The effect of copper on the precipitation of scorodite (FeAsO4·2H2O) under hydrothermal conditions: Evidence for a hydrated copper containing ferric arsenate sulfate-short lived intermediate

Vibrational Spectroscopy of Complex Synthetic and Industrial Products

“…This approach is often good enough to yield some reasonable results if a priori knowledge of species is assumed based on the matching of chemical elements from elemental analysis; however, this approach fails when the concetration of the phases is below the detection limit of lab based XRD (~ 4-5 w.t.%) or when the sample is not perfecly crystalline in nature. Indeed in our studies (Gomez et al, 2010b(Gomez et al, , 2011c) both scenerios were encountered in the industrial samples analyzed (Dymov et al, 2004;Defreyne et al, 2009;Mayhew et al, 2010;Bruce at al., 2011). For example, in the case of the gold produced residue (Figure 9), although the sample was crystalline in nature, the amount of arsenic (as AsO 4 ) in the solid was ~ 1 w.t.…”

“…It was found by comparison to our other vibrational data that the arsenate species found in the copper industrial residue again resembled that of our BFAS phase. It is worth for the reader to also note that in our work (Gomez et al, 2010b(Gomez et al, , 2011c only three phases (and intermixtures of these) could be detected, namely Scorodite, Ferric Arsenate Sub-hydrate/FAsH, Basic Ferric Arsenate Sulfate using the lab based techniques (XRD, ATR-IR, Raman) employed in these studies. Interestingly, Basic Ferric Sulfate (FeOHSO 4 ) was a species detected in previous works formed at high (200-225 °C) and higher Fe/As ratios (~4) but no clear evidence was obtained from our work using the lab based methods which included vibrational spectroscopy.…”

“…As a result, vibrational spectroscopy was employed to investigate the arsenic phase found in this industrial residue. In the case of the Raman spectroscopy (data now show here but refer to Gomez et al, 2011c), vibrational structure was obtained unlike the other case but was found to be largely dominated by the other expected species found in the sample as a result of the chemical process it undergoes (Defreyne et al, 2009;Mayhew et al, 2010;Bruce at al., 2011). For example, it is expected to have both hematite and elemental sulfur as the major constituent of this produced residue; however, upon the analysis of this product with Raman spectroscopy, only hematite could be observed and not in any way elemental sulfur nor any arsenate type of phase.…”

“…In particular, it was observed that the solid solution of SO 4 ↔ AsO 4 not only changed the amount of each group incorporated into the BFAS structure but also actually changed the symmetry of the molecular group expressed in the vibrational spectra and more importantly showed us that these groups could occupy the same type of crystallographic sites in the crystal structure, something that would become important later in the determination of its crystal structure (Gomez et al, 2011d). In terms of industrially produced samples, our work analyzed two industrially manufactured samples from the gold and copper industries (Gomez et al, 2010b(Gomez et al, , 2011c. In general for industrial practices XRD is the most common form of analysis employed due to www.intechopen.com the fact that is the easiest and most widely available tool with a large enough database for users to simply " click buttons" to get their desired solutions.…”

Factors to Enable Crystallization of Environmentally Stable Bioscorodite from Dilute As(III)-Contaminated Waters

“…Chemical composition of the resultant bioscorodite products ([Fe] im /[As] im ratio) generally became closer to 1.0 (the theoretical ratio for scorodite) at higher initial As(III) concentrations (Table 3). Slightly higher [Fe] im /[As] im ratios (1.2-1.5) observed at lower initial As(III) concentrations may be due to incorporation of SO 4 2-, as was reported in abiotic hydrothermal [25][26][27][28] and atmospheric scorodite synthesis [7]. • For possible practical application using the continuous process (supposedly composed of an aeration tank followed by a settling tank), recycling microbiologically active bioscorodite sludge could maintain both high cell density and seed pulp density to support steady As(III) and Fe(II) oxidation and the resultant scorodite crystallization.…”