Compleximetric determination of calcium in impure calcium carbonate and limestone

Calcium is determined in impure calcium carbonate and limestone samples by titrating with 0.01 M disodium EGTA at pH 12 in the presence of at least 0.6 mg of magnesium and a maximum of 500 μg of iron(III), using a pH 12.5 sodium hydroxide-potassium cyanide-sodium sulfide buffer and Calcon indicator. The results of such titrations are compared with those obtained by titrating at pH 10 the calcium perchlorate solutions derived from calcium oxalate, and with those of a modified LEWIS AND MELNICK method. The results for magnesium (% MgO) obtained by difference are in fair agreement. Magnesium can be titrated compleximetrically as magnesium perchlorate, but the reagent blank must be determined.     

Polymer vesicles as microreactors for bioinspired calcium carbonate precipitation

Giant polymer vesicles made by electroformation have been shown to encapsulate salts up to concentrations of about 10 mM. The impermeability of these "polymersomes" to calcium ions is demonstrated by the use of fluorescent probes dedicated to calcium analysis. Permeability to calcium ions can be triggered by the addition of calcimycin, an ionophore molecule that is able to transport cations selectively through the membrane. As a result, we show that the mineralization of calcium carbonate can be induced within the polymersomes, which were previously loaded with carbonate ions. This is a further step toward the use of polymersomes as microreactors and the study of mineralization schemes, including biomimetic ones, in confined environments.     

表面活性剂对纳米CaCO3形貌的调控

分别在AOT／异辛烷／水、CTAB／环己烷／水和OP-10／环己烷／水三种不同的反胶束体系中合成出具有不同形貌的纳米碳酸钙，讨论了表面活性剂的类型以及溶剂热过程对纳米碳酸钙的形貌及尺寸的影响．     

Separation and determination of radiostrontium in calcium carbonate matrices of biological origin

Radiostrontium is concentrated in the shells of mollusks and other animals due to the isomorphic substitution of strontium for calcium in the calcium carbonate shell matrix. Radiochemical separation of strontium from such matrices is difficult because of the chemical similarity between strontium and calcium. This paper describes a technique using a commerically-available, solid-phase extractant to separate Sr-89 and Sr-90 from high concentrations of Ca²⁺. The extractant removes Sr(NO₃)₂ from acidic nitrate media, and strontium activities are determined via conventional -counting techniques. This method has been used to process mollusk shells collected from contaminated reactor cooling ponds at the Savannah River Site and Chernobyl Nuclear Power Plant.     

Quick method for determination of equilibrium temperature of calcium carbonate dissociation

A quick method for determination of equilibrium temperature of high temperature reactions, which is inexpensive and suitable for small industrial laboratories, is reported. Reaction of high temperature dissociation of calcium carbonate is used as example for quick method application. The method is based on calorimetric measurement, Hess Law, and thermodynamic calculations. The calibrated calorimeter is used to determine enthalpy change for reactions CaCO₃(s)?+?HCl(l), Ca(s)?+?2HCl(l), and CaO(s)?+?2HCl(l). By application of Hess??s energy cycle, enthalpies of formation of calcium carbonate and calcium oxide were determined. Acquired results were used to calculate enthalpy change for carbonate dissociation reaction. Calculated enthalpy change value was used for free energy change in dependence of temperature and also for equilibrium constant in dependence of temperature calculation using equations derived from basic thermodynamic equations. Using this method, equilibrium temperature for calcium carbonate dissociation reaction is found to be equal to 1154.14?K, which confirms accuracy of the method.     

Quantitative determination of binary and tertiary calcium carbonate mixtures using powder X-ray diffraction

The ability to determine the calcium carbonate polymorphic ratio of calcite, aragonite and vaterite in a mixture is important for a variety of applications, particularly the fields of biomineralisation and crystal engineering. Raman spectroscopy and powder X-ray diffraction were used to quantitatively determine the polymorphic composition of both binary and tertiary mixtures of calcium carbonate. It was found that the quantitative detection limits of powder X-ray diffraction were superior to both Raman and infrared spectroscopy.     

Atomic absorption spectrometric determination of copper in calcium carbonate scale and carbonate rocks by direct atomization of solid samples

Powdered samples (1 mg) are mixed with 1 mg of powdered graphite and copper is determined by atomic absorption spectrometry in a miniature graphite cup placed in a graphite crucible. Optimum conditions were drying at 200 °C (30 s), ashing at 900 °C (30 s), atomizing at 2700 °C (15 s) and cleaning at 2800 °C (10 s). Samples were powdered to 1–10 μm particle size. Magnesium, manganese and iron did not interfere. The effect of calcium carbonate was eliminated by the graphite addition. Results for copper (0.5–5 μg g^?1) in the scale and rocks agreed well with values obtained for dissolved samples. Relative standard deviations (n=10) were 4.9% for 1.2 μg g^?1 copper and 14.8% for 0.577 μg g^?1.     

