Al Species Research Articles

Dissolution Behavior of Hydrated Tungsten Chlorides in Chloroaluminate Ionic Liquids and It's Application in Aluminum–Tungsten Alloy Electrodeposition

Introduction The demand for aluminum (Al) alloys as coating materials have increased owing to their high corrosion and oxidation resistance. In addition, electrodeposition technique has attracted attention for obtaining Al alloy coatings, and various non-aqueous electrolytic baths for Al alloy electrodeposition, including ionic liquids, have been developed. Alloying Al with refractory metals, such as tungsten (W) and molybdenum (Mo), significantly improves the pitting-corrosion resistance of Al. However, the salts of these metals have relatively low solubility in Al electrodeposition baths, and thus, it is difficult to obtain Al alloys with a high content of these metals.In our previous study, we reported that a W(II) salt, namely W6Cl12, which is dissolved in 1-ethyl-3-methylimidazolium (EMIC)–AlCl3 ionic liquids at a higher concentration than other salts such as WCl4, enables the electrodeposition of Al–W alloy films with a high W content[1]. However, the W6Cl12 used previously turned out to contain water due to the synthesis process, which may have increased the solubility of W6Cl12.In this study, we investigated the effect of water content on the solubility of W precursors in ionic liquids. Herein, three W precursors with different water contents were employed, namely anhydrous W6Cl12 and hydrated complexes W6Cl12·2H2O and (H3O)2[W6Cl14]·7H2O (Figure 1). Al–W alloy was electrodeposited using baths containing different W precursors. In addition, the chemical speciation of the hydrated complexes in the ionic liquids was conducted using, Raman, and Fourier transform infrared (FT-IR), ultraviolet-visible (UV-Vis) spectroscopy. Experimental Herein, three electrolytic baths were prepared by adding anhydrous salt W6Cl12, hydrated complex W6Cl12·2H2O, and (H3O)2[W6Cl14]·7H2O to an EMIC–AlCl3 ionic liquid with EMIC:AlCl3 molar ratio of 1:2. The saturation concentrations of W precursors were determined using inductively coupled plasma atomic emission spectroscopy (ICP-AES). Potentiostatic electrodeposition was performed on copper substrates at a bath temperature of 80 °C under an Ar atmosphere in a glove box. The W content, current efficiency, and impurity content derived from the hydration water in the electrodeposited material were evaluated by energy dispersive X-ray spectroscopy (EDX), ICP-AES, and X-ray photoelectron spectroscopy (XPS), respectively. The dissolved species in the baths were analyzed by Raman, FT-IR, and UV-Vis spectroscopy. Results and Discussion The saturation concentration of each W ion source in the EMIC–AlCl3 ionic liquid was less than 1 mM for anhydrous W6Cl12; however, it increased to ~80 and 120 mM for W6Cl12·2H2O and (H3O)2[W6Cl14]·7H2O, respectively. Potentiostatic electrodeposition at potentials lower than 0 V (vs. Al/Al(III)) produced films consisting of Al and W. The W content increased to ~1 and 15 at.% from the anhydrous salt bath and hydrated complex bath, respectively. The current efficiency for electrodeposition was close to 100%, even in baths with hydrated precursors. EDX and XPS measurements of Al–15 at.% W alloy film obtained from the hydrated complex bath showed that Al and W existed in metallic states in the film.The Raman spectra of each bath showed that the Al2Cl7 − concentration decreased and AlCl4 − concentration increased in the hydrated complex bath compared to the anhydrous salt bath. This suggests that the hydrated W complex reacted with AlCl3 to form other Al species, thereby decreasing the apparent AlCl3/EMIC ratio in the bath. The FT-IR spectra of baths with the addition of hydrated complex or liquid water showed that both the hydrated water and liquid water reacted with Al anions to produce Al–OH–Cl species[2]. The UV-Vis spectra of the anhydrous salt bath and hydrated complex baths showed two prominent peaks: one at 240 nm (λ1) and the other at ~270–300 nm (λ2). λ1 was almost constant for all the W precursors, whereas λ2 shifted to a lower wavelength for the hydrated complex baths. The dissolved W species estimated from these spectroscopic data and their relationship with solubility are discussed at the meeting.

