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Authors requiring further information regarding Elsevier’s archiving and manuscript policies are encouraged to visit: http://www.elsevier.com/copyright Author's personal copy Environment International 35 (2009) 1243–1255 Contents lists available at ScienceDirect Environment International journal homepage: www.elsevier.com/locate/envint Review article Secondary arsenic minerals in the environment: A review Petr Drahota a,b,⁎, Michal Filippi a a Institute of Geology, Academy of Sciences of the Czech Republic, v.v.i., Rozvojová 269, 165 00 Prague 6 — Lysolaje, Czech Republic b Institute of Geochemistry, Mineralogy and Mineral Resources, Faculty of Science, Charles University, Albertov 6, 128 43 Prague 2, Czech Republic article info abstract Article history: Information on arsenic (As) speciation in solid materials is critical for many environmental studies concerned Received 10 March 2009 with As stability and/or mobility in natural As-impacted soils and mining or industrial sites contaminated by Accepted 10 July 2009 As. The investigation of these systems has provided evidence for a number of secondary As minerals that Available online 7 August 2009 have often played a significant role in As mobility in the solid phase–water system. This paper presents a list of environmentally important secondary As minerals in contaminated soil and waste systems, summarizes Keywords: the information about their origin, occurrence, environmental stability and thermodynamics, and proposes Arsenic Secondary arsenic mineral several important avenues for further investigation. Environmental sample © 2009 Elsevier Ltd. All rights reserved. Solubility Environmental stability Contents 1. Introduction .............................................................. 1243 2. Environmentally important secondary as minerals ............................................ 1244 2.1. As oxides ............................................................ 1244 2.2. Fe arsenates .......................................................... 1244 2.2.1. Well-crystallized Fe arsenates .............................................. 1244 2.2.2. Poorly crystalline and amorphous Fe(III) arsenates .................................... 1248 2.2.3. Pharmacosiderite group ................................................. 1250 2.2.4. Ca–Fe(III) arsenates ................................................... 1250 2.3. Fe sulphoarsenates and sulphoarsenites ............................................. 1251 2.4. Ca, Mg and Ca–Mg arsenates ................................................... 1251 2.5. Other metal arsenates ...................................................... 1252 3. Summary and tasks for future research ................................................. 1253 Acknowledgements ............................................................. 1253 References ................................................................. 1253 1. Introduction sulphide minerals realgar and orpiment are also found. These primary As-bearing minerals are listed in Table 1. While As does not readily More than 300 arsenic (As) minerals are known to occur in nature. substitute into the structures of the major rock-forming minerals, it Of these approx. 60% are arsenates, approx. 20% are sulphides and can easily occur as a minor component in the abundant Fe sulphide sulphosalts, 10% are oxides and the rest are arsenites, arsenides, native mineral pyrite (e.g., Fleet et al., 1989, 1993; Savage et al., 2000; elements and metal alloys (Bowell and Parshley, 2001). The most Zachariáš et al., 2004; Blanchard et al., 2007). When these primary important primary As-bearing minerals are those where the As occurs minerals are exposed to the atmosphere and surface or ground waters, as the anion (arsenide) or dianion (diarsenide), or as the sulfarsenide alteration reactions cause formation of secondary As minerals, such as anion(s); these anions are bonded to metals such as Fe (löllingite, simple As oxides or more complex phases with As, oxygen and various arsenopyrite), Co (cobaltite) and Ni (gersdorffite). The simple As metals. The latter group of minerals comprises arsenite and arsenate minerals that are formed by linking As(III)-oxo-anion groups or As (V)-oxo-anion groups, respectively, to a variety of mono-, di- and ⁎ Corresponding author. Institute of Geochemistry, Mineralogy and Mineral Resources, Faculty of Science, Charles University, Albertov 6, 128 43 Prague 2, Czech Republic. trivalent metal