Controlled synthesized natroalunite microtubes applied for cadmium(II) and phosphate co-removal

3D printing calcium alginate adsorbents for highly efficient recovery of U(VI) in acidic conditions

In this study, a three-dimensional (3D) porous calcium alginate (3D CA) scaffold was successfully constructed using a direct-ink-writing-based 3D printing method combined with an in-situ calcium ion cross-linking procedure. The 3D CA contained orderly aligned microstructures with excellent structural robustness and an abundant number of active binding sites. The adsorption experiments verified that 3D CA had a considerably wide pH value (3-10) serving range, but also delivered a significantly higher adsorption capacity for U(VI) (117.3 mg/g at pH = 2.5) under acidic conditions, compared to other previously reported alginate-based porous adsorbents. The adsorption mechanisms originated from the synergistic effect of electrostatic interactions and ion exchange. The 3D CA eluted the adsorbed U(VI) in a strong acid solution through protonation mechanism, facilitating the continued enrichment and recycling of U(VI). In addition, the 3D CA demonstrated good microstructure stability and absorption capacity stability when it was immersed in hydrochloric acid solutions at different concentrations (3.6 × 10^-3 to 2 mol/L) for 24 h. Therefore, the 3D CA could be used for the removal and recycling of U(VI) from acidic solutions beyond its wide pH working range, due to its stronger acid stability and higher U(VI) adsorption capacity.

Removal and immobilization of arsenic from wastewater via arsenonatroalunite formation

Removal and immobilization of highly toxic arsenic form industrial wastewater using simple and effective methods is of important practical significance. Although the formation of natroalunite phase NaAl₃(SO₄)₂(OH)₆ has been demonstrated to be an effective method for arsenic immobilization in model system with chemical reagent grade arsenates as arsenic source, the further study is needed to investigate its immobilization for real industrial wastewater. This work reported the synthesis of natroalunite phase NaAl₃(SO₄)₂(OH)₆ using arsenic-containing industrial wastewater from benzyl acid production. The synthesis temperature and time were optimized to obtain the pure natroalunite phase composites with high crystallinity. When n(Al/As)_aq was greater than 3.0, the arsenic could almost precipitate exclusively as natroalunite phase after 60 min hydrothermal reaction at 200°C, with a maximum arsenic immobilization amount of 7.0 mol%. A maximum leaching concentration of 0.50 mg/L was observed at pH = 3.0 during the short-term (24 h) leaching test, which was lower than the US EPA TCLP test limit of 1 mg/L. The long-term leaching test up to 90 days revealed that the arsenonatroalunite could be a safe immobilization material for arsenic in pH 5.0-8.0 environments.

Removal of polystyrene nanoplastics from water by CuNi carbon material: The role of adsorption

Nanoplastics have attracted wide attention worldwide as a new potentially threatening pollutant, and they can cause harm to the organisms and pose threat to the water environment. Therefore, efficient removal techniques for nanoplastics are urgently needed. In this study, CuNi carbon material (CuNi@C) was prepared by hydrothermal method for the removal of polystyrene (PS) nanoplastics from water. CuNi@C was effectively adsorbed on PS nanoplastics. When the CuNi@C dosage increased from 0.1 g/L to 0.3 g/L, the removal efficiency of PS nanoplastics (10 mg/L) elevated from 32.72% to 99.18%. The images of the scanning electron microscope (SEM) and the Fourier transform infrared spectroscopy (FTIR) spectra of CuNi@C confirmed the adsorption of PS nanoplastics on the CuNi@C. The fitting results of adsorption kinetic models and isotherms equations demonstrated that physical adsorption and monolayer coverage were the predominant mechanisms of the PS nanoplastics adsorption on CuNi@C. Thermodynamics analysis illustrated the adsorption of PS nanoplastics on CuNi@C was a spontaneous and endothermic process. The electrostatic attraction occurred in adsorption progress, and the removal efficiency of PS nanoplastics in the acidic system was generally higher than that in the alkaline system. CuNi@C can be recycled via washing and drying treatment and these CuNi@C comparable PS nanoplastics removal performance to the original ones. After four times cycles, CuNi@C can still remove ~75% of total PS nanoplastics from water. This study reveals that CuNi@C can be used as promising techniques for the removal of PS nanoplastics from the aqueous environment.

