Solubility Of Sulfate Research Articles

Arsenic and zinc biogeochemistry in pyrite mine waste from the Aznalcóllar environmental disaster

This laboratory experiment systematically examines arsenic, iron, zinc, and sulfate solubility and fractionation in pyrite mine waste suspensions as affected by redox potential (Eh) at pH 7.0. Under aerobic conditions and pH 7.0, As solubility was low, however, under moderately reducing conditions (0–100 mV), As solubility significantly increased due to dissolution of iron oxy-hydroxides. Upon reduction to −250 mV, As solubility was controlled by the formation of insoluble sulfides, and as a result, soluble As contents dramatically decreased. Soluble Fe concentration increased with time under anaerobic conditions, however, it decreased under aerobic conditions likely due to formation of insoluble oxy-hydroxides. Under aerobic conditions and pH 7.0, soluble Zn significantly increased with incubation time and reached concentrations as high as 800 mg kg −1 waste. Perhaps zinc was initially present as insoluble zinc sulfides, however, after further oxidation, sulfide was transformed to sulfate and Zn 2+ was then released into the waste solution. Selective extraction of incubated wastes maintained at pH 7.0 illustrated that arsenic biogeochemistry was mainly controlled by As bound to: (a) amorphous Fe oxy-hydroxides and (b) insoluble organics and sulfides. Remediation of a site polluted by both arsenic and zinc is quite complicated because the redox conditions favoring insolubility of arsenic, however, favors maximum solubility of zinc, and vice versa. Therefore, the best way for the remediation of an arsenic- and zinc-polluted environment, in our opinion, is: (a) phyto-remediation with plants accumulating large amounts of Zn in their tissues, and (b) simultaneous addition of: (1) amorphous iron oxy-hydroxides (aerobic Eh) or (2) organic matter rich in S compounds (anaerobic Eh).

Mixing of the Organic Aerosol Fractions: Liquids as the Thermodynamically Stable Phases

An increasing number of single-particle measurements show that organic and inorganic constituents of the atmospheric aerosol are internally mixed within the particles. Therefore, the phases of the aerosol will be influenced by both mixing of the organic substances with each other and mixing between organic and inorganic constituents. In this work, the mixing properties of the organic aerosol fractions have been investigated theoretically and experimentally with respect to melting and deliquescence. We show that a liquid (or an amorphous solid) is the thermodynamically stable phaseeven in the absence of water as a solventprovided that a sufficiently high number of miscible components are present. Furthermore, we show experimentally that the deliquescence relative humidity of aqueous solutions of dicarboxylic acids decreases with an increasing number of components present in the solution. A five-component mixture consisting of malic, malonic, maleic, glutaric, and methylsuccinic acids deliquesces at a relative humidity (RH) as low as 45.4% RH, while the pure dicarboxylic acids exhibit deliquescence points between 72 and 96% RH. A further reduction of the deliquescence relative humidity is observed when an inorganic salt is added to the dicarboxylic acid five-component mixture. For NaCl, deliquescence of the eutonic composition occurred at 41.3%, for ammonium sulfate at 36.4%, and for ammonium nitrate even at 27.1% RH. Interactions between the solutes lead to either higher or lower solubilities in the multicomponent mixture as compared to the respective single-component aqueous solutions. In the mixed dicarboxylic acids/inorganic salt solutions, the solubilities of ammonium nitrate and sulfate are increased by ∼40%, the one of sodium chloride is decreased by a similar amount. In summary, these mixing properties suggest that small fractions of organic species prevent tropospheric aerosols from becoming fully solid, and the organic fraction may even stay fully liquid irrespective of tropospheric humidity.

