Al CO3 Research Articles

Zn–Al–CO3 layered double hydroxides prepared from a waste of hot-dip galvanizing process

Hot-dip galvanizing process is used worldwide to protect the steel or iron pieces from corrosion. This process is a large generator of waste, considered one of the so-called dirty industries. One of the important wastes, in terms of quantity, is zinc ash that contains a mixture of metallic zinc and zinc oxide with a total content of zinc between 70 and 90%. The aim of this study is the preparation and characterization of a series of Zn R –Al–CO3 (R = 2–4) layered double hydroxides (LDH) by using as zinc precursor the zinc chloride obtained after hydrochloric acid leaching of fine-grained zinc ash. Results presented herein clearly demonstrated that characteristics of the synthesized samples are close to those of similar materials synthesized starting from analytical grade reagents. At the same time, it was observed that impurities existent in the zinc chloride solution prepared by zinc ash leaching (Pb, Fe, Ca), are found at traces in the synthesized LDH materials; therefore, they have no significant influence on the obtained LDH structure and properties. By this approach, several important benefits may be simultaneously achieved: (1) preventing the pollution associated with hot-dip galvanizing process wastes, (2) obtaining of valuable products with minimized costs, keeping in mind that LDH have multiple utilizations at industrial scale, (3) saving energy and material costs, and (4) increase of product competitiveness with respect to the circular economy.

Anion Removal Potential of Complex Metal Oxides Estimated from Their Atomic Scale Structural Properties

The main common idea of two conference papers delivered at OMEE-2017 was to demonstrate an importance of the speciation level knowledge in modern adsorption materials science. In order to prove this, two groups of adsorptive materials were used: three samples of Mg–Al–CO3 layered double hydroxides produced by di erent synthesis methods and ten samples of Fe–Ce oxide-based composites with various ratios of Fe-to-Ce. In both cases of studies, it was not possible to find direct correlation between adsorptive performances of the materials and their structural properties obtained by conventional characterisation techniques. However, anion adsorptive removals of each group of inorganic composites correlated with their structural properties studied on the level of speciation. It was shown that strong anion removal potential of Mg–Al–CO3 layered double hydroxides was associated with richness in speciation of chemical elements (Mg, Al) and interlayer anions (CO2 3 −) as well as with generous hydration. Adsorptive performances of inorganic anion exchangers based on Fe–Ce hydrous oxides were explained by simulation extended X-ray absorption fine structures simulation. The best anion removers were found to be those Fe/Ce oxide-based composites whose Fe outer shells were formed from backscattering oscillations from both O and Fe atoms.

Anion Removal Potential of Complex Metal Oxides Estimated from Their Atomic Scale Structural Properties

The main common idea of two conference papers delivered at OMEE-2017 was to demonstrate an importance of the speciation level knowledge in modern adsorption materials science. In order to prove this, two groups of adsorptive materials were used: three samples of Mg–Al–CO3 layered double hydroxides produced by di erent synthesis methods and ten samples of Fe–Ce oxide-based composites with various ratios of Fe-to-Ce. In both cases of studies, it was not possible to find direct correlation between adsorptive performances of the materials and their structural properties obtained by conventional characterisation techniques. However, anion adsorptive removals of each group of inorganic composites correlated with their structural properties studied on the level of speciation. It was shown that strong anion removal potential of Mg–Al–CO3 layered double hydroxides was associated with richness in speciation of chemical elements (Mg, Al) and interlayer anions (CO2 3 −) as well as with generous hydration. Adsorptive performances of inorganic anion exchangers based on Fe–Ce hydrous oxides were explained by simulation extended X-ray absorption fine structures simulation. The best anion removers were found to be those Fe/Ce oxide-based composites whose Fe outer shells were formed from backscattering oscillations from both O and Fe atoms.

