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The very large surface associated with aerogels made them attractive in the field of sorption. Herein, silica aerogels were characterized and used for the sorption of U(VI) in solution. The effects of specific surface area (SSA), pH and coexistent electrolyte ions on the surface site density, aggregation and sorption properties have been carefully investigated. The site distributions of silica aerogels were calculated with Visual MINTEQ. The sorption of U(VI) is affected significantly by the solution pH. The sorption increases with increasing SSA due to the increased amount of surface active sites of silica aerogels. Electrolyte ions (Na + , K + , NO 3 − , Cl − ) were added to investigate the competition ability to U(VI) adsorbed on active sites. The influence of humic acid (HA), silicate and phosphate on U(VI) sorption in multiphase systems were also discussed. The kinetics data were used to investigate the sorption process and pseudo-second-order model was used to simulate the kinetic data. Spectroscopic analyses were also utilized to explain the role of OH groups in the U(VI) sorption. [ABSTRACT FROM AUTHOR]

Radioactive waste is usually sealed in steel canisters surrounded by a layer of compacted clay back-fill, and permanent buried in a deep geological repository. Unavoidably, the radionuclide contaminants can be released from repository and then sorbed onto the waste container corrosion products or the Fe-rich minerals. Herein, we characterized the Fe(III)-saturated montmorillonite (Fe(III)-MMT) by using Fourier transform infrared spectroscopy (FT-IR), X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and Brunauer-Emmett-Teller (BET), and found the changes of the surface incorporating Fe(III) and surface micropores. The sorption of U(VI) on Fe(III)-MMT and Na-montmorillonite (Na-MMT) was investigated by batch experiments. The larger surface area and cation exchange capacity, and the existence of Fe(III) (hydr)oxide phases in Fe(III)-MMT contributed greatly to its sorption capacity. In the whole pH range, the sorption of U(VI) on Fe(III)-MMT was higher than on Na-MMT, and the sorption was strongly depended on pH and ionic strength. The sorption isotherms were simulated well by the Langmuir and Freundlich models. The thermodynamic parameters ( ΔH, ΔS and ΔG) calculated from the temperature dependent sorption isotherms indicated that the sorption of U(VI) on Fe(III)-MMT was an endothermic and spontaneous process. The observations suggest that the interactions between U(VI) and Fe(III)-MMT are important in controlling U(VI) retention. The phenomena need to be considered in risk assessment and reactive transport modeling. [ABSTRACT FROM AUTHOR]

The effect of soluble silicate on the sorption of U(VI) to γ -Al 2 O 3 was investigated by batch experiments and extended X-ray absorption fine structure (EXAFS) method. The presence of silicate enhanced the sorption of U(VI) on γ -Al 2 O 3 surface and the sorption was attributed to inner-sphere surface complexation. The structure of the adsorbed U(VI) and silicate on γ -Al 2 O 3 was investigated in the analysis of EXAFS spectra. The fitting of the experimental EXAFS data was obtained by including two uranium coordination shells with 2 axial (O ax ) and 5 equatorial (O eq ) oxygen atoms at 1 . 79 ± 0 . 02 and 2 . 43 ± 0 . 02 Å, respectively, and the third coordination shells with Al atom at ∼3.35 Å. Silicate contributed to the formation of ternary inner-sphere surface complexes, acting as “bridge” between U(VI) and γ -Al 2 O 3 and enhanced the sorption of U(VI). The observations suggested that the interactions between U(VI) and silicate were important in controlling U(VI) retention. [ABSTRACT FROM AUTHOR]