Fine property-tuning through Ca content control in a facile synthesis of glasses-based self-setting injectable hydrogel

Self-setting injectable composite hydrogels are promising materials in tissue engineering. In this study a facile synthetic approach was designed based on traditional sol–gel method to produce particulate calcium aluminosilicate-type glasses, which were then formulated with potassium alginate to form a self-setting injectable hydrogel. In order to control the setting-time and mechanical properties of the composite materials, a series of samples were produced with different starting chemical composition. The change in chemical composition and morphology of the glass particles in response to varying initial Ca2+ content were further elucidated by a combination of EM, XRF and NMR spectroscopy, revealing that the binary aluminosilicate glass was preferably formed when low Ca content (<20%) was used in the formulation. At higher Ca content (>30%), calcium aluminosilicates were predominantly formed due to the change in the type of zeolite precursor formed during the low temperature nucleation process in the sol–gel approach. It was also found the hardening times of the alginate gels was positively correlated to the mole ratio of Ca/Al due to high acid resistance of high coordination number Al species. For hydrogels made with glass particle additions, the mechanical strengths were also positively correlated with the Ca/Al ratio for all formulations.

Underlying core-shell colloidal nanostructure for Beta zeolite membrane formation

Optimal design of Beta zeolite membrane of a three-dimensional 12-ring interconnected channel system can be vital for environmentally sustainable industrial separation application. A faster route of crystal growth from colloidal solution resulted to formation of poly (nanocrystalline) zeolite Beta membrane. The present SANS study probed the underlying functional diversity of core-shell precursor nanoparticle depending on form and structure factor towards the crystal growth for Beta membrane formation. The data clearly distinguished nanoscale structural arrangements of the synthesis solution before the hydrothermal heat treatment, during the induction and nucleation periods. Initially, shells consisting of organic template, reactive Al species and other dissolved ions surrounded the colloidal silica nanoparticles. Some of the silica cores sizes reduced while the shell thicknesses increased resulting to a heterogeneous colloidal solution system consisting of particles of different core-shell dimensions. The evolution of extra-small core and extra-large shell in the heterogeneous system may be nucleating particles as confirmed by XRD pattern corresponding of zeolite Beta. Deposition of such nucleating particles over the support might led to the formation of Beta zeolite membrane. The SANS profile of the solutions further showed that the nucleating particles were more readily deposited over the zeolite-seeded support than the non-seeded support.

Effect of CaO on hydration properties of one-part alkali-activated material prepared from tailings through alkaline hydrothermal activation

Enhancing the reactivity of mine tailings through the efficient and economical technology and using them as active precursors for alkali-activated materials is essential to effectively alleviate environmental issues caused by huge tailings emissions. In this study, an alkaline hydrothermal technology was proposed for increasing the reactivity of gold mine tailings. X-ray diffraction (XRD) analysis and leaching tests indicated that the crystalline structures of tailings were significantly destroyed and amorphous sodium aluminosilicate was identified as the major hydrothermal activation product, which dissolved in water, released large quantities of active Si and Al species, and created an alkaline environment for the slag activation. Subsequently, one-part alkali-activated materials (OPM) were prepared from activated tailings and slag. To improve the hydration properties of these materials, quicklime (CaO) was employed as an additive. OPM sample exhibited the optimum strengths of 8.4, 28.7, 39.5, and 42.5 MPa at 1, 3, 7, 28 days, respectively, when CaO content was controlled at ∼ 6 wt%. pH tests, XRD, thermogravimetric (TG), and scanning electron microscopy (SEM) analyses revealed that the addition of CaO improved the pH of the pore solution, increased the quantity of calcium-sodium aluminosilicate hydrate gel (C(N)-A-S-H, the main hydration reactant), and generated the compact microstructure, thereby enhancing the strength of the OPM samples. However, the strength was dramatically reduced when CaO content exceeded 6 wt% at later stages, mainly because of the severe carbonation of the sample.