Synthesis and characterization of crude hydrotalcite Mg–Al–CO3: study of thymol adsorption

The study of the adsorption of thymol on a hydrotalcite of synthesis Mg3Al–CO3 (HT3) of molar ratio Mg/Al = 3 and on its counterpart enabled at 500 °C (HT3-C) was conducted in hexane at a concentration of 40 mg L−1 of thymol. Hydrotalcite HT3 was prepared via coprecipitation at a constant pH of 10 and characterized by X-ray diffraction, infrared spectroscopy, nitrogen adsorption–desorption methods and thermal analysis (TGA/DTA). The adsorption of the thymol tests were monitored by UV–visible spectroscopy. The results show that the calcined hydrotalcite (HT3-C) has a capacity of adsorption of thymol (8 mg g−1) much greater than that of HT3 (4 mg g−1), and the experimental points are described by the isotherm model of the Freundlich of both materials.

Simultaneous activity and stability increase of co-precipitated Ni–Al CO2 methanation catalysts by synergistic effects of Fe and Mn promoters

The activity and stability of co-precipitated NiAlOx catalysts in the CO2 methanation reaction is targetedly enhanced by co-doping Fe and Mn.

Synthesis and characterisation of Al4O4C nanorod/CNT composites

Abstract A novel route has been developed to synthesise Al 4 O 4 C nanorod/CNT composites by heat-treating Al 4 SiC 4 in a furnace with carbon heater. The study of growth mechanism indicates that the Al 4 O 4 C nanorods grew by a vapour–vapour–solid (VVS) growth process. Al vapour evaporated from the Al 4 SiC 4 at high temperatures and reacted with CO to form the Al 4 O 4 C nuclei. Subsequently, Al 4 O 4 C nanorods grew upon the continuous deposition of Al vapour and CO on the Al 4 O 4 C nuclei. Low P CO and appropriate temperature are two important factors in the growth of such composites. Holding at 1500 °C for 1 h was determined to be the optimal conditions for growth of Al 4 O 4 C nanorod/CNT composites.

Size-dependent hydration mechanism and kinetics for reactive MgO and Al2O3 powders with respect to the calcia-free hydraulic binder systems designed for refractory castables

This work investigates the time-dependent hydration behavior of 1:1 molar ratio mixture of reactive α-Al2O3 nano- or micro-powder and reactive MgO in relation to the development of new hydraulic binder systems for in situ spinel refractory corundum castables. Mg–Al–CO3 hydrotalcite-like phases formed in the cementitious matrices cured in the corresponding curing condition up to 280 days of age at 50 °C were subjected to morphological, chemical and structural characterization using XRD, FT-IR, NMR, SEM and TEM techniques. The observations indicate that both the short-term cured MgO–nano-Al2O3 cementitious matrix and the long-term cured one containing micro-Al2O3 contain mainly OH–(Mg3) hydroxyl group, whereas the long-term cured MgO–nano-Al2O3 cementitious matrix is dominated by OH–(Mg2Al) hydroxyl group. The thermal stability of hydrotalcite-like compounds (Mg0.667Al0.333(OH)2(CO3)0.167(H2O)0.5, Mg6Al2CO3(OH)16·4H2O) (HTlcs) through combined DTA–TGA–EGA–MS analyses shows that HTlcs undergo dehydration first and then dehydroxylation overlapping with decarbonization processes. According to EGA–MS and FT-IR measurements, the Mg–Al cementitious matrices were progressively carbonated over curing time and then interlayer water molecules were preferably coordinated by interlayer CO32− ions that exist in a complex network of hydrogen bonds between octahedral layers. In the near-fully-hydrated binder paste, dehydration of crystalline water molecules occurs at 262 °C and the thermal stability of hydroxyl groups in HTlcs is OH–(Mg2Al) (422 °C) > OH–(Mg3) (337 °C) at a ramping rate of 10 °C/min. The basic information provided by the microcalorimetric measurement is such that the starting grain size significantly affects the heat flow curve. From the SEM and TEM images, the hydrates are found to be hexagonal in shape.

