Adsorption Of Ca Research Articles

Transport of humic and fulvic acids in relation to metal mobility in a copper-contaminated acid sandy soil.

The transport of inorganic and organic pollutants in water and soil can be strongly influenced by the mobility of natural dissolved organic matter (DOM). In this paper, the transport of a humic acid (HA) and a fulvic acid (FA) in a copper-contaminated acid sandy soil was studied. The data showed that the transport behavior of HA differed from that of FA. The breakthrough curves (BTCs) of HA were characterized by a rapid relatively sharp front followed by a plateau at a lower HA concentration than in the influent solution. The increase of the Ca concentration decreased the HA concentration further. Compared to HA, the BTCs of FA were retarded and showed an extended tailing, approaching complete breakthrough. The increase of the Ca concentration decreased the FA concentration only temporarily. On the basis of our model calculation, the characterization of HA transport could be explained by the coagulation of HA largely upon the binding of Al. The increase of the Ca concentration resulted in further coagulation of HA because of the increased Ca adsorption, which occurred mainly in the Donnan phase. For FA, the adsorption to the soil matrix was more likely the process that controls its solubility and mobility. The mobility of Al and Cu in the soil column was closely related to the solubility and transport of the DOM in soil solution. The concentration of Ca in the effluent was lower than in the influent because Ca was retained in the soil due to the retardation of HA and FA and due to the compensation of the other cations released from the soil to the solution.

Effect of surface chemistries and characteristics of Ti6Al4V on the Ca and P adsorption and ion dissolution in Hank's ethylene diamine tetra-acetic acid solution

This study examined the influence of chemistries and surface characteristics of Ti6Al4V on the adsorption of Ca and P species and ion dissolution behavior of the material exposed in Hank's solution with 8.0 m m ethylene diamine tetra-acetic acid at 37°C. The variation of chemistries of the alloy and nano-surface characteristics (chemistries of nano-surface oxides, amphoteric OH group adsorbed on oxides, and oxide thickness) was effected by surface modification and three passivation methods (34% nitric acid passivation, 400°C heated in air, and aged in 100°C water). X-ray photoelectron spectroscopy and Auger electron spectroscopy were used for surface analyses. The chemistries of nano-surface oxides in a range studied should not change the capability of Ca and P adsorption. Nor is the capability affected significantly by amphoteric OH group and oxide thickness. However, passivations influence the surface oxide thickness and the early stage ion dissolution rate of the alloy. The rate-limiting step of the rate can be best explained by metal-ion transport through the oxide film, rather than hydrolysis of the film. Variation of the chemistries of titanium alloy alters the electromotive force potential of the metal, thereby affecting the corrosion and ion dissolution rate.

Carbon adsorbents from brown coal tar

In this paper, we, for the first time report the properties of ash deposits collected from the combustion of lignite mixed with silica additive, in a 30 MWth pulverised-fuel boiler with sub-critical steam conditions. The combustion test was carried out continuously over ten months, and ash deposits were sampled from various locations in the boiler. As has been confirmed, the ash-related slagging and fouling have been controlled effectively. Apart from capturing volatile alkali and alkaline earth metals, silica added in an excess amount is beneficial in mixing with molten liquidus to promote their agglomeration, rather than adhering to the vicinity of coal burners for slagging. Compared to the formation of abundant Fe2+-slag that is prone to stick to coal burner vicinity in the raw coal case, the formation of friable calcium sulfate in fireside deposit is favored upon the mixing of silica with coal, which is even predominant in the fireside ash deposit. The calcium sulfate formed is highly layered in a plerospheric structure in which Ca-silicate is present as the core with calcium sulfate being the shell. The physical adsorption of free Ca on silicate surface is supposed to enhance its specific surface area for a quicker sulfation. The capture of Na by silica is also efficient, leading to the transformation of a remarkable portion of Na into coarse bottom ash with less being sulfated. This in turn alleviates the sulfate – relating fouling propensity on the water tube surface in the convection zone. A noticeable portion of Fe was noticed to remain as discrete grains outside the Ca-rich slag matrix. In contrast, the majority of Mg is highly crystallised as sub-micrometer Ca/Mg-silicate and oxide particles residing within slag matrix, which in turn increase the viscosity and decrease the sticking propensity of the molten slag.

