Combination of Acid and Base Activation of Montmorillonite Clay and Its Impact on the Basic Blue-41 Removal Properties: Regeneration and Single Batch Design
Thamer S. Alraddadi, Rawan Al‐Faze, Saheed A. Popoola, Mohd Gulfam Alam, Souad Rakass, Ahmed Mohmoud, Fethi Kooli
Abstract
The treatment with an alkali (sodium hydroxide) solution of acid-activated montmorillonite clay minerals resulted in a reduction in specific surface area. However, a significant enhancement in the removal of basic blue-41 dye solution was achieved compared to acid-activated samples only (first step of activation) and to the raw montmorillonite clay. The obtained products were characterized using different techniques. The results indicated that the acid-activated montmorillonites exhibited different physicochemical properties than the starting raw montmorillonite, with a reduction in the cation exchange capacity and improvements in the specific surface area (from 5 m2/g to 274 m2/g) and total pore volume (from 0.031 cm3/g to 0.450 cm3/g) due to the formation of the amorphous silica phase. However, the treatment with NaOH solution was accompanied by significant reductions in the specific surface area (from 274 m2/g to 18 m2/g) and total pore volume (from 0.450 cm3/g to 0.02 cm3/g) due to the dissolution of the formed amorphous silica phase, as confirmed through 29Si MAS NMR and FTIR techniques. In addition, the SiO2/Al2O3 molar ratios were close to those of the starting montmorillonite clay. The removal of the cationic basic blue-41 was optimized under different conditions, such as different initial concentrations, adsorbent doses, and pHs of the dye solution. The maximum removal capacities of acid-activated clays were in the range of 45 mg/g to 80 mg/g and decreased with the extent of the acid activation process. However, the capacities were enhanced after NaOH treatment and reached values in the range of 80 to 120 mg/g. Enhancing the surface area had less of an impact on the materials’ removal ability. The obtained materials performed well in seven adsorption–regeneration cycles, showing a 70% reduction in removal effectiveness.