Comparison of enhancement of anaerobic digestion of waste activated sludge through adding nano-zero valent iron and zero valent iron

The feasibility of adding nano-zero valent iron (NZVI: 0.6, 1.0, 4.0, 10.0 g L⁻¹) to enhance anaerobic digestion of waste activated sludge (WAS) was examined by comparison with ZVI, and the mechanisms of NZVI enhancement of the hydrolysis and methanogenesis processes were elucidated. NZVI could enhance hydrolysis–acidification of WAS by destroying the integrity of microbial cells. Both volatile fatty acids production and the acetic acid portion were greatly improved by NZVI additions, peaking at 4.0 g L⁻¹ NZVI. In anaerobic digestion, CH₄ production was promoted at a NZVI dosage ≤1.0 g L⁻¹. The optimum dosage of NZVI for methanogenesis was 1.0 g L⁻¹, and further addition of NZVI could cause inhibition of methanogenesis because of long-term accumulation of H₂. ZVI could also improve hydrolysis–acidification and the CH₄ yield, but its efficiency was relatively low compared with NZVI, and it could not induce cell wall rupture. 16S rDNA high-throughput sequencing results showed that NZVI addition at appropriate dosage facilitated increasing the proportion of microorganisms involved in WAS hydrolysis–acidification and methanogenesis.

The feasibility of adding nano-zero valent iron to enhance anaerobic digestion of waste activated sludge was studied by comparison with ZVI, and the mechanisms of NZVI enhancement of the hydrolysis and methanogenesis processes were elucidated.     

Enhanced phosphate removal with fine activated alumina synthesized from a sodium aluminate solution: performance and mechanism

Fine activated alumina (FAA) acting as an adsorbent for phosphate was synthesized from an industrial sodium aluminate solution based on phase evolution from Al(OH)₃ and NH₄Al(OH)₂CO₃. This material was obtained in the form of γ-Al₂O₃ with an open mesoporous structure and a specific surface area of 648.02 m² g⁻¹. The phosphate adsorption capacity of the FAA gradually increased with increases in phosphate concentration or contact time. The maximum adsorption capacity was 261.66 mg g⁻¹ when phosphate was present as H₂PO₄⁻ at a pH of 5.0. A removal efficiency of over 96% was achieved in a 50 mg L⁻¹ phosphate solution. The adsorption of phosphate anions could be explained using non-linear Langmuir or Freundlich isotherm models and a pseudo-second-order kinetic model. Tetra-coordinate AlO₄ sites acting as Lewis acids resulted in some chemisorption, while (O)_nAl(OH)₂⁺ (n = 4, 5, 6) Brønsted acid groups generated by the protonation of AlO₄ or AlO₆ sites in the FAA led to physisorption. Analyses of aluminum-oxygen coordination units using Fourier transform infrared and X-ray photoelectron spectroscopy demonstrated that physisorption was predominant. Minimal chemisorption was also verified by the significant desorption rate observed in dilute NaOH solutions and the high performance of the regenerated FAA. The high specific surface area, many open mesopores and numerous highly active tetra-coordinate AlO₄ sites on the FAA all synergistically contributed to its exceptional adsorption capacity.

A fine activated alumina with high specific surface area was prepared by phase evolution from sodium aluminate solution, Al(OH)₃ and NH₄Al(OH)₂CO₃. The maximum adsorption capacity was 261.66 mg g⁻¹ and the regenerated material exhibited high performance phosphate removal.     

High dispersions of nano zero valent iron supported on biochar by one-step carbothermal synthesis and its application in chromate removal

A one-step carbothermal synthesis and characterization of biochar-supported nanoscale zero-valent iron (nZVI/BC) was performed for the removal of hexavalent chromium (Cr(vi)) from aqueous solution. High dispersions of nanoscale zero-valent iron supported on biochar were successfully synthesized by the pyrolysis of an iron-impregnated biomass (corn stover) as the carbon and iron source under nitrogen atmosphere. The effects of the pyrolytic temperature on the Fe mineralogies formed on the biochar are discussed. In general, the effects of the treatment time, initial solution pH, and nZVI/BC dosage on the Cr(vi) removal are presented. The results showed high crystallinity and purity, and nZVI/BC was obtained at a pyrolytic temperature of 800 °C. The batch experimental results determined that the adsorption capacity of Cr(vi) decreases with the increase in the initial pH value from 4.0 to 10.0. The Cr(vi) adsorption kinetics data effectively followed a pseudo-second-order kinetics with a calculated rate constant of 0.0.3396 g mg⁻¹ min⁻¹. The calculated thermodynamic parameters, such as ΔG°, ΔH°, and ΔS°, were evaluated, and the results indicated that the Cr(vi) reduction on nZVI/BC was a spontaneous and endothermic process. The adsorption mechanism of Cr(vi) was investigated by XRD and XPS analyses and the results demonstrated that Cr(vi) was reduced to Cr(iii) and the oxidation of nZVI occurred during the reaction process. These results prove that nZVI/BC synthesized by a one-step carbothermal method can be considered as a potential candidate for the removal of Cr(vi) from aqueous solutions.