Coal ash utilization technology for civil industry

In this paper, we, for the first time report the properties of ash deposits collected from the combustion of lignite mixed with silica additive, in a 30 MWth pulverised-fuel boiler with sub-critical steam conditions. The combustion test was carried out continuously over ten months, and ash deposits were sampled from various locations in the boiler. As has been confirmed, the ash-related slagging and fouling have been controlled effectively. Apart from capturing volatile alkali and alkaline earth metals, silica added in an excess amount is beneficial in mixing with molten liquidus to promote their agglomeration, rather than adhering to the vicinity of coal burners for slagging. Compared to the formation of abundant Fe2+-slag that is prone to stick to coal burner vicinity in the raw coal case, the formation of friable calcium sulfate in fireside deposit is favored upon the mixing of silica with coal, which is even predominant in the fireside ash deposit. The calcium sulfate formed is highly layered in a plerospheric structure in which Ca-silicate is present as the core with calcium sulfate being the shell. The physical adsorption of free Ca on silicate surface is supposed to enhance its specific surface area for a quicker sulfation. The capture of Na by silica is also efficient, leading to the transformation of a remarkable portion of Na into coarse bottom ash with less being sulfated. This in turn alleviates the sulfate – relating fouling propensity on the water tube surface in the convection zone. A noticeable portion of Fe was noticed to remain as discrete grains outside the Ca-rich slag matrix. In contrast, the majority of Mg is highly crystallised as sub-micrometer Ca/Mg-silicate and oxide particles residing within slag matrix, which in turn increase the viscosity and decrease the sticking propensity of the molten slag.

Mechanism of bonelike apatite formation on bioactive tantalum metal in a simulated body fluid

Development of tantalum metal with bone-bonding ability is paid much attention because of its attractive features such as high fracture toughness, high workability and its achievement on clinical usage. Formation of bonelike apatite is an essential prerequisite for artificial materials to make direct bond to living bone. The apatite formation can be assessed in vitro using a simulated body fluid (SBF) that has almost equal compositions of inorganic ions to human blood plasma. The present authors previously showed that the apatite formation on tantalum metal in SBF was remarkably accelerated by treatment with NaOH aqueous solution and subsequent firing at 300°C, while untreated tantalum metal spontaneously forms the apatite after a long soaking period. The purpose of the present study is to clarify the reason why the NaOH and heat treatments accelerate the apatite formation on tantalum metal. X-ray photoelectron spectroscopy was used to analyze changes in surface structure of the tantalum metal at an initial stage after immersion in SBF. Untreated tantalum metal had tantalum oxide passive layer on its surface, while amorphous sodium tantalate was formed on the surface of the tantalum metal by the NaOH and heat treatments. After soaking in SBF, the untreated tantalum metal sluggishly formed small amount of Ta–OH groups by a hydration of the tantalum oxide passive layer on its surface. In contrast, the treated tantalum metal rapidly formed Ta–OH groups by exchange of Na + ion in the amorphous sodium tantalate on its surface with H 3O + ion in SBF. Both the formed Ta–OH groups combined with Ca 2+ ion to form a kind of calcium tantalate, and then with phosphate ion, followed by combination with large amount of Ca 2+ ions and phosphate ions to build up apatite layer. The formation rate of Ta–OH groups on the treated tantalum metal predominates the following process including adsorption of Ca 2+ ion and phosphate ion on the surface. It is concluded that the acceleration of the apatite nucleation on the tantalum metal in SBF by the NaOH and heat treatments was attributed to the fast formation of Ta–OH group, followed by combination of the Ta–OH groups with Ca 2+ and phosphate ions.

A series of Ca-induced reconstructions on Si([formula omitted]) surface

We have studied surface reconstructions induced by submonolayer Ca adsorption on a Si(111) surface using reflection-high-energy electron diffraction (RHEED) and scanning tunneling microscopy (STM). With increase of Ca coverage at substrate temperatures above 550°C, the RHEED pattern changed successively: clean 7×7→3×1→5×1→7×1→2×1. The 3×1 pattern transformed into a 3ד2” pattern including half-order streaks by cooling down to room temperature. The STM images of these reconstructions commonly showed striped structures with the periodicities corresponding to the RHEED patterns. Each stripe in the 3ד2”, 5×1, 7×1, and 2×1 structures is composed of several rows. The twofold periodicity along the stripes of the 3ד2” phase was observed in filled-state images as well as in empty-state ones; simple protrusions are arranged with the double periodicity in the empty-state image, while a dimerization of small protrusions occurs along the stripes in the filled-state image. From these results, atomic structure models for these Ca-induced reconstructions are suggested.

