Adsorption removal of fluoride from polluted drinking waters using Mn-Al-La oxide.

Trimetal oxides have received high attention in treatment of fluoride-polluted drinking waters. In this study, Mn-Al-La (MAL) oxide with a mole ratio of 2:1:1 was successively prepared and characterized by XRD, FTIR, XPS, and TEM. It exhibited as cotton-like assemblages (500-800 nm of axial lengths), and BET specific surface area was 52 m2/g. It was used to study fluoride adsorptions in aqueous solutions by batch experiments, under different adsorbent/adsorbate levels, times, temperatures, pH and coexisting anions, and treat simulated groundwater (with 2.85 mg/L fluoride and pH 7.0) by batch and column tests. Adsorption data well fitted to pseudo-second-order rate model (R2 = 0.996-0.999), and Langmuir (R2 = 0.962 - 0.997) and Freundlich (R2 = 0.964-0.989) isothermal models. Their maximum adsorption capacities could reach 45-113 mg/g. Only H2PO4- anions had a restrictive impact at pH 7.0, and there was a good removal ability at pH 3-9. Adsorption processes were spontaneous, endothermic, and random. Adsorption mechanisms were electrostatic interaction and ligand exchange at pH 7.0. Adsorption capacity could reach 73% of initial value at pH 7.0, after three cycles. All application data on the polluted groundwater treatments show MAL oxide is a potential adsorbent for fluoride removals.

Synthesis of ß-FeOOH/polyaniline heterogeneous catalyst for efficient photo-Fenton degradation of AOII dye.

Discharge of the untreated dye-containing wastewaters will induce water source pollution and further harm aquatic organisms. In this study, the akaganéite/polyaniline catalyst (ß-FeOOH/PANI, about 1.0 µm) could be successfully composed by polyaniline (PANI, (C6H7N)n, 200-300 nm) and akaganéite (ß-FeOOH, FeO(OH)1-xClx, less than 200 nm), according to the identification and characterization results of XRD, Ramon, FTIR, XPS, SEAD, EDS, and FESEM (or HRTEM). Due to PANI providing more photogenerated electrons, the ß-FeOOH/PANI composite (compared with ß-FeOOH) in photo-Fenton system had the more highly catalytic degradation capacity to Acid Orange II (AOII) under an optimal condition (7.5 mmol/L of H2O2 oxidant, 40 mg/L of AOII, 0.2 g/L of catalyst dosage, and pH 4.0). The AOII degradation kinetics could be well fitted by pseudo-first-order model. In photo-Fenton catalytic process of AOII dye, the ∙OH and h+ were the main reaction substances. The AOII in solutions could be gradually mineralized into non-toxic inorganic H2O molecule and CO2. The ß-FeOOH/PANI catalyst also had a good reusable ability of about 91.4% AOII degradation after 4 runs. These results can provide a reference for synthesis of catalyst used in photo-Fenton system and the applications in degradation removal of organic dye from wastewaters.

Chromium(III) adsorption removal from acidic solutions by isomeric and tunnel-structural iron oxyhydroxides.

Iron oxyhydroxides for heavy metal treatment have attracted wide attention. In this work, iron oxyhydroxides of isomeric FeOOH (GpI) and tunnel-structural schwertmannite/akaganéite (GpII) were selected to study chromium (Cr(III)) adsorption removal from acidic aqueous solutions by batch experiments, under various reaction time, adsorbate/adsorbent level, pH and anions. Adsorption processes well fitted to pseudo-second-order kinetics (R2 = 0.992-0.999, except for 0.829 for Lep). Isotherm data could be fitted by Langmuir (R2 = 0.901-0.985), Freundlich (R2 = 0.884-0.985) and Temkin (R2 = 0.845-0.961) models at pH 3.7. Langmuir maximum adsorption capacities (mg/g) were 10.4-18.8 (FeOOH, except for 3.08 for Gth2) in GpI, and 20.60/43.40 (Sch-Chem/Sch-Bio) and 12.80/24.70 (Aka-Chem/Aka-Bio) in GpII. Adsorption capacities would gradually increase as Cr(III) concentrations increased within 0-40 mg/L, and could be markedly affected by the SO42- and H2PO4- anions. There were stable adsorption capacities at about pH 3.7, and then increased at pH 3.7-4.1. The Fourier transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) results showed that adsorption mechanisms were electrostatic interaction and surface complexation. In addition, three optimal bio-/chem-schwertmannite and lepidocrocite adsorbents had good reusable properties and treating abilities of Cr(III)-polluted waters at pH 4.0. These results could provide a theoretical basis for the application of iron oxyhydroxides in removing Cr(III) from acid wastewaters.

