The current research describes the synthesis, characterization and application of CoFe₂O₄/g-C₃N₄/bentonite as a novel nanocomposite for the efficient degradation of aniline blue under solar irradiation. Powder XRD, TIR, SEM, TEM, VSM and UV-DRS were used to describe the formation and morphology of the composite. The composite has been used as a heterogeneous photocatalyst to degrade aniline blue in the presence of H₂O₂. In the presence of H₂O₂ in solar radiation, it was possible to degrade 88.5% of 10 ppm aniline blue solution just in 50 min using 50 mg of the composite. The improvement in photodegradation rate in the existence of H₂O₂ was attributed to the advanced oxidation process (AOP) mechanism of photo-Fenton involving the production of reactive hydroxyl and perhydroxyl radicals. The degradation was found to follow first-order kinetics with high regression coefficient with elevated rate constant.

Removal of textile azo-dyes from industrial wastewater is a concerning problem in the modern societies. Adsorption of organic dyes is an alternative for removing these pollutants, but efficient and low-cost adsorbents are required. In this work, a natural (crude) bentonite was used as adsorbent to remove a model cationic (basic) textile dye (basic red 46). Some parameters such as initial dye concentration, time, pH, and temperature were studied in semi-batch experiments to obtain the best conditions for adsorption of basic red 46 (BR-46) with minimal quantity of adsorbent (10 mg in 100 mL of solution). An experimental adsorption capacity (qₘ) of 594 mg g⁻¹ was determined directly from the adsorption curve for 60 mg L⁻¹, pH=7 and 25 °C. The thermodynamic parameters ΔG°, ΔH° and ΔS° were also estimated. Several adsorption isotherms (Langmuir, Freundlich, and Temkin) and kinetic models (pseudo-first order, pseudo-second order, and intra-particle diffusion) were applied to the experimental data; thus, the best settings were obtained by Langmuir isotherm and pseudo-second order kinetic model. The comparison of results obtained for this natural bentonite with respect to some materials published in the literature reveals the excellent performance of this material for adsorption of BR-46, allowing a fast and higher removal (94% ± 4, at 10 min), under mild conditions (neutral pH, 25 °C and atmospheric pressure). Graphical Abstract

Knowledge of the behavior of highly compacted expansive clays, as an engineered barrier, in disposal of high-level nuclear waste (HLW) systems to prevent the pollution due to migration of radionuclide is extremely essential. The prominent properties of globally and widely used bentonites have been extensively studied during past two decades. In China, GaoMiaoZi (GMZ) bentonite is the first choice as a buffer or backfill material for deep geological repositories. This review article presents the recent progresses of knowledge on water retention properties, hydromechanical behavior, and fractal characteristics of GMZ bentonite-based materials, by reviewing 217 internationally published research articles. Firstly, the current literature regarding hydrogeochemical and mechanical characteristics of GMZ bentonite influenced by various saline solutions are critically summarized and reviewed. Then, the role of osmotic suction π alongside the application of surface fractal dimension Dₛ is presented from the standpoint of fractal theory. Finally, the strength characteristics of GMZ bentonites using fractal approach have been discussed. Furthermore, this study sheds light on gaps, opportunities, and further research for understanding and analyzing the long-term hydromechanical characteristics of the designed backfill material, from the standpoint of surface fractality of bentonites, and implications of sustainable buffer materials in the field of geoenvironmental engineering.

Dissolved oxygen (DO) in the overlying water is important in influencing internal phosphorus (P) release. However, the potentially associative effect of DO on the P adsorption and immobilization by La-modified bentonite (LMB) has not been quantified. This 80-day incubation experiment showed the synergistic effect of DO and LMB in the overlying water, which caused the reduction of dissolved inorganic phosphorus (DIP) by 51% (DO = 5 mg L⁻¹) and 77% (DO = 7 mg L⁻¹) on average, respectively, compared with the DO of 3 mg L⁻¹. In addition, the DIP in the pore water decreased from 1.12 mg P L⁻¹ (control) to 0.014 mg P L⁻¹ (5 mg L⁻¹) and 0.004 mg P L⁻¹ (7 mg L⁻¹). Besides, the Fe²⁺ and NH₄⁺ concentrations were also reduced significantly in the pore water, suggesting the rise in the redox potential in the sediment, which helped P immobilization. Chemical P-fractionation experiments indicate that the Fe-P reduction in sediment was the most significant, reduced by 14%, followed by NH₄Cl-P (12%), causing a reduction by 13% (3 mg L⁻¹), 23% (5 mg L⁻¹) and 27% (7 mg L⁻¹) of mobile P in the surface 7-cm sediment, respectively. However, the released P ions were rapidly adsorbed by the Al ions and Ca ions, as well as their compounds, thereby leading to the obvious rise in inert P in the sediment. Accordingly, it was suggested that DO and LMB had a synergistic effect on external P adsorption and immobilization.

