Synthesis of highly ordered cubic zeolite A and its ion-exchange behavior

Well-ordered cubic zeolites 4A were synthesised using sol–gel process in the presence of different silica and aluminum sources. The aluminum and silica sources determined whether or not zeolites were formed at precise silica/alumina mole ratio. Zeolites were formed only when the aluminum source was sodium aluminate, the silica source was fumed silica, colloidal silica or sodium metasilicate. Our findings indicated that the type of zeolite invariably obtained was 4A and SEM images indicated that the produced zeolites are cubic shaped crystals with planar surfaces and well-defined edges and sharp crystals. In turn, synthesis parameters are seen to have a significant effect in maximizing heavy metals uptake (for example Cu²⁺, Cr³⁺, Cd²⁺ and Ni²⁺) by synthesized zeolites. Zeolite 4A gave better heavy metal uptakes than amorphous or non-zeolite crystalline materials. This was attributed to higher ion-exchange capacity and higher BET specific surface area 445 m²/g and pore volume 0.141 cm³/g. The latter attribute possibly translates to greater accessibility of ion-exchange sites and selectivity towards metal type by this zeolite followed the sequence: Cu²⁺ > Cr³⁺ ≥ Cd²⁺ > Ni²⁺.