Aqueous Ammonium Carbonate Solution Research Articles

Issledovanie udel'noy elektroprovodnosti reniysoderzhashchikh rastvorov karbonata ammoniya i raschet ee energii aktivatsii

The specific electrical conductivity dependence of aqueous solutions of ammonium carbonate and solutions of the ammonium carbonate—ammonium perrenate system on the reagents content in the range of their concentration of 0.1—1.8 mol/l for (NH4)2CO3, 0.01—0.1 mol/l for NH4ReO4 and solution temperatures in the range of 20-50 °C were investigated by the conductometric method. A linear increase in electrical conductivity with an increase in the temperature of electrolytes and a nonlinear increase with an increase in the concentration of reagents was revealed. The temperature coefficients values of electrical conductivity and the activation energy values of electrical conductivity in the studied range of concentrations and temperatures are calculated. A decrease in the activation energy of electrical conductivity with an increase in the temperature of the solution was noted. The calculated value of the activation energy of electrical conductivity indicates the diffusive nature of charge transfer.

Using sucrose to prepare submicrometric CaCO3 vaterite particles stable in natural rubber

Vaterite with submicrometer particles was successfully synthesized by adding sucrose at certain amounts (x = 0–50 %) to the aqueous solutions of ammonium carbonate ((NH4)2CO3) and calcium chloride (CaCl2) precursors prior to the precipitation. Typical polymorphic phases and morphological shapes of CaCO3 particles were characterized by XRD, FTIR, Raman spectroscopy, SEM, and TEM techniques. It is evident that when the sucrose concentration is increased, the average particle size of CaCO3 is decreased which was reduced from 0.81 µm at x = 0 % to 0.42 µm at x = 50 %. Simultaneously, the % quantitative of the vaterite phase was increased from 92.52 % at x = 0 % to 99.10 % at x = 50 %. In addition, the regular round shape of the vaterite particles was evidenced by SEM and TEM images. Generally, commercial CaCO3 which is a calcite polymorph with cubic form was used as an extender without reinforcing efficiency in rubber material. It is therefore challenging to incorporate the obtained round shape vaterite in natural rubber (NR) latex and it is interesting to find a stable vaterite CaCO3 polymorph in the NR, evidenced by XRD and FTIR results. The negative charges on the surface of NR particles were proposed to play an important role to stabilize the vaterite particles.

Synthesis of ZnO nanoparticles from electric arc furnace dust

This paper presents a hydrometallurgical treatment of electric arc furnace (EAF) dust taken from a Vietnamese steelmaking plant to obtain zinc oxide (ZnO) nanoparticles by using aqueous ammonium carbonate solution as a leaching agent. Characterization of the EAF dust was conducted by XRD technique, SEM observation, and manual wet chemical analysis. The results showed that total zinc (Zn) of the dust was 42.69 wt.% and existed mainly in the forms of zincite - ZnO, simonkolleite - Zn5(OH)8Cl2H2O, and franklinite - ZnFe2O4. The leached condition, in which the ammoniac carbonate concentration was 300 g/l and the time was 90 minutes, was found to provide the highest leaching efficiency of 85.29 % when the temperature was fixed at 60 oC and the ratio of solid/liquid was 1/6. After some steps of the subsequent treatment, the ZnO nanoparticles with the purity of 99.5 % and the size of 100 nm were obtained from thermal decomposition of zinc carbonate hydroxide - Zn5(CO3)2(OH)6.

Reversible pH Responsive Aggregation Behavior of Size-Controlled Calcium Carbonate Composite Nanoparticles by Phytic Acid in Aqueous Solution.