Effect of an Al2O3-based binder on the structure of extruded Fe-ZSM-5

The effect of an alumina-based binder on the structure of a commercial Fe-ZSM-5 catalyst has been investigated. Several ex-situ characterization techniques were used to show that the binder in the catalyst formulation allows obtaining a material that possesses improved features in terms of Fe species dispersion, framework Al content and acidity. UV–Vis and X-ray absorption spectroscopy showed that the extent of Fe agglomeration in the extruded catalyst was significantly lower compared to that in the catalyst without binder. 27Al and 29Si-MAS NMR spectroscopy demonstrated a remarkable difference in terms of framework Al migration. NH3-TPD experiments corroborated the NMR results suggesting a retention of Brønsted acidity in the extruded catalyst. We tentatively propose that by providing extra-framework Al species prior to the treatment at elevated temperature, the binder hinders the framework Al dislodgment and Fe agglomeration during calcination.

Adsorption of HF on gibbsite calcined at various temperatures: A solid-state NMR study of low-level fluorinated systems

The fluorination mechanism of low-level fluorinated materials obtained by calcination of Bayer gibbsite at different temperatures was studied by 27Al and 19F solid-state NMR spectroscopy and X-ray diffraction. Gibbsite was calcined at 400, 600, 800, and 1000 °C followed by treatment with anhydrous HF/N2 gas at 100 °C. Three types of Al–F species on the surface of fluorinated gibbsite calcined at 400, 600, and 800 °C are proposed on the basis of the 19F magic angle spinning (MAS) NMR spectra, which show peaks at about −132, −137, and −163 ppm, while the spectrum of fluorinated gibbsite calcined at 1000 °C showed five additional peaks, at about −139, −164, −176, −183, and −191 ppm. The fluorination process in aluminas is based on elementary exchange reactions in which F− replaces surface –OH groups according to their basicity. The 27Al MAS NMR and 19F-27Al cross-polarization–MAS experiments confirmed the presence of octahedral Al species.

Chemoselective decarboxylation of higher aliphatic esters to diesel-range alkanes over the NiCu/Al2O3 bifunctional catalyst under mild reaction conditions

An efficient and highly selective decarboxylation catalyst has been developed for the production of diesel-range alkanes from the conversion of higher aliphatic esters under mild reaction conditions. Using methyl stearate as a model substrate, the NiCu/Al2O3 bifunctional catalysts derived from layer double hydroxide (LDHs) precursors showed excellent catalytic performance with 100% conversion and 97.5% selectivity to heptadecane at 260 °C and 3.0 MPa H2. On the other hand, the catalytic performance of NiCu/Al2O3 catalyst was also tested in the conversion of soybean and waste cooking oils under the mild conditions. The results showed that a high yields of diesel-range alkanes (>80 wt%) were obtained from the conversion of soybean oil and waste cooking oil, respectively.Detailed characterization (XRD, H2-TPR, HRTEM, XPS, and NH3-TPD) indicates, after reduction at 500 °C in H2 atmosphere, the NiCu alloy phase is the predominant phase and the Ni, Cu, Al species exhibited homogeneous distribution in the NiCu/Al2O3 catalyst. The remarkable decarboxylation performance mainly results from the synergistic effect between the metal active sites of NiCu alloy and Lewis acid sites of support Al2O3. The Lewis acid sites (Al3+) of support serve as active sites for the activation of carbonyl group of higher aliphatic esters, while H2 dissociation and decarbonylation of intermediate fatty aldehyde are achieved on the NiCu alloy sites. Compared with the monometallic Ni/Al2O3 catalyst (183.8 kJ/mol), the introduction of Cu species in the bimetallic NiCu/Al2O3 catalyst greatly reduced the activation energy (138.1 kJ/mol) of fatty acid ester conversion via promoting the dispersion of Ni species, reducing the dissociation energy of hydrogen on Ni, and increasing the electron density of Ni, which results in high decarboxylation performance of NiCu/Al2O3 under mild reaction conditions.

