MAS NMR investigations on a metakaolinite-rich brick after zeolitization by alkaline treatments

Abstract

Abstract A metakaolinite-containing brick made by craftsmen in Central African Republic was treated with sodium hydroxide at 90 °C. After metakaolinite dissolution, gel state Na - aluminosilicates were initially formed and impregnated the surfaces of no-attacked brick grains (mainly sand). This gel changed progressively with time into crystal seeds at remaining brick surfaces. The generation of ‘low silica’ zeolites (NaA and NaP) with molar Si/Al ratios close to 1 was evidenced by the ESEM/EDS technique and their pore size distribution by using N2 adsorption-desorption isotherm at 77 K. 27Al and 29Si MAS NMR spectra of alkali-brick samples were recorded for studying their evolution with NaOH-reagent level and for characterizing newly-generated zeolitic materials in which Si and Al atoms are identified in the classification of alumino-silicates by the coordination number of the central silicon atom and the number of Si and Al second neighbors used. 27Al MQ (multiple quantum) MAS NMR was employed to study the aluminum coordination in synthesized zeolites. 23Na and 1H MAS NMR measurements were performed on alkali brick for evidencing the abundance of hydrated Na+ ions associated with negatively charged brick sites. After checking in the future the ability of zeolitized brick in the removal of heavy metals from wastewaters, this new composite should be of great interest in water treatments at low cost in Central African Republic.