Research Of Adsorption Characteristics On Fluoride And Arsenic Removal By Activated Red Mud

Fluoride and arsenic are very important naturally-occurring pollutants in the groundwater on global levels, Co-contamination of As and F-has universally found in groundwater which is a serious threat to flora and fauna including humans. Many methods have been developed to remove excessive F-or As from water, such as adsorption, ion exchange, et al. Red mud, a waste tailing from alumina production, was activated with calcination and acid treatment for F-and As removal from water solution.Factors affecting F-adsorption on activated red mud were investigated, including reaction time, dosage of adsorbent, initial F-concentration, temperature, coexisting anions, and pH in batch experiments. The models of thermodynamics and kinetics were modeling. Results showed that F-adsorption onto activated red mud generally achieved equilibrium at about18h. The kinetic data revealed that adsorption kinetics agreed well with the expression of Lagergren second-order rate. The higher the initial F-concentration, the greater the adsorption capacity was. The adsorption isotherm can be better described by Langmuir isotherm model, in comparison with Freundich isotherm model. Its maximum adsorption capacity was up to2.71mg/g. In addition, the coexistence of SO42-, Cl-, and NO3-(<1000mg/L) had no significant effects on F-adsorption. However, HCO3-and PO43-showed negative effects on F-removal. It demonstrated that F-adsorption was relatively independent on pH between3.5and11.0.Factors affecting simultaneous adsorption of F-and As on activated red mud were investigated, including reaction time, dosage of adsorbent, initial concentration, pH by batch experiments and interactive effects of As/F-on F-/As adsorption. Results showed that the adsorption equilibrium time of activated red mud for F-, As(Ⅴ) and As(Ⅲ) were18h,12h and48h, respectively. The kinetic data revealed that adsorption kinetics agreed well with the expression of Lagergren-second order kinetic model for F", As(Ⅴ) and As(Ⅲ). Langmuir and Freundlich models were used to fit the adsorption isotherms. Based on the parameters calculated from the Langmuir isotherm, its maximum adsorption capacity for F-was3.947mg/g attained in the presence of1.0mg/L As(Ⅴ), and for As(Ⅴ) up to5.165mg/g in the absence of F-, which is higher than adsorption capacity for As(Ⅲ)(2.15mg/g) in the presence of F-. It demonstrated that F-adsorption was generally independent of initial solution pH between3.5and11.0, and As adsorption was independent of initial solution pH lower than10.0.SEM (Scanning Electron Microscopy), FTIR (Fourier transform infrared spectroscopy) and BET specific surface areas results showed that the specific surface area of activated red mud increased to89.39m2/g after activated and the red mud developed a lot of small gaps during activation process, resulting in the increase in adsorption sites for F-and As. The functional groups of red mud increased after activated, especially the groups which are conducive to the adsorption of F-and As. It’s the main mechanism of F-and As adsorption.In summary, the activated red mud is an environmental-friendly adsorbent for both F-and As with high and stable adsorption capacity, which is of great advantage in practical application.