Dissolution Rate Constants Research Articles

Improvement of theophylline anhydrate stability at high humidity by surface-physicochemical modification

To improve the stability of theophylline anhydrate (THA) at high humidity and temperature, the surface of THA was modified by adsorption of n-butanol and phase transformation kinetics and dissolution kinetics were investigated. Hydration kinetics was evaluated using differential scanning calorimetry. The samples were stored in various saturated salt solutions at 30, 40 and 50 °C. A dissolution test was performed in distilled water at 37 °C, 100 rpm. Hydration of THA and surface-modified THA (STHA) at various levels of RH at 40 °C followed a two-dimensional growth of nuclei equation (Avrami equation) including an induction period (IP). The IP of STHA was significantly longer ( p < 0.05) than that of THA at each RH, but the k of STHA was not significantly different ( p > 0.05) from that at each relative humidity (RH). The IP of STMA was significantly longer at 40 and 50 °C, 93% RH ( p < 0.05) than at 30 °C, but there was no significant difference between 40 and 50 °C. The k of THA and STHA increased with the increase in storage temperature at 30–50 °C. Arrhenius plots of the k of THA and STHA showed a straight line. The activation energy of hydration of THA and STHA was 17.60 ± 1.38 and 28.92 ± 5.56 J/mol, respectively. Dissolution of THA and STHA followed the Hixson–Crowell equation, and the dissolution rate constant, K′, was 0.0306 ± 0.0041 and 0.0269 ± 0.0034 mg 1/3 s −1 ( n = 3), respectively.

Elemental composition of urban street dusts and their dissolution characteristics in various aqueous media

Street dust serves as an important archive for environmental contamination in industrialized countries. Heavy metals which are found in street dust such as Cd, Cu, Ni, Pb, and Zn cause pollution in different environmental media. This study was carried out to characterize the composition of different elements embedded in street dusts and to investigate their leaching behavior in the presence of different aqueous media. Samples of street dusts were collected on a weekly basis for 6 months from three different locations in Singapore, viz. residential, commercial and industrial areas, and processed in the laboratory to determine the concentration of 13 elements (Al, As, Co, Cd, Cr, Cu, Fe, Mn, Ni, Pb, Ti, V, and Zn). Concentrations showed considerable variations between sites, and within the same site over a period of time. Dust samples collected from the industrial area were of serious concern as they comprise elevated concentrations of most of the potentially toxic metals such as Cd, Cr, Cu, Pb, and Zn. The surface morphology and presence of different elements in street dust samples were confirmed using SEM/EDX analysis. The enrichment factor, used to describe the chemical characteristics of street dusts, revealed that most of the elements have anthropogenic origin. Of the different media used in dissolution of elements from street dusts, the river water and acidified deionized (DI) water (0.01 M HNO 3) were found to promote significant leaching of most of the elements. With the aid of dissolution kinetic data, the rate constants of dissolution of various elements were determined.

Barite Dissolution/Precipitation Kinetics in Porous Media and in the Presence and Absence of a Common Scale Inhibitor

Summary Field engineers and reservoir modelers often question if equilibrium conditions prevail downhole, and when do super(sub)saturation conditions exist. This questioning is especially critical in designing seawater injection for pressure maintenance caused by serious barite scale problems in barium-containing formation water. This paper: (1) discusses the experimental research on rock-brine interaction to determine if equilibrium conditions and kinetics prevail, and (2) develops realistic seawater/inhibitor injection schemes for scale control during seawater injection. We have examined the question from three points of view: (1) thermodynamic equilibrium, (2) mass transport kinetics, and (3) experimental testing of flow through columns with or without scale inhibitors. If the reaction direction is from undersaturated toward saturation, then equilibrium normally occurs rapidly, being observed within approximately 5 minutes. When the reaction is going from supersaturated to the equilibrium direction, such as during seawater injection into a barium-containing formation, the precipitation reaction is often slow (i.e., equilibrium is not observed after 10 minutes of contact time. Both barite dissolution and precipitation rates on clean core material are consistent with those reported in literature with a second order rate constants for dissolution (≈30,172 L2·mol−1·m−2·sec−1, 100°C) and precipitation (= 938 L2·mol−1·m−2·sec−1, 100°C). The kinetics of barite formation can significantly slow down in the presence of scale inhibitors, and the sulfate tolerance can be increased. The kinetics of both barite dissolution and precipitation are poorly understood at the present time. Combining sulfate reduction and scale-inhibitor application in intelligent engineering design can significantly reduce the problems and costs associated with seawater injection. Equations for the engineering design of such treatment were derived from nucleation kinetics, inhibition efficiency, and inhibitor adsorption and transport. Sulfate tolerance in the presence of scale inhibitors is measured and compared with the prediction from nucleation inhibition theory with excellent agreement. An innovative inhibitor treatment by way of coreflood has been done as proof-of-concept and is discussed herein.