Controlled Hydrothermal Precipitation of Alunite and Natroalunite in High-Aluminum Vanadium-Bearing Aqueous System

During the acid leaching process of black shale, with the destruction of the aluminosilicate mineral structure, a large amount of aluminum (Al) is leached, accompanied by the release of vanadium (V). To separate aluminum from the vanadium-containing solution, the precipitation behavior of aluminum ions (Al3+) was investigated under hydrothermal conditions with the formation of alunite and natroalunite. In the solution environment, alunite and natroalunite are able to form stably by the Al3+ hydrolysis precipitation process at a temperature of 200 °C, a pH value of 0.4 and a reaction time of 5 h. When Al3+ was precipitated at a K/Al molar ratio of 1, the aluminum precipitation efficiency and the vanadium precipitation efficiency were 64.77% and 1.72%, respectively. However, when Al3+ was precipitated at a Na/Al molar ratio of 1, the precipitation efficiency of the aluminum decreased to 48.71% and the vanadium precipitation efficiency increased to 4.36%. The thermodynamics and kinetics results showed that alunite forms more easily than natroalunite, and the reaction rate increases with increasing temperature, and the precipitation is controlled by the chemical reaction. Vanadium loss increases as the pH value increases. It can be deduced that the ion state of tetravalent vanadium (VO2+) was transformed into the ion state of pentavalent vanadium (VO2+) in the hydrothermal environment. The VO2+ can be adsorbed on the alunite or natroalunite as a result of their negative surface charges, ultimately leading to vanadium loss.

U(VI) adsorption on hematite nanocrystals: Insights into the reactivity of {001} and {012} facets

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-Fe₂O₃) 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.

Optimization of Cadmium Adsorption by Magnetic Graphene Oxide Using a Fractional Factorial Design

Graphene materials have attracted increasing interest in water remediation. In this study, magnetic graphene oxide (MGO) was prepared through the modified Hummers method and the adsorption behaviors of cadmium were investigated. Firstly, the sorption kinetics, isotherms, as well as the effects of pH were investigated. Then, fractional factorial design (FFD) was used to optimize the effects of pH, temperature, time, initial concentration of cadmium ion and NaCl on cadmium adsorption. The results indicate that MGO could effectively remove cadmium ions from an aqueous solution and the sorption data could be described well by pseudo-second-order and Freundlich models, showing that the adsorption rate of cadmium ions on MGO is multilayer adsorption and dominated by the chemical adsorption. According to the FFD results, the maximum adsorption capacity of cadmium ions was 13.169 mg/g under the optimum condition of pH value 8, 45 °C, contact time 60 min, initial cadmium concentration of 70 mg/L and NaCl concentration of 100 mg/L. Higher levels of the pH value, temperature and initial cadmium concentration are beneficial to the adsorption process. These results are important for estimating and optimizing the removal of metal ions by MGO composite.

Ultra-thin iron phosphate nanosheets for high efficient U(VI) adsorption

In this study, the ultra-thin iron phosphate Fe7(PO4)6 nanosheets (FP1) with fine-controlled morphology, has been designed as a new two-dimensional (2D) material for uranium adsorption. Due to its unique high accessible 2D structure, atom-dispersed phosphate/iron anchor groups and high specific surface area (27.77 m2⋅g-1), FP1 shows an extreme-high U(VI) adsorption capacity (704.23 mg·g-1 at 298 K, pH = 5.0 ± 0.1), which is about 27 times of conventional 3D Fe7(PO4)6 (24.51 mg·g-1 -sample FP2) and higher than most 2D absorbent materials, showing a great value in the treatment of radioactive wastewater. According to the adsorption results, the sorption between U(VI) and FP1 is spontaneous and endothermic, and can be conformed to single molecular layer adsorption. Based on the analyses of FESEM, EDS, Mapping, FT-IR and XRD after adsorption, the possibile adsorption mechanism can be described as a Monolayer Surface Complexation and Stacking mode (MSCS-Mode). Additionally, the research not only provide a novel preparing method for 2D phosphate materials but also pave a new pathway to study other two-dimensional adsorption materials.

Hydrothermal synthesis of natroalunite nanostructures and their F−-ion removal properties in water

The formation and growth mechanism of alunite crystallites by ionic liquid-assisted hydrothermal process was investigated.

Sandwich-like Nanosystem for Simultaneous Removal of Cr(VI) and Cd(II) from Water and Soil

In this work, a novel nanosystem with a sandwich-like structure was synthesized via face-to-face combination of two pieces of waste cotton fabrics (CFs) carrying ferrous sulfide (FeS) and carboxyl-functionalized ferroferric oxide microsphere (CFFM), respectively, and the obtained nanosystem was named as FeS/CFFM/CF. Therein, FeS has high reduction and adsorption capabilities for hexavalent chromium (Cr(VI)), CFFM possesses a high adsorption ability on cadmium ion (Cd(II)) through electrostatic attraction and chelation, and CF displays high immobilization ability for FeS and CFFM and adsorption performance on Cd(II). FeS/CFFM/CF could simultaneously remove Cr(VI) and Cd(II) from water and inhibit the uptake of Cr and Cd by fish and water spinach, ensuring the food safety. Besides, this technology could efficiently control the migration of Cr(VI) and Cd(II) in the sand-soil mixture, which was favorable to prevent their wide diffusion. Importantly, FeS/CFFM/CF possessed a high flexibility and could be conveniently produced with needed scale and shape and easily separated from water and soil, displaying a promising approach to remediate Cr(VI)-/Cd(II)-contaminated water and soil and a huge application potential.

Macroscopic and microscopic insight into the mutual effects of europium(iii) and phosphate on their interaction with graphene oxide

Graphene oxide (GO) has been proved to be very efficient for radionuclide enrichment.