A thermodynamic investigation of barium and calcium sulfate stability in sediments at an oceanic ridge axis (Juan de Fuca, ODP legs 139 and 169)

We have used a new thermodynamic model of barium and calcium sulfate solubilities in multicomponent electrolyte solutions (Monnin, 1999) to investigate the stabilities of barite and anhydrite in seawater or in marine sediment porewaters at high temperature and pressure. As a further test supplementing those previously carried out during model development, we have calculated the temperature at which standard seawater becomes saturated with respect to anhydrite. The model predicts that, upon heating at 500 bars, standard seawater becomes saturated with respect to anhydrite at 147 ± 5°C, which compares well with the literature value of 150°C (Bishoff and Seyfried, 1978). At 20 bars the calculated saturation temperature is 117 ± 3°C. This points to a non negligible pressure effect even at moderate pressures. We have calculated the barite and anhydrite saturation indices for the in situ temperatures and pressures, from the composition of porewaters collected at ODP Sites 855, 856, 857, 858, 1035 and 1036 during ODP Legs 139 and 169 (Juan de Fuca and Gorda ridges, NE Pacific). Calculated saturation indices for porewater samples collected at depths corresponding to temperatures between 70° and 110–120°C at an in situ pressure of about 260 bars yield equilibrium values for anhydrite and barite. Saturation indices of samples collected at depths where the temperature exceeds 110–120°C, however, yield values indicating supersaturation with respect to anhydrite and undersaturation with respect to barite. This result is consistent with the redissolution of anhydrite during cooling, leading to the well documented sampling artifact affecting porewater compositions in high temperature marine sediments: anhydrite dissolution increases the porewater sulfate content, which in turn induces a loss of barium from solution through barite precipitation (the common ion effect). We postulate that this redissolution occurs in sediment samples for which the in situ temperature exceeds 110–120°C: below this limit anhydrite remains at equilibrium or does not have time to significantly dissolve before porewaters are sampled.

Soil Saturation Extract Composition and Sulfate Solubility in a Tropical Semiarid Soil

Soil solution is the major source of plant nutrients, nutrient cycling in ecosystems, and pollutant transformation and transport in soil. I examined the composition of soil saturation extract of a cultivated and an uncultivated savanna Alfisol to determine the relations of Ca 2+ , Mg 2+ , and K + concentrations in soil solution with exchangeable Ca, Mg, and K; and to determine the solubility relations of SO 4 for which there is little information in savanna soils. The soil saturation extract had ionic strength (I) below 0.001 except for one field under intensive fertilization with NPK fertilizer and farmyard manure (FYM) whose ionic strength was between 0.001 and 0.002 at a depth below 40 cm due to leaching. The Ca 2+ , Mg 2+ , and K + in the soil saturation extract correlated weakly with exchangeable Ca, Mg, and K respectively, but K + intensity was fairly well predicted by percentage of K saturation of cation-exchange capacity (CEC), whereas the intensities of Ca 2+ , Md 2+ , and SO 4 2- in soil solution were best predicted by electrolytic conductivity of the saturation extract. The K activity ratios in solution defined as a K/( a Ca + a Mg) 1/2 were <0.01 in the cultivated soil, suggesting a preponderance of K adsorbed to edge rather than planar sites. The Ca 2+ activity ratios defined as a Ca/ [Σ a Cations] were <0.15 for the cultivated soil, indicating possible Ca deficiency. The SO 2- 4 activities in solution were in apparent equilibrium with basaluminite in the cultivated fields, whereas in the uncultivated field, SO 2- 4 activities were in apparent equilibrium with alunite.

Sulfate Cavity Filling in the Lower Werra Anhydrite (Zechstein, Permian), Zdrada Area, Northern Poland: Evidence for Early Diagenetic Evaporite Paleokarst Formed Under Sedimentary Cover

