Temperature dependent reduction of Cr(VI) to Cr(V) aroused by CaO during thermal treatment of solid waste containing Cr(VI)

Selective and Efficient Photoextraction of Aqueous Cr(VI) as a Solid-State Polyhydroxy Cr(V) Complex for Environmental Remediation and Resource Recovery

“…As confirmed in the full XPS spectrum (Figure a), only Cr, C, and O were detected. In the high-resolution spectrum of Cr 2p (Figure b), the binding energy at 577.52 eV is assigned to Cr­(V) 2p 3/2 , while the peak at 579.88 eV corresponds to Cr­(VI) 2p 3/2 , suggesting that the main component in the resulting precipitate is Cr­(V) with minor Cr­(VI). The UV–Vis spectrum of the precipitate (Figure S6) shows an intense absorption band at 378 nm because of ligand to metal charge transfer (LMCT) and a shoulder at 600–700 nm, which is ascribed to d–d transition band of Cr­(V) .…”

Synthesis, some Physicochemical and Biomedical Properties of colored Apatite‐Structured Compounds with Mn5+ and Cr5+

“…These measurements were performed to confirm the presence of Mn 5+ and Cr 5+ by comparison with existing literature. Compounds with apatite structure containing Mn 5+ and Cr 5+ in the tetrahedral position were used for comparison (there is limited information on Ca‐apatites with Mn 5+ and Cr 5+ in the tetrahedral position in the literature), [15–17,19,20,42,74] as well as other compounds with the corresponding elements [25,27,28,31–35,39,69,65] …”

“…Compounds with apatite structure containing Mn 5 + and Cr 5 + in the tetrahedral position were used for comparison (there is limited information on Ca-apatites with Mn 5 + and Cr 5 + in the tetrahedral position in the literature), [15][16][17]19,20,42,74] as well as other compounds with the corresponding elements. [25,27,28,[31][32][33][34][35]39,69,65] Five transitions are observed for the d 2 Mn 5 + ion in the wavelength range 250-1200 nm: three spin-resolved transitions from the 3 A 2 ground state to the 3 T 1 ( 3 P), 3 T 1 ( 3 F), and 3 T 2 levels at wavelengths around ~350, ~650, and ~880 nm, respectively, and two spin forbidden transitions from the 3 A 2 ground state to the 1 A 1 and 1 E levels at wavelengths around ~735, ~1160 nm, respectively. [42] The 1 A 1 and 1 E transitions from the ground state are phonon-free transitions, demonstrating that Mn 5 + isomorphically replaces P 5 + in the lattice.…”

“…There are considerably fewer studies dedicated to apatites containing Cr 5 + . [17,18,[30][31][32][33][34][35] The existence of Cr 5 + in such compounds has often been doubted, as it was assumed that chromium actually exists as a pair of Cr 3 + : 2Cr 6 + . The pentavalent chromium could not be detected with most standard chemical analyses as Cr 5 + disproportionates into Cr 3 + and Cr 6 + in acidic environments.…”

“…There are considerably fewer studies dedicated to apatites containing Cr 5+ [17,18,30–35] . The existence of Cr 5+ in such compounds has often been doubted, as it was assumed that chromium actually exists as a pair of Cr 3+ : 2Cr 6+ .…”