Adsorption of tannic acid from aqueous solution onto surfactant-modified zeolite

From Waste to Water Purification: Textile-Derived Sorbents for Pharmaceutical Removal

The presence of pharmaceuticals or their active metabolites in receiving waters is a sign of the inefficient removal of bioactive substrates from wastewater. Adsorption seems to be the most effective and inexpensive method of their removal. Waste management aimed at sorbents is a promising way to sustain several sustainable development goals. In the presented paper, the removal of the two most widely used drugs in the wastewater was examined. Diclofenac and carbamazepine were removed from water and wastewater using textile waste-derived sorbents. Their removal efficiency was verified by testing several process parameters such as the time of the sorption, the presence of interfering inorganic ions, the presence of dissolved organic matter, the initial pH and ionic strength of the solution, and various water matrices. The adsorption capacity was noted for diclofenac (57.1 mg/g) and carbamazepine (21.25 mg/g). The tested process parameters (pH, presence of inorganic ions, dissolved organic matter, ionic strength, water matrix) confirmed that the presented waste materials possessed a great potential for pharmaceutical removal from water matrices.

Preparation of nanocellulose light porous material adsorbed with tannic acid and its application in fresh-keeping pad

This study fabricated nanocellulose lightweight porous material (TOCNF-G-LPM-TA) as absorbent fresh-keeping pad for meat products, using TEMPO-oxidized cellulose nanofibril (TOCNF) and gelatin as structural skeleton and tannic acid (TA) as antibacterial component of TOCNF lightweight porous material (TOCNF-G-LPM). The adsorption kinetics, capacity and mechanism of TOCNF-G-LPM in different initial concentrations of TA solutions were investigated, the antioxidant and antibacterial properties of TOCNF-G-LPM-TA and its fresh-keeping effect on refrigerated pork at 4 ℃ were studied. Due to strong hydrogen bonding and porous structure, TOCNF-G-LPM exhibited excellent TA adsorption ability (230 mg/g) conforming with pseudo-second-order kinetic and Langmuir isotherm models. TA endowed TOCNF-G-LPM with good antioxidant and antibacterial activities. According to changes in appearance, pH and TVB-N values of pork during storage at 4 ℃, TOCNF-G-LPM-TA effectively extended the shelf life of refrigerated pork. This work provides a facile method for preparing nanocellulose based absorbent fresh-keeping pads.

Zeolite-supported manganese oxides decrease the Cd uptake of wheat plants in Cd-contaminated weakly alkaline arable soils

Cd pollution in arable soils has posed serious threats to food safety and human health. Mn oxides and Mn oxide-based materials have been widely applied to the removal of heavy metals for their high adsorption capacity, especially in water treatment. However, the performance and stability of Mn oxide-based materials and the underlying mechanism of Cd immobilization in upland soils remain unclear. Here, zeolite-supported Mn oxides were used as amendment to investigate their impact on the availability of soil Cd in wheat pot experiments. The decrease in soil available Cd content (by 44.3%) and increase in soil available Mn content (by 61.9%) significantly inhibited Cd accumulation in wheat plant tissues under the application of zeolite-supported Mn oxides. The exchangeable Cd was transformed to more stable fractionation of Fe-Mn oxide bound Cd, and the maximum decrease of Cd content in wheat grains, straw and roots reached 65.0%, 11.7% and 55.3%, respectively. Besides, zeolite-supported Mn oxides exhibited high chemical stability and stable Cd immobilization performance in two successive years of wheat pot experiments. These findings improve our understanding of Mn oxide-based materials for soil remediation and indicate that zeolite-supported Mn oxides have great potential for the remediation of Cd-contaminated alkaline upland soils.