A thermodynamic solution model for calcium carbonate: Towards an understanding of multi-equilibria precipitation pathways

Thermodynamic solubility calculations are normally only related to thermodynamic equilibria in solution. In this paper, we extend the use of such solubility calculations to help elucidate possible precipitation reaction pathways during the entire reaction. We also estimate the interfacial energy of particles using only solubility data by a modification of Mersmann’s approach. We have carried this out by considering precipitation reactions as a succession of small quasi-equilibrium states. Thus possible equilibrium precipitation pathways can be evaluated by calculating the evolution of surface charge, particle size and/or interfacial energy during the ongoing reaction. The approach includes the use of the Kelvin’s law to express the influence of particle size on the solubility constant of precipitates, the use of Nernst’s law to calculate surface potentials from solubility calculations and relate this to experimentally measured zeta potentials. Calcium carbonate precipitation and zeta potential measurements of well characterised high purity calcite have been used as a model system to validate the calculated values. The clarification of the change in zeta potential on titration illustrates the power of this approach as a tool for reaction pathway prediction and hence knowledge based tailoring of precipitation reactions.     

The nature of europium ion in carbonate solution and polarographic determination of micro amounts of europium

The nature of the complex europium carbonate ion in concentrated carbonate solution was studied polarographically. A polarographic method for the determination of micro amounts of europium ion in the presence of diverse ions (and especially lanthanides) was developed.     

The flame photometric determination of calcium in phosphate,carbonate, and silicate rocks

A flame photometric method of determining calcium in phosphate, carbonate, and silicate locks has been developed Aluminum and phosphate interference was overcome by the addition of a large excess of magnesium. The method is rapid and suitable for routine analysis Results obtained are within ± 2% of the calcium oxide content.     

Control of calcium carbonate particle size and shape by precipitation from CTAB/alcohol/hexadecane mixtures

 When used as a precipitation media, emulsified mixtures of cetyltrimethylammonium bromide/n-butanol (E), hexadecane (O) and water (W), controls the size and shape of calcium carbonate particles. Monodisperse 2-micron spherical-calcite particles were obtained in a water-rich region of the mixture, while 2-micron rhombohedral-calcite particles with an aspect ratio near one were obtained in the middle region of the mixture. Replacing n-butanol with i-butanol led to consistent formation of monodisperse spherical particles, while using n-propanol in place of n-butanol limited the number of spherical particles produced in the water-rich region. Received: 17 March 1997 Accepted: 2 May 1997     

Use of sulphide precipitation in separation and determination of molybdenum(V)

Molybdenum(V) is quantitatively precipitated as sulphide (99.7%) from 0.1 M At hydrochloric acid without formation of molybdenum blue and without need for a long digestion. Precipitation is more complete and co-precipitation less than with Mo(VI) sulphide. The precipitate can also be used directly for gravimetric estimation. In the presence of EDTA, molybdenum(V) sulphide is not precipitated from 0.1 M hydrochloric acid and can be separated from copper, bismuth, antimony and tin sulphides and determined cerimetrically in presence of the EDTA.     

Obtaining calcium carbonate in a multiphase system by the use of new rotating disc precipitation reactor

Rotating disc reactor (RDR) was constructed to conduct gas–liquid–solid reactions with controlled reagent transfer from gaseous to liquid phase. The concept is based on continuous formation of thin liquid films at a surface of rotating discs where the mass transfer proceed in diffusion–convective way. The reactor was employed to run precipitation reaction of CaCO₃ via carbon dioxide absorption in lime slurry. During each reaction pH changes and Ca²⁺ concentration in time were measured. Disc rotations and gas flows were changed during the experiment and their influence on the obtained CaCO₃ powders has been examined and fully discussed.     

Effects of microscale calcium carbonate and nanoscale calcium carbonate on the fusion,thermal, and mechanical characterizations of rigid poly(vinyl chloride)/calcium carbonate composites

A Haake torque rheometer equipped with an internal mixer has been used to study the influence of microscale calcium carbonate (micro‐CaCO₃) and nanoscale calcium carbonate (nano‐CaCO₃) on the fusion, thermal, and mechanical characteristics of rigid poly(vinyl chloride) (PVC)/micro‐CaCO₃ and PVC/nano‐CaCO₃ composites, respectively. The fusion characteristics discussed in this article include the fusion time, fusion temperature, fusion torque, and fusion percolation threshold (FPT). The fusion time, fusion temperature, and FPT of rigid PVC/calcium carbonate (CaCO₃) composites increase with an increase in the addition of micro‐CaCO₃ or nano‐CaCO₃. In contrast, the fusion torque of rigid PVC/CaCO₃ composites decreases with an increase in the addition of micro‐CaCO₃ or nano‐CaCO₃. The results of thermal analysis show that the first thermal degradation onset temperature (T_onset) of rigid PVC/micro‐CaCO₃ is 7.5 °C lower than that of PVC. Meanwhile, the glass‐transition temperature (T_g) of rigid PVC/micro‐CaCO₃ is similar to that of PVC. However, T_onset and T_g of PVC/nano‐CaCO₃ composites can be increased by up to 30 and 4.4%, respectively, via blending with 10 phr nano‐CaCO₃. Mechanical testing results for PVC/micro‐CaCO₃ composites with the addition of 5–15 phr micro‐CaCO₃ and PVC/nano‐CaCO₃ composites with the addition of 5–20 phr nano‐CaCO₃ are better than those of PVC. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 44: 451–460, 2006     

