Papers by Keyword: Calcium Ion

Abstract: Magnetic sodium alginate (SA)-based biosorbent Fe₃O₄@SA-Ca gel beads were synthesized by droplet polymerization using Ca²⁺ ions as crosslinking agent, and characterized by Scanning Electron Microscopy (SEM). Fe₃O₄@SA-Ca polymer was used for the removal of Direct Orange 26 (DO-26) dye from water. The ratio of raw materials and some important conditions affecting the adsorbent performance were carefully examined. The adsorption kinetics, isotherms and thermodynamics were investigated. When the concentrations of SA, CaCl₂ and Fe₃O₄ solutions were 1.9, 10 and 10 g/L, respectively, the black Fe₃O₄@SA-Ca gel beads with about 3 mm diameter were successfully prepared by curing 6h at room temperature. The polymer gel exhibits ultra-high adsorption capacity of 1252 mg/g and removal efficiency of 96.2 % for DO-26 under the conditions of 0.05 g polymer dosage, 2600 mg/L of dye initial concentration, solution pH 2.0 and 90 min of the adsorption time at 298 K. The dye removal efficiency can be all over 92 % in a wide pH range of 2.0 to 10.0. The adsorption process completely accorded with the pseudo-second-order rate model at different temperatures (298 ~ 328 K). The dye adsorption behavior was well in line with Freundlich model. The thermodynamic study indicated that the adsorption reaction was of spontaneous and exothermic nature. SEM analysis showed that the Fe₃O₄@SA-Ca gel beads appeared uneven surface with irregular folds and grooves. A high-cost-effective magnetic biosorbent, Fe₃O₄@SA-Ca can super effectively remove direct dyes from high-concentration wastewater in a wide range of acidity, and can be easily separated and recovered from water after adsorption without secondary pollution, and would have a good application prospect.

Abstract: A novel calcium alginate (SA/Ca) gel pellet adsorbent was prepared by ion exchange reaction and polymerization between sodium alginate (SA) and Ca²⁺ in the solution, and characterized by SEM, EDS, FTIR and XRD. Taking acid orange II ( AO II) dye as the adsorption object, the influence of some important conditions about preparation and adsorption on SA/Ca properties was discussed in detail. The adsorption kinetics were studied. The results show that SA/Ca adsorbent has good adsorption effect on AO II dye under the conditions of the mass concentration ratio 2 : 5 of SA and CaCl₂ solutions and reaction time of 2h at 25°C. When the adsorbent dosage is 4g/L and initial dye concentration of natural pH is 1000 mg/L, the adsorption equilibrium can basically reach in 180 min at 25°C with the adsorption capacity of 225mg/g and more than 90% of removal efficiency. The adsorption kinetics fully fit pseudo-second order model. The characterization results indicate that the SA powder is composed of various irregular particles, while dry SA/Ca solid are all pellets with diameter of about 1mm. The surface of inhomogeneous spheres is stacked with obstacles, and folds and ravines coexist. Ca²⁺ and most Na⁺ in SA molecule carried out ion exchange and formed a stable network-structure polymer SA/Ca gel pellets, which can effectively remove acid dyes from wastewater, and are easy to be separated after adsorption. As a biopolymer adsorbent with simple preparation method, environmental friendliness and non-toxic side effects, SA/Ca has good development potential and application prospects.

Abstract: Water quality is very important to food processing industry. Water hardness caused by calcium ions in water can affect the properties of food including aroma, texture, flavor and appearance. Chitosan has amino functional groups that can remove metal ions from aqueous solution. However, chitosan can give more effective removal of calcium ions if it is modified with functionalized substance such as thiamine hydrochloride. therefore, the objectives of this study were to synthesize the modified chitosan with thiamine hydrochloride (MCTH) and to determine its efficiency for removal of calcium ion in solution. Chitosan was prepared from crab shells and modified with thiamine hydrochloride at 30 °C. The morphology of both crab-shell chitosan (CSC) and MCTH was characterized by SEM, FTIR and NMR techniques. Batch adsorption experiments were conducted as a function of pH, contacted time and initial concentration of calcium (II) ions. The desorption of calcium(II) ion from both adsorbents was also investigated. The concentration of calcium in solution was measured by FAAS technique. The results indicated that the optimum pH for adsorption was 6.0 for both CSC and MCTH. The adsorption capacity for MCTH (48.31 mg g^-1) was greater than that of CSC (1.52 mg g^-1). The isotherm showed that the adsorption process of calcium (II) ions onto MCTH was fitted to Langmuir isotherm model. Calcium desorption from MCTH was lower than that of CSC.

Abstract: A novel composite material, calcium/chitosan/fly ash (Ca/CTS/FA) adsorbent prepared by adding a small amount of chitosan (CTS) and calcium ion(Ca) on fly ash (FA) was applied to the adsorption of three direct dyes including direct orange S (DO-S), direct green BE (DG-BE) and direct bordeaux BE (DB-BE). Adsorption equilibrium, isotherms and adsorption thermodynamics were studied . The results show that the adsorption rates of three direct dyes to Ca/CTS/FA are high and the adsorption equilibrium can be reached within 60 minutes. isothermal adsorption data agree with Langmuir model, and the saturated adsorption capacities are 1667mg/g for DO-S, 1111mg/g for DG-BE and 1111mg/g for DB-BE respectively at 298K. Dubinin-Radushkevich (D-R) model is used to investigate the adsorption behavior of direct dyes, and theaverage adsorption energy is in the range of 17.2 ~ 23.6kJ/mol at different temperatures. the thermodynamic parameters indicate that the adsorption processes of direct dyes to Ca/CTS/FA are spontaneous and endothermic from 298K to 328K. Characterization results by FT-IR indicate that Ca/CTS/FA composite is successfully prepared. As a low-value composite adsorbent, Ca/CTS/FA has very high adsorption capacity for direct dyes.

