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This work elucidated the performance and mechanisms of Pb2+ adsorption by kaolinite, montmorillonite, goethite and ferrihydrite using batch experiments. The contributions of various adsorption mechanisms were quantified using a stepwise extraction method. Several characterizations (scanning electron microscopy, X-ray diffraction, Fourier-transform infrared spectroscopy, point of zero charge analysis and X-ray fluorescence) were utilized to analyse the physicochemical properties and the potential adsorption mechanisms. The results indicated that the adsorption processes of montmorillonite and goethite approached equilibrium within 20 min, while 60 min were required for the adsorption processes of kaolinite and ferrihydrite. The adsorption processes of Pb2+ by the four minerals best fit the pseudo-second order model. The adsorption capacities of the four minerals for Pb2+ followed the order: montmorillonite > goethite > ferrihydrite > kaolinite, and the maximum adsorption capacities were 69.20, 46.95, 34.32 and 18.62 mg g–1, respectively. The stepwise extraction test showed that the adsorption mechanism of Pb2+ was dominated by ion exchange for montmorillonite, precipitation and complexation for goethite and complexation for kaolinite and ferrihydrite.

Photocatalysis is considered a promising method for wastewater treatment; however, most synthesized photocatalysts have complex structures and are costly. Thus, in this study, a novel CaWO4 sample was synthesized by a co-precipitation method in one step. The characteristic results show that CaWO4 has good dispersibility, a large specific surface area, and good photoresponse under UV light. The synthesized CaWO4 can be used to degrade methylene blue (MB) and carmine (CR) under UV light without the addition of oxidants. The effects of a water matrix, including pH value, solid–liquid ratio, light intensity, and initial concentration of pollutants on photocatalytic degradation were studied. According to the optimization of these factors, the optimal photocatalytic degradation condition was found under the catalyst concentration of 1.0 g/L and ultraviolet light intensity of 80 W. The optimal pH is 8.2 for the MB system and 6.0 for the CR system. The optimal photocatalytic degradation of MB and CR at 100 mg/L can be achieved as 100%. According to the results of scavenger experiments, holes and hydroxyl radicals dominate the degradation of MB while hydroxyl radicals and superoxide anions are mainly responsible for the degradation of CR. Further analyses showed that photogenerated electrons generated on the surface of the CaWO4 can form electron–hole pairs, thereby producing hydroxyl radicals and superoxide anions to degrade dyes. In addition, the CaWO4 has a good cycling performance in the process of degrading MB (more than 80% after five cycles). It provides a new idea for the photocatalytic degradation of dyes using mineral-like materials.

International audience; Ca-Al-layered double hydroxide (Ca/Al-LDH) is an excellent sorbent for wastewater decontamination and is widely used in the treatment of this phosphate and fluoride-containing wastewater. In this study, we propose a strategy using the wastes generated from treating high-concentration phosphate wastewater process to treat fluoride wastewater to maximize the value of LDH. The effects of environmental parameters such as reaction time, initial fluoride and phosphate concentrations, adsorbent concentration, and pH were investigated. The experimental results showed that when the initial F- concentration was 10 mg L-1, the removal rates of F- were over 90%. To further understand the adsorption mechanism of F- on solid waste, we employed characterization methods such as X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), and Fourier transform infrared spectroscopy (FTIR), which were also able to characterize the adsorption products before and after the reaction. It was found that hydroxyapatite was formed after the removal of phosphate, while fluorapatite was formed at the F-substituted hydroxyl position after the removal of fluorine. The adsorption process of fluorine removal is a spontaneous endothermic adsorption process. This study shows that Ca/Al-LDH can be a promising material with a high development value, and the new strategy of sequentially removing phosphorus and fluorine using this material can maximize the value of this adsorbent.