Schwertmannite and akaganéite for adsorption removals of Cr(VI) from aqueous solutions.

Iron hydroxides have received high attention in the treatment of chromium (Cr) polluted wastewater. In this study, the obtained chemical (or biological) pincushion-schwertmannite spheres had a diameter of 2 - 5 µm (0.5-1 µm), and akaganéite rods had a length of 300-500 nm (100-150 nm) at an axial ratio of about 3. The average diameters (µm) of their agglomerated particles in solutions were 20.6-32.5 (only 0.480 for Aka-Chem). Schwertmannites and akaganéites were used to investigate Cr(VI) adsorption behaviors in aqueous solutions by batch experiments, under various reaction times, initial Cr(VI) and adsorbent levels, pH values, temperature and anions of NO3-, Cl-, CO32-, SO42-, and H2PO4-. Adsorption data well fitted to pseudo-second-order rate model (R2 = 0.999), and Langmuir (R2 = 0.954-0.988) and Freundlich (R2 = 0.984-0.996) isothermal models at pH 7.0. Maximum Cr(VI) adsorption capacities were 119/133 for Sch-Chem/Sch-Bio, and 14.6/83.6 for Aka-Chem/Aka-Bio. The H2PO4- than SO42-/CO32- had a stronger effect on Cr(VI) adsorption. Adsorbents with pHZPC of near to 4.0 still had a good Cr(VI) removal ability at pH 3.0-8.0. The possible Cr(VI) adsorption mechanisms by FTIR and XPS results for schwertmannite and akaganéite were electrostatic attractions and ion exchanges between hydroxyl (or sulfate) and chromate ions. The Cr(VI) adsorption of optimal schwertmannite and bioakaganéite was a spontaneous, endothermic and random process at the temperatures of 288-318 K. They had a good regeneration ability for Cr(VI) adsorption, and removal ratios could reach to about 80% of original values (60-70% in aqueous solution with 60 mg/L Cr(VI) and pH7.0, and 35-50% in wastewater with 120 mg/L Cr(VI) and about pH4.0), after three cycles. Herein, schwertmannite/bioakaganéite have a promising application in treatment of acidic/neutral wastewater with chromate.

Adsorption removal of arsenic from aqueous solutions and groundwater by isomeric FeOOH.

FeOOH as a naturally abundant, relatively low-cost and effective adsorbent have been gradually valued in wastewater field rich in arsenic pollution, which can make for environmental remediation. In this study, FeOOH samples included Gth1/Gth2 as goethite, Aka1/Aka2 as akaganéite, and Lep as lepidocrocite, were prepared and used as adsorbents, and adsorption kinetic and isotherm experiments of As(III) were analyzed. Meanwhile, the effects of pH, adsorbent content, arsenic initial concentration and electrolyte solutions on adsorption processes were also discussed in detail to study adsorption behaviors and mechanism. The results showed that As(III) could be effectively adsorbed on goethite, akaganéite and lepidocrocite, the adsorption equilibrium achieved after 24 h. When As(III) concentration ranged in 40 mg/L, the saturated adsorption amounts (mg/g) calculated by the Langmuir equation were 12.3 (Gth1), 7.50 (Gth2), 6.29 (Aka1), 23.4 (Aka2), and 17.7 (Lep). The increase of adsorbent and adsorbate levels was favorable to improve the adsorption capacities of As(III) within a certain range. Removal efficiency of As(III) with Na2SO4 and NaH2PO4 as electrolyte reduced by about 10% and 30%, respectively. Therefore, the appropriate parameters in the adsorption process for investigation were isomeric FeOOH of 1.0 g/L, pH 7.0 and NaNO3 as electrolyte. In simulated groundwater filter system initially with 200 µg/L of arsenic species at about pH 7.0, arsenic removal strength for five FeOOH adsorbents (0.8 g) was Aka2 > Aka1 and Gth1 > Lep and Gth2. Some differences were present in the infrared (IR) spectra of arsenic-loaded and original isomeric FeOOH. These outcomes could give the aim at seeking high efficient materials for the purification of arsenic contaminated groundwater and put out the suggestion.