Abstract: Based on the unique redox property of electrically conductive polymers, Ca²⁺ was incorporated into polypyrrole (PPy) film that previously doped with polyelectrolyte heparin. Then the apatite-forming ability of the Ca²⁺-doped PPy was examined by a biomimetic method using stimulated body fluid (SBF), which has ion concentration nearly equal to those of human blood plasma. It was found that the Ca²⁺-doped PPy successfully formed bonelike apatite deposition on its surface after soaking in SBF for only 3 days, whereas the similar apatite deposition was formed on Ca²⁺-free PPy after soaking in SBF for 7 days. These indicated that the entrapment of Ca²⁺ into PPy could accelerate the formation of apatite deposition and the Ca²⁺-doped PPy was possessed of enhanced bioactivity. It is expected that the Ca²⁺-doped PPy would be a useful bioactive coating material of metallic medical devices or tissue engineering scaffolds to promote the bone tissue regeneration.

Abstract: Calcium ions released from calcium-alginate hydrogel can promote inflammatory responses when injected subcutaneously in mice. In this study, a novel alginate hybrid hydrogel was prepared using sodium alginate (SA) and Glycyrrhizic acid (GA) design for reduce calcium concentration in the hydrogel. nanoCalcium carbonate was wrapped in an alginate solution and internal gelling was induced by the Ca²⁺ released from CaCO₃ by adding of GA. As varying of the amounts of GA and CaCO₃ in alginate solution, the gelling time could be controlled within 10 min. Taking advantage of short gelation time and controlled hydrogel shape, GA calcium alginate hydrogel system has great potential for tissue engineering applications.

Abstract: This paper presents the adsorption behaviors of humic acid (HA) on coal ashes and powdered activated carbons (PACs). A bituminous coal, with or without calcium-loading, was used as a feedstock for coal ash preparation. The working solution of HA with a concentration of 20 mg/L was used in all adsorption tests. The results showed that calcium-enriched coal ash (CECA) gave rise to the removal rate of HA as high as 84.05%, much higher than those of raw coal ash (RCA) and PACs. The impacts of solution pH and adsorbent dosage on HA adsorption capacity were also investigated. It was found that lower pH facilitated to the removal of HA from aqueous solution by means of CECA, and the optimal CECA dosage was about 1.0g/L at pH 7.00. The data obtained in this study suggested that calcium-enriched coal ash could be useful and cost-effective in the treatment of wastewaters containing HA-like organic macro-molecules.

Abstract: Several methods were employed to study the time dependent film formation of a self synthesized anionic latex dispersion in water and cement pore solution. First, a model carboxylated styrene/n-butyl acrylate latex dispersion possessing a minimum film forming temperature (MFFT) of 18 °C and a glass transition temperature (T_g) of 30 °C was synthesized via emulsion polymerization. Next, its film forming behaviour was studied at 40 °C, using an ESEM instrument. The analysis revealed that upon removal of water, film formation occurs as a result of particle packing, particle deformation and finally particle coalescence. Film formation is significantly hindered in synthetic cement pore solution. This effect can be ascribed to adsorption of Ca²⁺ ions onto the surface of the anionic latex particles and to interfacial secondary phases. This layer of adsorbed Ca²⁺ ions hinders interdiffusion of the macromolecules and subsequent film formation of the latex polymer.

Abstract: The effects of gellan gum and calcium ions concentration on gelation characteristics and rheological behavior were investigated using TA(texture analysis)and mechanical rheometer which monitored respectively press strength and the evolution of G′. At a premium gellan gum content of 0.02g in 100ml buffer solution, increasing calcium ions concentration led to an increase in the gelation strength, but when calcium ions content reached a critical concentration values range from 0.015% to 0.02%, gelation strength begin to decrease. While in the same content of calcium ions, calcium lactate exhibits grater effects on gelation strength than calcium chloride. The temperature at the onset of gelation and the gelation rates showed an increase with the increasing of gellen and calcium ions content. At the same calcium ions concentration, the evolution of modulus storage (G′), gel temperature and rate are higher with the addition of calcium lactate than using calcium chloride. Our study indicated exponential relationship between gelling temperature (gelling rate) and calcium concentration.

Abstract: Experimental research on calcium alginate fibers thermal degradation and flame retardancy under catalysis of metallic salts was done by limiting oxygen index (LOI), scanning electron microscopy (SEM), and thermogravimetric analysis (TG) methods. LOI results show that with increasing calcium ions content, the flame retardant properties of the calcium alginate fibers improves further. The residues of calcium alginate fibers gradually retained fiber shape and on the surface of the residues the holes reduced, with the calcium ion content increasing. TG indicates temperature at maximum rate of weight loss (T-max) was clearly shifted from 246 °C for alginic acid fibers to 244°C, 236°C, 208°C, 205 °C and 203°C (SCa-1-1# calcium alginate fibers, SCa-2-2# calcium alginate fibers, SCa-3-3# calcium alginate fibers, SCa-4-4# calcium alginate fibers, SCa-5-5# calcium alginate fibers), respectively. The thermal degradation residues at 1000°C for different calcium alginate fibers are 13.7%, 16.1%, 17.2%, 18.2%, 18.4%, 19.2%, separately. Further discussion of the combustion process and flame retardant mechanism is presented.