Cadmium ions adsorption in simulated wastewater using structured alumina–silica nanoparticles

Some results on the removal of cadmium ions from simulated industrial wastewater using sol–gel structured nanoparticles of silica and alumina are presented. Two different core-shell nanoparticles were prepared: Al–Si particles (alumina core surrounded by a silica shell) with a molar composition Al:Si of 1:5, and Si–Al particles (silica core and alumina shell) with a molar composition Si:Al of 1:5. Different amounts of cadmium ions were added and the flocculation process of these particles, induced by the ions adsorption, was followed using dynamic light scattering. The efficiency of the ions adsorption was determined using atomic absorption spectroscopy. The results show that it is possible to reduce the cadmium concentration from 140 ppm to less than 5 ppb using Si–Al particles, meeting some international regulations for this contaminant (New European Directive 98-83). The Al–Si particles were not so efficient because the cadmium was only reduced from 125 ppm to less than 90 ppb. The sol–gel technique allows to synthesize model nanoparticles with different morphologies to be used as a prototypes, allowing to choose the better morphology and scaling this knowledge to an industrial level using commercially available silica and alumina nanoparticles chemically modified on the surface.