Enhanced Flotation Separation of Cassiterite from Calcite Using Metal-Inorganic Complex Depressant

At present, the research on flotation separation of cassiterite and gangue minerals is mainly focused on the development of new collectors or depressants, while the research on combined depressants is rare. In this study, the flotation separation of cassiterite and the typical gangue mineral, calcite, was investigated using the metal-inorganic complex depressant AlSS, composed of aluminum sulfate (Al2(SO4)3) and water glass (Na2SiO3·4H2O). The flotation results indicated that, with the assistance of Al3+, the inhibition effect of SS (water glass) on calcite is significantly enhanced, while the inhibition effect on cassiterite is almost unchanged. The zeta potential and adsorption measurements proved that the formation of the negatively charged colloidal particles composed of Alm(OH)n3m−n and SiOm(OH)n4−2m−n tended to adsorb on the positively charged calcite surface, inhibiting the adsorption of sodium oleate (NaOL), while the adsorption of the colloidal particles on the negatively charged cassiterite surface is relatively less. The contact angle measurements indicate that the contact angle of cassiterite in the NaOL + AlSS solution is obviously larger than that of calcite, which indicates that cassiterite has better floatability in this system. The X-ray photoelectron spectroscopy (XPS) analysis confirms the Al and Si species are adsorbed on the surface of calcite, but not on the cassiterite. In addition, the adsorption of AlSS on cassiterite and calcite changes the chemical environment on the calcite surface, indicating that the adsorption of AlSS on the mineral surface is more inclined to be through a chemical reaction.

Enhancement of soil microstructural stability and alleviation of aluminium toxicity in acidic latosols via alkaline humic acid fertiliser amendment

Alkaline humic acid fertiliser amendment (HAFA) can significantly enhance the microstructural stability of soils, as well as alleviate Al toxicity. Thus, the potential effects of HAFA on soil have attracted increased attention. A soil incubation experiment was conducted to evaluate the effects of HAFA. A typical acidic latosol was cultured for 51 days with five fertiliser treatments—unfertilised (CK), 0.32 g of inorganic fertiliser (IF), 0.32 g of inorganic fertiliser combined with 1.00 g lime (IF.CaO), 0.32 g of HAFA (HAFA0.32), and 0.42 g of HAFA (HAFA0.42)—to investigate the effects of HAFA on the microstructural stability and Al toxicity of soils. The results indicate that HAFA increased the number of aggregates and their honeycomb structures in latosol, as well as enhanced the adsorption capacity of the aggregates. HAFA not only increased latosol pH by 0.72–0.92, but also reduced the exchangeable acid content by 39.49–43.03% as compared with CK, which was similar to the lime treatment; it also significantly increased the soil organic matter content and the availability of N, P, and K, and improved the cation exchange capacity. However, HAFA decreased the effect of increasing the amount of exchangeable Ca when compared to the lime treatment. Additionally, the total amounts of reactive and exchangeable Al in the HAFA treatments were reduced by 45.84–54.59% and 56.67–67.53%, respectively. Both HAFA and lime applications effectively decreased the concentrations of phytotoxic Al species in latosols when compared to the application of inorganic fertiliser alone, with the HAFA0.42 treatment being more effective than lime application in decreasing the amount of dissolved and exchangeable Al. The HAFA0.42 treatment was also the best amendment for stabilising the microstructure, increasing the nutrient content, and mitigating Al toxicity in the potted acidic latosol.

An enhancement of singlet oxygen generation from dissolved oxygen activated by three-dimensional graphene wrapped nZVI-doped amorphous Al species for chloramphenicol removal in the Fenton-like system

Three-dimensional graphene wrapped nZVI-doped amorphous Al species (3D-GN@Fe/a-Al) was fabricated as a novel Fenton-like catalyst for efficient removal of chloramphenicol (CAP) within a wide pH range. The mechanism of singlet oxygen (1O2) generation from dissolved oxygen (DO) activated by 3D-GN@Fe/a-Al was discovered. 3D-GN@Fe/a-Al was characterized by field emission scanning electron microscopy combined with an energy dispersive spectrometer (SEM-EDS), Brunner–Emmet–Teller (BET) measurement, X-ray diffraction (XRD) pattern and Raman spectroscopy to investigate the morphological and physicochemical properties. The catalytic performance of 3D-GN@Fe/a-Al for DO activation was estimated by the factor experiments of CAP degradation, including CAP concentration, catalyst dose, reaction temperature and pH value. Based on the evolution of the ultraviolet spectrum during the reaction and the results of high performance liquid chromatography-mass spectrometry (HPLC-MS) detection, the degradation pathway of CAP in the 3D-GN@Fe/a-Al–DO system was proposed. More importantly, the generation of singlet oxygen from DO activation mediated by the Al3+-promoted single electron delivery was further explored by the experiments of scavengers, electron spin resonance spectroscopy (ESR), X-ray photoelectron spectroscopy (XPS) analysis and electrochemical tests. The mechanism of 1O2 generation provides a new strategy for improving the degradation of organic pollutants in water by Fenton-like systems.

