Mechanisms of chromate adsorption on boehmite

Chromate adsorption on selected soil minerals: Surface complexation modeling coupled with spectroscopic investigation

“…In accordance with their results, the DLM median stability constants describe the pH-dependent explanation for these discrepancies, in accordance with prior studies of metal adsorption mechanisms [10,11,19,23], is the formation of outer-sphere complexes that could not be described by the DLM. Although previous studies differ in their perspective on the mechanisms of Cr adsorption onto hydrous ferric oxide and goethite, the adsorption behavior of Cr(VI) are generally well described using a combination of inner-and outer-sphere complexes [20,47,[50][51][52].…”

“…In general, increasing ionic strength promotes the adsorption of bidentate chromate complexes ( Figure S3). Likewise, EXAFS analyses suggest that Cr(VI) binds to birnessite via inner-sphere bidentate complexes at pH 3.5-4.5 (Figure 3), which is in good accordance with other spectroscopic studies performed on Fe or Al oxyhydroxides [22,23] …”

“…Assuming a low surface concentration of Cr and thus incomplete coverage by monodentate complexes, the dominant broad peak at 951 cm -1 could indicate contributions from outer-sphere hydrogenchromate, which is dominant at low pH. This finding is in agreement with Johnston and Chrysochoou [23], who showed that both inner-and outer-sphere complexes must be considered particularly at acidic pH. Moreover, the high total Cr concentration (0.96 M Cr(VI)) used in the adsorption experiments here should allow the formation of dichromate according to the speciation modeling and Johnston and Chrysoshoou [22].…”

“…On the other hand, the predictions obtained from SCMs need to be confirmed by direct spectroscopic analyses. Different techniques have been previously tested for the identification of Cr(VI) complexes on Fe or Al oxyhydroxide surfaces [22][23][24][25]. In addition, the redox transformation of Cr(VI) during adsorption onto environmentally relevant surfaces, including oxides and clay minerals have been investigated using X-ray photoelectron spectroscopy (XPS), Fourier transformed infrared spectroscopy (FTIR), and X-ray absorption spectroscopy (XAS) [22,[26][27][28].…”

Cesium and cobalt adsorption on synthetic nano manganese oxide: A two dimensional infra-red correlation spectroscopic investigation

“…However, it has been reported that the Infrared (IR) spectroscopy reveals more complexes than the EXAFS [6,7]. Infrared spectroscopy can be used to analyze both metal oxides, and their adsorption mechanism due to its sensitivity to amorphous regions and those with short-range and/or long-range order [5,8,9].…”