Addition Of Ca Salts Research Articles

A novel strategy for preparing nanoporous biphasic calcium phosphate of controlled composition via a modified nanoparticle-assembly method

Biphasic calcium phosphate (BCP) consisting of hydroxyapatite (HAp) and β-tricalcium phosphate is usually prepared by thermal decomposition of calcium-deficient HAp (CDHAp). However, the calcium deficiency and morphology of CDHAp are difficult to manipulate in parallel. In this study, we report a novel strategy for controlling the composition of nanoporous BCP by using only CDHAp nanoparticles with specific properties (Ca/P molar ratio, 1.61; particle size, 50nm) as a building block and by adjusting the calcium deficiency of the nanoparticle-assembled CDHAp (Ca/P molar ratio, 1.50–1.67; pore size, 8nm) with the addition of water-soluble Ca(NO3)2 or (NH4)2HPO4. After thermal treatment at 1000°C, the composition of BCP could be predictably controlled by adjusting the Ca/P ratio of the nanoparticle-assembled CDHAp. Changes in the Ca/P ratio did not significantly affect the surface morphology of BCP, but the grain size (210–300nm) and pore size (140–170nm) tended to increase slightly as the Ca/P ratio decreased. The porosity significantly decreased upon the addition of Ca salts (porosity, 20%) or PO4 salts (porosity, 14%) compared with that of the sample without additives (porosity, 53%). In vitro tests demonstrated enhanced cell adhesion on nanoporous BCP compared with densely sintered pure HAp, and cell differentiation was promoted on the nanoporous pure HAp.

Impacts of Metal Salt Addition on Water Chemistry of Lake Elsinore, California: 2. Calcium Salts

ABSTRACT Laboratory studies using water samples collected from Lake Elsinore in June 2002 demonstrated that addition of CA2+ substantively changed the water chemistry. The addition of agricultural gypsum, rock gypsum and CaCl2 all lowered equilibrium pH and alkalinity levels, while increasing the dissolved Ca2+ concentration. Solution pH decreased linearly with increasing Ca2+ dose, from 9.0 with no added Ca2+, to about 8.4 at a dose of 200 mg·L−1. Alkalinity decreased from 10.5 to about 3.5 meq·L−1, while dissolved Ca2+ levels increased from 20.6 to approximately 100 mg·L−1 over this same dose range. Addition of CaO and Ca(OH)2 had a comparatively small effect on equilibrium chemistry and maintained high pH, high alkalinity and low Ca2+ levels in the water. The kinetics of these changes were quite slow; equilibrium was generally reached between 4–7 days depending upon Ca-salt used and the rate of mixing. The Ca-salt additions resulted in modest (30–40%) reductions in total phosphorus (TP) and chlorophyll levels. Sorption and core-flux experiments demonstrated limited capacity of precipitated CaCO3 to sorb soluble-reactive phosphorus (SRP). More substantial removal was achieved, however, via coprecipitation of SRP with CaCO3 formed in situ from Ca2+-amended recycled water added to Lake Elsinore water, although removal efficiencies remained well below those typically achieved with alum. Based upon these findings, some general recommendations can be made about Ca2+ addition to lakes for the control of phosphorus: (i) Ca2+ addition to lakes will be more effective during periods of high SRP concentrations; (ii) addition of Ca-salts that promote coprecipitation of SRP with CaCO3 formed in situ is more effective at removing SRP from the water column than adsorption to preformed CaCO3; and (iii) the form and dose of the Ca-salt dramatically influences the final chemical condition of the water.