Composite colloidal nanoparticles were prepared by a carbonate controlled-addition method in the presence of phytic acid, in which an aqueous ammonium carbonate solution was added into an aqueous solution of phytic acid and CaCl2. The number-average particle size of the colloidal particles was 76 ± 18 nm formed by using the molar ratio [phytic acid]/[Ca2+] = 0.5 from the complexation time of 1 h. The composite nanoparticles were stable for more than 5 days in the suspension under the quiescent condition. After isolation of the nanoparticles by ultrafiltration, the dried samples could be redispersed in water. Effects of the complexation times of the aqueous solution of phytic acid and CaCl2 and the molar ratio ([phytic acid]/[Ca2+]) were studied. Increasing the concentration of the calcium reagents as well as increasing the complexation times increased the particle sizes. The minimum and maximum average particle sizes of 29 and 142 nm were obtained. The plot of the transmittance at 350 nm of the aqueous solution of the dispersion against pH values after addition of 0.05 M HCl for 6 h showed that, by gradually increasing turbidity with decreasing pH from 9.6 to 7.3, precipitates were recognized at below pH 7.5, and turbidity decreased with further decreasing pH beyond 7.2. Dynamic light scattering analysis showed that the particle diameters increased from 90 to 200 nm with decreasing pH from 9.6 to 7.2. When increasing the pH from 6.2, the precipitate was redispersed and the turbidity increased to a pH of 7.4. No precipitates were observed above a pH of 7.4. These results suggest that the present phytic acid stabilized nanoparticles exhibit pH-dependent reversible precipitation and redispersion without degradation under slightly acidic conditions.

Wolframite Conversion in Treating a Mixed Wolframite–Scheelite Concentrate by Sulfuric Acid

Complete wolframite conversion in sulfuric acid is significant for expanding the applicability of the sulfuric acid method for producing ammonium paratungstate. In this paper, the conversion of wolframite in treating a mixed wolframite–scheelite concentrate by sulfuric acid was studied systematically. The results show that the conversion of wolframite in sulfuric acid is more difficult than that of scheelite, requiring rigorous reaction conditions. A solid H2WO4 layer forms on the surfaces of the wolframite particles and becomes denser with increasing H2SO4 concentration, thus hindering the conversion. Furthermore, the difficulty in wolframite conversion can be mainly attributed to the accumulation of Fe2+ (and/or Mn2+) in the H2SO4 solution, which can be solved by reducing Fe2+ (and/or Mn2+) concentration through oxidization and/or a two-stage process. Additionally, the solid converted product of the mixed wolframite–scheelite concentrate has an excellent leachability of tungsten in an aqueous ammonium carbonate solution at ambient temperature, with approximately 99% WO3 recovery. This work presents a route for manufacturing ammonium paratungstate by treating the mixed concentrate in sulfuric acid followed by leaching in ammonium carbonate solution.

Scheelite conversion in sulfuric acid together with tungsten extraction by ammonium carbonate solution

Aiming to treat scheelite concentrate for producing ammonium paratungstate efficiently and cleanly, the conversion of scheelite to H2WO4 and CaSO4·nH2O in H2SO4 solution was firstly studied in this work. The results show that H2SO4 concentration, temperature, time, stirring speed, and particle size affect the conversion efficiency. Moreover, this work reveals that solid H2WO4 layer on the surface of CaWO4 particles forms and develops from thickness and looseness to thinness and denseness with increasing H2SO4 concentration, and thus hinders the conversion of CaWO4 to H2WO4, whereas CaSO4·nH2O almost does not deposit in the layer. Meanwhile, H2WO4 layer on CaWO4 surface is resulted by isopolytungstate ions diffusion-tungstic acid deposition in diffusion layer. Additionally, the performance of separating H2WO4 from CaSO4·nH2O by leaching the converted product with aqueous ammonium carbonate solution was examined, showing that the converted product has an excellent leachability of tungsten in aqueous ammonium carbonate solution at ambient temperature with WO3 leaching efficiency of about 99%. This work has the potential to develop a novel technique for tungsten extraction from scheelite concentrate under atmospheric pressure, bypassing the conversion of Na2WO4 to (NH4)2WO4.

Thermodynamic and XRD analysis of reaction behaviors of gangue minerals in roasting mixture of scheelite and calcium carbonate for Ca3WO6 preparation

