Inorganic sulphate extraction from SO₂‐impacted Andosols

Abstract

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 À1 ) 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 À1 , 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.

Hydric properties of high charge, halloysitic clay soils from the tropical South Pacific region

“…Finally, S contents (not shown) ranged between 0.1 and 0.5 g kg − 1 in the clay fraction. Most probably, this element should appear as sulphate anion likely sorbed onto colloidal surfaces of iron oxides (Delfosse et al, 2005). The carbon loss in the liquid volume (L) used for dispersion was actually moderate, as it ranged between 1 and 15% of total C content, and was generally below 6%.…”

Sulphate sorption at high equilibrium concentration in Andosols

“…occlusion (Delfosse et al, 2005a). Although most of the inorganic SO 4 2− in these soils tends to be retained by an adsorption mechanism, precipitation also may contribute to SO 4 2− sorption for a significant part (Prietzel and Hirsch, 2000;Delfosse et al, 2005a,c).…”

Highly accumulated sulfur constituents and their mineralogical relationships in Andisols from central Japan

“…The Andisols of Masaya Volcano receive continuous inputs of SO 2 gas (200-700 mg m − 2 day − 1 ; Delmelle et al, 2001). Delfosse et al (2005a) suggested that this SO 2 promotes Al-hydroxy sulfate precipitation as a result of enhanced weathering caused by strong acid loading and the large sulfate concentrations in soil solutions.…”

“…Among the newly proposed solvents for determining sulfates, oxalate and NH 4 F do not have the risk of converting organic S into inorganic S (Prietzel and Hirsch, 2000;Delfosse et al, 2005a). Delfosse et al (2005a) showed that compared to NH 4 F, oxalate extracted more inorganic sulfates from Andosols.…”

“…Recent studies of Andosols from Masaya Volcano (Nicaragua) have shown that these soils retain large amounts of both precipitated and occluded sulfates (Delmelle et al, 2003;Delfosse et al, 2005a). The Andisols of Masaya Volcano receive continuous inputs of SO 2 gas (200-700 mg m − 2 day − 1 ; Delmelle et al, 2001).…”