Equilibrium Solution Concentration Research Articles

Étude thermodynamique du mélange chlore – acide isocyanurique en milieu aqueux

A method of calculation of the equilibrium concentrations in aqueous solution of cyanuric acid and its chlorinated derivatives as a function of pH, molar ratio of chlorine/cyanuric acid, and chloride ion concentration is presented. The influence of each of these parameters is studied in conditions close to those used for these compounds in swimming pools.

合成無機吸着剤によるめっき浴中の微量不純物の除去 Ｉ シリカ‐チタニア吸着剤によるめっき浴中の鉛（ＩＩ）と亜鉛（ＩＩ）の相互分離

Lead (II) impurity in zinc or zinc-alloy plating baths has an adverse effect on the finish. To remove this lead (II) we attempted the separation of lead (II) and zinc (II) coexisting in aqueous solutions using silica-titania gel, which is known to be porous and stable at high temperatures.It was first found that in a solution containing 10mg dm-3 of both lead (II) and zinc (II) equimolar silica-titania gel solely adsorbed lead (II) at pH 2.4 and it was therefore realized that the separation of both metals dissolved in solutions was possible at this pH range by means of gel adsorption. At the zinc concentrations up to 104mg dm-3, lead removal efficiency was high. The relationship between the equilibrium concentration in solution and the amount of metal adsorbed obeyed the Freundrich adsorption isotherm. The optimum composition of silica-titania gel here was 3:1. The silica-titania gel may be reused repeatedly with elution of the adsorbed lead (II) using 1M nitric acid, followed by surface treatment with 1M sodium nitrate solution.

Crystallization of a rapidly solidified Al 2O 3-ZrO 2 eutectic glass

Glasses of the Al 2 O 3 -ZrO 2 eutectic composition were prepared by a melt extraction technique, and subjected to a variety of heat treatments. The first phase to crystallize from the glass was tetragonal ZrO 2 at 944 °C, followed by S-Al 2 O 3 above 1000 °C, α-Al 2 O 3 and m-ZrO 2 appeared at 1450 °C. The early crystalline phases exhibited enhanced mutual solid solubility. The δ-Al 2 O 3 phase contained up to 10.2 mol% ZrO 2 and the tetragonal ZrO 2 phase contained up to 14.1 mol% Al 2 O 3 for crystallite sizes ≤ 40 ran. As the crystallite size increased to a few 100 nm under heat treatment, equilibrium solute concentrations were attained. The largest tetragonal ZrO 2 particle observed was 0.3 μ m. There was no detectable difference between the Al 2 O 3 content in tetragonal and monoclinic particles of similar sizes. The apparent activation energy for growth of the tetragonal ZrO 2 in the temperature range of 950 °C to 1200 °C is found to be 10.8 × 10 4 J/mol.

Meteoric water-basalt interactions. I: A laboratory study

Rates, stoichiometry and activation energy of dissolution, pH vs. time and activity-activity paths were determined by dissolving basaltic rocks under simulated natural conditions at 25 to 60°C. Dissolution follows a linear rate law, with basaltic glass dissolving about 10 times faster than crystalline basalt. Rates are independent of pH from 7 to 9.5. The basaltic glass dissolves near stoichiometrically at 25°C, but this is not so for the crystalline basalt. The average activation energy for dissolution of basaltic glass is 32 kJ/ mol (±3). For individual elements leached from crystalline basalt, it ranges from 35 to 15 kj/mol. This indicates that under experimental conditions reactions on the surfaces of the solids are the rate-determining step in the dissolution mechanism. Ca, Mg, and Si reached steady state or equilibrium concentrations in solutions at 45 and 65°C. Alteration minerals formed in vugs on the solids but did not form a continuous protective layer on the solids. Reaction paths for the experimental solutions are strongly dependent on their pH versus time evolution. Solutions sealed off from the atmosphere evolve into the Ca-zeolite field, whereas those open to the atmosphere evolve into the clay mineral fields. During the experiments the consumption of hydrogen by solids at 25°C (10 −5 mol/kg) is not sufficient to significantly change the hydrogen isotope ratio of the experimental solutions.

Adsorption of mercury compounds by tropical soils III. Adsorption isotherms

Isotherms for sorption of 2-methoxyethylmercury chloride (Aretan) and HgCl2 showed that all three soils investigated had a large capacity to adsorb these Hg compounds, the order being Morogoro > Arusha > Dar es Salaam. For all soils, surface horizons adsorbed more Hg at any given concentration of Hg in solution as compared to subsurface horizons. Adsorption isotherms of Aretan, especially at lower equilibrium concentration in soil solution, were much steeper in all horizons and in all profiles. The Freundlich equation described the adsorption of HgCl2 better than that of Aretan. The adsorption isotherms for Aretan and HgCl2 showed different forms, implying probably that different adsorption mechanisms were involved.

