A study of the removal of selenite and selenate from aqueous solutions using a magnetic iron/manganese oxide nanomaterial and ICP-MS

Selenium (Se) is naturally occurring in the environment and is an essential nutrient in mammals. However, environmental Se can be increased to toxic levels through different industrial practices. The potential adsorption of the Se oxoanions, selenite and selenate, from aqueous solutions onto nanosynthesized MnFe₂O₄ was investigated using batch techniques and DRC-ICP-MS spectroscopy. The nanomaterial (NM) was laboratory synthesized through slow titration of a mixture of Fe²⁺ and Mn²⁺ ions. X-ray diffraction and Scherrer's equation were used to determine the phase of the material and crystallite size, respectively. The effects of pH, reaction time, competitive anions, and the adsorption capacity of the synthesized NM to bind selenite and selenate were investigated. The Langmuir isotherm was used to determine the binding capacity of the NM. Results showed that the phase of the nanomaterial was similar to Jacobsite with a size of 27.5 nm. Results also showed that the sorption of either 100 ppb of selenite or selenate was pH independent in the pH range 2 to 6 and occurred within 5 min of contact time. The introduction of Cl⁻ and NO₃⁻ anions individually added to solution had no significant effect on the sorption of either selenite or selenate. However, it was found that the addition of SO₄²⁻ had a competitive effect only on the sorption of selenate, first seen at 10 ppm and more pronounced at 100 ppm of SO₄²⁻. In the presence of 100 ppm of PO₄³⁻, the adsorption of selenate decreased to 87% while selenite sorption decreased to 20%. From the Langmuir isotherm equation it was determined that the nano-Jacobsite had a selenite and selenate binding capacity of 6573.76 and 769.23 mg Se/kg of NM, respectively.     

Aspects of ZnSe electrosynthesis from selenite and selenosulfite aqueous solutions

Cathodic electrodeposition of ZnSe is studied in aqueous acidic selenite (Se^(IV)O₂) baths of free Zn²⁺ ions and alkaline selenosulfite (Se⁰SO₃^2–) baths of zinc complex ions. The synthesis of polycrystalline, cubic ZnSe by Se^(IV)-diffusion-controlled electrodeposition from acidic solutions is optimized in terms of selenite concentration, while the effect of Ti, Ni, anodized Ti and CdSe substrates on the obtained layers growth and structural properties is investigated. Furthermore, the production of stoichiometric though amorphous ZnSe is demonstrated using selenosulfite solutions. The results are valuated by means of X-ray diffraction, scanning electron microscopy and reflectance spectroscopy techniques.     

Characterization of Co(II) removal from aqueous solution using bentonite/iron oxide magnetic composites

The bentonite/iron oxide magnetic composites were prepared by co-precipitation method, and characterized by Fourier transform infrared spectroscopy, X-ray powder diffraction and scanning electron microscope. The prepared bentonite/iron oxide magnetic composites were used as a sorbent for the removal of Co(II) ions from radioactive wastewater. The results demonstrated that the sorption of Co(II) was strongly dependent on pH and ionic strength at low pH values. The sorption of Co(II) was dominated by outer-sphere surface complexation or ion exchange at low pH whereas inner-sphere surface complexation was the main sorption mechanism at high pH. The presence of iron oxide in the composites also contributes to the sorption of Co(II) ions on the magnetic composites. The experimental data were well described by Langmuir model. The thermodynamic parameters (∆G ^°, ∆S ^°, ∆H ^°) calculated from the temperature-dependent sorption isotherms indicated that the sorption of Co(II) on bentonite/iron oxide magnetic composites was an endothermic and spontaneous processes.     

Removal of U(VI) from aqueous solutions by using attapulgite/iron oxide magnetic nanocomposites

The attapulgite/iron oxide magnetic nanocomposites were prepared by coprecipitation method and characterized by scanning electron microscopy, X-ray diffraction, vibrating sample magnetometer and Fourier transform infrared sorption spectroscopy. The results of characterization showed that iron oxides were successfully deposited on the surfaces of attapulgite. The prepared magnetic nanocomposites were applied to remove radionuclide U(VI) ions from aqueous solutions by using batch technique and magnetic separation method. The results showed that the sorption of U(VI) on attapulgite/iron oxide magnetic composites was strongly dependent on ionic strength and pH at low pH values, and was independent of ionic strength at high pH values. The interaction of U(VI) with the magnetic nanocomposites was mainly dominated by outer-sphere surface complexation or ion exchange at low pH values, and was controlled by inner-sphere surface complexation or multinuclear surface complexation at high pH values. With increasing temperature, the sorption of U(VI) on attapulgite/iron oxide magnetic composites increased and the thermodynamic parameters calculated from the temperature dependent sorption isotherms suggested that the sorption of U(VI) on the magnetic nanocomposites was a spontaneous and endothermic process. The high sorption capacity and easy magnetic separation of the attapulgite/iron oxide magnetic composites make the material as suitable sorbent in nuclear waste management.     