Effect of ammonium compounds on dissolution rate of South African calcium-based material

The rate at which limestone dissolves is very important in wet flue gas desulphurisation process (FGD). High dissolution rates provide better alkalinity that is important for sulphur dioxide (SO 2) absorption. The dissolution characteristics have been studied by using a pH-Stat method at 60 °C, at pH value of 5, stirrer speed of 100 rpm and particle size of 44 μm. This paper examines the use of ammonium compound as the possible additives that will enhance the dissolution rate of limestone. The dissolution rates were measured according to the shrinking core model with surface control, i.e. (1 −(1 − X) 1/3) = k r t. It was found that the dissolution rate increases in the presence of ammonium compounds. Upon addition of 0.5 g of ammonium nitrate, the dissolution rate constants increased by 170%. As the pH is increased the dissolution rate decreases. The dissolution reaction follows a shrinking core model with the chemical reaction control as the rate-controlling step.

CO2地中貯留への適用のための玄武岩質岩石の溶解実験

Dissolution rates of three basaltic rock samples from Japan (Fuji (sample1) and Hachijyojima (sample 2) fresh basaltic rocks, and Kitamatsuura (sample 3) altered basaltic rock) were experimentally determined in a pH range from 3 to 11 at 25°C. Initial dissolution rate constants are high (-9.9 ∼ -10.4 in logarithmic unit) . It is inferred that the initial dissolution rate is controlled by proton-cation (alkali, alkali earth and aluminium) ion exchange reaction and breakdown of Si-O bond in silicate. Long-term dissolution rate constants for Si determined are -11.5 ∼ -11.8 (in logarithmic unit) (sample1) and -11.3 ∼ -11.8 (sample 2) . These values are lower than those for artificial basalt glass previously obtained. The rate constant determined for sample 3 is consistent with those of feldspar previously studied. In future based on the present results on the dissolution rate of basaltic rocks, we will perform calculation on the temporal changes of the amount of carbonates precipitating from groundwater reacting with basaltic host rocks in order to estimate the amount of CO2 fixed by mineral trapping for underground CO2 sequestration in basaltic rock area in Japan.

Development of matrix controlled transdermal delivery systems of pentazocine: In vitro/in vivo performance

The present study aimed to develop hydroxypropyl methylcellulose based transdermal delivery of pentazocine. In formulations containing lower proportions of polymer, the drug released followed the Higuchi kinetics while, with an increase in polymer content, it followed the zero-order release kinetics. Release exponent (n) values imply that the release of pentazocine from matrices was non-Fickian. FT-IR, DSC and XRD studies indicated no interaction between drug and polymer.The in vitro dissolution rate constant, dissolution half-life and pharmacokinetic parameters (C(max), t(max), AUC(s), t(1/2), Kel, and MRT) were evaluated statistically by two-way ANOVA. A significant difference was observed between but not within the tested products. Statistically, a good correlation was found between per cent of drug absorbed from patches vs. C(max) and AUC(s). A good correlation was also observed when per cent drug released was correlated with the blood drug concentration obtained at the same time point. The results of this study indicate that the polymeric matrix films of pentazocine hold potential for transdermal drug delivery.

UC oxidation with HNO2 in aqueous solutions of HNO3 and HClO4

The oxidation of UC powder was studied in 0.5–6.0 M HNO 3 and HClO 4 , containing 0.01–0.1 M NaNO 2 , at ambient temperature. The addition of nitrous acid caused the oxidation potential to exceed 400 mV/SCE and thus accelerated the dissolution and increased the dissolution yield to exceed 95%. One hundred percent dissolution at room temperature was achieved within 30 to 40 min when 3.0–6.0 M HNO 3 was used that contained more than 0.005 M HNO 2 .The dissolution rate increased with increasing HNO 3 concentration and initial solid-to-liquid ratio. The effective dissolution rate constants and reaction orders were estimated for the UC oxidation with H + , NO 3 - and HNO 2 in 0.5–6.0 M HClO 4 . The rate of UC oxidation with HNO 2 exceeded 50–80 times its oxidation rates with NO 3 - ions. During UC oxidation with HNO 2 in 0.5–6.0 M HClO 4 , 60–85% carbon was oxidized to CO 2 . The C/U(VI) ratio in the dissolver solution decreased from 0.5 to 0.1 mg eq/mol with increasing of HClO 4 and HNO 2 solution concentration. Two to five percent of the carbon remained in the insoluble residue of the HNO 3 dissolver solutions, even when a 100% U(VI) yield was observed. Scanning electron microscopy of the insoluble residue showed the carbon particle size between 1.0 and 5.0 μm.