Sewage sludge and solid residues from biogas production derived biochar as an effective bio-waste adsorbent of fulvic acids from water or wastewater

Due to environmental concern, direct utilization of sewage sludge or residues from biogas production is restricted. Conversion of problematic bio-wastes into biochars can be a very effective solution. In the presented study, the adsorption of fulvic acids onto series of biochars produced from bio-wastes such as sewage sludge, residues from biogas production, and plant (Miscanthus sp.) were performed to examine the behavior of biochars in the environment and interactions with fulvic acids as the representatives of dissolved organic matter. The results clearly indicate that the highest excess of fulvic acids, 93-96 mg g^-1, was chemisorbed onto biochar obtained specifically from sewage sludge. The mechanism of the adsorption was independent from applied biochar feedstock. Monolayer coverage was dominant onto all biochars. Generally, adsorption was assumed to be controlled by polar interactions between fulvic acids and the biochars or pre-adsorbed and residual fulvic acids molecules (which were dominant) and the strong π-π interactions. The obtained high values of the adsorption capacity of sewage sludge derived biochars confirmed that thermal treatment is a very effective tool of bio-waste management.

Insights into the adsorption mechanism of tannic acid by a green synthesized nano-hydroxyapatite and its effect on aqueous Cu(II) removal

The polyphenolic tannic acid (TA) has been widely used in the stabilization and surface modification of nanomaterials. The interaction mechanism of TA with the biogenic nano-hydroxyapatite (nHAP) and its environmental importance, however, are poorly understood. This study explored the adsorption of TA using the green synthesized, eggshell-derived nHAP and implications of this process for the removal of aqueous Cu(II) via batch adsorption experiments, Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS) investigations. TA adsorption by nHAP was a complex pH-dependent process and significantly correlated with TA molecule speciation and amphoteric properties of nHAP via multiple adsorption modes including surface complexation, electrostatic attraction, and hydrogen bond. The maximum TA adsorption amount was found to be 94.8 mg/g for less crystalline nHAP with lower calcination temperature. In the ternary Cu-TA-nHAP systems, TA promoted Cu(II) adsorption at pH < 5 and reduced Cu(II) uptake at pH > 5. Further studies of the effects of ionic strength and addition sequences, as well as Raman, FTIR, and XPS analyses revealed Cu(II) adsorption on nHAP was mainly dominated by inner-sphere surface complexation. These results can shed light on not only the utility of biogenic nHAP for TA and Cu(II) adsorption but also the evaluation of the effect of TA on the environmental behavior of heavy metals.

Preparation and pore-forming mechanism of hydrogen bond and ionic bond double-driven chitosan-based mesoporous carbon

Using chitosan as the carbon source, F127 as the template, and sodium tripolyphosphate as cross-linking agent, a hydrogen bond and ionic bond double-driven mesoporous carbon material was prepared via the sol-hydrothermal method and its formation mechanism was discussed. According to the results from FTIR, Raman, XPS, physical adsorption analyzer, SEM, TEM, and TG-IR, the mesoporous carbon material was formed under the synergistic effect of hydrogen bond and ionic bond has a mesoporous volume of 0.44 cm³/g, a BET surface area of 262 m²/g, and possesses the ideal unimodal distribution around 2.20 nm. The mesopores are originated from the degradation of hydrophobic segment PPO of F127, and the micropores come from the gases CO₂, CO, NH₃, CH₄, tetraethylene glycol dimethyl ether, and 2,6-diisopropylphenyl isocyanate produced during the degradation of prepolymers. The maximum adsorption capacity of this mesoporous carbon for tannic acid (Sips model) at 30 °C is 70.4 mg/g.

Synthesis, Characterization, Adsorption Isotherm, and Kinetic Study of Oil Palm Trunk-Derived Activated Carbon for Tannin Removal from Aqueous Solution

