Preparation of Silica Gel Obtained from Early Cretaceous Sidi Aich Sands (Central Tunisia) and its Potential to Remove Pollutant Dye Anionic from Wastwaters

The present study concerns the elimination by retention of the anionic dye orange II (OII) from aqueous solutions was studied using a silica gel prepared from Tunisian silica sands (Barremian age). These Sidi Aich sands were collected in central Tunisia. The collected raw silica sand from the Jebel Meloussi (central Tunisia) was characterised by different techniques, such as X-ray diffraction (XRD), X-ray fluorescence (XRF) and scanning electron microscopy (SEM). X-ray diffraction showed a predominance of quartz and potassic feldspars and lower amounts of kaolinite and calcite. The N-2 adsorption isotherms show that these are mesoporous materials with high chemi-physical adsorption capabilities, and indicated a multilayer process for N-2 absorption. They had pore diameters between 60 and 118 angstrom (mesoporous) and specific surface areas up to 183 m(2)/g, close to those reported for commercial silica gel materials. Maximum retention rates of the anionic dye orange II (OII, up to 89.73 % after 180 min contact time) were achieved with products prepared in acidic medium (pH 3). The adsorption is mechanism was well described with both Langmuir and Freundlich models, allowing for a multilayer coverage process of OII molecules on the gel surface, and the pseudo-second-order model is the most reliable for determining the order of absorption kinetics of OII by silica gel. The values of the adsorption capacities at equilibrium calculated (Qe = 242 mg / g) by the pseudo-second-order model are very close to the Qe determined experimentally (224 mg / g), and to those of an industrial silica gel (234 mg / g).

Automated summary

This study investigated the elimination of anionic dye orange II from aqueous solutions using silica gel prepared from Tunisian silica sands. The silica gel exhibited high chemi-physical adsorption capabilities and achieved a maximum retention rate of 89.73% under acidic conditions. The adsorption mechanism was well described by both Langmuir and Freundlich models, with the pseudo-second-order model providing reliable kinetics for the absorption process. The equilibrium adsorption capacities of the silica gel were close to experimental values and those of industrial silica gel.