Aqueous Calcium Research Articles

Properties of iron-containing nanohydroxyapatite-based composites

The paramagnetic properties of compounds resulting from the synthesis of nanohydroxyapatite in the presence of Fe(III) ions have been studied by electron paramagnetic resonance, Mossbauer spectroscopy, and magnetochemistry. Based on the obtained results on the mechanism of the reaction between an orthophosphoric acid solution and an aqueous calcium hydroxide suspension, we have found conditions for incorporating Fe(III) impurity ions into hydroxyapatite. We have studied samples differing in the sequence in which reagents were mixed and in hydroxyapatite crystallite formation conditions. It has been shown that, in all instances, the composition and properties of the iron-containing phases in the composites depend significantly on both synthesis and heat treatment conditions.

전산유체역학을 이용한 이산화탄소 광물 탄산화 반응기 분석: 용액 내 고체 반응물 교반 향상을 위한 내부 구조 설계

산화 칼슘 수용액을 통해 이산화탄소를 포집하는 수성 광물 탄산화 공정은 안정적으로 이산화탄소를 고립시킬 뿐아니라 생성물의 부가 가치를 기대할 수 있는 대표적인 CCU (Carbon Capture & Utilization) 기술이다. 이 공정의 핵심은 고체 반응물인 산화칼슘의 용해 속도를 최대로 높이는 것인데, 이를 위해 반응기 전체에 고체 반응물이 균일하게 분포되도록 혼합하는 적절한 반응기의 설계가 필요하다. 본 논문에서는 하루에 40ton의 이산화탄소 포집이 가능한 파일럿 규모의 광물 탄산화 반응기를 대상으로, 반응기의 내부 구조 설계에 따라 고체 반응물의 분산도가 어떻게 변하는 지에 대해 전산 유체 역학적 모델링(Computational Fluid Dynamics (CFD) modeling)을 통해 연구하였다. 교반 탱크 반응기(stirred tank reactor) 형태를 기반으로 외부 구조는 고정한 상태에서 교반기의 종류/갯수/지름/유격/회전 속도, 칸막이의 높이/너비를 변수로 선정하여 다양한 조합의 경우(case)들을 해석하였다. 각 설계 변수에 대한 민감도를 분석함 으로써 각 변수의 영향을 파악하고, 중요한 변수를 판별할 수 있었다. 동시에 고체 부피 분율(solid volume fraction)의 높이 방향 표준 편차가 0.001에 가까운 균일한 분포를 만들 수 있는 내부 설계안을 제안하였다.

Experimental determination of barite dissolution and precipitation rates as a function of temperature and aqueous fluid composition

Barite dissolution and precipitation rates were investigated in closed system reactors, in which total aqueous NaCl concentrations ranged from 0 to 1.5molal, pH from 2 to 9, and temperature from 25 to 90°C. Measured barite dissolution and precipitation rates exhibited a reaction order of 0.2 and 1, respectively, with respect to the barite saturation state. Although these different reaction orders suggest distinctly different mechanisms for dissolution and precipitation, the rates for both processes approach equilibrium with a similar slope on a rate versus saturation state plot, consistent with the concept of micro-reversibility. Barite dissolution rate constants increase as a linear function of the square root of ionic strength but vary only slightly with pH. The dissolution rate dependence on temperature is consistent with an activation energy of 25± 2kJmol−1. Barite dissolution and precipitation rates are not significantly affected by the presence of aqueous calcium, magnesium or strontium. The rates measured in the study were generated in fluids similar to those found in sedimentary basins, ocean floor sediments and oil field reservoirs so the data may provide close estimates for the reactivity of barite during a variety of natural and industrial processes.

Governing Principles of Alginate Microparticle Synthesis with Centrifugal Forces.

