Formation Of Surface Complexes Research Articles

Effects of Cations/Anions in Recycled Tailing Water on Cationic Reverse Flotation of Iron Oxides

It is well known that reverse flotation performance of iron oxides is affected by water quality. Since many potential variations among water sources recycling in a mineral processing plant bring unpredictable effects on the flotation system of iron oxides: disturbing ions/compounds, pH, hardness, residual reagents, etc. In this study, the recycled tailing water from a local plant, characteristically constituting of Ca2+, Mg2+, Na+, K+, Al3+, Fe3+, Cl−, SO42− etc., was introduced into the cationic reverse flotation process of an iron ore. A series of bench flotation tests using iron ores, micro-flotation tests using pure fine quartz, water chemical analyses, and zeta potential measurement were conducted with the objective of identifying the possible influences of both cations and anions in the recycled tailing water on the flotation performance. The flotation results pointed out that the cation with higher valency had more severe influences on the recovery of iron oxides. The formation of the pH-dependent surface complexes on mineral surfaces, for example, Fe(OH)+, Fe(OH)2+, and Fe(OH)3 resulted from Fe3+ ions adsorption, contributed to the less negative zeta potentials of the quartz, and consequently weakened its interaction with the amine collector. It is worthy to note that SO42− ions seem to have a more positive effect on the recovery of iron oxides than Cl− ions. This is probably attributed to the formation of inner/outer- sphere surface complexes on the iron oxides, inhibiting the dissolution of the iron ions/species, and the coordination with these cations from the recycled tailing water, shielding their disturbances in the flotation.

Fabrication of carboxyl and amino functionalized carbonaceous microspheres and their enhanced adsorption behaviors of U(VI)

Design and fabrication of materials with abundant functional groups represent an important and promising direction in the remediation of aqueous contaminants. In recent years, carbon-based materials have drawn widespread concern on account of their low cost, large specific surface area, good chemical stability as well as controllable porosity. The U(VI) binding onto raw carbon-based materials is still confronted with the problem of limited adsorption capacity, which severely hinders the practical applications of materials. Herein, amino- and carboxyl-functionalized carbonaceous spheres (denoted as ACSs and CCSs) were fabricated by in-situ polymerization and simply annealing methods, respectively. The highest adsorption amounts of ACSs and CCSs towards U(VI) were calculated to be 73.83 and 401.61 mg·g−1 from Langmuir model at pH = 4.0 and 298 K, which were higher to that of raw carbonaceous material (19.31 mg·g−1). Interestingly, the Freundlich model could well simulate U(VI) sorption isotherms on ACSs at these temperatures (T = 298, 313 and 328 K), while U(VI) sorption isotherms on CCSs were able to significantly conform to the Langmuir model. According to FT-IR and XPS analysis, U(VI) was enriched on both materials on account of the ample functional groups on ACSs (e.g. CNOH/CNH2) and CCSs (e.g. OH/COOH). In addition, effect of ionic strength manifested that U(VI) elimination on ACSs and CCSs were greatly caused by the formation of outer-sphere and inner-sphere surface complexes, respectively. This work promises to provide two facile approaches for engineering diverse functionalized materials towards a highly rapid and efficient sequestering U(VI) from contaminated water.

Fabrication of porous carbon and application of Eu(III) removal from aqueous solutions

An efficient and easy-made material for elimination of radioactive pollution from environment is highly desirable while remains challenging. Herein, porous carbon material (PC) was fabricated by hydrothermal carbonization method for radionuclide adsorption. The characterization revealed that PC had a large amount of micropores with an average size of 100–200 nm. The adsorption mechanism of Eu(III) on PC were explored by batch and spectroscopic techniques. Batch experiments showed that Eu(III) adsorption onto PC was independent of ionic strength, indicating the formation of inner-sphere surface complexes. The maximum adsorption capacity of PC calculated from Langmuir model were 28.6 mg·g−1 for Eu(III) at pH 6.0. FT-IR and XPS analysis revealed that the interaction of Eu(III) onto PC was mainly ascribed to the surface complexation and/or electrostatic interaction of Eu(III) and hydroxyl groups. This work indicated that PC can be regarded as a promising adsorbent for rapid and efficient sequestration of Eu(III) from aqueous solution.