The conversion of unleachable scheelite (CaWO4) to readily soluble Ca3WO6 in aqueous ammonium carbonate solution by roasting is crucial to the development of a green manufacturing technique for ammonium paratungstate. To better understand the influences of gangue minerals on the conversion of CaWO4 to Ca3WO6, the reaction behaviors of gangue minerals in the scheelite concentrate such as quartz (SiO2), apatite (Ca5(PO4)3F), cassiterite (SnO2), pyrite (FeS2), molybdenite (MoS2), and arsenopyrite (FeAsS) in the roasting process were investigated systematically in this work. Thermodynamic analyses and experimental results show that the gangue minerals except Ca5(PO4)3F can react with CaCO3 or Ca3WO6 to form corresponding calcium-containing compounds in roasting. There are Ca3Fe2WO9, CaMoO4, CaSO4, and Ca3(AsO4)2, etc. observed in the products when roasting in an oxidizing atmosphere, and Ca2FeWO6, CaS in a neutral or weakly reducing atmosphere, while the formations of Ca2SiO4, Ca4Si2O7F2, Ca5(PO4)3F, CaSnO3, and Ca2SnO4, etc. are independent of roasting atmosphere. The results suggest that these gangue minerals consume calcium and thus affect the conversion of CaWO4 to Ca3WO6 in the roasting process, which can help determine the appropriate composition dosage for the complete conversion of CaWO4 to Ca3WO6.

Ca3 − x(Fe, Mn)xWO6 (0 < x ≤ 1) prepared from tungsten-containing materials and its leachability in aqueous ammonium carbonate solution

The conversion of tungsten-containing materials to a readily soluble substance in ammoniacal solution is significant in the development of a cleaning process for manufacturing ammonium paratungstate. In this work, Ca3−x(Fe, Mn)xWO6 (0<x≤1) was prepared by roasting a mixture of tungsten-containing materials and calcium carbonate. The leachability of the roasted products in aqueous ammonium carbonate solution was then tested. Thermodynamic analyses and experimental results showed that Ca2FeWO6 and Ca2MnWO6 can be obtained by roasting the mixture with appropriate ingredients in neutral or weakly reducing atmosphere, and Fe(II) in Ca2FeWO6 can be substituted by Ca to form Ca3−xFexWO6 (0<x<1) with an excess of calcium carbonate. With increased roasting temperature and carbon addition, Fe3W3C and Mn3W3C can be generated. Additionally, leaching results showed that Ca3−x(Fe, Mn)xWO6 had excellent leachability in aqueous ammonium carbonate solution with 99% WO3 recovery. The results presented can be used to exploit a novel technique with recycling solutions for ammonium paratungstate production.

Preparation and Characterization of Transitional Alumina Obtained through Ammonia Treatment

In this study, different aluminas were obtained by precipitating Al(NO3 )3·9H2O with different concentration of aqueous solution of ammonium carbonate. The obtained aluminas were treated by 50 (vol/vol) % ammonia via low temperature immersing and high temperature hydrothermal treatment, respectively, then, the treated aluminas were calcined again. The crystal types, morphology, textural properties, and pore distribution of the original alumina, ammonia‐treated alumina, and the second calcined alumina were studied by characterizations of X‐ray diffraction, thermogravimetric analyses, nuclear magnetic resonance, Brunauer‐Emmett‐Teller (BET), transmission electron microscopy, and so on. Several modified aluminas with specific morphology, desired pore structure, and pure crystal types were obtained, which can be used in some specific industrial application.

Ca3WO6 prepared by roasting tungsten-containing materials and its leaching performance

Aiming to develop a novel technique to alleviate the environmental stresses caused by waste-water in the prevalent ammonium paratungstate manufacture process, preparation process of tricalcium tungstate (Ca3WO6) from tungsten-containing materials by roasting was studied systematically in this paper. Thermodynamic analyses and experimental results show that Ca3WO6 could be formed by reactions of CaWO4/Fe(Mn)WO4 with CaO, Ca(OH)2 or CaCO3 in air. Increasing roasting temperature not only accelerates the conversion of CaWO4 to Ca3WO6 but also eliminates the dependence of the conversion on calcium compound types. Moreover, additive CaF2 can greatly reduce roasting temperature for complete conversion of tungsten-containing minerals in mixed concentrate of scheelite and wolframite to Ca3WO6. Additionally, Ca3WO6 clinker prepared by mixed concentrate has good leachability in aqueous ammonium carbonate solution with WO3 recovery of 98.4%. The work presented is favorable for developing a promising technique with recycling both auxiliary materials and solutions for cleaner production of ammonium paratungstate.