Growth of pot plants in treated coir dust as compared to peat

Coir dust has been introduction in Dutch horticulture, however, in some crops problems have arisen. Growth was restricted. Substrate and plant analysis revealed deficiencies of both calcium (Ca) and magnesium (Mg). This was linked to the high potassium (K) and sodium (Na) content and the adsorption of Ca and Mg to the coir. It was proposed that in coir, where the Na and K contents are low and no adsorption occurred of Ca and Mg, growth of plants should be better than or equal to peat, the standard substrate. To prove this a trial has been conducted with four types of pot plants. Coir was washed with a Ca and Mg containing solution to leach excess K and Na and this material is referred to as ‘treated’ coir dust. Growth of Begonia, Dendranthema, and Schefflera in ‘treated’ coir dust was equal to that in peat. Kalanchoe showed a stronger vegetative growth in coir dust than in peat. Growers should avoid the risk of Ca and/or Mg deficiency and use the ‘treated’ coir dust.

Chemistry of surface water at a volcanic summit area, Norikura, Central Japan: Multivariate statistical approach

Many hydrochemical studies on chemical formation of shallow ground water have been reported as results of water–rock interaction, and contamination of paleo-brine or human activities, whereas the preliminary formation of precipitation source in the recharged region has not been established yet. The purpose of this research work is to clarify the geochemical process of water formation from a water source unpolluted by seawater or human activity. Norikura volcano, located in western part of central Japan provided a suitable source for this research purpose, and hence chemical compositions of water samples from the summit and the mountainside area of Norikura volcano were determined. Most samples in the summit area showed very low electrical conductivity, and lower than 12 μS/cm . On the basis of the chemical compositions, principal component analysis (PCA) and factor analysis (FA), such as kinds of multivariate statistical techniques were used to extract geochemical factors affecting hydrochemical process. As a result, three factors were extracted. The first factor showed high loading on K +, Ca 2+, SO 4 2− and SiO 2, and this factor was interpreted due to influence of the chemical interaction between acidic precipitated water and rocks. The second factor showed high loading on Na + and Cl −, and it was assumed to be an influence of seawater salt. The third factor showed loading on NO 3 −, and it was interpreted to be caused by biochemical effect of vegetation. The proportionate contributions of these factors to the evolution of water chemical composition were found to be 45%, 20% and 10% for factors 1, 2 and 3, respectively. The same exploration at the mountainside of Norikura volcano revealed that the chemical variances of the non-geothermal water samples were highly influenced by water–rock interactions. The silicate dissolution showed 45% contribution for all chemical variances, while the adsorption of Ca 2+ and Mg 2+ by precipitation or ion exchange showed 20% contribution. The seawater salt influence or biochemical effect was statistically negligible in this area. The clear differentiation of geochemical process on water formation was found between the summit area and the mountainside area.

1,2-Bis(o-aminophenoxy)ethane-N,N,N′,N ′-tetraacetic Acid (BAPTA) Covalently Bound to a Polysulfone and to an Insoluble Polystyrene: Synthesis and Applications to the Selective Adsorption of Ca2+ from Mg2+ in Water

1,2-Bis(o-aminophenoxy)ethane-N,N,N′,N ′-tetraacetic Acid (BAPTA) Covalently Bound to a Polysulfone and to an Insoluble Polystyrene: Synthesis and Applications to the Selective Adsorption of Ca2+ from Mg2+ in Water

Interaction between calcium and phosphate adsorption on goethite.