A controlled synthesis of polymeric particles is becoming increasingly important because of emerging applications ranging from medical diagnostics to self-assembly. Centrifugal synthesis of hydrogel microparticles is a promising method, combining rapid particle synthesis and the ease of manufacturing with readily available laboratory equipment. This method utilizes centrifugal forces to extrude an aqueous polymer solution, sodium alginate (NaALG) through a nozzle. The extruded solution forms droplets that quickly cross-link upon contact with aqueous calcium chloride (CaCl2) solution to form hydrogel particles. The size distribution of hydrogel particles is dictated by the pinch-off behavior of the extruded solution through a balance of inertial, viscous, and surface tension stresses. We identify the parameters dictating the particle size and provide a numerical correlation predicting the average particle size. Furthermore, we create a phase map identifying different pinch-off regimes (dripping without satellites, dripping with satellites, and jetting), explaining the corresponding particle size distributions, and present scaling arguments predicting the transition between regimes. By shedding light on the underlying physics, this study enables the rational design and operation of particle synthesis by centrifugal forces.

Flexible Asymmetric Encapsulation for Dehydration-Responsive Hybrid Microfibers.

A new class of smart alginate microfibers with asymmetric oil encapsulates is introduced. These fibers are produced by injecting an aqueous alginate solution into an outer aqueous calcium chloride solution to form alginate fibers, which are asymmetrically loaded with oil entities through eccentrically aligned inner capillaries. The fiber morphology and its degree of asymmetry can be tuned via altering the size, location, and frequency of the oil encapsulates. These asymmetric fibers reveal significant potential for applications where conventional symmetric fibers fail to perform. It is shown how asymmetric oil-encapsulated fibers can become dehydration-sensitive, and trigger the release of encapsulates if their hydration level drops below a critical value. It is also shown how the triggered response could be switched off on demand by stabilizing the oil encapsulates. The capability of asymmetric fibers to carry and release multiple cargos in parallel is demonstrated. The fibers loaded with equal-sized spheres are more asymmetric than those containing unequal drops, have a higher tensile strength, and show better potential for a triggered response.

The fabrication technique for hollow gel microparticles using microbubble templates

Hollow gel microparticles with shells composed of functional polymer gels are expected to be useful in the production of food additives or anti-reflective films for liquid crystal displays. However, few studies have addressed methods for the simple and efficient production of hollow gel microparticles. Hollow gel microparticles would be expected to find widespread applications if they could be fabricated more easily. In this study, we succeeded in fabricating hollow gel microparticles simply by atomizing a gas-supersaturated aqueous sodium alginate solution into aqueous calcium chloride solution. The gas-supersaturated aqueous sodium alginate solution was prepared by gas pressurization; following a rapid pressure decrease, the excess dissolved gas appeared as microbubbles in the atomized droplets. When the atomized droplets, with encapsulated microbubbles, came into contact with the aqueous calcium chloride solution, the droplets were converted to a gel by ionic crosslinking between sodium alginate and calcium ions, and any remaining bubbles were trapped inside the droplets. With this method, we can fabricate calcium alginate hollow gel microparticles of less than 100 μm with multi-voids. Furthermore, these hollow structures can be controlled by changing the compression pressure, which changes the amount of dissolved gas in the liquid.

Combined Percutaneous Iliosacral Screw Fixation With Sacroplasty Using Resorbable Calcium Phosphate Cement for Osteoporotic Pelvic Fractures Requiring Surgery

Osteoporotic sacral fractures, including acute and chronic insufficiency fractures, are increasing in frequency and present a number of management problem. Many of these patients are treated nonoperatively with relative immobility (eg, bedrest, wheelchair, or weight-bearing restrictions) and analgesics, which likely make the osteoporotic component worse. Surgery in this patient population may be desirable in some cases with the goals of improving mobility, relieving pain, and healing in an aligned position while minimizing deformity progression. However, internal fixation of the osteoporotic pelvis can be difficult. Large unicortical lag screws are the workhorse of posterior pelvic fixation, and yet fixation in cancellous bone corridors of an osteoporotic sacrum seems unlikely to achieve optimal fixation. As a result, the operative management and clinical results of these difficult injuries may not be uniformly successful. The authors present a technique for treating osteoporotic patients with a sacral fracture when operative treatment is indicated using percutaneous screw fixation combined with screw augmentation using a resorbable calcium phosphate bone substitute or "cement." The guide wire for a 7.3-mm or other large cannulated lag screw is fully inserted along the desired bony sacral corridor as is standard. The lag screw is then inserted over the wire to the depth where cement is desired. The guide wire is removed, and the aqueous calcium phosphate is injected through the screw's cannulation. For acute fractures, cement was applied to the areas distant to the fracture; whereas in insufficiency fractures, the cement was inserted along most of the screw path. The guide wire then can be reinserted and the lag screw fully inserted. The rationale for using these 2 modalities is their synergistic effect: the cannulated screw provides typical screw fixation and also a conduit for cement application. The cement augments the lag screw's purchase in osteoporotic bone, enhancing fixation strength. The authors propose that combining percutaneous screw fixation with calcium phosphate augmentation may provide an improved biomechanical environment for healing of these difficult fractures that might translate into earlier mobility, better pain control, and improved outcomes.

