The uptake of uranium by tea wastes investigated by batch, spectroscopic and modeling techniques

Adsorption and safe immobilization of Sr ions in modified zeolite matrices

In the present study, an Iranian natural zeolite (Sabzevar region) was evaluated as a natural adsorbent for the elimination and immobilization of strontium ions from an aqueous solution. For improving the adsorption efficiency of strontium ion, the zeolite surface was modified by the Schiff base ligand of bis (2-hydroxybenzaldehyde)1,2-diaminoethane (H2L). The natural zeolite and zeolite/H2L were characterized using Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), X-ray fluorescence (XRF), BET and scanning electron microscope (SEM). Analysis of the natural zeolite showed that the zeolite is from the type of clinoptilolite and has a crystalline structure with the specific surface area 29.74 m2/g. The results showed that strontium adsorption onto modified zeolite increases compared to unmodified zeolite from 64.5% to 97.2% (at pH = 6). The effective parameters pH, adsorbent dosage, initial concentration of strontium ions, contact time, temperature, and interfering ions, were studied and optimized. The maximum adsorption efficiency was confirmed by modified zeolite and found to be 97.5% after 60 min of equilibrium time at pH 6, 0.05g as adsorbent dosage, and at 25 °C. Adsorption of strontium was confirmed by Langmuir model with maximum adsorption capacity of 10.31 mg/g. Kinetic studies showed that the adsorption of strontium ions on the adsorbent follows pseudo-second-order (PSO) model. Also, the thermodynamics of the adsorption process indicated that the adsorption of strontium on zeolite/H2L is an endothermic and spontaneous process, and the adsorption mechanism is a combination of physical and chemical adsorption. Finally, to manage the secondary waste generated from the adsorption process, strontium ions were immobilized in a zeolite structure. The results showed that the stabilization is well done with the thermal preparation process. After thermal treatment at 25-900 °C, modified zeolite satisfactorily retains strontium during back-exchange tests with NaCl solution. According to the results, the amount of strontium released from the adsorbent phase decreases from 52.6 to 1.6% with increasing heat treatment temperature.

Radioactive decontamination in low-temperature environments by using a novel high-strength strippable coating

Accidents involving nuclear leakage and radioactive source diffusion will result in a substantial amount of radioactive pollution, posing a threat to the world's environment as well as human safety. To get rid of the pollution, this work describes a new type of strippable detergent coating designed to remove radioactive contamination, especially in low-temperature conditions. In situ polymerization was employed to make EC/PUA/PVAc detergent from degradable ethyl cellulose (EC), tea polyphenols (TP), and polyvinyl acetate (PVAc), and polytetramethylene ether glycol bis-para-aminobenzoate (P1000). The film-forming performance, decontamination efficiency, and mechanical properties of the decontamination coating formed by the detergent were studied. Designed to work in a low-temperature environment, the detergent can be sprayed and peeled to remove surface radioactive staining. A universal material testing machine was used to assess the low-temperature rheometry, SEM, EDX, FT-IR, and other variables and to characterize the decontamination coating and the decontamination mechanism of the detergent. At -10-10 °C, the EC/PUA/PVAc detergent has good fluidity and sprayability and forms a strippable coating. The tensile strength of the decontamination coating can be as high as 26.4 MPa, and its 180° peel strength on ceramic tile, glass, stainless steel, cement, marble are 0.49 ± 0.08 N/m, 1.82 ± 0.41 N/m, 3.03 ± 1.65 N/m, 35.60 ± 1.17 N/m, 44.43 ± 4.10 N/m, respectively. The decontamination factors ranged from 3.32 to 10.02, with a decontamination rate above 85%.

Biosorption of Uranium from aqueous solution by green microalga Chlorella sorokiniana

Uranium and its compounds are radioactive and toxic, as well as highly polluting and damaging the environment. Novel uranium adsorbents with high biosorption capacity that are both eco-friendly and cost-effective are continuously being researched. The non-living biomass of the fresh water green microalga Chlorella sorokiniana was used to study the biosorption of uranium from aqueous solution. The biosorption of uranium from aqueous solutions onto the biomass of microalga C. sorokiniana was investigated in batch studies. The results showed that the optimal pH for uranium biosorption onto C. sorokiniana was 2.5. Uranium biosorption occurred quickly, with an equilibrium time of 90 min. The kinetics followed a pseudo-second-order rate equation, and the biosorption process fit the Langmuir isotherm model well, with a maximum monolayer adsorption capacity of 188.7 mg/g. The linear plot of the DKR model revealed that the mean free energy E = 14.8 kJ/mol, confirming chemisorption adsorption with ion exchange mode. The morphology of the algal biomass was investigated using a scanning electron microscope and energy dispersive X-ray spectroscopy. The FTIR spectroscopy analysis demonstrated that functional groups (carboxyl, amino, and hydroxyl) on the algal surface could contribute to the uranium biosorption process, which involves ion exchange and uranium absorption, and coordination mechanisms. Thermodynamic simulations indicated that the uranium biosorption process was exothermic (ΔH = -19.5562 kJ/mol) and spontaneous at lower temperatures. The current study revealed that C. sorokiniana non-living biomass could be an efficient, rapid, low-cost, and convenient method of removing uranium from aqueous solution.