Size-Controlled Vaterite Composite Particles with a POSS-Core Dendrimer for the Fabrication of Calcite Thin Films by Phase Transition

Vaterite composite particles with a size-controlled sphere were obtained by a carbonate controlled-addition method by using a carboxylate-terminated poly(amidoamine) (PAMAM)-type polyhedral oligomeric silsesquioxane (POSS)-core dendrimer. An aqueous ammonium carbonate solution was added to an aqueous solution of the dendrimer and CaCl2 at different times (3 min, 30 min, and 1 h) and stirred for 1 h at 30 °C. When the complexation time of the POSS-core dendrimer-CaCl2 solution was increased from 3 min to 1 h, the average particle sizes of the spheres increased from 0.71 ± 0.08 to 1.86 ± 0.22 μm, respectively. However, the average particle sizes decreased with decreasing temperature. Particles with minimum sizes of 70 ± 6 nm were obtained when COONa to calcium ion molar ratio was 16 and the complexation time was 3 min at 20 °C. Incubation of the vaterite composite particles in distilled water for 3 days led to complete phase transition to calcite. Negative zeta potential values, ranging from -30 to -10 mV, were detected for the vaterite particles, indicating that the POSS-core dendrimers were exposed on the CaCO3 particles. The CaCO3 particle surfaces were successfully coated with poly(diallyldimethylammonium chloride) (PDDA) in aqueous dispersions by adding a controlled concentration of the polymer. Alternate vaterite composite particles and polyelectroyte multilayer films were prepared by a layer-by-layer method. The obtained (PDDA/vaterite)10(PDDA) multilayer films were incubated in distilled water at 30 °C. Incubation for 5 days led to complete phase transition to calcite, as estimated by Fourier transform infrared (FTIR) spectroscopic and XRD analyses. The SEM observation of the sample after 5 days of incubation showed a granular network structure of irregularly shaped calcite particles. Although some patches and pores were present in the films, the SEM image clearly demonstrated that large-area and continuous CaCO3 films were formed.

A rapid and green synthetic approach for hierarchically assembled porous ZnO nanoflakes with enhanced catalytic activity

Three dimensionally (3D) assembled hierarchical porous ZnO structures are of key importance for their applications in sensors, lithium-ion batteries, solar cells and in catalysis. Here, the controlled synthesis of 3D hierarchically porous ZnO architectures constructed of two dimensional (2D) nano-sheets through the calcination of a hydrozincite [Zn5(CO3)2(OH)6] intermediate is presented. The intermediate 3D hierarchical hydrozincite has been synthesized by a novel organic surfactant and solvent free aqueous protocol at room temperature using an aqueous solution of ammonium carbonate and laboratory grade bulk ZnO in a short time (20–30 min). The amount of carbonate and the reaction temperature play a crucial role in the formation of the 3D hierarchical morphology and on the basis of the experimental results a probable reaction mechanism is proposed. On calcination, the synthesized 3D hierarchical hydrozincite resulted in ZnO with an almost identical morphology to the parental hydrozincite. On decomposition a porous structure having a surface area of 44 m2 g−1 is obtained. The synthesized hierarchical ZnO morphology exhibits an improved catalytic activity for the synthesis of 5-substituted-1H-tetrazoles with different nitriles and sodium azide than that of nanocrystalline ZnO and bulk ZnO, as well as other developed solid catalysts. The catalyst is easily recyclable without a significant loss in catalytic activity.

A carbonate controlled-addition method for size-controlled calcium carbonate spheres by carboxylic acid-terminated poly(amidoamine) dendrimers

Size-controlled calcium carbonate particles were obtained using a ‘carbonate controlled-addition method’ with G0.5 poly(amidoamine) (PAMAM) dendrimer with carboxylate groups at the external surface. An aqueous ammonium carbonate solution was added to an aqueous solution of the dendrimer and CaCl2 at different time periods (3 min, 1 h or 24 h) and was stirred for 1 day. Both crystal phases obtained at incubation times of 1 and 24 h were vaterite. The dendrimer–CaCl2 solution incubated for 3 min produced vaterite particles that coexisted with calcite. The average particle size of the spheres decreased from 2.2±0.2 to 0.61±0.24 μm with an increase in the incubation time of the dendrimer–CaCl2 solution. When the products were kept in the reaction mixtures for 3 days, the CaCO3 phase of the precipitates obtained after incubating the dendrimer–CaCl2 solution for 3 min and 1 h was calcite. However, the product obtained after incubating for 24 h was vaterite. The present results demonstrate that the interaction and the reaction kinetics of the dendrimer–Ca2+ complex have an important role in the mineralization and stabilization of CaCO3 particles. Vaterite particles were obtained by a ‘carbonate controlled-addition method’ by G0.5 poly(amidoamine) (PAMAM) dendrimer with carboxylate groups at the external surface. The average particle sizes of the spheres decreased from 2.2±0.2 to 0.61±0.24 μm and the stability of the spheres increased with an increase in the incubation time of the G0.5–CaCl2 solution from 3 min to 24 h. The interaction and reaction kinetics of the dendrimer–Ca2+ complex have an important role in the mineralization of CaCO3.