Due to its advantages of high efficiency, simplicity of operation, and no secondary pollution, photocatalysis is considered as a promising method for wastewater treatment. Most synthesized photocatalysts are structure complex and costly. Thus, in this study, a novel CaWO4 sample was synthesized by a co-precipitation method in one step and proved as a preferable photocatalytic material by a series of characterization methods. The synthesized CaWO4 can be used as a catalyst to degrade dyes as methylene blue (MB) and carmine (CR), under UV light without the addition of oxidants. The effects of water matrix, including pH value, solid-liquid ratio, light intensity, and initial concentration of pollutants on photocatalytic degradation were studied. According to the results of scavengers experiments, holes and hydroxyl radicals dominate the degradation of MB while hydroxyl radical and superoxide anion are mainly responsible for the degradation of CR. Furthermore, i-t curves demonstrate the CaWO4 has good photoelectric response capability. It means that photogenerated electrons generated on the surface of the CaWO4 can form electron hole pairs, thereby forming hydroxyl radical and superoxide anion to degrade dyes. In addition, the CaWO4 has good cycling performance in the process of degrading MB. Results indicate that minerals-based photocatalyst can be synthesized in one step by simple coprecipitation and exhibit good photocatalytic effect. It provides a new idea for the study of photocatalytic degradation of dyes by mineral-like materials.

In this work, bismuth hexacyanoferrate/graphene/carbon fibers composite (BiHCF/GN/CFs) was used as a multifunctional air diffusion electrode, which exhibited a promising catalytic effect in air O2 reduction (ORR) during photo-electro-Fenton process (PEF). BiHCF/GN/CFs, being a heterogeneous photo-electro-Fenton catalyst in PEF, could further simultaneously generate H2O2 and ·OH in ORR, and the generating rate of ·OH was 0.31 mmoL h−1. The photo-electro-catalytic properties of BiHCF/GN/CFs in PEF process were evaluated using three types of dye wastewater including methyl orange (MO), methylene blue (MB) and rhodamine B (RB). MO, MB and RB could be, respectively, decolorized with three first-order kinetic constants of 8.9 h−1, 3.3 h−1 and 3.0 h−1 at the same mass ratio of 3.8/1 in pH 4.0, 0.1 M Na2SO4. The degradation efficiency of MO was excellent with a higher TOC removal rate.

Herein, we tailored a series of ultrathin MnO

Although it is well known that phosphate retention in soils and sediments is strongly influenced by binding to secondary iron oxides, there have been relatively few studies examining its adsorption/desorption behavior on multicomponent particles of realistic natural complexity. In this study, natural Mn-rich limonite (LM), was used to prepare naturally complex Fe- and Mn-oxide composite materials to examine phosphate adsorption/desorption. To clarify the role of the Mn-oxides, results for the LM sample were compared to those for an acid treated version (LAT), in which the acid-extractable Mn-oxide fraction has been selectively eliminated while leaving the Fe-oxide fraction intact. The saturated adsorption capacity on LAT was almost double that on LM, suggesting that phosphate adsorption to the iron oxides is strongly occluded by the Mn-oxide fraction. This result is reinforced by the comparing the pH dependence and fits to adsorption isotherms, and by desorption experiments and STEM-EDS mapping showing that phosphate loading on Mn-oxides was limited. Hence, although the collective results confirm that phosphate uptake and strong binding is selectively controlled by the Fe-oxide fraction, our study reveals that the Mn-oxide fraction strongly interferes with this process. Therefore, phosphate uptake behavior on metal oxides cannot be predicted solely on the basis of the Fe-oxide fraction present, but instead must take into account the deleterious impacts of other intimately associated phases. For co-diagenetic Fe/Mn-oxide composites in particular, Mn-oxides appear to severely limit phosphate uptake on the Fe-oxide fraction, either by hindering access to binding sites on the Fe-oxide or by lowering their affinity for P.

