Effect of pre-treatment of bentonite with sodium and calcium ions on phosphate adsorption onto zirconium-modified bentonite

Recent advances of application of bentonite-based composites in the environmental remediation

Bentonite-based composites have been widely utilized in the removal of various pollutants due to low cost, environmentally friendly, ease-to-operate, whereas the recent advances concerning the application of bentonite-based composites in environmental remediation were not available. Herein, the modification (i.e., acid/alkaline washing, thermal treatment and hybrids) of bentonite was firstly reviewed; Then the recent advances of adsorption of environmental concomitants (e.g., organic (dyes, microplastics, phenolic and other organics) and inorganic pollutants (heavy metals, radionuclides and other inorganic pollutants)) on various bentonite-based composites were summarized in details. Meanwhile, the effect of environmental factors and interaction mechanism between bentonite-based composites and contaminants were also investigated. Finally, the conclusions and prospective of bentonite-based composites in the environmental remediation were proposed. It is demonstrated that various bentonite-based composites exhibited the high adsorption/degradation capacity towards environmental pollutants under the specific conditions. The interaction mechanism involved the mineralization, physical/chemical adsorption, co-precipitation and complexation. This review highlights the effect of different functionalization of bentonite-based composites on their adsorption capacity and interaction mechanism, which is expected to be helpful to environmental scientists for applying bentonite-based composites into practical environmental remediation.

Removal of phosphorus by modified bentonite:polyvinylidene fluoride membrane-study of adsorption performance and mechanism

Enhanced phosphorus management, geared towards sustainability, is imperative due to its indispensability for all life forms and its close association with water bodies' eutrophication, primarily stemming from anthropogenic activities. In response to this concern, innovative technologies rooted in the circular economy are emerging, to remove and recover this vital nutrient to global food production. This research undertakes an evaluation of the dead-end filtration performance of a mixed matrix membrane composed of modified bentonite (MB) and polyvinylidene fluoride (PVDF) for efficient phosphorus removal from water media. The MB:PVDF membrane exhibited higher permeability and surface roughness compared to the pristine membrane, showcasing an adsorption capacity (Q) of 23.2 mgP·m-2. Increasing the adsorbent concentration resulted in a higher removal capacity (from 16.9 to 23.2 mgP·m-2) and increased solution flux (from 0.5 to 16.5 L·m-2·h-1) through the membrane. The initial phosphorus concentration demonstrates a positive correlation with the adsorption capacity of the material, while the system pressure positively influences the observed flux. Conversely, the presence of humic acid exerts an adverse impact on both factors. Additionally, the primary mechanism involved in the adsorption process is identified as the formation of inner-sphere complexes.

The increasing risk of ammonia volatilization in farmland from the recovery product of magnesium-modified biochar after nitrogen and phosphorus adsorption

Many studies have shown that magnesium modified biochar (MgBC) can recover nutrients from wastewater and be applied as an excellent slow-release fertilizer in farmland. However, the recovery products (NP-loaden MgBC), represented by struvite or magnesium phosphate, have a high degree of self-alkalinity, which may significantly increase the ammonia (NH3) volatilization in farmland. In this study, the optimal adsorption parameters, self-alkaline regulation process and co-adsorption mechanism of MgBC for ammonium ion (NH4+) and phosphate ion (PO43-) were studied through batch experiments. A field experiment was conducted with three treatments, including local conventional fertilization (N1B0) and the application of 5 t·ha-1 or 10 t·ha-1 NP-loaden MgBC in combination with local conventional fertilization (N1B1 and N1B2, respectively), to determine the impact of NP-loaden MgBC on NH3 volatilization, surface water c(NH4+-N) and pH. The results indicated that the maximum NH4+ and PO43- synergistic recovery of MgBC under the optimal adsorption parameters (dosage of 0.6 g·L-1; initial NH4+ and PO43- concentrations of 120 and 60 mg·L-1 and pH of 8) were 59.96 and 98.60 mg·g-1, respectively. Self-regulating alkaline MgBC maintained pH suitable for struvite, and precipitation mechanism controlled the adsorption. The presence of NP-loaden MgBC raised the pH levels in surface water during the basal fertilization stage and increased c(NH4+-N) in surface water during the topdressing stages. This, in turn, led to a significant increase in NH3 volatilization loss during the entire rice-growing period, with N1B1 and N1B2 experiencing a 23.87 % and 48.91 % increase respectively, compared to N1B0. Therefore, it is imperative to take into account the adverse impact of NP-laden MgBC on NH3 loss in paddy fields when considering its application in future field studies.

Study on phosphate removal from aqueous solutions using magnesium-ammonium- and zirconium-modified zeolites: equilibrium, kinetic, and fixed-bed column study

Eutrophication is an environmental issue which occurs when the environment becomes enriched with nutrients. Phosphorus (P) is a key nutrient limiting the phytoplankton and algal growth in many aquatic environments. Therefore, P removal could be a promising technique to control the eutrophication. Herein, a natural zeolite (NZ) was modified by two practical techniques, including zirconium (ZrMZ) and magnesium-ammonium modification (MNZ), and employed for phosphate removal. Batch, equilibrium, and column experiments were conducted to determine various adsorption parameters. Equilibrium data were fitted to two different isotherms and Freundlich isotherm provided the best fit which confirms multi-layer adsorption of phosphate ions on the adsorbents. The kinetic experiments demonstrated that the adsorption process is fast with more than 80% of phosphate adsorbed in the first 4 h, and a subsequent equilibrium was established after 16 h. The kinetic data were well described by pseudo-second-order model, suggesting that chemisorption is the mechanism of sorption. Intraparticle diffusion showed a rate-limiting step for phosphate adsorption on all the adsorbents, especially MNZ and ZrMZ. The fixed-bed column study showed that the phosphate concentration in the outlet (C) of ZrMZ column did not reach the initial concentration (C₀) after passing 250 bed volume (BV), while it reached C₀ after 100 BV when the MNZ was employed. Given the considerable improvement were seen, the results of this study suggest that surface of zeolite can be modified with zirconium (and in a less extent magnesium-ammonium) to enhance adsorption of phosphate from many eutrophic lakes.

