Speciation and Characterization of Arsenic in Ketza River Mine Tailings Using X-ray Absorption Spectroscopy

Abstract

Ketza River mine tailings deposited underwater and those exposed near the tailings impoundment contain approximately 4 wt % As. Column-leaching tests indicated the potential for high As releases from the tailings. The tailings are composed dominantly of iron oxyhydroxides, quartz, calcite, dolomite, muscovite, ferric arsenates, and calcium-iron arsenates. Arsenopyrite and pyrite are trace constituents. Chemical compositions of iron oxyhydroxide and arsenate minerals are highly variable. The XANES spectra indicate that arsenic occurs as As(V) in tailings, but air-drying prior to analysis may have oxidized lower-valent As. The EXAFS spectra indicate As-Fe distances of 3.35-3.36 A for the exposed tailings and 3.33-3.35 A for the saturated tailings with coordination numbers of 0.96-1.11 and 0.46-0.64, respectively. The As-Ca interatomic distances ranging from 4.15 to 4.18 A and the coordination numbers of 4.12-4.58 confirm the presence of calcium-iron arsenates in the tailings. These results suggest that ferric arsenates and inner-sphere corner sharing or bidentate-binuclear attachment of arsenate tetrahedra onto iron hydroxide octahedra are the dominant form of As in the tailings. EXAFS spectra indicate that the exposed tailings are richer in arsenate minerals whereas the saturated tailings are dominated by the iron oxyhydroxides, which could help explain the greater release of As from the exposed tailings during leaching tests. It is postulated that the dissolution of ferric arsenates during flow-through experiments caused the high As releases from both types of tailings. Arsenic tied to iron oxyhydroxides as adsorbed species are considered stable; however, iron oxyhydroxides having low Fe/As molar ratios may not be as stable. Continued As releases from the tailings are likely due to dissolution of both ferric and calcium-iron arsenates and desorption of As from high-As bearing iron oxyhydroxides during aging.

Vibrational Spectroscopy of Complex Synthetic and Industrial Products

“…From this analysis as shown above, it was confirmed that this structure have water molecules, hydroxyl groups that were found to still exist even after heating the sample to > 600 °C (Figure 1). Therefore, based on all this vibrational evidence our preference for a "new"(similar to work by Moore & Ito, 1974) (Tyrrell & Graham, 1913;Jambor 1966;Ross & Post 1997;Pieczka et al, 1998;Paktunc et al, 2003Paktunc et al, , 2004Nishikawa et al, 2006;Becze and Demopoulos 2007;Walker et al, 2009;Garavelli et al, 2009). Finally, in this work it was observed that for arseniosiderite, and additional arsenate IR and Raman active vibrations occurred ~ 900 cm -1 indicative of protonated arsenate groups.…”

“…Arseniosiderite has been indicated to be more crystalline counter part of yukonite (Garavelli et al, 2009) and generally has slightly more calcium content in both natural and synthetic (Paktunc et al, 2003(Paktunc et al, , 2004Garavelli et al, 2009;Gomez et al, 2010a) samples then yukonite. More interesting, it was noted that the chemical formula commonly used in the literature (Paktunc et al, 2003(Paktunc et al, , 2004Fillipi et al, 2004Fillipi et al, , 2007Garavelli et al, 2009) Ca 2 Fe 3 (AsO 4 ) 3 O 2 ·3H 2 O had a peculiar form in that the use of peroxide types of molecular g r o u p s w e r e u s e d b u t a l s o n o h y d r o x y l g r o u p s w e r e i n c l u d e d i n t h e f o r m u l a s a s i n yukonite. Interestingly, most of these works where the formula was written in that fashion had no reference given to the earlier work of Moore and co-workers (Moore & Ito, 1974; (Burns & Hughes, 2003;Bastians et al, 2004).…”

“…Paktunc et al (2003) reported via As K-edge EXAFS that the coordination number and bond lengths of the As-O and As-Fe units were essentially identical in yukonite and arseniosiderite, and that at the local structural level, the only difference between yukonite and arseniosiderite was the As-Ca coordination number (4.17 and 2.44, respectively). It should be noted that Paktunc et al (2003) failed to reference any of the extensive work done by Moore & Ito (1974), and later Moore & Araki (1977a,1977b on the structure of mitridatite (and as extension arseniosiderite) but still somehow managed to fit the EXAFS structure of arseniosiderite and came up with a As-Ca coordination number of 2.44. However, Moore & Araki (1977a) clearly stated that"each Ca unit is coordinated to four phosphate/arsenate oxygens" thus rendering the previous EXAFS results inaccurate.…”

“…No further arsenic stability tests for arseniosiderite exist to date but due to its crystalline nature they should perform similar or better than yukonite under the same conditions. Since these Ca(II)-Fe(III)-AsO 4 phases (Yukonite and Arseniosiderite) were some of the most important arsenic phases found to occur in the Gold mining tailing operations around the world {Yukon territory, (Paktunc et al, 2003(Paktunc et al, , 2004 and Nova Scotia, Canada (Walker et al ,2005 and2009)] as well in the Mokrsko-west gold deposits, Czech Republic (Filippi et al, 2004;Filippi et al, 2007;)} and as a result of the fact that our experimental evidence showed that synthetic Ca(II)-Fe(III)-AsO 4 produced phases (in particular yukonite) resulted in excellent environmental arsenic retention properties (Becze & Demopoulos, 2007;Becze et al, 2010) under similar industrial conditions used in the Uranium industry disposal sites such as those found in Northern Saskatchewan, Canada. Yet, in spite of all these studies and important relevance in academia as well as industry, the true molecular nature of these Ca(II)-Fe(III)-AsO 4 phases (yukonite and arseniosiderite) and how these phases were related was still not yet well understood.…”

Arsenic speciation and mobility in mine wastes from a copper–arsenic mine in Devon, UK: a SEM, XAS, sequential chemical extraction study

“…Neutral-alkaline conditions promote desorption of As bound to iron oxyhydroxides (Pierce and Moore, 1982) as well as dissolution of thermodynamically unstable iron and calcium arsenate minerals (Dove and Rimstidt, 1985;Paktunc et al, 2004). Arsenate mineral solubilities increase from ferric arsenates to calcium arsenates (Rochette et al, 1998;Paktunc et al, 2003). Both factors might account for the higher As release from the crusher material.…”