at 50°C and 90°C with a 6M solution of hydrochloride acid for different time lengths. Total chemical compositions of leached samples were determined by ICP- AES and their chemical, mineralogical and morphological/textural properties were characterized by using an environmental scanning electron microscope equipped with an energy dispersive X-ray spectrometer, 27 Al solid-state MAS NMR spectrometry, N2 adsorption - desorption (BET) method. The acid-modified brick was found to possess a higher surface area as a result of structural and compositional collapses with significant Fe an Al losses which reached up to 85 wt.% for Fe and 55 wt.% for Al. Pore size distributions had allowed us to show the predominance of mesoporous structures with roughly two pore-diameter maxima at 7.6 nm and 14.6 nm. Higher surface acidity was also detected on HCl-treated brick pellets, indicating the generation of Bronsted and/or Lewis acid sites on their surfaces; These acid centers were evidenced by 1 H-MAS NMR spectrometry and also by FT-IR using pyridine as a probe molecule. The quantification of these acid sites was performed firstly by pHmetry with a NaOH solution under a strictly controlled N2 atmosphere, and secondly by adsorption - desorption studies of pyridine versus temperature using ThermoGravimetric (TGA)/Differential Thermal (DTA) analyses and TGA coupled to Mass spectrometry. The acid treatment of brick led to a higher surface area mesoporous material that was used in the present work as an adsorbent for removing Fe 2+ ions from aqueous solutions after deposition of iron oxy-hydroxides. The efficiency of this new composite was confirmed in the laboratory by carrying out fixed-bed column experiments.