Simultaneous removal of phosphate, calcium, and ammonia nitrogen in a hydrogel immobilized reactor with bentonite/lanthanum/PVA based on microbial induced calcium precipitation

In recent years, it is urgent to solve nitrogen and phosphorus pollution in domestic wastewater. The target strain Pseudomonas sp. Y1 was immobilized using polyvinyl alcohol (PVA) matrix coupled with bentonite and lanthanum (La), respectively, to fabricate four hydrogel materials that used to construct bioreactors. The optimal operating parameters and dephosphorization mechanism were discussed, and the effects of hydrogel materials and different loads on the performance of the bioreactor were contrastively analyzed. The results manifested that when the hydraulic retention time (HRT) was 6.0 h, the C/N was 6.0, and the Ca²⁺ concentration was 100.0 mg L^-1, the bioreactors had the best heterotrophic nitrification-aerobic denitrification (HNAD) and biomineralization capacity, and the maximum removal efficiencies of Ca²⁺, PO₄^3--P, and NH₄⁺-N were 82.57, 99.17, and 89.08%, respectively. The operation data indicated that the addition of bentonite significantly promoted HNAD, and the bioreactor had stronger dephosphorization ability in the presence of La. The main phosphorous removal mechanisms were confirmed to be adsorption and co-precipitation. Finally, high-throughput sequencing results indicated that Pseudomonas accounted for the paramount proportion in the bioreactor, and the prediction of functional genes indicated that the C/N of 6.0 is more favorable for the expression of nitrogen removal-related functional genes in the bioreactor system. This study highlights the superiority of microbial induced calcium precipitation (MICP) combined with PVA hydrogel, and provides a theoretical basis for simultaneous nitrogen and phosphate removal of wastewater.

Control of phosphorus release from sediment by hydrous zirconium oxide combined with calcite, bentonite and zeolite

This study investigated the effectiveness and mechanism for the control of internal phosphorus (P) liberation from sediment by hydrous zirconium oxide (HZrO₂) combined with calcite, bentonite and zeolite. The results suggested that coexisting calcite, calcium-modified bentonite (CaBT) and calcium-modified zeolite (CaZ) all had the ability to promote the adsorption of phosphate (PO₄^3-) onto HZrO₂. The mechanisms of PO₄^3- elimination by HZrO₂/calcite mixture involved the adsorption of PO₄^3- on calcite, the precipitation of PO₄^3- with Ca²⁺, and the inner-sphere complexation of PO₄^3- with HZrO₂. The amendment of sediment with HZrO₂/calcite, HZrO₂/CaBT or HZrO₂/CaZ mixture can effectively prevent the sedimentary P release, and the immobilization of mobile P in the sediment and the uptake of dissolved reactive P (DRP) from the interstitial water by the amendment material played a key role in the control of P release from sediment by the combined amendment. Capping sediment with HZrO₂/calcite, HZrO₂/CaBT or HZrO₂/CaZ mixture also can effectively intercept sediment P release, and the formation of P static layer attributed to the uptake of interstitial water DRP and DGT (diffusive gradient in thin-films)-unstable P in the upper sediment by the capping material was a key to the inhibition of sedimentary P migration into the overlying water by the combined capping. The great majority of P immobilized by the HZrO₂/calcite, HZrO₂/CaBT or HZrO₂/CaZ combined covering layer is stable P and it has a low re-releasing risk under dissolved oxygen-deficit and pH 5-9 condition. The stability of P bound by the combined covering layer was larger than that by the single HZrO₂ covering layer. The results of this research show that the combined use of HZrO₂ and calcite, HZrO₂ and CaBT, or HZrO₂ and CaZ as a capping material has great potential in the reduction of sediment P loading.

Adsorption kinetics and mechanism of atrazine on iron-modified algal residue biochar in the presence of soil

Atrazine has been widely used as an herbicide, and its harm has attracted more and more attention. In this study, magnetic algal residue biochar (MARB) was prepared from algae residue, a by-product of aquaculture, by ball milling it with ferric oxide to study the adsorption and removal of the triazine herbicide atrazine in a soil medium. The adsorption kinetics and isotherm results showed that atrazine removal by MARB reached 95.5% within 8 h at a concentration of 10 mg·L^-1, but the removal rate dropped to 78.4% in the soil medium. The pseudo-first- and pseudo-second-order kinetics and Langmuir isotherms best described atrazine adsorption on MARB. It is estimated that the maximum adsorption capacity of MARB can reach 10.63 mg·g^-1. The effects of pH, humic acids, and cations on the adsorption performance of MARB for atrazine were also studied. When pH was 3, the adsorption capacity of MARB was twice that of other pHs. Only in the presence of 50 mg·L^-1 HA and 0.1 mol·L^-1 NH₄⁺, Na, and K, the adsorption capacity of MARB to AT decreased by 8% and 13%, respectively. The results showed that MARB had a stable removal profile over a wide range of conditions. The adsorption mechanisms involved multiple interaction forms, among which the introduction of iron oxide promoted hydrogen bonding formation and π-π interactions by enriching -OH and -COO on the surface of MARB. Overall, the magnetic biochar prepared in this study can be used as an effective adsorbent to remove atrazine in complex environments and is ideal for algal biomass waste treatment and environmental governance.^+.

Ferrihydrite-loaded water hyacinth-derived biochar for efficient removal of glyphosate from aqueous solution

Ferrihydrite-loaded water hyacinth-derived biochar (FH/WHBC) was prepared by in-situ precipitation method to treat glyphosate-containing wastewater. The adsorption properties and mechanism, and actual application potential were deeply studied. Results showed that the adsorption performance of FH/WHBC was closely related with the precipitation pH condition, and the adsorbent prepared at pH 5.0 possessed the highest adsorption capacity of 116.8 mg/g for glyphosate. The isothermal and kinetic experiments showed that the adsorption of glyphosate was consistent with Langmuir model, and the adsorption process was rapid and could be achieved within 30 min. The prepared FH/WHBC was more suitable for application under high acidity environment, and could maintain the great adsorption performances in the presence of most co-existing ions. Besides, it also possessed a good regenerability. Under dynamic condition, the adsorption performance of FH/WHBC was not affected even at high flow rate and high glyphosate concentration. Furthermore, the FH/WHBC can keep excellent removal efficiency for glyphosate in wastewater treatment, and the concentration of glyphosate can be reduced to 0.06 mg·L^-1, which was lower than the groundwater quality of class II mandated in China. Fourier transform infrared (FTIR) spectroscopy and X-ray photoelectron spectroscopy (XPS) characterization indicated that the adsorption of glyphosate on FH/WHBC was mainly accomplished through electrostatic adsorption and the formation of inner-sphere complexes. In brief, the prepared sorbent FH/WHBC was expected to be used in the treatment of industrial glyphosate wastewater.

Adsorption performance of phosphate in water by mixed precursor base geopolymers

Design of low-cost and high-removal efficiency phosphate adsorbents is of great significance for the control of eutrophication. In this study, fly ash and metakaolin were used as raw materials to evaluate the capability of phosphate adsorption and to investigate the mechanism of phosphate adsorption. The results of comparing the adsorption effect of geopolymers prepared with different modulus of alkali activator showed that the removal efficiency of phosphate in water at 0.8 M was on average 30.33% higher than 1.2 M. Therefore, FA + MK-0.8 had the maximum removal efficiency of 94.21% for phosphate in water with the maximum adsorption capacity of 36.02 mg/kg. In addition, the adsorption of phosphate could be well fitted by pseudo-second-order model and the process was mainly controlled by film diffusion. The alkali activation process can destroy the octahedral structure of the raw material, so the geopolymer are mainly tetrahedral in structure. Interestingly, new zeolite structures were formed in the mineral crystal phase of FA + MK-0.8, which may facilitate the adsorption of phosphate by geopolymers. Furthermore, the combined FTIR and XRD analysis results indicated that the underlying mechanisms of phosphate adsorption were electrostatic gravitation, ligand exchange, and surface complexation. This research not only synthesizes low-cost and high removal efficiency wastewater purification materials, but also provides a promising application for the elimination and resource utilization of industrial solid waste.

