Effect of glutamic acid on copper sorption onto kaolinite - Batch experiments and surface complexation modeling

Iron Oxide Nanoparticle-Assisted Delamination of Ti3C2Tx MXenes: A New Approach to Produce Magnetic MXene-Based Composites

Ti3C2Tx MXene is one of the most comprehensively studied 2D materials in terms of its adsorptive, transport, and catalytic properties, cytotoxic performance, etc. Still, conventional MXene synthesis approaches provide low single-flake MXene yield and frequently uncontrollable properties, demanding further post-processing. The MXene family also lacks magnetism, which is helpful for producing effective nanoadsorbents as their magnetic decantation is the cheapest and most convenient way to remove the spent adsorbent from water. Composite materials consisting of magnetic nanoparticles grown on top of MXene flakes are commonly used to provide magnetic properties to the resulting nanocomposite. In this paper, we study the possibility to delaminate multilayer Ti3C2Tx MXene sheets directly by growing iron oxide magnetic nanoparticles inside their interlayer spacing. We find out that, with a mass fraction of particles comparable or exceeding that of MXenes, their growth is accompanied by an effective enhancement of single-layer MXene yield and suitable magnetic properties of the resulting composite. The developed approach can be further used for simplifying synthesis protocols to obtain magnetic MXene-based nanoadsorbents with tunable properties.

Contemporary Techniques for Remediating Endocrine-Disrupting Compounds in Various Water Sources: Advances in Treatment Methods and Their Limitations

Over the years, the persistent occurrence of superfluous endocrine-disrupting compounds (EDCs) (sub µg L⁻¹) in water has led to serious health disorders in human and aquatic lives, as well as undermined the water quality. At present, there are no generally accepted regulatory discharge limits for the EDCs to avert their possible negative impacts. Moreover, the conventional treatment processes have reportedly failed to remove the persistent EDC pollutants, and this has led researchers to develop alternative treatment methods. Comprehensive information on the recent advances in the existing novel treatment processes and their peculiar limitations is still lacking. In this regard, the various treatment methods for the removal of EDCs are critically studied and reported in this paper. Initially, the occurrences of the EDCs and their attributed effects on humans, aquatic life, and wildlife are systematically reviewed, as well as the applied treatments. The most noticeable advances in the treatment methods include adsorption, catalytic degradation, ozonation, membrane separation, and advanced oxidation processes (AOP), as well as hybrid processes. The recent advances in the treatment technologies available for the elimination of EDCs from various water resources alongside with their associated drawbacks are discussed critically. Besides, the application of hybrid adsorption–membrane treatment using several novel nano-precursors is carefully reviewed. The operating factors influencing the EDCs’ remediations via adsorption is also briefly examined. Interestingly, research findings have indicated that some of the contemporary techniques could achieve more than 99% EDCs removal.

Sorption of DONs onto clay minerals in single-solute and multi-solute systems: Implications for DONs mobility in the vadose zone and leachability into groundwater

Dissolved organic nitrogen (DON) with a mixture of various organic nitrogen (N) is recognized as an emerging groundwater contaminant. Investigating the behavior and mechanism of DON sorption onto clay minerals, which are key components of vadose zone media, is crucial to evaluating its leaching potential. Considering the interactions among multiple DON compounds (DONs) may influence their sorption behaviors, the sorption of three typical DONs (amino acid, protein and urea) to clay minerals in single-, binary- and ternary-solute systems were explored, respectively. In addition, a combination of multiple methods, including physiochemical characterization, Fourier Transform Infrared Spectroscopy (FTIR), X-ray diffraction (XRD) and pH variation analysis, were used to provide insight into the governing mechanisms. Results indicated that the sorption kinetics and isotherms of single systems were well-fitted by pseudo-second-order and Freundlich isotherm models, respectively. The mechanisms involved in the sorption of DONs onto clay minerals varied with the sorption time. The dominant interactions included van der Waals forces, ligand exchange, and hydrogen bonding (H-bonding) in the initial phase of the sorption process, whereas electrostatic interactions were predominant in the later stage as H⁺ was released into the solution. In binary-solute systems, either cooperative or competitive sorption was observed depending on the co-solute combination. For instance, the sorption behaviors of amino acids and urea were simultaneously enhanced in the binary system because of the formation of highly charged complexes as new active sites. Proteins sorption, however, was inhibited by the coexistence of urea as a result of active site depletion and protein denaturation. In ternary-solute systems, the sorption of DONs was balanced by cooperative and competitive sorption processes. These findings elucidated the sorption behaviors of DONs onto clay minerals in multi-solute systems and contributed to the evaluation of the mobility of DONs in the vadose zone and their leachability into groundwater.

