Search Results (3)

Manganese co-precipitated with goethite (Mn-FeOOH) is ubiquitous within (sub-)surface environments, which are considered one of the most important sinks for phosphorus pollution management. Accordingly, various mole ratios of Mn-FeOOHs are synthesized and characterized by XRD, FE-SEM, FTIR, BET, XPS, hysteresis loop, acid–base titration and zero potential. According to XRD and FESEM images, the substitution of Mn causes subtle alterations in the microstructure and crystal structure of goethite, and the morphology of Mn-FeOOHs is transformed from needle-shaped goethite to a short-rod-shaped rough surface with increasing Mn substitution. Based on the analysis of BET and acid–base titration, the substitution of Mn into goethite significantly improved the surface area, pore volume, surface properties and active sites of goethite, thereby establishing a theoretical basis for effective subsequent adsorption. Batch experiment results show that the removal rate of phosphate decreases with the increasing solution pH, indicating that acidic groundwater conditions are more conducive to the removal of phosphate. In addition, the adsorption of phosphate on Mn-FeOOHs is independent of ionic strength, indicating that the inner-sphere surface complexation predominated their adsorption behaviors. The isotherm experiment results showed that Mn-G15 exhibits the strongest adsorption capacity for phosphate at pH 5.5 and T = 318 K, with a maximum adsorption capacity of 87.18 mg/g. These findings highlighted the effect of Mn content on the fixation of phosphate onto Mn-FeOOHs from (sub-)surface environments in pollution management. Full article

Mn-substituted FeOOH with different Mn/(Mn + Fe) molar ratios are synthesized, and characterized using FESEM, XRD, FTIR, ICP-OES, BET, Zeta potential, TG-DSC, XPS, and VSM. The results show that the actual doping amounts of Mn are 0%, 3.05%, 6.13%, 9.04%, 12.70%, and 15.14%, respectively. The substitution of Mn promotes the transformation of goethite from FeOOH to MnFe₂O₄, resulting in a saturation magnetization intensity of up to 14.90 emu/g for G-Mn15%, laying a theoretical foundation for magnetic recovery. The specific surface area of Mn-substituted FeOOH increases from 57.15 m²/g to 315.26 m²/g with an increasing Mn substitution amount. Combined with the abundant oxygen-containing functional groups such as -OH, Fe-O, and Mn-O on the surface, sufficient active sites are provided for the efficient adsorption of U(VI). The TG-DSC analysis results indicate that the substitution of Mn improves the thermal stability of goethite. In addition, XPS analysis results indicate that the substitution of Mn leads to the conversion of Fe³⁺ to Fe²⁺ in goethite, and the conversion of Mn²⁺ to Mn³⁺ replaces Fe³⁺ in the structure of goethite. Fe-O and Mn-O coordinate participate in the adsorption and reduction process of U(VI). The batch experiment results show that the substitution of Mn promotes the adsorption performance of goethite for U(VI). When T = 303 K, pH = 4.0, m/V = 0.5 g/L, and I = 0.01 mol/L NaCl, the maximum adsorption capacity of G-Mn15% for U(VI) is 79.24 mg/g, indicating the potential value of Mn substitution for goethite in the treatment of uranium-containing wastewater. Full article

Marine Co-rich ferromanganese crusts and polymetallic nodules, which are widely distributed in oceanic environments, are salient potential mineral resources that are enriched with many critical metals. Many investigations have achieved essential progress and findings regarding critical metal enrichment in Fe-Mn crusts and nodules. This study systematically reviews the research findings of previous investigations and elaborates in detail on the enrichment characteristics, enrichment processes and mechanisms and the influencing factors of the critical metals enriched in Fe-Mn crusts and nodules. The influencing factors of critical metal enrichments in Fe-Mn crusts and nodules mainly include the growth rate, water depth, post-depositional phosphatization and structural uptake of adsorbents. The major enrichment pathways of critical metals in marine Fe-Mn (oxy)hydroxides are primarily as follows: direct substitution on the surface of δ-MnO₂ for Ni, Cu, Zn and Li; oxidative substitution on the δ-MnO₂ surface for Co, Ce and Tl; partition between Mn and Fe phases through surface complexation according to electro-species attractiveness for REY (except for Ce), Cd, Mo, W and V; combined Mn-Fe phases enrichment for seawater anionic Te, Pt, As and Sb, whose low-valence species are mostly oxidatively enriched on δ-MnO₂, in addition to electro-chemical adsorption onto FeOOH, while high-valence species are likely structurally incorporated by amorphous FeOOH; and dominant sorption and incorporation by amorphous FeOOH for Ti and Se. The coordination preferences of critical metals in the layered and tunneled Mn oxides are primarily as follows: metal incorporations in the layer/tunnel-wall for Co, Ni and Cu; triple-corner-sharing configurations above the structural vacancy for Co, Ni, Cu, Zn and Tl; double-corner-sharing configurations for As, Sb, Mo, W, V and Te; edge-sharing configurations at the layer rims for corner-sharing metals when they are less competitive in taking up the corner-sharing position or under less oxidizing conditions when the metals are less feasible for reactions with layer vacancy; and hydrated interlayer or tunnel-center sorption for Ni, Cu, Zn, Cd, Tl and Li. The major ore-forming elements (e.g., Co, Ni, Cu and Zn), rare earth elements and yttrium, platinum-group elements, dispersed elements (e.g., Te, Tl, Se and Cd) and other enriched critical metals (e.g., Li, Ti and Mo) in polymetallic nodules and Co-rich Fe-Mn crusts of different geneses have unique and varied enrichment characteristics, metal occurrence states, enrichment processes and enrichment mechanisms. This review helps to deepen the understanding of the geochemical behaviors of critical metals in oceanic environments, and it also bears significance for understanding the extreme enrichment and mineralization of deep-sea critical metals. Full article