Potential of Fatty Acid Methyl Ester as Diesel Blends Produced from Free Fatty Acid in Waste Cooking Oil Catalyzed by Montmorillonite-Sulfonated Carbon

This research, biodiesel production from waste cooking oil (WCO), was conducted using a montmorillonite-sulfonated carbon catalyst from molasses. The biodiesel product would be blended with diesel fuel with various volume variations to see its fuel properties. The catalyst was assessed by Fourier-transform infrared spectroscopy (FTIR), scanning electron microscope (SEM), N2 adsorption-desorption isotherm, and acidity analysis using the titration method. The effect of the weight ratio of montmorillonite to sulfonated carbon was also evaluated. The process of esterification reaction was optimized using the response surface methodology with a central composite design (RSM-CCD). The study showed that the weight ratio of montmorillonite to sulfonated carbon of 1:3 generated the highest acidity of 9.79 mmol/g with a prominent enhanced surface area and was further employed to optimize the esterification reaction. The optimum condition was obtained at a reaction temperature of 78.12°C, catalyst weight of 2.98 g, and reaction time of 118.27 with an FFA conversion of 74.101%. The optimum condition for the mixture of FAME and diesel fuel was achieved at the composition of the B20 blend, which met the FAME standard. The reusability study revealed that the catalyst had adequate stability at three consecutive runs, with a reduced performance was 18.60%. The reduction of FFA conversion was due to the leaching of the catalyst’s active site. This study disclosed that the FAME generated from the esterification of FFA on WCO-catalyzed montmorillonite-sulfonated carbon had a promising option as biodiesel blends for increasing the quality of commercial diesel.

Efficient Removal of Phosphate from Wastewater by a Novel Phyto-Graphene Composite Derived from Palm Byproducts

The increased demand for clean water especially in overpopulated countries is of great concern; thus, the development of eco-friendly and cost-effective techniques and materials that can remediate polluted water for possible reuse in agricultural purposes can offer a life-saving solution to improve human welfare, especially in view of climate change impacts. In the current study, the agricultural byproducts of palm trees have been used for the first time as a carbon source to produce graphene functionalized with ferrocene in a composite form to enhance its water treatment potential. Scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy, X-ray diffraction (XRD), ultraviolet-visible, Fourier transform infrared spectroscopy, zeta potential, thermogravimetric analysis, and Raman techniques have been used to characterize the produced materials. SEM investigations confirmed the formation of multiple sheets of the graphene composite. Data collected from the zeta potential revealed that graphene was supported with a negative surface charge that maintains its stability while XRD elucidated that graphene characteristic peaks were evident at 2θ = 22.4 and 22.08° using palm leaves and fibers, respectively. Batch adsorption experiments were conducted to find out the most suitable conditions to remove PO₄ ^3- from wastewater by applying different parameters, including pH, adsorbent dose, initial concentration, and time. Their effect on the adsorption process was also investigated. Results demonstrated that the best adsorption capacity was 58.93 mg/g (removal percentage: 78.57%) using graphene derived from palm fibers at 15 mg L^-1 initial concentration, pH = 3, dose = 10 mg, and 60 min contact time. Both linear and non-linear forms of kinetic and isotherm models were investigated. The adsorption process obeyed the pseudo-second-order kinetic model and was well fitted to the Langmuir isotherm.

Using ZrO2 coated sludge from drinking water treatment plant as a novel adsorbent for nitrate removal from contaminated water

This study aimed to produce a novel efficient absorbent using sludge generated from drinking water treatment plants (DWTPs) as a low-cost absorbent and applied to treat nitrate (NO₃^-) from contaminated water. Before the ZrO₂ coating experiment, the drinking water sludge (DWS) from DWTPs was pretreated by thermal treatment (80 °C, 200 °C, and 500 °C). After that, ZrO₂ coated drinking water sludge (DWS@ZrO₂) was produced by a simple precipitated reaction. The synthesized DWS@ZrO₂ was characterized by FTIR, SEM, and EDS with mapping analysis, XRD, and VSM. The results revealed that DWS@ZrO₂ could improve the pore filling in the adsorption experiment. The highest nitrate adsorption capacity was achieved (30.99 mg g^{- 1}) at pH 2 with DWS500@ZrO₂. Adsorption kinetics indicated that pyrolyzed DWS at 500 °C provided the highest nitrate adsorption capacity, followed by 200 °C, and 80 °C. Thermodynamic results showed that the obtained nitrate removal was an endothermic and spontaneous process. The possible nitrate adsorption mechanism of DWS@ZrO₂ could mainly involve pore filling, electrostatic interaction, and ligand exchange. The experimental results suggest that DWS@ZrO₂ is a feasible absorbent with high-efficiency, low-cost, high recyclability, and eco-friendly characteristics for treating nitrate in an aqueous solution.

Hydrocracking of crude palm oil to a biofuel using zirconium nitride and zirconium phosphide-modified bentonite

In this study, bentonite modified by zirconium nitride (ZrN) and zirconium phosphide (ZrP) catalysts was studied in the hydrocracking of crude palm oil to biofuels. The study demonstrated that bentonite was propitiously modified by ZrN and ZrP, as assessed by XRD, FTIR spectroscopy, and SEM-EDX analysis. The acidity of the bentonite catalyst was remarkably enhanced by ZrN and ZrP, and it showed an increased intensity in the Lewis acid and Brønsted acid sites, as presented by pyridine FTIR. In the hydrocracking application, the highest conversion was achieved by bentonite-ZrN at 8 mEq g⁻¹ catalyst loading of 87.93%, whereas bentonite-ZrP at 10 mEq g⁻¹ showed 86.04% conversion, which suggested that there was a strong positive correlation between the catalyst acidity and the conversion under a particular condition. The biofuel distribution fraction showed that both the catalysts produced a high bio-kerosene fraction, followed by bio-gasoline and oil fuel fractions. The reusability study revealed that both the catalysts had sufficient conversion stability of CPO through the hydrocracking reaction up to four consecutive runs with a low decrease in the catalyst activity. Overall, bentonite-ZrN dominantly favored the hydrocracking of CPO than bentonite-ZrP.

In this study, bentonite modified by zirconium nitride (ZrN) and zirconium phosphide (ZrP) catalysts was studied in the hydrocracking of crude palm oil to biofuels.