Recovery of Calcium Phosphates from Composted Chicken Manure

To recover phosphorus from composted chicken manure, a batch method with aqueous HNO3, HCl and H2SO4 was used to examine the elution behavior of the aqueous calcium and phosphate contained in the manure. Since the main components in manure are Ca2+ and K+ along with PO4 3- and those ions can be dissolved using an acidic eluate, it was expected that most of the aqueous Ca2+, K+ and PO4 3- could be obtained via the elution. Therefore, it seemed plausible that the removal of the aqueous K+ obtained by the elution of composted chicken manure would result in the formation of calcium phosphates. If calcium phosphates are formed, they can be used for phosphate rock, which also consists of various calcium phosphates. When using 0.1 mol/L HNO3, HCl or H2SO4, the elution behavior of the PO4 3- was not dependent on the acids. However, 0.1 mol/L H2SO4 was not sufficient for the elution of Ca2+, probably due to the precipitation of the calcium sulfate. The eluted amount of K+ using 0.1 mol/L HNO3 was lower than that using 0.1 mol/L of either HCl or H2SO4. Since the poor elution of K+ should enrich the concentrations of Ca2+ and PO4 3- in the acidic aqueous solution after the elution, it was suggested that aqueous HNO3 would be suitable as an eluate in the present system. After the elution of the composted chicken manure, when 0.1 mol/L HNO3 was used to adjust the solution pH of the acidic aqueous solution to greater than 6, Ca2+ and PO4 3- were precipitated, but K+ was not. The precipitate was calcium hydroxyapatite, one of the typical components of phosphate rock, which showed that composted chicken manure could be replaced phosphate rock as a new source of phosphorus.

Use of Smokeless Tobacco in Medical Students and Hypertension

Tobacco is being used in various forms including cigarette, shisha, cigar and bidi smoking and smokeless tobacco. Smokeless tobacco constitutes various forms of tobacco i-e paan/ betel quid, tobacco with lime, naswar, gutka, qiwam, tobacco tooth powder, minpuri, areca nut (supari) [1,2]. Qiwam consists of thick paste of boiled tobacco mixed with powdered spices such as saffron, cardamom, aniseed and aroma, while paan/ betel quid is a mixture of the leaf of the Piper betle vine, aqueous calcium hydroxide paste [slaked lime] [1,2]. Smokeless tobacco is commonly used in South Asia, where it has become part of South Asian culture. Furthermore, South Asia is a major producer and exporter of tobacco and over one-third of tobacco consumed in South Asia is smokeless [2]. Traditional forms like, tobacco with lime; betel quid and tobacco tooth powder are commonly used among South Asian population [2]. With the passage of time, tobacco usage is increasing not only among men but also among women of reproductive age, children, teenagers, medical and dental students [2].

Tensile strengths of flocculated compacted unsaturated soils

Flocculating agents can be introduced to soils through a number of natural or anthropogenic processes. This paper investigates the effect of flocculant addition (aqueous calcium chloride (CaCl2)) on the tensile strengths of two soils of differing flocculation susceptibility. Tensile strengths were found using the Brazilian (direct splitting) test for a range of suction values. A decrease in tensile strength was found for a soil with high clay content, which was consistent with previous findings in the literature. However, the strength of the soil with lower clay content unexpectedly increased. Results were interpreted using the extended Mohr–Coulomb (EMC) yield criterion fitted to data above the residual suction value. Changes in EMC parameters were used to infer changes in material behaviour on calcium chloride addition. Results have important implications for the design of geotechnical structures, for example engineered cover systems, exposed to flocculating conditions.