Natural siderite was selected as a raw material for preparing nano zero-valent iron (nZVI). The efficiency of the as-synthesized nZVI for PO3−4–P removal was investigated, and the effects of the annealing temperature, pH, initial PO3−4–P concentration, adsorption temperature and oxygen were investigated. The results indicated that after annealing at 550 °C, nZVI exhibited an average crystal size of 56.3 nm and a surface area of 14.1 m2/g. A decrease in pH and an increase in oxygen availability enhanced the removal efficiency. The adsorption process, which was spontaneous and exothermic according to the thermodynamic analysis, agreed well with the pseudo-second-order kinetic model. Based on the Langmuir equilibrium isotherms, the capacity of nZVI to adsorb phosphorus was determined to be 33.18 mg/L. The optimized conditions for the experimental conditions were defined by an orthogonal experiment as follows: initial P concentration 2 mg/L, initial pH 4, iron dose 2 g/L, adsorption time 60 min. The experimental results suggested that the as-prepared nZVI was a promising adsorbent for the removal of phosphate.

To achieve a low-cost, high-activity denitrification catalyst with excellent water and sulfur resistance, goethite and Ce(SO

A laboratory-scale up-flow anaerobic sludge blanket (UASB) reactor was developed and constructed for the treatment of landfill leachate and acid mine drainage (AMD). The removal of chemical oxygen demand (COD), sulfate, and metal ions was studied. The maximum COD and sulfate removal efficiency reached 75% and 69%, respectively, during the start-up phase of the UASB. The hydraulic retention time (HRT) had a significant influence on the system. The maximum removal efficiency for COD and sulfate reached 83% and 78%, respectively, at an HRT of 20 h. The methane production process competed with the sulfate reduction process in the UASB. The fractionation of metals in the sludge was analyzed to facilitate metal recovery in a later processing stage. The most abundant sulfate-reducing bacteria was Desulfobulbus, and the methanogen archaeal community in the reactor was mainly composed of Methanobacterium.

Siderite is a naturally occurring mineral that can be found extensively in coal. The structural evolution of siderite in the process of coaling and its performance in the transformation of NO in the presence of NH3 were investigated in this work. In addition, the effects of the coexisting component, including vapor, SO2, and the alkali metal K, were also discussed. Heat treatment was performed at 450, 500, 550, 600, and 700 °C to obtain siderite-derived α-Fe2O3, which was then evaluated in de-NOx via the selective catalytic reduction (SCR) of NO with NH3 in a fixed bed. The X-ray diffraction (XRD), the X-ray fluorescence spectrometer (XRF), N2 adsorption-desorption (BET), the X-ray photoelectron spectrometer (XPS), the scanning electron microscope (SEM), and the transmission electron microscope (TEM) were used to investigate the variations in the morphology and structure of the thermally treated siderite. The results showed that siderite was gradually oxidized and decomposed into α-Fe2O3 with a nanoporous structure and large surface area of 27.27 m2 g−1 after calcination under an air atmosphere. The α-Fe2O3 derived from siderite at 500 °C (H500) exhibited an excellent SCR performance, where the NO conversion rate was great than 90% between 250 and 300 °C due to the pore structure and high specific surface area, additional adsorbed oxygen states, abundant oligomeric Fe oxide clusters, and large amount of acid sites. Regardless of the vapor content, SO2 concentration, and reaction temperature, the α-Fe2O3 derived from siderite at 500 °C (H500) still favored the conversion of NO. When the reaction temperature was lower than 350 °C, H500 favored the conversion of NO even in the presence of an alkali metal (K). The experimental data demonstrated the positive effect of siderite-derived α-Fe2O3 in SCR technology and provided insight into NO behavior in coaling flue gas after NH3 injection.