Selective dealumination of ZSM-5 by steaming and its effect on ethanol to propene

The effects of steaming at varying times and temperatures on ZSM-5 pore structures, framework Al distribution, acid properties and ethanol to propene (ETP) catalytic performance were systematically studied in this study. The results show that the crystallinity and specific surface areas of steam treated ZSM-5 samples decrease with the increase treatment time and temperature. 27Al MAS NMR and Co(II) exchange-ICP results show that the isolated framework Al species (Alsingle) can be preferentially removed from the zeolite framework, while the paired Al sites (Alpairs) remain relatively stable after steam treatment. The characterization of Py-IR reveals that the concentration of B acid sites and the acid strength are all declined with the steaming time or temperature increase. The catalytic results of ETP at 450°C show that the sample after steaming gives improved selectivities to propene and butene at the expense of ethene conversion and alkanes selectivity relative to the unmodified zeolite. Besides, a good positive correlation between ethylene conversion and Alsingle concentration is found, whereas the propene formation is influenced by the combination effect of Alsingle and Alpairs sites.

Variation of Al species during water treatment: correlation with treatment efficiency under varied hydraulic conditions

Abstract The concentration of hydrolyzed coagulant ion species is a key factor in determining drinking water treatment efficiency. Direct correlation of water treatment efficiency with changes in species during coagulation has not been addressed. We investigated the correlation under different hydraulic conditions and water treatment efficiencies including changes in removal of turbidity, ultraviolet adsorption at 254 nm (UV254) and dissolved organic carbon (DOC). Results highlighted that Al species (monomeric species as Ala, medium polymeric species as Alb and colloidal species as Alc) behaved differently during coagulation and treatment efficiencies were affected. When varying the mixing speed, the removal of Alc species had a strong negative correlation with water treatment efficiency but under other hydraulic conditions positive correlations were found. The removal of Ala species was positively correlated with water treatment efficiency, but under other hydraulic conditions the low abundance of Ala species meant the correlation was difficult to observe. The Alb species were significantly and positively correlated with water treatment efficiency with the highest correlation coefficient (R2) of 0.87. The correlation of metallic species with removal efficiencies of the DOC and the UV254 produced higher R2 values. Correlation of the rate of removal of Alb species with the removal efficiencies of the DOC or the UV254 was better than for Alc.

Operando leaching of pre-incorporated Al and mechanism in transition-metal hybrids on carbon substrates for enhanced charge storage

Operando leaching of pre-incorporated Al and mechanism in transition-metal hybrids on carbon substrates for enhanced charge storage

Activity of Cu-Al-Oxo Extra-Framework Clusters for Selective Methane Oxidation on Cu-Exchanged Zeolites.

Cu-zeolites are able to directly convert methane to methanol via a three-step process using O2 as oxidant. Among the different zeolite topologies, Cu-exchanged mordenite (MOR) shows the highest methanol yields, attributed to a preferential formation of active Cu–oxo species in its 8-MR pores. The presence of extra-framework or partially detached Al species entrained in the micropores of MOR leads to the formation of nearly homotopic redox active Cu–Al–oxo nanoclusters with the ability to activate CH4. Studies of the activity of these sites together with characterization by 27Al NMR and IR spectroscopy leads to the conclusion that the active species are located in the 8-MR side pockets of MOR, and it consists of two Cu ions and one Al linked by O. This Cu–Al–oxo cluster shows an activity per Cu in methane oxidation significantly higher than of any previously reported active Cu–oxo species. In order to determine unambiguously the structure of the active Cu–Al–oxo cluster, we combine experimental XANES of Cu K- and L-edges, Cu K-edge HERFD-XANES, and Cu K-edge EXAFS with TDDFT and AIMD-assisted simulations. Our results provide evidence of a [Cu2AlO3]2+ cluster exchanged on MOR Al pairs that is able to oxidize up to two methane molecules per cluster at ambient pressure.