[Display omitted] • Piezocatalysis extraction of U(VI) was first achieved using minerals. • The energy band cyclically matching is proved theoretically. • Charge transfer at the interface of Ca(Al 2 Si 2 O 8)/Fe 2 O 3 is enhanced. • Piezocatalysis efficiency achives 96%. • The heterojunction show great potential in U(VI) extraction from seawater. Energy and environmental issues make the generation of H 2 O 2 and the separation of U(VI) from water very important topics. In this work, we disclosed a low-cost, high-efficiency method for separating U(VI) from water based on the naturally formed catalyst (red volcanic stone powders, RVSP) of Ca(Al 2 Si 2 O 8)/Fe 2 O 3 heterojunction through a piezocatalytic pathway induced by ultrasonication. The charges were found to be elevatedly separated due to the formation of the heterojunction. It is found that under ultrasonication, charges were effectively separated and then reacted with water to form H 2 O 2 with a high yield of 196.7 μmol·g −1 in 4 h , which further solidifies U(VI) to form a solid of UO 2 O 2. The removal rate of U(VI) in water reached 96 % (50 ppm) within 150 min. Furthermore, the results calculated by VASP show that the cyclic variation of the conduction bands under a cyclic force field facilitates the charge separation, and thus may promote piezocatalysis. Most importantly, the application study in real seawater indicates that U(VI) piezocatalysis based on natural minerals has great potential. This work presents a comprehensive investigation of U(VI) piezocatalysis by Ca(Al 2 Si 2 O 8)/Fe 2 O 3 and provides a new idea for piezocatalytic extraction of uranium. [ABSTRACT FROM AUTHOR]

• Tribocatalysis elimination of uranium was first achieved. • Attapulgite is used as tribocatalysis. • Tribocatalysis efficiency achieves 87.88 %. • Uranium extraction from seawater without secondary pollution has been adopted. Due to most of the U(VI) extraction methods suffering the issues of high cost and low efficiency, finding a new method is still urgent. In this work, we report a way to remove U(VI) from water by tribocatalysis, where a natural mineral of attapulgite is used as the tribocatalyst. By a careful investigation, it is confirmed that the ultrasonic-generated microbubbles rub with the attapulgite to form free radicals of h+, ·O 2 -, and ·OH, which could then be transformed to H 2 O 2 to react with U(VI) to form UO 2 O 2. The extraction rate of U(VI) from water is up to 87.88% (50 ppm) in 200 min. This work using the natural mineral attapulgite being tribocatalyst has the advantages of low cost and high efficiency, which also provide new insight into the conversion of U(VI) in natural conditions and will have great potential in the treatment of nuclide wastewater and seawater. [Display omitted] [ABSTRACT FROM AUTHOR]

• A green and economical MgO/biochar material was synthesized. • Adsorption process accords to pseudo-second-order rate model and the Langmuir model. • The complexation between the surface hydroxyl groups and U(VI) contributes to U(VI) adsorption. A magnesium oxide/biochar (MgO/biochar) composite, which was green and economical compared with numerous materials, was synthesized by a facile method. And MgO/biochar performed excellent adsorption ability in the sequestration of U(VI) with the satisfied maximum adsorption capacity (514.72 mg g−1) at pH = 4.0, m/V = 0.2 g L−1, C U(VI)initial = 10 mg L−1, I = 0.01 M NaNO 3 , T = 298 K. The morphology, spectroscopic properties, chemical composition, etc. of MgO/biochar were characterized systemically by scanning electron microscopy (SEM), powder X-ray diffraction (XRD), Fourier transform infrared (FTIR). The batch experiments showed that the adsorption process was predominated by pseudo-second-order rate model and the adsorption isotherm conformed to the Langmuir model. The prepared MgO/biochar exhibited commendable U(VI) adsorption performance in a wide pH range. X-ray photoelectron spectroscopy (XPS) analysis suggested that the interactions between U(VI) and the hydroxyl groups on the surface of the MgO/biochar contribute greatly to the efficient adsorption process. This work underlines new opportunities in combining the advantages of MgO and biochar, and further broadens new horizons of separating pollutants from the aquatic environment by an environment-friendly materials. [ABSTRACT FROM AUTHOR]