Dissolution kinetics of biogenic silica collected from the water column and sediments of three Southern California borderland basins

Understanding biogenic silica (bSi) dissolution kinetics in margin environments is important in assessing the global silicon cycle, a cycle closely linked to the global carbon cycle. This understanding is also essential to answer the question of whether bSi content in marine sediment is a valid indicator of productivity in the overlying surface ocean. In this study, plankton tow, sediment trap, and sediment samples were collected at sites in three Southern California borderland basins. Batch dissolution experiments with plankton tow and sediment trap materials (conducted in the laboratory at 22 °C) showed linear dissolution kinetics, from which mean dissolution rate constants of 0.05 d − 1 for plankton tow samples and 0.07 d − 1 for sediment trap samples could be calculated. The dissolution rate constants for both types of samples showed seasonal variability but not the same seasonal patterns. Faster dissolution was observed with sediment trap samples collected at 800 m than at 550 m. With sediment multi-core samples, non-linear dissolution kinetics was observed, which complicates the direct comparison of dissolution rates. Nonetheless, dissolution appeared to be slower for the sediments samples than for samples collected from the water column and to decrease with depth in the sediments. Rate constants for surface sediment (0–0.5 cm) were at least 3–5 times less, and sediments at depths > 2 cm had rate constants at least 6–13 times less than those for material sinking to the sediment surface at these sites. Dissolution experiments conducted with Santa Barbara Basin surface sediment samples amended with dissolved aluminum (Al) and San Pedro Basin trap samples amended with enriched detrital materials (obtained by leaching bSi from sediment samples) suggested that dissolution was inhibited by Al and that the sediments from the different basins varied in the extent of Al release.

Coupled alkali-feldspar dissolution and secondary mineral precipitation in batch systems: 1. New experiments at 200 °C and 300 bars

Batch reactor experiments were conducted to assess perthitic alkali-feldspar dissolution and secondary mineral formation in an initially acidic fluid (pH = 3.1) at 200 °C and 300 bars. Temporal evolution of fluid chemistry was monitored by major element analysis of in situ fluid samples. Solid reaction products were retrieved from two identical experiments terminated after 5 and 78 days. Scanning electron microscopy revealed dissolution features and significant secondary mineral coverage on feldspar surfaces. Boehmite and kaolinite were identified as secondary minerals by X-ray diffraction and transmission electron microscopy. X-ray photoelectron spectroscopy analysis of alkali-feldspar surfaces before and after reaction showed a trend of increasing Al/Si ratios and decreasing K/Al ratios with reaction progress, consistent with the formation of boehmite and kaolinite. Saturation indices of feldspars and secondary minerals suggest that albite dissolution occurred throughout the experiments, while K-feldspar exceeded saturation after 216 h of reaction. Reactions proceeded slowly and full equilibrium was not achieved, the relatively high temperature of the experiments notwithstanding. Thus, time series observations indicate continuous supersaturation with respect to boehmite and kaolinite, although the extent of this decreased with reaction progress as the driving force for albite dissolution decreased. The first experimental evidence of metastable co-existence of boehmite, kaolinite and alkali feldspar in the feldspar hydrolysis system is consistent with theoretical models of mineral dissolution/precipitation kinetics where the ratio of the secondary mineral precipitation rate constant to the rate constant of feldspar dissolution is well below unity. This has important implications for modeling the time-dependent evolution of feldspar dissolution and secondary mineral formation in natural systems.

Measurement of the pure dissolution rate constant of a mineral in water

We present here a methodology, using holographic interferometry, enabling to measure the pure surface reaction rate constant of the dissolution of a mineral in water, unambiguously free from the influence of mass transport. We use that technique to access to this value for gypsum and we demonstrate that it was never measured before but could be deduced a posteriori from the literature results if hydrodynamics is taken into account with accuracy. It is found to be much smaller than expected. This method enables to provide reliable rate constants for the test of dissolution models and the interpretation of in situ measurements, and gives clues to explain the inconsistency between dissolution rates of calcite and aragonite, for instance, in the literature.