In order to find efficient catalysts for low-temperature selective catalytic reduction with ammonia (NH3-SCR), several MnO2 with different crystal structure have been supported on high-purity palygorskite (Pal) by a hydrothermal method. The effect of MnO2 crystal structures on the NH3-SCR performance of the catalysts was investigated. All catalysts were characterized by X-ray diffraction (XRD), N2 adsorption-desorption, Raman spectrum, Thermo gravimetric analysis/Differential thermo gravimetric (TG/DTG), ammonia-temperature programmed desorption (NH3-TPD), hydrogen-temperature programmed reduction (H2-TPR), Transmission electron microscope (TEM) and X-ray energy dispersive spectroscopy (EDS) and X-ray photoelectron spectrometer (XPS). The presented results suggested that α-MnO2/Pal catalyst exhibit the highest catalytic activity among four type MnO2/Pal catalysts in the temperature range of 50–400°C, own promising stability during a 24 h continuous denitration experiment. Furthermore, the crystal structure affords α-MnO2/Pal with the highest specific surface area and more acidic sites, which is beneficial for the SCR reaction. It has improved the NH3 adsorption ability and catalytic activity of the catalyst.

Despite the biogeochemical importance of phosphate fate and transport in aquatic environments, little is known about how competition with other common aqueous oxyanions affects its retention by mineral surfaces. Here, we examined the competitive uptake of phosphate and silicate on goethite over a wide pH range, using batch measurements supported by DFT calculations. The results show selective adsorption of phosphate at pH4 and silicate at pH10 with little to no competitive effect. However, between 4pH10, the total phosphate and silicate loading was found to be almost equal to that of silicate loading from single-component solution, revealing a proportionate competition for surface site types and a competitive effect controlling their mutual retention. DFT-calculated adsorption energies and charge density redistributions for various surface complexes on different charged (101) and (210) facets are consistent with the trends observed in batch measurements, suggesting that the observed behavior reflects the primary controlling influence of goethite surface chemistry at the molecular scale. An important implication is that at the circumneutral pH in most environmental systems, where iron oxyhydroxides comprise much of the reactive interfacial area, unbound phosphate concentrations may be strongly controlled by dissolved silicate concentration, and vice versa.

A system of Cu

In this work, the effect of Co substitution in the Fe

In this study, a new low-cost carbon-based material was prepared via the carbonization of methylene blue adsorbed halloysite (CMH) at different temperatures in a nitrogen atmosphere, which was named CMH-T (T-Temperature). The performance of CMH-T was explored and the effects of initial pH values, catalyst dosage, phenol (PE) concentrations, peroxymonosulfate (PMS) concentrations, and water background compounds on PE degradation were investigated systematically. The results indicated that CMH800 exhibited the best performance to activate PMS for degrading PE. Specifically, 92% PE was degraded within 30 min with a constant rate (k

Naturally occurring Mn-rich limonite mainly composed of goethite and manganese oxides was used to remove tetracycline (TC) from the aqueous solution. The physicochemical properties of limonite were illustrated by various characterization techniques such as XRD, FE-TEM, XPS and FT-IR. The effects of dosage, initial solution pH, temperature and coexisting anions on TC removal were investigated. The results showed that TC could be efficiently adsorbed by limonite with high specific surface area and mesoporous structure through electrostatic interaction and complexation. The co-existence of PO43- inhibited the adsorption of TC by limonite due to the competition with TC for active sites. In addition, manganese oxides exhibited oxidative properties to TC, and the singlet oxygen (1O2) generated during the redox reaction was responsible for TC degradation. Furthermore, the regenerated limonite displayed an efficient recycling performance after four cycles. This study revealed that the Mn-rich limonite was a promising adsorbent for TC removal from aqueous solutions and promoted the application of natural mineral material in the environmental field.