New nanostructured activated biochar for effective removal of antibiotic ciprofloxacin from wastewater: Adsorption dynamics and mechanisms

Developing green inexpensive and effective adsorbents is critically needed for elimination of antibiotics from contaminated water. The current study assessed the nanostructured activated biochar (nPPAB) derived from pomegranate peels (PP) as a promising sorbent for efficient removal of the antibiotic ciprofloxacin (CIP). The results affirm that the second order and Langmuir models fit well to adsorption kinetics and equilibrium data respectively. The nPPAB adsorption capacity of Langmuir (q_max) for CIP was 142.86 mg g^-1 which is 26.85 times greater than that of bulk PP. Hydrogen bonding, π-π interaction, hydrophobic and electrostatic interactions are the dominant mechanisms of CIP adsorption by nPPAB. The efficiency of nPPAB for CIP removal from real wastewater using batch and packed-bed reactor were 89.94 and 84.74% respectively. This study clearly demonstrated the substantial capacity of nPPAB as an ecofriendly, feasible, and in-expensive adsorbent for successful elimination of CIP from wastewater.

A review on adsorptive separation of toxic metals from aquatic system using biochar produced from agro-waste

Water is a basic and significant asset for living beings. Water assets are progressively diminishing due to huge populace development, industrial activities, urbanization and rural exercises. Few heavy metals include zinc, copper, lead, nickel, cadmium and so forth can easily transfer into the water system either direct or indirect activities of electroplating, mining, tannery, painting, fertilizer industries and so forth. The different treatment techniques have been utilized to eliminate the heavy metals from aquatic system, which includes coagulation/flocculation, precipitation, membrane filtration, oxidation, flotation, ion exchange, photo catalysis and adsorption. The adsorption technique is a better option than other techniques because it can eliminate heavy metals even at lower metal ions concentration, simplicity and better regeneration behavior. Agricultural wastes are low-cost biosorbent and typically containing cellulose have the ability to absorb a variety of contaminants. It is important to note that almost all agro wastes are no longer used in their original form but are instead processed in a variety of techniques to improve the adsorption capacity of the substance. The wide range of adsorption capacities for agro waste materials were observed and almost more than 99% removal of toxic pollutants from aquatic systems were achieved using modified agro-waste materials. The present review aims at the water pollution due to heavy metals, as well as various heavy metal removal treatment procedures. The primary objectives of this research is to include an overview of adsorption and various agriculture based adsorbents and its comparison in heavy metal removal.

Adsorption of U(VI) from aqueous solution by using KMnO4-modified hazelnut shell activated carbon: characterisation and artificial neural network modelling

This study is based on U(VI) removal from wastewater by KMnO₄-modified hazelnut shell activated carbon (KM-HSAC) using adsorption technology. A characterisation study of KM-HSAC was conducted through scanning electron microscope and energy-dispersive X-ray spectroscopy (EDS) analysis. The rough surface of KM-HSAC contains many irregular microspores. The EDS pattern confirmed the U(VI) adsorption on the KM-HSAC. A batch study experiment gave optimum results for U(VI) at pH 6, contact time of 160 min, initial U(VI) concentration of 155.56 mg/L and KM-HSAC dosage of 4 g/L, with a maximum adsorption capacity of 22.27 mg/g. The prediction performance of artificial neural network models was validated through the low values of statistical error (2.708 and 8.241 for RMSE of training and testing data, respectively) and the high determination coefficient value (0.987 and 0.906 for training and testing data, respectively). Experimental results suggest that KM-HSAC has a high potential for the removal of U(VI) from wastewater.