ABSTRACT Paleokarst developed in sulfate deposits is common, and it is usually formed along the contact with the overlying permeable rocks or it is due to near-surface dissolution of bedded evaporites. In the Lower Werra Anhydrite (Zechstein) of northern Poland the paleokarst cavities are usually filled by bluish semitransparent anhydrite and more rarely by celestite, polyhalite, halite, and carbonate. In small cavities (a few centimeters across), a rim of rod-like anhydrite crystals arranged in narrow bundles occurs, and the inner part of the cavity is filled with a mosaic aggregate of short prismatic crystals of anhydrite and celestite as well as coarse irregular anhydrite. Celestite crystals and fan-shaped aggregates as well as spherulites of anhydrite are rare. In bigger cavities (some ten centimeters across), multiple zones of fibrous anhydrite are arranged in different directions in the middle part of the cavity fill. The innermost parts of large karst cavities remain hollow in some cases, with the cavity walls encrusted by coarse, well-developed crystals of anhydrite and celestite. The karst cavities in the Lower Werra Anhydrite developed in the subsurface by dissolution of CaSO4 strata in halite-rich intervals due to gypsum dehydration water. During gypsum dehydration, dissolution of that halite would have increased the sodium chloride content of the solution and thus the solubility of calcium sulfate. Dissolved calcium sulfate was removed from a leaching zone by diffusion and/or downward flow in interstitial space, and the minerals in karst cavities precipitated from the same solutions as those solutions became oversaturated because of decreases in NaCl concentration over time. This study suggests that karst in sulfate deposits can develop in the subsurface and without uplift and/or near-surface conditions.

Determination of the solubility of inorganic salts by headspacegas chromatography

This work reports a novel method for determination of salt solubility using headspace gas chromatography. A very small amount of volatile compound (such as methanol) is added in the studied solution. Due to the molecular interaction in the solution, the vapor–liquid equilibrium (VLE) partitioning coefficient of the volatile species will change with different salt contents in the solution. Therefore, the concentration of volatile species in the vapor phase is proportional to the salt concentration in the liquid phase, which can be easily determined by headspace gas chromatography. Until the salt concentration in the solution is saturated, the concentration of volatile compound in the vapor phase will continue to increase further and a breakpoint will appear on the VLE curve. The solubility of the salts can be determined by the identification of the breakpoint. It was found that the measured solubility of sodium carbonate and sodium sulfate in aqueous solutions is slightly higher (about 6–7%) than those reported in the literature method. The present method can be easily applied to industrial solution systems.

Volume Change Behavior of Arid Calcareous Soils

Arid climate, alkaline environment, and geology govern the formation and behavior of coastal calcareous sediments in the Arabian Gulf region. The presence of clay and nonclay minerals in these sediments causes geotechnical hazards of variable nature and intensity. Alternating volume change due to phase transformation and solubility of calcium sulfate adds to the severity of problems associated with the host expansive clay strata. Based on laboratory investigation, this paper gives an account of the volume change behavior of calcium sulfate-rich calcareous soils of eastern Saudi Arabia. Laboratory testing conducted on identical samples containing equal amounts of clay and anhydrous calcium sulfate shows that sample hydration leads to volume increase, whereas fluid permeation through the samples causes collapse under load. Volume decrease is more pronounced in an alkaline environment that favors easy removal of Ca2+ and SO42- ions.

Short-term natural weathering of MSWI bottom ash as a function of particle size

The chemical and material composition of MSWI bottom ash depends on the particle size; this suggests that the mechanisms and kinetics of natural weathering are also a function of particle size. This paper reports the effects of short-term natural weathering on the leaching of heavy metals (mainly Pb, Cu and Zn) from MSWI bottom ash. Initial concentrations of heavy metals were higher for the smallest particle size fractions, but these levels fell dramatically during the first 50 days of weathering before levelling off. The main differences between size fractions were in the pH and the solubility of calcium and aluminium. For the initial stages of weathering and small size fractions, portlandite solubility seemed to control the pH. In contrast, for fractions bigger than 6 mm, the formation of ettringite was the reaction controlling the pH and the solubility of sulphates, aluminium and calcium.

Spring and surface water quality of the Cyprus ophiolites

Abstract. A survey of surface, spring and borehole waters associated with the ophiolite rocks of Cyprus shows five broad water types (1) Mg-HCO3, (2) Na-SO4-Cl-HCO3, (3) Na-Ca-Cl-SO4-OH-CO3, (4) Na-Cl-SO4 and (5) Ca-SO4. The waters represent a progression in chemical reactivity from surface waters that evolve within a groundwater setting due to hydrolysis of the basic/ultrabasic rock as modified by CO2-weathering. An increase in salinity is also observed which is due to mixing with a saline end-member (modified sea-water) and dissolution of gypsum/anhydrite. In some cases, the waters have pH values greater than 11. Such high values are associated with low temperature serpentinisation reactions. The system is a net sink for CO2. This feature is related not only to the hydrolysis of the primary minerals in the rock, but also to CaCO3 or Ca-Mg-CO3 solubility controls. Under hyperalkaline conditions, virtually all the carbon dioxide is lost from the water due to the sufficiently high calcium levels and carbonate buffering is then insignificant. Calcium sulphate solubility controls may also be operative when calcium and sulphate concentrations are particularly high. Keywords: Cyprus, Troodos, ophiolite, serpentinisation, spring, stream, water quality, bromide, iodine, boron, trace elements, hyperalkaline.

