Dissolution Kinetics of Sulfate from Schwertmannite Under Variable pH Conditions
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Sulfate mobilization was investigated under controlled laboratory conditions. Microbially synthesized schwertmannite (14.7 m2/g specific surface area with 4.7 Fe:S molar ratio) was interacted at room temperature for 4 months with aqueous solutions between pH 5 and 8. More than 50% of the solid-phase sulfate was released during the initial 2 months and the rate was positively influenced by pH due to the competition of hydroxyl ions for SO4 2−. More than 90% of the solid-phase sulfate was released within 4 months at pH 8. Infrared spectra demonstrate diminution and splitting of SO4 2− adsorption bands, indicating possible structural changes within the solid phase as a result of SO4 2− release. Transformation of schwertmannite to goethite was triggered by pH increase and was primarily responsible for the sulfate mobilization. Thus, schwertmannite that interacts with neutral to alkaline water can add significantly to the sulfate load of a stream.
KeywordsAcidity generation Acid mine drainage Dissolution kinetics FTIR Pyrite oxidation Schwertmannite, schwertmannite transformation, sulfate pollution
The work was supported by the German Academic Exchange Service (DAAD) and the Geotechnologien program (BMBF, No-03G0714A).
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