Goethite catalyzed Cr(VI) reduction by tartaric acid via surface adsorption

The surface catalysis of goethite on the Cr(VI) reduction by tartaric acid was examined together with its adsorption characteristics towards the two reactants. The results showed the adsorption of tartaric acid by goethite was favorable at low pH and adsorption isotherm could be properly described by Langmuir model. The adsorption kinetic curves for both reactants obeyed the pseudo second-order rate model (R2 >0.99). The FTIR spectrum suggested the formation of bidentate binuclear surface complexes between tartaric acid and goethite. At pH 4.50, the reduction percentage of 0.1 mM Cr(VI) by 1.0 mM tartaric acid alone was about 12% after 72 h, while which was increased to 100% in the presence of goethite within 24 h. Kinetic results revealed the Cr(VI) reduction only occurred between the adsorbed tartaric acid and the aqueous Cr(VI) since the Cr(VI) adsorption was completely inhibited under the examined conditions. Meanwhile, the catalysis of aqueous Fe(III) released from the goethite surfaces was excluded due to its low concentration (<5 μM). With the initial concentration of tartaric acid decreased to 0.1 mM, Cr(VI) reduction could be completed within 4 h, confirmed by the XPS result that only Cr(III) species existed on the goethite surfaces. In this case, electron transfer was suggested to occur directly between the two adsorbed reactants or goethite was believed to serve as an ideal channel to allow electron excited from the adsorbed tartaric acid to transfer to the adsorbed Cr(VI). The findings above were helpful for us to understand the Cr(VI) reduction by organic compounds in soils with rich contents of Fe-oxides.

Removal of tetracycline by BiOBr microspheres with oxygen vacancies: Combination of adsorption and photocatalysis

Oxygen vacancy-containing BiOBr microspheres with dual functions of adsorption-photocatalysis were synthesized by a simple solvothermal method. The as-prepared samples were characterized by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS), electron paramagnetic resonance spectroscopy (EPR) and UV–vis diffuse reflectance spectroscopy (DRS). BiOBr microspheres with oxygen vacancies exhibited a higher adsorptive and photocatalytic activity for the removal of tetracycline (TC) than that of defect-deficient BiOBr microspheres. After adsorption for 30 min and visible light irradiation for 90 min, about 94% of TC was removed by oxygen vacancy-containing BiOBr microspheres, and TC removal efficiency performed effectively in a wide pH range from 3.1 to 11.00. Almost all inorganic anions, such as Cl−, SO2− 4, PO3− 4, CO2− 3and NO− 3, inhibited the removal of TC by BiOBr microspheres and their inhibition effects followed the order of PO3− 4 > SO2− 4 > CO2− 3 > Cl−>NO− 3. The surface hydroxyl groups had no effect on TC adsorption, and the adsorption of TC on BiOBr was mainly through the anion exchange process. The existence of oxygen vacancies facilitated the generation of superoxide radicals (O2−•), which were the dominant reactive oxygen species for TC degradation in BiOBr suspension. The adsorptive and photocatalytic performance of oxygen vacancy-containing BiOBr decreased to different degrees after three cycles mainly due to the formation of surface complex.

Preconcentration of Uranium(VI) from Aqueous Solution by Amidoxime‐Functionalized Microspheres Silica Material: Kinetics, Isotherm and Mechanism Study

AbstractIn present study, amidoxime‐functionalized MCM‐41 microspheres silica materials (denoted as MCM‐41‐AO) were synthesized and applied to enrich uranium from aqueous mediums. The adsorbents were characterized in detail by SEM, TEM, EDS, FT‐IR, elemental analysis and the zero point of change (pHzpc) test. The effects of the pH, ionic strength, contact time, coexisting cations and temperature on the adsorption properties of U(VI) were investigated. The highest sorption capacity of U(VI) on MCM‐41‐AO was evaluated to be 384.59 mg⋅g−1 by Langmuir isotherms model at pH=5.00 ± 0.05 and T=298 ± 2 K. The adsorption thermodynamics and thermodynamic studies suggest that the U(VI) adsorbed on the amidoxime functionalized microspheres silicas is a chemisorption, spontaneous and endothermic process. In addition, the adsorption mechanism for U(VI) on MCM‐41‐AO also has been explored by the XPS and FT‐IR. The results manifest that the effective adsorption U(VI) is mainly ascribed to the steady formation of surface complexes between uranium ions and the amidoxime ligands.