Calcium sulphate solubilities in simulated zinc processing solutions

Calcium sulphate solubilities in simulated zinc processing solutions, as well as the densities of the corresponding saturated solutions, were determined on heating and cooling in a series of experiments carried out from 20 to 95 °C. In dilute ZnSO 4 media, increasing H 2SO 4 concentrations in the range of 0.0–0.6 M H 2SO 4 strongly increase the solubility of calcium sulphate, but have little additional effect for acid concentrations >0.6 M H 2SO 4. In more concentrated zinc sulphate solutions, however, increasing acid concentrations in the range from 0.0 to 2.0 M H 2SO 4 slightly decrease the solubility of calcium sulphate. In dilute H 2SO 4 media, the solubility of calcium sulphate decreases with increasing ZnSO 4 concentrations, and the decrease is most pronounced for concentrations in the range 0.0–0.2 M ZnSO 4. Higher ZnSO 4 concentrations further depress the solubility at temperatures below 70 °C, but have a complex effect at higher temperatures. Increasing ferric sulphate concentrations to 1.0 M Fe(SO 4) 1.5 in 0.3 M H 2SO 4–1.15 M ZnSO 4 media depress the solubility of calcium sulphate to a modest extent. The addition of up to 1.25 M MgSO 4 also decreases the solubility of calcium sulphate in 0.3 M H 2SO 4–1.15 M ZnSO 4 media. In contrast, the solubility of calcium sulphate in 2.5 M ZnSO 4–0.4 M MgSO 4–0.18 M MnSO 4 solutions, at pH values ranging from 3.6 to 4.6, is not significantly affected by the presence of up to 0.25 M Na 2SO 4 or up to 0.09 M (NH 4) 2SO 4. Supporting mineralogical studies showed that the solubility depends strongly on whether the saturating solid phase is gypsum (CaSO 4·2H 2O) or anhydrite (CaSO 4). The transition from gypsum to anhydrite was found to depend on the temperature, the H 2SO 4 concentration and the total sulphate concentration of the solution. Unlike the solubilities, which varied in a complex manner, the densities of the calcium sulphate-saturated solutions increased systematically with increasing concentrations of any of the solution species and decreased slightly with increasing temperature.

Redox potentials and kinetics of the Ce 3+/Ce 4+ redox reaction and solubility of cerium sulfates in sulfuric acid solutions

Experimental work was performed with the aim of evaluating the Ce 4+/Ce 3+ redox couple in sulfuric acid electrolyte for use in redox flow battery (RFB) technology. The solubility of cerium sulfates in 0.1–4.0 M sulfuric acid at 20–60 °C was studied. A synergistic effect of both sulfuric acid concentration and temperature on the solubility of cerous sulfate was observed. The solubility of cerous sulfate significantly decreased with rising concentration of sulfuric acid and rising temperature, while the solubility of ceric sulfate goes through a significant maximum at 40 °C. Redox potentials and the kinetics of the cerous/ceric redox reaction were also studied under the same temperature–concentration conditions. The redox potentials were measured using the combined redox electrode (Pt–Ag/AgCl) in equimolar Ce 4+/Ce 3+ solutions (i.e.[Ce 3+]=[Ce 4+]) in sulfuric acid electrolyte. The Ce 3+/Ce 4+ redox potentials significantly decrease (i.e. shift to more negative values) with rising sulfuric acid concentration; a small maximum is observed at 40 °C. Cyclic voltammetric experiments confirmed slow electrochemical kinetics of the Ce 3+/Ce 4+ redox reaction on carbon glassy electrodes (CGEs) in sulfuric acid solutions. The observed dependencies of solubilities, the redox potentials and the kinetics of Ce 3+/Ce 4+ redox reaction on sulfuric acid concentration are thought to be the result of inequivalent complexation of the two redox species by sulfate anions: the ceric ion is much more strongly bound to sulfate than is the cerous ion. The best temperature–concentration conditions for the RFB electrolytes appear to be 40 °C and 1 M sulfuric acid, where the relatively good solubility of both cerium species, the maximum of redox potentials, and the more or less satisfying stability of CGE s were found. Even so, the relatively low solubility of cerium salts in sulfuric acid media and slow redox kinetics of the Ce 3+/Ce 4+ redox reaction at carbon indicate that the Ce 3+/Ce 4+ may not be well suited for use in RFB technology.