Cell-shape assemblage and nanostructure of akaganéite bioformed in FeCl2 solutions.

Akaganéite (ß-FeOOH) with a tunnel structure typically occupied by chloride can undergo anion-exchange reactions in aqueous solutions for pollutant removal. In this work, we studied bioformation of akaganéite in FeCl2 solutions with Acidithiobacillus ferrooxidans cells at pH 2.9, during 36-h incubation. The obtained products were analyzed and characterized by XRD, FTIR, EDS, FETEM, and HRTEM. Results showed that in acidic media with pH 2.9, the cells facilitated ferrous biooxidation and ferric precipitation. The resulting ferric precipitates were identified as polycrystalline akaganéite powders and had a morphology of nanospindles with a length of less 100 nm. The correlatively chemical formula for akaganéite collected at 1 h was reckoned as Fe8O8(OH)6.71(Cl)1.29 with 6.6% Cl. It was observed that ferric precipitates along exterior structures of cells or their extruded organic polymers grew and assembled into cellular shape. The evolved cell-shape akaganéite assemblages were twice of cells (about 2 µm) in size. These results could contribute to understanding of laboratorial bioformation of akaganéite and its biomineralization in acidic environments and promoting its practical applications.

Synthesis of nanospindle-akaganéite and its photocatalytic degradation for methyl orange.

Iron oxyhydroxides as important catalysts and environmental mineral materials have drawn significant interest for their potential applications in the field of wastewater treatment. In this work, we investigated the influence of nonionic surfactant Brij30 or glucose (0.01 wt%) on the formation of iron precipitates in iron(III) chloride solutions for 3 days at 40, 60 and 80 °C. The results showed that the presence of glucose or Brij30 could promote the nanospindle-akaganéite formation and the akaganéite with a length of 300-500 nm obtained at 60 °C was the optimal catalyst for organic photocatalysis degradation. Further, we investigated the capacity of C60 akaganéite for degradation removal of methyl orange (MO) under the action of hydrogen peroxide (H2O2) addition and/or UV irradiation, and in the presence of different radical scavengers at pH 4.5. We also researched the effects of various levels of H2O2 and catalyst, and the reaction pH values. It was found that akaganéites could remove almost 100% of MO under 100 mg·L-1 of catalyst and H2O2 at pH 4.5. Akaganéite maintained 86% of MO removal capacity after four successive cycles. Our results can be used as a reference for the synthesis of environmentally functional material and the application in photocatalytic degradation of organic pollutant.

Adsorption removal of Cr(VI) by isomeric FeOOH.

The aim of this work is to study the performances of isomeric α-, ß-, and γ-FeOOH (goethite, akaganéite and lepidocrocite, including five samples named as Gth1 and Gth2, Aka1 and Aka2, and Lep, respectively) for removing hexavalent chromium (Cr(VI)) from aqueous solutions. The adsorption mechanisms were explored by kinetic and isothermal experiments. Adsorption efficiencies under the different pH values, anions, and the levels of adsorbate and adsorbent were also measured. Results showed that the Cr(VI) adsorption by isomeric FeOOH could be best described by pseudo-second-order kinetic model. The processes of Cr(VI) isothermal adsorption could be greatly fitted by the Langmuir and Freundlich equations with the high correlation coefficients of R2 (>0.92). Also, there were the optimum pH values of 3.0-8.0 for FeOOH to adsorb Cr(VI), and their adsorption capacities were tightly related with the active sites of adsorbents. Cr(VI) adsorptions by these adsorbents were easily influenced by H2PO4 -, and then SO4 2-, while there were little effects by Cl-, CO3 2- and NO3 -. These obtained results could provide a potentially theoretical evidence for isomeric FeOOH materials applied in the engineering treatment of the polluted chromate-rich waters.