A one-step carbothermal synthesis and characterization of biochar-supported nanoscale zero-valent iron (nZVI/BC) was performed for the removal of hexavalent chromium (Cr(vi)) from aqueous solution.     

A novel zero valent metal bismuth for bromate removal: direct and ultraviolet enhanced reduction

Bromate (BrO₃⁻) is a carcinogenic and genotoxic by-product of the ozone disinfection process. In this study, a new zero-valent metal, bismuth, was used to reduce bromate. Bismuth samples were prepared by a solvothermal method and characterized by powder X-ray diffraction (PXRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The morphology of the bismuth powder was microspheres assembled with dense nanosheets. The kinetics of the direct bromate reduction by bismuth accorded with the pseudo-first-order kinetics model. The rate coefficients of the initial bromate concentration of 1.00 mg L⁻¹, 2.50 mg L⁻¹, 5.00 mg L⁻¹ were identically close to 0.08 min⁻¹. For 0.20 mg L⁻¹, a reaction rate coefficient near 0.10 min⁻¹ was obtained. The reducing products of bromate included bromide ions (Br⁻) and bismuth oxybromides. The bromate removal efficiency was enhanced remarkably in the presence of ultraviolet (UV) light, and the corresponding kinetic coefficient was 4 times higher than that of direct reduction. The mechanism of ultraviolet enhancement was analyzed by diffuse reflectance spectroscopy (DRS), the density functional theory (DFT) calculation, open circuit potential (OCP) analysis, photocurrent measurement and linear sweep voltammetry (LSV). Besides, the influence of dissolved oxygen (DO) on bromate reduction efficiency and the sustainability of the as-prepared sample were investigated. DO inhibited the reduction rate obviously, but showed a slight effect on the formation of bromide ions. In the long-term periodic experiments, the kinetic coefficient decay occurred in both direct (without UV irradiation) and ultraviolet assisted bromate reduction. However, the kinetic coefficient of UV-assisted reduction (0.115 min⁻¹) was about 2 times higher than that of the direct reduction in the last cycle of periodic experiments. In conclusion, the novel bromate reduction strategy based on the zero-valent bismuth metal material has been proved efficient and sustainable, which contributes to the development of drinking water treatment technologies.

The inert metal bismuth is proved to be effective for the direct reduction of bromate while the reducing process is dramatically promoted under the presence of ultraviolet light, since bismuth is a typical semi-metal.     

Mechanism of phosphate removal from aqueous solutions by biochar supported nanoscale zero-valent iron

The purpose of this study was to investigate the removal mechanism of phosphate by rape straw biochar (RSBC) supported nanoscale zero-valent iron (nZVI). BET, TEM, FTIR and XPS characterizations of the composite material (nZVI-RSBC) indicated that nZVI was successfully supported on the RSBC, and nZVI-RSBC had a high specific surface area and abundant oxygen-containing functional groups. Batch experiments showed that the adsorption data could be fitted well with the Sips isotherm model and pseudo-second-order kinetic model, suggesting that phosphate adsorption onto RSBC and nZVI-RSBC was due to surface and chemical processes. The maximum adsorption capacities of RSBC and nZVI-RSBC for phosphate obtained by the Sips isotherm model fitting were 3.49 mg g⁻¹ and 12.14 mg g⁻¹, respectively. The pH value of the solution greatly affected the adsorption capacity of nZVI-RSBC for phosphate. The combined results of batch experiments and characterizations revealed that the possible mechanism was the complexation of oxygen-containing functional groups on the surface of nZVI-RSBC with phosphate, hydrogen bonding, and electrostatic attraction between phosphate and the positively charged adsorption sites under acidic conditions. Such a strong adsorption capacity, as well as the characteristics of easy availability, excellent recyclability and low cost, make nZVI-RSBC potentially suitable for the treatment of phosphate-rich water.