Effect of mechanical processing on the dissolution rate of MgO

The kinetics of MgO dissolution after attrition grinding have been studied using photometry and pH measurements. The dissolution rate constant, limiting magnesium ion concentration, and solution pH have been shown to pass through a maximum at a certain attrition time. The effect of attrition time on the dissolution rate is interpreted in terms of the surface condition and aggregation of the powder particles.

Dissolution of Biogenic and Synthetic UO2 under Varied Reducing Conditions

The chemical stability of biogenic UO2, a nanoparticulate product of environmental bioremediation, may be impacted by the particles' surface free energy, structural defects, and compositional variability in analogy to abiotic UO(2+x) (0 < or = x < or = 0.25). This study quantifies and compares intrinsic solubility and dissolution rate constants of biogenic nano-UO2 and synthetic bulk UO2.00, taking molecular-scale structure into account. Rates were determined under anoxic conditions as a function of pH and dissolved inorganic carbon in continuous-flow experiments. The dissolution rates of biogenic and synthetic UO2 solids were lowest at near neutral pH and increased with decreasing pH. Similar surface area-normalized rates of biogenic and synthetic UO2 suggest comparable reactive surface site densities. This finding is consistent with the identified structural homology of biogenic UO2 and stoichiometric UO2.00 Compared to carbonate-free anoxic conditions, dissolved inorganic carbon accelerated the dissolution rate of biogenic UO2 by 3 orders of magnitude. This phenomenon suggests continuous surface oxidation of U(IV) to U(VI), with detachment of U(VI) as the rate-determining step in dissolution. Although reducing conditions were maintained throughout the experiments, the UO2 surface can be oxidized by water and radiogenic oxidants. Even in anoxic aquifers, UO2 dissolution may be controlled by surface U(VI) rather than U(IV) phases.

Dissolution kinetics of dehydroxylated nickeliferous goethite from limonitic lateritic nickel ore

The dissolution kinetics in 2 M H 2SO 4 of variously dehydroxylated nickeliferous goethites was investigated for five oxide-type lateritic nickel deposits. Goethite was the main constituent with minor amounts of quartz, talc, kaolinite and Mn oxides. Dissolution of Fe from heated materials followed the Kabai equation. There was a 9–34-fold increase in the Kabai dissolution rate constant ( k) for samples heated at 340–400 °C due to both the increased surface area (1.5–2.6 fold) and higher density of structural defects (5–10 fold) in the variously dehydroxylated products. The presence of structural Al and Cr in goethite appears to reduce dissolution rate possibly through the greater M 3+–OH, O bond strength relative to Fe 3+, Ni 2+–OH, O. Nickel showed congruent dissolution with Fe indicating that Ni was uniformly incorporated in the goethite structure. Pre-heating goethite to 600–800 °C for 30 min resulted in incongruent dissolution of Fe and Ni. It is postulated that some Ni is ejected from the neo-formed hematite structure and resides on the crystal surface or in voids. These results may contribute to the development of more efficient procedures for Ni extraction including heap leaching of lateritic nickel ores.

Comparison of catalytic decomposition of hydrogen peroxide and catalytic degradation of phenol by immobilized iron oxides

Abstract Immobilized iron oxides on silica matrixes in fluidized bed reactors, including SiG1, SiG2, C1, and the commercial catalyst FeOOH, were used in the catalytic decomposition of H2O2 and the catalytic degradation of phenol. They were characterized using XRD, SEM, N2-sorption, and elucidation of the kinetics of dissolved iron by oxalic acid in dark surroundings. XRD patterns reveal that SiG1, SiG2, and C1 exhibit amorphous structures, and FeOOH exhibits the poor crystallinity of goethite. The SEM images reveal that the surfaces of all the iron oxides are smooth and that the iron oxides are aggregated by the iron oxide floc. The N2-sorption isotherm indicates that SiG1 and SiG2 are non-porous materials, and that C1 and FeOOH are typical type II and typical type IV materials, respectively. A kinetic model for iron dissolved by oxalic acid is established. The order of apparent first-order dissolution rate constants (kc) is SiG1 > SiG2 > FeOOH ∼ C1. The immobilized iron oxides, SiG1 and SiG2, are weakly bonded to the support (silica sand) in the presence of oxalic acid. The decomposition of H2O2 follows pseudo-first-order kinetics. The number of active sites for the decomposition of H2O2 is similar among all iron oxides at a particular kapp (1.8 × 10−3 min−1). There are no interactions between phenol and iron oxides in the absence of hydrogen peroxide at pH 4. SiG1 and SiG2 exhibit much higher catalytic activities in phenol degradation than either C1 or FeOOH. The reactivity of iron oxides in catalyzing the phenol degradation by H2O2 relates to the tendency of iron to be dissolved by oxalic acid. The intermediates of phenol degradation, such as catechol and oxalic acid, promote the dissolution of iron from SiG1 and SiG2 by reductive and non-reductive pathways and lower the pH values. The catalyses of SiG1 and SiG2 involve heterogeneous and homogeneous reactions.

