Precipitation Of Solid Phase Research Articles

Trace elements in the thermal groundwaters of Vulcano Island (Sicily)

The chemical concentrations of many trace elements that have never before been examined in Vulcano Island groundwaters are reported. Chemical data indicate that rock composition is not the only factor determining the metal content in the aqueous system. The observed concentrations depend mainly on: (1) the chemical composition of the host rocks; (2) the chemical–physical conditions of the weathering solution (temperature, acidity, redox conditions); (3) input of magmatic gases; (4) adsorption of metal ions on oxide particles, formation of soluble complexes and/or precipitation of solid phases. Chloride complexes in solution are of minimal significance for all elements with the exception of Cd, whereas carbonate complexes are important for Pb, UO2, Zn and Ni. Temperature and trace element distribution maps are also presented.

Softening and Melting Characteristics of Self-fluxed Pellets with and without the Addition of BOF-slag to the Pellet Bed.

When using 100% self-fluxed pellets in the blast furnace burden, top charged fluxes, especially the BOFslag, may cause irregularities in operation. The major reason has been theoretically attributed to the problematic slag formation in the furnace. As the melting of pellets is the first step of the slag formation process, the softening and melting properties of LKAB’s self-fluxed pellets with and without addition of fluxes are studied experimentally. The results show that the softening and melting properties of the two types of LKAB’s self-fluxed pellets are quite suitable for blast furnace operation. Contrarily, the melting-down characteristics of BOF-slag are variable and harmful to the slag formation under a reducing atmosphere. Adding 5% BOF-slag to the selffluxed pellets can considerably worsen the softening and melting properties of pellets. It can either increase the softening and melting temperature interval substantially or cause the precipitation of solid phases, mainly di-calcium silicates, in the slag. It is quite likely that the resulting slag will therefore become very viscous, even entirely blocking the melting down of the pellets up to a temperature 1 520°C.

Unseeded precipitation of calcium and magnesium phosphates from modified seawater solutions

Homogeneous (unseeded) nucleation and precipitation kinetics of Ca and Mg phosphates from modified seawater solutions with variable pH, Mg 2+, HCO 3 −, F −, and organic acid concentrations were investigated at 20°C. The induction period of nucleation and the composition of precipitated solid phases were determined as a function of saturation state (6–2000 with respect to octacalcium phosphate (OCP)), Mg 2+/Ca 2+ activity ratio (0–10) and solution pH (7.2–9.1). The addition of Mg 2+, HCO 3 −, F −, polycarboxylic, aromatic, and amino acids along with variations in pH has a weak effect on the nucleation kinetics of Ca–Mg phosphates in seawater solutions with a 35% salinity. Mg-bearing solutions produce an amorphous precipitate with a Ca : Mg : P molar ratio varying from 6.5 : 1 : 5 to 2.6 : 1 : 2.5 depending on ( a Mg 2+ / a Ca 2+ ) ratio. The precipitation of this amorphous phase in Mg-bearing solutions corresponds to the formation of a metastable hydrous Ca–Mg phosphate ((Ca,Mg) 4H(PO 4) 3· xH 2O) as a precursor of apatite which normally precipitates in Mg-free solutions. Spontaneous inorganic precipitation of Ca phosphate in most natural aquatic systems is kinetically impossible.

Influence of electromagnetic fields on the microstructure of precipitated calcium phosphate nanometric-Grains

Extremely low frequency electromagnetic fields (EM-ELF) of 3mT and 1300Hz in frequency were applied during spontaneous precipitation processes of calcium phosphates mixtures from their supersaturated aqueous solutions of calcium chloride and sodium phosphates. At the temperature of 37° C and at an aqueous solution with pH 7·4, for any total precipitation time ranging between 15min and 5h, the precipitated solid phase is formed by octacalcium phosphate (OCP) and by non-stoichiometric hydroxyapatite (ns-OHAp). The EM-ELF forces do not produce any effect in changing the chemical composition of the precipitated mixture. For any precipitation time the powders obtained under the action of the EM-ELF fields are characterised by a specific surface area values which are lower then the ones corresponding to samples obtained without EM-ELF applied by a percentage ranging between 18 and 36%. The crystallites sizes of both samples range between 10 and 20nm, but the EM-ELF samples are characterised by an average crystallites size which is about the 40% bigger than that of one concerning the specimen precipitated without any EM-ELF applied. Experimental evidences are given to support the hypothesis that the action of the EM-ELF fields is active at the beginning of the precipitation process when the calcium phosphate particles are still in a colloidal-like status. Critical discussions, based on a theory that the authors previously described, establish that the dimension of the particles on which the applied exogenous field can have an effect is of the order of 0·1nm.