In our previous study on petrogenesis of quartz syenite and granite porphyry, the host rocks of the Late Mesozoic Shapinggou Mo deposit in the Qinling–Dabie orogenic belt, we found that the initial Sr isotopic composition of the host rocks is strongly affected by the degree of K-alteration. Here, we provide further isotopic evidence of the host rocks and their minerals to investigate the geochemical behaviour of trace elements and isotopes during the alteration and to explain the phenomenon of decoupling of Sr–Nd isotopic composition. The quartz syenite and granite porphyry are altered by K-alteration in varying degrees and have high K2O and Rb contents and low Na2O, CaO, Sr, and Ba contents. Rock samples of both quartz syenite and granite porphyry have variable Rb/Sr ratios and initial 87Sr/86Sr values (even &lt, 0.70) but contain quite homogeneous εNd(t) values (−12.8 to −14.8). Minerals from the rocks of moderate to intense K-alteration have very low initial 87Sr/86Sr values (even &lt, −17), while those from the weakly altered rocks have 87Sr/86Sr(t) values of 0.7044 to 0.7084. The same phenomenon of the decoupling in Sr–Nd isotopic composition can be observed from several Mo deposits within the eastern Qinling–Dabie orogenic belt. This fact suggests similar hydrothermal features and a comparable origin for both the magmatic rocks and hydrothermal fluids in this belt. A comparison between porphyry Mo and porphyry Cu deposits shows that elements and the Rb–Sr isotope system have different behaviours during the K-alteration, implying distinct material sources and igneous rocks for porphyry Mo and porphyry Cu deposits, respectively.

The transformation of Al-substituted goethite in oxidative and reductive atmosphere, which models natural fire, was investigated in detail. Various characterization results indicated that Al-substituted goethite transformed into hematite in an oxidative atmosphere and magnetite followed by zero-valent iron in a reductive atmosphere. Interestingly, the substitution of Al for Fe not only changed the crystal morphology affecting crystal surface reactivity, but also restrained the transformation of goethite into hematite, magnetite and zero-valent iron. In addition, the Al in the goethite was embedded into the crystal structure of thermally formed hematite and magnetite, considerably influencing their surface reactivity. The macroscopic adsorption results indicated that the substitution of Al for Fe increased the adsorption capacity of goethite and the corresponding derivatives except zero-valent iron. For the same Al amount, the adsorption capacity followed an order of goethite > hematite > magnetite, implying a loss of phosphate in goethite-rich soil after experiencing natural fire. However, with increasing in temperature in the reductive atmosphere, Al-magnetite transformed into a mixture of Al-magnetite and zero-valent iron which displayed excellent phosphate adsorption capacities increasing to 1.21–5.96 mg/g. The phosphate adsorption behaviors to thermally formed products were fitted well by surface complexation modeling with five complexation sites, which were more obvious for goethite than for hematite and magnetite. These findings presented in this study represent significant progress toward an understanding of the migration, enrichment and transformation of phosphate in Al-substituted goethite-rich soil in cases experiencing natural fire.

A series of palygorskite-supported manganese oxide (MnOx/PG) catalysts were prepared by a precipitation method using different manganese precursor. The as-prepared MnOx/PG catalysts were used to evaluate the catalytic oxidation of HCHO and characterized by BET, XRD, TG, Raman spectroscopy, TEM, H2-TPR, XPS, and chemical titration. The results showed that the crystalline phase, distribution and Mn valence states of MnOx on the surface of PG depended on the precursors. Birnessite-type manganese oxide (δ-MnO2) formed and uniformly coated on the surface of PG when potassium permanganate (PP) was used as the precursor. The MnOx/PG-PP catalyst showed the best catalytic activity for HCHO removal at low temperature among these catalysts and achieved complete HCHO conversion at 150 °C. More importantly, the dynamic single-pass removal efficiency of MnOx/PG-PP catalyst for ppm-level HCHO oxidation was as high as 95% under high GHSV (300 L/g·h) at ambient temperature. MnOx/PG-PP catalyst also exhibited excellent cycling stability and long-term activity at low and ambient temperature. The kinetic results of MnOx/PG-PP catalyst showed that the oxidation of HCHO followed the Mars-van Krevelen mechanism. The possible reaction pathway of HCHO oxidation was proposed based on in situ DRIFTS and TPSR studies. The large specific surface area, highly distributed active component, a high proportion of Mn4+ species, and lattice oxygen content are responsible for the high catalytic activity of MnOx/PG-PP for oxidation of formaldehyde. This work developed a natural mineral supported manganese oxide as an inexpensive and efficient catalyst for the purification of HCHO in industrial or indoor air environment.