Selective Adsorption of Aspartate Facilitated by Calcium on Brucite [Mg(OH)2

Dissolved ions present in an aqueous environment may significantly improve biomolecule attachment at mineral surfaces through the formation of cooperative surface complexes. To test whether this phenomenon results in the selective adsorption of an organic species, we conducted batch adsorption experiments with an equimolar mixture of the amino acids aspartate, glycine, lysine, leucine, and phenylalanine onto powdered brucite [Mg(OH)2] at pH 10.2. We performed the batch experiments in triplicate both without and with 4.1 mM CaCl2. In experiments without CaCl2, we observed that up to 0.7 μmol m–2 of aspartate and about 0.4 μmol m–2 each of the remaining four amino acids adsorbed onto brucite. When we added CaCl2, we found that up to 1.6 μmol m–2 of aspartate selectively adsorbed onto the brucite surface relative to between 0.2 and 0.3 μmol m–2 of the other amino acids. We measured the brucite particle surface charge to be slightly positive without added CaCl2, but the surface charge becomes significantly mo...

Adsorption characteristics of ammonium ion onto hydrous biochars in dilute aqueous solutions

This research aims at studying the characteristics of ammonium adsorption onto hydrous bamboo biochar. Results showed that pH played the most important role in ammonium adsorption. High ionic strength enhanced the ammonium adsorption capacity of bamboo biochar. Ammonium adsorption was exothermic and spontaneous. FTIR results showed shift, disappearance, or appearance of specific functional groups on the bamboo biochar surface. Surface precipitation and complex formation contributed to the adsorption of ammonium onto hydrous bamboo biochar. Biochar can be an effective adsorbate for ammonium removal from water. Additionally, the formation of nitrogen containing precipitates on the biochar surface, potentially, leads to the in-situ synthesis of slow-release fertilizer.

Mechanism of Goethite Precipitation on Magnetite and Maghemite Nanoparticles Studied by Surface Complexation/Precipitation Modeling

Precipitation of goethite on magnetic nanoparticles (MNPs) has been proposed as an effective means to separate goethite from calcium sulfate in the iron removal process of zinc hydrometallurgy, which allows reuse of the hazardous residues. This study focuses on investigating the underlying mechanisms of goethite precipitation on magnetite and maghemite MNPs, providing insights on Fe(III)aq adsorption and nucleation of goethite on MNPs. A predictive surface complexation/precipitation model of the system was developed based on the results from two different types of experiments: the potentiometric titration of MNPs to calculate proton binding constants ( Ka) of discrete MNP surface functional groups and the corresponding site concentrations; and adsorption of Fe(III)aq onto MNP surfaces to determine metal binding constants ( Kf). The composition of the surface complexes on MNPs was determined by time-of-flight secondary ion mass spectrometry. The results indicated the formation of polynuclear surface complexes. The content of polynuclear surface complexes was found to be significantly higher on maghemite MNPs than on magnetite MNPs. This trend is consistent with our experimental results of a greater goethite precipitation on maghemite than on magnetite. Overall, the formation of Fe(III) polynuclear surface complexes correlates directly to the nucleation and precipitation of goethite on the surfaces of both types of MNPs.

Enhanced removal of arsenite and arsenate by a multifunctional Fe-Ti-Mn composite oxide: Photooxidation, oxidation and adsorption

In order to attain a high-efficiency and low-cost adsorbent for both arsenate (As(V)) and arsenite (As(III)) removal from As-contaminated water, a novel nanostructured Fe-Ti-Mn composite oxide (FTMO) was fabricated through a one-step simultaneous oxidation and co-precipitation method. Batch control experiments and series of spectroscopy detection technologies were carried out to investigate the surface change of the FTMO adsorbent and the respective role of Fe, Ti and Mn content in the arsenic adsorption process. The results showed that the FTMO adsorbent had a high adsorption capacity for both As(V) and As(III) (especially for the latter one) via the formation of inner-sphere complexes at the water/oxide interface under both darkness and light conditions. The material could effectively oxidize As(III) to As(V) and light illumination could further apparently enhance the As(III) oxidation, thus achieving high adsorption efficiency of As(III). Combined with the characterizations from FTIR, ESR and XPS, it was assumed that the predominant As(III) removal mechanism could be attributed to the coupling of various processes including photooxidation, oxidation and adsorption. The Ti and Mn contents were dominant for the As(III) oxidation, while the Fe content mainly played an important role for the adsorption of newly formed As(V). However, the involvement of surface hydroxyl groups and the formation of inner-sphere surface complexes were primarily responsible for the As(V) adsorption mechanism. Moreover, the successful removal of arsenic from real water matrices made the FTMO a potentially attractive adsorbent for both As(V) and As(III) removal.

