Highly efficient production of mesoporous nano-silica from unconventional resource: Process optimization using a Central Composite Design

New mesoporous nano-silica with special physicochemical properties was successfully produced from silica-rich rocks using alkaline-based chemical treatment and low temperature. Pumice is a high quality silica-rich rock and used as raw material. An experimental design based on Response Surface Methodology (RSM) combined to Central Composite Design (CCD) was chosen to model and optimize the process parameters using three major independent variables that affect the production yield of nano-silica (reaction temperature, reaction time and molar ratio (n = n(NaoH)/n(silica)). From analysis of variance (ANOVA), the three chosen variables were recognized as the influential factors for the silica production yield. The mesoporous nano-silica produced under optimum reaction conditions was characterized by various techniques. The chemical composition of nano-silica products is confirmed by X-Ray Fluorescence (XRF) and Energy Dispersive Spectroscopy (EDS) and the amorphous nature by X-Ray Diffraction (XRD). The microstructural analysis reveals that the nano-silica exhibits a mesoporous structure with an average pore diameter around 5.5 nm and an irregular distribution of nanoparticles as agglomerated clusters with an average value of 8 nm and very high specific surface area (422 m(2) g(-1)) compared to the conventional silica (257 m(2) g(-1)). The mesoporous nano-silica obtained here is economically inexpensive by comparison with other existing methods.