Preparation and characterization of silicagel from silicate solution obtained by autoclave treatment of copper slag

Abstract

The formation of silicagel from sodium silicate solution obtained by alkaline autoclave treatment of copper slag was investigated. The influence of the parameters of the gelation process (type of acid used, the pH of the medium, and drying conditions) on the structure and properties of the resulting silicagel, were studied. Silicagels obtained under different conditions were characterized by XRD, low-temperature nitrogen adsorption, FTIR, SEM, and TEM analyses. All silicagels are amorphous with a different degree of crosslinking. The physicochemical characterizations show that the type of acid, the mode of drying and pH influence the dispersity and the morphology of the silicagels prepared. Silicagels obtained at low-pH medium have a higher specific surface area and porosity than silicagels obtained at high-pH medium. Silicagels obtained at low-pH medium have no micropores and their porosity is only expressed by a narrow mesopore distribution. Freeze-drying improves the porosity of the silicagels obtained at high-pH medium. It is confirmed that the dilution of the sodium silicate solution affects the initial pH and the time of gelation.The moisture absorption capacity of the prepared silicagels increases in the following order: silicagel obtained at high-pH medium, dried in air < silicagel obtained at high-pH medium, freeze-dried < silicagel obtained at low-pH medium, dried in air.