Geochemistry of Iron and Sulfur in the Zone of Microbial Sulfate Reduction in Mine Tailings

The cycling of iron and sulfur in mine tailings depends on various chemical and microbial reactions. The present study was undertaken in order to assess the role played by populations of sulfate-reducing bacteria (SRB) on the fate of Fe and SO4 2- in Cu–Zn and Au tailings. Samples were taken along a 50-cm deep profile at all sites and analyzed for SRB populations, solid-phase mineralogy and porewater geochemistry. Results indicated that the Cu–Zn tailings were highly oxidized near the surface, as shown by the very low pH, high redox potential, large concentrations of soluble Cu, Zn and sulfate in the porewaters, and the depletion of pyrite. On the other hand, Au tailings were more pH neutral, slightly anoxic, and showed low concentrations of Fe and SO4 2- in the porewaters and very little pyrite oxidation. SRB populations in the Cu–Zn tailings increased with depth, just below the oxic/anoxic interface and were linked to a decline of sulfate and DOC concentrations around the same depths. However, large concentrations of dissolved Fe were also observed around the same depth intervals. Our results suggest that SRB could be involved in sulfate reduction in the Cu–Zn tailings, because the solubility of sulfate was not controlled by the precipitation of sulfate-rich minerals. However, the presence of soluble Fe in the reduced portion of the tailings was also indicative of the presence of iron reducing bacteria (IRB). These bacteria were not enumerated in the present study, but their co-occurrence with SRB has been reported in the past in similar mining environments. The decline of sulfate and the release of soluble iron into the porewaters were also paralleled by a pH increase and the generation of alkalinity. In the Au tailings, SRB populations were generally constant throughout the depth profile and could not be ascribed to sulfate reduction in the porewaters. The solubilities of sulfate and iron in these tailings were partially controlled by jarosite and Fe-oxide minerals. It is then clear that SRB populations could be recovered from various mining sites, but their activity cannot be ascertained based on microbial enumeration and geochemical data.

Thermodynamics and kinetics for mixed calcium carbonate and calcium sulfate precipitation

The effects of CaSO 4 on CaCO 3 precipitation were studied in the batch tests at 60, 70 and 80°C in mixtures having calcium carbonate as the dominant salt and at a given total initial calcium concentration of 0.03 M with sulfate concentration ranging from 0 to 0.01 M . Solubility products and rate constants were determined from thermodynamic and kinetic studies and the results indicated that even minute amounts of calcium sulfate affect the thermodynamics, kinetics and the scale structure and no longer the solubility data and rate constants for the pure salt were applicable. Presence of CaSO 4 from 0.002 to 0.01 M increased the calcium carbonate solubility product more than an order of magnitude. The effect of salt mixture on the solubility constant of non-dominant salt (calcium sulfate) was reverse as calcium sulfate solubility increased to its pure value with increases in its molar ratio. In addition, the rate equation suggested in the literature (J. Colloid Interface Sci. 37 (1971) 824; J. Colloid Interface Sci. 36 (1971) 166) for pure salt was not applicable to the experimental data. The general observations indicated that the presence of CaSO 4 had weakened the CaCO 3 scale which is usually very adherent. The experimental results did take into account the effect of solution ionic strength, however, they suggest that data for pure salt precipitation seem not to be extendable to co-precipitation.