Recent developments in alginate-based adsorbents for removing phosphate ions from wastewater: a review

The huge development of the industrial sector has resulted in the release of large quantities of phosphate anions which adversely affect the environment, human health, and aquatic ecosystems. Naturally occurring biopolymers have attracted considerable attention as efficient adsorbents for phosphate anions due to their biocompatibility, biodegradability, environmentally-friendly nature, low-cost production, availability in nature, and ease of modification. Amongst them, alginate-based adsorbents are considered one of the most effective adsorbents for removing various types of pollutants from industrial wastewater. The presence of active COOH and OH^- groups along the alginate backbone facilitate its physical and chemical modifications and participate in various possible adsorption mechanisms of phosphate anions. Herein, we focus our attention on presenting a comprehensive overview of recent advances in phosphate removal by alginate-based adsorbents. Modification of alginate by various materials, including clays, magnetic materials, layered double hydroxides, carbon materials, and multivalent metals, is addressed. The adsorption potentials of these modified forms for removing phosphate anions, in addition to their adsorption mechanisms are clearly discussed. It is concluded that ion exchange, complexation, precipitation, Lewis acid-base interaction and electrostatic interaction are the most common adsorption mechanisms of phosphate removal by alginate-based adsorbents. Pseudo-2^nd order and Freundlich isotherms were figured out to be the major kinetic and isotherm models for the removal process of phosphate. The research findings revealed that some issues, including the high cost of production, leaching, and low efficiency of recyclability of alginate-based adsorbents still need to be resolved. Future trends that could inspire further studies to find the best solutions for removing phosphate anions from aquatic systems are also elaborated, such as the synthesis of magnetic-based alginate and various-shaped alginate nanocomposites that are capable of preventing the leaching of the active materials.

Chitosan based adsorbents for the removal of phosphate and nitrate: A critical review

The tremendous development in the industrial sector leads to discharging of the several types of effluents containing detrimental contaminants into water sources. Lately, the proliferation of toxic anions particularly phosphates and nitrates onto aquatic systems certainly depreciates the ecological system and causes a deadly serious problem. Chitosan (Cs) is one of the most auspicious biopolymer adsorbents that are being daily developed for removing of various contaminants from polluted water. This is due to its unparalleled benefits involving biocompatibility, non-toxicity, facile modifications and low-cost production. Nevertheless, chitosan displays considerable drawbacks including low adsorption capacity, low surface area and lack of reusability. Therefore, few findings have been established regarding the aptitude of modified chitosan-based adsorbents towards phosphate and nitrate anions. This review elaborates an overview for the current advances of modified chitosan based-adsorbent for phosphate and nitrate removal, in specific multivalent metals-modified chitosan, clays and zeolite-modified chitosan, magnetic chitosan and carbon materials-modified chitosan. The efforts that have been executed for enriching their adsorption characteristics as well as their possible adsorption mechanisms and reusability were well addressed. Besides, the research conclusions for the optimum adsorption conditions were also discussed, along with emphasizing the foremost research gaps and future potential trends that could motivate further research and innovation to find best solutions for water treatment problems facing the world.

Modification of bentonite clay & its applications: a review

Bentonite clay is one of the oldest clays that humankind has been using from ancient times as traditional habits and remedies. In recent years researchers have found many applications of bentonite clay due to its various physio-chemical properties. In the present work, various physical and chemical properties of bentonite such as surface area, adsorption, swelling properties, cation exchange properties, etc. have been studied. This study also includes various procedures of modification of bentonite clay into Chitosan/Ag-bentonite composite, Fe-Modified bentonite, Hydroxyl-Fe-pillared-bentonite, Organo Bentonite, Organophilic clay, Arenesulfonic Acid-Functionalized Bentonite, Bentonite clay modified with Nb2O5. The study reveals that bentonite clay has large surface area due to similar structure with montmorillonite and it is found that the functionality of bentonite can be increased by increasing total surface area of the clay. Due to high cation exchangeability of bentonite, various cations can be incorporated into it. After purification and modification, the absorbent aluminum phyllosilicate bentonite clay can be used as an efficient catalyst in various types of catalytic reactions. Moreover, bentonite clay can be applied in various field like drilling, civil engineering, agriculture and water treatment.

Seasonal variations of polycyclic aromatic hydrocarbons in coastal sediments of a marine resource hot spot: the case of pars special economic energy zone, Iran

Polycyclic aromatic hydrocarbons (PAHs) are an important group of compounds of major environmental concern, which are in the class of persistent organic pollutants. Therefore, the key purpose of this research was to analyze seasonal fluctuations and to determine the probability of polycyclic aromatic hydrocarbons in coastal sediments of the Iranian Marine Resource Center based on the evaluation of 16 US-EPA important PAH compounds. These compounds have been collected from intertidal sediments located in the marine resources of southern Iran in different seasons. These samples of the surficial sediment were collected at the PSEEZ area using a stainless steel grab sampler in four seasons, from depths between 0.5 and 30 m. Surface sediment samples were removed by spoons and carefully placed in an aluminum foil; they were taken to the laboratory on ice and held at 20° C until their study. After extraction, by using a rotary evaporator apparatus, samples were condensed. The assay was added to roughly 2 g of activated copper flasks in the refrigerator for 36 h for desulfurization. Among different seasons, the highest concentration was observed in winter, with a mean of 281.3 ng g^-1. According to ecological risk assessment (concentrations of possible effects, low effect range, degree of threshold effects, and median effect range), PAH risks in surface sediments of PSEEZ were lower than the threshold results levels (TEL), possible effects levels (PEL), low range of effects (ERL), and median range of effects (ERM), indicating that a biological effect would rarely occur. The dry weight scale of the concentration of ∑PAHs ranges from 145.7 to 348.42 ng g^-1 with a mean quantity of 260.52 ng g^-1. Therefore, according to the amount of ∑PAH concentration, the sediments in the PSEEZ area indicated moderate to heavy pollutions. In this way, the sedimentary surface ecosystems of the Persian Gulf were considered as moderately polluted compared with other ecosystems worldwide. Our study highlighted some of the research gaps in PAH contamination studies and the level of PAH contamination. Therefore, this study will provide a scientific background, planning, and policies for PAH pollution control and environmental protection in Iran and similar regions around the world.

Exploiting the Different Parameters on the Adsorption of Phosphate Ions and Its Subsequent Recovery Using Complex Nickel-Aluminum-Zirconium Hydroxide

In this study, the effect of contact time, temperature, pH, and coexistences on the adsorption of phosphate ions using the complex nickel-aluminum-zirconium hydroxide (NAZ) was evaluated. Moreover, the recovery of adsorbed phosphate ions from NAZ using desorption solution with different concentrations was demonstrated. The results showed that the quantity of phosphate ions adsorbed gradually increased with time, and the adsorption equilibrium was achieved within 24 h after adsorption. This kinetic data could be well described by the pseudo-second-order model with the correlation coefficient in the value of 0.997. Additionally, the quantity of phosphate which was adsorbed increased as temperature increased, and these results corresponded well with both the Langmuir, the correlation coefficient ranged from 0.920-0.949, and Freundlich models, the correlation coefficient ranged from 0.863-0.995. These results showed that the adsorption of phosphate ion was monolayer adsorption onto the NAZ surface. The optimal pH for removal of phosphate ions from aqueous media was during 4-8. In addition, chloride, nitrate, and sulfate ions did not significantly affect to the adsorption capability of phosphate ions in the complex solution system. Finally, the phosphate ions which were adsorbed onto NAZ could be recovered using sodium sulfate solution (recovery percentage: approx. 50% using sodium sulfate solution at 1000 mmol/L). These results highlight the potential of using NAZ as the cost-effectiveness adsorbent for phosphate ions removal from aqueous media.