Selenium Removal from Sulfate-Containing Groundwater Using Granular Layered Double Hydroxide Materials

Due to recent changes in regulatory discharge limits, selenium removal from electric utility wastewaters is becoming an important issue. In this work, Mg–Al–CO3 layered double hydroxide (LDH) in granular form was evaluated for treatment of selenium-containing groundwater in small scale column tests. The LDH material showed good capacity for removing selenate from groundwaters that contained very high levels of sulfate and total dissolved solids. Column tests were investigated using the granular LDH to treat groundwater containing trace levels of selenium <2 ppb. Removal of sulfate using chemical pretreatment of the groundwater resulted in about 3× higher selenium loading onto the granular LDH. The structural changes in the media after exhaustion and analysis of the effluent water from the column test were also studied to better understand the species removed by the LDH. These results show that the LDH is a promising sorbent for removing selenium from wastewaters with high levels of sulfate and background ...

Intercalated hydrotalcite‐like materials and their application as thermal stabilizers in poly(vinyl chloride)

ABSTRACTThe preparation of hydrotalcites with traditional materials is often based on the corresponding salts and alkali solutions. In this study, to facilitate industrial synthesis and take advantage of the lower cost during the process, a Ca–Al–HPO3–layered double hydroxide (LDH) was directly synthesized with calcium hydroxide, aluminum hydroxide, and sodium phosphite powders. X‐ray diffraction, Fourier transform infrared, and scanning electron microscopy analyses confirmed the successful synthesis of the phosphite‐intercalated hydrotalcite. Compared with Ca–Al–CO3–LDH, Ca–Al–HPO3–LDH enhanced the heat stability of poly(vinyl chloride) (PVC) in terms of both short‐term and long‐term stability because phosphite replaced the allyl chloride and reacted with the conjugated double bonds in PVC; this was deduced through a thermal aging test. The composites of Ca–Al–HPO3–LDH, zinc stearate, and calcium stearate had a synergetic effect when added to PVC and exhibited excellent thermal stability. In addition, the phosphite reacted with ZnCl2 in case of the phenomenon of zinc burning. © 2017 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2017, 134, 44896.

Enhancement of Mercury Sorbent Using Metal Aluminate Carbonates with Chloride under Hydrothermal Conditions

Mercury sorbents M–Al–CO3 (M=Mg2+, Mn2+, Fe2+, Cu2+, or Zn2+) were prepared by the coprecipitation of M2 + and Al3+ in an alkaline NaOH/Na2CO3 solution. The formation of a layered double hydroxide structure significantly enhanced Hg removal, uniquely with a suitable binder as a support. Both Hg(NO3 )2 and HgCl2 were used to perform the capture test. The calcined sorbent exhibited superior efficiency, particularly for materials having bivalent states of mixed oxide (MO), such as calcined Mn and Fe. Chloride ions effectively raised the mercury scrubber efficiency, regardless of the type of sorbent. The results show that synthetic sorbents can provide 96% removal of Hg at 200°C. In addition, a suitable binder such as TiO2 can be used as a support for dispersing metal oxides, which significantly decreases the MO content while maintaining a high equivalent capture capacity.

Basicity-Tuned Hydrotalcite-Supported Pd Catalysts for Aerobic Oxidation of 5-Hydroxymethyl-2-furfural under Mild Conditions

An environmentally benign and homogeneous base-free route for 5-hydroxymethyl-2-furfural (HMF) aerobic oxidation to 2,5-furandicarboxylic acid (FDCA) in water was reported using Mg–Al–CO3 hydrotalcite-supported Pd nanoparticles (xPd/HT-n) as catalyst. The influences of the Mg/Al molar ratio of hydrotalcite and Pd loading amount on the catalytic performance of these catalysts were originally systematically investigated. These catalysts exhibited excellent catalytic activity and FDCA selectivity in the HMF oxidation, especially for 2%Pd/HT-5 and 2%Pd/HT-6; >99.9% FDCA yields were achieved for 8 h under ambient pressure and homogeneous base-free conditions. The remarkably improved catalytic performance could be attributed to the suitable basicity of the Mg–Al–CO3 hydrotalcite and the abundant OH– groups on the surface of hydrotalcite. The plausible reaction mechanism was proposed based on the results of a series of controlled experiments. Furthermore, these catalysts were quite stable and could be reused at ...