U(VI) adsorption on hematite nanocrystals enclosed with {001} and {012} facets. • The hematite {012} facet is more reactive than {001} facet toward U(VI) adsorption. • The facet reactivity difference originates from surficial site type and density. • Different coordination geometries of U(VI) complex formed on two hematite facets. • The experimental, spectroscopic and theoretical methods are combined. • The study helps to better understand U(VI) behavior and fate in aquatic environments. Predicting the environmental behavior of U(VI) relies on identification of its local coordination structure on mineral surfaces, which is also an indication of the intrinsic reactivity of the facet. We investigated the adsorption of U(VI) on two facets ({001} and {012}) of hematite (α-Fe 2 O 3) by coupling experimental, spectroscopic and theoretical studies. Batch experiments results indicate higher removal capacity of the hematite {012} facet for U(VI) with respect to the {001} facet, due to the existence of extra singly and triply coordinated oxygen atoms with higher reactivity on the {012} facet while only doubly coordinated oxygen atoms exist on the {001} facet. The formation of surface complexes containing U(VI) is responsible for the appearance of a new sextuplet by Mössbauer spectra. The local structures of an inner-sphere edge-sharing bidentate complex on the hematite {001} and a corner-sharing complex on the {012} facet was deciphered by extended X-ray absorption fine structure spectroscopy. The chemical plausibility of the proposed structures was further verified by density functional theory calculation. This finding reveals the important influence of surficial hydroxyl groups reactivity on ions adsorption, which is helpful to better understand the interfacial interactions and to improve the prediction accuracy of U(VI) fate in aquatic environments. [ABSTRACT FROM AUTHOR]

Uranium is not merely a momentous resource for nuclear energy, but also a highly toxic pollutant which has aroused global attention. The efficient handling of uranium from contaminated water is urgent. Herein, to acquire the improved performance of MOFs for U(VI) capture, a 2D/3D hybrid NH 2 -UiO-66/g-C 3 N 4 (NU6CN) adsorbent was designed and fabricated through one-step hydrothermal approach. With the newly synthesized efficient NU6CN composite, the U(VI) loading amount could reach 195.55 mg·g−1, which significantly outperformed that of the individual NH 2 -UiO-66 (134.09 mg·g−1) and g-C 3 N 4 (53.69 mg·g−1) at pH 5.0 and 298 K. The adsorption process conformed to the Langmuir and pseudo-second-order model. Subsequently, based on this system, the underlying interaction mechanism between U(VI) and NU6CN was carefully investigated. The formation of an inner-sphere complex on NU6CN surface was determined by the macroscopic and microscopic data. In the light of XPS analysis, the adsorption of U(VI) on NU6CN was attributable to the synergism of the ample nitrogen- and oxygen-bearing functional groups (e.g., N C N, O C O, C O) derived from g-C 3 N 4 and NH 2 -UiO-66. Additionally, NU6CN revealed good recoverability and recyclability by adsorption/desorption test. These findings presented herein demonstrated the remarkable potential of as-prepared adsorbents for the uranium-contaminated water remediation. [ABSTRACT FROM AUTHOR]