Solid–liquid equilibria for solutions of binary globular‐protein mixtures

AbstractA theory of the van der Waals form is used to establish solid–fluid phase diagrams for aqueous solutions containing two kinds of globular proteins. Theory is based on a one‐fluid model that uses a composition‐dependent hard‐sphere diameter and a composition‐dependent solvent‐mediated effective temperature to represent protein solutions. The hard‐sphere reference equation of state is based on the model of Young that correlates computer simulations of fluid–solid coexistence curves for binary hard‐sphere mixtures. The attractive perturbation term uses the inverse‐power potential with variable exponent n. Based on the correlation of George and Wilson and Rosenbaum et al., the optimum range of effective temperature is determined for protein crystallization. For binary protein systems, as the size difference increases, the mutual solubility of unlike proteins declines sharply in the precipitated solid phase. The theoretical results obtained here may be useful for design of protein‐separation processes by crystallization.

Modelling of the Interaction Between an Engineered Clay Barrier and Concrete Structures in a Deep Storage Vault

AbstractThe degradation of concrete structures in a storage vault will release an alkaline plume influencing the geochemical evolution of clay engineered barriers or plugs. The studied configuration has a representative scale and is composed of a rectangular clay barrier interfaced on one side with a cement block and on the other side with an external granitic field. A clay model including major and accessory minerals is used; cement material is supposed to be made of portlandite and CSH minerals. The clay barrier and the cement block are assumed to be initially saturated and in equilibrium with their respective interstitial water. Diffusive transport of aqueous species coupled to chemistry is simulated in a one dimension space up to 10000 y. The feed-back of the porosity evolution on the transport properties is not taken into account. The temperature is supposed to be constant (25°C). Calculations are performed with the TRIO-EF coupled transport-chemistry code.The main results deal with the evolution of the pH profile across the clay barrier, the dissolution of clay minerals and the precipitation of new solid phases in the clay such as albite, gibbsite and CSH. These simulations show that the pH excursion includes only a minor part of the clay barrier at 10 000 y and that the CSH precipitation retards the alkaline plume progression. The appearance of local accumulations of newly precipitated minerals might reduce strongly the porosity. Future developpements of this work include: (i) the completion of the geochemical model by introducing other minerals in concrete (other CSH phases and sulfo-aluminates) and ion exchange sites within the clay, (ii) the implementation of a precipitation/dissolution model in order to describe on a realistic way the porosity profile evolution and possible clogging phenomena.

Time-resolved in situ X-ray diffraction study of MCM-41 structure formation from a homogeneous environment

Formation of an ordered hexagonal mesoporous structure of siliceous materials in a homogeneous environment using Na2SiO3 as a silica source and cetyltrimethylammonium bromide as a structure directing agent has been studied by means of a time-resolved insitu X-ray diffraction technique. In this synthesis route the precipitation of solid phase is due to acidification of the reaction mixture, achieved by the hydrolysis of ethyl acetate. Before acidification, the reaction mixture contains disordered elongated rod-like surfactant micelles, whose surfaces are partly covered with silicate anions. Owing to the decrease in pH, silicate anions begin to polymerize; micelles are arranged into a hexagonal array through the intermicellar silicate condensation. Thus, the polycondensation of silicate species represents the driving force of the formation of solid particles. Due to the replacement of OH groups by Si–O–Si bonds in the course of polycondensation, the structure contracts; the increasing density of silica pore walls results in the increasing integral net intensity of the (100) reflection. Since the integral width of this reflection remains practically constant, the size of coherent regions does not change during the reaction mixture ageing from the size that has been achieved at the earlier stages of the synthesis.

Precipitation of calcium and magnesium carbonates from homogeneous supersaturated solutions

Homogeneous (unseeded) precipitation of calcium and magnesium carbonates in the CaO–MgO–CO 2–H 2O system in supersaturated solutions was investigated. The induction period ( τ) of spontaneous nucleation and the composition of precipitated solid phases were determined. The influence of saturation degree (chemical affinity) and Mg 2+/Ca 2+ activity ratio in solution on the kinetics of CaCO 3 nucleation was studied. The order of CaCO 3 homogeneous nucleation equals to 4. The surface energy of CaCO 3 nucleus was measured to be 63 mJ/m 2. The main factor which controls the Mg content in the solid phase being formed during unseeded precipitation of carbonates is the saturation index of MgCO 3 in solution.

