Adsorption kinetics of silicic acid on akaganeite

As part of a series of studies on the interaction between ferric ions and silicic acid in the hydrosphere, the adsorption of silicic acid on akaganeite was investigated kinetically at various pH values. The adsorption of silicic acid increased with increasing pH over an initial pH range of 4–11.5. In the kinetic experiment, the Cl− was released from akaganeite much faster than silicic acid was adsorbed. From this result, we concluded that chloride ions bound on the surface of akaganeite are released and Fe–OH or Fe–O− sites are formed, which then acts as an adsorption site for silicic acid. The uptake mechanism of silicic acid by akaganeite is significantly different from that by schwertmannite, despite the presence of the same tunnel structure.

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► The adsorption behavior of silicic acid on akaganeite was examined.
► The amount of adsorbed silicic acid on akaganeite increased with increasing pH.
► Chloride ions bound to akaganeite are released forming Fe–OH or Fe–O− sites.
► The Fe–OH or Fe–O− sites acts as an adsorption site of silicic acid.