Vibrational spectroscopic study of the mineral pitticite Fe, AsO4, SO4, H2O

Mineralogical Controls on the Bioaccessibility of Arsenic in Fe(III)–As(V) Coprecipitates

“…The spectra show vibrational features of three different components, namely H 2 O (or OH), SO 4 , and AsO 4 . The broad peak at 3380 cm –1 corresponds to bulk H 2 O/OH stretching vibrations as observed for scorodite at ∼3300 cm –1 and for ferrihydrite at 3430 cm –1 , while the band at around 1625 cm –1 is caused by the corresponding OH bending vibrations. − With increasing As content, a second band became more pronounced at 3190 cm –1 (Figure a and SI Figure S6a–e), which may be attributed to the OH stretching vibrations of water molecules H-bonded to oxygens of AsO 4 3– as in scorodite and pitticite (Fe 3+ x (AsO 4 ) y (SO 4 ) z · n H 2 O) . In the spectra of coprecipitates synthesized at pH ≤ 6 (R > 0.8), four SO 4 bands (symmetric (ν 1 ) and triply degenerate asymmetric S–O stretching (ν 3 ) vibrations) became visible at 1190, 1130, 1058, and 990 cm –1 (Figures , , and SI Figure S6).…”

“…57−59 With increasing As content, a second band became more pronounced at 3190 cm −1 (Figure 2a and SI Figure S6a−e), which may be attributed to the OH stretching vibrations of water molecules H-bonded to oxygens of AsO 4 3− as in scorodite 60 and pitticite (Fe 3+ x (AsO 4 ) y (SO 4 ) z •nH 2 O). 61 In the spectra of coprecipitates synthesized at pH ≤ 6 (R > 0.8), four SO 4 bands (symmetric (ν 1 ) and triply degenerate asymmetric S−O stretching (ν 3 ) vibrations) became visible at 1190, 1130, 1058, and 990 cm −1 (Figures 2, 3, and SI Figure S6). These bands are consistent with a C 2v symmetry of SO 4 and indicate the formation of bridging innersphere complexes.…”

The nature of synthetic basic ferric arsenate sulfate (Fe(AsO4)1−x(SO4)x(OH)x) and basic ferric sulfate (FeOHSO4): their crystallographic, molecular and electronic structure with applications in the environment and energy

“…7a, S5, ESI 3 and Table S9, ESI3). Such disorder may explain the reason why this phase has been reported in previous studies to be metastable 12,15 or nano-colloidal 15,28 in nature before transforming to the most stable phase (e.g. scorodite or ferric arsenate subhydrate).…”

“…Determination of the exact type of arsenate-bearing phase formed in industrial mineral processing operations is important from an environmental protection point of view as typically these compounds end up in mineral waste disposal sites that potentially can leach out to surrounding waters. Characterization of residues generated in the gold and copper extraction industries by our group and others has found evidence that the main mineralogical form of arsenic produced in industrial autoclave processes resembles that of a BFAS like phase, [10][11][12]15 while lately it has been reported to resemble to a natural nano-colloidal mineral (''pitticite'') 28 found in acid mine waste dumps and tailings dams. Therefore, this BFAS phase is one of the main environmental controls of arsenic in industrially produced waste materials (tailings).…”

“…In industrial hydrometallurgical processes of arsenic-bearing copper concentrates 10,15,27 it has been shown that BFAS is one of the dominant arsenic controls in the produced residues that are disposed in the environment. In 2012, Frost et al 28 reported the vibrational spectra of a nano-colloidal mineral (''pitticite'') often found in mine waste dumps and tailings dams, which can serve an important role in the environment as an arsenic control, but due to its physical nature (''nano-colloidal''), shows no X-ray diffraction or structure. Interestingly, the vibrational spectra of this naturally occurring nano-mineral was noted to resemble closely to our synthetic BFAS product, 26 highlighting once again its importance as an environmentally sensitive industrially produced material.…”