Aqueous Ca Research Articles

Removal of Phosphate by Ivory Coast Shale in a Homogeneous Reactor and Under Hydrodynamic Conditions: Influence of Soluble Species

AbstractDeveloping low cost and effective phosphate adsorbents is crucial to prevent eutrophication of natural waters. Here, phosphate removal by a natural and abundant shale from the Ivory Coast was investigated in both batch and column experiments with special attention devoted to understand the adsorption process. Batch experiments were carried out to assess the influence of initial phosphate concentration, sorbent dosage, contact time, and pH on phosphate removal. The phosphate removal efficiency increased with increased shale dosage while phosphate uptake decreased. Aqueous Ca, Mg, Al, and Fe species concentrations decreased in the presence of phosphate. Additionally, phosphate uptake strongly decreased with pH increases in the range 2–11, but then increased at pH 12. The kinetics were well described using a pseudo-second order model, and Langmuir adsorption isotherms were used for the equilibrium surface reactions. Adsorption to nanoparticles of goethite was hypothesized to be the major phosphate removal mechanism in the pH range 4–10. Column experiments with a flow rate of 1 mL min−1 and an initial phosphate concentration of 25 mg L−1 showed a breakthrough point at a V/Vp value of ~17, where Vis the volume of phosphate solution added to the column and Vp is the pore volume. A V/Vp value of ~17 corresponded to a phosphate uptake of 0.17 mg/g, which was in agreement with the batch experiments. Column experiments revealed a strong correlation between the aqueous concentrations of Ca, Mg, Al, and Fe species and phosphate removal and, thus, suggest that phosphate removal by the shale occurred by aqueous dissolution/precipitation.

Leaching behaviour of co-disposed steel making wastes: Effects of aeration on leachate chemistry and vanadium mobilisation

Steelmaking wastes stored in landfill, such as slag and spent refractory liners, are often enriched in toxic trace metals (including V). These may become mobile in highly alkaline leachate generated during weathering. Fresh steelmaking waste was characterised using XRD, XRF, and SEM-EDX. Batch leaching tests were performed under aerated, air-excluded and acidified conditions to determine the impact of atmospheric CO2 and acid addition on leachate chemistry. Phases commonly associated with slag including dicalcium silicate, dicalcium aluminoferrite, a wüstite-like solid solution and free lime were identified, as well as a second group of phases including periclase, corundum and graphite which are representative of refractory liners. During air-excluded leaching, dissolution of free lime and dicalcium silicate results in a high pH, high Ca leachate in which the V concentration is low due to the constraint imposed by Ca3(VO4)2 solubility limits. Under aerated conditions, carbonation lowers the leachate pH and provides a sink for aqueous Ca, allowing higher concentrations of V to accumulate. Below pH 10, leachate is dominated by periclase dissolution and secondary phases including monohydrocalcite and dolomite are precipitated. Storage of waste under saturated conditions that exclude atmospheric CO2 would therefore provide the optimal environment to minimise V leaching during weathering.

Uranium isotope fractionation by abiotic reductive precipitation

Significant uranium (U) isotope fractionation has been observed during abiotic reduction of aqueous U, counter to the expectation that uranium isotopes are only fractionated by bioassociated enzymatic reduction. In our experiments, aqueous U is removed from solution by reductive precipitation onto the surfaces of synthetic iron monosulfide. The magnitude of uranium isotopic fractionation increases with decreasing aqueous U removal rate and with increasing amounts of neutrally charged aqueous Ca-U-CO3 species. Our discovery means that abiotic U isotope fractionation likely occurs in any reducing environment with aqueous Ca ≥ 1 mM, and that the magnitude of isotopic fractionation changes in response to changes in aqueous major ion concentrations that affect U speciation. Our results have implications for the study of anoxia in the ancient oceans and other environments.