Oil palm trunk (OPT) represents one of the five main oil palm biomass wastes with high carbon content that can be economically converted to a large surface area, porous activated carbon (AC) adsorbent to treat palm oil mill effluent wastewater in Indonesia and Malaysia. In the first portion of this work, the design of the experiment was used to determine the optimum set of synthesis parameters required to maximize the iodine number of AC [i.e., Brunauer-Emmett-Teller (BET) specific surface area indicator] prepared from OPT via chemical activation route using H3PO4. The iodine numbers of AC and AC yield were probed as the impregnation ratio, the activation time, and the activation temperature were varied in the range of 0.28-3.47, 5.68-69.32 min, and 379-521 °C, respectively. An impregnation ratio of 2.29, an activation time of 6 min, and an activation temperature of 450 °C were identified as the optimum set of synthesis parameters. In the second portion of the work, the AC synthesized using the optimum parameters were then characterized and tested as an adsorbent for tannin. N2 sorption results revealed that the AC exhibits type IV isotherm, that is, contains micropores and mesopores and displays a relatively high BET specific surface area of 1657 m2 g-1. Adsorption equilibria isotherms for tannin adsorption onto the AC were collected at three different pH of 2, 4, and 6 and were nonlinearly fitted using Langmuir and Freundlich isotherm models, where the Langmuir isotherm gave better fitting than Freundlich. The higher adsorption capacity at lower pH can be explained in terms of the absence of electrostatic repulsion interaction between the AC surface and the tannic acid species as suggested by the point of zero charges (pHpzc) of 4.8 and an increasing ionization of tannic acid with pH rise between 4 and 7. Adsorption kinetics data were also obtained at four different pH of 2, 4, 6, and 8 where the nonlinear pseudo-first-order model best fitted the kinetic at pH of 2 and the nonlinear pseudo-second-order model represented the kinetic best at the remaining higher pH, which suggests that tannin adsorption onto AC occurred by physisorption at pH of 2 and by chemisorption at pH of 4, 6, and 8.

Modulation of cytotoxicity by consecutive adsorption of tannic acid and pesticides on surfactant functionalized zeolites

This study investigated the environmental application of FAU type zeolites modified with cationic surfactants (cetylpyridinium chloride, tetrapropylammonium chloride and benzalkonium chloride). Adsorbent characterization was conducted using Fourier-transform infrared and Raman spectroscopy, thermogravimetry and differential thermal analysis, atomic force microscopy and X-ray powder diffraction. The efficiency for tannic acid adsorption from aqueous solution on the surface of prepared composites is studied and the adsorption process was modelled with different isotherm equations. Surfactant modifications of zeolites led to improved adsorption properties compared to FAU zeolites alone. The proposed mechanism controlling the adsorption of tannic acid onto surfactant modified zeolites mainly relies on π-π and hydrophobic interactions. The investigated materials are promising adsorbents for tannic acid and similar phenolics and may be important for environmental and dietary aspects of polyphenol persistence and usage. Further on, functionalized zeolites were studied for insecticide acetamiprid removal, prior to and after tannic acid retention. Promising findings of insecticide co-adsorption with tannic acid led to cytotoxicity evaluation. The cytotoxicity modulation effect of zeolites and tannic acid on acetamiprid points to the essential role of both components in insecticide toxicity reduction.

Adsorptive removal of apramycin antibiotic from aqueous solutions using Tween 80-and Triton X-100 modified clinoptilolite: experimental and fixed-bed modeling investigations

This study examined the performance of natural clinoptilolite (NC) modified with two surfactants of Triton X-100 (NC-Triton) and Tween 80 (NC-Tween) on apramycin (APR) adsorption from wastewater in batch and continues systems. The optimum pH, contact time, adsorbent dosage, and temperature were achieved. The findings revealed that the sorption was best described using the Langmuir isotherm compared to other isotherms. The maximum adsorption capacity of NC-Triton was greater than NC and NC-Tween. The lumped method was applied to solve the fixed-bed equations; predict breakthrough curve; determine axial dispersion coefficient and overall mass transfer coefficient parameters; and compare theoretical results with experimental results. Good fitness of experimental data with kinetic models of intra-particle diffusion, pseudo-first-order/liquid film diffusion and pseudo-second-order for NC, NC-Tween and NC-Triton, respectively, indicated that they were more suitable than the other models. Endothermic and spontaneous processes were resulted from positive enthalpy and negative Gibbs free energy changes, respectively.