The purpose of this study was to investigate the removal mechanism of phosphate by rape straw biochar (RSBC) supported nanoscale zero-valent iron (nZVI).     

Enhanced removal of chromium(vi) by Fe(iii)-reducing bacterium coated ZVI for wastewater treatment: batch and column experiments

In order to effectively destroy the structure of the passive oxidation film that covers zero-valent iron (ZVI), an Fe(iii)-reducing strain, namely Morganella sp., was isolated from anaerobic activated sludge and coated on ZVI, which was distributed in porous ceramsite made of iron dust, kaolin and straw, with a ratio of 7 : 3 : 1. Batch experiments showed that under the optimized conditions, the maximum removal amount of Cr(vi) by ZVI increased from 7.33 mg g⁻¹ to 26.87 mg g⁻¹ in the presence of the Fe(iii)-reducing bacterium. The column experiment was performed with the addition of the agar globules to supply nutrients to the strain. Compared with ZVI, the column penetration time and maximum capture amount of RB-ZVI increased to 17 h and 112.5 mg g⁻¹, respectively, on the 15^th day. Furthermore, the service life of RB-ZVI was prolonged in the existence of the strain. Based on X-ray diffraction, Raman spectroscopy and X-ray photoelectron spectroscopy analyses, the key mechanisms for the removal of Cr(vi) by ZVI coated with Fe(iii)-reducing bacterium were determined to be adsorption, reduction, coprecipitation and biomineralization.

To effectively destroy the structure of the passive oxidation film covering zero-valent iron (ZVI), an Fe(iii)-reducing strain, Morganella sp., was isolated from anaerobic activated sludge and coated on the ZVI.     

Correction: Nano zero valent iron (nZVI) particles for the removal of heavy metals (Cd2+, Cu2+ and Pb2+) from aqueous solutions

Correction for ‘Nano zero valent iron (nZVI) particles for the removal of heavy metals (Cd²⁺, Cu²⁺ and Pb²⁺) from aqueous solutions’ by Mekonnen Maschal Tarekegn et al., RSC Adv., 2021, 11, 18539–18551. DOI: 10.1039/D1RA01427G.

The authors regret that reference 48 was incorrect. The correct reference is given below as reference 1.¹The Royal Society of Chemistry apologises for these errors and any consequent inconvenience to authors and readers.     

Nano zero valent iron (nZVI) particles for the removal of heavy metals (Cd2+, Cu2+ and Pb2+) from aqueous solutions

For the past 15 years, nanoscale metallic iron (nZVI) has been investigated as a new tool for the treatment of heavy metal contaminated water. The removal mechanisms depend on the type of heavy metals and their thermodynamic properties. A metal whose redox potential is more negative or close to the reduction potential of Fe(0) is removed by the reduction process, while the others will be mediated by precipitation, complexation or other sorption processes. This review summarises our contemporary knowledge of nZVI aqueous chemistry, synthesis methods, mechanisms and actions (practical experiences) of heavy metal (Cd, Cu and Pb) removal and challenges of nZVI practical applications. Its inner core (iron(0)) has reducing ability towards pollutants, while the iron oxide (FeO) outer shell provides reaction sites for chemisorption and electrostatic interactions with heavy metals. Emerging studies highlighted that nZVI surfaces will have negatively charged species at higher pH and have good affinity for the removal of positively charged species such as heavy metals. Different sizes, shapes and properties of nZVI have been produced using various methods. Ferric salt reduction methods are the most common methods to produce stable and fine graded nZVI. Higher uptake of copper(ii), lead(ii) and cadmium(ii) has also been reported by various scholars. Practical pilot tests have been conducted to remove heavy metals, which gave highly satisfactory results. Challenges such as agglomeration, sedimentation, magnetic susceptibility, sorption to other fine materials in aqueous solution and toxicity of microbiomes have been reported. Emerging studies have highlighted the prospects of industrial level application of nano zero valent particles for the remediation of heavy metals and other pollutants from various industries.

Heavy metals (Cd²⁺, Cu²⁺ and Pb²⁺) removal mechanisms of nZVI from aqueous solution.     