Kinetic modeling analysis for the removal of cesium ions from aqueous solutions using polyaniline titanotungstate

Polyaniline titanotungstate has been synthesized by incorporation of organic polymer polyaniline into the inorganic precipitate of titanotungstate. This material was characterized using X-ray, IR and TGA studies. The influences of initial concentration of metal ions, particle size and temperature have been reported. The comparison of composite and inorganic materials was studied and indicating that the composite material is better than the inorganic in selectivity of Cs⁺ ions. Thermodynamic parameters, such as changes in Gibbs free energy (ΔG), enthalpy (ΔH), and entropy (ΔS) have been calculated. The numerical values of ΔG decrease with an increase in temperature, indicating that the sorption reaction of adsorbent was spontaneous and more favorable at higher temperature. The positive values of ΔH correspond to the endothermic nature of sorption processes and suggested that chemisorptions were the predominant mechanism. A comparison of kinetic models applied to the sorption rate data of Cs⁺ ions was evaluated for the pseudo first-order, the pseudo second-order, intraparticle diffusion and homogeneous particle diffusion kinetic models. The results showed that both the pseudo second-order and the homogeneous particle diffusion models were found to best correlate the experimental rate data. Self diffusion coefficient (D_i), Activation energy (Ea) and entropy (ΔS^*) of activation were also computed from the linearized form of Arrhenius equation.     

Efficiency of succinylated-olive stone biosorbent on the removal of cadmium ions from aqueous solutions

Chemical functionalization of olive stone wastes with succinate linkers can potentially improve the performance of wastewater treatment technologies via enhanced adsorption and high affinity of the covalently attached succinate groups for heavy metals. In this study, a novel reusable adsorbent material based on agricultural waste has been synthesized by esterifying the lignocellulosic matrix of olive stones with succinic anhydride in toluene under basic conditions. Characterization of the as-prepared material by FTIR and solid-state MAS ¹³C NMR spectroscopies and TGA confirmed that the heterogeneous esterification has proceeded very efficiently to yield the succinylated-olive stone (S–OS). Subsequent alkaline treatment of S–OS with saturated NaHCO₃ aqueous solution led to the resulting sodic material (NaS–OS), which was subjected to batch experiments in order to evaluate its cadmium-removing efficiency from aqueous solutions at realistic concentrations of cadmium found in industrial effluents. The results obtained from the sorption characteristics have revealed that NaS–OS material is highly effective in removing cadmium from aqueous solutions, with a maximum uptake capacity of 200 mg g⁻¹ (1.78 mmol g⁻¹). The Langmuir isotherm model was found to fit adequately the equilibrium isotherm data. Cadmium adsorption occurs rapidly and the adsorption mechanism is a chemical sorption via ionic exchange between the adsorbate and adsorbent. Thermodynamic parameters were also evaluated from the effect of temperature studies. Regenerability of NaS–OS material was ascertained by quantitative desorption of cadmium with 1 M aqueous NaCl and the reusability of the matrix after five repeated cycles led to nearly no attenuation in its performance (less than 2% in the sorption capacity), indicating that repeated use of NaS–OS is quite feasible. Compared to other low-cost adsorbents utilized for the removal of Cd(II) from water/wastewater, NaS–OS shows higher sorption capacity. These results have important implications for the design of low-cost adsorbents based on agricultural wastes.     

Ion exchange recovery of chromium (VI) and manganese (II) from aqueous solutions

Sorption recovery of toxic ions – chromium (VI) and manganese (II) – from aqueous solutions with different acidity (0.001–0.5 M HCl) was investigated on cation and anion exchangers synthesized with long-chained cross-linking agents (LCA). The initial concentrations of Cr(VI) and Mn(II) were 1 g/L and 5 g/L, respectively. It was shown that the resins with LCA possess high ionic permeability due to the elasticity of polymeric skeleton. High selectivity and good kinetic properties of these sorbents allowed to achieve quantitative (∼100%) recovery and separation of manganese (II) and chromium (VI) in counter-current columns, which results in the complete purification of solutions from toxicants (below the maximum permissible limits), whereas the valuable components (chromium and manganese) can be returned back to industrial process.     