Behavior and Mechanism of Tannic Acid Adsorption on the Calcite Surface: Isothermal, Kinetic, and Thermodynamic Studies

Tannic acid is a calcite flotation agent widely used in mineral processing. To better understand the physicochemical reactivity of tannic acid toward calcite, the present work focused on studying the mechanisms involved during the adsorption process. Hence, in order to determine the optimal physicochemical parameters, tannic acid adsorption onto calcite was investigated at various experimental conditions such as contact time, initial tannic acid concentration, solution pH, particle size, and temperature. The obtained results showed that the adsorption capacity of tannic acid increased significantly with initial tannic acid concentration. Furthermore, tannic acid adsorption onto calcite was highly dependent on solution pH, and the optimal adsorption amount was found to be at pH 8. Therefore, the behavior controlling the studied adsorption process could be attributed to ion exchange. Moreover, the adsorption mechanism has been determined by isothermal, kinetic, and thermodynamic studies. Thus, the Sips isotherm model was the one that best predicted equilibrium data. Adsorption kinetics followed a pseudo-second-order model, indicating that the adsorption process was controlled by the chemical reaction. The estimated thermodynamic parameters revealed that the adsorption reaction was exothermic in nature and the system entropy decreased nonsignificantly during this process. Based on these results, the study of the physicochemical interaction between tannins and carbonates has potential application in mineral processing as well as in other fields.

Adsorption, Antibacterial and Antioxidant Properties of Tannic Acid on Silk Fiber

Natural bioactive compounds have received increasing attention in the functional modification of textiles. In this work, tannic acid was used to impart antibacterial and antioxidant functions to silk using an adsorption technique, and the adsorption properties of tannic acid on silk were studied. The adsorption quantity of tannic acid on silk increased with decreasing pH in the range of 3–7. The rates of the uptake of tannic acid by silk were well correlated to the pseudo-second-order kinetic model, and the calculated activation energy of adsorption was 93.49 kJ/mol. The equilibrium adsorption isotherms followed the Langmuir model. The adsorption rate and isotherm studies demonstrated that the chemical adsorption of tannic acid on silk occurred through the ion-ion interaction between tannic acid and silk. Tannic acid displayed good building-up properties on silk. The silk fabric treated with 0.5% tannic acid (relative to fabric weight) exhibited excellent and durable antibacterial properties. Moreover, the silk fabrics treated with 2% and 5% tannic acid had good and durable antioxidant properties. The treatment by tannic acid had less impact on the whiteness of the silk fabric. In summary, tannic acid can be used as a functional agent for preparing healthy and hygienic silk materials.

Enhanced Adsorption Performance of Oxytetracycline by Desugared Reed Residues

The performance of oxytetracycline adsorption by untreated reed roots, stems and leaves, as well as the desugared reed roots, stems and leaves, was investigated with scanning electron microscopy, Fourier-transform infrared spectroscopy, elemental analysis and surface area analysis to understand the adsorption mechanism. The results showed that the adsorption capacities of untreated reed were 416.35 mg/kg for roots, 341.92 mg/kg for stems and 280.21 mg/kg for leaves, and can be increased significantly by a factor of 8–12 after desugarization. The pseudo-first-order kinetic model was more suitable for describing the adsorption kinetics of reed residues, and the isothermal adsorption process was fitted well by both the Langmuir and Freundlich models. The thermodynamic process suggested that the adsorption was a spontaneous endothermic reaction, and mainly physical adsorption-dominated. The desugared reed tissues had a larger surface area and smaller pore area, and the aromaticity of reed residues increased; on the other hand, the polarity and hydrophilicity decreased after desugarization, thus revealing the mechanism of enhanced OTC(oxytetracycline) adsorption by desugared reed residues. This study suggests that the reed residues contribute the complex adsorption ability for both inorganic and organic contaminates. Corruption of the reed can enhance the adsorption; thus, protecting the natural reed residue and letting it naturally corrupt, rather than artificially cleaning it up, can effectively promote the adsorption of pollutants in the environment and protect environmental and public health.