Convenient pH-responsive removal of Acid Black 1 by green l-histidine/iron oxide magnetic nanoadsorbent from water: performance and mechanistic studies

This study was aimed at developing green histidine-modified Fe₃O₄ nanoparticles (His-MNPs) for the adsorptive removal of Acid Black 1 (AB1) from aqueous solution. The His-MNPs were characterized by atomic force microscopy, scanning electron microscopy-energy dispersive X-ray spectrometry, infra-red spectra and thermogravimetry. These MNPs were spherical (average diameter 11–28 nm) with polydispersity index of 1.40 and about 13% mass coating of histidine. To optimize AB1 adsorption on His-MNPs and understand its mechanism, the influences of different operational variables (pH, adsorbent amount, temperature, initial AB1 concentration, contact time, ionic strength, etc.) on adsorption were examined with adsorption isotherms, kinetics and thermodynamic studies. The AB1 adsorption from water was fast with equilibrium time ≤ 45 min. The adsorption equilibrium was best fitted to the Langmuir isotherm model (q_max = 166.7 mg g⁻¹ at the adsorbent dose of 0.2 g L⁻¹, temperature 30 °C and pH 4). The linearity order for other isotherms was as follows: Dubinin–Radushkevich (D–R) < Temkin < Freundlich. The kinetics of the AB1 adsorption demonstrated the best compliance with the pseudo-second-order model, predominantly controlled by film diffusion as compared to intraparticle diffusion. Thermodynamic parameters (ΔH° and ΔG°) reflected the exothermic and spontaneous adsorption process. The values of ΔG°, ΔH°, activation energy and D–R free adsorption energy were all consistent with the physisorptive removal of AB1. The spectral (electronic and IR) and pH studies further corroborated the mechanism of AB1 removal by His-MNPs. The His-MNPs showed efficient adsorption, easy regeneration and excellent reusability, assisted by their pH-responsive properties. The prepared adsorbent can provide a safe, effective and economical alternative strategy for removing azo dyes from wastewater.

Effective and eco-friendly separation of Acid Black 1 dye from water by electrostatic adsorption onto reusable Histidine-Fe₃O₄ nanoparticles, credited to their pH-responsiveness.     

Melamine-based functionalized graphene oxide and zirconium phosphate for high performance removal of mercury and lead ions from water

Heavy metal ions are highly toxic and widely spread as environmental pollutants. This work reports the development of two novel chelating adsorbents, based on the chemical modifications of graphene oxide and zirconium phosphate by functionalization with melamine-based chelating ligands for the effective and selective extraction of Hg(ii) and Pb(ii) from contaminated water sources. The first adsorbent melamine, thiourea-partially reduced graphene oxide (MT-PRGO) combines the heavier donor atom sulfur with the amine and triazine nitrogen''s functional groups attached to the partially reduced GO nanosheets to effectively capture Hg(ii) ions from water. The MT-PRGO adsorbent shows high efficiency for the extraction of Hg(ii) with a capacity of 651 mg g⁻¹ and very fast kinetics resulting in a 100% removal of Hg(ii) from 500 ppb and 50 ppm concentrations in 15 second and 30 min, respectively. The second adsorbent, melamine zirconium phosphate (M-ZrP), is designed to combine the amine and triazine nitrogen''s functional groups of melamine with the hydroxyl active sites of zirconium phosphate to effectively capture Pb(ii) ions from water. The M-ZrP adsorbent shows exceptionally high adsorption affinity for Pb(ii) with a capacity of 681 mg g⁻¹ and 1000 mg g⁻¹ using an adsorbent dose of 1 g L⁻¹ and 2 g L⁻¹, respectively. The high adsorption capacity is also coupled with fast kinetics where the equilibrium time required for the 100% removal of Pb(ii) from 1 ppm, 100 ppm and 1000 ppm concentrations is 40 seconds, 5 min and 30 min, respectively using an adsorbent dose of 1 g L⁻¹. In a mixture of six heavy metal ions at a concentration of 10 ppm, the removal efficiency is 100% for Pb(ii), 99% for Hg(ii), Cd(ii) and Zn(ii), 94% for Cu(ii), and 90% for Ni(ii) while at a higher concentration of 250 ppm the removal efficiency for Pb(ii) is 95% compared to 23% for Hg(ii) and less than 10% for the other ions. Because of the fast adsorption kinetics, high removal capacity, excellent regeneration, stability and reusability, the MT-PRGO and M-ZrP are proposed as top performing remediation adsorbents for the solid phase extraction of Hg(ii) and Pb(ii), respectively from contaminated water.