Development of a solution model to correlate solubilities of inorganic compounds in water vapor under high temperatures and pressures

A solution model, based on the regular solution theory coupled with Flory-Huggins entropy term, was developed for the calculation of solubilities of inorganic compounds in water vapor under high temperatures and pressures. The solubilities of sodium chloride (NaCl), potassium hydroxide (KOH), sodium sulfate (Na 2SO 4), lead oxide (PbO), silicon oxide (SiO 2), lithium nitrate (LiNO 3), sodium nitrate (NaNO 3) and potassium nitrate (KNO 3) were correlated by optimizing internal energies and molar volumes of inorganic compounds which give their solubility parameters.

Effect of Sugarbeet By-Products on the Solubility and Availability of Ferrous Sulfate in Soil

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Salt and cosolvent effects on ionic drug loading into microspheres using an O/W method

Salt effects on aqueous solubility and microsphere entrapment efficiency of a model ionic drug (quinidine sulfate) were studied. Poly- d,l-lactic acid (PLA) microspheres were prepared using an O/W solvent evaporation method with various electrolytes added in different concentrations to the aqueous phase. Salts affect microsphere drug loading by changing the aqueous solubility of both the drug and the organic solvent (dichloromethane, DCM). Quinidine sulfate solubility was depressed by either a common ion effect (Na 2SO 4) or by formation of new, less soluble drug salts (e.g., bromide, perchlorate, thiocyanate) for which solubility products ( K sp) were estimated. Inorganic salts depress DCM aqueous solubility to different extents as described by the Hofmeister series. NaClO 4 and NaSCN depressed drug solubility to the highest extent, resulting in microspheres with high drug loading (e.g., >90%). Other salts such as Na 2SO 4 did not depress quinidine sulfate solubility to the same extent and did not improve loading. The use of a cosolvent (ethanol) in the organic phase improved microsphere drug loading and resulted in a uniform microsphere drug distribution with smooth release profiles.

Interfacial Properties of Barium Sulfate Suspensions. Implications in Their Stability

A surface characterization of barium sulfate particles in aqueous suspensions was carried out in this work. With the aim of predicting the stability conditions of these widely used suspensions, the electrical surface properties of the particles were first studied by electrophoretic mobility determinations. It was found that both H+ and OH− ions can be considered as potential‐determining ions for the barium sulfate/water interface. The same conclusion was reached concerning the lattice ions, Ba2+ (mainly) and SO42−. It was also found that increasing the concentration of sodium chloride in the dispersion medium can even change the sign of the zeta (ζ) potential: it is suggested that this behavior is an indirect effect provoked by changes in the solubility of barium sulfate with the ionic strength. To compute the van der Waals (LW) attraction between the particles as well as the acid‐base contribution to the total energy of interaction, a thermodynamic characterization of the interface was also carried out by measuring the rate of penetration of selected liquids through plugs of the particles. It was found that barium sulfate particles are essentially monopolar in nature; that is, they show electron‐donor character as demonstrated by the essentially zero value of the electron‐acceptor component of their surface free energy. Pretreatment of the particles with 10−2 M solutions of BaCl2 and CaCl2 significantly reduced the electron‐donor component, whereas both NaCl and Na2SO4 provoked the opposite effect. This result is explained in terms of the acid–base character of the ions added. These data were used to calculate the interaction energy between the particles. The effect of electrolyte concentration on the stability of the suspensions was analyzed on the basis of the dependence with distance of the interaction energy between the particles. Our results suggest that more stable suspensions of barium sulfate are predicted if moderate amounts of SO42− ions are added to the dispersion medium. © 2000 Wiley‐Liss, Inc. and the American Pharmaceutical Association J Pharm Sci 89: 1134–1142, 2000

