Adsorption Of Ca Ions Research Articles

Synergic effect of defects on carbon nanoparticles under interaction with calcium silicate hydrate composites

One- and two- dimensional carbon nanoparticles, i.e. graphene and CNT, are amongst the most potent additives in cementitious matrices. Their potential lies within the higher hydration degree, nano-filler effect and cracking-bridging effect that are only realized with a strong connection between the cementitious matrix and graphene. Here, Density functional theory (DFT) and molecular dynamics (MD) used to determine the nature of the interactions between the Tubermorite 14 Å and graphene. We observed that the carbon atoms on the periphery of various types of defects on the surface of a graphene nanosheet and carbon nanotube can form electrophile regions that adsorb silicate chains within the cementitious matrix, forming SiOC covalent bonds between the two species. Single vacancies are highly likely to bond with the silicate chains, with a bond energy of −90 kcal/mol at 1.5 Å length, which is also the case for the silicate – carbon nanotube (CNT) interactions. This is accompanied by the adsorption of Ca ions in Calcium Silicate Hydrates (CSH) on O atoms of functional groups in graphene interactions at the intralayer space, increasing the bond energy between the two nanostructures to 120 kcal/mol. Molecular dynamics (MD) simulations confirm the consolidation of the CSH – graphene around the two interactions, which causes a significant reduction in the mobility of the nanoparticle within the cementitious matrix. These findings provide essential information from the interactions within the interlayer and intralayer regions of CSH with carbon nanoparticles at the molecular level.

Zeta potential of anoxygenic phototrophic bacteria and Ca adsorption at the cell surface: Possible implications for cell protection from CaCO3 precipitation in alkaline solutions

Electrophoretic mobility measurements and surface adsorption of Ca on living, inactivated, and heat-killed haloalkaliphilic Rhodovulum steppense, A-20s, and halophilic Rhodovulum sp., S-17-65 anoxygenic phototrophic bacteria (APB) cell surfaces were performed to determine the degree to which these bacteria metabolically control their surface potential equilibria. Zeta potential of both species was measured as a function of pH and ionic strength, calcium and bicarbonate concentrations. For both live APB in 0.1M NaCl, the zeta potential is close to zero at pH from 2.5 to 3 and decreases to −30 to −40mV at pH of 5–8. In alkaline solutions, there is an unusual increase of zeta potential with a maximum value of −10 to −20mV at a pH of 9–10.5. This increase of zeta potential in alkaline solutions is reduced by the presence of NaHCO3 (up to 10mM) and only slightly affected by the addition of equivalent amount of Ca. At the same time, for inactivated (exposure to NaN3, a metabolic inhibitor) and heat-killed bacteria cells, the zeta potential was found to be stable (−30 to −60mV, depending upon the ionic strength) between pH 5 and 11 without any increase in alkaline solutions. Adsorption of Ca ions on A-20s cells surface was more significant than that on S-17-65 cells and started at more acidic pHs, consistent with zeta potential measurements in the presence of 0.001–0.01mol/L CaCl2. Overall, these results indicate that APB can metabolically control their surface potential to electrostatically attract nutrients at alkaline pH, while rejecting/avoiding Ca ions to prevent CaCO3 precipitation in the vicinity of cell surface and thus, cell incrustation.

Fertilization and pH effects on processes and mechanisms controlling dissolved inorganic phosphorus in soils

We used of a set of mechanistic adsorption models (1-pK TPM, ion exchange and Nica-Donnan) within the framework of the component additive (CA) approach in an attempt to determine the effect of repeated massive application of inorganic P fertilizer on the processes and mechanisms controlling the concentration of dissolved inorganic phosphorus (DIP) in soils. We studied the surface layer of a Luvisol with markedly different total concentrations of inorganic P as the result of different P fertilizer history (i.e. massive or no application for 40 years). Soil pH was made to vary from acid to alkaline. Soil solutions were extracted with water and CaCl 2 (0.01 M). The occurrence of montmorillonite led us to determine the binding properties of P and Ca ions for this clay mineral. Satisfactory results were obtained using generic values for model parameters and soil-specific ones, which were either determined directly by measurements or estimated from the literature. We showed that adsorption largely controlled the variations of DIP concentration and that, because of kinetic constrains, only little Ca-phosphates may be precipitated under alkaline conditions, particularly in the P fertilized treatment. The mineral-P pool initially present in both P treatments did not dissolve significantly during the course of the experiments. The adsorption of Ca ions onto soil minerals also promoted adsorption of P ions through electrostatic interactions. The intensity of the mechanism was high under neutral to alkaline conditions. Changes in DIP concentration as a function of these environmental variables can be related to changes in the contribution of the various soil minerals to P adsorption. The extra P adsorbed in the fertilized treatment compared with the control treatment was mainly adsorbed onto illite. This clay mineral was the major P-fixing constituent from neutral to alkaline pH conditions, because the repulsion interactions between deprotonated hydroxyl surface sites and P ions were sufficiently counterbalanced by Ca ions. The drastic increase of DIP observed at acid pH was due to the effect of the lower concentration of surface sites of Fe oxides and kaolinite. In addition to confirming the validity of our approach to model DIP concentrations in soils, the present investigation showed that adsorption was the predominant geochemical process even in the P fertilized soil, and that Ca ions can have an important promoting effect on P adsorption. However the influence of the dissolution of the mineral-P pool under field conditions remained questionable.

Molecular Dynamics Computer Simulations of Calcium-Alumino-Silicate Intergranular Films between the basal and prism planes of α-Al2O3

ABSTRACTMolecular dynamics computer simulations using a robust multibody potential were used to study the structure of the intergranular films (IGFs) formed between two different crystallographic orientations of α-Al2O3crystals. The simulations show a localized ordering of the IGF at the interface of both the basal and prism planes caused by preferential adsorption of specific ions from the IGF onto the crystal planes. However, the results of the adsorption have significantly different effects on crystal growth of the specific orientations. The preferential adsorption of Ca ions from the IGF onto the (0001) surface inhibit growth in the <0001> direction. However, Ca does not affect adsorption of O and Al from the IGF onto the (1120) surface and potential growth of this orientation in the <1120> direction. The results are consistent with experimental data regarding anisotropic grain growth in this system and provide an atomistic view of this behavior.

Role of pH and dissolved mineral species in Pittsburgh no. 8 coal flotation system — II. Separation of pyrite and non-pyritic minerals from coal

The role of pH and of dissolved mineral species on the separation of pyrite and non-pyritic minerals from Pittsburgh No. 8 coal by flotation was investigated. In the pH range of 4 to 8, enhanced pyrite rejection was obtained at higher pH. However, pH itself had no measurable effect on the separation of non-pyritic minerals from coal in the pH range of 4 to 10. The precipitation/adsorption of the dissolved mineral ions resulted in a measurable decrease in the selectivity for non-pyritic minerals separation. Increased pyrite rejection with pH increase was shown, by induction time measurements, to be mainly due to the decrease of the pyrite hydrophobicity. The adsorption of Ca ions in the coal flotation systems had a positive effect on the pyrite separation, although it did not affect coal recovery to a measurable extent. This could be due to the selective precipitation/adsorption of Ca species on the pyrite surface. The precipitation/adsorption of Fe species had no measurable effect on the selectivity, even though it depressed coal flotation considerably. This is attributed to the non-selective precipitation of Fe species between the surfaces of coal and pyrite.