Physico-Chemical Processes.

This review is on the research literature published in 2016 related to the physico-chemical processes for water and wastewater treatment. The review is divided into granular and membrane filtration, sedimentation, coagulation/flocculation, flotation, oxidation, and adsorption.

Physico-Chemical Processes.

This review is on the research literature published in 2015 related to the physico-chemical processes for water and wastewater treatment. The review is divided into six sections, including filtration, sedimentation, coagulation/flocculation, flotation, oxidation, and adsorption.

Physico-Chemical Processes.

This review is on the research literature published in 2014 related to the physico-chemical processes for water and wastewater treatment. The review is divided into six sections, including coagulation/flocculation, filtration, sedimentation, oxidation, flotation, sorption process.

Yolk@Shell Nanoarchitecture of Au@r-GO/TiO2 Hybrids as Powerful Visible Light Photocatalysts.

Yolk@shell nanostructures of Au@r-GO/TiO2 with mesoporous shells were prepared by a sol-gel coating process sequentially with GO and TiO2 on Au/SiO2 core/shell spheres, followed by calcination and template removal, where the silica interlayer acts as a template not only to produce the void space but also to promote the coating of the r-GO and TiO2 layer. The evaluation of visible light photocatalytic activities in dye decomposition and water-splitting H2 production demonstrated their superior photocatalytic performance, which indicates their potential as powerful photocatalysts.

Nanostructured hybrid shells of r-GO/AuNP/m-TiO2 as highly active photocatalysts.

Nanostructured hybrid shells of r-GO/AuNP/m-TiO2 were synthesized using SiO2 spheres as templates, followed by graphene oxide (GO) and Au nanoparticle (AuNP) deposition and TiO2 coating, and then post-treatments of template removal and calcination. Evaluation of their photocatalytic activity by degradation of Rhodamine B (RhB) under the irradiation of UV, visible light, and simulated daylight demonstrated the superior photocatalytic performance of the sandwich-like hollow hybrid shells, which could be attributed to the porous nature of the hybrid shells and the enhanced charge separation and visible-light absorption of r-GO and AuNPs.

Isolation, identification and arsenic-resistance of Acidithiobacillus ferrooxidans HX3 producing schwertmannite.

Schwertmannite, a ubiquitous mineral present in iron oxyhydroxides formed in iron- and sulfate-rich acid media, favors incorporation of some toxic anions in its structure. We reported an iron-oxidizing bacterial strain HX3 from a municipal sludge that facilitates the formation of pure schwertmannite in cultures. Ferrous iron oxidation by the isolated strain HX3 was optimum at an initial pH of 2.0-3.3 and temperature of 28-35°C. Pure schwertmannite was found through bacterial oxidation of ferrous iron at an initial pH2.8 and temperature 28°C. Following 16S rDNA gene sequence analysis the bacterial strain HX3 was identified as Acidithiobacillus ferrooxidans. The arsenic-resistance A. ferrooxidans HX3 showed the potential of environmental application in arsenic removal from the As(III)- and iron-rich acid sulfate waters directly by As(III) adsorption or the formation of schwertmannite in the environment.

[Characterization and spectral analysis of the stable mineral phases alpha, beta-FeOOH included in iron oxyhydroxides].

In the present work, based on the stable phase of alpha-FeOOH and beta-FeOOH easily formed in ferric solutions of Fe (NO3)3 and FeCl3 at the appropriate pH values, respectively, the phase and crystallizability, morphologies and sizes for the particles of FeOOH minerals prepared under the conditions of heating at 40 and 70 degreeC, and magnetic stirring at 25 degreeC were identified and examined by X-ray diffraction (XRD), transmission/scanning electron microscopy (TEM/SEM) and laser scattering particle analyzer. Meanwhile the surface chemistry properties were also detected and analyzed by Fourier transform infrared spectrometer (FTIR). Investigation results showed that the prepared minerals Gth-T70 (alpha-FeOOH), Aka-T40 and Aka-T70 (beta-FeOOH) have good properties of nanocrystallity, homogeneous particles and higher specific surface areas, which induced that the above alpha, beta-FeOOH are potentially excellent adsorbent materials for removal of some contaminants in circumstances.