Reduction of Cr, Mo, Se and U by Desulfovibrio desulfuricans immobilized in polyacrylamide gels.

Intact cells of Desulfovibrio desulfuricans, immobilized in polyacrylamide gel, removed Cr, Mo, Se and U from solution by enzymatic-mediated reduction reactions. Lactate or H2 served as the electron donor and the oxidized Cr(VI), Mo(VI), Se(VI) and U(VI) served as electron acceptors. Reduction of the oxidized metal species resulted in the precipitation of solid phases of the metals. Metal removal efficiencies of 86-96% were achieved for initial concentrations of 1 mM Mo, Se, and U and 0.5 mM Cr. Insoluble metal phases accumulated on both the surface and the interior of the polyacrylamide gel. In column tests conducted for U removal, effluent concentrations less than 20 micrograms L(-1) were achieved with initial concentrations of 5 mg L(-1) and 20 mg L(-1) U and residence times from 25-37 h. The enzymatic reduction of Cr, Mo, Se, and U by immobilized cells of D. desulfuricans may be a practical method for removing these metals from solution in a biological reactor.

Carbonate diagenesis during thermo-convection: Application to secondary porosity generation in clastic reservoirs

Carbonate mass transfer due to a slow convective circulation within a sedimentary layer is modeled to assess the geometry of dissolution and precipitation zones as well as the time constant necessary for a significant dissolution or precipitation of solid phases. This study is focused on the effect of aluminosilicates, and in particular kaolinite on the time constant and location of carbonate diagenetic reactions and thus on porosity redistribution. When kaolinite, albite and chlorite are present in a carbonate system, dissolution and precipitation rates are increased by a factor up to 50 compared to the pure carbonates case. Moreover, carbonates tend to dissolve with increasing temperature, and secondary porosity occurs at the bottom of downwelling currents. It should be emphasized, however, that the net carbonate dissolution may result from calcite precipitation associated with dolomite dissolution. In several instances, the whole chemical system is dominated by a single reaction, such as cation exchange in carbonates or the acid-base reaction between kaolinite and chlorite. This generally implies that the dissolution of every solid phase is proportional to that of calcite. Moreover, when the variance of the chemical system is sufficiently low, absolute dissolutions can be analytically derived from the variation with temperature of the reaction equilibrium constants. This implies that a sufficient knowledge of the chemical system behavior could avoid numerical computations. It is shown that uncertainties in the thermodynamical properties of aluminosilicates minerals may result in variations of more than one order of magnitude in computed dissolution rates. In some cases, the dominant reaction in the system is changed and therefore the whole pattern of dissolution and precipitation zones is disrupted. This points out the need of reliable thermodynamic data bases to model mass transfer induced by convective circulations in porous layers.

Sodic Soil Reclamation Using Multicomponent Transport Modeling

High contents of soluble salts accumulated in a soil can significantly decrease the value and productivity of agricultural lands. Present recommendations for reclamation are usually based only on relatively simple and often empirical relations. In this paper we give a brief overview of many unique physical and chemical factors important to reclamation contained in the one-dimensional multicomponent transport model UNSATCHEM and demonstrate its use for evaluating the reclamation of a sodic soil using various amendments and management strategies. We evaluate particular reclamation strategies based on the following considerations: (1) the quantity of water needed; (2) the quantity of amendments to be used; and (3) the time required for reclamation to be completed. Our study concentrates primarily on such chemical reactions as cation exchange, precipitation, and dissolution of solid phases (reclamation amendments) and on the effect of solution composition on the soil hydraulic properties and corresponding changes in the water flow and solute transport rates.

Mine waste dumps and heavy metal pollution in abandoned mining district of Boccheggiano (Southern Tuscany, Italy)