Effects of air-drying on the adsorption and desorption of phosphate and levels of extractable phosphate in a group of acid soils, New Zealand

The effects of air-drying field-moist soils on the adsorption and desorption of added phosphate and on the levels of extractable native soil phosphate were examined using the A and B horizons of a group of four acid soils. Air-drying increased the capacity of all the soil samples to adsorb phosphate. At an equilibrium solution concentration of 0.5 μg P ml −1, the increase in the quantity of phosphate adsorbed following drying ranged from 23% to 70% of that adsorbed by the moist samples. Considerable hysteresis in phosphate adsorption—desorption isotherms was observed for both moist and dried soil samples indicating that the additional phosphate adsorbed by the dried samples was held with the same strength as that held by the moist samples. Air-drying the soil samples caused a small decrease in soil pH of approximately 0.1 pH unit and a general increase in levels of EDTA-extractable Fe, Al and organic matter. Quantities of native soil phosphate extractable with EDTA, resin and NaHCO 3 were also increased. Concentrations of oxalate- and pyrophosphate-extractable Fe and Al and exchangeable Al were, however, unaffected by drying. It was also shown that when the phosphate content of NaHCO 3 extracts is measured using the conventional molybdenum blue method, orthophosphate plus a differing amount of acid-hydrolysable organic P present in the extract is measured.

Equilibrium solute concentration surrounding elastically interacting precipitates

Elastically induced equilibrium solute concentration profiles surrounding a single isolated precipitate and two elastically interacting precipitates are determined under the conditions of an applied shear and tensile stress, as well as an isotropic stress-free transformation strain. The self consistent open-system elastic constants approach is employed to account explicitly for the coupling between the stress and concentration fields. Substantial concentration changes are predicted near the surfaces of the particles which can sometimes exceed 50 pct. With self consistency to first-order in the concentration change, no net solute enhancement is observed surrounding isolated particles while net solute segregation is observed for elastically interacting particles.

Ion exchange/complexation of the uranyl ion by Rhizopus biosorbent

Nonliving biomass of nine Rhizopus species effectively sequestered the uranyl ion from solution, taking up 150-250 mg U/g dry cells at 300 ppm U equilibrium concentration in solution, and 100-160 mg U/g dry cells with 100 ppm U in solution. The affinity of this biosorbent for the uranyl ion was found to be affected by timing of harvesting and medium composition. Uptake of the uranyl ion by nonliving biomass of Rhizopus oligosporus was due to ion exchange or complexation, since binding was reversed by the addition of complexing ligands or the reduction of pH to a value less than 2. Uptake isotherms were interpreted in terms of a model of multiple equilibria. At pH </= 2, or in the presence of NO(3) (-), Cl(-), SO(4) (2-), or EDTA (ethylenediamine-tetra-acetate), the quantity of UO(2) (2+) that was bound was a constant fraction of that bound at pH 4 in the absence of ligands. This action indicated simple competition for uptake sites between H(3)O(+) and UO(2) (2+) for uptake sites, or for UO(2) (2+) between the biomass and ligands in solution. If oxalate or thiocyanate was present, however, the complexed species were sequestered by the biomass. Biomass of Rhizopus arrhizus, which grew as pellets, was subsequently used in a packed sorption column where it exchanged hydrogen ions for uranyl ions (2 H(+): 1 UO(2) (2+)). Concentrated uranyl solutions were eluted in sulfuric or nitric acids, and the biomass was reused eight times with no apparent deterioration of the biosorbent.

Computer simulated dissolution of carbide precipitates in alloys

AbstractConventional theory on the dissolution of a spherical particle of a second phase in an alloy is shown to be inappropriate when considering carbide species. In particular, the assumptions of an error function solute concentration profile and a constant equilibrium solute concentration level at the interface cannot be made. A model for computer simulated dissolution is therefore proposed which is based on the diffusion of solute away from a carbide particle across discrete shell increments. The method is used to predict times for complete and partial dissolutions of M23C6 particles in Nimonic 80A (registered trade mark of Henry Wiggin and Co. Ltd). As a result, the effect of solution heat treatment of the alloy is more clearly understood and practical improvements are recommended.

The adsorption of copper by soil samples from scotland at low equilibrium solution concentrations

At low solution concentrations of copper in the presence of 0.05 M CaCl 2, adsorption isotherms for copper on soil samples were essentially linear. Although no direct correlations were found between isotherm gradients and individual soil properties, the gradients were of the same order of magnitude as predictions based on gradients obtained for some specific soil components. The soil components which appear to be most important in copper adsorption and which were used to obtain the predictions were organic matter and iron and manganese oxides. The amounts of adsorbed copper remaining isotopically exchangeable or extractable with EDTA in the short term increased with the amount of copper adsorbed but the proportions of adsorbed copper estimated by each of these techniques remained constant. Concentrations of copper in solution increased (adsorption decreased) at pH values below 4.5 and above 6.5.