碳酸钙微米球的制备与表征

采用醋酸钙和碳酸钠为原料,在反应温度为5℃和柠檬酸三钠质量百分浓度为15%的条件下,采用沉淀法合成出了粒度为1～4μm、分散性好的球形碳酸钙粉体。用扫描电子显微镜(SEM)、X射线衍射仪(XRD)、红外光谱仪(IR)、原子力扫描探针显微镜(ASPM)、光学显微镜、粒度分析仪等对样品进行了表征,并用光学显微镜跟踪考察了碳酸钙微米球的形成过程。结果表明,碳酸钙微米球是由大量纳米级颗粒组装而成。     

Indirect determination of chloride and carbonate by reversed flow-injection analysis coupled with atomic-absorption spectrometry and in-line preconcentration by precipitation

Chloride and carbonate are determined indirectly by reversed flow-injection analysis with preconcentration by precipitation. The anions are precipitated in a Tygon tube containing glass beads and connected to an atomic-absorption spectrophotometer, and are then dissolved by suitable reagents. Chloride is precipitated as silver chloride, which is then dissolved with ammonia, sodium thiosulphate or potassium cyanide solution. Carbonate is precipitated as calcium carbonate, which is dissolved with hydrochloric acid. The response of the system has been optimized with respect to concentration, precipitation time, solution flow-rate and other AAS variables. Detection limits are 3 × 10⁻⁷ and 5 × 10⁻⁷M for chloride and carbonate, respectively, with thiosulphate and hydrochloric acid as the dissolution agents.     

Fabrication and properties of poly(propylene carbonate)/calcium carbonate composites

Composites of poly(propylene carbonate) (PPC) reinforced with micrometric and nanometric calcium carbonate particles were prepared via melt mixing followed by compression molding. The morphology and mechanical and thermal behaviors of the composites were investigated. Static tensile tests showed that the tensile strength, stiffness, and ductility of the composites tended to increase with increasing contents of micrometric calcium carbonate particles. This improvement in the tensile properties was attributed to good interfacial adhesion between the fillers and matrix, as evidenced by scanning electron microscopy examination. However, because of the agglomeration of calcium carbonate nanoparticles during blending, those composites with nanoparticles exhibited the lowest tensile strength. Thermogravimetric measurements revealed that the incorporation of calcium carbonate into PPC resulted in a slight improvement in its thermooxidative stability. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1806–1813, 2003     

X-ray absorption and diffraction analysis for determination of the amount of calcium carbonate and porosity in paper sheets

Papers are mostly made with lignocellulose and additives among which calcium carbonate has a primarily importance. Calcium carbonate as a filler provides specific properties to the paper like brightness, porosity, etc. Because of low retention, calcium carbonate remains in large quantities in the waste water when at the final stage, the paper is couched and pressed. It is therefore interesting to develop some methods to analyze in a nondestructive way the content of calcium carbonate that remains in the paper. We report in this article an X-ray study of paper sheets with the aim to determine not only the content of calcium carbonate in a nondestructive way but also the porosity of the paper sheets. The analysis is carried out in a quantitative way by refining the wide angle X-ray diffraction patterns using the Rietveld method and by modeling the absorption of the direct beam through paper sheets.     

Use of calcium carbonate – fumed silica mixtures as filler in polyurethane adhesives

Natural ultramicronized calcium carbonate and mixtures of fumed silica‐natural ultramicronized calcium carbonate are proposed as fillers of solvent based polyurethane (PU) adhesives. PU adhesive containing only calcium carbonate shows similar rheological, thermal, mechanical, surface and adhesion properties than the PU adhesive without filler. Addition of 90 wt% fumed silica +10 wt% calcium carbonate mixture to PU adhesive produced a similar performance than the PU adhesive containing only famed silica. The increase in the amount of natural calcium carbonate in respect to fumed silica in the filler mixture produced detrimental effect on the rheological and mechanical properties of the PU adhesives (in respect to those provided by the PU adhesive only containing fumed silica), although the surface and adhesion properties were not noticeably modified.     

Zeta potential measurement of calcium carbonate

The problem of scaling, which one finds in industrial heat exchangers, particularly in atmospheric coolers in nuclear power stations, depends on calcium carbonate deposits from fresh water. To better understand this phenomenon, we have examined the eventual implication of superficial electric charge of precipitated crystal nuclei. After a bibliographical review showing a fundamental divergence from already published results, this paper describes an experimental plant to measure the zeta potential in controlled conditions of thermodynamic equilibrium, oversaturation, or undersaturation of a CaCO(3)-H(2)O-CO(2) system taking into account simultaneously the three phases: gas, liquid, and solid. The zeta potential is measured by a crystalline-plug method with calcite or aragonite crystals. The potential cancels at thermodynamic equilibrium and is always negative for other conditions, in particular for oversaturation where the possibility of scaling exists. The analysis of these results suggests that the potential determining ions of the system are Ca(2+) and HCO(-)(3).