Ecofriendly remediation technologies for wastewater contaminated with heavy metals with special focus on using water hyacinth and black tea wastes: a review

Treatment of water contaminated with heavy metals is challenging. Heavy metals are non-degradable, persistent in the environment, have a high dispersion capacity by water, can bioaccumulate, and represent risks to human and environmental health. Conventional treatment methods have disadvantages; however, adsorption in biomass is a highly promising method with high efficiency and low cost that avoids many of the disadvantages of conventional methods. Black tea (BT) wastes and water hyacinth (WH) have attracted attention for their ability to remove heavy metals from wastewater. Utilizing these approaches can remove contaminants and effectively manage problematic invasive species and wastes. The conventional uses of BT and WH were efficient for removing heavy metals from wastewater. Due to the unique and distinct properties and advantages of biochar and nano-forms of biosorbents, the use of BT and WH in these forms is promising to achieve sustainable heavy metals removal from wastewater. However, more study is needed to confirm preliminary results.

Electrochemical synthesis of EuVO4 for the adsorption of U(VI): Performance and mechanism

The efficient removal of uranium from aqueous solution remains of great challenge in securing water environment safety. In this paper, we reported a high temperature electrochemical method for the preparation of EuVO₄ with different morphologies from rare earth oxides and vanadate, which solved the problems of rare earth and vanadium recovery. The effects of pH, ionic strength, contact time, initial concentration and reaction temperature on the adsorption of U(VI) by prepared adsorbent were studied by static batch experiments. When the concentration of U(VI) standard is 100 mg g^-1, the maximum adsorption capacity of EuVO₄ is 276.16 mg g^-1. The adsorption mechanism was elucidated with zeta potential and XPS: 1) negatively charged EuVO₄ attracted UO₂²⁺ by electrostatic attraction; 2) exposed Eu, V, and O atoms complexed with U(VI) through coordination; 3) the hybrid of Eu was complex, which accommodated different electrons to interact. In the multi-ion system with Al³⁺, Zn²⁺, Cu²⁺, Ni²⁺, Cr²⁺ and Mn²⁺, EuVO₄ also showed good selective adsorption properties for U(VI). Five adsorption and desorption cycle experiments demonstrated that EuVO₄ possessed good renewable performance.

Kinetics and adsorption equilibrium of some radionuclides on polyaniline/SiO2 composite

The sorption kinetics and equilibrium isotherms of zirconium, uranium, and molybdenum ions onto synthetic polyaniline/SiO2 composite (PAn/SiO2) have been studied using batch-sorption techniques. This study was carried out to examine the sorption behavior of the PAn/SiO2 for the removal of Zr(IV), U(VI), and Mo(VI) ions from an aqueous solution. The influence of some parameters on the sorption process was also studied. The maximum sorption for Zr(IV), U(VI), and Mo(VI) ions was achieved at 60 min shaking time. Langmuir isotherm model is the most representative for discussing the sorption process with a maximum sorption capacity of 24.26, 21.82, and 13.01 mg/g for Zr(IV), U(VI), and Mo(VI) ions, respectively. Kinetic modeling revealed that the sorption of all ions follows the pseudo-second-order kinetic model. The results demonstrated that both the external and intra-particular diffusion are taken into account in determining the sorption rate. Thermodynamic parameters like ΔG°, ΔH°, and ΔS° for the sorption process were evaluated. The synthetic composite has been successfully applied for the removal and recovery of U(VI) ions from real solution (monazite leachate) using a chromatographic column packed with PAn/SiO2 composite with a breakthrough capacity equal to 239.70 mg/g.

Highly-efficient and easy separation of hexahedral sodium dodecyl sulfonate/δ-FeOOH colloidal particles for enhanced removal of aqueous thallium and uranium ions: Synergistic effect and mechanism study

Thallium (Tl) and uranium (U) contaminants pose serious threats to the ecological environment and human health. In this research, a cost-effective feroxyhite (δ-FeOOH) dispersed with sodium dodecyl sulfonate (SDS) was prepared and a series of experiments were optimized to explore the removal mechanism of Tl⁺ and UO₂²⁺ from the effluent. The SDS/δ-FeOOH exhibited highly dispersed colloidal particles and showed significantly enhanced adsorption performance on the removal of Tl and U in the presence of H₂O₂ and pH of 7.0. Equilibrium uptakes of 99.5% and 99.7% were rapidly achieved for Tl⁺ and UO₂²⁺ within 10 min, respectively. The Freundlich isotherm model fitted well with the adsorption data of Tl and U. The maximum isotherm sorption capacity of SDS/δ-FeOOH for Tl⁺ and UO₂²⁺ was 182.9 and 359.6 mg/g, respectively. The sorption of Tl followed the pseudo-second-order kinetic model, whereas the sorption of U followed the pseudo-first-order kinetic model. The uptake of Tl and U by SDS/δ-FeOOH was notably inhibited at Na⁺, K⁺ concentrations over 5.0 mM, and a high content of dissolved organic matter (over 0.5 mg/L). The mechanistic study revealed that ion exchange, precipitation, and surface complexation were main mechanisms for the removal of Tl and U. The findings of this study indicate that stabilizer dispersion may serve as an effective strategy to facilitate the treatment of wastewater containing Tl and U by using δ-FeOOH.