Thermodynamic description of the plutonium – α–d–isosaccharinic acid system ii: Formation of quaternary Ca(II)–Pu(IV)–OH–ISA complexes

The quaternary system Ca(II)–Pu(III/IV)–OH–ISA was investigated in a series of solubility experiments where equilibrium conditions were reached from undersaturation conditions with PuO2(ncr,hyd) at T = (22 ± 2) °C under Ar atmosphere. Experiments were performed in 0.1 m NaCl–NaOH–NaISA–CaCl2 solutions at 8 ≤ pHm ≤ 12.5 (pHm = –log [H+], in molal units), 10−5 m ≤ m(ISA)tot ≤ 10−2 m and 10−3.5 m ≤ m(Ca)tot ≤ 0.02 m. Reducing conditions were adjusted and buffered with hydroquinone (HQ) or Sn(II), which allowed us to work in the (pe + pHm) region ≈ 9 and ≈ 1.5, respectively.Solid phase characterization (in-situ XRD, XANES and EXAFS) and analogy with the ternary system Pu–OH–ISA previously studied by our group indicate that PuO2(ncr,hyd) remains unaltered in the course of the solubility experiments at pHm ≤ 12 and controls the solubility of Pu under reducing conditions in the presence of ISA and Ca(II). In HQ-systems, the impact of ISA on the solubility of PuO2(ncr,hyd) is clearly enhanced compared to Ca(II)-free solutions of analogous composition, thus indicating the formation of quaternary complexes of the type Ca(II)–Pu(IV)–OH–ISA in the aqueous phase. The combination of slope analysis of the solubility data and DFT calculations support the predominance of the two aqueous quaternary complexes Ca(II)Pu(IV)(OH)3ISA–H+ and Ca(II)Pu(IV)(OH)3ISA–2H(aq) below and above pHm ≈ 11, respectively. The same speciation scheme explains properly the solubility of Pu in Sn(II)-buffered systems at pHm > 11. Below this pHm, solubility data under these very reducing conditions suggest the possible formation of ternary Pu(III)–OH–ISA aqueous complexes, although the scatter of the data does not allow a definitive conclusion to be drawn. The presence of Ca(II) in solution destabilizes Pu–ISA colloids, which significantly enhance Pu solubility in comparable, Ca-free systems. Based on these experimental and theoretical results, a thermodynamic model for the system Ca2+–Pu4+–OH––Cl––ISA––H2O(l) is derived.This study provides quantitative tools to evaluate the solubility behavior of Pu in reducing cementitious environments containing ISA, as expected in underground repositories for low- and intermediate-level radioactive waste (L/ILW) due to the degradation of cellulosic materials.

Adsorption Performance of SiO2/CPAM Composites for Aqueous Ca(II)

Silica/cationic polyacrylamide (SiO2/CPAM) composites with a dendritic structure were prepared via in situ polymerization based on silica containing vinyl groups and acrylamide monomers. The structure and surface properties of the composites were revealed with scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier-transformed infrared spectroscopy (FT-IR) and X-ray photoelectron spectroscopy (XPS). The adsorption behavior and properties of aqueous Ca(II) on the SiO2/CPAM composites were also investigated. The effect of the pH value, the initial Ca(II) concentration, adsorption time, and temperature on adsorption properties were examined. The results showed that the SiO2/CPAM composites displayed a high adsorption performance for aqueous Ca(II). The maximum adsorption capacity of the SiO2/CPAM composites for Ca(II) was 123.4 mg•g-1 at room temperature and pH 9. The adsorption behavior was in agreement with the Langmuir isotherm model. The adsorption was an endothermic and spontaneous process. Adsorption kinetics fitted well with the pseudo-second-order model. The adsorption of Ca(II) on the SiO2/CPAM composites was mainly attributed to chemical interaction, and chelation was more significant than electrostatic interaction.