Enhanced removal of arsenic from water by using sub-10 nm hydrated zirconium oxides confined inside gel-type anion exchanger

Given high selectivity and excellent stability, zirconium oxides are very promising in selective removal of arsenic, fluorine, and phosphorus from water. Nevertheless, it remains challenging to prepare sub-10 nm zirconium oxides of ultra-high adsorptive reactivity. Herein, we prepared hydrated zirconium oxides (HZO) of 4.88 ± 1.02 nm by conducting in-situ precipitation of nanoparticles (NPs) inside the gel-type anion exchanger (GAE). GAE was swollen in water and contained lots of < 10 nm swollen pores, restricting excess growth of HZO NPs. In comparison, the NPs formed inside the macroporous anion exchanger (MAE) possessed an average diameter of 30.91 ± 8.98 nm. XPS O1s analysis indicated that the oxygen sites in the gel-type nanocomposite (HZO@GAE) possessed a much higher proportion (48.9%) of reactive terminal oxygen (-OH) than the macroporous nanocomposite (HZO@MAE, 21.2%). Thus, HZO@GAE exhibited significantly enhanced adsorption reactivity toward As(V)/As(III) than HZO@MAE. The exhausted HZO@GAE could be fully regenerated by alkali treatment for repeated use without any loss in decontamination efficiency. In column assays, the HZO@GAE column successively produced ~2400 bed volume (BV) clean water ([As]<10 μg/L) from synthetic groundwater, exceeding twice the amount produced by the HZO@MAE column. This study may shed new light on developing highly efficient nanocomposites for water decontamination.

Synthesis and characterization of tannic acid pillared bentonite composite for the efficient adsorption of aflatoxins

Tannic acid (TA) is a hydrolysable polyphenol with established antioxidant and antibacterial activity along with its tendency to bind both organic and inorganic ions/molecules. In the present study, the sequestration performance of TA pillared bentonite for various aflatoxins (AFs) including AFB1, AFB2, AFG1 and AFG2 from aqueous solutions and simulated poultry gastrointestinal model solution was studied via adsorption. The adsorbents were characterized by scanning electron microscopy (SEM), energy dispersive X-ray (EDX) analysis, Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), N₂ adsorption-desorption study and X-ray photoelectron spectroscopy (XPS). The reaction conditions including pH, agitation time, initial toxin concentration and temperature were systematically optimized. The Langmuir adsorption capacity of the adsorbent reached to 86, 71, 74 and 149 mg/g for AFB1, AFB2, AFG1 and AFG2 respectively. Adsorption kinetics and thermodynamic studies showed rapid AFs uptake and the exothermicity of the adsorption reaction respectively. Simultaneous removal of AFs by BTA3 revealed their independent and uninterrupted adsorption and the adsorption mechanism of AFs over BTA3 was elaborated with the help of XPS results. The outstanding AFs sequestering capability of BTA3 in aqueous solution and simulated poultry gastrointestinal model can be envisioned of great promise for the remediation of AFs and other hazardous pollutants from food and poultry industrial products.

Adsorptive Removal of Phosphate from Aqueous Solutions Using Low-Cost Volcanic Rocks: Kinetics and Equilibrium Approaches

The contamination of surface and groundwater with phosphate originating from industrial and household wastewater remains a serious environmental issue in low-income countries. Herein, phosphate removal from aqueous solutions was studied using low-cost volcanic rocks such as pumice (VPum) and scoria (VSco), obtained from the Ethiopian Great Rift Valley. Batch adsorption experiments were conducted using phosphate solutions with concentrations of 0.5 to 25 mg·L⁻¹ to examine the adsorption kinetic as well as equilibrium conditions. The experimental adsorption data were tested by employing various equilibrium adsorption models, and the Freundlich and Dubinin-Radushkevich (D-R) isotherms best depicted the observations. The maximum phosphate adsorption capacities of VPum and VSco were calculated and found to be 294 mg·kg⁻¹ and 169 mg·kg⁻¹, respectively. A pseudo-second-order kinetic model best described the experimental data with a coefficient of correlation of R² > 0.99 for both VPum and VSco; however, VPum showed a slightly better selectivity for phosphate removal than VSco. The presence of competitive anions markedly reduced the removal efficiency of phosphate from the aqueous solution. The adsorptive removal of phosphate was affected by competitive anions in the order: HCO₃⁻ >F⁻ > SO₄⁻² > NO₃⁻ > Cl⁻ for VPum and HCO₃⁻ > F⁻ > Cl⁻ > SO₄⁻² > NO₃⁻ for VSco. The results indicate that the readily available volcanic rocks have a good adsorptive capacity for phosphate and shall be considered in future studies as test materials for phosphate removal from water in technical-scale experiments.

Zirconium-modified natural clays for phosphate removal: Effect of clay minerals

Excessive amount of phosphate entering water bodies may cause eutrophication and have detrimental effects on ecosystems. Clay-based materials have been drawing attractive attention in mitigating phosphate release to aquatic environment. In this study, we prepared a series of zirconium (Zr)-modified clays to investigate the effect of clay structure and expansion property on phosphate adsorption. Kaolinite, montmorillonite, and vermiculite were selected as three representative natural clays for Zr modification, and the resulting Zr-modified clays were characterized using various techniques that included powder X-ray diffraction, scanning electron microscopy, and zeta potential measurement. Different Zr-modified clays exhibited substantially different phosphate adsorption behaviors, which may be related to the distinct structural and expansion properties of each clay substrate. Particularly, Zr-modified montmorillonite had fastest phosphate adsorption kinetics and highest phosphate adsorption capacity among all Zr-modified clays, which may be attributed to the good expansion property of montmorillonite that favored the uniform intercalation of Zr species, making the adsorption sites easily accessible by phosphate. Furthermore, all Zr-modified clays showed robust performance for phosphate adsorption under various water chemistry conditions. Combined aqueous sorption and solid characterization analyses suggested that formation of inner-sphere surface complexes may be the primary mechanism for phosphate adsorption by Zr-modified clays.