Mining activity in the Boccheggiano-Fontalcinaldo area (Southern Tuscany) dates back at least to the 16th century AD and lasted up to very recent times. Copper-rich hydrothermal veins, massive pyrite deposits, and their gossans were exploited. Two mine waste dumps (Fontalcinaldo, Fontebona), one flotation tailings impoundment (Gabellino), and one roasting/smelting waste dump (Merse-Ribudelli) in the study area were selected to ascertain the environmental effects of such protracted mining activity. Primary waste mineralogy is mainly characterized by pyrite, gypsum, quartz, carbonates, chlorites, and micas. Secondary oxidation mineralogy includes Fe and Cu sulfates and hydroxy sulfates, Cu carbonates, Fe and Al oxyhydroxides, and other phases [neogenic cassiterite at Fontalcinaldo; probable calkinsite, (Ce,La)2(CO3)3· 4H2O, at Fontebona]. Mine waste samples show extremely variable contents of toxic elements (Cu, Pb, Zn, Bi, Cd, As), with average values in the order of hundreds to thousands of parts per million (except for Bi and Cd). In some samples, the abundance of proper minerals of these metals cannot account for the entire metal load. Conceivably, either solid solution substitutions or adsorption processes contribute to the intake of released metals into newly formed minerals. Release and transport of pollutants was affected to variable degrees by acid-neutralization processes. The highest metal and acid concentrations occur close to the investigated wastes and rapidly decrease moving downstream some hundreds of meters or less, with the partial exception for Mn and Fe. Other than dilution effects, this phenomenon may be ascribed to metal adsorption and precipitation of solid phases.

Effects of pH on Heavy Metal Sorption on Mineral Apatite

The sorption of aqueous Pb, Cd, and Zn onto a mineral apatite from North Carolina was investigated in relation to a wide range of pH. The effects of pH on solid-phase precipitation were particularly emphasized. The heavy metals were applied as single or multiple species. Solution pH greatly affected metal sorption mechanism by apatite and metal−apatite reaction products. The sorption of aqueous Pb was primarily through a process of the dissolution of apatite followed by the precipitation of variable pyromorphite-type minerals under acidic condition or of hydrocerussite [Pb3(CO3)2(OH)2] and lead oxide fluoride (Pb2OF2) under alkaline condition. Otavite (CdCO3), cadmium hydroxide [Cd(OH)2], and zincite (ZnO) were formed in the Cd or Zn system, especially under alkaline condition; while hopeite [Zn3(PO4)2·4H2O] might precipitate only under very acidic condition. Alternative sorption mechanisms other than precipitation of the crystalline phases were important in reducing Cd and Zn concentrations by the apatit...

The effect of Mo addition on the liquid-phase sintering of W heavy alloy

The morphological and compositional changes of grains have been investigated in the initial stage of liquid-phase sintering of W-Mo-Ni-Fe powder compacts. Both large (5.4-μm) and small (1.3-μm) W powders have been used to vary their time of dissolution in the liquid matrix. When 8OW-10M0-7Ni-3Fe (wt pct) compacts of fine (about 1- to 2-μm) Mo, Ni, and Fe and coarse (5.4-μm) W powders are liquid-phase sintered at 1500 °C, the Mo powder and a fraction of the W powder rapidly dissolve in the Ni-Fe liquid matrix. The W-Mo grains (containing small amounts of Ni and Fe) nucleate in the matrix and grow while the W particles slowly dissolve. In this transient initial stage of the liquid-phase sintering, duplex structures of coarse W-Mo grains and fine W particles are obtained. As the W particles dissolve in the liquid matrix during the sintering, the W content in the precipitated solid phase also increases. The dissolution of the small W particles is assessed to be driven partially by the coherency strain produced by Mo diffusion at the surface. During sintering, the W particles continuously dissolve while the W-Mo grains grow. When the compacts are prepared from a fine (1.3-μm) W powder, the W grains dissolve more rapidly, in about 1 hour, and only W-Mo grains remain. These observations show that the morphological evolution of grains during liquid-phase sintering can be strongly influenced by the chemical equilibrium process.

A model for inverse segregation: The case of directionally solidified AlCu alloys

A model for predicting macrosegregation during solidification of casting alloys has been developed. The continuum formulation was used to characterize the macroscopic mass, energy and momentum transports for two-phase systems. It was assumed that the interdendritic liquid flow was driven by thermal and solutal buoyancy, as well as by solidification contraction. The movement of free surface during solidification contraction and of precipitated solid phases in the early stage of solidification was taken into account. Validation of this model was performed for the case of inverse segregation in a directionally solidified Al-4.0% Cu casting with equiaxed grains. Calculated results show that positive segregation is formed in the vicinity of the bottom chill, associated with negative segregation in the mushy zone.

