Hierarchical porous structured zeolite composite for removal of ionic contaminants from waste streams
Zeolite A was synthesised and supported over carbon-based materials to produce a hierarchical structured composite. The method is based on the surface chemistry modification of supports. Carbonaceous supports have been prepared using residues such as cherry stones and hazelnut shells by thermal treatment.
Carbons were conditioned using cationic surfactant to promote the zeolites´ attachment. Supports were covered with a zeolites layer and results showed that surface modification had a positive effect on the zeolites deposition. Copper adsorption experiments showed that the distribution of zeolite on the supports improved their uptake efficiency from 33.53 mg g-1 to 69.30 mg g-1. Kinetic results showed that materials follow the pseudo-second order equation. Composites have been prepared to allow encapsulation metals by vitrification reducing the volume of final disposal.
Zeolites are microporous aluminosilicates that have a negative surface charge due the AlO4 tetrahedra presence in the framework, which is neutralized by ions or protons that are easily exchangeable (1). Nevertheless, ionic species encounter intra-particle diffusion problems with inner adsorption sites due to restrictive pore dimensions and large diffusion path lengths (2). In addition, zeolitic powders tend to agglomerate, making inaccessible a large amount of active surface area. Hierarchical zeolitic structures have shown to be able to overcome some diffusion drawbacks (3-4) as they can maximize the exposure to active surface area and avoid agglomeration. Many supports and templates for hierarchical zeolitic structures have been used but usually they are expensive and often cause secondary contamination problems when removed by thermal methods (5-6). In recent years, there has been an increasing interest in the size reduction of particles because it has been seen that, from micro to nano scale, their properties such as mass transfer resistances change considerably having a significant effect on many applicatio ...