Two novel chelating adsorbents are developed for the effective and selective extraction of Hg(ii) and Pb(ii) ions from contaminated water sources.     

Anionic azo dyes removal from water using amine-functionalized cobalt–iron oxide nanoparticles: a comparative time-dependent study and structural optimization towards the removal mechanism

The current study is aimed at synthesizing and characterizing magnetic cobalt–iron oxide nanoparticles (CoFeNPs) functionalized with two different amino reagents, hydrazine and dodecylamine, resulting in CoFeNPs1 and CoFeNPs2, respectively. Both types of cobalt–ferrite nanoparticles were investigated for the removal of six different negatively charged azoic dyes (Amaranth, Acid Orange 7, Naphthol Blue Black, Reactive Orange 16, Acid Orange 52 and Reactive Red-P2B) from water, and their removal efficiency was compared as a function of different factors such as time, type of anchored amine, size of CoFeNPs and structure of the dye. CoFeNPs were successfully characterized by FT-IR spectra, AFM, SEM-EDS, surface charge (ζ-potential) and thermal analysis. CoFeNPs1 revealed 44.5–82.1% dye removal at equilibrium (attained within 28–115 min) with an adsorptive capacity (q_e) of 5.4–13.5 mg g⁻¹ observed under unoptimized conditions (temp. 30 °C, adsorbent dose 0.67 g L⁻¹, pH 6, dye concentration 20 μmol L⁻¹). Use of CoFeNPs2 significantly enhanced the removal of each dye (percent dye removal 68.0–98.9%, q_e 6.6–23.5 mg g⁻¹) compared to CoFeNPs1 under similar conditions. From a comparative structural study, a larger size, more complex structure, hydrophobic character and greater number of phenyl SO₃⁻ groups among the tested dyes facilitated their removal by CoFeNPs2, while all of these structural factors were negatively related to dye removal by CoFeNPs1. CoFeNPs2 showed some dye aggregation along with adsorption, while in the case of CoFeNPs1, only adsorption was observed as confirmed by FT-IR and UV-visible spectral studies. Dye removal data in all cases was in best compliance with pseudo-second order kinetics in comparison to pseudo-first order or the Elovich model, where film diffusion was a dominant phenomenon compared to intra-particle diffusion. Adsorption isotherms, thermodynamics and reusability of the CoFeNPs were studied selecting Reactive Orange 16. Adsorption equilibrium was best fitted to the Langmuir isotherm. ΔG° and ΔH° indicated spontaneous and exothermic adsorption. Amine-functionalized CoFeNPs are recommended as potential cost-effective adsorbents with excellent reusability that could be applied efficiently for rapid and selective dye removal from textile effluents considering the size, structure, charge and number of S atoms in the target azo dyes.

Efficient and selective removal of azo dyes from water by amine-functionalized-CoFe₂O₄ nanoparticles reliant on structural features such as size, charge, hydrophobicity/hydrophilicity, and S/C atoms.     

Efficient removal of sulfamerazine (SMR) by ozonation in acetic acid solution after enrichment SMR from water using granular activated carbon

Sulfamerazine (SMR) as a persistent organic pollutant in waste streams is of growing environmental concern. This study explores the extraction SMR from water into an acetic acid (AA) solution using granular activated carbon (GAC), and removal of SMR by ozonation in AA solution. Systematic experiments have shown that GAC can be used as an adsorbent to transfer sulfamerazine from water to AA solution. SMR removal efficiency is 99.5% in 10% AA aqueous solution, which is better than in water. The removal rate of SMR in the AA solution decreased as the initial molar ratio of SMR and O₃ increased. The removal rate of SMR decreased with Fe³⁺ present in the reactive system. The removal of SMR is dominated by indirect ozonation in water, while the SMR removal is an effect of both direct and indirect ozonation in AA solution. It is a very efficient process for the degradation of SMR in micro polluted water when using combined GAC adsorption–desorption in AA solution and ozonation of the resulting solution.

Sulfamerazine (SMR) as a persistent organic pollutant in waste streams is of growing environmental concern.     