Heavy metal pollution in lacustrine sediments is a worldwide environmental issue. In the present study, eight heavy metals including Zn, Pb, Co, Cr, Cd, Mn, As and Cu in sediment cores collected from Chaohu Lake, Eastern China were determined, and potential sources and risks of selected heavy metals were evaluated using multivariate statistical techniques and pollution indices. Results show that all sampling areas were extremely contaminated by Cd, and were not significantly affected by Mn. High accumulation of Zn, Pb and Cu in urban area related sites implies they were generally derived from urban sources including municipal and industrial sewage. Whereas high concentrations of As and Cd, and Co in rural locations possibly suggests agricultural sources. Possible decreasing trends for most elements in the sediment cores indicate the reduction of total input amounts which would be attributed to the increasing operation of wastewater treatment plants in the urban areas. Different intercorrelations between each two elements for four sampling sites reflect the different input sources. Cluster analysis also indicates the residual elements in sediment cores of Chaohu Lake were generally from natural materials for Mn, from urban origins for Cu, Zn and Pb, and from agricultural activities for the remaining elements. The results from both contamination factors and geo-accumulation index (Igeo) suggest sediments were not polluted by Mn, extremely contaminated by Cd, and slightly to moderately impacted by the remaining elements. But all samples were examined with significant metal pollution given their pollution level index values higher than 1.0.

Cobalt oxide/hematite (Co3O4/α-Fe2O3) composites were synthesized by using goethite as precursor via co-precipitation calcination method and employed in the catalytic degradation of benzene. The catalysts properties of the Co3O4/α-Fe2O3 composites were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), N2 adsorption measurement (BET), X-ray photoelectron spectroscopy (XPS) and H2 temperature programmed reduction (H2-TPR) techniques, respectively. The results showed that the Co3O4/α-Fe2O3 composite had excellent catalytic oxidative performance on catalytic degradation of gaseous benzene, and its catalytic activity were influenced markedly by the ratio of Co3O4 and the calcination temperature. When the composite catalyst with the Co/Fe molar ratio of 0.6, calcined temperature at 500 °C and benzene initial concentration was 1000 mg/m3, the catalyzed oxidative temperature which benzene completely conversion and 91.7% CO2 selectivity was 400 °C. Large specific surface area, abundant surface oxygen species and strong redox properties which were ascribed to the interaction between Fe2O3 and Co3O4 play an important role in the catalyzed oxidative degradation of benzene.

Magnetite and maghemite are important components of iron oxides that determine the magnetic properties of rocks, soils, and sediments, and are also materials with broad industrial applications. We investigated the reduction and transformation of both phases with a strain of sulfate-reducing bacteria (SRB). SRB growth resulted in 28.1% and 7.1% sulfate to acid volatile sulfur conversion in magnetite and maghemite, respectively. Transmission electron microscopy and X-ray photoelectron spectroscopy (XPS) analyses indicate that monosulfides (mackinawite and greigite) and polysulfides are the main secondary sulfides in the magnetite experiment, while the maghemite experiment also contained a high proportion of pyrite. XPS analyses indicate the reduction of Fe(III) to Fe(II) on the surface of magnetite and maghemite both by dissolved sulfides and SRB. Mossbauer spectroscopy measurements reveal the formation of superparamagnetic phases in microbial experiments, which indicates the dissolution and particle size decrease of the two minerals both by dissolved sulfides and SRB. X-ray diffraction and Mossbauer spectroscopy analyses suggest a complete transformation of nanomaghemite to nanomagnetite under the mediation of SRB through solid phase Fe(III) reduction. This transformation controls the changing and different patterns of both magnetic susceptibility and magnetic hysteresis for the two minerals. It is suggested that the structural similarity between magnetite and maghemite, and the conductivity of magnetite, constrain the unique solid phase transformation. Our findings indicate that the maghemite–magnetite solid solution is a potential natural battery for the growth of anaerobic microbes in sulfidic environments.