Effect of DTPA on europium sorption onto quartz - Batch sorption experiments and surface complexation modeling

Sorption of radionuclides on mineral surfaces retards their migration in the environment of a repository. Presence of organic ligands, however, affects sorption and consequently influences their transport behavior. In this study, we quantify the sorption of Eu(III) onto quartz surfaces as a function of pH in the absence and presence of diethylenetriaminepentaacetic acid (DTPA). Batch sorption experiments show a pH-dependent sorption of Eu(III) on quartz. The presence of DTPA results in slightly higher sorption of Eu(III) at neutral to slightly acidic pH and considerably lower sorption at alkaline conditions. Sorption experiments were simulated using the Diffuse Double Layer Model (DDLM) with single sorption sites (≡QOH) and monodentate surface complexation. The reactions were established based on the aqueous speciation calculation under the experimental conditions, and the thermodynamic constants of surface reactions were obtained and refined by numerical optimization. Results of surface complexation modeling show the formation of a surface species ≡QOHEuDTPA^2-, explaining the elevated sorption of Eu(III) at neutral to slightly acidic pH. In contrast, dissolved EuDTPA^2- complex species are present at alkaline pH, resulting in an enhanced mobility of Eu(III).

Glutamic acid leaching of synthetic covellite - A model system combining experimental data and geochemical modeling

For Kupferschiefer mining established pyrometallurgical and acidic bioleaching methods face numerous problems. This is due to the finely grained and dispersed distribution of the copper minerals, the complex mineralogy, comparably low copper content, and the possibly high carbonate and organic content in this ore. Leaching at neutral pH seemed worth a try: At neutral pH the abundant carbonates do not need to be dissolved and therewith would not consume excessive amounts of provided acids. Certainly, copper solubility at neutral pH is reduced compared to an acidic environment; however, if copper complexing ligands would be supplied abundantly, copper contents in the mobile phase could easily reach the required economic level. We set up a model system to study the effect of parameters such as pH, microorganisms, microbial metabolites, and organic ligands on covellite leaching to get a better understanding of the processes in copper leaching at pH ≥ 6. With this model system we could show that glutamic acid and the microbial siderophore desferrioxamine B promote covellite dissolution. Both experimental and modeling data showed that pH is an important parameter in covellite dissolution. An increase of pH from 6 to 9 could elevate copper extraction in the presence of glutamic acid by a factor of five. These results have implications for both development of a biotechnological process regarding metal extraction from Kupferschiefer, and for the interaction of bacterial metabolites with the lithosphere and potential mobilization of heavy metals in alkaline environments.

Influence of Fe(II) on the Se(IV) sorption under oxic/anoxic conditions using bentonite

⁷⁹Se, one of the key radionuclides for nuclear waste disposal, threatens the quality of the environment, as well as human health. Therefore, it needs to be permanently isolated from the biosphere. The aim of the study was to investigate the effects of Fe(II)/Fe(III) on the removal of ⁷⁹Se using bentonite in the pH range of 2.0-10.0 under oxic/anoxic conditions. Under oxic conditions, Se(IV) prefers to form inner-sphere complexes with Fe(III)-oxyhydroxide, derived from the oxidization of Fe(II) using oxygen. Interestingly, Se(IV) will interact with Fe(III) and form a poorly soluble ferric selenite at pH ∼4 under oxic conditions. Under anoxic conditions, however, the concentration of Fe(II) is closely related to the sorption process of Se(IV) on bentonite. When the concentration of Fe(II) was less than 1%, Fe(II) combined with the hydroxyl, forming Fe(OH)₂, which generated a disproportionation at pH ∼8 and formed a new sorbent, Fe₃O₄. However, when the concentration of Fe(II) was increased to 5%, reduction precipitation was the primary way to remove Se(IV) in aqueous solution. XANES (X-ray Absorption Near Edge Structure) spectra showed that higher pH values are beneficial for the formation of the final thermodynamic reduction product, Fe selenide. These results suggested that Fe(II) significantly affect the Se(IV) sorption. Overall, this study confirmed the significant role of Fe(II) on the retardation of ⁷⁹Se and on remediation for Se(IV) contamination in the hydrosphere.