Adsorption Behavior and Mechanism for the Uptake of Fluoride Ions by Reed Residues

The adsorption behavior and mechanism for the uptake of fluoride ions by untreated and desugared reed residues (roots, stems and leaves) were studied through adsorption experiments, elemental analysis, infrared spectroscopy and surface area analysis. The results showed that the adsorption capacity of untreated and desugared reeds followed the order: desugared roots 2136 mg/kg > desugared leaves 1825 mg/kg > desugared stems 1551 mg/kg > untreated roots 191 mg/kg > untreated stems 175 mg/kg > untreated leaves 150 mg/kg, so adsorption capacity of desugared reeds was larger than that of the untreated reeds. The adsorption kinetic of fluoride ions followed a pseudo-first-order model. A Langmuir model could be used to fit the isothermal adsorption process which was a spontaneous endothermic reaction involving mainly physical adsorption. The ΔG for the uptake of fluoride by the desugared reeds was more negative, so the degree of spontaneity was higher than for the use of the untreated reeds. After samples were desugared, the specific surface area and aromaticity of the reed increased, while the polarity and hydrophilicity decreased, which explained the adsorption amount of desugared reed was higher than that of the untreated. This study enriches techniques and methods of removing fluoride ions from water.

Adsorption Property and Mechanism of Oxytetracycline onto Willow Residues

To elucidate the adsorption property and the mechanism of plant residues to reduce oxytetracycline (OTC), the adsorption of OTC onto raw willow roots (WR-R), stems (WS-R), leaves (WL-R), and adsorption onto desugared willow roots (WR-D), stems (WS-D), and leaves (WL-D) were investigated. The structural characterization was analyzed by scanning electron microscopy, Fourier-transform infrared spectra, and an elemental analyzer. OTC adsorption onto the different tissues of willow residues was compared and correlated with their structures. The adsorption kinetics of OTC onto willow residues was found to follow the pseudo-first-order model. The isothermal adsorption process of OTC onto the different tissues of willow residues followed the Langmuir and Freundlich model and the process was also a spontaneous endothermic reaction, which was mainly physical adsorption. After the willow residues were desugared, the polarity decreased and the aromaticity increased, which explained why the adsorption amounts of the desugared willow residues were higher than those of the unmodified residues. These observations suggest that the raw and modified willow residues have great potential as adsorbents to remove organic pollutants.

Analysis of adsorption processes of dissolved organic matter (DOM) on ferrihydrite using surrogate organic compounds

Ferrihydrite (Fh) has been recently used in water treatment for removing dissolved organic matter (DOM), but its governing interactions with low-molecular weight DOM are largely unknown. This study aimed to elucidate the influence of chemical structure of DOM on the interactions between functional groups of DOM and Fh using various surrogates representing DOM in natural waters. We tested four surrogate compounds: L-glutamic acid, resorcinol, L-serine, and tannic acid, which represent the main chemical groups of carboxylic and hydroxyl groups; and the Suwannee River NOM (SRNOM) that represents the composition of DOM in natural aquatic systems. Batch adsorption experiments revealed that the DOM adsorption onto Fh was significantly influenced by the steric arrangements of -COOH and -OH functional groups. Both L-serine with α-carboxyl group and resorcinol with hydroxyl groups in meta-position were marginally removed by Fh, indicating that the adsorption of DOM on Fh was determined by their chemical structures and the relative positions of carboxylate and hydroxyl groups. The adsorption of L-glutamic acid was controlled by the pH-dependent ligand exchange of γ-carboxyl groups, which was similar to the SRNOM adsorption. In contrast, adsorption of tannic acid was not affected by pH, which can be explained by a two-step adsorption, namely, ligand exchange followed by multi-layer adsorption to the partitioning phase. The results of kinetic experiments demonstrated that adsorption of DOM by Fh was significant and rapid. The kinetic adsorption data can be expressed by the pseudo-second-order equation, indicating that the adsorption step might be the rate-limiting step.