Effects of chloride acclimation on iron oxyhydroxides and cell morphology during cultivation of Acidithiobacillus ferrooxidans.

Iron oxyhydroxides as the efficient scavengers for heavy metals have been extensively investigated in iron-rich acid sulfate waters in the presence of Acidithiobacillus ferrooxidans (A. ferrooxidans, an especially important chemolithoautotroph for bioleaching and desulfurization of coal). In this study, we observed the morphology and elemental composition of cells in stationary phase and examined the dynamic variation of iron oxyhydroxides produced in cultures of A. ferrooxidans incubated in modified 9K medium initially including 0.15 M of ferrous iron, in the absence/presence of 0.2 M of chloride (NaCl/FeCl(2)). Results showed that chloride acclimation had little effect on cellular morphology and elemental uptake that was mainly related to culture medium. Furthermore, schwertmannite with the typical morphology of aggregated spheres covered by some "pincushions" was precipitated first in bacterial cultures in the favorable pH range of 2.9 ± 0.1 to 2.6 ± 0.1. Some of schwertmannite could be transformed to lozenge-shaped jarosite, due to a successively decreasing of pH values. However, the jarosite transformation represented a lag period of 5 and 4 days in the chloride-rich cultures with sulfate at a low level, compared to the cultures with sulfate at a high level, which could be attributed to the influence of sulfate requirement and chloride acclimation.

[Preparation of nanocrystalline goethite (alpha-FeOOH) by gel-network precipitation method and spectral properties].

Iron oxyhydroxides (FeOOH), as an environmental mineral material, can adsorb and coprecipitate the contamination from the medium. The ability of removing contamination is decided by the morphology and structural characteristic and the synthesis methods of the obtained mineral. In the present, the used synthesis methods of iron oxyhydroxides (FeOOH) include ferric iron hydrolyzation and ferrous chemical oxidation. But the products of iron oxyhydroxides prepared by these two chemical methods are easily agglomerated and form bigger particles. Thus, in the present study, a novel gel-network precipitation method was developed to synthesize the nanoparticles of goethite (alpha-FeOOH) as environmental mineral material. During formation of alpha-FeOOH nanoparticles by this method, FeCl3 acted as the reaction material and glutin played a role of the reaction medium, which prevents the presence of agglomeration of precipitate particles. So the obtained alpha-FeOOH nanoparticles had smaller size, no aggregation and basic monodispersity, compared with that prepared by the coprecipitation method. At the same time, we introduced the spectrum analysis measures, and studied the effect of different concentration of glutin and FeCl3 solution on the crystallizability and morphology of products. The structure and morphology of alpha-FeOOH nanocrystallites were determined by means of XRD, FTIR and SEM. The results of the spectrum analysis showed that the particle sizes and shapes and crystallizability of the obtained alpha-FeOOH precipitate products were highly related to the network structure of gelatin. And the goethite particles with better monodispersity, prepared by the optimum concentrations of glutin (12%) and FeCl3 solution (0.6 mol x L(-1)), had a short rod-type shape approximately 110 nm in length with an average diameter of about 35 nm.

[Spectral analysis of FeOOH prepared through hydrolysis and neutralization of ferric solutions under different conditions].

