In this study natural bentonite (NB) and acid-thermal co-modified bentonite (MB) were utilized as adsorbents for the removal of Thymol Blue (TB) from aqueous solution. The batch adsorption experiments were conducted under different experimental conditions. The artificial neural network (ANN) and adaptive neuro fuzzy inference systems (ANFIS) were applied to estimate removal percentage (%) of TB. Mean squared error (MSE), root mean square error (RMSE) and coefficient of determination (R2) values were used to evaluate the results. In addition, the experimental data were fitted isotherm models (Langmuir, Freundlich and Temkin) and kinetic models (pseudo first order (PFO), pseudo second order (PSO) and intra-particle diffusion (IPD)). The adsorption of TB on both the NB and MB followed well the PSO kinetic model, and was best suited Langmuir isotherm model. When the temperature was increased from 298 K to 323 K for 20 mg/L of TB initial concentration, the removal percentage of TB onto the NB and MB increased from 74.91% to 84.07% and 81.19% to 93.12%, respectively. This results were confirmed by the positive ΔH° values indicated that the removal process was endothermic for both the NB and MB. The maximum adsorption capacity was found as 48.7805 mg/g and 117.6471 mg/g for the NB and MB, respectively (at 323 K). As a result, with high surface area and adsorption capacity, the MB is a great candidate for TB dye removal from wastewater, and the ANFIS model is better than the ANN model at estimating the removal percentage of the dye.

Natural colloids such as clays and natural organic matter (NOM) are universally present in environments, which could interact with microplastics (MPs) and thus alter the fate and transport of MPs in porous media. The co-effects of clays and NOM on MPs transport in saturated porous media were systematically explored at both low and high ionic strength (IS) conditions. Specifically, bentonite and humic acid (HA) were employed as representative clays and NOM. 5 mM NaCl and 1 mM CaCl₂ solutions were used as low IS conditions, while 25 mM NaCl and 5 mM CaCl₂ solutions were employed as high IS conditions. We found that formation of MPs-bentonite heteroaggregates had great effects on MPs transport under different conditions. Without HA, the small MPs-bentonite heteroaggregates formed under low IS increased MPs transport via serving as mobile carriers, while larger MPs-bentonite heteroaggregates formed at high IS led to the decreased MPs mobility. When both HA and bentonite were copresent in MPs suspension, we found that HA could inhibit the formation of larger sized MPs-bentonite heteroaggregates. Particularly, when the two types of natural colloids copresent in MPs suspensions, MPs transport behaviors were similar to those with only bentonite present in MPs suspensions at low IS, while MPs transport was greatly increased at high IS comparing with those only with bentonite in suspensions. Clearly, without HA in suspensions, bentonite played the dominant role on MPs transport under all examined conditions concerned in this study. Instead, when both HA and bentonite copresent in MPs suspensions, MPs transport was mainly controlled by bentonite at low IS, while both bentonite and HA had major contributions at high IS. The results showed that under solution conditions concerned in present study, MPs mobility in porous media would be greatly affected (either enhanced or inhibited) by the two types of natural colloids.

Establishment of submerged macrophyte beds and application of chemical phosphorus inactivation are common lake restoration methods for reducing internal phosphorus loading. The two methods operate via different mechanisms and may potentially supplement each other, especially when internal phosphorous loading is continuously high. However, their combined effects have so far not been elucidated. Here, we investigated the combined impact of the submerged macrophyte Vallisneria denseserrulata and a lanthanum-modified bentonite (Phoslock®) on water quality in a 12-week mesocosm experiment. The combined treatment led to stronger improvement of water quality and a more pronounced reduction of porewater soluble reactive phosphorus than each of the two measures. In the combined treatment, total porewater soluble reactive phosphorus in the top 10 cm sediment layers decreased by 78% compared with the control group without Phoslock® and submerged macrophytes. Besides, in the upper 0–1 cm sediment layer, mobile phosphorus was transformed into recalcitrant forms (e.g. the proportion of HCl–P increased to 64%), while in the deeper layers, (hydr)oxides-bound phosphorus species increased 17–28%. Phoslock®, however, reduced the clonal growth of V. denseserrulata by 35% of biomass (dry weight) and 27% of plant density. Our study indicated that Phoslock® and submerged macrophytes may complement each other in the early stage of lake restoration following external nutrient loading reduction in eutrophic lakes, potentially accelerating the restoration process, especially in those lakes where the internal phosphorus loading is high.

Powder adsorbents show an excellent adsorption capacity for arsenic(As) due to the large specific surface area. However, the performance of powder adsorbents decreases significantly by channeling in the adsorption bed, and the powder is released from the bed. Pelletization of power adsorbent can solve the problems, and bentonite was proposed as a binder to improve the strength. The adsorption capacity and lifetime of pelletized adsorbent were evaluated through a batch and column study. The addition of bentonite decreased adsorption capacity by 16% of pellet without bentonite, but improved compressive strength of adsorbent up to 3.6 times. In the batch test, the maximum adsorption capacity of pelletized adsorbent is 22.2 mg As/g, which is about 40% of powder adsorbent. However, in the column study, pellet adsorbent showed similar adsorption performance and lifetime to commercial and powder adsorbent. As a result, the pellet adsorbent using bentonite is a potential low-cost adsorbent to remove effectively As in the aqueous phase.