Effects of carbon nanotubes on phosphorus adsorption behaviors on aquatic sediments

Aquatic sediments are believed to be an important sink for carbon nanotubes (CNTs). With novel properties, CNTs can potentially disturb the fate and mobility of the co-existing contaminants in the sediments. Only toxic pollutants have been investigated previously, and to the best of our knowledge, no data has been published on how CNTs influence phosphorus (P) adsorption on aquatic sediments. In this study, multi-walled carbon nanotubes (MWCNTs) were selected as model CNTs. Experimental results indicated that compared to pseudo-first order and intraparticle diffusion models, the pseudo-second-order model is better for describing the adsorption kinetics of sediments and MWCNT-contaminated sediments. Adsorption isotherm studies suggested that the Langmuir model fits the isotherm data well. With the increase in the MWCNT-to-sediment ratio from 0.0% to 5.0%, the theoretical maximum monolayer adsorption capacity (Q_max) for P increased from 0.664 to 0.996mg/g. However, the Langmuir isotherm coefficient (K_L) significantly decreased from 4.231L/mg to 2.874L/mg, indicating the decrease in the adsorption free energy of P adsorbed on the sediments after MWCNT contamination. It was suggested that P was released more easily to the overlying water after the re-suspension of sediments. Moreover, the adsorption of sediments and sediment-MWCNT mixture was endothermic and physical in nature. Results obtained herein suggested that the change in the specific surface area and zeta potential of sediments is related to MWCNT contamination, and the large adsorption capacity of MWCNTs is probably the main factor responsible for the variation in the adsorption of P on aquatic sediments.

Adsorption behavior of lead on aquatic sediments contaminated with cerium dioxide nanoparticles

Aquatic sediments serve as an important sink for engineered nanomaterials (ENMs), such as metal oxide nanoparticles (MeO NPs) and carbon nanotubes (CNTs). Owing to their remarkable properties, ENMs demonstrate significant potential to disturb the adsorption behavior of other contaminants in aquatic sediments, thereby altering the bioavailability and toxicity of these contaminants. Thus far, most studies have investigated the effect of CNTs on the adsorption of other contaminants on sediments. Cerium dioxide nanoparticles (CeO₂ NPs), as one of the important MeO NPs, are also inevitably discharged into aquatic sediments because of their widespread use. In this study, we investigated the adsorption behavior of Pb²⁺ on sediments spiked with CeO₂ NPs at a weight ratio of 5.0%. The results showed that the adsorption rates at three stages occurring during adsorption clearly increase for sediments contaminated with CeO₂ NPs. Moreover, the results obtained from the adsorption isotherms indicated that the Langmuir isotherm model best fits the isotherm data for both sediments and those contaminated with CeO₂ NPs. After spiking the sediments with CeO₂ NPs, the theoretical maximum monolayer adsorption capacity (Q_max) for Pb²⁺ increased from 4.433 to 4.995 mg/g and the Langmuir isotherm coefficient (K_L) decreased from 8.813 to 7.730 L/g. The effects of CeO₂ NPs on the surface charge and pore surface properties of sediments were also studied as these properties affect the adsorption of several chemicals in sediments. The results showed that pH_zpc, S_BET, S_ext, and average pore size of sediments clearly decrease for sediments contaminated with CeO₂ NPs. Hence, the strong adsorption capacity of CeO₂ NPs and the changes of sediment surface charge and pore surface properties caused by CeO₂ NPs are important factors affecting the adsorption behavior of Pb²⁺. The potential risk of Pb²⁺ in aquatic environment may increase with CeO₂ NPs buried in sediments.

Analysis of trihalomethane precursor removal from sub-tropical reservoir waters by a magnetic ion exchange resin using a combined method of chloride concentration variation and surrogate organic molecules

In small reservoirs in tropical islands in Japan, the disinfection by-product formation potential is high due to elevated concentrations of dissolved organic matter (DOM) and bromide. We employed a combined method of variation of chloride concentrations and the use of DOM surrogates to investigate removal mechanisms of bromide and different fractions of DOM by chloride-based magnetic ion exchange (MIEX®) resin. The DOM in reservoir waters was fractionated by resins based on their hydrophobicity, and characterized by size-exclusion chromatography and fluorescence excitation-emission matrix spectrophotometry. The hydrophobic acid (HPO acid) fraction was found to be the largest contributor of the trihalomethane (THM) precursors, while hydrophilic acid (HPI acid) was the most reactive precursors of all the four THM species. Bromide and DOM with a molecular weight (MW) greater than 1kDa, representing HPO acid (MW 1-3kDa) and HPI acid (MW 1-2kDa), were effectively removed by MIEX® resin; however, DOM with a MW lower than 1kDa, representing HPI non-acid, was only moderately removed. The removal of THM precursors by MIEX® resin was interfered by high chloride concentrations, which was similar to the removal of glutamic acid (HPI acid surrogate) and bromide. However, elevated chloride concentrations had only a minor effect on tannic acid (HPO acid surrogate) removal, indicating that HPO acid fraction was removed by a combination of ion exchange and physical adsorption on MIEX® resin. Our study demonstrated that the combined use of DOM surrogates and elevated chloride concentrations is an effective method to estimate the removal mechanisms of various DOM fractions by MIEX® resin.

