Acid and alkali treatments for regulation of hydrophilicity/hydrophobicity of natural zeolite

Hydrophilicity/hydrophobicity property of zeolite has been received much attention in recent years. Regulation of hydrophilicity/hydrophobicity of zeolite using relative simply process and cheap raw materials is needed to be further investigated and solved. The aim of this study is to investigate effect of acid and alkali treatments on structure, hydrophilicity/hydrophobicity of natural zeolite. The structure of the samples was characterized using ICP, XRF, XRD, laser particle size analyzer, N-2 adsorption-desorption, XPS, SEM-EDX, etc. The hydrophilicity/hydrophobicity of the samples was determined using water vapor adsorption method coupled with BET specific surface area results. The results showed that acid treatment removed 5.05-23.26 wt% of aluminum from the framework of clinoptilonite using 0.1-3 M nitric acid while alkali treatment removed 0.49-7.64 wt% of silicon from the framework of clinoptilonite using 0.05-0.8 M sodium hydroxide. Accompanied by the removal of Al and Si, the specific surface area of zeolite obviously increased and decreased, respectively. Water vapor adsorptions on the alkali and acid treated zeolites with ascending SiO2/Al2O3 ratio gradually decreased which confirmed the increase of hydrophobicity and decease of hydrophilicity for the samples. This acid/alkali treatment method appears to be a simple and effective way to regulate hydrophilicity/hydrophobicity of natural zeolite.