Study on the adsorption of fluoride ion onto Vietnamese red mud activated with sulfuric acid

Abstract

The work is devoted to the study of adsorption of F- ions on red mud, which is a waste of Vietnam's alumina plant. The red mud was previously activated with a solution of H2SO4 (2M) with a solid / liquid ratio of 1: 2. Investigation of adsorption at pH = 6.8; room temperature and adsorption time of 120 minutes showed that the maximum adsorption capacity of F- ions reached 9.4 mg / g. The kinetic regularities of the process are described by a second-order equation, the isotherm of the adsorption of F- ions is characterized by the equations of Langmuir and Freundlich. The test of the activated red mud on real samples of wastewater containing fluoride ions showed that the quality of the water after treatment satisfies the permissible standard of Vietnam for industrial wastewater.

Study on Dyes Adsorption From Aqueous Solution Using Red Mud Activated by Sulfuric Acid

“…In all cases, red mud, which is activated by acid, increases the adsorption capacity. Activated by acid red mud, in addition to increasing its own specific surface area (55 to 92 m 2 /g [20][21][22][23]) also protonates the active center on the surface.…”

“…It can be seen that the process of dyes adsorption is beneficial in acidic media, where the pH> 5 adsorptive capacity of all dyes is greatly reduced. This can be interpreted similarly to the adsorption of other anions on red mud, dye anions, which tend to form electrostatic bonds with positive charge centers on the adsorbent surface in low pH environments [22,[23][24][25]26]. In the case of a high pH, a negatively charged surface of the material, adsorption will not occur.…”

“…In this study, red mud was obtained from Alumin Tan Rai plant, Lam Dong, Vietnam. Red mud was activated by 2M H2SO4 with liquid/solid ratio 2 mL/g, stirred and heated at 90 °C within 2 h according to our recent work [20][21][22][23]. In this acid activation process part of aluminum oxide, iron oxide on red mud will be dissolved into solution, thereby increasing the specific surface area of the remaining solid phase (from 55 m 2 /g to 92 m 2 /g), the amount of red mud dissolved in the solution is about 30% weight [21].…”