Chromium (VI) adsorption on boehmite

Mitigation of Cr(VI) Aqueous Pollution by the Reuse of Iron-Contaminated Water Treatment Residues

“…This result indicates that the removal of Cr(VI) with both Be-Fe(0) and bentonite is endothermic in nature. The endothermic nature of Cr(VI) removal process with both materials is confirmed by the positive value of ΔH (Table S1, supplementary material), while the positive value of ΔS (Table S1, supplementary material) reflects an increased randomness at the solid/solution interface during the adsorption process [33]. Figure 8 and Figure S9 (supplementary material) also reveal that the very low efficiency of Cr(VI) removal with bentonite was only slightly improved when the temperature was raised from 6 to 22 °C, and then significantly enhanced by further increasing the temperature from 22 to 32 °C; this is confirmed by the positive values of the ΔG observed for the process of Cr(VI) removal with bentonite at 6 °C and 22 °C, suggesting that, at these temperatures, the process is not spontaneous; instead, the Cr(VI) removal with bentonite was much more efficient at high temperatures (32 °C), when it was found to be spontaneous (Table S1, supplementary material).…”

“…The enhancement of adsorption efficacy with increasing temperature may be attributed to better interactions between Fe(II) and bentonite, as a result of the creation of new adsorption sites, or of increased rates of intraparticle diffusion of Fe(II) ions into the pores of bentonite at higher temperatures [32]. The positive value of ΔH (Table S1, supplementary material) supports the endothermic nature of adsorption, while the positive value of ΔS (Table S1, supplementary material) reflects an increased randomness at the solid/solution interface during the adsorption process [33]. In addition, the positive value of the ΔG at 6 °C suggests that, at low temperatures, the adsorption of Fe(II) on bentonite is not spontaneous; however, the process becomes spontaneous at temperatures ≥ 22 °C, when negative ΔG values were obtained (Table S1, supplementary material).…”

Adsorption of Cr(VI) from Aqueous Solution onto a Mesoporous Carbonaceous Material Prepared from Naturally Occurring Pongamia pinnata Seeds

“…The Freundlich exponent, n, should have values lying in the range of 1-10 for classification as favorable adsorption [33]. These parameters are determined from a plot lnq e versus lnCe (Figure 9).…”

Fluoride Removal from Aqueous Solutions by Boehmite

“…On the other hand, boehmite is an aluminum oxyhydroxide (AlOOH) that is the most important precursor of alumina compounds that contain in their crystalline structure hydroxyl groups on the outer surface, which are considered adsorption sites for water molecules (Caiut et al 2009). Boehmite has been synthesized and probed as an adsorption material for cobalt (Granados-Correa and Jiménez-Becerril 2009) or arsenious ions (Ogata et al 2006), and its adsorption property was related to the surface hydroxyl groups. In the particular case of activated alumina prepared from pseudo-boehmite, the fluoride removal was attributed to electrostatic attraction and chemisorption mechanisms but not to ion exchange (Leyva-Ramos et al 2008).…”