Increasing applications of rare earth elements (REEs) and improving technologies have led to increased demand. Because of their limited availability and depletion of most resources, the recovery of these elements from waste has become important. The use of cost-effective materials for this purpose and the high value that can potentially be recovered would be beneficial and attractive to many industries using REEs. In this study, natural zeolite and bentonite were used in batch studies to recover REEs (La, Y, Lu, Sm, Pr, Tm, Ce, Nd, Yb, Gd, Eu, Er, Ho, Dy, and Sc) from aqueous solutions. The effect of adsorbent dosage, pH, concentration, contact time, and competing ions on recovery was investigated. Desorption studies were conducted using ammonium sulphate. Adsorption onto zeolite was found to increase with pH, whereas uniform adsorption was observed for bentonite, except at pH 2 (16% less efficiency). The pH values of 6.2 and 3.2 were selected as the optimum for zeolite and bentonite, respectively. For zeolite, the average adsorption efficiencies for REEs at 0.5, 1.0, 2.0, 5.0, and 10 mg L⁻¹ were found to be 91, 96, 89, 40, and 20% respectively but, > 98% adsorption efficiencies were achieved with bentonite at all concentrations. The zeolite and bentonite adsorption data were better described by Langmuir though, for bentonite, the coefficients of determination (R² values) for the Freundlich and Dubinin-Radushkevich isotherm models were also significant. There was no significant difference (p > 0.05) on the adsorption of the elements in the presence of competing ions. Bentonite proved to perform better, most likely as a result of its higher surface area. Generally, the good adsorption performance of both adsorbents in their natural forms makes them an attractive and potential cheap option for the recovery of REEs from wastewaters.

Copper bioavailability, specially to plants, is strongly dependent on its chemical form, as for most metals. Copper-contaminated soil can be treated in situ by the addition of minerals such as Na-bentonite, which mixed with surface soil, can transform this pollutant to non-bioavailable forms. In this work, shelter experiments were conducted to study the time evolution of Cu speciation, in pristine soil as well as in amended one. A selective sequential extraction method was employed to determine the metal speciation in the samples. The results show that the major metal fraction is the organic matter-bound one, whereas the exchangeable fraction is very low, even the first day after Cu addition. The time evolution shows a slow decrease of the organic-bound Cu and a corresponding increase of the most stable mineral fractions. With the addition of Na-bentonite to copper-contaminated soil, the most stable mineral fractions increase whereas the organic-bound one decreases, showing essentially similar time dependence of the several metal fractions. Sodium bentonite could be effectively used for remediation of soils polluted with Cu.

Calcium nitrate and a lanthanum-modified bentonite (Phoslock®) were investigated for their ability to control the release of phosphorus from contaminated sediment. Their effectiveness and mode of action were assessed using microcosm experiments by monitoring the variation of physiochemical parameters and phosphorus and nitrogen species over time following the treatment for 66 days. Phoslock® was more effective reducing phosphorus in overlaying water and controlling its release from sediment. Calcium nitrate improved redox condition at the sediment-water interface and temporally reduce phosphorus in overlaying water but phosphorus level returned back in a long run. Phosphorus fractionation suggested that Phoslock® converted mobile phosphorus to more stable species while calcium nitrate increased the fractions of mobile phosphorus species. Phoslock® generally showed no effect on nitrogen species. Whereas calcium nitrate temporally increased nitrate, nitrite, and ammonium concentrations but their concentrations quickly reduced likely due to the denitrification process. Results suggested that Phoslock® can be more effective in controlling the release of phosphorus from sediment than calcium nitrate. However, calcium nitrate can improve the redox condition at the sediment-water interface, which may provide other benefits such as stimulating biodegradation.