The role of siderite in catalyzing the H2O2 degradation of carmine was studied by using batch experiments. The effects of the size of siderite particles, ratio of H2O2 to siderite, initial pH, reaction time, and reaction temperature were examined, and the degradation mechanism and kinetics were discussed. The size of siderite slightly affected the degradation of carmine, and the ratio of H2O2 to siderite significantly influenced degradation; a ratio of 6:1 resulted in maximum carmine degradation. Although the optimal reaction pH was 3, excellent degradation efficiency was also found at pH 4 and 5. In the H2O2/siderite system, the kinetic reaction order is 1.04, and the rate constant is 10.15 min−1; 99.97% of the chroma was removed, and 80.61% of the TOC was degraded when the ratio of H2O2 to siderite was 6:1 with an initial pH of 3. The slow release of Fe2+ in siderite played an important role in the catalytic H2O2 degradation of carmine. Moreover, siderite was cycled eight times without affecting decolorization efficiency. The experimental data illustrated that siderite provided the catalyst for the Fenton process and that siderite has great application value and potential in carmine degradation; this data serves as a foundation for the industrial use of recycled natural mineral materials.

Porous maghemite (PM) was prepared by two-step calcinations. The crystallographic and magnetic changes of PM upon SO42− and CO32− adsorption were investigated. The crystallite size (~ 27 nm) and PM texture remain unchanged after adsorption. Fourier transform infrared spectra showed that SO42− and CO32− are adsorbed on the PM mainly through outer- and inner-sphere surface complexations, respectively. X-ray photoelectron spectra showed the increase and decrease of binding energy for Fe 2p3/2 electrons after SO42− and CO32− adsorption, respectively. Sulfate adsorption increases the magnetic susceptibility (χ) of PM by ~ 4.5%, and decreases the saturation magnetization (Ms) of PM by 24.6%. By comparison, carbonate adsorption decreases χ by ~ 3.7% and increases Ms by 17.8%. The magnetic changes upon SO42− and CO32− adsorption are attributed both to the electronegativity of anions and the size distribution of PM.

Bismuth tungstate/palygorskite (Bi2WO6/Pa) composite photocatalyst was prepared by hydrothermal method and characterized by X-ray diffraction (XRD), Fourier transform-infrared (FT-IR), scanning electron microscope (SEM), transmitting electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), nitrogen adsorption-desorption measurement (BET), UV–Vis reflection spectrometer (DRS) and photoluminescence (PL). The effects of composite catalysts with different preparation conditions on the degradation of benzene were discussed. The results showed that the composite catalyst had excellent catalytic performance on gaseous benzene degradation. When benzene initial concentration was 50 mg/m3, over Bi2WO6/palygorskite with mass ratio was 8:2, calcined temperature was 250 °C and the precursor pH value was 3, the benzene degradation efficiency reached 68.2% and the mineralization efficiency reached 62.7% after 120 min 365 nm UV light irradiation. The high activity and stability of composite catalyst could be attributed to its large specific surface area which improved the condition of photoinduced electron-hole recombination, and electron-hole and superoxide radicals played an important role in the photo-degradation of benzene.

Iron oxide dry desulfurization is one method for the removal of hydrogen sulfide. This work investigates the physicochemical properties and performance of oolitic hematite upon desulfurization at h...

