Conditions of synthesis and structure of metakaolin-based geopolymers: application as heavy metal cation sorbent

This study presents the synthesis of geopolymer materials designed for application as self-supporting zeolite membranes. For this purpose, batches of metakaolin activated with sodium silicate and sodium hydroxide were used. During synthesis, it was assumed that low temperatures are sufficient to receive the membranes. The composition of raw materials and temperature of activation were selected in such a way so as to correspond to the basic chemical compositions and synthesis conditions of sodalite as well as zeolites A and X. Additionally, the structural and textural properties of geopolymers were determined. The results show that it is possible to obtain composite zeolite structures in an amorphous matrix. A number of synthesized materials were used in the sorption of selected heavy metal cations (Ni²⁺, Zn^2+, Pb²⁺ and Cd²⁺). It was concluded that the investigated geopolymerization process may be applied to obtain a material with potential use as a heavy metal sorbent.