• 2D MOFs nano-sheets were successfully prepared in a one-step and cost-effective synthetic route. • The solvent ratios have a great effect on their structural morphologies. • The Qmax of 2D MOFs nano-sheets can be as high as 591.79 mg g−1 for U(VI) immobilization. • The U(VI) immobilization process is exothermic and spontaneous. • The U(VI) immobilization mechanism is proposed via the binding interactions between U(VI) and −OH/C–N(H) groups. In this study, a new kind of thin 2D MOFs nano-sheets (MNS) was successfully prepared through complexation between 2-methylimidazole and Cu(II) by a one-step, and cost-effective route. The structural morphologies can be tuned by adjusting the ratio of MeOH/H 2 O. The synthesized MNS (MNS-1, MNS-2, MNS-3 and MNS-4) were fully characterized and the results indicated that the synthesized MNS were freestanding and possess micro-sized lateral dimensions and nanoscale thickness of sub-25 nm. All the obtained MNS display great performance with the adsorption capacity hierarchy of MNS-2 (591.79 mg·g-1) > MNS-3 (409.49 mg·g−1) > MNS-4 (387.07 mg·g−1) > MNS-1 (384.84 mg·g−1) at pH ˜ 6.0, and 298 K. The thermodynamic parameters indicated the exothermic and spontaneous nature of U(VI) immobilization. The U(VI) immobilization mechanism was achieved through the complexation between U(VI) and C–N(H) /−OH groups. This work supplies a facile and purposeful approach for developing 2D MOFs nano-sheets toward a highly efficient immobilization of U(VI), and it also promotes the preparation of structure-based design of nanomaterials for radionuclide-containing-medium pretreatment. [ABSTRACT FROM AUTHOR]

In this work, magnetic porous nitrogen doped carbon structures containing well-dispersed active Fe nanocrystals (Fe/N-C) are fabricated conveniently via Fe 3+ -mediated polymerization of dopamine as precursor combined with in situ post carbonization process, thus allowing the entire encapsulation of active Fe nanocrystals in the interior. The obtained functional hybrid materials at 700 °C (Fe/N-C-700) show spherical structure, high proportion of metallic Fe nanocrystals, ultrahigh surface area, and easy magnetic separation property, affording excellent U(VI) removal capability (232.54 mg·g −1 ), surpassing the Fe/N-C samples pyrolyzed at different temperatures and nano zero-valent iron. During the adsorption process, effects of water chemistries ( i.e. , reaction time, pH, carbonates concentration and temperature) on U(VI) adsorption on Fe/N-C-700 are full explored, and the well-dispersed Fe nanocrystals play important role in reducing into U(IV). Meanwhile, nitrogen dopant could make function well in the electrostatic interaction and partial reduction of U(VI). The present study demonstrates that Fe/N-C-700 nanospheres derived from Fe-PDA have potential application for the preconcentration and immobilization of U(VI). [ABSTRACT FROM AUTHOR]

A novel magnesium silicate/diatomite sorbent (MSD) was fabricated using a facile hydrothermal method. The interaction mechanism of U(VI) on MSD was investigated by batch, spectroscopic and modeling techniques. The maximum adsorption capacity of MSD for U(VI) (31.54 mg/g) is significantly higher than that of diatomite (12.74 mg/g). XPS analysis indicated that the oxygen-containing groups (e.g., Si OH) of MSD were responsible for the high efficient removal of U(VI) from aqueous solutions. The fitted results of surface complexation modeling showed that the adsorption of U(VI) on MSD at pH < 4.0 and pH > 4.5 was attributed to cation exchange and inner-sphere surface complexation, respectively. These findings suggested that MSD could be a favorable sorbent for the efficient removal of U(VI) in the environmental cleanup. [ABSTRACT FROM AUTHOR]

Novel hierarchical core/shell structured polydopamine@MgAl-layered double hydroxides (PDA@MgAl-LDHs) composites involving MgAl-layered double hydroxide shells and PDA cores were fabricated thought one-pot coprecipitation assembly and methodically characterized by X-ray diffraction, Fourier transformed infrared spectroscopy, scanning/transmission electron microscopy, selected area electron diffraction, elemental mapping, thermogravimetric analysis and X-ray photoelectron spectroscopy technologies. U(VI) and Eu(III) sorption experiments showed that the PDA@MgAl-LDHs exhibited higher sorption ability with a maximum sorption capacity of 142.86 and 76.02 mg/g at 298 K and pH 4.5, respectively. More importantly, according to XPS analyses, U(VI) and Eu(III) were sorbed on PDA@MgAl-LDHs via oxygen-containing functional groups, and the chemical affinity of U(VI) by oxygen-containing functional groups is higher than that of Eu(III). These observations show great expectations in the enrichment of radionuclides from aquatic environments by PDA@MgAl-LDHs. [ABSTRACT FROM AUTHOR]