Correlation between the d-value and the M2 +:M3 + cation ratio in Mg–Al–CO3 layered double hydroxides

Twenty-six samples of natural layered double hydroxides (LDHs: hydrotalcite, pyroaurite and quintinite) from various localities worldwide have been studied by means of single-crystal, powder X-ray diffraction and electron microprobe analysis. High crystallinity of samples allowed for the good accuracy of the measured d-values and reliable values of the M2+:M3+ ratios. Based on the obtained data, it has been found out that d-value for LDHs depends upon the M2+:M3+ ratio that can be explained by purely crystal chemical reasons. The ideal d-values for M2+:M3+=2:1 (quintinite group) and 3:1 (hydrotalcite group) are 7.56 and 7.80Å, respectively, whereas intermediate cation ratios correspond to the intermediate d-values. The observed quantitative correlation between d-value and M2+:M3+ cation ratio for carbonate LDHs can be described by the linear function d=0.2385×R+7.0852 (R=M2+:M3+), which allows for the estimation of M2+:M3+ on the basis of d-value and vice versa.

Removal of the anionic dye Biebrich scarlet from water by adsorption to calcined and non-calcined Mg–Al layered double hydroxides

A native layered double hydroxide Mg–Al–CO3, denominated LDH, containing Mg(II) and Al(III) in the layers, was prepared by a co-precipitation method. Its calcined form Mg–Al, (CLDH), was obtained by calcination at 500°C. Both materials were characterized by powder X-ray diffraction (PXRD), Fourier transformation infrared spectroscopy, thermogravimetric analysis, and the determination of the point of zero charge. The porous structure of the solids was investigated by nitrogen adsorption at 77 K. The adsorptive affinity of these materials for Biebrich Scarlet was studied as a function of dye–adsorbent contact time, initial pH of the solution, initial dye concentration, and temperature. Sorption kinetics data fitted best to a pseudo-second-order model suggesting that the process of BS adsorption is controlled by reaction rate for interaction of dye molecules rather than by diffusion. Equilibrium data for both adsorbents were in accordance with both Sips and Langmuir isotherm models. The sorption capacity of CLDH was found to be almost independent on the initial pH, while sorption capacity of LDH was lower in neutral and alkaline conditions than at acidic pH. The adsorption process was also found to be spontaneous and endothermic in nature.

Interaction of pristine hydrotalcite-like layered double hydroxides with CO2: a thermogravimetric study

Metal oxides in general have surface acidic sites, but for exceptional circumstances, are not expected to mineralize CO2. Given their intrinsic basicity and an expandable interlayer gallery, the hydrotalcite-like layered double hydroxides (LDHs) are expected to be superior candidate materials for CO2 mineralization. However, the incorporation of Al3+ adversely impacts the ability of the metal hydroxide layer to interact with CO2 in the gas phase in comparison with the unitary Mg(OH)2. Thermogravimetric analysis shows that the decomposition reaction of the [Mg–Al–CO3] LDH is only marginally delayed in flowing CO2 in comparison with flowing N2, showing only an apparent marginal CO2 uptake. Al3+ ion severely attenuates the surface basicity of the LDHs, as the unitary Al(OH)3 is acidic in comparison with Mg(OH)2 and shows little or no interaction with CO2 in the gas phase.