Quantitatively, little is known about the ion interaction processes that are responsible for the binding of phosphate in soil, water, and sediment, which determine the bioavailability and mobility of phosphate. Studies have shown that metal hydroxides are often responsible for the binding of PO4 in soils and sediments, but the binding behavior of PO4 in these systems often differs significantly from adsorption studies on metal hydroxides in laboratory. The interaction between PO4 and Ca adsorption was studied on goethite because Ca can influence the PO4 adsorption equilibria. Since adsorption interactions are very difficult to discriminate from precipitation reactions, conditions were chosen to prevent precipitation of Ca-PO4 solids. Adsorption experiments of PO4 and Ca, individually and in combination, show a strong interaction between adsorbed Ca and PO4 on goethite for conditions below the saturation index of apatite. It is shown that it is possible to predict the adsorption and interaction of PO4 and Ca on electrostatic arguments using the model parameter values derived from the single-ion systems and without invoking ternary complex formation or precipitation. The model enables the prediction of the Ca-PO4 interaction for environmentally relevant calcium and phosphate concentrations.

Deposition of calcium ions on rutile (110): a first-principles investigation

The deposition of calcium ions is the first and most crucial step of apatite nucleation on ceramic supports from ionic solution. This process is believed to initiate the growth of bone-like material on the surface of biocompatible implants. We have investigated the adsorption of Ca 2+ from water solution on the rutile TiO 2 (110) surface by means of first principles techniques. The preferential binding site of the calcium ion on the hydrated oxide surface was determined through a series of static calculations. Molecular dynamics simulations were then performed to elucidate the deposition pathway. The driving force for adsorption is identified in the electrostatic interaction between the Ca 2+ complexes and negatively charged deprotonated sites present on the hydrated TiO 2 (110) surface.

Effect of Reversible Cross-linker, N,N‘-Bis(acryloyl)cystamine, on Calcium Ion Adsorption by Imprinted Gels

Imprinted gels incorporating two different breakable cross-linkers, a PbMAA2 complex and a disulfide (S−S) bond, were prepared by radical polymerization. After the lead ions were removed by washing, these gels showed a high affinity for calcium ions. Breakage and subsequent reconnection of the S−S bonds in the absence of Ca2+ decreases the Ca2+ binding affinity of the gel. This indicates that random reconnection of the S−S bonds produces a frustration in the adsorption of Ca2+ by the carboxyl groups. However, if the S−S bonds were reconnected in the presence of Ca2+ and the Ca2+ was subsequently removed (the post-imprinting technique), the resulting gels showed a higher binding affinity for Ca2+. This indicates that the post-imprinting technique creates a more favorable conformation for Ca2+ binding in the polymer network. We interpret our data to mean that “memory” of target-binding sites was encoded effectively into the polymer network by the initial imprinting technique and then enhanced by the post-im...

Specific cation adsorption on protein-covered particles and its influence on colloidal stability

Protein coated particles present an anomalous colloidal stability at high ionic strength when the classical theory (DLVO) predicts aggregation. This observed deviation from DLVO behaviour appears for electrolyte concentrations above some critical bulk value. As we have suggested in previous publications the existence of an additional short-range repulsive ‘hydration force’ due to specific hydrated cation adsorption could explain this anomalous stability. The overlap of the hydration layers when two particles approach should provoke this repulsive force. New evidence of this mechanism has been observed when electrophoretic mobilities of protein-carrying latex particles were measured at various concentrations of sodium and calcium chloride. In the latter case a sign reversal of zeta-potential was found, probably due to the specific adsorption of Ca 2+ ions on protein molecules. The adsorption increases with the medium pH. These results have been analyzed following the treatment proposed by Ohshima and co-workers for large charged colloidal particles coated with a layer of protein. This study shows an increase in the positive fixed-charge density on the protein caused by the adsorption of cations.

INTERACTIONS ON THE SOIL-RAINFALL SYSTEM OF A LIME-STABILIZED SLUDGE AS SURFACE AMENDMENT

Sludge from a wastewater treatment plant can be applied to soil to make use of its fertilizing properties, neverthelessit is necessary to study all the effects of this deposition to ascertain any possible hazardous properties. Interactions among the soil, the water, and a lime-stabilized waste watersludge were studied, both in batch experiments, and in columnpercolation experiments. Firstly a physico-chemical characterization of the soil and the sludge used for the experiments was carried out. This analysis included pH, organic matter, cation exchange capacity, metals and cations.The kinetics and equilibrium of the sludge-water and leachate-soil systems were studied in batch experiments; thekinetics were fitted to a first order differential equation and distribution coefficients were found for the equilibrium.Experiments in columns (10 cm diameter × 50 cm height) were carried out with a bed of sludge over a bed of soil usingdifferent sludge/soil ratios and then 6 L of water (rainfall)was poured over the beds. Results showed good adsorption of Ca and a complete leaching of the aqueous phase of this ion afterpassing a volume of water equivalent to three volumes of the column. The concentration of heavy metals (Zn, Ni, Hg, Cd, Pb and Cr) in the leachates did not reach the admissible legal limits (Spanish and European regulations) in any case.