In this work, a highly efficient uranium extraction method from water by the piezo catalytic reduction-oxidation process is reported by utilizing a hollow cubic shaped Zn 2 SnO 4 /SnO 2 as piezo catalyst. The electrons and holes in Zn 2 SnO 4 /SnO 2 are separated efficiently under the irradiation of ultrasound. After that, some of the piezo electrons reduce the adsorbed U(VI) to UO 2 , the others react with soluble oxygen to form H 2 O 2 , and oxidize UO 2 to generate (UO 2)O 2 ∙2H 2 O, which could be efficiently separated from the solution. U(VI) piezo catalytic extraction rate could reach ~ 90% under the irradiation of ultrasonic waves (40 kHz, 120 W) within 5 h and only decreased by ~ 3% after four cycles. The present work advances piezo catalysis as a new route for uranium extraction from water, which may be applied in the extraction or removal of U(VI) in the U-containing wastewaters, providing new opportunities for resource-saving and environmental enhancement. [Display omitted] • U(VI) was extracted by piezo catalytic method efficiently for the first time. • The extraction product was confirmed to be (UO 2)O 2 ∙2H 2 O for easy extraction. • The U(VI) was firstly reduced to U(IV), then oxidized by H 2 O 2. [ABSTRACT FROM AUTHOR]

Highlights: [•] Water-soluble polyacrylamide coated-Fe3O4 magnetic composites were synthesized successfully. [•] PAM@Fe3O4 showed high efficient enrichment of U(VI) from wastewater. [•] The Q max of U(VI) on PAM@Fe3O4 reached 220.9mg/g. [•] Amide groups on the surface of PAM@Fe3O4 facilitated U(VI) sorption. [•] The used PAM@Fe3O4 could be effectually regenerated. [ABSTRACT FROM AUTHOR]

Abstract: In this study, the sorption and desorption of U(VI) from contaminated groundwater by nanoporous and non-nanoporous alumina were investigated under ambient conditions. The nanoporous and non-nanoporous alumina were characterized by XRD, specific surface area analysis, TEM and potentiometric acid–base titration. The nanoporous alumina exhibited high sorption capacity, large specific surface area, high surface acidity constants, low difference of surface acidity constants and high pHPNZC (point of net zero charge) due to the nanoporous effect. The worm-like shape nanoporous alumina was transferred into the floc-like shape gibbsite after the sorption in terms of TEM images. Sorption kinetics and sorption isotherms of U(VI) on both nanoporous and non-nanoporous alumina can be interpreted by pseudo-second order kinetic model and the Langmuir model, respectively. The sorption of U(VI) on nanoporous alumina is strongly dependent on pH and independent of ionic strength, whereas U(VI) sorption on non-nanoporous alumina is dependent on pH and ionic strength. The sorption mechanism is assumed to be mainly inner-sphere surface complexation for nanoporous alumina and outer-sphere surface complexation for non-nanoporous alumina. Approximately 100% of U(VI) was desorbed from non-nanoporous alumina while only ∼5% of U(VI) was extracted from nanoporous alumina when the concentration of NaHCO3 was increased to 0.01M in terms of sequential desorption experiments. The nanoporous alumina can be used as an efficient material for in situ immobilization of U(VI) from contaminated groundwater. [Copyright &y& Elsevier]