Studies on the performance of bentonite and its composite as phosphate adsorbent and phosphate supplementation for plant

Organo-bentonite (OrB) was prepared by modifying bentonite with chitosan, and natural surfactant extracted from Sapindus rarak fruit. The physical alteration post-modification, performance of phosphates (Pi) adsorption, and possibility as a Pi-supplementation for plants of OrB were assessed and compared to acid-activated bentonite (AAB). The physical alteration due to modification of bentonite was characterized. SEM images were not indicating significant morphology differences between OrB and AAB. Existence of chitosan layers in OrB causes a decrease in basal spacing as characterized using XRD. The BET surface area of OrB was decreased compared to AAB due to pore coverage by chitosan. Adsorption studies reveal that OrB has a higher adsorption capacity towards Pi than AAB, which is 97.608 and 131.685 mg/g at 323 K for AAB and OrB, respectively. The H-shape isotherm curve indicates that chemisorption is dominantly controlling the adsorption. The isotherm and kinetics adsorption were well fitted to Langmuir and Pseudo-second order models, respectively. Performance of AAB and OrB as Pi-supplementation was assessed based on growth phenotypes of Arabidopsis thaliana; seedlings show that supplementation of Pi@AAB and Pi@OrB (at half doses) can promote primary root extension. These results also demonstrate the safety of direct disposal of the materials into the soil.

Increasing phosphate sorption on barium slag by adding phosphogypsum for non-hazardous treatment

Barium slag (BS) is a waste residue in the barium salt industrial procedure. Due to its high leaching concentration of Ba²⁺, BS is classified as a kind of hazardous waste. Industrial waste phosphogypsum (PG) is effective to immobilize barium ion in BS owing to the slightly soluble sulfate included. In this study, two different proportions of PG were selected for mixing with BS to solidify soluble barium ion. The non-hazardous BS samples treated with the proportions of PG (BS-PG1, BS-PG3) were then functionally used for phosphate removal in solution. Batch experiments for removal of phosphate were performed to evaluate the adsorption efficiency of BS-PG1 and BS-PG3. The effect of various factors such as contact time, initial pH, and reaction temperature on sorption performance was investigated. BS-PG1 and BS-PG3 reached adsorption equilibrium in approximately 3h at the initial concentration of 15 mg/L, and BS-PG1 exhibited adsorption capacity of 12.47 mg P/g, higher than that of BS (11.49 mg P/g) under the condition of solid:liquid, 1g:1L, 25 °C, natural pH. The results show that the adsorption processes of phosphates ions onto both BS-PG1 and BS-PG3 fitted well with the pseudo-second-order kinetic model. The Langmuir isothermal model was considered as the appropriate equation for experimental data, showing a maximum adsorption capacity for phosphate up to 13.67 mg P/g and 11.59 mg P/g for BS-PG1 and BS-PG3. In comparison with other adsorbents, BS-PG1 and BS-PG3 could be considered as efficient materials for the removal of phosphate.

Biochar-loaded Ce3+-enriched ultra-fine ceria nanoparticles for phosphate adsorption

Biochar-loaded Ce³⁺-enriched ultra-fine ceria nanoparticles (Ce-BC) was prepared by a facile impregnation-precipitation-pyrolysis process and applied as adsorbents to adsorb phosphate from water. The crystal size of ceria nanoparticles in the Ce-BC was as small as 2-5 nm and the concentration of Ce³⁺ was high to 59.6 %, which was benefited from the rapid precipitation, N₂ pyrolysis atmosphere and the presence of the biochar during preparation. Ce-BC exhibited a fast adsorption kinetics for phosphate and the adsorption equilibrium could be reached within 10 min. The maximum phosphate adsorption capacity was up to 77.7 mg P g^-1 at pH 3.0. Based on Fourier transform infrared (FTIR), X-ray powder diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM) and X-ray photoelectron spectroscopy (XPS) analysis, Ce³⁺ of ceria was demonstrated playing the vital role on phosphate removal and the formation of CePO₄ nanocrystals was the main adsorption mechanism. This work provides a facile strategy for preparing high Ce³⁺ contenting materials and shows a great potential application for the phosphate removal for its high-effective and high stability.

Novel, recyclable active capping systems using fabric-wrapped zirconium-modified magnetite/bentonite composite for sedimentary phosphorus release control

A zirconium-modified magnetite/bentonite composite (M-ZrFeBT) was synthesized, characterized and combined with water-permeable fabric to construct novel, recyclable active capping systems for sedimentary phosphorus (P) release control. Three fabric-wrapped M-ZrFeBT capping devices with different shapes were designed, i.e., CAP-1, CAP-2 and CAP-3, and they are disc-shaped, cuboid-shaped and spindle-shaped capping devices, respectively. The behavior and mechanism for phosphate adsorption onto M-ZrFeBT was studied. The impact of CAP-1, CAP-2 and CAP-3 capping on the mobilization of P in sediments was investigated. The results showed that M-ZrFeBT possessed good phosphate adsorption ability, with a largest monolayer adsorption capacity of 8.02 mg P/g. The replacement of Fe/Zr bound hydroxyl groups with phosphate through ligand-exchange reactions to generate the inner-sphere Fe-O-P and Zr-O-P bonding played a key part in the uptake of phosphate from water by M-ZrFeBT. Sediment capping with fabric-wrapped M-ZrFeBT not only brought about a significant decline in the concentrations of soluble reactive P (SRP) and DGT (diffusive gradient in thin films)-labile P (LP_DGT) in the overlying water, but also gave rise to the diminished SRP and LP_DGT concentrations in the upper sediment. Most (96.5%-98.2%) of P bound by the M-ZrFeBT in the capping layers was in the form of NaOH extractable inorganic P, HCl-extractable P and residual P, which were considered to be hard to be released back into the water column under common pH and oxygen-deficient conditions. The reduction of pore water SRP and LP_DGT in the upper sediment layer induced by the adsorption of SRP on the M-ZrFeBT-based capping layer played a key part in the interception of SRP liberation from the sediment solid into the overlying water. Results indicate that fabric-wrapped M-ZrFeBT capping is promising for controlling the internal P loading from sediments in shallow freshwater bodies.

Surface Modification of Bentonite with Polymer Brushes and Its Application as an Efficient Adsorbent for the Removal of Hazardous Dye Orange I

Poly(2-(dimethylamino)ethyl methacrylate)-grafted bentonite, marked as Bent-PDMAEMA, was designed and prepared by a surface-initiated atom transfer radical polymerization method for the first time in this study. Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), scanning electron microscopy (SEM) and thermal gravimetric analysis (TGA) were applied to characterize the structure of Bent-PDMAEMA, which resulted in the successful synthesis of Bent-PDMAEMA. As a cationic adsorbent, the designed Bent-PDMAEMA was used to remove dye Orange I from wastewater. The adsorption property of Bent-PDMAEMA for Orange I dye was investigated under different experimental conditions, such as solution pH, initial dye concentration, contact time and temperature. Under the optimum conditions, the adsorption amount of Bent-PDMAEMA for Orange I dye could reach 700 mg·g-1, indicating the potential application of Bent-PDMAEMA for anionic dyes in the treatment of wastewater. Moreover, the experimental data fitted well with the Langmuir model. The adsorption process obeyed pseudo-second-order kinetic process mechanism.