At present, plastic concrete is widely used in anti-seepage engineering, and its strength and hydraulic conductivity are important indexes of plastic concrete cutoff walls. The pondus hydrogenii (pH) and electrical conductivity (EC) have an important effect on the strength and hydraulic conductivity of plastic concrete cutoff walls. However, it is not clear why the pH and EC are related to the strength and permeability of these walls. For this reason, plastic concrete composed of sand, cement, water, and bentonite was taken as the research object to study the influence of different mix ratios and curing ages on the unconfined compressive strength and permeability of plastic concrete. The pH and EC of the corresponding mix ratio and curing age were measured. The effects of the pH and EC on the strength and permeability of plastic concrete were studied, and the internal reason was explored from the product type and hydration reaction degree of plastic concrete. Furthermore, the quantitative relationship between pH and EC and the strength and hydraulic conductivity of plastic concrete was established. With increasing cement content, the strength, pH, and EC of plastic concrete increase continuously, while the hydraulic conductivity decreases. With increasing curing age, the strength increases, the hydraulic conductivity decreases, and both the pH and EC show a trend of first increasing and then decreasing. The pH value and electrical conductivity can reflect the product type and hydration reaction degree of plastic concrete, further affecting its strength and hydraulic conductivity. Under different dosage and curing age conditions, the pH showed three stages, namely, 11.7–12.27, 12.27–2.5, and 12.5–12.75, and there is a good power functional relationship among the EC and strength and hydraulic conductivity at each stage.

Four artificial soils (AS) were prepared based on a mixture of humus, bentonite, kaolinite, and polyvinyl chloride (PVC), as inert matter, in the following proportion: 0%, 12.44%, 37.50%, 78.55% of humus, 10.5% of bentonite, 10.5% of kaolinite, and 78.92%, 66.26%, and 41.46% of PVC. The AS were prepared with variable content of organic matter (OM) in order to evaluate the retention of lead (II) due solely to the content of OM. The results indicated that retention capacity of Pb⁺² increases (19.74 mg/g, 20.89 mg/g, 61.61 mg/g, and 79.48 mg/g) as OM increases (0%, 1%, 5%, and 10%); however, this retention is not proportional to the OM increment. An increase of background solution concentration of 0.01 M to 0.1 M resulted in a 50% decrease in the lead retention capacity. The fitting of lead adsorption was performed by the regression coefficient (R²). All R² of the Langmuir model fit successfully to all types of AS (0.973 for 10-OM, 0.9845 for 5-OM, 0.999 for 1-OM, 0.994 for 0-OM). The adsorption kinetics also fits well to the pseudo-second-order model (R²₁₀₋OM = 0.989, R²₅₋OM = 0.999, R²₁₋OM = 0.999, and R²₀₋OM = 0.999). The thermodynamic values of the Gibbs free energy (ΔG⁰₁₀₋OM = − 10.62, ΔG⁰₅₋OM = − 11.50, ΔG⁰₁₋OM = − 14.23, and ΔG⁰₀₋OM = − 17.06) indicated that it was a spontaneous process, and the energy of the process suggests a retention mechanism by ion exchange. A soil with high content of OM does not guarantee high retention of lead, even more so when the adsorption mechanism is given by ion exchange.

In this research, the sorption behavior (kinetic, isotherm, and thermodynamic modeling) of heavy metals (Cu (II) and Fe (II)) and pigments (carotenoid and chlorophyll) onto activated bentonite clay was investigated for soybean oil under industrial (IBM) and ultrasonic bleaching method (UBM). A nonlinear fitting approach was used to determine the best-fit isotherm and kinetic models by two statistical criteria including the coefficient of determination (R²) and chi-square (χ²). The adsorption of metal ions and pigments onto activated bentonite clay under UBM was quite well by the pseudo-first-order model. In both bleaching methods, the equilibrium adsorption data follows the Toth isotherm model, presenting the sorption occurrence tends to be on a heterogeneous surface. The results indicated that the adsorption thermodynamics was endothermic in nature and the process was spontaneous between 35 and 65 °C.

In the present investigation, a novel Fe-TiO₂ composite was fabricated by mixing fly ash (FA), foundry sand (FS), and bentonite clay for the degradation of paracetamol (PCM). This composite acts as a surface for immobilizing the TiO₂ catalyst (using the dip-coating method) besides facilitating the leaching of iron (FA and FS) in acidic conditions. Leached iron (in the form of Fe(II), Fe(III), and total iron) promotes the photo-Fenton (with the addition of H₂O₂ in the system) while the surface-active TiO₂ layer leads to photocatalysis, thus leading to in situ dual process combining photocatalysis and photo-Fenton in one system. This dual process led to a synergy of 75% in comparison to the photocatalysis and photo-Fenton process owing to the large production of •OH. Various parameters such as H₂O₂ dose (525 mg l⁻¹), number of beads (80), degradation time (215 min), and volume (200 ml) were optimized, and 96.6% of reduction in PCM was observed. Durability study of catalyst showed a minor reduction in the activity of the catalyst after 30 cycles. The TiO₂ catalyst was still intact as a film, and iron leaching was also occurring from the beads even after recycling, thus confirming their long-term durability in terms of dual effect. The stability and durability of the composite were confirmed by characteristic analysis such as SEM/EDS. Mineralization of PCM was concluded through the estimation of degradation by-products using GC-MS analysis followed by estimation of nitrate and nitrite ions.

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.