The effect of pH upon the copper and cupric ion concentrations in soil solutions

SummarySoil samples whose pH had been adjusted to between 4.5 and 7.5 either for long periods in the field or short periods in the laboratory were incubated after wetting with water or 0.01 m CaCl2. Copper concentrations in the soil solutions decreased only slightly as the solution pH increased, but free cupric ion concentrations decreased considerably. The copper concentrations were smaller and the proportion of copper present in solution as cupric ion at a given pH was larger when CaCl2 rather than water was used. Complexed organic species made up most of the copper in all solutions. The duration of pH adjustment did not affect these results.Copper adsorption isotherms were determined on the soils using low equilibrium solution concentrations. As a given copper concentration the quantity of copper adsorbed increased and the proportion of copper in solution present as cupric ion decreased with pH increase; again the duration of pH adjustment did not affect the results.

Relationship between phosphorus intensity and capacity parameters in Finnish mineral soils: II Sorption-desorption isotherms and their relation to soil characteristics

The relationship between P intensity and capacity parameters in 104 mineral soil samples was studied by means of sorption-desorption isotherms of two types. In the isotherm A the P exchange was expressed as a function of P concentration in the initial solution, in the isotherm B as a function of P concentration in the final equilibrium solution. Both isotherms conformed to the equation y = a + bx, where y stands for the amount of P sorbed or desorbed and x the P concentration in the solution. In the isotherm A the constant a is the intensity factor expressing the amount of water soluble P at a given soil-solution ratio. The term a in the isotherm B, on the contrary, was only poorly related to water soluble P in soil. In both isotherms the slope b of the line seemed to be most effectively affected by oxalate extractable Al. The relative importance of oxalate soluble Fe appeared to be greater in affecting the effectiveness of sorption-desorption reactions than in affecting the buffer reactions. However, the slope b of both isotherms was found to be a semi-intensive parameter: it was quite markedly dependent also on soil characteristics which control the level of water soluble P in soil. The ratio of the term —a to b (termed as EBS or EPC), expressing the zero point of net P exchange, varied from 0.003 to 13.89 mg P per liter, the lowest values tending to be in the heavy clay soils and the highest ones in the non-clay soils. The practical significance of this quantity was discussed.

Diffusion controlled ledge growth in a medium of finite extent

Steady ledge motion during lateral growth in solid-solid phase transformations is examined in an untransformed matrix of finite lateral extent. It is assumed that volume diffusion in the parent phase is the predominant contribution to the growth rate. Results are presented for the step speed (Peclet number) as a function of the lateral extent of the untransformed parent phase for a given dimensionless normalized supersaturation. One striking result is that this steady step speed tends to zero when the ratio of the remaining thickness of untransformed matrix to the step height is equal to 1/Ω0 where Ω0 = (c∞−ce)/(cp−ce) is the normalized supersaturation. cp is the solute concentration of the precipitate, ce the equilibrium solute concentration in the matrix at the precipitate matrix interface and c∞ the initial concentration of the untransformed matrix.

Adsorption of frothers at coal/water interfaces

The adsorption of phenol and three commonly used frothers, namely, terpineol, methylisobutylcarbinol (MIBC) and cresol, on coal surfaces has been studied through UV spectrophotometric and gas chromatographic techniques. The rate of attaining adsorption equilibrium of these alcohols onto coal is very slow, possibly due to pore diffusion. The adsorption isotherms are of typical Langmuir-type except for MIBC, where the adsorption density rises linearly with equilibrium concentration in solution in the range of concentration under study. Free energies of adsorption were calculated from the adsorption isotherms. The results indicate that adsorption occurs through hydrophobic interactions between the frother molecules and the coal surface. The effect of oxidation and pH on adsorption behavior was also studied. Oxidized coal is more hydrophilic and hence the adsorption of these nonionic surface-active agents is reduced after oxidation.

Ionic Activity Products and Crystal Forms of Calcium and Magnesium Carbonates Precipitated from Calcium‐Magnesium Bentonites

AbstractA series of laboratory experiments were conducted to study quantities, mineral forms, and solubility of alkaline earth carbonates precipitated from Ca‐Mg‐bentonite systems. The effects of Mg on carbonate precipitation and solubility were assessed in isolation from other carbonate precipitation inhibitors commonly found in soils. Five bentonite systems were preconditioned by saturation with different proportions of exchangeable Ca and Mg. Calcium/magnesium ratios ranged from 99:1 to 8:92. Portions of each system were seeded with calcite, and both seeded and unseeded systems were equilibrated with deionized water or NaHCO3. Equilibrium solution concentrations of Ca, Mg, Na, HCO3, and Cl and also pH served as input data to the WATEQF solution chemistry computer program for calculations of ion strength, ion pairs, ion activities, and carbonate ionic activity products (IAP).The data obtained from the series of experiments clearly demonstrated that solubility characteristics of calcium carbonate in the Ca‐Mg‐bentonite systems were influenced by incongruent properties of freshly precipitated carbonate surfaces. The data further show that Mg inhibited crystallization and increased solubility of calcium carbonate and that high concentrations of Mg in the NaHCO3‐bentonite precipitation medium induced crystallization of Mg calcite. In some systems, Mg was precipitated in forms which were not identified by either x‐ray diffraction analysis or IAP characteristics.

