Adsorption of heavy metal ions on composite materials prepared by modification of natural silica

Recently because of increasing of environmental consciousness and demands, several discussions about the preservation of natural resources have led to more efforts concerning materials of good selectivity and high sorption capacity [1]. We have developed new composite materials with improved adsorptive properties thanks to the presence of Algerian silica (Kieselgühr) [2], after undergoing suitable treatments. We have investigated the effect of different amounts of silica on the performance and adsorptive behaviour of the resulting composites. Thus, the work herein describes our investigations on the adsorption of heavy metal ions onto the composite materials from aqueous solutions in relation to different variables, such as shaking time, concentration of metal ions and pH. The adsorption behaviour of the concerned material is explained on the basis of its chemical nature and porous texture.

The goal of this work was to determine the sorption behaviour of new composite materials ICM towards lead that belongs to the most harmful pollutants in order to test the efficiency of these solids as adsorbing materials. The undertaken study focused essentially on the examination of different factors treated separately: pH, shaking time and metal concentration. So, it was observed that kinetics of adsorpion of metallic ions of lead was reasonably fast. Its study enables us to suppose that the adsorption of this metal on the particles of the ICM obey to the law of diffusional mechanisms in which the intraparticular diffusion plays a dominating role in the time necessary for equilibrium. The pH of initial solutions has also an influence on the adsorption of the metal ions studied. Indeed, the rate of the ions adsorbed on all the invested solids was considerably improved by the increase of pH. Adsorption is also improved by the increase of the initial concentration of Pb2+ in aqueous solution. The isotherms of adsorption obtained are in agreement with the models of Langmuir and Freundlich in the whole range of the concentrations studied. In what precedes, various aspects affecting adsorption were underlined, in particular, the formation of metal hydroxides, the ionization level, the ionic ray, the distribution of the surface functional sites, as well as the charge of the surface of adsorbent. After using scanning electron microscopy (SEM) and the gas adsorption techniques, it can be noticed that the prepared ICM are characterised by a very developed porous texture and high specific surfaces as well as by the adherence of charcoal on the silicic matrix and the obtaining of a mesostructure onto the different solids. The results presented here and their analyses indicate that the two applied treatments lead to a considerable enhancement of the properties on the prepared ICM with a good adsorption capacity. Hence, the different ICM show an ability to adsorb metal ions, and so can be successfully used in the environmental applications.