Determination of Amoxicillin in Catfish and Salmon Tissues by Liquid Chromatography with Precolumn Formaldehyde Derivatization

A liquid chromatographic (LC) method with fluorescence detection was developed for analysis of amoxicillin in catfish and salmon tissues. The tissue was extracted with phosphate buffer (pH 4.5), followed by trichloroacetic acid (TCA) precipitation of proteins and solid-phase (C18) extraction. Trace amounts of nonpolar interfering substances present after solid-phase extraction were removed by ether liquid-liquid extraction. The extract was reacted with formaldehyde and TCA at 100 degrees C for 30 min. A fluorescent derivative was extracted with ether, concentrated, and analyzed by reversed-phase LC with fluorescence detection. Average recoveries of amoxicillin spiked at 2.5-20 ppb were > 80% for catfish and > 75% for salmon muscle tissue, with coefficients of variation of < 6%. Limits of detection (LOD) and quantitation (LOQ) for catfish tissue were 0.5 and 1.2 ppb, respectively. LOD and LOQ for salmon muscle tissue were 0.8 and 2.0 ppb, respectively.

Attack of YBa2Cu3O6.8 by acidic aqueous solutions

The dissolution of YBa2Cu3O6.8 in acidic aqueous solutions was studied at 298 Kas a function of pH, nature and concentration of present anions and time, t. In the range 2.0 ≤ pH ≤ 4.0, dissolution is congruent and proceeds to completion; dissolution profiles are deceleratory and comply with a contracting volume rate law up to t0.5. The rate of dissolution, which is limited by slow surface reactions, decreases with increasing pH; the kinetic order on proton concentration is a fractional and variable number. At higher pH values, dissolution is arrested at intermediate conversion values. In these cases, congruent dissolution is followed by the precipitation of less soluble solid phases which form a passive layer. The nature of this passive layer depends on pH and on the nature and concentration of present anions, which also define the extent of conversion attained at passivation. The dissolution behaviour of YBa2Cu3O6.8 is described in terms of two consecutive surface reactions: fast equilibrated protonation of surface metal ions is followed by the slow release of cations. Barium surface ions are identified as the more reactive sites. The effect of the fast initial leaching of barium ions on the reactivity of yttrium and copper sites is discussed. The influence of the formal Cu(III) oxidation state is also stressed.

5451370 High-density lipoprotein solid-phase precipitation assay device : Jones Ronald M Mountain View, CA, United States assigned to Cholestech Corporation

5451370 High-density lipoprotein solid-phase precipitation assay device : Jones Ronald M Mountain View, CA, United States assigned to Cholestech Corporation

The effect of morphological changes on the coprecipitation of strontium by calcium phosphate

The coprecipitation of strontium by a calcium phosphate phase formed at an elevated pH 10.8 was investigated. The first phase obtained under these conditions in the amorphous calcium phosphate (ACP) which is transformed into crystalline hydroxyapatite (HA) after the induction period. Is has been shown that this transformation together with morphological changes of the precipitated solid phase, influences the amount of the sorbed strontium significantly. The possible consequences of this finding on practical application of coprecipitation of strontium by calcium phosphate have been discussed.

Formation of polyhedral N2 bubbles during reactive sputter deposition of epitaxial TiN(100) films

Cross-sectional transmission electron microscopy has been used to investigate the formation of polyhedral N2 bubbles in single-crystal TiN(100). Thin TiN films were deposited on MgO(100) substrates by reactive magnetron sputtering in pure N2 atmospheres at growth temperatures Ts between 550 and 800 °C and negative substrate biases Vs between 0 and 500 V resulting in a deposition rate between 0.35 and 0.33 nm s−1. The energy per incident nitrogen was ∼eVs/2 and the irradiation fluxes were ≤2.5×1015 N+2 cm−2 s−1. Nitrogen bubbles were observed in films grown at 550≤Ts&amp;lt;800 °C with Vs&amp;gt;300 V. In as-deposited films grown at Ts=650 °C with Vs=500 V, the bubbles were distributed in two shapes and size distributions. The largest bubbles were orthorhombohedra, i.e., cubes elongated along [100] directions normal to the growth direction, with 5–20 nm faces on {100} planes most of which exhibited {110} and {111} faceting. Small (≤5 nm) octahedral bubbles with {111} faces were also observed. In situ annealing experiments in the transmission electron microscope showed that the bubbles transformed from orthorhombohedra to octahedra at Ts=350 °C and then returned to orthorhombohedral shape with either continued heating to Ts=600 °C or upon cooling to room temperature. Assuming quasiequilibrium conditions, the surface energy γ of N2 bubbles in TiN was found to be anisotropic and to vary as γ100&amp;lt;γ110&amp;lt;γ111. Some of the smaller orthorhombohedral bubbles exhibited Moiré fringes with a spacing indicative of solid-phase precipitation of cubic α-N2.