A Dissolution-Diffusion Model and Quantitative Analysis of Drug Controlled Release from Biodegradable Polymer Microspheres

Controlled release behaviours of nifedipine loaded poly (D,L-lactide) (PLA) and poly(D,L-lactide-co-glycolide) (PLGA) microspheres are investigated and modelled in this paper. Based on the integrated consideration of diffusion, finite dissolution rate, moving front of dissolution and size distribution of microspheres, a mathematic model is presented to quantitatively describe the drug release kinetics. The coupled partial differential equations are numerically solved. Dynamic concentration profiles of both dissolved and undissolved drug in the microspheres are analyzed. In comparison with the diffusion model and Higuchi model, the proposed dissolution-diffusion model is characteristic of describing the whole release process without limitation of different dissolution rate or dissolubility. The diffusion coefficient and the dissolution rate constants are evaluated from measured release profiles. The effects of microstructures of polymer microspheres on release behaviours are related to parameters of the model. Based on the mathematical model and in vitro release data, intrinsic mass transfer mechanism is further investigated.

Determining the partial currents of silver ionization, its oxide formation, and chemical dissolution by multicycle chronoammetry with an RRDE

A multicycle chronoammetry with a rotating disc electrode with a ring (RRDE) enables one to experimentally discriminate between the partial currents of the substrate metal ionization, anodic formation of the oxide, and chemical dissolution of the oxide in the summary polarization current of the disc. The technique is approved by an example of Ag|Ag2O|OH−(H2O) system. In a range of relatively small anodic potentials of the Ag disc (0.48 to 0.51 V), the active dissolution of silver at the open surface sites and via pores in the surface film dominates; the phase formation current and, accordingly, the current efficiency of the process rapidly drop. At the potentials of the voltammogram maximum (0.52 to 0.53 V) when the silver active dissolution current is suppressed, the phase formation currents prevail and substantially exceed the chemical dissolution rate of the oxide. The thickness of an Ag2O film rapidly increases under these conditions, and the current efficiency of the oxide formation is close to 100% for the whole polarization period. The rate constant of the chemical dissolution of an Ag(I) oxide is practically independent of the anodic phase-formation potential, but slightly depends on the oxide film thickness, reflecting changes in the film structure and, possibly, in its composition, from AgOH to Ag2O.

Modelling chemical depletion profiles in regolith

Chemical or mineralogical profiles in regolith display reaction fronts that document depletion of leachable elements or minerals. A generalized equation employing lumped parameters was derived to model such ubiquitously observed patterns: C = C 0 C 0 − C x = 0 C x = 0 exp ( Γ ini · k ˆ · x ) + 1 Here C, C x = 0 , and C o are the concentrations of an element at a given depth x, at the top of the reaction front, or in parent respectively. Γ ini is the roughness of the dissolving mineral in the parent and k̂ˆ is a lumped kinetic parameter. This kinetic parameter is an inverse function of the porefluid advective velocity and a direct function of the dissolution rate constant times mineral surface area per unit volume regolith. This model equation fits profiles of concentration versus depth for albite in seven weathering systems and is consistent with the interpretation that the surface area (m 2 mineral m − 3 bulk regolith) varies linearly with the concentration of the dissolving mineral across the front. Dissolution rate constants can be calculated from the lumped fit parameters for these profiles using observed values of weathering advance rate, the proton driving force, the geometric surface area per unit volume regolith and parent concentration of albite. These calculated values of the dissolution rate constant compare favorably to literature values. The model equation, useful for reaction fronts in both steady-state erosional and quasi-stationary non-erosional systems, incorporates the variation of reaction affinity using pH as a master variable. Use of this model equation to fit depletion fronts for soils highlights the importance of buffering of pH in the soil system. Furthermore, the equation should allow better understanding of the effects of important environmental variables on weathering rates.