Multicomponent transport of major cations predicted from binary adsorption experiments

Accurate modeling of multicomponent sorption and transport of major cations in subsurface porous media is a prerequisite for predicting complex environmental processes, such as the movement of trace metals in soils and aquifers. In this study, various cation exchange models were compared in their ability to predict ternary Ca–Mg–Na transport in an acidic soil from binary Ca, Mg, and Na adsorption data. A flow-through reactor technique was used to measure binary adsorption isotherms of Ca, Mg, and Na over wide concentration ranges of the adsorptive and the respective background cations. High-resolution transport experiments were conducted in water-saturated chromatographic glass columns. Three sorption models based on cation exchange equations were compared: a 1-site Gaines–Thomas (1-GT), a 1-site Rothmund–Kornfeld (1-RK), and a 3-site Gaines–Thomas (3-GT) model. Although the fit of adsorption data was clearly improved from the 1-GT to the 1-RK to the 3-GT model, transport predictions were overall not improved compared to the 1-GT model. While predictions by the 1-GT and the 3-GT model were virtually identical, predictions by the 1-RK model were partly improved and partly deteriorated. The most simple 1-GT model, therefore, seems to be adequate for predicting multicomponent transport phenomena involving major cations, however, multi-site models may be useful for predicting transport of trace metals in the presence of several major cations. Regardless of the model used, accurate determination of the cation exchange capacity at the pH conditions of interest is extremely critical in cation transport modeling.

Experimental measurements of the reversibility of metal–bacteria adsorption reactions

This study tests the reversibility of metal–bacteria interactions by comparing estimated extents of desorption based on surface complexation modeling, to those we observed in the experimental adsorption/desorption systems. The experiments also determine if extended adsorption contact time affects desorption kinetics. The experiments involved Ca and Cd adsorption/desorption onto the surface of a gram positive bacterium: Bacillus subtilis. Three types of experiments were performed: (1) Ca and Cd desorption from the cell wall of B. subtilis after 1 h of adsorption contact; (2) Cd and Ca desorption from the cell wall of B. subtilis after >15 h of adsorption contact; and (3) Ca and Cd desorption as a function of pH after 1 h of adsorption contact. Both the adsorption and desorption reactions are rapid, and the desorption kinetics are independent of adsorption contact time. Steady-state conditions are attained within 2 h for all adsorption reactions studied, and within 1 h for all desorption reactions studied. Furthermore, the extent of adsorption or desorption remains constant for at least 24 h (and up to 80 h for Cd). The observed extent of desorption in the experimental systems is in excellent agreement with the amount estimated from a surface complexation model based on independently conducted adsorption experiments. Therefore, this study indicates that the adsorption of Cd and Ca on B. subtilis is a rapid, fully reversible, and hence an equilibrium process. Therefore the use of surface complexation modeling of aqueous metal adsorption onto bacterial surfaces yields accurate estimates of the distribution of metals in bacteria-bearing solutions.

Restructuring process of the Si(111) surface upon Ca deposition

Using scanning tunneling microscopy and high-resolution spot profile analysis low-energy electron diffraction (SPA-LEED), the process of Si(111)3×1-Ca phase formation induced by Ca adsorption on Si(111)7×7 samples has been studied. Our observation revealed that what has been considered to be 3×1 reconstruction is actually a mixture of 3×2 and c(6×2) reconstructions. The redistribution of Si atoms in a top Si(111) layer has been found to play a critical role in the Si(111)3×2-Ca growth. From the quantitative consideration of Si mass transport balance, top Si atom density of Si(111)3×2-Ca phase has been determined to be a 4/3 monolayer.