Heat of absorption of CO 2 in aqueous ammonia and ammonium carbonate/carbamate solutions

A reaction calorimeter was used to determine the enthalpies of absorption of CO 2 in aqueous ammonia and in aqueous solutions of ammonium carbonate at temperatures of 35–80 °C. The heat of absorption of CO 2 with 2.5 wt% aqueous ammonia solution was found to be about 70 kJ/mol CO 2, which is lower than that with MEA (around 85 kJ/mol) at 35 and 40 °C. The value decreases with increased loading, but not to as low a value as expected by the carbonate–bicarbonate reaction (26.88 kJ/mol). The enthalpy of absorption of CO 2 in aqueous ammonia at 60 and 80 °C decreases with loadings at first, then increases between 0.2 mol CO 2/mol NH 3 and 0.6 mol CO 2/mol NH 3, and then decreases again. The behavior of the heat of absorption of CO 2 in 10 wt% ammonium carbonate solution was found to be the same as that of aqueous ammonia at loadings above 0.6 mol CO 2/mol NH 3. The heat of absorption increases with increasing temperature. The heats of absorption are directly related to the extent of the various reactions with CO 2 and can be assessed from the species variation in the liquid phase.

A Carbonate Controlled-Addition Method for Amorphous Calcium Carbonate Spheres Stabilized by Poly(acrylic acid)s

Stable amorphous calcium carbonate (ACC) composite particle with a size-controlled monodispersed sphere was obtained by a new simple carbonate controlled-addition method by using poly(acrylic acid) (PAA) (Mw = 5000), in which an aqueous ammonium carbonate solution was added into an aqueous solution of PAA and CaCl2 with a different time period. The obtained ACC composite products consist of about 50 wt % of ACC, 30 wt % of PAA, and H2O. Average particle sizes of the ACC spheres increased from (1.8 +/- 0.4) x 102 to (5.5 +/- 1.2) x 102 nm with an increase of the complexation time of the PAA-CaCl2 solution from 3 min to 24 h, respectively. The ACC formed from the complexation time for 3 min was stable for 10 days with gentle stirring as well as 3 months under a quiescent condition in the aqueous solution. Moreover, the ACC was also stable at 400 degrees C. Stability of the amorphous phase decreased with an increase of the complexation time of the PAA-CaCl2 solution. No ACC was obtained when the lower molar mass PAAs (Mw = 1200 and 2100) were used. In the higher molar mass case (Mw = 25 000), a mixture of the amorphous phase and vaterite and calcite crystalline product was produced. The present results demonstrate that the interaction and the reaction kinetics of the PAA-Ca2+-H2O complex play an important role in the mineralization of CaCO3.

Synthesis and characterization of mesoporous ceria/alumina nanocomposite materials via mixing of the corresponding ceria and alumina gel precursors

Mesoporous ceria/alumina, CeO 2/Al 2O 3, composites containing 10, 20 and 30% (w/w) ceria were prepared by a novel gel mixing method. In the method, ceria gel (formed via hydrolysis of ammonium cerium(IV) nitrate by aqueous ammonium carbonate solution) and alumina gel (formed via controlled hydrolysis of aluminum tri-isopropoxide) were mixed together. The mixed gel was subjected to subsequent drying and calcination for 3 h at 400, 600, 800 and 1000 °C. The uncalcined (dried at 110 °C) and the calcined composites were investigated by different techniques including TGA, DSC, FTIR, XRD, SEM and nitrogen adsorption/desorption isotherms. Results indicated that composites calcined for 3 h at ⩽800 °C mainly kept amorphous alumina structure and γ-alumina formed only upon calcinations at 1000 °C. On the other hand, CeO 2 was found to crystallize in the common ceria, cerinite, phase and it kept this structure over the entire calcination range (400–1000 °C). Therefore, high surface areas, stable surface textures, and non-aggregated nano-sized ceria dispersions were obtained. A systematic texture change based on ceria ratio was observed, however in all cases mesoporous composite materials exposing thermally stable texture and structure were obtained. The presented method produces composite ceria/alumina materials that suit different applications in the field of catalysis and membranes technology, and throw some light on physicochemical factors that determine textural morphology and thermal stability of such important composite.