Fabrication and Evaluation of a Bioactive Sr–Ca–P Contained Micro-Arc Oxidation Coating on Magnesium Strontium Alloy for Bone Repair Application

Considering the compatibility between degradation and bioactivity of magnesium-based implants for bone repair, micro-arc oxidation is used to modify the magnesium alloy surface in aqueous electrolytes, allowing strontium, calcium, and phosphorus to be incorporated into the coating. The thickness, composition, morphology and phase of this Sr–Ca–P containing coating are characterized by scanning electron microscopy equipped with energy dispersive X-ray spectrometer and X-ray diffraction. The in vitro and in vivo degradation of the coating is evaluated by immersion test, electrochemical test and implantation test. Moreover, the cytocompatibility is tested with osteoblast cell according to ISO 10993. The results show that Sr, Ca and P elements are incorporated into the oxide coating, and a refined structure with tiny discharging micro-pores is observed on the surface of the coating. The Sr–Ca–P coating possesses a better corrosion resistance in vitro and retards the degradation in vivo. Such coating is expected to have significant medical applications on orthopedic implants and bone repair materials.

Simulation of calcium acetylide and acetylene production

Abstract Design simulation of a reactor for acetylene production from calcium acetylide and its purification in the gaseous phase is presented. Simulations were performed using the program ASPEN+ which is a very flexible and useful tool for the simulation and optimization of various types of chemical technologies including gas-liquid-solid systems. The first step of the acetylene synthesis, based on coal as the raw material, is the production of calcium acetylide. This substance is obtained from coke and limestone in an electric arc furnace at elevated temperatures. Raw materials used in this process contain relatively large amounts of impurities that are converted and entrapped in the desired product of the above reaction. Some of the impurities, e.g. metallic iron or its alloys, can be separated easily. However, most of the other elements present in the form of their compounds with calcium remain a part of “technical grade” calcium acetylide. Acetylene is commercially produced by the reaction of “technical grade” calcium acetylide with water under controlled reaction conditions in an inert atmosphere. Depending on the purity of calcium acetylide used, the produced raw acetylene contains a variety of admixtures that lower its quality. As a consequence, prior to its expedition to the customer, raw acetylene should be submitted to a down-stream processing that consists of the separation of basic and acidic pollutants present in acetylene by absorption. The final processing step is adsorption and/or freezing-out of water vapor from the purified acetylene stream. Besides acetylene, the reaction of calcium acetylide with an excess of water provides aqueous calcium hydroxide. In order to commercialize this byproduct, the content of water in the mixture should be lowered to the required level. In this contribution, development of a model of calcium acetylide and acetylene production as well as the simulation of these processes in ASPEN+ are presented. Simulation results of a realistic production line model correlate very well with the actual data from the technology used in Fortischem, a.s., Novaky, Slovakia.

Effect of CaO Treatment on Quality Characteristics and Storage of Mulberry (Morus alba L.) Fruits in Yecheon

The effects of aqueous calcium oxide (CaO) treatment on the quality characteristics and shelf life of mulberry (Morus alba L.) were investigated. Mulberry fruits were immersed in 0, 0.5, 1, and 2 g·L -1 CaO solutions for 0, 1, 3, 6, and 12 min. Mulberries were then rinsed with potable tap water for 1 min and stored at -1℃ for 14 days. CaO treatment was effective at promoting the retention of titratable acid, pH, and ascorbic acid as well as total flavonoid contents. CaO concentration and treatment time were significant factors affecting the sensory qualities of the fruits, including off-odor, flavor, and texture. For shelf life determinations, the total bacterial count was reduced by CaO treatment so that the samples treated with 1 g·L -1 CaO for 12 min had bacterial levels at 14 days comparable to those of the control at 4 day, and no coliform group was detected after CaO treatment. These results indicate that calcium oxide treatment is a promising approach for the preservation of mulberry fruit.