Preparation, uranium (VI) absorption and reuseability of marine fungus mycelium modified by the bis-amidoxime-based groups

Bis-amidoxime-based claw-like-functionalized marine fungus material (ZZF51-GPTS-DCDA-AM) was prepared for study to absorb the low concentration uranium (VI) from aqueous solution. A series of characterization methods such as SEM, TGA and FT-IR were applied for the functionalized materials before and after modification and adsorption. The experimental results suggested that the amidoxime groups were successfully grafted onto the surface of mycelium powder and provided the special binding sites for the absorption of uranium (VI). In the absorption research, uranium (VI) initial concentration, pH and equilibrium time were optimized as 40 mg L−1, 6.0, and 110 min by L4 3 orthogonal experiment, respectively, and the maximum absorption capacity of the prepared material was 370.85 mg g−1 under the optimum batch conditions. After five cycling process, the desorption rate and regeneration efficiency of the modified mycelium were found to be 80.29 % and 94.51 %, respectively, which indicated that the material had an adequately high reusability property as a cleanup tool. The well known Langmuir and Freundlich isotherm adsorption model fitting found that the modified materials had both monolayer and bilayer adsorption to uranium (VI) ions. Simultaneously, the pseudo-second-order model was better to illustrated the adsorption kinetics process. The enhanced adsorption capacity of uranium (VI) by the modified fungus materials over raw biomass was mainly owing to the strong chelation of amidoxime groups and uranium (VI) ions.

Preparation of a magnetic reduced-graphene oxide/tea waste composite for high-efficiency sorption of uranium

The preparation and application of adsorptive materials with low cost and high-efficiency recovery of uranium from nuclear waste is necessary for the development of sustainable, clean energy resources and to avoid nuclear pollution. In this work, the capacity of tea waste and tea waste hybrids as inexpensive sorbents for uranium removal from water solutions was investigated. Composites of graphene oxide (GO) and tea waste (TW) exhibited a promising adsorption performance for uranium from aqueous solutions. The composites GOTW and magnetic rGO/Fe₃O₄/TW show high adsorption capacities (Q_{m (TW)} = 91.72 mg/g, Q_{m (GOTW)} = 111.61 mg/g and Q_{m (rGO/Fe3O4/TW)} = 104.95 mg/g) and removal rates (~99%) for U(VI). The equilibrium sorption of the adsorbents fitted well to the Langmuir model, and the sorption rate fitted well to a pseudo-second-order kinetic model. The thermodynamic parameters indicated that sorption was spontaneous and favourable. The prepared adsorbents were used for the removal of uranium from real water samples as well. The results revealed that GOTW and rGO/Fe₃O₄/TW can be used to remediate nuclear industrial effluent as a potential adsorbent.

Study of ciprofloxacin removal by biochar obtained from used tea leaves

In this study, used tea leaves (UTLs) were pyrolyzed to obtain used tea-leaf biochar (UTC), and then the UTC was used as an adsorbent to remove ciprofloxacin (CIP) from aqueous solutions. Batch experiments were conducted to investigate the CIP adsorption performance and mechanism. The results showed that the CIP-adsorbing ability first increased and then declined as the UTC pyrolysis temperature increased. The UTC obtained at 450°C presented excellent CIP-absorbing ability at pH6 and 40°C. The maximum monolayer adsorption capacity was 238.10mg/g based on the Langmuir isotherm model. The pseudo-second-order kinetic equation agreed well with the CIP adsorption process, which was controlled by both external boundary layer diffusion and intra-particle diffusion. The characterization analysis revealed that the OH groups, CC bonds of aromatic rings, CH groups in aromatic rings and phenolic CO bonds play vital roles in the CIP adsorption process, and that the NC, NO, OCO and COH groups of UTC were consumed in large quantities. π-π interactions, hydrogen bonding and electrostatic attraction are inferred as the main adsorption mechanisms. The present work provides not only a feasible and promising approach for UTLs utilization but also a potential adsorbent material for removing high concentrations of CIP from aqueous solutions.