[Display omitted] • An available and facile way for the magnetic MOF-NH 2 was reported. • The adsorption efficiency of the magnetic MOFs towards U(VI) was improved dramatically. • The interactional mechanism between the tuned amine groups and U(VI) was revealed. A magnetic metal organic framework was finely tuned by abundant amine groups (Mag MOF-NH 2) for the purpose of improving the U(VI) removal from solution. The Mag MOF-NH 2 displays outstanding removal capacity (80 mg⋅g−1) to U(VI) (10 ppm, 400 mL) within 15 min. To illuminate the adsorption mechanism of Mag MOF-NH 2 , the microstructure, the magnetic property, chemical composition of Mag MOF-NH 2 and the reaction system were characterized. The adsorption mechanism was systematically investigated. Equilibrium adsorption experiments verifies the improved adsorption capability from nearly 0 for MIL-101 to 82 mg⋅g−1 for Mag MOF-NH 2 , which could be explained mainly by the interaction between the amine groups and targeted ions. The effect of humic acid (HA) and coexisting ions on the U(VI) adsorption were also investigated. The Ca2+ and Mg2+ ions have passive impact on the adsorption and the high pH value can facilitate the process. Mag MOF-NH 2 holds great potential for the practical application owing to the outstanding U(VI) removal and satisfied regeneration in simulative wastewaters. [ABSTRACT FROM AUTHOR]

• U(VI) is photoreduced to a stable α-U 3 O 8 under visible light irradiation. • U(VI) can be photoreduced ithout adding radical sacrificial agents. • The photoreduction of U(VI) is a photocorrosion-related process. • The photoreduction can only be done in SCC. • The photoholes oxidize S2− to S0 and the photoelectrons transfer to SnO 2 to reduce U(VI). Reducing soluble U(VI) to insoluble U(IV) is an ideal strategy to collect/remove uranium in water. In this work, a new way is reported to achieve this reduction through a photocorrosion-related photocatalysis process of SnO 2 /CdCO 3 /CdS (SCC) under visible light irradiation. The mechanism is systematically studied and discussed through a variety of characterization methods, such as X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), Mott-Schottky test, etc. The matching of energy band ensures the separation of photoelectrons and holes, which results in the decrease of charges' recombination rate and the enhancement of photoreduction activity. The reduction process can be efficiently performed in the ternary complex of SCC in that the photo-generated holes are consumed by oxidization of S2− to S0 on CdS in SCC. Furthermore, uranium extraction could be achieved by SCC without any protective gases or electronic sacrificial agent, which shows great advantages in applications of U(VI) collection/removal. [ABSTRACT FROM AUTHOR]

• 3D flower-like phos-LDH was synthesized by one pot hydrothermal technique. • phos-LDH showed ultrafast and ultrahigh adsorption performance toward to U(VI). • The U(VI) adsorption on phos-LDH was dominated by electrostatic attraction and inner-sphere surface complexation. • The phos-LDH is a low-cost and promising material for urgent radionuclides' pollution remediation. Elimination of U(VI) from polluted solutions is important for human health and environmental safety. In this work, a relatively low-cost 3D flower-like phosphate-functionalized layered double hydroxides (phos-LDH) was fabricated by a one-pot hydrothermal method. The prepared phos-LDH inherited the structure of 3D flower-like layered double hydroxides (LDH), and had a higher specific surface area (∼203.4 m2⋅g−1) than that of LDH. The kinetic process indicated that U(VI) adsorption onto phos-LDH achieved equilibrium within 15 min and obeyed general order model. The adsorption isotherms of phos-LDH illustrated that the U(VI) adsorption obeyed Langmuir model, the adsorption capability of phos-LDH can reach 923.1 mg⋅g−1 at 298 K. The U(VI) adsorption was a spontaneous and endothermic process according to the thermodynamic data. There was the electrostatic attraction between U(VI) and phos-LDH at pH = 5.0. FTIR and XPS analyses educed that the hydroxyl and phosphate groups played a very useful role for the complexation between U(VI) and phos-LDH. In addition, the excellent selective adsorption capability for U(VI) in competitive cation and anion solutions further confirmed the practical application of phos-LDH in real wastewater treatment. [ABSTRACT FROM AUTHOR]