Physical and Release Properties of Metronidazole Suppositories

Purpose: A study was made of the effects of some bases and adjuvants on the physical and release properties of metronidazole suppositories with a view to providing more information for the optimization of the rectal formulation of metronidazole. Method: Suppositories (1g) containing 200mg of metronidazole each were prepared in witepsol (H15 and E75) and polyethylene glycol (PEG 2850 and 4650) bases, using different concentrations of Tween 80, sodium salicylate and methylcellulose as adjuvants. The setting time, solidification point and melting range of the suppositories were determined, along with their crushing strength, disintegration time and the time for 80% of metronidazole to be released from the suppositories (t80). Results: The ranking of setting time for the suppositories was witepsol H15 > PEG 2850 > witepsol E75 > PEG 4650, while the ranking of solidification point, melting range, crushing strength, disintegration time and the time for 80% of metronidazole to be released from the suppositories (t80) was the reverse of that for setting time. Optimal concentrations of Tween 80 and sodium salicylate were observed for the suppository formulations. Using Kitazawa plots, all formulations showed two dissolution rate constants, k1 and k2 intersecting at time t1, with formulations containing 5 to 20 % w /w of methylcellulose exhibiting a third dissolution rate constant, k3 intersecting with k2 at time t2. Conclusion: The physical and release properties of metronidazole suppositories are influenced considerably by the bases and adjuvants employed. Tween 80 and sodium salicylate can probably be used to formulate only immediate-release suppositories while methylcellulose can be useful for sustained-release metronidazole suppositories. Some insight into these inferences can be obtained from parameters derived from Kitazawa plots.

Study of Electroless Copper Deposition on Fe Powder

The electrolytic deposition of an electropositive metal is often accompanied by electroless deposition. However, this process is very difficult to control. For that reason, our study has been aimed at the conditions of the electroless deposition of copper coating onto the iron powder particles from sulphate electrolyte. The process consists of two partial reactions; solid iron substrate dissolves into the solution, thus providing the electrons necessary for reduction of copper. The course of the electroless process depends to a large extent on the composition and pH of the electrolyte as well as on the size and concentration of the iron powder particles in the electrolyte. In order to suppress the spontaneous electroless deposition of copper, sodium citrate as complexing agent was used. The following parameters were determined to characterize the reaction course: the heterogeneous rate constant of Fe powder dissolution and degree of Fe conversion as well as thickness of the Cu layer on the Fe powder, both of the latter evaluated upon attaining the stationary state. The main influence exhibited on the reaction course is the efficient surface area available for electroless deposition.

Effect of Inorganic Ligands and Hydrogen Peroxide on ThO2 Dissolution. Behaviour of Th0.87Pu0.13O2 during Leaching Test

The dissolution of ThO2 powdered samples was examined in various conditions of pH and concentration of anions in the leachate. The first part of this paper describes the influence of pH on the dissolution of ThO2 in both nitric and hydrochloric media. The partial order relative to the proton concentration and the apparent normalized dissolution rate constants were determined. The second part of the paper describes the influence of other ligands such as perchlorate, chloride, sulfate, and hydrogen peroxide on the dissolution kinetics (at pH 1). An increase of RL was observed correlatively with the increase of complexing affinity of the ligand with Th. While nitric and hydrochloric media, which are weakly complexing, lead to RL values with the same order of magnitude as those for perchlorate media, the presence of sulfate or peroxide in the leachate significantly enhances the dissolution of ThO2. Consequently, the dissolution mechanism can be explained by the weakening of Th-O bonds through the formation of surface complexes at the solid/liquid interface, which enhance the detachment and thus accelerate the global dissolution. In addition, the dissolution of Th 0.87Pu 0.13O2 solid solution was also examined. The increase of the dissolution kinetics of Th 0.87Pu 0.13O 2, in comparison with that of ThO2, is considered to be caused by the presence of hydrogen peroxide formed by radiolysis of the leachate. Moreover, the redox properties of plutonium in acidic media, like disproportionation of Pu(IV) and Pu(V) and reduction of Pu(VI) and Pu(IV) in Pu(III) by H2O2, probably increase the dissolution of plutonium.