Recent advances on biosorption by aerobic granular sludge

Aerobic granular sludge is a form of microbial auto-aggregation, and a promising biotechnology for wastewater treatment. This review aims at providing the first comprehensive, systematic, and in-depth overview on the application of aerobic granules as biosorbents. The target pollutants encompass heavy metals (both cationic and oxyanionic), nuclides, dyes, and inorganic non-metal substances. Different granule types are discussed, i.e. intact and fragmented, compact and fluffy, original and modified, and the effects of granule surface modification are introduced. A detailed comparison is conducted on the characteristics of granular biomass, the conditions of the adsorption tests, and the resultant performance towards various sorbates. Analytical and mathematical tools typically employed are presented, and possible interactions between the pollutants and granules are theorized, leading to an analysis on the mechanisms of the adsorption processes. Original granules appear highly effective towards cationic metals, while surface modification by organic and inorganic agents can expand their applicability to other pollutants. Combined with their advantages of high mechanical strength, density, and settling speed, aerobic granules possess exceptional potential in real wastewater treatment as biosorbents. Possible future research, both fundamental and practical, is suggested to gain more insights into the mechanism of their function, and to advance their industrial application.

Investigation of uranium (VI) adsorption by polypyrrole

The purpose of this study was to investigate the adsorption of uranium (VI) ions on the polypyrrole adsorbent. Polypyrrole was synthesized by a chemical method using polyethylene glycol, sodium dodecylbenzenesulfonate, and cetyltrimethylammonium bromide as the surfactant and iron (III) chloride as an oxidant in the aqueous solution. The effect of various surfactants on the synthesized polymers and their performance as the uranium adsorbent were investigated. Adsorbent properties were characterized by scanning electron microscopy (SEM) and Fourier transform infrared spectroscopy (FTIR) techniques. The effect of different parameters such as pH, contact time, initial metal ion concentrations, adsorbent dose, and the temperature was investigated in the batch system for uranium adsorption process. It has been illustrated that the adsorption equilibrium time is 7min. The results showed that the Freundlich model had the best agreement and the maximum adsorption capacity of polypyrrole for uranium (VI) was determined 87.72mg/g from Langmuir isotherm. In addition, the mentioned adsorption process was fast and the kinetic data were fitted to the Pseudo first and second order models. The adsorption kinetic data followed the pseudo-second-order kinetic model. Moreover, the thermodynamic parameters ΔG⁰, ΔH⁰ and ΔS⁰ showed that the uranium adsorption process by polypyrrole was endothermic and spontaneous.

Highly selective defluoridation of brick tea infusion by tea waste supported aluminum oxides

BACKGROUND

Brick tea usually contains very high fluoride, which may affect human health. Biosorbents have received much attention for selective removal of fluoride because of low cost, environmental friendliness, and relative safeness.

RESULTS

In the present study, a highly selective fluoride tea waste based biosorbent, namely, aluminum (Al) oxide decorated tea waste (Tea-Al), was successfully prepared. The Tea-Al biosorbent was characterized by energy-dispersive spectrometry, Fourier transform infrared spectroscopy, powder X-ray diffraction and X-ray photoelectron spectroscopic analysis. The Tea-Al sample exhibited remarkably selective adsorption for fluoride (52.90%), but a weaker adsorption for other major constituents of brick tea infusion, such as catechins, polyphenols and caffeine, under the same conditions. Fluoride adsorption by Tea-Al for different times obeyed the surface reaction and adsorption isotherms fit the Freundlich model. In addition, the fluoride adsorption mechanism appeared to be an ion exchange between hydroxyl and fluoride ions.

CONCLUSION

Results from this study demonstrated that Tea-Al is a promising biosorbent useful for the removal of fluoride in brick tea infusion. © 2016 Society of Chemical Industry.

Uranium biosorption from aqueous solution onto Eichhornia crassipes

Batch experiments were conducted to investigate the biosorption of U(VI) from aqueous solutions onto the nonliving biomass of an aquatic macrophyte Eichhornia crassipes. The results showed that the adsorption of U(VI) onto E. crassipes was highly pH-dependent and the best pH for U(VI) removal was 5.5. U(VI) adsorption proceeded rapidly with an equilibrium time of 30 min and conformed to pseudo-second-order kinetics. The Langmuir isotherm model was determined to best describe U(VI) biosorption with a maximum monolayer adsorption capacity of 142.85 mg/g. Thermodynamic calculation results indicated that the U(VI) biosorption process was spontaneous and endothermic. Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy analysis implied that the functional groups (amino, hydroxyl, and carboxyl) may be responsible for the U(VI) adsorption process, in which the coordination and ion exchange mechanisms could be involved. We conclude that E. crassipes biomass is a promising biosorbent for the removal of uranium pollutants.