Apparent molar volumes, Vф, of calcium acetate (Ca(Ch3COO)2(aq)) at 273.15 to 353.15 K and pressures up to 100 MPa

Pressure, density and temperature (p, ?, T) data and apparent molar volumes, V?o, of aqueous calcium acetate solutions Ca(CH3COO)2(aq) over a wide range of temperatures from 273.15 to 353.15 K, pressures up to p = 100 MPa and molalities m, of 0.04918, 0.09367, 0.23797, 0.36365, 0.85923, 1.06930, 1.35223 and 1.81668 mol?kg-1 of Ca(CH3COO)2 are reported. The combined expanded uncertainty of the density (?) measurements at the 95 % confidence level with a coverage factor of k = 2 was estimated to be Uc(?) = ?0.3 kg?m?3. The measurements were realized with an Anton Paar DMA HPM vibration tube density meter. The system was calibrated using double-distilled water, aqueous NaCl solutions, methanol, toluene and acetone. An equation of state for fitting of the (p, ?, T) data of aqueous calcium acetate was developed as a function of pressure, temperature and molality. After a thorough analysis of literature values and validity of the constructed equation of state, various thermophysical properties, such as isothermal compressibility, isobaric thermal expansibility, differences in isobaric and isochoric heat capacities, thermal pressure coefficient and internal pressure at the investigated state parameter intervals were calculated.

Effects of interaction between montmorillonite and Sphingomonas sp. GY2B on the physical and chemical properties of montmorillonite in the clay-modulated biodegradation of phenanthrene

Environmental contextInteractions between microbes and minerals can influence geochemical reactions, and hence are of fundamental importance in natural environmental processes. We investigate the effects of Sphingomonas sp. on the structure and physicochemical properties of montmorillonite, a common clay mineral, and determine how this interaction influences the biodegradation of phenanthrene. The findings have profound impact on the clay-modulated biodegradation of organic compounds in the environment. AbstractWe investigate the effect of Sphingomonas sp. GY2B on the structure and physicochemical properties of montmorillonite (Mt). The simultaneous biodegradation of a polycyclic aromatic hydrocarbon compound, phenanthrene, was also monitored. After interaction with bacteria for 2 days, the increases of the specific surface area (SSA) and micropore volume, differences of the thermogravimetric analysis and differential scanning calorimetry (TGA-DSC) patterns and the morphological changes revealed modification of the physicochemical properties and mineral surface. Although the interlayer spacing of Mt remained unchanged, the appearance and shift of several vibration peaks in the Fourier transform infrared (FTIR) spectra confirmed the structural changes of Mt arising from bacterial activities. Concentrations of the major elements of montmorillonite changed greatly in the aqueous solution, especially Si, Al, Fe and Ca. Based on the analyses of X-ray diffraction (XRD) and FTIR, these changes were mainly ascribed to the formation of precipitates and minerals in the biotic experiment. Changes in the release rate of different elements also substantiated that the GY2B strain has a considerable impact on the dissolution of montmorillonite. Additionally, a preferential release of Si and the 27Al and 29Si cross-polarisation magic-angle spinning nuclear magnetic resonance (CP/MAS NMR) spectra of bacteria-untreated samples demonstrated that tetrahedral sheets were preferentially destroyed and octahedral sheets in montmorillonite were dissolved. These results showed that microorganisms can greatly affect the physical and chemical properties of clay minerals in the clay-modulated biodegradation of hydrophobic organic contaminants. This study provides valuable insight into the clay-modulated microbial remediation of organic pollutants in the environment.

Effect and mechanism of phosphoric acid in the apatite/dolomite flotation system

To elucidate how phosphoric acid (H3PO4) as a depressant achieves selective separation of apatite and dolomite, the flotation response of these minerals was investigated using both single and mixed mineral flotation. Microflotation results demonstrated that H3PO4 exhibits a selective depressive effect on apatite. Flotation kinetics analyses also revealed that the presence of H3PO4 increases the dolomite/apatite selectivity index significantly. The adsorption mechanisms were examined using zeta potential tests, X-ray photoelectron spectroscopy, solution chemistry analysis, and thermodynamic analysis. H2PO4− was found to be the pivotal ion for depressing apatite under slightly acidic conditions (pH=5.0–6.0), where the separation of these minerals most effective. H2PO4− reacts with free Ca2+ to depress the acidolysis of apatite and promote the formation of aqueous CaHPO4. H3PO4 chemisorbs onto apatite surface by the formation of aqueous CaHPO4 and Ca(H2PO4)2, with the former being the major species to depress apatite. Moreover, dissolution of Mg2+ and Ca2+ from the dolomite surface is thermodynamically more favorable than that of Ca2+ from the apatite surface. As Mg(H2PO4)2 is soluble, H3PO4 only exhibits a weak depressive effect on dolomite. Further, the collector (sodium oleate) maintains excellent dolomite floatability in the presence of H3PO4, because chemisorption of the collector on the dolomite surface is enhanced by reaction with abundant Mg2+. Therefore, H3PO4 selectively depresses apatite in the apatite/dolomite flotation system.

