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Inorganic sulphate extraction from SO 2 ‐impacted Andosols
Author(s) -
Delfosse T.,
Delmelle P.,
Givron C.,
Delvaux B.
Publication year - 2005
Publication title -
european journal of soil science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.244
H-Index - 111
eISSN - 1365-2389
pISSN - 1351-0754
DOI - 10.1111/j.1365-2389.2004.00647.x
Subject(s) - oxalate , ferrihydrite , chemistry , oxalic acid , precipitation , ammonium oxalate , soil water , weathering , extraction (chemistry) , sulfate , mineral , inorganic chemistry , mineralogy , nuclear chemistry , environmental chemistry , adsorption , geology , soil science , chromatography , geochemistry , physics , organic chemistry , meteorology
Summary Sulphate sorption on to the surface of short‐range ordered minerals and precipitation of Al‐hydroxy sulphate contribute to the acid neutralizing capacity of soils. The correct measurement of total inorganic sulphate is thus essential in soils that are accumulating SO 4 2– anions. We extracted SO 4 2– by various solutions, namely 0.005 m Ca(NO 3 ) 2 , 0.016 m KH 2 PO 4 , 0.5 m NH 4 F and 0.2 m acidic NH 4 ‐oxalate (pH 3), from Vitric and Eutric Andosols exposed to prolonged deposition of acid and SO 2 from an active volcano (Masaya, Nicaragua). We attributed sulphate extractable by KH 2 PO 4 (20–3030 mg kg −1 ) to anion‐exchangeable SO 4 2– , which was much smaller than NH 4 F‐ and oxalate‐extractable SO 4 2– (400–9680 and 410–10 480 mg kg −1 , respectively). Our results suggest the occurrence of a sparingly soluble Al‐hydroxy‐mineral phase extractable by both NH 4 F and oxalate. The formation of Al‐hydroxy minerals would result from the combination of enhanced weathering caused by strong acid loading and simultaneous occurrence of large SO 4 2– concentrations in soil solution. Oxalate extracted slightly more inorganic SO 4 2– than did NH 4 F, this additional amount of SO 4 2– correlating strongly with oxalate‐extractable Si and Fe contents. Preferential occlusion of SO 4 2– by short‐range ordered minerals, especially ferrihydrite, explains this behaviour. If we exclude the contribution of occluded sulphate then oxalate and NH 4 F mobilize similar amounts of SO 4 2– and are believed to mobilize all of the inorganic SO 4 2– pool.