Adsorption of Methylene Blue and Congo Red on Bentonite Modified with CaCO<sub>3</sub>

Abstract

Both bentonite and CaCO3 are cheap and abundant superior regional non-metal ores in Guangxi province, so it is very meaningful to jointly exploit bentonite and CaCO3 for real applications. In this study, bentonite modified with CaCO3 (CCB) was prepared and its adsorption performance of Congo Red (CR) and Methylene Blue (MB) was evaluated by investigating the adsorption influencing effects of initial pH, SDBS and phosphate. Adsorption isotherms and adsorption kinetics models were also fitted to analysis the corresponding kinetic characteristics of CCB. The results show that CCB exhibited superior adsorption performance with the respective > 90% MB and CR removal within the initial pH range 2 ~ 10. To a certain extent, MB removal efficiencies by CCB can be increased with the addition of SDBS. On the other hand, CR adsorption on CCB was inhibited slightly in presence of SDBS. But as a whole, removal efficiencies of MB and CR by CCB were kept constant when SDBS co-existed. MB and CR adsorption on CCB decreased to some extent because of competitive adsorption effect when phosphate co-existed. It also demonstrated that CCB can remove phosphate at the same time with dyes. Adsorption models including adsorption isotherms adsorption kinetics indicated that MB and CR adsorption on CCB was a monolayer process, and the adsorption rate depended on both adsorbent and adsorbate. In summary, CCB is a promising adsorbent for dyes removal with many advantages such as simple preparation technology, excellent adsorption performance for anionic and cationic dyes, broad fitting pH range and SDBS resistance. Besides, it can remove dyes together with phosphate at the same time. Therefore, this study is very useful for the dyeing wastewater treatment and exploiting the resources of bentonite and CaCO3.