Pretreatment method for the utilization of the coal ash landfilled in ash ponds

The coal ash (CA) generated from coal-fired power plants (CPPs) is collected in ash ponds (APs), most of which are actually full, so there are concerns regarding the potential contamination of the environment around them. Thus, in the present study, a method for improving the utilization of coal pond ash (CPA) was proposed. Here the CA landfilled in an AP was regarded as CPA. Furthermore, the CPA characteristics (particle size and weight distributions, chemical composition, unburned carbon (UC) content, particle image, and mineralogical analysis) were investigated. Next, experiments were conducted on the main separation processes: screening with five standard sieves having 0.15-, 0.3-, 0.6-, 1.18-, and 2.36-mm diameter grids; float–sink experiments with four different specific gravities (SGs) of under 1.8 SG, 1.8–2.2 SG, and 2.2–2.5 SG and over 2.5 SG; flotation with a column-type glass reactor under the conditions of pH 2, 7, and 12; grinding with a batch-type ball mill for 5, 10, 20, and 40 min; wet magnetic separation with four magnetic forces (0.1, 0.5, 1, and 2 T). Based on these results, a pretreatment method was proposed and the final materials could be categorized into UC, amorphous compounds (ACs) with Al species (Al2O3∙xH2O) and glassy phases, inorganic materials with Si and Al, and ferrous material groups. Besides, six additional pretreatment methods were suggested through various combinations of each separation process. As a case of South Korea, the applicability of this method to the entire CPA in South Korea was also confirmed.

Acidity-regulated synthesis of a bifunctional mesoporous silica composite with simultaneously enhanced adsorption and catalytic performance

An Al/Cu bifunctional mesoporous silica was successfully synthesized through an acidity-regulated method. AlCl3 instead of HCl was served as catalyst for the hydrolysis and condensation of siliceous source and forming the mesostructure. Cu and Al species were then feasibly incorporated into the matrix of mesoporous SiO2 under the mildly acidic conditions. The obtained Al/Cu-SiO2 bifunctional composite preserves structural ordering of the mesopores. Al is highly dispersed and Cu nanoparticles of ca. 54 nm are decorated on Al/Cu-SiO2. The Al/Cu-SiO2 material presents large adsorption capacity, remarkable catalytic behavior and good cycling performance in the degradation of organic methylene blue from aqueous solutions.

Spectroscopic Signature and Structure of the Active Sites in Ziegler-Natta Polymerization Catalysts Revealed by Electron Paramagnetic Resonance.

Despite decades of extensive studies, the atomic-scale structure of the active sites in heterogeneous Ziegler-Natta (ZN) catalysts, one of the most important processes of the chemical industry, remains elusive and a matter of debate. In the present work, the structure of active sites of ZN catalysts in the absence of ethylene, referred to as dormant active sites, is elucidated from magnetic resonance experiments carried out on samples reacted with increasing amounts of BCl3 so as to enhance the concentration of active sites and observe clear spectroscopic signatures. Using electron paramagnetic resonance (EPR) and NMR spectroscopies, in particular 2D HYSCORE experiments complemented by density functional theory (DFT) calculations, we show that the activated ZN catalysts contain bimetallic alkyl-Ti(III),Al species whose amount is directly linked to the polymerization activity of MgCl2-supported Ziegler-Natta catalysts. This connects those spectroscopic signatures to the active species formed in the presence of ethylene and enables us to propose an ethylene polymerization mechanism on the observed bimetallic alkyl-Ti(III),Al species based on DFT computations.