Formulation of sustained release aqueous Zn–hirudin suspensions

Sustained release formulations for recombinant hirudin (rHir), an anticoagulant thrombin-specific inhibitor, were developed. Zn–rHir suspensions were formed by precipitation with zinc salts at neutral pH. Characterization of protein precipitation was by UV analysis, capillary electrophoresis (CE), zinc analysis, light and electron microscopy, and particle size analysis. The precipitation of aqueous rHir solution with ZnCl 2 solution at neutral pH resulted in Zn–rHir suspensions. Optimum yields of pelletized Zn–rHir were obtained between pH 7.0 and 7.4. For complete precipitation (∼100%) a molar ratio of zinc to rHir of >28 was necessary. As shown by electron microscopy, the smallest resolvable unit of Zn–rHir suspensions was 20 nm. Agglomerates of up to 200 μm were observed by light microscopy. Zinc salt-induced precipitation phenomena were also investigated using ZnBr 2, ZnI 2, Zn(NO 3) 2 and ZnSO 4 instead of ZnCl 2. ZnSO 4 showed the lowest precipitation efficiency. All other salts behaved similar to ZnCl 2. Upon storage the pelletized protein content of the ZnCl 2 based precipitates was stable (∼95% rHir after 1 year at room temperature), whereas the pelletized protein content of ZnSO 4 based precipitates dropped sharply after precipitation (2% remaining after 13 days at room temperature). This indicates a transition of the ZnSO 4 based precipitates to hexagonal basic zinc sulfate plates and free rHir. The driving force is the lower aqueous solubility of basic zinc sulfate as compared to the higher solubility of basic zinc chloride.

Artificia Therio-Responsive Membrane Able to Control On-Off Switching Drug Release through Nude Mice Skin without Interference from Skin-Penetrating Enhancers

The influence of skin-penetrating enhancers such as Azone, ethanol and propylene glycol (PG) on the on-off switching penetration behavior of salbutamol sulfate through the thermo-responsive cholesteryl oleoyl carbonate (COC)-embedded membrane with or without application to the excised nude mice skin was examined. Without the nude mice skin, gel formulations without any enhancer and with Azone showed higher drug penetration across the COC-embedded membrane than those with ethanol and propylene glycol (PG). Moreover, the on-off switching function of COC-embedded membrane still existed. These results indicate that Azone did not alter the thermo-responsive property of COC-embedded membrane. A lower penetration behavior associated with ethanol or PG was probably due to the increased solubility of salbutamol sulfate in each gel formulation and improved drug-carbopol gel interaction. The application of COC-embedded membrane to excised nude mice skin resulted in a similar on-off switching penetration behavior to the gel, but the penetration was significantly weakened compared to the gel formulation that only penetrated through the COC-embedded membrane. However, passage of salbutamol sulfate across the COC-embedded membrane applied to the excised nude mice skin was severely restricted when an enhancer was absent from the gel. Obviously, the excised skin was the predominant barrier to drug penetration. The present study suggests that skin-penetrating enhancer does not alter the structure of the COC embedded in membrane to change the thermo-responsive on-off switching penetration behavior of salbutamol sulfate from gel formulas through COC-embedded membrane.

The Solubility of Sodium Sulfate and the Reduction of Aqueous Sulfate by Magnetite under Near-Critical Conditions

The solubility of Na2SO4 (s) (thenardite) and the interactions between magnetiteand aqueous Na2SO4 near the critical point of water have been determined in azirconium-alloy flow reactor at temperatures 350°C ≤ t ≤ 375°C and isobaricpressures 190 ≤ p ≤ 305 bar. The experimental solubility data are describedwell as a function of temperature and solvent density ρ1 byln x(Na2SO4, aq.) = −10.47 − 27550/T +(4805/T) ln ρ1.The interaction between magnetite and Na2SO4 (aq.) was examined from 250 to370°C at molalities near the saturation composition of Na2SO4 (s). While no solidreaction products were observed, HS− (aq.) was observed to form above 350°Cby sulfate reduction, as a product of the reaction8 Fe3O4(s) + Na2SO4 (aq.) + H2O(l)= 12 Fe2O3 (s) + NaHS (aq.) + NaOH (aq.).The reduction reaction appears to be controlled by surface reaction kinetics, ata level well below the equilibrium molality of HS− (aq.). Metallic iron reactedwith Na2SO4 (aq.) in a similar fashion at temperatures above 350°C, to yieldhigher molalities of HS− (aq.).