Hot water treatment in combination with calcium ascorbate dips increases bioactive compounds and helps to maintain fresh-cut apple quality

Fresh-cut ‘Braeburn’ apple slices were dipped into cold water (4°C for 2min) or hot water (HWT, 48°C or 55°C for 2min) followed by dips into 0 or 6% w/v aqueous calcium ascorbate (CaAsc, 2min, 0°C) and stored in air up to 28 d at 4°C. Microbial counts, changes in browning and sensory acceptance were determined to indicate changes in quality. Changes in antioxidant levels were measured using free radical scavenging activity (DPPH), reducing activity (FRAP), ascorbic acid content (AA) and polyphenolic content (by HPLC). CaAsc dips had a strong impact reducing the browning through increasing the flesh luminosity and hue angle. 6% CaAsc in fresh-cut apples extended the overall acceptability from less than 7 d to 14 d. Immediately after CaAsc treatment, AA content was 5 fold higher (0.25–1.25gkg−1) than those not dipped into CaAsc. However, the combination of HWT treatments and CaAsc dips led to seven fold increased levels of AA inside the apple tissue (0.25–1.85gkg−1) and consequently increased the antioxidant activity. HWT did not increase the AA content when not combined with CaAsc dips. The HWT CaAsc dip extended the overall acceptability to 21 d compared to 14 d for samples not heated but dipped into CaAsc. Shelf life was ultimately limited by sensory quality. At day 28, total plate counts were reduced from 5.3logcfu/g (untreated slices) to 4.6logcfu/g in the 6% CaAsc dips and further to 3.9logcfu/g with the combination of HWT and CaAsc dip. Changes in the content of phenolic compounds with time, HWT and CaAsc dip were generally not significant except for slightly increased quercetin and phloridzin levels and decreased p-coumaric and procyanidins over time. The combination of HWT at 48°C for 2min followed by 6% CaAsc dip would be best for preserving the eating quality of apple slices.

Strategies for calcium sulphate scale control in hydrometallurgical processes at 80 °C

In order to control calcium sulphate scale formation in hydrometallurgical processes, strategies for lowering the concentration of soluble calcium in simulated solutions at 80°C (conditions in the Pressure Acid Leach thickener tank) below the solubility limit of calcium sulphate at 140°C (conditions in the medium pressure slurry pre-heater) were investigated. Reagents known to form insoluble products with calcium such as: Na2CO3, H2C2O4, Na2C2O4 and Na3PO4, were investigated and the kinetics and selectivity of the precipitation process were evaluated as well. Both Na2CO3 and Na2C2O4 successfully and selectively lowered aqueous calcium concentration below the solubility limit at 80°C at 1:1 stoichiometric ratios with respect to calcium, while excess of H2C2O4 was required in order to achieve advanced calcium removal; Na2CO3 in a 2:1 ratio reached even lower values, below the solubility limit at 140°C. Na3PO4 in a 1:1 ratio proved highly inefficient, removing only 67% of the total calcium.

A Multi-Analytical Approach for the Evaluation of the Efficiency of the Conservation-Restoration Treatment of Moroccan Historical Manuscripts Dating to the 16th, 17th, and 18th Centuries.

The most critical steps during the conservation-restoration treatment applied in Moroccan libraries are the deacidification using immersion in a saturated aqueous calcium hydroxide (Ca(OH)2) solution and the consolidation of degraded manuscripts using Japanese paper. The present study aims to assess the efficiency of this restoration method using a multi-analytical approach. For this purpose, three ancient Arabic Moroccan manuscript papers dating back to the 16th, 17th, and 18th centuries were investigated to characterize the paper support and make a comparative study between pre-restoration and post-restoration states. Three structural and molecular characterization techniques including solid-state nuclear magnetic resonance spectroscopy on (13)C with cross-polarization and magic-angle spinning nuclear magnetic resonance ((13)C CP-MAS NMR), attenuated total reflectance Fourier transform infrared spectroscopy (ATR FT-IR), and X-ray diffraction (XRD) were used to elucidate the cellulose main features, to identify the inorganic composition of the papers, and to study the crystallinity of the samples. Inductively coupled plasma atomic emission spectrometry (ICP-AES) allowed us to obtain a qualitative and quantitative characterization of the mineral fillers used in the manufacturing of the papers. Scanning electron microscopy coupled to energy dispersive spectrometry (SEM-EDS) ascertained the state of conservation of the different papers and helped us to study the elemental composition of the samples. After restoration, it was shown that the deacidification improved the stability of papers by providing an important alkaline buffer, as demonstrated using FT-IR and energy dispersive spectrometry (EDS) results. However, XRD and ICP-AES did not confirm the pertinence of the treatment for all samples because of the unequal distribution of Ca on the paper surface during the restoration. The consolidation process was studied using SEM analysis; its effectiveness in restoring torn areas was found to be significant.