ADSORPTION OF METAL IONS ON STEARIC ACID-NONADECANE PARTICLES IN AQUEOUS SOLUTION

The adsorption of metal ions at the stearic acid/electrolyte and nnonadccane-stearic acid mixture/electrolyte interface was investigated by means of the potentiometric titration, zeta potential and adsorption measurements. It was found that the studied colloidal suspensions exhibited an adsorption affinity towards multivalent metal ions. The adsorption of Ca2+, Cd2+ and Al3+ ions caused a strong decrease of surface charge density and zeta potential values in this systems. The adsorption reactions occur by way of cation exchange with protons from two surface carboxyl groups. Al high metal concentrations, in adsorption reactions there are involved also carboxyl groups from the subsurface layer. On the basis of the adsorption data, the cation surface complexation constants were calculated by Shindler's method.

Competitive adsorption of metal cations onto two gram positive bacteria: testing the chemical equilibrium model

In order to test the ability of a surface complexation approach to account for metal-bacteria interactions in near surface fluid-rock systems, we have conducted experiments that measure the extent of adsorption in mixed metal, mixed bacteria systems. This study tests the surface complexation approach by comparing estimated extents of adsorption based on surface complexation modeling to those we observed in the experimental systems. The batch adsorption experiments involved Ca, Cd, Cu, and Pb adsorption onto the surfaces of 2 g positive bacteria: Bacillus subtilis and Bacillus licheniformis. Three types of experiments were performed: 1. Single metal (Ca, Cu, Pb) adsorption onto a mixture of B. licheniformis and B. subtilis; 2. mixed metal (Cd, Cu, and Pb; Ca and Cd) adsorption onto either B. subtilis or B. licheniformis; and 3. mixed or single metal adsorption onto B. subtilis and B. licheniformis. %Independent of the experimental results, and based on the site specific stability constants for Ca, Cd, Cu, and Pb interactions with the carboxyl and phosphate sites on B. licheniformis and B. subtilis determined by Fein et al. (1997), by Daughney et al. (1998) and in this study, we estimate the extent of adsorption that is expected in the above experimental systems.Competitive cation adsorption experiments in both single and double bacteria systems exhibit little adsorption at pH values less than 4. With increasing pH above 4.0, the extent of Ca, Cu, Pb and Cd adsorption also increases due to the increased deprotonation of bacterial surface functional groups. In all cases studied, the estimated adsorption behavior is in excellent agreement with the observations, with only slight differences that were within the uncertainties of the estimation and experimental procedures. Therefore, the results indicate that the use of chemical equilibrium modeling of aqueous metal adsorption onto bacterial surfaces yields accurate predictions of the distribution of metals in complex multicomponent systems.

Metal sorption to dolomite surfaces

Potential human intrusion into the Waste Isolation Pilot Plant (WIPP) might release actinides into the Culebra Dolomite where sorption reactions will affect of radiotoxicity from the repository. Using a limited residence time reactor the authors have measured Ca, Mg, Nd adsorption/exchange as a function of ionic strength, P CO 2 , and pH at 25°C. By the same approach, but using as input radioactive tracers, adsorption/exchange of Am, Pu, U, and Np on dolomite were measured as a function of ionic strength, P CO 2 , and pH at 25°C. Metal adsorption is typically favored at high pH. Calcium and Mg adsorb in near-stoichiometric proportions except at high pH. Adsorption of Ca and Mg is diminished at high ionic strengths (e.g., 0.5M NaCl) pointing to association of Na + with the dolomite surface, and the possibility that Ca and Mg sorb as hydrated, outer-sphere complexes. Sulfate amplifies sorption of Ca and Mg, and possibly Nd as well. Exchange of Nd for surface Ca is favored at high pH, and when Ca levels are low. Exchange for Ca appears to control attachment of actinides to dolomite as well, and high levels of Ca 2+ in solution will decrease K ds. At the same time, to the extent that high P CO 2 s increase Ca 2+ levels, K ds will decrease with CO 2 levels as well, but only if sorbing actinide-carbonate complexes are not observed to form (Am-carbonate complexes appear to sorb; Pu-complexes might sorb as well. U-carbonate complexation leads to desorption). This indirect CO 2 effect is observed primarily at, and above, neutral pH. High NaCl levels do not appear to affect to actinide K ds.