Control of temperature and aqueous Mg2+/Ca2+ ratio on the (trans-)formation of ikaite

The calcium carbonate hexahydrate mineral ikaite (CaCO3⋅6 H2O) has been documented in aquatic environments at near-freezing temperatures. An increase of the prevailing temperature in the depositional environment, results in the transformation of natural ikaite into less soluble calcium carbonate phases occasionally leaving calcite pseudomorphs in the sediments, which are considered asan indicator for primary cold water temperatures. Detailed understanding on the physicochemical parameters controlling ikaite (trans-)formation however, such as temperature and reactive solution chemical composition, are still under debate. In order to study the formation of ikaite, we conducted precipitation experiments under controlled physicochemical conditions (pH = 8.3±0.1; T=6, 12, and 18±0.1°C) at defined aqueous molar Mg/Ca ratios. The transformation of ikaite into anhydrous calcium carbonate polymorphs was investigated in solution and at air exposure. The obtained results reveal the formation of ikaite at temperatures up to 12°C, whereas Mg-rich amorphous calcium carbonate precipitated at 18°C. In contact with the reactive solution ikaite transformed into aragonite at aqueous molar Mg2+/Ca2+ ratios of ≥14. In contrast, ikaite separated from the Mg-rich solution and exposed to air transformed in all cases into calcite/vaterite. The herein obtained temperature limit of ≤12 for ikaite formation is significantly higher than formerly expected and most probably caused by (i) the high saturation degree of the solution with respect to ikaite and (ii) the slow dehydration of the aqueous Ca2+ ion at low temperatures. This result questions the suitability of calcite pseudomorphs (i.e. glendonites) as a proxy for near-freezing temperatures. Moreover, our findings show that the CaCO3 polymorph formed from ikaite is strongly controlled by the physicochemical conditions, such as aqueous molar Mg2+/Ca2+ ratio of the reactive fluid and H2O availability throughout the transformation process.

Solution chemistry of cubic and orthorhombic tricalcium aluminate hydration

This paper presents a solution chemistry-focused analysis of orthorhombic and cubic tricalcium aluminate (orth-C3A and cub-C3A, respectively) hydration. It is shown that the different solubilities of cub- and orth-C3A influence the bulk aqueous Ca to Al concentration ratio and the C3A/solution interface chemistry. The results are consistent with the bulk solution chemistry controlling orth-C3A dissolution, and with cub-C3A dissolution controlled by the formation of an Al-rich leached layer and adsorption of Ca‑sulfur ion pair complexes onto this layer. The polynaphthalene sulfonate-based admixture used here is identified to modify the solution chemistry and retard cub-C3A dissolution. Strategies to inhibit C3A dissolution in Portland cement are discussed.

Mechanism of Vanadium Leaching during Surface Weathering of Basic Oxygen Furnace Steel Slag Blocks: A Microfocus X-ray Absorption Spectroscopy and Electron Microscopy Study.