Sorption behavior of copper, lead and zinc by a constructed wetland treating urban stormwater

Sorption behaviors of copper (Cu), lead (Pb) and zinc (Zn) in a stormwater constructed wetland (CW) have been investigated by combining CW sample analysis and batch sorption experiments. The mass balance calculations suggest retention/remobilization along the CW sequence for Zn, unlike Pb and Cu. According to the mixed Tessier-BCR sequential extractions results, Pb and Zn are both mainly associated to residual fractions (incorporated in the lattice or at surfaces of primary clays, or in heavy minerals) and to Fe/Mn oxihydroxyde fractions, whereas Cu is possibly associated to carbonates minerals in the CW. In CW field conditions (metals at trace concentrations and pH lower than 7.5), batch experiment results suggest that the global affinity of the CW substrate for metals attends the following order: Pb=Cu > Zn. Pb and Cu form surface complexes on high and weak affinity sites of the substrate, as hydroxyl groups of iron oxides. Zn is involved in ion exchange and/or compensation of negative charges at the surface of CW substrate (pH < 5). The metals sorption capacities of the substrate reveal that Zn is potentially desorbable from the substrate under the field conditions, on the contrary Cu and Pb removal efficiencies are above 90%.

Kinetics of dissolution of Th0.25U0.75O2 sintered pellets in various acidic conditions

In order to gain insights into the kinetics of dissolution of Gen(IV) MOX fuels, sintered pellets of Th0.25U0.75O2 were prepared as surrogates. The study of the kinetics of dissolution was achieved to determine the impact of the incorporation of 25 mol % of thorium in UO2 on the rate and on the mechanism of dissolution. Especially, various acidic media were used to evidence changes occurring in the rate of the limiting step and to establish specific rate laws. For most of the investigated dissolution media the dissolution reaction was found to be congruent. The homogeneity of the Th0.25U0.75O2 solid/solutions allowed both elements to be recovered at the same rate. The way of synthesis by oxalate co-precipitation, then conversion in mixed oxide, allowed the quantitative dissolution of the elements. In aerated hydrochloric acid solutions, the kinetics of the overall dissolution reaction appeared to be controlled by adsorption and desorption of protons on activated surface sites. The dissolution rate determined in aerated sulfuric acid solution was enhanced compared to hydrochloric acid solution of the same acidity. This result was interpreted in terms of formation of sulfate ions surface complexes that favor the detachment of the actinides from the mixed oxide solid solution. In nitric acid solutions, the dissolution of the Th0.25U0.75O2 pellets followed several successive steps. During this first steady state period, the kinetics of the overall dissolution reaction appeared to be controlled by the oxidation of U(IV) by HNO3 at the solid/solution interface. A rate law was established by adding a redox contribution to the proton-promoted surface contribution defined for aerated hydrochloric acid solutions. Then, an increase of the normalized dissolution rate was observed, which was attributed to the simultaneous increase of the specific surface area of the pellet and of the HNO2 concentration in solution.

Visible-light-driven photocatalytic degradation of 4-CP and the synergistic reduction of Cr(VI) on one-pot synthesized amorphous Nb2O5 nanorods/graphene heterostructured composites

In this study, Nb2O5 nanorods/graphene composites (NbO NRs/GR) are prepared by one-pot alkaline hydrothermal process, utilizing the new roles of graphene oxide (GO) as the structure-directing and morphology-controlling agent for the growth of NbO NRs. Compared to blank NbO, NbO/GR composites exhibit significantly improved photocatalytic activity for 4-CP degradation under visible-light irradiation, although 4-CP and NbO do not absorb visible light themselves. The in-situ formation of surface complexes between 4-CP and NbO and the subsequent charge transfer based on LMCT mechanism can be responsible for the visible photocatalytic activity. And meanwhile, the photoelectrons transferred to GR surface from in-situ formed complex (NbO/4-CP) via NbO NRs can initiate the synergistic Cr(VI) reduction. The GR contents and NbO crystalline phase have great effects on the photocatalytic activity of NbO/GR composites toward simultaneous 4-CP degradation and Cr(VI) reduction. The amorphous NbO/GR composite with 4.0 wt% GR (NbO-400/GR-4.0%) shows the highest photocatalytic activity. The influences of various experimental conditions (including the surface fluorination of NbO/GR, the initial concentrations of 4-CP and Cr(VI), pH, reaction atmosphere, and adding radical scavengers) on the visible photocatalytic activities are investigated in detail. According to the catalytic activity, UV-vis DRS and FT-IR spectra of NbO/4-CP or NbO/GR/4-CP, and photocurrent response in aqueous 4-CP solution, the formation of the surface complex is evidenced and the visible-light catalytic mechanism based on LMCT process is proposed.