Struvite crystallization is one of the most promising routes for phosphorus recovery from phosphorus-rich sludge. However, the adsorption of alginic acid, a surrogate of extracellular polymeric substances in phosphorus-rich sludge, on struvite crystals has been proved to significantly inhibit struvite crystallization. To comprehensively understand the inhibitory mechanism, the adsorption behavior was evaluated at various adsorption time, the concentration of alginic acid, pH and ionic strength in the present study. Subsequently, adsorption equilibrium isotherm, kinetic and thermodynamics models were employed to fit the adsorption data. Interestingly, the adsorption mechanism was explored by X-ray photoelectron spectra (XPS) and Fourier transform infrared spectroscopy analysis (FTIR), which was further elucidated by triple-layer model (TLM). The results indicated that the adsorption capacity of struvite crystals almost reached a plateau value within the first 30 min. Meanwhile, the adsorption capacity was significantly reduced with increasing pH, but slightly increased with increasing ionic strength. Moreover, the adsorption process obeyed pseudo-second order kinetic model and Langmuir adsorption isotherm model, whereas intra-particle diffusion was a main rate-limited step. Furthermore, hydrogen bonding and surface complexation between alginic acid and struvite crystals dominated the adsorption mechanism. Additionally, alginic acid underwent surface reactions by virtue of two outer-sphere surface complexes and one inner-sphere surface complex. The findings presented herein will facilitate understanding of the inhibitory mechanism of organic matters on struvite crystallization from phosphorus-rich sludge.

Siderite as a Fe(II)-bearing mineral often be naturally weathered and oxidized into goethite, which would decrease the surface chemical activity of the siderite. The chemical activity of siderite is improved by decomposing weathering-formed goethite at low temperature (350 °C). The activated natural siderite (ANS) was utilized to remove U(VI) from aqueous solutions. Batch experiments revealed that ANS after thermal treatment at 350 °C (ANS350) exhibited excellent uptake performance toward U(VI) (14.65 mg/g) which was better than natural siderite (9.00 mg/g) at pH = 4.0 and T = 293 K. Meanwhile, the uptake percents of U(VI) on NS and the uptake process was involved electrostatic attraction on the surface of adsorbents. The characterization results illustrated that activated natural siderite at 350 °C presented the better uptake capacity due to its larger specific surface area and smaller average pore size compared to natural siderite, which was optimized to adsorb U(VI) from aqueous solutions. The spectroscopic analysis demonstrated that the abundant surface oxygenated functional groups of ANS facilitated the uptake process of U(VI). Meanwhile, reduction was also involved in the process. Additionally, the U(VI) reduction amount can be enhanced to some extent after calcination. These findings give insight into the further development of activated natural mineral obtained by heating in low temperature, for using as potential candidate in immobilization of uranium(VI) from contamination water in actual environmental management.

In this paper, the nanostructured hematite was prepared by heat treatment of siderite in air atmosphere. The influence of ultrasonic time on the physicochemical properties of nano structured hematite was studied. The effects of reaction time, pH, ionic strength and initial concentration on the adsorption of Eu(III) hematite with different ultrasonic time were investigated. The series of characterization showed that nanostructured hematite can be formed by heating siderite. The size and crystallinity of nanoscale hematite were further reduced by ultrasound, resulting in increasement of the specific surface area. Compared with the nanostructured hematite without ultrasound, nanostructured hematite (PCH-3) after ultrasound for 1 h obtained the biggest specific surface area (29.37 m2/g). Batch experiments results indicated that PCH-3 had the maximum rate constant ( K 2=3.49 g/(mg min)) and the maximum adsorption capacity (4.88 mg/g) for Eu(III) adsorption at T = 288 K, pH 5.5. X-ray photoelectron spectroscopy (XPS) analysis confirmed that oxygen-containing functional groups (especially hydroxyl groups) were the main adsorption sites of Eu(III) enriched by nano structured hematite. The results showed that proper ultrasound treatment can significantly improve the surface reactivity of the nano structured. This work is of great theoretical value for the adsorption of heavy metal ions by nanostructured mineral materials.