Adsorption capability of virgin and calcined wheat bran for molybdenum present in aqueous solution and elucidating the adsorption mechanism by adsorption isotherms, kinetics, and regeneration

Abstract

In this study, we prepared wheat bran (WB), a type of waste biomass, and studied the characteristics of virgin WB and WB calcined at 200, 400, 600, 800, and 1000 °C (denoted by WB200, WB400, WB600, WB800, and WB1000). Subsequently, their adsorption isotherms, kinetics, and regeneration were evaluated. Specific surface area of calcined WB is larger compared to that of virgin WB. Amount of molybdenum (Mo) adsorbed is in the following order: WB400 (0 mg/g) = WB600 (0 mg/g) < WB800 (2.9 mg/g) < WB200 (12.9 mg/g) < WB (24.7 mg/g) < WB1000 (29.8 mg/g). The data for adsorption isotherms was applied to both the Freundlich (0.911–0.989) and the Langmuir (0.985–0.992) models. The amount of Mo adsorbed increased with increasing temperature and decreasing pH of the solution. We confirmed that the intensity of Mo on the adsorbent surface was greater after the adsorption treatment than before the treatment. In addition, the amount of Mo adsorbed on virgin WB was greater than that adsorbed on WB treated with different concentrations of hydrochloric acid, which suggests that the adsorption mechanism was related to the three-dimensional protein structure. Finally, adsorbed Mo on WB could be easily desorbed by treatment with sodium hydroxide solution. The recovery percentage of Mo using 1 and 100 mmol/L sodium hydroxide solution is 95.0% and 94.2% respectively. These results indicate that WB has great potential for Mo adsorption from aqueous solutions.