Pronounced Antagonism of Zinc and Arsenate on Toxicity to Barley Root Elongation in Soil

Zinc (Zn) and arsenic (As) occur as mixed contaminants in soil and the interactions between them remain unclear. Here, we investigated a Zn2+ and H2AsO4− mixture interaction and their effects on plant growth. Three different soils were spiked with ZnCl2 and NaH2AsO4, each dosed singly or in combination. The soils were leached to remove excessive salt and were aged (&gt;7 days), before toxicity testing using a 5-day root elongation of barley (Hordeum vulgare L.). In the single treatments, the 50% inhibitory effect concentrations in the soil (EC50, total measured concentration) were 2000–3800 mg Zn kg−1 and 96–620 mg As kg−1, depending on the soils. The mixture analyses based on the total concentrations showed overall and significant Zn–As antagonism in two soils, either based on the concentration addition (CA) or independent action (IA) model, whereas no significant interactions (either CA or IA) were found in one soil, which had the lowest content of Fe-oxides. The soil solution composition showed a decreased As concentration upon the addition of ZnCl2 at an equal soil As total concentration; however, the reverse was not found, in line with the cation–anion electrostatic interaction or formation of ternary surface complexes on Fe-oxides. The data revealed that the Zn–As antagonisms (total concentrations) are partially related to the increased Zn immobilizing As in soil.

Np(V) sorption and solubility in high pH calcite systems

Np(V) behaviour in alkaline, calcite containing systems was studied over a range of neptunium concentrations (1.62 × 10−3 μM–1.62 μM) in two synthetic, high pH, cement leachates under a CO2 controlled atmosphere. The cement leachates were representative of conditions expected in an older (pH 10.5, Ca2+) and younger (pH 13.3, Na+, K+, Ca2+) cementitious geological disposal facility. These systems were studied using a combination of batch sorption and solubility experiments, X-ray absorption spectroscopy, and geochemical modelling to describe Np behaviour. Np(V) solubility in calcite equilibrated old and young cement leachates (OCL and YCL) was 9.7 and 0.084 μM, respectively. In the OCL system, this was consistent with a Np(V)O2OH(am) phase controlling solubility. However, this phase did not explain the very low Np(V) solubility observed in the YCL system. This inconsistency was explored further with a range of pH 13.3 solubility experiments with and variable Ca2+(aq) concentrations. These experiments showed that at pH 13.3, Np(V) solubility decreased with increasing Ca2+ concentration confirming that Ca2+ was a critical control on Np solubility in the YCL systems. X-ray absorption near-edge structure spectroscopy on the precipitate from the 42.2 μM Np(V) experiment confirmed that a Np(V) dioxygenyl species was dominant. This was supported by both geochemical and extended X-ray absorption fine structure data, which suggested a calcium containing Np(V) hydroxide phase was controlling solubility. In YCL systems, sorption of Np(V) to calcite was observed across a range of Np concentrations and solid to solution ratios. A combination of both surface complexation and/or precipitation was likely responsible for the observed Np(V) reaction with calcite in these systems. In the OCL sorption experiments, Np(V) sorption to calcite across a range of Np concentrations was dependent on the solid to solution ratio which is consistent with the formation of a mono-nuclear surface complex. All systems demonstrated slow sorption kinetics, with reaction times of weeks needed to reach apparent equilibrium. This could be explained by slow recrystallisation of the calcite surface and/or the presence of Np(V) colloidal species. Overall, these data provide valuable new insights into Np(V) and actinide(V) behaviour in alkaline conditions of relevance to the disposal of intermediate level radioactive wastes.