Modified hydrotalcites for improved corrosion protection of reinforcing steel in concrete – preparation, characterization, and assessment in alkaline chloride solution

Six MgAl hydrotalcites (Mg/Al = 2 and 3) were synthesized through the modification of two carbonate hydrotalcites (i.e., Mg(2)AlCO3 and Mg(3)AlCO3) by two amino acids (11aminoundecanoic acid and paminobenzoic acid) and sodium nitrite. They were characterized by means of XRD, FTIR, TG/DSC, and elemental analysis. The ion exchange of the modified hydrotalcites (MHTs) were investigated in alkaline chloride solution and the results showed that ion exchange occurred between free chloride ions and the intercalated inhibitive anions in MHT. The corrosion inhibition of three MHTs (Mg/Al = 2) was evaluated based on the open circuit potential and linear polarization resistance evolution of steel coupons in 0.1 M NaOH solution stepwise enriched with chlorides and the results showed that MHT, in particular, Mg(2)AlpAB exhibited an improved corrosion inhibiting effect in terms of a higher chloride threshold compared to its constituent free inhibitor ions (i.e., pAB). This study confirms the dual protection that MHT, in particular, Mg(2)AlpAB, offers to the steel: capturing chlorides and simultaneously releasing the intercalated inhibitors to further protect the steel from corrosion.

Characterization of Novel Sorbents for Mercury Removal at Elevated Temperature

The novel carbonate sorbents of Mg–Al–CO3 and (Mg3−x, Cux)–Al–CO3, were synthesized by co-precipitation method with individual nitrate salt of metal ions under alkaline conditions. The synthetic sorbent was characterized by analysis techniques such as BET surface area analysis, X-ray diffraction (XRD), and scanning electron microscopy (SEM). Elemental mercury capture experiments were carried out in a fixed-bed reactor including Hg permeation source, furnace, and Hg analyzer, which was conducted at temperature ranging from 30 to 300 o C. The major results showed that the surface area of material was significantly increased via incorporating Cu2+ into Mg–Al–CO3, accordingly enhancing Hg retention capacity of sorbents. SEM imagines displayed the layer appearance of Mg/Al and Mg/Cu/Al sorbents. Crystalline analysis indicated lamella structure accompanied with metal oxides within materials. Mercury removal tests demonstrated that the breakthrough time increased with temperature by adding transition metals to Mg–Al–CO3 as (Mg3−x, Cux)–Al–CO3. Hg uptake by the (Mg3−x, Cux)–Al–CO3 sorbent rapidly increased with elevated temperature up to 200 o C and reached the maximum capacity of 12.93 μg/g, and then gradually decreased after 300 o C. Surface area and unique properties of transition metals are the reason toward improving Hg capture sorbent. These results represent the feasibility of using such Hg sorbents for elemental mercury removal under elevated temperature conditions, and the detail mechanism is needed to be further studied.

Mg–Al–CO3 hydrotalcite removal of persistent organic disruptor — Nonylphenol from aqueous solutions

The paper addresses study of adsorption of widely used and persistent ionic surfactant nonylphenol (NP) onto Mg–Al–CO3 hydrotalcite (HT) and its calcined form (cHT). A combination of experimental techniques (gas chromatography, X-ray diffraction, and FTIR spectroscopy) was used for the characterization of adsorption products and for determination of the residual concentration of NP in the aqueous solution. NP deprotonation at equilibrium pH (7.22 for HT and 9.43 for cHT) was negligible. Adsorption efficiency of HT and cHT in the range 88.3–92.9% was achieved. It was found that for HT and cHT, the same adsorption mechanisms is applied, and depends on the initial concentration of NP in the solution. For the initial concentration c0<3mgdm−3 the mono-layer adsorption occurs as a result of the polar interaction of the phenolic group of the NP — positively charged surface of HT or rehydratable cHT, whereas for c0≥3mgdm−3 multi-layered adsorption prevails. Intercalation of NP into the interlayer space of HT and cHT was not confirmed. The saturation capacity of HT and cHT in the event of the mono-layered adsorption was set at 1.80mgg−1. The physical nature of the adsorption suggests the possibility of easy regeneration of the adsorbent, and thus its reuse.