Influence of electrolytes on EDTA extraction of Pb from polluted soil

Because the economics of soil extraction processes depend on conservation and reuse of costly chelating agents, the ability of various electrolytes to modify EDTA extraction of Pb from a grossly-contaminated soil (PbT=21%) was investigated using batch equilibration experiments. In the absence of added electrolyte, a single 5-hr. extraction with 0.04 M EDTA (corresponding to 1∶1 PbT to EDTA ratio) released 65% of PbT over the pH 5 to 9 range. Under these conditions, Na+-, Li+-, and NH4ClO4 salts at 0.5 M increased Pb desorption to nearly 80%, probably from exchange displacement of soilbound Pb2+ and increased solubility of Pb-containing phases at higher ionic strength. Because Cl− and ClO4− salts were equally effective, chlorocomplex formation was insignificant. Under slightly acidic conditions, Ca(ClO4)2 and Mg(ClO4)2 at 0.167 M caused roughly the same elevation in Pb recovery as 0.5M of the monovalent electrolytes. However, with progressively higher pH, Ca, and to a lesser extent Mg, suppressed Pb solubilization by competitive chelation of EDTA. Pb recovery by EDTA soil washing could be enhanced by addition of Ca salts at pH 4 to 6. Subsequent pH elevation in the presence of Ca would promote decomposition of Pb-EDTA complexes and separation of Pb as a hydroxide precipitate.

Effects of initial soil calcium content on ammonia losses from surface-applied urea and calcium-urea

Ammonia loss from surface-applied urea occurs because urea hydrolysis increases the pH of the placement site microenvironment. Addition of Ca-salts with urea will control or reduce the microsite pH, thus reducing NH3 losses. The degree of Ca-saturation of the cation exchange sites may influence the ratio of calcium:urea required to control ammonia loss. A laboratory study was conducted to determine if adsorbed Ca or CaCO3 additions (acid soils only) had a measureable impact on Ca control of NH3 loss from surface applied urea at various Ca:urea ratios.

Role of the Accompanying Anion in the Effect of Calcium Salts on Potassium Uptake by Excised Barley Roots

The effect of addition of Ca salts on accumulation of K from 5 mN KCl or K(2)SO(4) solutions was found to depend on whether Ca was added as Cl or SO(4) salt. Chloride as well as K uptake was increased when Ca and Cl concentrations in culture solutions were increased. Pre-treatment of roots with CaCl(2) stimulated subsequent K uptake from K(2)SO(4) solutions as compared to pre-treatment with distilled water but pre-treatment with CaSO(4) did not. The results indicate that addition of Ca salts to KCl or K(2)SO(4) solutions increased anion uptake and the effect of the addition of the Ca salts on K uptake was in part the result of increased anion uptake and not entirely a direct effect of Ca.In contrast, accumulation of Na and K from solutions containing these ions as SO(4) or Cl salts was changed from preferential uptake of Na to preferential uptake of K by addition of either CaCl(2) or CaSO(4). Thus, while Ca salts may influence K accumulation partly as a result of effects on anion uptake, the selectivity for K uptake depends on the presence of Ca and is influenced little by the accompanying anion.

THE INFLUENCE OF SOIL PROPERTIES AND SOIL AMENDMENTS ON THE SR90 CONTENT OF OATS GROWN IN SELECTED CANADIAN SOILS

Oats were grown in the greenhouse in six soils varying widely in pH, organic matter content, C.E.C., per cent saturation, and exchangeable calcium. Sr90 was added to all soils and its concentration in oats, as influenced by soil properties or soil treatment, was determined.The Sr90 content of oats grown in six soils, which included both saturated and unsaturated soils, was highly significantly correlated with the reciprocal of the exchangeable Ca contents of the soils with correlation coefficients of 0.99 for both the straw and the grain. The correlation coefficients between Sr90 concentration and the reciprocal of the C.E.C. for oat straw and oat grain were 0.65 and 0.55 respectively, which were not significant at the 5 per cent level.When calcium salts were added to three acid soils the larger applications of CaCl2 and CaSO4 lowered the soil pH, whereas CaCO3 raised the soil pH, but all three salts caused a decrease in Sr90 concentration in oats. A greater decrease in Sr90 content was effected by the addition of Ca salts to soil with low exchangeable Ca and low percentage Ca saturation than to soil with high percentage Ca saturation. It was concluded that the exchangeable Ca content, not C.E.C. or pH, was the dominant soil property upon which the Sr90 concentration in plants depended.