Synthesis of magnetic graphene oxide nanoribbons composite for the removal of Th(IV) from aqueous solutions

Journal of Radioanalytical and Nuclear Chemistry - Functionalized magnetic graphene oxide nanoribbons (MGONRs) composite material was synthesized by hydrothermal treatment method using graphene...     

Impact of environmental conditions on the removal of Ni(II) from aqueous solution to bentonite/iron oxide magnetic composites

The sorption of radionuclide ⁶³Ni(II) on bentonite/iron oxide magnetic composites was investigated by batch technique under ambient conditions. The effect of contact time, solid content, pH, coexistent electrolyte ions, fulvic acid, and temperature on Ni(II) sorption to bentonite/iron oxide magnetic composites was examined. The results demonstrated that the sorption of Ni(II) was strongly dependent on pH and ionic strength at pH <8.0, and was independent of pH and ionic strength at high pH values. The sorption of Ni(II) was dominated by outer-sphere surface complexation or ion exchange at low pH, whereas inner-sphere surface complexation was the main sorption mechanism at high pH. The experimental data were well fitted by Langmuir model. The thermodynamic parameters (∆G°, ∆S°, ∆H°) calculated from the temperature-dependent sorption isotherms indicated that the sorption of Ni(II) on bentonite/iron oxide magnetic composites was an endothermic and spontaneous processes. The results show that bentonite/iron oxide magnetic composites are promising magnetic materials for the preconcentration and separation of radionickel from aqueous solutions in environmental pollution.     

Sorption characteristics and separation of tellurium ions from aqueous solutions using nano-TiO2

Titanium dioxide nanoparticles (nano-TiO₂) were employed for the sorption of Te(IV) ions from aqueous solution. A detailed study of the process was performed by varying the sorption time, pH, and temperature. The sorption was found to be fast, equilibrium was reached within 8 min. When the concentration of Te(IV) was below 40 mg L⁻¹, at least 97% of tellurium was adsorbed by nano-TiO₂ in the pH range of 1-2 and 8-9. The sorbed Te(IV) ions were desorbed with 2.0 mL of 0.5 mol L⁻¹ NaOH. The sorption data could be well interpreted by the Langmuir model with the maximum adsorption capacity of 32.75 mg g⁻¹ (20 ± 0.1 °C) of Te(IV) on nano-TiO₂. The kinetics and thermodynamics of the sorption of Te(IV) onto nano-TiO₂ were also studied. The kinetic experimental data properly correlated with the second-order kinetic model (k₂ = 0.0368 g mg⁻¹ min⁻¹, 293 K). The overall rate process appeared to be influenced by both boundary layer diffusion and intra-particle diffusion. The mean energy of adsorption was calculated to be 17.41 kJ mol⁻¹ from the Dubinin-Radushkevich (D-R) adsorption isotherm at room temperature. Moreover, the thermodynamic parameters for the sorption were estimated, and the ΔH⁰ and ΔG⁰ values indicated the exothermic and spontaneous nature of the sorption process, respectively. Finally, Nano-TiO₂ as sorbent was successfully applied to the separation of Te(IV) from the environmental samples with satisfactory results (recoveries >95%, relative standard deviations was 2.0%).     

Ultrasound facilitates and improves removal of triphenylmethane (crystal violet) dye from aqueous solution by activated charcoal: A kinetic study

This work was aimed at removing crystal violet (CV) from an aqueous solution via an ultrasound-aided sorption process. Different operational parameters, such as contact time, ultrasonic power, and the sorbent dosage, were investigated. The results indicated that the sorption process was more rapid compared with the previously stated process; a sorption equilibrium was obtained after 1.5 h. The increase in the dose from 0.02 to 5.0 g/L increased the adsorption efficiency by 100%. The decolorization of the CV pigment occurred very rapidly at the highest sound power, 200 W, and it reached ～85%. The kinetics study indicated that the sorption process fitted the pseudo-second-order model with the chemisorption mechanism. The sorption isotherm data were also interpreted by the mass-transfer model, which established the intraparticle diffusion. Additionally, to estimate the rate-limiting step mechanisms, the intraparticle diffusion was not considered as the sole rate-controlling step. The maximum sorption capacity (q_max) increased from 19.0 to 24 mg/g during the ultrasound and indicated the positive synergistic effect of the ultrasound. The proposed sonosorption technique is a low cost-effective method for purifying water and wastewater from organic pollutants.     