Basic oxygen furnace (BOF) steelmaking slag is enriched in potentially toxic V which may become mobilized in high pH leachate during weathering. BOF slag was weathered under aerated and air-excluded conditions for 6 months prior to SEM/EDS and μXANES analysis to determine V host phases and speciation in both primary and secondary phases. Leached blocks show development of an altered region in which free lime and dicalcium silicate phases were absent and Ca-Si-H was precipitated (CaCO3 was also present under aerated conditions). μXANES analyses show that V was released to solution as V(V) during dicalcium silicate dissolution and some V was incorporated into neo-formed Ca-Si-H. Higher V concentrations were observed in leachate under aerated conditions than in the air-excluded leaching experiment. Aqueous V concentrations were controlled by Ca3(VO4)2 solubility, which demonstrate an inverse relationship between Ca and V concentrations. Under air-excluded conditions Ca concentrations were controlled by dicalcium silicate dissolution and Ca-Si-H precipitation, leading to relatively high Ca and correspondingly low V concentrations. Formation of CaCO3 under aerated conditions provided a sink for aqueous Ca, allowing higher V concentrations limited by kinetic dissolution rates of dicalcium silicate. Thus, V release may be slowed by the precipitation of secondary phases in the altered region, improving the prospects for slag reuse.

Calcium decline reduces population growth rates of zooplankton in field mesocosms

Regional calcium (Ca) decline, a legacy of acid deposition and logging, is a potential threat to aquatic organisms. Lake surveys and laboratory studies indicate that Ca-rich daphniids are likely most susceptible, allowing for competitive release of other taxa with low Ca demand. Indeed, dramatic shifts in zooplankton community structure have been documented in lakes where Ca has declined, amid multiple other stressors. Given the perceived threat of this large-scale stressor, manipulative studies are needed to evaluate causal relationships between Ca decline and zooplankton community structure. We analysed per capita growth rates of zooplankton from three independent mesocosm experiments where we manipulated aqueous Ca concentrations to reflect current and future Ca concentrations. In two experiments where Ca concentration was reduced to 0.6 or 0.9 mg/L, we observed reduced growth rates for several taxa, including daphniids, bosminids, and copepods. No effect of Ca was detected in the experiment where Ca concentrations ranged from 1.2 to 2.5 mg/L, a gradient representing 68% of lakes in south-central Ontario. These results suggest that future Ca decline in soft-water Canadian Shield lakes may be accompanied by shifts in community structure and overall declines in zooplankton production.

Effect of replacing maize grain and soybean meal with a xylose-treated wheat grain on feed intake and performance of dairy cows

ABSTRACTThis study evaluated wheat grain which was treated with xylose in aqueous Ca–Mg lignosulphonate solution at elevated temperatures (WeiPass®) in order to reduce ruminal degradation of starch and crude protein. The two tested isoenergetic and isonitrogenous diets contained on dry matter (DM) basis either 16% maize grain and 6.4% soybean meal (Diet CON) or 17.8% xylose-treated wheat and 4.6% soybean meal (Diet Wheat). Thirty-six German Holstein dairy cows were assigned to one of the two groups according to parity, body weight after calving, and milk yield during the previous lactation. Data collection started at 21 d before the expected calving date until 120 d in milk. The average of DM intake, energy-corrected milk (ECM) yield, and milk fat and protein yields (all given as kg/d) were 18.9, 28.7, 1.25, and 1.02 for Diet CON and 19.3, 32.5, 1.36, and 1.11 for Diet Wheat, respectively. Only ECM and milk protein yields were greater (p < 0.05) for cows receiving Diet Wheat. In conclusion, the xylose-treated wheat grain can replace maize grain and part of soybean meal in diets for lactating dairy cows and may be an alternative feedstuff depending on overall ration composition and availability and costs of grain sources.

Solute pools in Nikanotee Fen watershed in the Athabasca oil sands region

Overburden and tailings materials from oil sands production were used as construction materials as part of a novel attempt to create a self-sustaining, peat accumulating fen-upland ecosystem. To evaluate the potential for elemental release from the construction materials, total elemental concentrations in the tailings sand, petroleum coke and peat used to construct a fen ecosystem were determined using microwave-assisted acid digestions and compared to a leaching experiment conducted under environmentally-relevant conditions. A comparison of solid phase to aqueous Na, Ca, S and Mg concentrations showed they were highly leachable in the materials. Given that the concentrations of these elements can affect plant community structure, it is important to understand their leachability and mobility as they migrate between materials used to construct the system. To that end, a mass balance of aqueous Na, Ca, S and Mg was conducted based on leaching experiments and materials analysis coupled with existing data from the constructed system. The data indicate that there is a large pool of leachable Na, Ca, S and Mg in the system, estimated at 27 t of Na, 14 t of Ca, 37.3 t of S and 8.8 t of Mg. Since recharge mainly drives the fen-upland system water regime, and discharge in the fen, evapo-accumulation of these solutes on the surface may occur.