Tinospora cordifolia derived biomass functionalized ZnO particles for effective removal of lead(ii), iron(iii), phosphate and arsenic(iii) from water

Owing to the vast diversity in functional groups and cost effectiveness, biomass can be used for various applications. In the present study, biomass from Tinospora cordifolia (TnC) was prepared and grafted onto the surface of ZnO particles following a simple method. The TnC functionalized ZnO particles (ZnO@TnC) were characterized and exhibited excellent adsorption properties towards Pb²⁺ (506 mg g⁻¹), Fe³⁺ (358 mg g⁻¹) and PO₄³⁻ (1606 mg g⁻¹) and the Fe³⁺ adsorbed ZnO@TnC adsorbs AsO₂¹⁻ (189 mg g⁻¹); the metal ions and anions were analyzed by ICP and IC. For reuse of ZnO@TnC, a desorption study was successfully carried out using NaOH and EDTA for PO₄³⁻ and Pb²⁺, respectively; Fe³⁺ was further used for adsorption of As(iii). The adsorption fits well with the Langmuir adsorption isotherm model and the adsorption kinetic data are best fitted with a pseudo-second-order equation. The system developed may be useful for treatment of waste water and industrial effluents.

Owing to the vast diversity in functional groups and cost effectiveness, biomass can be used for various applications.     

Enhanced quinoline removal by zero-valent iron-coupled novel anaerobic processes: performance and underlying function analysis

Quinoline is toxic and difficult to degrade biologically; thus, it is a serious threat to the safety of ecosystems. To promote quinoline reduction, zero-valent iron (ZVI) was introduced into an anaerobic digestion (AD) system through batch experiments. The performance of three different types of ZVI (i.e., iron powder, iron scrap and rusty iron scrap) on quinoline degradation, methane production, formation of volatile fatty acids (VFAs) and chemical oxygen demand (COD) removal were investigated systematically. Compared to the AD system alone, quinoline and COD removal as well as the production of methane and acetic acid were effectively enhanced by ZVI, especially rusty iron scrap. The removal efficiencies of quinoline and COD were increased by 28.6% and 19.9%, respectively. The enhanced effects were attributed to the high accumulation of ferrous ions and high pH self-buffering capability, which were established by ZVI addition. Furthermore, high-throughput sequencing analysis indicated that the functional microorganisms in the ZVI-AD system were higher than in the AD system, and the added types of ZVI played important roles in structuring the innate microbial community in waste activated sludge (WAS). Especially, high enrichment of microorganisms capable of degrading quinoline, such as Pseudomonas and Bacillus, in the coupled system was detected.

The addition of different types of ZVI affects the efficiency of quinoline degradation and methane production in WAS digestion.     

Separation of neodymium and dysprosium by solvent extraction using ionic liquids combined with neutral extractants: batch and mixer-settler experiments

A solvent extraction method based on the combination of the ionic liquid trihexyl(tetradecyl)phosphonium thiocyanate or nitrate ([C101][SCN], [C101][NO₃]) and the neutral extractants Cyanex 923 or tri-n-butyl phosphate (TBP) has been investigated for the separation of Nd(iii) and Dy(iii) from chloride media. High distribution ratios and separation factors were obtained when using Cyanex 923 diluted in [C101][SCN] 40 : 60 (wt%) and extracting from chloride media. The addition of Cyanex 923 to the ionic liquid has four advantages: (1) increase in the distribution ratios of the rare earths, (2) decrease of the viscosity of the organic phase, hence an improved mass transfer, (3) increase in the loading capacity of the ionic liquid and (4) improvement of the coalescence and phase disengagement, which is of importance when carrying out separations in continuous mode. Different extraction parameters were optimized: concentration of Cyanex 923, chloride concentration in the aqueous phase, equilibration time, pH of the aqueous phase, type of scrubbing and stripping agents. The ionic liquid combined with Cyanex 923 was recycled up to three times without losing its extraction efficiency. McCabe–Thiele diagrams were constructed to determine the number of stages needed for the separation of Nd(iii) and Dy(iii). Stripping of Dy(iii) from the organic phase was easily achieved with water. The feasibility to run this process in continuous mode was tested in a battery of small mixer-settlers (0.12 L and 0.48 L effective volume in the mixer and the settler, respectively). As a result, this process constitutes a novel and scalable alternative for the separation of Nd(iii) and Dy(iii).

The combination of ionic liquids with Cyanex 923 improves the separation of Nd(iii) and Dy(iii).     