Infrared study of the adsorption of propionitrile on silica immersed in liquid hydrocarbons

Infrared spectra have been recorded of silica which had been evacuated at 423 K and subsequently immersed in solutions of propionitrile in toluene, 2,2,4-trimethylpentane and toluene + 2,2,4-trimethylpentane mixtures. The adsorption process involved the formation of hydrogen bonds between surface hydroxyl groups and the cyano groups of propionitrile molecules. The adsorption of propionitrile on silica was impeded by strong lateral interactions between adjacent surface silanol groups. Only isolated hydroxyl groups and weakly interacting hydroxyl groups acted as adsorption sites. Increasing strength of interaction between the predominant (hydrocarbon) components of the liquid phase and surface silanol groups decreased the surface concentration of propionitrile molecules for a particular equilibrium concentration in solution.

Adsorption of Several Dyes from Aqueous Solutions on Silica-Containing Complex-Oxide Gels

Abstract Removal of dyes from aqueous solutions was investigated in a batchwise operation using binary or ternary silica-containing complex-oxide gels as adsorbents. The following three combinations of gels showed the best results: (1) silica-titania-magnesia gel for C.I. Acid Blue 40, (2) silica-titania gel for C.I. Basic Blue 3, and (3) silica-titania gel treated with alkali for C.I. Reactive Red 5. The adjustment of the initial pH of the dye solution was effective in all cases. Freundlich-type adsorption isotherms related the amount of dye adsorbed to its equilibrium concentration in solution. The gels which adsorbed the dye abundantly were effectively regenerated for reuse by heating them at 600°C, which caused decomposition of the dye.

THE ADSORPTION OF COPPER BY SOIL MATERIALS AT LOW EQUILIBRIUM SOLUTION CONCENTRATIONS

SummaryThe adsorption of copper by individual soil components (organic matter fractions, oxides and clay minerals) was examined at equilibrium solution concentrations of copper within the range found in natural soils, the distribution of copper between solution and solid phases being measured by means of labelling with radioactive 64Cu. At these low solution concentrations it was found that the copper adsorption isotherms were essentially linear. The oxides and organic materials adsorbed the greatest amounts of copper. The concentration of copper in natural soil solutions will be controlled by these materials to a far greater extent than by the clay minerals, the influence of which may be negligible in some soils. Solution concentrations of copper are relatively unaffected by both the background concentration of major cations and by changes in pH within the ionic strength and pH range found in normal agricultural soils.Copper adsorption studies with humic and fulvic acids showed that total solution copper concentrations could be greatly enhanced above the equilibrium levels for ionic copper by the presence of soluble organic complexes. The importance of taking into account the presence of such copper complexes in soil copper studies is emphasised.

The plant availability of sulphur from a sulphate-aluminium hydrous oxide complex

Ryegrass was grown in sand containing35S-labelled sulphate adsorbed onto the surface of Al-hydrous oxide. S from this source was available to ryegrass even at very low surface coverage; and maximum yield of ryegrass occurred at an equilibrium solution concentration of 2 μM S corresponding to about 10% coverage on the hydrous oxide.

Liming and Lime‐Phosphorus‐Zinc Interactions in Two Nigerian Ultisols: I. Interactions in the Soil

AbstractInteractions of lime, phosphorus (P), and zinc (Zn) in two coarse‐textured Ultisols from southeastern Nigeria were examined by means of factorial soil incubation and phosphate sorption experiments.In both soils, liming reduced exchangeable aluminum (Al) saturation from 45% to &lt; 5% at pH 5.0 and soil solution Al concentration to &lt; 1.0 µg/ml also near pH 5.0. There was no significant lime‐P interaction on active Al levels, indicating a lack of any ameliorating value of P on Al toxicity. Adsorption isotherms showed that liming reduced P adsorption in both soils at equilibrium solution concentrations of approximately 0.2 µg P/ml or higher, but at lower concentrations the effect became inconsistent. Soil incubation studies indicated that the concentration of P in soil solution (null‐point estimate) was first reduced by lower rates of lime then increased when soils were limed to approximately pH 6.0 or higher.Zinc activity in soil solution declined sharply when soils were limed to pH above 5.0, but was unaffected by P applications within the pH range studied (pH 4.3 to 7.2).