Water Treatment Residuals as a Resource for the Recovery of Soil and Water Polluted with Sb(V): Sorption and Desorption Trials at Different pH Values

In this study, the ability of two different water treatment residuals (Fe- and Al-WTRs) to accumulate antimony(V) from an aqueous solution was investigated at different pH values (pH 4.5 and 6.5). Both WTRs showed a maximum Sb(V) sorption capacity of approx. 0.22 mmol g−1 at pH 4.5 which declined at pH 6.5, particularly for Fe-WTR (i.e., 0.059 and 0.163 mmol g−1 of Sb(V) sorbed by Fe- and Al-WTRs respectively). The greater capacity of WTRs to accumulate antimonate at pH 4.5 seemed to be linked to their chemical properties, such as the pHPZC and the specific surface area. At both pH values, the Sb(V) sorption by Al- and Fe-WTRs followed a pseudo-second-order kinetic model, while the sorption isotherms data fitted the Freundlich model better than the Langmuir one, suggesting the presence of heterogeneous Sb(V) adsorption sites. The sequential extraction of WTR-Sb(V) systems showed that a significant amount of Sb(V) was retained by WTRs through chemical interactions, i.e., through the formation of inner sphere surface complexes [e.g., Fe/Al–O–Sb(V)]). This was particularly relevant at higher pH values (pH 6.5) where more than 60 and 50% of the Sb(V) sorbed by Fe- and Al-WTRs respectively was retained by specific chemical bonding. The residual Sb(V) was higher for the Al-WTR at both pH values, and the highest amount of residual Sb(V) was recorded at pH 4.5 [> 65% of the total Sb(V) sorbed]. SEM-EDX analysis of the WTR-Sb(V) systems showed that antimony was mainly associated with Fe and Al, thus supporting the Sb(V) affinity for Al/Fe oxy-hydroxides. Treatment of WTR-Sb(V) systems with citric and malic acids, at concentrations relevant in the rhizosphere, indicated that Sb(V) could be released by both acids, with 4.5 mM citric acid favoring the highest Sb(V) release in both WTRs. The results from this study suggest that WTRs could be used as alternative amendments for the in situ immobilization of Sb(V) in acidic or circumneutral polluted soils.

Combining batch technique with theoretical calculation studies to analyze the highly efficient enrichment of U(VI) and Eu(III) on magnetic MnFe2O4 nanocubes

The progress of efficient and low-cost materials for environmental remediation is highly desirable but remains challenging. Herein, we fabricated magnetic bimetal oxide MnFe2O4 nanocubes (NCs) by co-precipitation phase inversion method. Characterization of the as-prepared nanomaterials revealed that MnFe2O4 NCs had an average size of 50–70 nm and possessed unique magnetic properties for adsorbent separation. The adsorption behavior and interaction mechanism of U(VI)/Eu(III) on MnFe2O4 were explored by batch experiment and spectroscopy analysis combined with density functional theory (DFT) calculations. Batch experimental results showed that U(VI)/Eu(III) sorption onto MnFe2O4 were independent of ionic strength, indicating the formation of inner-sphere surface complexes. The maximum sorption capacities of MnFe2O4 calculated from Langmuir isotherm model at 298.15 K were 119.90 mg·g−1 for U(VI) at pH 5.0 and 473.93 mg·g−1 for Eu(III) at pH 7.0, respectively. Furthermore, the excellent regeneration and reusability of MnFe2O4 could support long-term application in wastewater and sewage treatment. The analysis of FT-IR and XPS in combination with DFT calculations revealed that the interaction of U(VI)/Eu(III) onto MnFe2O4 was mainly ascribed to the strong ionic bonds (MO) and hydroxyl (OH) groups via electrostatic interaction and surface complexation. The resulting MnFe2O4 further exhibited high effective retention and recovery for U(VI)/Eu(III) from synthetic water systems and real seawater. This work highlighted that MnFe2O4 NCs were exceptionally capable in rapidly and efficiently sequestering U(VI)/Eu(III) from natural water and sewage, which would be a great prospect and further widely used in other lanthanides/actinides remediation.

Effect of graphene oxide surface modification on the elimination of Co(II) from aqueous solutions