Enhanced removal of fluoride by zirconium modified tea waste with extrusion treatment: kinetics and mechanism

To improve the adsorption efficiency of tea-based biosorbents for removing fluoride in drinking water, the novel and effective adsorbent was formed by treating tea waste with extrusion technology. In this study, the extrusion technology was applied to the preparation of adsorbents for the first time. A low-priced and more efficient adsorbent was prepared by loading zirconium onto extruded tea waste (EXT-Zr). Extruded tea waste increased the surface pore size, which could provide more loading sites for zirconium. The EXT-Zr effectively removed fluoride from water in a pH range of 3.0–10.0, which is wider than the pH range of zirconium-loaded tea waste (Tea-Zr). The adsorption was fitted by a pseudo-second order kinetic model and the Langmuir adsorption model. The maximum adsorption capacity was 20.56 mg g⁻¹. The EXT-Zr adsorbent was characterized by Scanning electron microscopy (SEM), Energy-Dispersive Spectroscopy (EDS), X-ray diffraction (XRD), a Brunauer–Emmett–Teller (BET) method, Fourier-transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) to prove the mechanism of how EXT-Zr adsorbs fluoride. The results proved that EXT-based adsorbent will be effective for the enhanced removal of fluoride in drinking water.

Extruded tea waste (EXT) increased the pore size by extrusion technology. Extruded tea waste (EXT-Zr) modified by Zr performed well.     

Super rapid removal of copper,cadmium and lead ions from water by NTA-silica gel

Copper (Cu²⁺), cadmium (Cd²⁺) and lead ions (Pb²⁺) are toxic to human beings and other organisms. In this study, a silica gel material modified with nitrilotriacetic acid (NTA-silica gel) was sensibly designed and prepared via a simple amidation procedure for the removal of Cu²⁺, Cd²⁺ and Pb²⁺ from water. The NTA-silica gels showed rapid removal performances for the three metal ions (Pb²⁺ (<2 min), Cu²⁺ and Cd²⁺ (<20 min)) with relatively high adsorption capacities (63.5, 53.14 and 76.22 mg g⁻¹ for Cu²⁺, Cd²⁺ and Pb²⁺, respectively). At the same concentration of 20 mg L⁻¹, the removal efficiencies of the three metals by the adsorbent ranged from 96% to 99%. The Freundlich and Langmuir models were utilized to fit the adsorption isotherms. The adsorption kinetics for the three metal ions was pseudo-second-order kinetics. The removal performance of the NTA-silica gels increased in a wide pH range (2–9) and maintained in the presence of competitive metal ions (Na⁺, Mg²⁺, Ca²⁺ and Al³⁺) with different concentrations. In addition, the NTA-silica gels were easily regenerated (washed with 1% HNO₃) and reused for 5 cycles with high adsorption capacity. This study indicates that the NTA-silica gel is a reusable adsorbent for the rapid, convenient, and efficient removal of Cu²⁺, Cd²⁺, and Pb²⁺ from contaminated aquatic environments.

A silica gel material modified with nitrilotriacetic acid (NTA-silica gel) was sensibly designed and prepared via a simple method for the super rapid removal of Cu²⁺, Cd²⁺ and Pb²⁺ from water.     

Preparation and optimization of activated nano-carbon production using physical activation by water steam from agricultural wastes

Production of activated nano-carbon from agricultural wastes was studied in this work. To obtain the optimum production conditions by a physical activation method, influence of temperature (850, 900, 950 and 1000 °C), activation residence time (30, 60 and 90 min), and mill rotation (200, 300 and 400 rpm) were investigated using three different raw materials including walnut, almond and pistachio shells. To prepare activated nano-carbon, all the samples were heated up to the final activation temperature under a continuous steam flow of 130 cm³ min⁻¹, and at a heating rate of 3 °C min⁻¹, and were held at the different activation temperatures for 30, 60 and 90 minutes. BET surface area of the obtained activated carbons was measured from nitrogen adsorption data in the relative pressure range between 0 to 1. Activated nano-carbon standard indexes were evaluated according to the ASTM standard and the samples were compared. First, the cellulose raw material was heated in the carbonization furnace at 600 °C and then activated in the advanced activation furnace at a temperature between 850 to 1000 °C for 30, 60 and 90 minutes with water vapor. Ash percentage, iodine content, moisture content, specific area, elemental analysis, and FESEM were used for product characterization. The results of the analysis showed that by using the water vapor physical activation method and optimizing the parameters of this process including time and rotation of the mill up to 10 min and 400 rpm, resulted in a significant increase in specific surface area, cavity volume and the iodine number of the final product.