84.Ca(OH)_2水溶液による石炭脱灰時の化学反応

84.Ca(OH)_2水溶液による石炭脱灰時の化学反応

Aqueous Date Fruit Extract can’t Ameliorate β-amyloid Induced Memory Impairments in Male Rats

Aqueous Date Fruit Extract can’t Ameliorate β-amyloid Induced Memory Impairments in Male Rats

Thermodynamic model of aqueous Mg2+ – Na+ – K+ – Cl− quaternary system

We present a thermodynamic model for the aqueous Mg2+ – Na+ – K+ – Cl− quaternary system based on symmetric electrolyte Non-Random Two Liquid (eNRTL) theory. This work is a continuation of our previous study on the aqueous Ca2+ – Na+ – K+ – Cl− quaternary system and part of a larger effort to develop a comprehensive engineering thermodynamic model for high salinity produced water in oil and gas production. The eNRTL theory requires two binary interaction parameters for each molecule-molecule, molecule-electrolyte, and electrolyte-electrolyte pair to correlate composition dependence of the solution nonideality. The binary interaction parameters, including their temperature coefficients, are identified for the (Mg2+-Cl−):H2O pair, (Mg2+-Cl−):(K+-Cl−) pair, and (Mg2+-Cl−):(Na+-Cl−) pair using available thermodynamic data. The binary parameters for the other pairs are taken directly from the literature. Together, the eNRTL model and the binary parameters yield a satisfactory thermodynamic model for the quaternary system and its subsystems with temperatures ranging from 273.15 to 473.15 K and salt concentrations up to saturation.

Effect of ferrous iron on the nucleation and growth of CaCO3in slightly basic aqueous solutions

The precipitation of calcium carbonate, CaCO3 and the growth of calcite has been studied in aqueous solutions containing ferrous iron (Fe2+). Two different types of bulk experiments have been carried out: nucleation experiments at constant pH, following the procedure developed by Gebauer et al. (2008), revealed the stabilisation of aragonite induced by the presence of the foreign ions at the expense of calcite and vaterite. Growth experiments, using the constant composition method (Tomson and Nancollas, 1978), clearly showed that calcite growth is inhibited by the presence of Fe2+ and the characterisation of the re-grown calcite crystals by HR-TEM confirmed the predictions obtained with molecular dynamics simulations. Additionally, in situ atomic force microscopy (AFM) flow-through growth experiments directly showed the distortion of the normal calcite growth spirals that lead to macroscopic inhibition of calcite growth. Finally, thermodynamic considerations for the solid solution – aqueous solution system Ca–Fe–CO2–H2O are discussed that allow the modelling of geochemical processes involved in this system, such as geological carbon storage in basaltic rocks.

Thermal Na+ conditioning of natural clinoptilolite for softening removal of aqueous Ca2+ from simulated cooling-water environment

Thermal Na+ conditioning of natural clinoptilolite for softening removal of aqueous Ca2+ from simulated cooling-water environment

Synthesis of CaCO3 using CO2 at room temperature and ambient pressure

Reducing greenhouse gas has been important issue in recent years. Directly capturing CO2 gas as a solid form is attractive method to reduce the greenhouse gas and uses as a natural resource. CaCO3 has been synthesized by bubbling CO2 gas into an aqueous Ca(OH)2 medium with NH4OH catalyst. The reaction occurred within 3min and significantly precipitated within 5min. The characteristic absorption peaks of CaCO3 at 1450, 875 and 712cm−1 were increased by increasing the amount of NH4OH. The size of spheres increased with increasing the amount of NH4OH. Using completely dissolved Ca(OH)2 with NH4OH catalyst is one of the effective method not only capturing CO2 greenhouse gas and use as a resource.