Research PaperRemoval of cesium ion from contaminated water: Improvement of Douglas fir bark biosorption by a combination of nickel hexacyanoferrate impregnation and TEMPO oxidation

•New biosorbents for cesium ion removal were developed from forestry residue.•Combination of nickel hexacyanoferrate impregnation and TEMPO oxidation was tested.•TEMPO oxidation improved nickel hexacyanoferrate impregnation.•Bark sorption capacity was increased by a factor of 7 thanks to a synergistic effect.•Stability of nickel hexacyanoferrate crystals during cesium adsorption was studied.

New biosorbents derived from a forestry waste, Douglas fir bark, were developed to remove cesium ion (Cs+) from water. Crude bark was oxidised either by 2,2,6,6-tetramethylpiperidine-1-oxy radical (TEMPO)-mediated oxidation or by the Fenton reaction to create carboxyl groups onto the bark's surface. Subsequently, nickel (II) hexacyanoferrate (III) (NiHCF) was incorporated into crude and oxidised barks. Crude bark has good intrinsic property for Cs+ sorption and TEMPO is the best tested oxidant able to improve this capacity. Structural analyses showed increase as well as important structural modification of bark surface following TEMPO oxidation. A link was established between the observed modifications and the amount of incorporated NiHCF. Combination of TEMPO oxidation and NiHCF impregnation increased Cs+ maximum sorption capacity (qmax) of crude bark by a factor of 7 to reach 1.51 mmol g−1. In addition, NiHCF/TEMPO bark could be used within pH range 4-10 with full sorption capacity. Finally, the release of nickel, iron and cyanide during incubation of NiHCF/TEMPO bark with water remained within the legal limits defined by U.S. EPA. Due to its high trapping capacity, pH stability and structural properties, NiHCF/TEMPO bark appears as a promising sorbent for removal of Cs+ from contaminated water.

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