Production of activated nano-carbon from agricultural wastes was studied in this work.     

Removal of contaminants by activating peroxymonosulfate (PMS) using zero valent iron (ZVI)-based bimetallic particles (ZVI/Cu,ZVI/Co,ZVI/Ni,and ZVI/Ag)

In this study, four different ZVI/M-PMS systems (e.g., ZVI/Cu, ZVI/Co, ZVI/Ni and ZVI/Ag) were fabricated to investigate the removal of contaminants (Rhodamine B (RB), 2,4-dichlorophenol (2,4-DCP), bisphenol A (BPA), bisphenol F (BPF), levofloxacin (LFX), and chloramphenicol (CAP)). The results indicated that ZVI/Cu and ZVI/Ag exhibited a superior performance to activate PMS compared with the ZVI. The mechanism of the investigation showed that a relatively positive correlation between the release of iron ions (Fe²⁺) and contaminant removal efficiency was found in different ZVI/M-PMS systems. This revealed that galvanic couples affected iron corrosion, and the ZVI/Cu and ZVI/Ag bimetallic systems facilitated the corrosion of ZVI but the ZVI/Co and ZVI/Ni bimetallic systems restrained the corrosion of ZVI. The electron paramagnetic resonance (EPR) analysis and the radical quenching experiments apparently supported the roles of the hydroxyl radical (˙OH), sulfate radical (SO₄˙⁻) and superoxide radicals (O₂˙⁻), which suggest that these reactive radicals were primarily responsible for the degradative route, and the contribution rate may follow the order of SO₄˙⁻ < O₂˙⁻ < ˙OH. Furthermore, investigation of crucial parameters showed that the contaminant removal ratio increased with an increase in the metal ratio (M : ZVI) to a certain limit, and a higher bimetal catalyst dosage and extremely acidic conditions (except for ZVI/Co, which showed the best catalytic performance under neutral condition) enhanced the degradation of contaminants. In the evaluation of real water samples, there was almost no influence from the water matrices compared to the control condition, and the ZVI/Cu and ZVI/Ag bimetallic particles showed great potential to treat various wastewater. Therefore, this study helps to understand the application of oxidation process based on bimetallic particles.

In this study, four different ZVI/M-PMS systems (e.g., ZVI/Cu, ZVI/Co, ZVI/Ni and ZVI/Ag) were fabricated to investigate the removal of contaminants (Rhodamine B, 2,4-dichlorophenol, bisphenol A, bisphenol F, levofloxacin, and chloramphenicol).     

Enhanced visible light photocatalytic degradation of dyes in aqueous solution activated by HKUST-1: performance and mechanism

HKUST-1 is a copper-based metal–organic framework (MOF) and potential photocatalyst, but minimal research has addressed the performance and mechanism of HKUST-1 in the visible light photocatalytic degradation of dyes. In the present work, HKUST-1 was applied as a photocatalyst to activate peroxomonosulfate (PMS) under visible light (Vis) for dye removal in aqueous solution. The results showed that the removal efficiency of two cationic dyes [rhodamine B (RhB) and methylene blue (MB)] was greater than 95% within 120 min. Free radicals such as SO₄⁻˙, ·OH were present in the degradation process, with SO₄⁻˙ playing a dominant role. Zeta potential, X-ray photoelectron spectroscopy, and photoluminescence spectroscopy data were used to investigate the degradation mechanism. In the degradation process, surface charge attraction between HKUST-1 and cationic dyes promotes removal efficiency, with the degradation efficiency of cationic dyes (MB and RhB) more than 50% higher than for anionic dyes [acid orange 7 (AO₇) and methyl red (MR)]. On the other hand, HKUST-1 has been proved to activate PMS by conducting photoelectrons, which accelerated the degradation of dyes. Compared with the reaction conditions of PMS/Vis, when the HKUST-1 was present (HKUST-1/PMS/Vis), the degradation rates of MB and RhB increased by 62.7 and 63.2%, respectively.

HKUST-1 is a copper-based metal–organic framework (MOF). The HKUST-1/PMS/Vis system can effectively degrade RhB and MB but accomplish poor removal of AO₇ and MR, which is attributed to the repulsion between surface charges.