cations. Secondary arsenite minerals are rare in natural E-mail address: [email protected] (P. Drahota). environments, usually occurring as the products of hydrothermal 0160-4120/$ – see front matter © 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.envint.2009.07.004 Author's personal copy 1244 P. Drahota, M. Filippi / Environment International 35 (2009) 1243–1255 Table 1 arsenolite, is a relatively common secondary mineral formed from Ideal formulas of the most common primary As-bearing minerals referred to in the text. oxidation of native As, arsenopyrite, löllingite, and from weathering of Mineral Formula System scorodite. Arsenolite has occurred as efflorescencents on the walls of Arsenopyrite FeAsS Monoclinic former underground mine workings, such as in the Jáchymov ore district, Cobaltite CoAsS Orthorombic Czech Republic (e.g., Ondruš et al.,1997). This mineral has been also found Enargite Cu3AsS4 Orthorombic in association with scorodite and native sulphur in arsenopyrite/ fi Gersdorf te NiAsS Cubic löllingite-rich processing waste (Filippi, 2004)(Figs. 2 and 3a, b, c), Löllingite FeAs Orthorombic 2 weathered saprolite (Bowell,1994), and in an old tailings pile (e.g., Ashley Orpiment As2S3 Monoclinic Pyrite FeS2 Cubic and Lottermoser, 1999; Juillot et al., 1999; Borba et al., 2003; Haffert and Realgar AsS Monoclinic Craw, 2008). Tennantite (Cu, Ag, Fe, Zn)12As4S13 Cubic The monoclinic dimorph of As trioxide, claudetite, is often intimately associated with arsenolite. It has occurred as the oxidation product of native As in dump wastes (Matsubara et al., 2001), as the alterations under mildly reducing conditions. Conversely, secondary speleothem related to the alteration of enargite, tennantite, or arsenate compounds comprise a large class of minerals that have been arsenopyrite in the breccia-pipe mineralization at Corkscrew Cave, found in many oxidized environments. Similar to phosphate minerals, Arizona (Onac et al., 2007), and as the efflorescents at the furnace and the arsenate tetrahedra is bonded to octahedrally coordinated condensed flue sites (Ashley and Lottermoser, 1999). It is assumed transition metal ions (e.g., Fe, Mn, Ni) or to large, divalent cations that claudetite could represent an important secondary reservoir of As (e.g., Ca, Ba, Pb). Because of variations and multiples of the bonding in the metasedimentary rocks of the Maine watershed, USA, patterns, the relatively open structures of some arsenate minerals originating from the orpiment and arsenopyrite oxidation (Foley cause extensive substitution of cations, anions and water, and solid and Ayuso, 2008). In situ formation of claudetite in the absence of Fe solutions (e.g., Mutter et al., 1984; Behrens et al., 1998). All the oxyhydroxides and aqueous Fe complexes from oxidation of orpiment secondary As minerals mentioned in the text are listed in Table 2. is assumed in the reaction (Eq. (1)) (Foley and Ayuso, 2008): Recently, the investigation of both the natural and anthropogenic ð Þþ ð Þþ ð Þ→ ð Þþ þð Þþ 2−ð ÞðÞ As geochemical anomalies, using modern analytical tools (micro- As2S3 s 3H2O l 6O2 g As2O3 s 6H aq 3SO4 aq 1 Raman, XAS techniques), has provided a better picture of As bonding to a The stabilities of arsenolite and claudetite are quite similar, since particular substrate. Wang and Mulligan (2008) compiled the research they have nearly similar free energies of formation: arsenolite on the surface structure and surface complexing of As species in the −576.34 kJ/mol and claudetite −576.53 kJ/mol (Nordstrom and inorganic solid phase that play an important role in governing As Archer, 2003). Nevertheless, claudetite is slightly more stable than mobility in most natural systems. As another result of this approach, a arsenolite under ambient conditions (the difference −0.19 kJ/mol). large number of secondary As minerals have been found in highly Arsenolite and claudetite dissolve at pHb8 and temperature to 90 °C contaminated soils, stream sediments, former industrial sites and mine according to the Eq. (2) (Pokrovski et al., 1996); these are stable in tailings (e.g., Utsunomiya et al., 2003; Paktunc et al., 2004; Cancès et al., equilibrium with waters of high pH (Nordstrom and Archer, 2003). 2008; Filippi et al., 2009). The ability of secondary As minerals to immobilize As and control its dissolved concentrations depends on the ð Þþ ð Þ→ 0ð ÞðÞ As2O3 s 3H2O l 2H3AsO3 aq 2 solubility of these phases, which is highly variable. Precipitation of secondary As minerals has always been