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 ICPAES 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, 27Al 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 Brönsted and/or Lewis acid sites on their surfaces; These acid centers were evidenced by 1H-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 Fe2+ 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.
Highlights
In developing countries, ground water in rural area is often used as drinking water
[35], it was found that raw crushed brick made in Bangui region is composed of the following minerals: quartz (61wt %), metakaolinite (21wt.%), illite (3-4 wt. %), Fe oxides/hydroxides ( 4 wt.%), and to a lesser extent: mica and feldspath both representing less than 2 wt.%
Al and Fe losses with time reached rapidly a plateau at around 2 h, and this trend continued up to 26 h, indicating that the structure/ composition of the resulting treated material did not change any more. This explained why we focused our attention mainly on the chemical analyses of brick pellets when leached them with a 6M HCl solution at 90°C for reaction times no longer than 6h
Summary
Ground water in rural area is often used as drinking water. These freshwaters contain frequently undesirable and naturally occurring inorganic/ organic (microbial) contaminants, and poverty prevents people from acquiring modern treatment technologies. To remove soluble iron from these waters, a bulk material, brick commonly made by local craftsmen was tested in our laboratory as a low cost adsorbent contrary to most of those employed for water purification treatments with possible industrial applications This material is found to be mainly composed of sand and clays minerals. There is evidence in the literature that clay minerals could be chemically modified to improve their adsorption capacity when they were treated with concentrated inorganic acids [25,26,27,28] In this context, a detailed examination of physicochemical mineralogical and morphological properties of crushed brick subjected to thermal treatment and HCl leaching had been undertaken in the present work. Effluent samples were collected at various time intervals, and the concentration of soluble iron in the effluent was analyzed with time using ICP-AES
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