Synthesis and characterization of a new magnetic bromochromate hybrid nanomaterial with triethylamine surface modified iron oxide nanoparticles

We describe a novel method for the synthesis a new magnetic bromochromate hybrid nanomaterial, Fe3O4@SiO2@TEA@[CrO3Br], as a catalyst. The physical properties, morphology and magnetic investigations of magnetic bromochromate hybrid nanomaterials are identified by transmission electron microscopy （TEM）, scanning electron microscopy （SEM） and vibrating sample magnetometer （VSM） techniques. Fourier transform infrared （FT-IR）, elemental analysis, X-ray fluorescence （XRF）, X-ray diffraction （XRD） were also used for structural identification. The quantity of chromium is approximately 0.38%, which confirms to the immobilization amount of [CrO3Br]- and is equal to 0.007 mol/100 g.     

Biosorption of lanthanum from aqueous solutions using magnetic alginate beads

Magnetic alginate beads are potential biosorbent for sorption of lanthanum(III) from an aqueous medium. Batch experiments were carried out to study the equilibrium, kinetics, and thermodynamics of lanthanum sorption. The effects of initial solution pH, initial lanthanum concentration, and temperature on lanthanum sorption were investigated. The optimum pH value was defined to be 4. Kinetic and isotherm experiments were carried out at the optimum pH. It was enough to reach the adsorption equilibrium at 4 hours, and the maximum uptake capacity was (1.8 mmol g^?1) at 25°C. Uptake kinetics and sorption isotherms were obtained and modeled using conventional and simple equations: best results were respectively obtained with the pseudo-second-order rate equation and the Langmuir equation. The La(III) loaded magnetic alginate beads were regenerated using 0.1 M CaCl₂ without activity loss.     

锰负载钛锆和钛锡复合氧化物催化剂烟气脱汞实验研究

采用共沉淀法制备了TiO_2、TiZr和TiSn载体,浸渍锰制备了10%MnO_2的MnTi、MnTiZr和MnTiSn催化剂。采用BET、XRD、H_2-TPR、FT-IR和XPS等对样品进行表征,并对三种催化剂进行固定床脱汞性能实验。结果表明,在100-300℃,MnTiZr和MnTiSn催化剂脱汞性能均优于MnTi催化剂,这归因于Sn和Zr的引入提升了催化剂比表面积和低温氧化还原性能增加了催化剂表面的酸性位点数量、高价态锰离子和O~*含量;在反应温度为150-300℃,MnTiSn催化剂脱汞效率均高于MnTiZr催化剂这是由于前者具有更好的氧化还原性能,表面具有更多含量的高价态锰离子、O~*含量和酸性位点数量;在Hg~0脱除过程中催化剂表面活性组分如高价态锰离子和O~*均消耗,参与了Hg~)氧化为Hg~(2+)的反应且MnTiSn催化剂表面活性组分的消耗量更多。     

Synthesis,crystal structure and magnetic property of a three-dimensional manganese(II) complex

The solvothermal reaction of MnCl₂·4H₂O, H₂asp and CH₃ONa gave rise to a new manganese(II) complex, {[Mn(asp)(H₂O)]·(H₂O)₂} _n (1) (H₂asp?=?5-aminoisophthalic acid). Single-crystal X-ray diffraction analysis reveals that complex 1 is a three-dimensional consisting of two-dimensional layers extended by hydrogen bonding interactions. The two-dimensional layer contains 8-, 14-, and 16-membered rings. A variable temperature magnetic measurement of 1 displays weak antiferromagnetic behavior.     

