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The transformation of Al-substituted goethite in oxidative and reductive atmosphere, which models natural fire, was investigated in detail. Various characterization results indicated that Al-substituted goethite transformed into hematite in an oxidative atmosphere and magnetite followed by zero-valent iron in a reductive atmosphere. Interestingly, the substitution of Al for Fe not only changed the crystal morphology affecting crystal surface reactivity, but also restrained the transformation of goethite into hematite, magnetite and zero-valent iron. In addition, the Al in the goethite was embedded into the crystal structure of thermally formed hematite and magnetite, considerably influencing their surface reactivity. The macroscopic adsorption results indicated that the substitution of Al for Fe increased the adsorption capacity of goethite and the corresponding derivatives except zero-valent iron. For the same Al amount, the adsorption capacity followed an order of goethite > hematite > magnetite, implying a loss of phosphate in goethite-rich soil after experiencing natural fire. However, with increasing in temperature in the reductive atmosphere, Al-magnetite transformed into a mixture of Al-magnetite and zero-valent iron which displayed excellent phosphate adsorption capacities increasing to 1.21–5.96 mg/g. The phosphate adsorption behaviors to thermally formed products were fitted well by surface complexation modeling with five complexation sites, which were more obvious for goethite than for hematite and magnetite. These findings presented in this study represent significant progress toward an understanding of the migration, enrichment and transformation of phosphate in Al-substituted goethite-rich soil in cases experiencing natural fire. [ABSTRACT FROM AUTHOR]

Europium (Eu(III)) has been extensively used as an analogue of trivalent lanthanide in the radioactive wastewater from nuclear industry. The adsorption of Eu(III) on the Al-substituted goethite was investigated by characteristic and batch techniques. The characteristic results illustrated that the Al-substituted goethite was synthesized successfully and the acicular-like structure goethite was transformed to multi-domain jagged crystal with the increase of Al content, respectively. The adsorption amount of Eu(III) on Al-substituted goethite was increased with an increase of pH from 4.0 to 8.0. The thermodynamic parameters revealed that the adsorption of Eu(III) on Al-substituted goethite was a spontaneous and endothermic process. The increase of Al content increased the adsorption capacity of Al-substituted goethite to Eu(III). The maximum Eu(III) adsorption capacity was determined to be 6.75 mg/g for α-(Fe 0.85 Al 0.15 )OOH at pH = 5.5 and T = 293 K using Langmuir model. Furthermore, XPS (X-ray photoelectron spectroscopy) analysis verified that oxygen-containing functional groups were responsible for the major adsorption mechanism and the effect of ionic strength on the adsorption displayed the inner-sphere surface complexation of Al-substituted goethite dominated the adsorption process. [ABSTRACT FROM AUTHOR]

The Al-Fe 2 O 3 with different aluminum contents were synthesized by heating Al-substituted goethite and were characterized by FESEM, XRD, FT-IR and XPS techniques. The characteristic results showed that the Fe 3 + ion in hematite was partly substituted by Al 3 + ion, leading to the change of crystal structure. The batch experiments indicated that the adsorptions of Sr(II) on Al-Fe 2 O 3 slowly increased with increasing pH starting from 2 to 11. The pseudo-second-order kinetic and the Langmuir model gave the better fits to the adsorption kinetics and isotherms, respectively. The thermodynamic parameters indicated that the adsorption of Sr(II) on Fe 2 O 3 was an endothermic and spontaneous process. The XPS analysis demonstrated that the oxygen-containing functional groups were responsible for the Sr(II) adsorption. These findings indicated that Al-Fe 2 O 3 may be a valuable candidate for pre-concentration and solidification of radionuclides from aqueous solutions. [ABSTRACT FROM AUTHOR]

Abstract Siderite as a Fe(II)-bearing mineral often be naturally weathered and oxidized into goethite, which would decrease the surface chemical activity of the siderite. The chemical activity of siderite is improved by decomposing weathering-formed goethite at low temperature (350 °C). The activated natural siderite (ANS) was utilized to remove U(VI) from aqueous solutions. Batch experiments revealed that ANS after thermal treatment at 350 °C (ANS350) exhibited excellent uptake performance toward U(VI) (14.65 mg/g) which was better than natural siderite (9.00 mg/g) at pH = 4.0 and T = 293 K. Meanwhile, the uptake percents of U(VI) on NS and the uptake process was involved electrostatic attraction on the surface of adsorbents. The characterization results illustrated that activated natural siderite at 350 °C presented the better uptake capacity due to its larger specific surface area and smaller average pore size compared to natural siderite, which was optimized to adsorb U(VI) from aqueous solutions. The spectroscopic analysis demonstrated that the abundant surface oxygenated functional groups of ANS facilitated the uptake process of U(VI). Meanwhile, reduction was also involved in the process. Additionally, the U(VI) reduction amount can be enhanced to some extent after calcination. These findings give insight into the further development of activated natural mineral obtained by heating in low temperature, for using as potential candidate in immobilization of uranium(VI) from contamination water in actual environmental management. Highlights • Natural siderite was activated by thermal treatment at low temperature. • ANS350 exhibited excellent uptake performance toward U(VI) (14.65 mg/g). • Abundant oxygenated functional groups facilitated the uptake process of U(VI). • Reduction was involved the U(VI) uptake and calcination at low temperature could enhance the reduction amount. [ABSTRACT FROM AUTHOR]