Static and dynamic adsorptive removal of selenite and selenate by alkoxide-free sol–gel-generated Mg–Al–CO3 layered double hydroxide: Effect of competing ions

Adsorption/ion exchange is a major separation approach capable of recovering the valuable Se component from various multicomponent solutions or to reduce its concentration. In this study, we report a method for selenite and selenate adsorptive removal based on the application of Mg–Al–CO3 layered double hydroxide (LDH) generated via an alkoxide-free sol–gel synthesis method developed by the authors. The selenite and selenate removal capability of Mg–Al LDH was examined under static and dynamic adsorption conditions, focusing on the influence of the competing anions (phosphate, sulphate, carbonate, silicate, chloride). The adsorption capacities of Mg–Al LDH for selenite and selenate obtained from the equilibrium isotherms were not influenced by the presence of the competing sulphate, retaining the highest values of 168 and 103mg [Se]/gdw for Se(IV) and Se(VI) at pH 5, respectively. This inorganic ion exchanger is capable of functioning across the broad range of pH values from 5 to 9. Mg–Al LDH could purify 16,200 and 4200 bed volumes (BVs) of the selenite/selenate-containing solutions (∼50μg [Se]/L initial concentration), respectively, until reaching a selenium concentration of zero in the effluents. The presence of phosphate and a 74-times higher concentration of sulphate compared with selenate or selenite in the adsorbate showed nearly no influence on the dynamic adsorptive performance of Mg–Al LDH for selenite. An equivalent concentration of phosphate did not influence the dynamic adsorptive removal of selenate. Markedly higher concentrations of sulphate, however, decreased the time to breakthrough for selenate but did not affect the quality of its removal. Mg–Al LDH is a promising inorganic ion exchanger for the removal of both of the aqueous selenium species and will be tested on industrial scales.

Adsorption of Cd(II) by Mg–Al–CO3- and magnetic Fe3O4/Mg–Al–CO3-layered double hydroxides: Kinetic, isothermal, thermodynamic and mechanistic studies

Understanding the adsorption mechanisms of metal cations on the surfaces of solids is important for determining the fate of these metals in water and wastewater treatment. The adsorption kinetic, isothermal, thermodynamic and mechanistic properties of cadmium (Cd(II)) in an aqueous solution containing Mg–Al–CO3- and magnetic Fe3O4/Mg–Al–CO3-layered double hydroxide (LDH) were studied. The results demonstrated that the adsorption kinetic and isotherm data followed the pseudo-second-order model and the Langmuir equation, respectively. The adsorption process of Cd(II) was feasible, spontaneous and endothermic in nature. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy were used to explain the adsorption mechanisms. The characteristic XRD peaks and FTIR bands of CdCO3 emerged in the LDH spectra after Cd(II) adsorption, which indicated that the adsorption of Cd(II) by LDHs occurred mainly via CdCO3 precipitation, surface adsorption and surface complexation. Furthermore, the magnetic Fe3O4/Mg–Al–CO3-LDH can be quickly and easily separated using a magnet before and after the adsorption process.

Photostability enhancement of azoic dyes adsorbed and intercalated into Mg–Al-layered double hydroxide

Abstract Two azoic dyes 4-aminoazobenzene-4-sulfonic (AS) and ethyl orange (EO) were adsorbed on or intercalated into Mg–Al–CO 3 layered double hydroxide (LDH) for photostability enhancement. Fluorescence analysis results showed that the photostability of two dyes could be greatly improved after being adsorbed on the surface of Mg–Al–CO 3 -LDH matrix. Furthermore, photostability of adsorbed dyes was superior to that of intercalated dyes. It was suggested that AS or EO was adsorbed on LDHs surface through a strong chemisorption interaction, resulting in the enhancement of photostability. After the UV irradiation under N 2 atmosphere, the absorbed dyes not only show great increase of fluorescence intensity but also exhibited high stability against UV irradiation. This work provides a feasible approach to enhance the photostability of azoic dye confined in an inorganic two-dimensional (2D) matrix via changing the microenvironment, which may be considered to be a promising method of improving photostability of solid fluorescent materials.