Moso bamboo biochar modified with polyethyleneimine can be used for the efficient enrichment of U(VI) in aqueous solution. • PEI-alkali/acid-biochar was prepared for the removal of U(VI) in aqueous solution. • The adsorption capacity of PEI-alkali/acid-biochar for U(VI) is 9–10 times higher than that of pristine biochar. • The complexation between U(VI) and amine groups contributes to U(VI) adsorption. This study investigated the modification of moso bamboo biochar with polyethyleneimine (PEI) for the efficient enrichment of U(VI) in aqueous solution. The alkali/acid treated biochars with amine groups (PEI-alkali-biochar or PEI-acid-biochar) were characterized by SEM, BET, TGA, FTIR and XPS. The effects of contact time, U(VI) concentration, pH and ionic strength on U(VI) adsorption by PEI-alkali/acid-biochar were studied. U(VI) adsorption process on PEI-alkali/acid-biochar obeys pseudo-second-order model. Intraparticle diffusion model was used to investigate the controlled factors of the adsorption process. The fitting of Langmuir model gives the maximum adsorption capacities of 212.7 mg/g for PEI-alkali-biochar and 185.6 mg/g for PEI-acid-biochar, which are almost 9–10 times higher than that of pristine biochar (20.1 mg/g). The thermodynamic parameters illustrate that U(VI) adsorption on PEI-alkali/acid-biochar is an exothermic and spontaneous process. The FTIR and XPS analyses imply that U(VI) adsorption by PEI-alkali/acid-biochar is mainly controlled by complexation between U(VI) and amine groups. PEI-alkali/acid-biochar could be considered as a low-cost and outstanding material for U(VI) removal from radionuclide wastewater in practical application. [ABSTRACT FROM AUTHOR]

In natural environments, the sequestration or release of U(VI) is usually affected by the coexistence of natural organic matters (NOM). Former works mainly concentrated on the design of novel adsorbents for the preconcentration of U(VI), while there is a knowledge gap between the coupled adsorption process in the mixed U(VI)-advanced materials-NOM system. Herein, the incorporation of multi-walled carbon nanotubes into zeolitic imidazolate framework-8 (denoted as MWCNTs/ZIF-8) was achieved and applied to sequester U(VI) and humic acids (HA) simultaneously from aquatic environments. The mutual effects of simultaneous U(VI) and HA adsorption affected by various water chemistry and the U(VI)/HA addition sequences were studied systematically. The saturated adsorption amounts were 200.77 and 55.68 mg/g for U(VI) and HA at pH 5.0, respectively, which are higher than most traditional adsorbents. U(VI) adsorption onto MWCNTs/ZIF-8 was pH-dependent but independent on ionic strength, revealing that the coordination between Zn atoms and U(VI) ions was the main reason for U(VI) sequestration, which was further evidenced by the X-ray photoelectron spectroscopy. U(VI) adsorption was improved significantly with the coexistence of HA owing to the appearance of HA-U(VI)-MWCNTs/ZIF-8 ternary complexes, but was independent on the addition sequences, disclosing that U(VI) ions preferred to bind directly onto MWCNTs/ZIF-8 instead of via HA. The addition sequence exerted an obvious effect on HA adsorption due to the different adsorption scenario. These findings are essential to predict U(VI) behaviors in geological environments. Both mechanistic and quantitative understanding on the mutual effects of U(VI) and humic acid in the binary U(VI)/humic acids-MWCNTs/ZIF-8 system and ternary U(VI)-humic acids-MWCNTs/ZIF-8 system was studied. Unlabelled Image • Hierarchical MWCNTs/ZIF-8 composites were prepared via precise stepwise control. • MWCNTs/ZIF-8 showed high adsorption properties for both U(VI) and HA in the binary systems. • U(VI) and HA adsorption in the coexisting ternary system was of mutual promotion. • U(VI) adsorption rate by MWCNTs/ZIF-8 was independent on the addition sequences. • The addition sequence exerted an obvious effect on HA adsorption onto MWCNTs/ZIF-8. [ABSTRACT FROM AUTHOR]