Fe₃O₄and Fe₃O₄/bentonite were prepared by chemical co-precipitation method. They were characterized by X-ray powder diffraction (XRD), Fourier infrared spectroscopy (FTIR), and transmission electron microscope (TEM). Adsorption of cobalt(II) on the bentonite, Fe₃O₄, and Fe₃O₄/bentonite nanocomposite was studied. The results indicated that the metal oxides mainly occurred in the form of spinel structure of Fe₃O₄and the presence of Fe₃O₄significantly affect the surface area and pore structure of the bentonite. The specific surface area (Brunauer–Emmett–Teller (BET) method) of bentonite, Fe₃O₄, and Fe₃O₄/bentonite were determined to be 34.44, 98.44, and 140.5 m² g⁻¹, respectively. TEM image of Fe₃O₄/bentonite shows the particle diameter at 10 nm. The maximum adsorption capacity of cobalt(II) by Fe₃O₄/bentonite nanocomposite was determined to be 18.76 mg g⁻¹. The adsorption strongly depends on pH, where the removal efficiency increases as the pH turns to alkaline range (pH 9). The results suggest that higher adsorption capacity of composite than bentonite is attributed to the presence of Fe₃O₄. The adsorption process follows pseudo-second-order kinetics. The equilibrium data was analyzed by Langmuir model showing high correlation coefficient. The thermodynamic study of adsorption process showed that the adsorption of Co(II) onto Fe₃O₄/bentonite was carried out spontaneously.

The study investigated phosphate adsorption from aqueous solutions using chemical- and thermal-modified bentonite in batch system. The adsorbent was characterized by SEM, BET, and FTIR spectroscopy. Contact time, beginning phosphate concentration, pH of the solution, and the effects of the temperature on phosphate adsorption capacity were determined by a series of experimental studies. In a wide pH range (3–10), high phosphate removal yields were obtained (between 94.23 and 92.26 %), and with the increase in temperature (from 25 to 45 °C), phosphate removal increased. Langmuir and Freundlich isotherms were used to determine the sorption equilibrium, and the results demonstrated that equilibrium data displayed better adjustment to Langmuir isotherm than the Freundlich isotherm. Phosphate sorption capacity, calculated using Langmuir equation, is 20.37 mg g⁻¹ at 45 °C temperature and pH 3. Mass transfer and kinetic models were applied to empirical findings to determine the mechanism of adsorption and the potential steps that control the reaction rate. Both external mass transfer and intra-particle diffusion played a significant role on the adsorption mechanism of phosphate, and adsorption kinetics followed the pseudo-second-order-type kinetic. Furthermore, thermodynamic parameters (ΔH°, ΔG°, ΔS°) which reveal that phosphate adsorption occur spontaneously and in endothermic nature were determined. The results of this study support that bentonite, which is found abundant in nature and modified as an inexpensive and effective adsorbent, could be used for phosphate removal from aqueous solutions.

Management strategies that prevent the onset of nuisance and noxious cyanobacteria blooms are needed to preserve the integrity and safety of freshwater resource uses. Scientifically defensible data are needed regarding efficacy of proactive approaches in order to assist water resource managers in making informed decisions. As phosphorus availability has been indicated as a crucial aspect of cyanobacteria presence/dominance in freshwater systems, the integration of novel technologies to inactivate phosphorus is a critical component to achieve improved water quality. Phoslock (Phoslock Water Solutions, Ltd.) phosphorus locking technology is composed of the element lanthanum in a bentonite clay matrix that has a high specificity to bind and inactivate soluble reactive phosphorus. This research evaluated the phosphorus binding efficiency of Phoslock in aqueous and sediment matrices and the consequent impact on algae assemblage composition and water quality parameters. Laguna Niguel Lake in California afforded an opportunity to evaluate the operational effectiveness of Phoslock in a system historically plagued by high phosphorus concentrations, potentially toxic cyanobacteria (Aphanizomenonflos-aquae dominant), and lake closures. Phoslock was able to rapidly (<2 weeks) and significantly (p < 0.0005) decrease total (>80 %) and free reactive (>95 %) phosphorus in the water column and shift potentially releasable sediment phosphorus fractions to residual forms after treatment. Despite documented cyanobacteria blooms and high pretreatment cell densities, cyanobacteria levels remained below or near detection limits and only comprised a small fraction of the algae assemblage following Phoslock application. This study provides water resource managers an information on operational implementation and efficacy of a phosphorus binding technology.