Experiments on Integral and Local Crystallization Fouling Resistances in a Double-Pipe Heat Exchanger With Wire Matrix Inserts

Wire matrix inserts are used in different applications of tubular heat exchangers to improve tube side heat transfer. They have also been used to suppress fouling in crude oil refining services. In this paper it is investigated whether the changed hydrodynamic and thermal conditions when applying wire matrix inserts have an impact on crystallization fouling compared to the plain tube. With a turbulent flow, at Reynolds number of 9877 and an inlet temperature of 42°C, fouling tests with an aqueous calcium sulfate solution for two wire matrix inserts with a different packing density were carried out and compared with a plain tube. Integral and local measurements of the fouling were performed. The experiments were realized in a double-pipe heat exchanger with a pipe length of 2000 mm. The integral fouling resistances between the inserts and the plain tube showed no significant difference, whereas major differences of the local fouling resistances were observed. Compared to the plain tube, the inserts showed an increased heat transfer up to a maximum of 35% but also a significantly increased pressure drop. Fouling on the inserts themselves, which was observed optically, is the possible explanation for this behavior.

Control of biomimetic hydroxyapatite deposition on polymer substrates using different protein adsorption abilities

We recently developed a system for coating polystyrene (PS) substrates with hydroxyapatite (HAp) by utilizing serum protein adsorption layers as mediators to induce the heterogeneous nucleation of HAp in simulated body fluids (SBFs). In this study, the selective deposition of HAp on polymer substrate surfaces with different protein adsorption abilities was investigated using PS and poly(methyl methacrylate) (PMMA). Atomic force microscopic observations and the results of a quantitative analysis using a quartz-crystal microbalance (QCM) revealed that the amounts of proteins such as human serum albumin (HSA) and human immunoglobulin G (hIgG) adsorbed on PS substrate surfaces were markedly greater than those on PMMA substrate surfaces. A markedly larger amount of HAp was deposited on protein-treated PS substrate surfaces than on PMMA substrate surfaces, reflecting protein adsorption to polymers. We also revealed that the deposition of HAp on protein-adsorbed PS substrate surfaces was enhanced by aqueous calcium chloride treatments before immersion in 1.5SBF. In the case of 2.5M calcium chloride treatment, these surfaces were completely covered with deposits.

Reversible absorption of SO2 from simulated flue gas by aqueous calcium lactate solution

The capture of SO2 by recyclable absorbents has drawn much attention all over the world. In this work, it was found that aqueous calcium lactate (CaL2) solution can be used as a recyclable absorbent for the capture of SO2. The solution shows high SO2 absorption capacities up to 24.8 g SO2/kg absorbent at 40 °C. The effects of temperature, excessive lactic acid and CaL2 concentration on the absorption of SO2, the desorption of SO2, and the reuse of aqueous CaL2 solution were systemically studied. Furthermore, the difference between CaL2 method and traditional calcium method was discussed. Compared with traditional calcium method, there are some advantages, such as regeneration of absorbent, recovery of SO2 and reduction of CaSO4. This work suggests that aqueous CaL2 solution, which can be obtained at quite low cost, is a promising recyclable absorbent in the process of desulfurization of flue gas.

Reactive transport of CO2-saturated water in a cement fracture: Application to wellbore leakage during geologic CO2 storage

Time dependence of fluid flux up a leaky well has significant implications for the feasibility of geologic CO2 storage. We present laboratory experiments that study various boundary conditions, fluid fluxes, and residence times to understand the range of behavior in fractured cement cores. Carbonic acid progressively reacts with cement by dissolving phases which neutralize the acid and liberate calcium ions. This dissolution does not increase the aperture of the fracture, due to the formation of an amorphous silicate residue. Where aqueous calcium concentration and pH are sufficiently high calcium carbonates become insoluble and precipitate in the open fracture. When the driving force for fluid flux is a constant pressure differential precipitation leads to a progressive reduction in fluid flux and the development of self-limiting behavior. With sufficient residence time precipitation leads to sealing of the leaky well.