Oxidation-induced surface deposition of tannic acid: towards molecular gates on porous nanocarriers for acid-responsive drug delivery

Efficient surface deposition of TA by the oxidation via MSN led to the pore occlusion and the subsequent easy construction of polyphenol based metal–phenolic network (MPN) and boronate–phenolic network (BPN) for controlled drug release.

Effective solidification/stabilisation of mercury-contaminated wastes using zeolites and chemically bonded phosphate ceramics

In this study, two kinds of zeolites materials (natural zeolite and thiol-functionalised zeolite) were added to the chemically bonded phosphate ceramic processes to treat mercury-contaminated wastes. Strong promotion effects of zeolites (natural zeolite and thiol-functionalised zeolite) on the stability of mercury in the wastes were obtained and these technologies showed promising advantages toward the traditional Portland cement process, i.e. using Portland cement as a solidification agent and natural or thiol-functionalised zeolite as a stabilisation agent. Not only is a high stabilisation efficiency (lowered the Toxicity Characteristic Leaching Procedure Hg by above 10%) obtained, but also a lower dosage of solidification (for thiol-functionalised zeolite as stabilisation agent, 0.5 g g(-1) and 0.7 g g(-1) for chemically bonded phosphate ceramic and Portland cement, respectively) and stabilisation agents (for natural zeolite as stabilisation agent, 0.35 g g(-1) and 0.4 g g(-1) for chemically bonded phosphate ceramic and Portland cement, respectively) were used compared with the Portland cement process. Treated by thiol-functionalised zeolite and chemically bonded phosphate ceramic under optimum parameters, the waste containing 1500 mg Hg kg(-1) passed the Toxicity Characteristic Leaching Procedure test. Moreover, stabilisation/solidification technology using natural zeolite and chemically bonded phosphate ceramic also passed the Toxicity Characteristic Leaching Procedure test (the mercury waste containing 625 mg Hg kg(-1)). Moreover, the presence of chloride and phosphate did not have a negative effect on the chemically bonded phosphate ceramic/thiol-functionalised zeolite treatment process; thus, showing potential for future application in treatment of 'difficult-to-manage' mercury-contaminated wastes or landfill disposal with high phosphate and chloride content.

Clinoptilolite nano-particles modified with aspartic acid for removal of Cu(ii) from aqueous solutions: isotherms and kinetic aspects

Clinoptilolite nano-particles modified with aspartic acid can remove Cu(ii) cations by ion exchange and complexation processes.

Removal of natural organic matter (NOM) from an aqueous solution by NaCl and surfactant-modified clinoptilolite

Zeolitic tuffs are found in different parts of the world. Iranian zeolite is a low-cost material that can be frequently found in nature. Surfactant-modified zeolite (SMZ) can be used for the adsorption of natural organic matter (NOM) from aqueous solutions. The adsorption study was conducted to evaluate the adsorption capacity of SMZ; furthermore, the effects of contact time, initial pH, and the initial adsorbent dose on the adsorption process were investigated in a batch system. The kinetic studies showed that the adsorption of NOM on SMZ was a gradual process. The optimum initial pH values for the adsorption of NOM on SMZ were in the acidic ranges. The batch kinetic experiments showed that the adsorption followed the pseudo-second-order kinetic model with good correlation coefficients. The equilibrium data were well described by the Langmuir isotherm model. The results show that the natural zeolite being modified with NaCl and hexadecyltrimethylammonium bromide as a cationic surfactant was an appropriate adsorbent for the removal of NOM.