Fe(III)-polyhydroxy cations supported onto K10 montmorillonite for removal of phosphate from waters

Since phosphate is strongly related to eutrophication of environmental waters, several research groups quest for materials that can efficiently remove phosphate from wastewaters before it contaminates lakes and reservoirs. In the present work, a commercial clay mineral (K10 montmorillonite) modified with Fe³⁺ polyhydroxy cations was investigated as an adsorbent for phosphate. The incorporation of the polycations did not alter the main conformational characteristics of the montmorillonite, as verified by specific surface area measurements, X-ray diffractometry, FTIR, electron microscopy, and zeta potential titrations. On the other hand, the materials supporting Fe³⁺ polyhydroxy cations exhibited a significant enhancement of adsorption capacity, as determined by Langmuir-Freundlich isotherms, from 39 ± 2 to 104 ± 15 μmol g⁻¹. The different ratios of OH⁻ to Fe³⁺ did not affect the adsorption capacities. The adsorption kinetics was best described by the pseudo 2^nd order model, approaching the equilibrium after 120 min of contact time. A variation of pH between 4.6 and 8.5 did not affect the adsorption percentages. The adsorption capacities increased with the increase of the ionic strength, thus suggesting that the formation of inner-sphere complexes prevails over electrostatic interactions as the adsorption mechanism. The materials removed phosphate from three polluted water samples having phosphate concentrations between 0.0919 and 1.211 mg L⁻¹. The remaining phosphate concentration was below the limit of quantification of the analytical method (0.063 mg L⁻¹ in P, or 2.0 μmol L⁻¹). The presence of 10 mg L⁻¹ humic of fulvic acid did not affect the performance of the materials. In conclusion, the modification of clay minerals with Fe³⁺ polyhydroxy cations is useful in producing low-cost adsorbents for phosphate.

Removal of phosphate from wastewater by modified bentonite entrapped in Ca-alginate beads

Methods of removing phosphate from wastewater with a low phosphate concentration are of great environmental significance. In this study, immobilized beads were prepared by entrapping modified bentonite powder in calcium-alginate (Al-NaBT-CA), and the potential of the beads for phosphate removal from wastewater was investigated. The effects of pH (1-10) and initial phosphate concentration (0.5-50 mg/L) were also examined in batch experiments with Al-NaBT-CA beads. The optimum pH value for phosphate removal by Al-NaBT-CA beads was pH 3. In addition, a high initial phosphate concentration promoted phosphate adsorption. Adsorption kinetics showed that the adsorption of phosphate using beads followed a pseudo-second-order kinetic model (R² = 0.98-0.99). The adsorption isotherm data was well fitted by the Sips adsorption model. The maximum phosphate adsorption capacity of the Al-NaBT-CA beads was 15.77 mg/g, which was slightly less than that of the modified powder. The specific surface area of the Al-NaBT-CA beads was 17.01 m²/g, and their average pore size was 13.41 nm. Scanning electron microscopy suggested that the high inner porosity and rough outer surface of the beads facilitated phosphate transfer.

Impact of application mode on the control of phosphorus release from sediments using zirconium-modified bentonite as geo-engineering material

In this study, the influence of zirconium-modified bentonite (ZMBT) addition, capping, and addition/capping on the transport and transformation of phosphorus (P) in sediments were comparatively investigated using incubation experiments to determine the effect of ZMBT application mode on the controlling efficiency. Results showed that the release of soluble reactive P (SRP) from sediment to the overlying water was effectively intercepted by all the ZMBT treatments. The inactivation of pore-water SRP, diffusive gradients in thin films-labile P (DGT-LP) and mobile P (Mob-IP) in sediment played a pivotal role in the regulation of SRP liberation from the sediment to the overlying water by ZMBT. An application mode change from capping and addition/capping to addition resulted in a decline of the reduction efficiency of overlying water SRP by the ZMBT treatment to some extent. The variation in the reduction efficiency of pore-water SRP and DGT-LP in the uppermost sediment were responsible for the change of the reduction efficiency of overlying water SRP by the ZMBT treatment. A change in application mode from capping to addition/capping and addition caused an obvious increase in the immobilization efficiency of pore-water SRP, DGT-LP and Mob-IP in the lower sediment by the ZMBT treatment. Results of this work indicate that, when the ZMBT capping layer on the top of sediment was completely mixed with the sediment, although the stability of P in the lower sediment obviously increases, the controlling efficiency of SRP liberating from the sediment to the overlying water decreases to some extent. Thus, the repeated addition of ZMBT to form a covering layer on the ZMBT-amended sediment is very necessary for the effective control of sediment-P release to the overlying water.

Improvement of Ultrafiltration for Treatment of Phosphorus-Containing Water by a Lanthanum-Modified Aminated Polyacrylonitrile Membrane

Phosphorus contamination in fresh water has posed a great risk to aquatic ecosystems and human health due to extensive eutrophication. In this paper, we are reporting a lanthanum (La)-modified aminated polyacrylonitrile (PAN) adsorptive membrane for effective decontamination of phosphorus from the simulated water. The PAN membrane was first aminated to introduce the amine group as an active site for La and then followed by the in situ precipitation of La particles. The kinetics study showed that the rapid adsorption occurred within the initial 4 h with the equilibrium established at 8 h. The membrane worked well in the acidic pH region, with optimal pH 4 and 5 without and with the pH control, respectively. The maximum adsorption capacities were 50 and 44.64 mg/g at pH 5 and 7, respectively. The adsorption of phosphorus was not affected by the existence of commonly existing anions except fluorides in water. In the filtration study, it was observed that the removal of phosphorus remained the optimum, although the operating pressure was increased from 1 to 3 bar. The modified membrane was able to treat 0.32 L of a 10 mg/L phosphate solution to meet the maximum allowable limit of 0.15 mg/L for the trade effluent. The mechanism study revealed that the removal was primarily associated with the ion exchange between a phosphorus ion and a hydroxyl group from the La particles.

Evaluation of phosphate adsorption on zirconium/magnesium-modified bentonite

In this work, a zirconium/magnesium-modified bentonite (ZrMgBT) was prepared and characterized by SEM, EDS, XRD and pH_PZC. The performance and mechanism of phosphate adsorption onto ZrMgBT was evaluated in detail using batch experiments and ³¹P NMR. Results showed the adsorption isotherm data were well described by the Langmuir, Freundlich and Dubinin-Radushkevich models, and the kinetic data fitted better to the pseudo-second-order kinetic model than the pseudo-first-order kinetic model. The phosphate adsorption capacity of ZrMgBT was slightly affected by the presence of Na⁺, K⁺, Cl^-, [Formula: see text] and [Formula: see text], but it was enhanced by coexisting Mg²⁺ and [Formula: see text]. The mechanism for phosphate adsorption onto ZrMgBT at pH 7 was mainly the complexation reaction between phosphate and zirconium. In addition, ZrMgBT exhibited more excellent adherence to phosphate than zirconium-modified bentonite (ZrBT). Especially, the maximum monolayer phosphate adsorption capacity for ZrMgBT at pH 7 and 0.5 g/L of adsorbent dosage calculated based on the Langmuir isotherm model (13.0 mg P/g) was 67.5% higher than that for ZrBT. The higher phosphate adsorption capacity for ZrMgBT than ZrBT could be attributed to the higher specific surface area as well as higher Mg²⁺ releasing ability of the former. The enhancement of phosphate adsorption by the release of Mg²⁺ from ZrMgBT could be mainly due to the formation of [Formula: see text] in the solution firstly and then the adsorption of [Formula: see text] on ZrMgBT forming ≡Zr(OPO₃H)Mg on the ZrMgBT surface. In general, we conclude that ZrMgBT is a more promising adsorbent for phosphate removal from aqueous solution than ZrBT.