Analysis of raw materials, intermediates and subsidiary colours in Food Yellow No. 5 (Sunset Yellow FCF) by LC/MS

Raw materials, intermediates and subsidiary colours in Food Yellow No. 5 (Sunset Yellow FCF) were determined using liquid chromatography/mass spectrometry (LC/MS) with electrospray ionization. A gradient consisting of acetonitrile and 0.04% aqueous ammonium carbonate solution was used for the HPL C mobile phase. Quasi-molecular ions of impurities were used as monitor ions. It was necessary to use fragment ions of the sodium salts of 6-hydroxy-5-phenylazo-2-naphthalenesulphonic acid (SS-AN) and 4-(2- hydroxy-1- naphthylazo) benzenesulphonic acid (2N-SA) as monitor ions because the compounds are not resolved by chromatography and have the same molecular weight. Fifteen samples of commercial Sunset Yellow FCF were examined. The results obtained by UV-Vis spectroscopy were in good agreement with the results of LC/MS analyses. The detection limits of the impurities in Sunset Yellow FCF ranged from 0.01 to 0.1%.

XPS Analysis of Carbon Fiber Surfaces—Anodized and Interfacial Effects in Fiber–Epoxy Composites

High strength carbon fibers were electrochemically treated in an aqueous ammonium carbonate solution, with increasing electric current density, using an original continuous treatment process. The electrochemical treatment induced a modification of the surface properties, i.e., surface functional groups as observed by XPS. As a result, the O1s/C1s and the N1s/C1s ratios of the fiber surfaces increased with the increase of current intensity of the electrochemical treatment in the interval of about 30–50 A m−2. However, no significant change in the surface functional activity characters was observed for strong treatments. Hence, a moderate treatment (30 A m−2) was sufficient to obtain optimum (O1s + N1s)/C1s ratios in this system. This treatment is possibly suitable for carbon fibers to be incorporated in a polar organic matrix, resulting in increasing the interlaminar shear strength (ILSS) of the resulting composites.

Technetium(VII) extraction by a primary amine and technetium(VII) coprecipitation with ammonium diuranate in hydrofluoric acid solution

The separation of technetium(VII) from uranium(VI) has beeen studied through experiments on the coprecipitation of Tc(VII) with ammonium diuranate precipitate, and in the extraction of Tc(VII) from an aqueous hydrofluoric acid solution using a primary amine (Primene JMT) as an extractant dissolved inn-heptane. The extraction of Tc(VII) reached a quantitative level after several repetitions of the extraction procedure. Also, the stripping of Tc(VII) into 3M aqueous solution of ammonium carbonate was enhanced to a level over 99% by repeating the stripping cycles.

Extraction of technetium(VII) from uranium(VI) in nitric acid system by primary amine — n-heptane solution

Separation of technetium(VII) from uranium(VI) has been studied through experiments on the coprecipitation of technetium(VII) with precipitation of ammonium diuranate, and on the extraction of technetium(VII) from a 3M aqueous nitric acid solution using, as extractant, a primary amine (Primene JMT) dissolved in either chloroform or n-heptane solution. Ammonium diuranate precipitation proved to provide the most satisfactory means of separating technetium(VII) from uranium(VI) in solution. Extraction of technetium(VII) contained in nitric acid solution using Primene JMT dissolved in n-heptane solution proved to be quantitative after several cycles of the procedure and alternatively, upon raising to 5∶1 the volume ratio between the organic phase containing the extractant and the aqueous phase containing technetium(VII). Stripping of technetium(VII) into 2M aqueous ammonium carbonate solution was enhanced to quantitative level by repetition of the stripping procedure, and alternatively, by adding the ammonium carbonate in a volume ratio of 5∶1 with respect to the organic phase containing technetium(VII).