The adsorption performance of aluminum onto powdered activated carbons: Effects of pH and carbon properties

Abstract

The effects of PAC properties on aluminum (Al) adsorption behavior have not been well understood. In this study, nine commercial powdered active carbons (PACs) with different physical and chemical properties were applied to adsorb Al at different initial pH (5.5, 6.5, 7.5, which were selected based on Al species). The results demonstrated that the Al adsorption by different PACs all followed the pseudo-second-order kinetic at pH 5.5, 6.5 and 7.5. Moreover, the Al adsorption capacity and rate under acidic conditions were much greater than those under pH 6.5 and 7.5. At pH 5.5, the Al adsorption was mainly due to the complexion and thus acidic and phenolic hydroxyl groups were correlated to Al adsorption performance. When pH was 6.5, Al adsorption by PAC was mainly due to the surface deposition, consequently, mesopore and total pore volume were critical properties. For pH 7.5, Al transformed to Al(OH)3 colloids around the acidic micro-area caused by the PAC surface oxygen groups and then deposited onto the PAC surface. Therefore, surface area as well as acidic and phenolic hydroxyl groups contributed to Al adsorption. Above all, this study could provide sufficient guidance for PAC selection in residual Al removal. HIGHLIGHTS Acidic condition was more beneficial for Al adsorption.; At pH 5.5, the Al adsorption is mainly due to the complexion effect.; At pH 6.5, Al adsorption by PAC was mainly due to surface deposition.; At pH 7.5, Al was transformed to Al(OH)3 colloids and deposited onto the PAC surface.;

Keywords

• adsorption
• aluminum species
• powdered activated carbon