Enhanced removal of phosphonates from aqueous solution using PMS/UV/hydrated zirconium oxide process

Traditional treatment processes cannot completely remove phosphonates in circulating cooling water by one-step method. Herein, we designed peroxymonosulfate/UV irradiation/hydrated zirconium oxide (PMS/UV/HZO) coupling process to enhance the phosphonates removal. In particular, nitrilotris-methylenephosphonic acid (NTMP) removal efficiency by PMS/UV/HZO process was much higher than that of PMS/UV process, UV/HZO process and other processes in comparison experiments. Specifically, almost 97.2% NTMP in water was degraded, and the total phosphorous (TP) reduced from 9.3 mg/L to 0.26 mg/L at pH 7 within 180 min. TP removal efficiency still reached above 90% after 5 cycles adsorption-desorption of HZO. Moreover, Clˉ, NO₃ˉ and SO₄²ˉ ions all had negligible effect on NTMP removal. During the process, NTMP was first destroyed to form phosphates and other intermediates by the reactive oxygen species (ROS), then phosphates were in situ immobilized via HZO adsorption. Sulfate radical (SO₄^??) has been confirmed to be the major ROS in the reaction system by quenching experiment and electron paramagnetic resonance (EPR) characterization. And the excellent selective adsorption capacity of HZO for phosphate produced was attributed to the strong inner-sphere coordination between H₂PO₄ˉ/HPO₄²ˉ and Zr-OH on the surface of HZO. These results suggest that PMS/UV/HZO process is a promising technique for enhanced phosphonates decontamination.     

Highly efficient removal of toxic lead ions from aqueous solutions using a new magnetic metal‐organic framework nanocomposite

A magnetic metal‐organic framework (MOF) nanocomposite was successfully prepared by a new and green strategy through reasonable design. Magnetic MOF of Fe₃O₄‐NHSO₃H@HKUST‐1 nanocomposite use for removal of lead ions as an environmental pollutant. The experimental results indicated that the nano adsorbent of Fe₃O₄‐NHSO₃H@HKUST‐1 can removed lead ions under optimum operational conditions. The dosage of the nanocomposite, pH of the sample solution, and contact time were obtained to be 10 mg, 7.0, and 90 min, respectively, while the initial concentration of Pb(II) ions of 400 mg/L was used. A kinetic study indicated that a pseudo‐second‐order model agreed well with the experimental data. The isotherm experiments revealed that the Langmuir model attained better fits to the equilibrium data than the Freundlich model. The maximum adsorption capacity of the adsorbent for the removal of lead under the optimum operational conditions of pH 7.0 and temperature 25°C was found to be 384.6 mg/g. The thermodynamic parameters indicate that the adsorption of lead is spontaneous and endothermic. The magnetic MOF nanocomposite could be recovered easily and reused many times without significant loss of its nano‐adsorbent activity. The proposed method is simple, eco‐friendly, low cost, and efficient in the removal of lead ions from aqueous solutions.     

A structural study of saturated aqueous solutions of some alkali halides by X-ray diffraction

The structure of nearly saturated or supersaturated aqueous solutions of NaCI [6.18 mol (kg H₂O)^–1], KCI [4.56 mol (kg H₂O)^–1], KF [16.15 mol (kg H₂O)^–1] and CsF [31.96 mol (kg H₂O)^–1] has been investigated by means of solution X-ray diffraction at 25°C. In the NaCI and KCI solutions about 30% and 60%, respectively, of the ions form ion pairs and the Na⁺–Cl^– and K⁺–Cl^– distances have been determined to be 282 and 315 pm, respectively. The average hydration numbers of Na⁺ and Cl^– ions are 4.6 and 5.3, respectively, in the NaCI solution and those of K⁺ and Cl^– ions in the KCI solution are both 5.8. In the KF solution, clusters containing some cations and anions, besides 1:1 (K⁺–F^–) ion pairs, are formed. The K⁺–F^– interatomic distance has been determined to be 269 pm, and nonbonding K⁺...K⁺ and F^–...F^– distances in the clusters are 388 and 432 pm, respectively, and the average coordination numbers n _KF , n _KK and n _FF have been estimated to be 2.3, 1.9, and 1.6, respectively. In the highly supersaturated CsF solution an appreciable amount of clusters containing several caesium and fluoride ions are formed. The Cs⁺–F^– distance in the cluster has been determined to be 312 pm, while the nonbonding Cs⁺...Cs⁺ and F^–...F^– distances are estimated to be 442 and 548 pm, respectively, the distances being about and times the Cs⁺–F^– distance, respectively. The coordination numbers n _CsF , n _CsCs , and n _FF in the first coordination sphere of each ion are 3.3, 2.3 and 5.3, respectively, and the result shows the formation of clusters of higher order than 1:1 and 2:2 ion pairs. These ion pairs and clusters may be regarded as embryos for the formation of nuclei of crystals and the results obtained in the present diffraction study support observations for the nucleation of the alkali halide crystals studied by molecular dynamics simulations previously examined.