Adsorption and bonding strength of chromium species by ferrihydrite from acidic aqueous solutions

Abstract

The adsorption behavior of Cr(III) and Cr(VI) ions onto laboratory-synthesized 2-line ferrihydrite was investigated under a batch method as a function of initial chromium concentration (0.1–1000 mg L−1) and pH (3.0 and 5.0). Moreover, the effect of the type of anion (chloride and sulfate) on Cr(III) adsorption was studied. The affinity of Cr(III) ions for the ferrihydrite surface depended on both the type of anion and pH of the solution and the maximum adsorption capacities decreased as follows: q (SO42−, pH 5.0) > q (SO42−, pH 3.0) > q (Cl−, pH 5.0) > q (Cl−, pH 3.0), and were found to be 86.06 mg g−1, 83.59 mg g−1, 61.51 mg g−1 and 40.67 mg g−1, respectively. Cr(VI) ions were bound to ferrihydrite in higher amounts then Cr(III) ions and the maximum adsorption capacity increased as the pH of the solution decreased and was 53.14 mg g−1 at pH 5.0 and 83.73 mg g−1 at pH 3.0. The adsorption process of Cr species was pH dependent, and the ions were bound to the surface of ferrihydrite by surface complexation. The Sips isotherm was the best-fit model to the results obtained from among the four isotherm models used, i.e., Freundlich, Langmuir, Dubinin-Radushkevich and Sips, indicating different adsorption centers participate in Cr uptake. In order to assess the bonding strength of the adsorbed chromium ions the modified BCR procedure, dedicated to the samples with a high iron content, was used. The results of the sequential extraction showed that Cr(III) ions were bound mainly in the immobile residual fraction and Cr(VI) ions were bound in the reducible fraction. The presence of Fe (oxyhydr)oxides in soil and sediments increases their adsorption capacity for Cr, in particular for hexavalent Cr in an acid environment due to their properties (high pHPZC).

Effect of pH and Al Cations on Chromate Inhibition of Galvanic-Induced Corrosion of AA7050-T7451 Macro-Coupled to 316SS

“…13). This observation is consistent with findings reported in previous studies on other substrates 25,51,52 ) depending on the pH and total [Cr(VI)]. 50,[53][54][55] In low pH media (< 6), Cr(VI) exists as a distribution of HCrO 4 − and Cr 2 O 7 2− with the former favored for total [Cr(VI)] < 10 −2 M. In contrast, Cr(VI) speciates entirely as CrO 4 2− at higher pH (> 7) regardless of concentration.…”

Batch and Fixed-Bed Column Studies on Palladium Recovery from Acidic Solution by Modified MgSiO3

“…Using the Sips isotherm to model the obtained experimental data leads to a parameter 1/ n s value deviated from unity, suggesting the heterogeneity of the adsorbent surface [ 68 ]. Regardless of the extractant used for functionalization, the Sips model better describes the adsorption process, reflected by the highest correlation coefficient (R 2 ) values.…”

Thermally grown Zn-doped hematite (α-Fe2O3) nanostructures for efficient adsorption of Cr(VI) and Fenton-assisted degradation of methyl orange

“…Related studies agree that the adsorption of HCrO 4 − onto α-Fe 2 O 3 involves the formation of a surface complex [47,52,56,57]. It was suggested that HCrO 4 − may have undergone ligand exchange with the surface hydroxyl groups of α-Fe 2 O 3 , ultimately forming an inner sphere surface complex [52], as represented in Eq.…”