In the present work, the iron oxyhydroxides were prepared by hydrolysis and neutralization of ferric ion from FeCl3, Fe(NO3)3 and Fe2 (SO4)3 salts, under the conditions of various pH values and aging for about 6 days at 60 degrees C. These iron minerals were identified and characterized using X-ray diffraction (XRD), infrared spectroscopy (IR) and scanning electron microscopy (SEM). In addition, particle size distributions of FeOOH suspension were also determined by LS-230 model laser grainsize analyzer. Results showed that ferrihydrite formed in the ferric solutions containing Cl-, NO3- and SO4(2-) at pH values of 8 and 10. It was testified that the presence of Cl- was favorable for the formation of akaganéite. Meanwhile, the poor crystalline goethite phase was observed to be formed in FeCl3 or Fe(NO3)3 solution, but not be formed in Fe2 (SO4)3 solution at pH 12. It indicated that the presence of SO4(2-) obviously inhibited the formation of goethite. However, the goethite phase formed in Fe2 (SO4)3 solution with addition of ferrous ion, indicating that ferrous ion could promote the formation of goethite in SO4(2-) -rich solution. In addition, it was usually easy for the crystalline goethite to be transformed from the above generated ferrihydrite precipitates by aging at 60 degrees C. Furthermore, the phase of akaganéite also was obtained in the Cl(-) -rich acid (pH < or = 5) solution by aging at 60 degrees C. In conclusion, the prepared FeOOH samples show some differences in their properties such as the phase, surface properties, morphology structures and particle size.

Biosynthesis of nanocrystal akaganéite from FeCl2 solution oxidized by Acidithiobacillus ferrooxidans cells.

Akaganéite (beta-FeOOH) is a major iron oxyhydroxide component in some soils, marine concretions, and acid mine drainage environments. Recently, synthetic beta-FeOOH has been found to be a promising absorbent in the treatment of metal-contaminated water. It has been recognized in previous study that akaganéite could be formed via FeCl2 chemical oxidation under specific conditions. Here we report a novel and simple method for akaganéite bioformation from FeCl2 solution oxidized by Acidithiobacillus ferrooxidans LX5 cells at 28 degrees C. After acclimation in modified 9K medium containing 0.2 M chloride, Acidithiobacillus ferrooxidans cells had great potential for oxidization of Fe2+ as FeCl2 solution, and then resulted in the formation of precipitates. The resulting precipitates were identified by powder X-ray diffraction and transmission FT-IR analyses to be akaganéite. Scanning electron microscopy images showed the akaganéite was spindle-shaped, approximately 200 nm long with an axial ratio of about 5, and the spindles had a rough surface. X-ray energy-dispersive spectral analyses indicated the chemical formula of the crystalloid akaganéite could be expressed as Fe8O8(OH)7.1(Cl)0.9 with Fe/Cl molar ratio of 8.93. The biogenetic akaganéite had a specific surface area of about 100 m2 g(-1) determined by BET method.

Influence of chloride and sulfate on formation of akaganéite and schwertmannite through ferrous biooxidation by Acidithiobacillus ferrooxidans cells.

Iron (oxyhydr)oxides play important roles in the fixation of toxic elements and also in the distribution of nutrients for plants in soils. Akaganéite and schwertmannite, as the iron oxyhydroxides having an analogous tunnel structure, have been widely recognized in Fe-rich environments. The objective of this study was to examine the formation of akaganéite/ schwertmannite via biooxidation of 0.1 M of ferrous solution containing only Cl-, SO4(2-) or both the anions with a Cl-/SO4(2-) mole ratio of 1, 3, 6, and 10 by chloride-acclimated Acidithiobacillus ferrooxidans cells. Results showed that ferrous iron in chloride/sulfate-containing solutions could be easily biooxidized to ferric iron, and subsequent Fe(III)-hydrolysis/precipitation could result in the formation of large quantity of akaganéite/schwertmannite precipitates. The resulting precipitates were identified to be the pure akaganéite (Fe8O8(OH)7.1(Cl)0.9, the pure schwertmannite (Fe8O8(OH)4.42(SO4)1.79, and the main schwertmannite phase (Fe8O8(OH)(8-2x)(SO4)x, with 1.09 < or = x < or = 1.73), respectively, under different Cl-/SO4(2-) mole ratio conditions. Obviously, sulfate inhibited drastically the bioformation of akaganéite but facilitated schwertmannite phase occurrence in the ferrous solution containing both sulfate and chloride. However, the presence of chloride ion in initial ferrous solution containing sulfate and Acidithiobacillus ferrooxidans cells would affect the morphology and other characteristics of schwertmannite generated.