Behaviour of ozone in the hybrid ozonation-coagulation (HOC) process for ibuprofen removal: Reaction selectivity and effects on coagulant hydrolysis

Simultaneous ozonation and coagulation can be realized in one unit in the developed hybrid ozonation-coagulation (HOC) process. To reveal the reaction sequence within the HOC process, the ibuprofen (IBP) removal efficiency of the ozonation only, HOC and HOC-PO43− (inhibition of the reactions between ozone and metal coagulant) processes at pH 5 and different ozone dosages were investigated. The removal efficiency is almost the same for the three processes at a low ozone dosage (4.8 mg/L), and higher removal performance can be achieved by the HOC process with increasing ozone dosage. It can be implied that ozone preferentially reacts with OH− to generate OH which react with IBP in the HOC process, and subsequently reacts with the surface hydroxyl groups of hydrolysed Al species to enhance OH generation. Moreover, based on the kinetics, X-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FT-IR) analyses, the synergistic reactions between ozone and the metal coagulants (SOC) started to take effect from ozone dosage of 9.6 mg/L, which further verified that ozone will be involved in the IBP ozonation prior to the SOC reactions. The subsequent SOC reactions also resulted in the increased generation of polymeric Al species and more abundant intermediates in the HOC process.

Coupling of cathodic aluminum dissolution and anodic oxidation process for simultaneous removal of phosphate and ammonia in wastewaters

Removal of excessive nutrients (N and P) is one of the most concerned issues for wastewater treatment. This study presents a paired electrolytic system consisting of Al cathode and RuO2/Ti anode for the simultaneous removal of phosphate and ammonia in wastewaters. The comparative study on the dissolving behaviors of Al cathode and Al anode showed that Al cathode could achieve a continuous and stable dissolution of aluminum, thereby forming flocs and small amounts of water soluble aluminum species for decontamination. The electrogenerated OH– in the vicinity of cathode raised the local alkalinity and caused the chemical dissolution of aluminum. According to the experiment of non-electrolytic dissolution of aluminum in alkaline solution, the local pH resulting in the cathodic dissolution of Al was estimated. The paired electrolytic system showed the capability to simultaneously remove ammonia and phosphate in simulated wastewater, and the pH neutralizing effect in association with the formation of Al species could promote the electrochemical oxidation of ammonia. When the paired electrolytic system was applied to the treatment of landfill leachate, 96.9% of ammonia nitrogen, 87.4% of total phosphorous and 89.9% of COD could be eliminated after three hours of electrolysis at 80 mA/cm2. The results shown in study reveal that the dissolution process of Al cathode enables a convenient control on the dissolving-out amounts of aluminum via regulating the applied current density, and the paired electrolytic system can be developed as an energy-efficient electrochemical wastewater treating method.

Coagulation-ultrafiltration integrated process for membrane fouling control: Influence of Al species and SUVA values of water

Natural organic matter (NOM) pollution is a great challenge for the ultrafiltration (UF) process owing to the inevitable membrane fouling. In this study, three Al species coagulants (Ala/Alb/Alc) and their composites in combination with Poly dimethyl ammonium chloride (PolyDMDAAC) were used as a pretreatment strategy for the UF process. Then, test waters with different NOM fractions (i.e., humic acid, fulvic acid, protein, and polysaccharide) were prepared to analyze the effects of NOM characteristics on membrane fouling behaviors. The results indicated that compared with Alb and Alc, Ala showed higher removal efficiencies for hydrophobic NOM, aromatic organic matters, and suspended particles, but a limited effect on removing dissolved organic carbon (DOC). Ala or Ala-PolyDMDAAC effectively mitigated membrane fouling by removing the hydrophobic NOM in the coagulation process and forming the porous cake layer in the UF process. The test waters with higher specific ultraviolet absorbance (SUVA) resulted in more severe total and reversible membrane fouling but lighter irreversible fouling. After pretreatment by Ala or Ala-PolyDMDAAC, water samples with the medium SUVA value exhibited remarkable alleviation of membrane fouling due to the formation of large, compact, and robust flocs, as well as the construction of loose and poriferous cake layer on the membrane surface. Although hydrophilic NOM was challenging to be removed by coagulation, the interception and re-adsorption of porous cake layers contributed to the alleviation of irreversible fouling.