Graphene oxide (GO) was applied as adsorbent to efficiently eliminate the heavy metal ions from wastewater because of its large amount of functional surface groups and high surface areas. However, the contribution of different functional surface groups on the high preconcentration of heavy metal ions to GO is still unclear. Herein the GO was applied as adsorbent for the efficient preconcentration of Co(II) and the effect of functional surface groups on Co(II) removal was studied by batch sorption experiments. The results showed that the maximum sorption capacities of Co(II) on GO, NGO, MGO and NMGO were 43.6, 27.3, 23.2 and 14.6 mg/g, respectively. The elimination of Co(II) was significantly influenced by ionic strength and pH, indicated that the interaction mechanism was primarily controlled by strong surface complexation. The DFT calculation further evidenced that the oxygen-containing surface groups could form shorter bond distance with Co(II) ions than the nitrogen-containing functional groups, and the calculated adsorption energies (Ead) for GO–COOH–Co (44.05 kcal/mol) and GO–OH–Co (16.44 kcal/mol) were much higher than that for NGO–Co (6.33 kcal/mol). The density of states (DOS) and charge density differences of combined complexes further illustrated the strong surface complexes were formed between Co(II) and the oxygen-containing surface groups of GO surfaces. This work highlighted that the oxygen-containing surface groups played a vital role in the formation of surface complexes with Co(II) on GO, which is crucial for the preparation and application of GO in the radioactive pollution cleanup.

Preparation of a Phosphate-Modified Flower-Like α-FeOOH Composite and Its Application for Aqueous U(VI) Removal

Goethite is a stable and widespread mineral in soil, which affects the transportation and immobilization of heavy metals in soil. Here, the three-dimensional flower-like goethite (TDFLG) was synthesized by refluxing precipitation method. The modified three-dimensional flower-like goethite (MTDFLG) was prepared by NaH2PO4 with dipping method. The obtained samples were characterized by scanning electron microscopy (SEM), energy-dispersive X-ray (EDX) analysis, N2 adsorption–desorption (BET), and X-ray diffraction (XRD). SEM images showed that the modification of phosphate had no major changes on the morphology of the original sample and the morphology of MTDFLG after adsorbed U(VI) had clearly change. For the goethite and modified goethite, the BET-specific surface area was 229.96 and 203.17 m2/g, respectively. Moreover, the effects of adsorption time, sorbent dose, solution pH, and initial uranium concentration on the uranium adsorption behaviors were investigated using the two materials as adsorbent for the treatment of uranium-containing wastewater. The results showed that MTDFLG had better adsorption capacity than TDFLG on uranium. The increase in uranium removal on MTDFLG was due to the formation of ternary surface complexes (≡FePO4UO2). TDFLG and MTDFLG followed the pseudo-second-order kinetic model and the Langmuir adsorption isotherm model, which indicated that uranium adsorption on TDFLG or MTDFLG is mainly based on chemisorption, and the maximum adsorption capacity of two adsorbents is 48.24 and 112.36 mg/g, respectively.

Variable Ni isotope fractionation between Fe-oxyhydroxides and implications for the use of Ni isotopes as geochemical tracers

Abstract Nickel (Ni) isotopes have recently emerged as a new biogeochemical tracer in marine environments, but our understanding of the mechanisms of Ni isotope fractionation in natural systems with regards to its fractionation by mineral surfaces is incomplete. This study aims to provide experimental constraints on Ni isotope fractionation during adsorption to goethite and 2-line ferrihydrite, two Fe minerals that vary in terms of distinct crystalline properties. We conducted two types of adsorption experiments: one with variable pH (5.0 to 8.0) and constant initial Ni concentration, one at a constant pH of 7.7 and variable initial Ni concentrations. Isotopic measurements were made on both the solid phase and the supernatant solutions in order to determine the Ni isotope fractionation factors (Δ60/58Nimin-aq = δ60/58Nimin − δ60/58Niaq) between the mineral and aqueous phases. Our results show preferential adsorption of lighter Ni isotopes during adsorption of Ni to Fe oxyhydroxides presumably under conditions of near equilibrium conditions. Adsorption to goethite generates the greatest fractionation, with Δ60/58Nimin-aq = −0.77 ± 0.23‰ (n = 14, 2sd), whereas adsorption to 2-line ferrihydrite samples yield Δ60/58Nimin-aq = −0.35 ± 0.08‰ (n = 16, 2sd). Using Ni K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy, we found that Ni forms an inner-sphere complex and that its coordination environment does not vary significantly with pH nor with surface loading. In addition, we found no evidence of Ni incorporation into the mineral. We suggest that the more than two-fold increase in Ni isotope fractionation in goethite relative to 2-line ferrihydrite is due to the lower Ni-Fe coordination number in the second shell, which results in the formation of a weaker surface complex and thus favors the adsorption of lighter Ni isotopes. These results show that Ni isotope fractionation during sorption by Fe-oxyhydroxides is dependent on mineralogy, which has important implications for the use of Ni isotopes as environmental tracers and the interpretation of their record in sedimentary rocks.