Synthèse des aluminosilicates de type géopolymères et zéolite LTA à partir des kaolins. Application à l’adsorption des métaux lourds (Cu(II), Cr(VI)) et des colorants textiles (jaune bezanyl, vert nylomine)

Abstract

Releases of varying micropollutants (anionic dyes, heavy metals…) in the environment are increasing, these pollutants, toxic and poorly degradable, are usually the source of many harmful health effects. Zeolite LTA was synthesized by the autoclave method, in alkaline medium, using the DD3 Algerian clay. The synthesized zeolite LTA can be efficiently used for bezanyl yellow (BY) and nylomine green (NG) adsorption (25 mg/L) at very low adsorbent doses (0.1 gzeolite LTA /gsolution), natural pH (~7) and temperatures below 60 °C. However, preliminary dilution of nylomine green (NG) containing effluents would decrease the steric hindrance of the sized NG molecules and improves therefore the adsorption capacities. On the other hand, very acidic and very alkaline pH improves the adsorption but enhances the zeolite dealumination. Freundlich isotherm and pseudo–second–order kinetics were found to be the most appropriate models to describe the removal of BY (Ea = 23.4±1 kJ/mol) and NG (Ea = 18.34 kJ/mol) from water. Free energy (ΔG°), enthalpy (ΔH°), and entropy (ΔS°) changes during physisorption were carefully evaluated at temperatures below 60 °C in order to avoid the contribution of thermodynamic parameters of dyes dissolution. The effect of simultaneously controlled humidity and temperature adopted in view to produce nanostructured geopolymers derived from metakaolin for functional applications was done. Geopolymer samples were prepared by dissolving high-quality metakaolin in water-glass solutions then cured and dried using well controlled humidity and temperature conditions for different aging times. Chemical stability, mechanical properties and sorption ability have been investigated with the aim to further explore their potential functional applications. Incorporation of polymers, such as alginic acid and pluronic-123, yields functional nanorachitectures that display ability for removal of heavy metal ions in solution (e.g. Cr VI and Cu II).