Municipal solid waste biochar-bentonite composite for the removal of antibiotic ciprofloxacin from aqueous media

This study investigates the adsorption of ciprofloxacin (CPX) onto a municipal solid waste derived biochar (MSW-BC) and a composite material developed by combining the biochar with bentonite clay. A bentonite-MSW slurry was first prepared at 1:5 ratio (w/w), and then pyrolyzed at 450 °C for 30 min. The composite was characterized by scanning electron microscopy (SEM), Powder X-ray diffraction (PXRD) and Fourier transform infrared (FTIR) spectroscopy before and after CPX adsorption. Batch experiments were conducted to assess the effect of pH, reaction time and adsorbate dosage. The SEM images confirmed successful modification of the biochar with bentonite showing plate like structures. The PXRD patterns showed changes in the crystalline lattice of both MSW-BC and the composite before and after CPX adsorption whereas the FTIR spectra indicated merging and widening of specific bands after CPX adsorption. The optimum CPX adsorption was achieved at pH 6, and the maximum adsorption capacity of the composite calculated via isotherm modeling was 190 mg/g, which was about 40% higher than the pristine MSW-BC. The Hill isotherm model along with pseudo-second order and Elovich kinetic models showed the best fit to the adsorption data. The most plausible mechanism for increased adsorption capacity is the increased active sites of the composites for CPX adsorption through induced electrostatic interactions between the functional groups of the composite and CPX molecules. The added reactive surfaces in the composite because of bentonite incorporation, and the intercalation of CPX in the clay interlayers improved the adsorption of CPX by the biochar-bentonite composite compared to the pristine biochar. Thus, MSW-BC-bentonite composites could be considered as a potential material for remediating pharmaceuticals in aqueous media.

Insights into the phosphate adsorption behavior onto 3D self-assembled cellulose/graphene hybrid nanomaterials embedded with bimetallic hydroxides

3D self-assembled cellulose/graphene hybrids (3D cell/GO hybrids) were used as the host for encapsulating the Zr and La hydroxides, forming the Zr/La-cell/GO hybrids. After phosphate adsorption, the crystallization peaks of LaPO₄·xH₂O in saturated Zr/La-cell/GO hybrids were observed and they were reduced with the increase in pHs. Especially, a low crystallization was observed at pH 10.0 as compared with those at pH 3.0 and 6.0; this also corresponded well to the varied adsorption capacity as a function of pHs. The increased humic acid (HA) amounts (150 mg/L) only resulted in a low capacity loss (16.3%) in phosphate uptake from 25.3 to 21.2 mg/g. A noticeable La leach (2.1 mg/L) was observed at the HA level of 150 mg/L but no Zr leach was detected, and therefore, complexation of La with HA seemed a potential explanation for the increased La leaching. The interference of different coexisting anions on phosphate uptake followed the order as F^- > SiO₃^2- > HCO₃^- > SO₄^2- > NO₃^- > Cl^-. Phosphate uptake by Zr/La-cell/GO hybrids was significantly reduced at the co-existing fluoride partially due to the stronger electro-negativity of fluoride to combine with the protonated Zr/La hydroxides. In addition, Ca²⁺ laden on the Zr/La-cell/GO hybrids significantly enhanced the adsorption of phosphate by Zr/La-cell/GG hybrids due to the formation of calcium phosphate precipitation in framework of Zr/La-cell/GG hybrids.

Assessment of sediment capping with zirconium-modified bentonite to intercept phosphorus release from sediments

Three different types of zirconium-modified bentonites (ZrMBs) including zirconium-modified original bentonite (ZrMOB), zirconium-modified magnesium-pretreated bentonite (ZrMMgB), and zirconium-modified calcium-pretreated bentonite (ZrMCaB) were synthesized and used as active covering materials to suppress the release of phosphorus (P) from sediments. To assess the covering efficiency of ZrMBs to inhibit P release from sediments, we examined the impact of ZrMB covering layer on P mobilization in sediments at different depths as well as the release of P through the interface between sediment and overlying water (SWI) by use of simulating P release control experiments and diffusive gradients in thin films (DGT) technology. The results showed that the amount of soluble reactive P (SRP) in the overlying water greatly decreased after covering with ZrMBs. Moreover, both pore water SRP and DGT-liable P (DGT-P) in the top sediments decreased after capping with ZrMBs. An obvious stratification of DGT-P was observed along the vertical direction after covering with ZrMBs, and static and active layers were found in the top sediment and in the lower sediment directly below the static layer, respectively. Furthermore, ZrMB covering led to the change of P species from easily released P to relatively or very stable P, making P in the top sediment more stable compared to that without ZrMB covering. Besides, an overwhelming majority of P immobilized by ZrMBs is hard to be re-released into the water column in a common environment. Overall, the above results demonstrate that sediment covering with ZrMBs could effectively prevent the transport of SRP from sediments into the overlying water through the SWI, and the control of P transport into the overlying water by ZrMB covering could be mostly due to the immobilization of pore water SRP, DGT-P, and mobile P in the top sediment by ZrMBs.

New insight of tertiary-amine modified bentonite amendment on the nitrogen transformation and volatile fatty acids during the chicken manure composting

In this study, the main objective was to investigate the potential effect of tertiary-amine modified bentonite (TAMB) on the nitrogen transformation and the volatile fatty acids (VFAs) degradation during the chicken manure (CM) composting. Six dosages of TAMB (0%, 2%, 4%, 6%, 8% and 10%) were amended into the mixture of CM and wheat straw and then composted for 50 days. The results revealed the TAMB amendment could prolong the thermophilic phase and enhance the organic matter (OM) degradation. With the increasing dosage of TAMB, the ammonia volatilization was reduced by 15.41%-65.35%. Meanwhile, the TAMB addition had a positive effect on VFAs degradation and reducing odor unit_MAX (OU_MAX) by 17.61%-59.24%. Moreover, CH₄ was reduced by 12.15%-32.78% in TAMB applied treatments compared to control. Finally, combined with all results, it indicated that TAMB amendment could reduce VFAs, CH₄ emission and nitrogen loss to improve the compost quality.