Transformation of jarosite during simulated remediation of a sandy sulfuric soil

Iron‑sulfur geochemistry and acidity retention in hydrologically active macropores of boreal acid sulfate soils: Effects of mitigation suspensions of fine-grained calcite and peat

“…In contrast to the reference columns, the columns treated with different mitigation suspensions did not contain any jarosite as predicted by the LCF-EXAFS analysis (Table 2). This is reasonable, because this mineral is only stable in highly-oxidizing (ORP > 400 mV) and acidic conditions (pH = 3-4), and will otherwise either not form or undergo dissolution and hydrolysis (Madden et al, 2012;Trueman et al, 2020;Kölbl et al, 2021). As reported by Högfors-Rönnholm et al ( 2022), the treatments have led to a shift from oxic and acidic conditions in the reference columns to circumneutral/weakly-acidic and sub-oxic conditions in the treated soil columns.…”

“…However, the low levels of reduction (e.g., limited Fe(III) reduction and no/negligible sulfate reduction) and (near-)complete conversion of jarosite to Fe hydroxides observed for peat treatments are desirable, because (i) complete reduction of Fe and S will lead to the formation of Fe sulfides, which will be re-oxidized during future aeration events and ultimately result in renewed reacidification; and (ii) (near-)complete loss of jarosite (hosting most of the retained acidity in acid sulfate soils) will lead to a strong decrease in the acidity stored in the soils. Establishment of such weakly-moderately reducing conditions favoring the transformation of jarosite to Fe hydroxides while circumventing Fe-sulfide formation has been recently recommended as a desirable remediation option for jarosite-bearing sulfuric soils (Kölbl et al, 2021;Kölbl et al, 2022). In addition, as compared to the reference columns, the peat-treated columns released lower amounts of metals (e.g., Al, Co and Ni) (Högfors-Rönnholm et al, 2022), suggesting that peat can additionally act as efficient sorbents for metals under the weakly-acidic conditions.…”

“…In acid sulfate soil landscapes with slightly higher pH (pH = 4.5-5), sulfate can be additionally retained as Al(III) oxyhydroxysulfates (e.g., basaluminite) (Bigham and Nordstrom, 2000;Jones et al, 2011). These secondary Fe(III) and Al (III) minerals are metastable, and thus can progressively transform into thermodynamically more stable forms (Bigham and Nordstrom, 2000;Burton et al, 2008;Vithana et al, 2015;Kölbl et al, 2021), during which trace metal(loid)s retained by the metastable minerals (via surface sorption or structural substitution) might be partially released or become more labile (Burton and Johnston, 2012;Karimian et al, 2017;Schoepfer and Burton, 2021). In addition, the transformation of Fe(III)/Al(III) oxyhydroxysulfates to Fe(III)/Al(III) hydroxides liberates substantial amounts of additional acidity, thus sustaining a high and long-lasting level of acidity in welloxidized acid sulfate soils (Vithana et al, 2013;Karimian et al, 2018).…”

Improving the Chemical Properties of Acid Sulphate Soils from the Casamance River Basin

“…Consequently, the soil solution was rusty in colour and a fine orange layer appeared in the soil several mm under the soil surface. In a later work, Kölbl et al [67] showed that under moderate reducing conditions, iron evolved into mineral forms (goethite and lepidocrocite), which were not prone to oxidation and re-acidification with future aeration.…”

Effects of Straw Return and Moisture Condition on Temporal Changes of DOM Composition and Cd Speciation in Polluted Farmland Soil

“…DOM contains abundant functional groups (e.g., carboxyl, phenol, and hydroxyl), which can form complexes with Cd [21][22][23]. In a sandy sulfuric soil, the addition of straw DOM was found to rapidly induce redox processes and pH increase [24]. It has been well known that redox potential (Eh) and pH are key environmental factors in controlling the solubility and bioavailability of Cd in soils [25].…”