Uptake and release of arsenic and antimony in alunite-jarosite and beudantite group minerals

Abstract

Arsenic and antimony are highly toxic to humans, animals and plants. Incorporation in alunite, jarosite and beudantite group minerals can immobilize these elements and restrict their bioavailability in acidic, oxidizing environments. This paper reviews research on the magnitude and mechanisms of incorporation of As and Sb in, and release from, alunite, jarosite and beudantite group minerals in mostly abiotic systems. Arsenate-for-sulfate substitution is observed for all three mineral groups, with the magnitude of incorporation being beudantite (3-8.5 wt. % As) > alunite (3.6 wt. % As) > natroalunite (2.8 wt. %) > jarosite (1.6 wt. % As) > natroalunite (1.5 wt. % As) > hydroniumalunite (0.034 wt. % As). Arsenate substitution is limited by the charge differences between sulfate (-2) and arsenate (-3), deficiencies in B-cations in octahedral sites and for hydroniumalunite, difficulty in substituting protonated H2O-for-OHgroups. Substitution of arsenate causes increases in the c-axis for alunite and natroalunite, and in the c-and a-axes for jarosite. The degree of uptake is dependent on, but limited by, the AsO4/TO4 ratio. Aerobic and abiotic As release from alunite and natroalunite is limited, especially between pH 5 and 8. Release of As is also very limited in As-bearing jarosite, natrojarosite and ammoniumjarosite at pH 8 due to formation of secondary maghemite, goethite, hematite and Fe arsenates that resorb the liberated As.Abiotic reductive dissolution of As-bearing jarosite at pH 4, 5.5 and 7 is likewise restricted by the formation of secondary green rust sulfate, goethite and lepidocrocite that take up the As. Similar processes have been observed for the aerobic dissolution of Pb-As-jarosite (beudantite analogue), with secondary Fe oxyhydroxides resorbing the released As at pH 8. Higher amounts of As are released, however, during microbial-driven jarosite dissolution. Natural jarosite has been found to contain up to 5.9 wt. % Sb 5+ substituting for Fe 3+ in the B-site of the mineral structure. Sb(V) is not released from jarosite at pH 4 during abiotic reductive dissolution, but at pH 5.5 and 7, up to 75% of the mobilized Sb can be structurally incorporated into secondary green rust sulfate, lepidocrocite or goethite. Further research is needed on the co-incorporation of As, Sb and other ions in, and the uptake and release of Sb from, alunite, jarosite and beudantite group minerals, the influence of microbes on these processes and the long-term (>1 year) stability of these minerals.

Arsenic-Imposed Effects on Schwertmannite and Jarosite Formation in Acid Mine Drainage and Coupled Impacts on Arsenic Mobility

“…Differences in ammonium oxalate extractions for 4 h at 80 °C (which recovers both crystalline and poorly ordered phases) versus 2 h at room temperature (which recovers poorly ordered phases only) indicate that the jarosite in this sample had molar Fe/K, Fe/S and Fe/As ratios of 7.90, 1.88, and 6.80, respectively. The extraction results also indicate a molar Fe/(S + As) ratio of 1.48 which, in light of AsO 4 3– substitution for SO 4 2– within jarosite, agrees closely with an ideal molar Fe/(S + As) ratio of 1.5. Considered together, the molar ratios of crystalline As and S further indicate ∼22 mol % substitution of AsO 4 3– for SO 4 2– in jarosite within the sample ZA-DrSt.…”

“…jarosite,38 agrees closely with an ideal molar Fe/(S + As) ratio of 1.5. Considered together, the molar ratios of crystalline As and S further indicate ∼22 mol % substitution of AsO 4 3− for SO 4 2− in jarosite within the sample ZA-DrSt.…”

“…Arsenic(V)-bearing jarosite has been observed previously in mine wastes and associated AMD systems. 38,82 Several studies have shown that jarosite can accommodate As(V) within its crystal structure by substitution of AsO 4 3− for SO 4 2− . 84−86 In the present study, the highest observed molar As/(As + S) ratio in jarosite equates to 22 mol % substitution of AsO 4 3− for SO 4 2− (based on extraction data for where scorodite was absent and jarosite was the only detectable crystalline Asand S-bearing phase) (Supporting Information, Figure S5b).…”

Synthesis, Crystal Structure, and Excellent Selective Pb2+ Ion Adsorption of New Layered Compound (NH4)In3(SO4)2(OH)6

“…The formula of this class of natural minerals can be written as AB 3 (TO 4 ) 2 (OH) 6 , where A is a monovalent or divalent cation (such as H + , NH 4 + , Na + , Ca 2+ , Sr 2+ ), B is normally corresponding to Al 3+ , Fe 3+ , and T is a hexavalent or pentavalent element (P 5+ , As 5+ , S 6+ ) . Within the supergroup, it is divided into alunite, jarosite, and beudantite subgroups based on the occupation of the T and B sites . The alunite group differs from the jarosite minerals in that it contains more Al 3+ than Fe 3+ at the B site.…”

“…Each octahedron is connected to four bridging hydroxyl groups with a slight distortion. Cations either in the host layer or interstitial site are exchangeable, which are often used to immobilize toxic elements such as arsenic (As) and antimony (Sb) in mine waste . The incorporation of As in alunite, jarosite, and beudantite subgroup minerals can be realized by replacing SO 4 2– with AsO 4 3– in the T site, and the substitution of Fe 3+ by Sb 5+ in the B site of jarosite subgroup minerals is a facile process due to the similar ionic sizes (Sb 5+ , 0.60 Å; Fe 3+ 0.65 Å) .…”