Measured Dissolution Rates Research Articles

A method for preparation and cleaning of uniformly sized arsenopyrite particles.

BackgroundThe oxidative dissolution of sulfide minerals, such as arsenopyrite (FeAsS), is of critical importance in many geochemical systems. A comprehensive understanding of their dissolution rates entails careful preparation of the mineral surface. Measurements of dissolution rates of arsenic from arsenopyrite are dependent on the size and degree of oxidation of its particles, among other factors. In this work, a method was developed for preparation and cleaning of arsenopyrite particles with size range of 15-250 μm. Four different cleaning methods were evaluated for effectiveness based on the removal of oxidized species of iron (Fe), arsenic (As) and sulfur (S) from the surface. The percentage oxidation of the surface was determined using X-ray photoelectron spectroscopy (XPS), and surface stoichiometry was measured using scanning electron microscopy - energy dispersive X-ray spectroscopy (SEM-EDS).ResultsResults indicate that sonicating the arsenopyrite particles and then cleaning them with 12N HCl followed by 50% ethanol, and drying in nitrogen was the most effective method. This method was successful in greatly reducing the oxide species of Fe while completely removing oxides of As and S from the arsenopyrite surface.ConclusionsAlthough sonication and acid cleaning have been widely used for mineral preparation, the method described in this study can significantly reduce grain size heterogeneity as well as surface oxidation, which enables greater control in surface and dissolution experiments.Electronic supplementary materialThe online version of this article (doi:10.1186/s12932-014-0014-9) contains supplementary material, which is available to authorized users.

Corrosion mechanisms of Zn(Mg,Al) coated steel: The effect of HCO3− and NH4+ ions on the intrinsic reactivity of the coating

The effect of NH4+ and/or HCO3− ions on the reactivity of hot dip galvanized steel and Zn - 3.7wt. % Mg–3wt. % Al coated steel in aqueous solutions containing Cl− was studied by direct measurement of the elemental dissolution rates of Zn, Mg and Al by atomic emission spectroelectrochemistry at open circuit potential and under alternating anodic (0.95V vs SCE) and cathodic (-1.15V vs SCE) potentiostatic pulses. The anodic reactivity of ZnMgAl coating was higher compared to a standard hot dip galvanized coating in all electrolytes. Mg rich phases were selectively dissolved. NH4+ increased the anodic reactivity of Zn in both coatings, suppressed the accumulation of zinc corrosion products, and inhibited Al dissolution at open circuit. HCO3− increased the accumulation of insoluble zinc corrosion products as well as the anodic reactivity. The cathodic current on the fresh surface of ZnMgAl in 0.1M NaCl and in the mixture of 0.1M NH4Cl and 0.1M NaHCO3 was the same but cathodic dissolution of Al was higher in the mixed electrolyte. A series of alternating anodic and cathodic potentiostatic pulses demonstrated that the preliminary anodic polarization modified the following response of ZnMgAl on the cathodic pulse: the cathodic Al dissolution was significantly delayed and the cathodic current increased in mixed electrolyte. The cathodic current in NaCl was not affected by the preliminary anodic polarization. The effect was interpreted using a hypothesis of the formation of low soluble Mg carbonates during anodic polarization. Layered double hydroxides were not detected on ZnMgAl coatings after short experiments in mixed electrolyte. In contrast, Mg(OH)2, which is thermodynamically less stable at slightly alkaline pH, was detected. This indicates the importance of kinetic factors for the formation of corrosion products during the first stages of corrosion.

Experimental study of alcoholic retarded acid systems for high temperature gas wells acidizing process

Matrix acidizing treatments are applied to gas wells to remove near-wellbore permeability impairment (formation damage). This work relates to the use of some alcoholic components as a retarding agent in gas field acidizing operations to reduce rate of calcium carbonate (dolomite MgCa(CO3)2) dissolution by acid. The retarding agent is feasible to “retard” acid formulations and slow down their reaction rates to allow deeper penetration of live acid or preferential creation of large wormholes through any near-wellbore damage. In this study, two new alcoholic retarding acid systems (RE 1, RE 2) are presented. RE 2 is stable up to 75°C, highly retarded compared to the straight acid. Laboratory data comparing alcoholic retarding acid with commercial retarding acid (F-98) and straight acid are shown at temperatures ranging up to 75°C. Moreover, results show that RE 1 is a proper retarding agent for low temperature and deep gas well acidizing. Reaction rates of RE 1 and RE 2 (acid systems) with dolomite MgCa(CO3)2 are slower than the reaction rate of commercial retarding acid system (F-98) at low and high temperatures. Experiments are conducted in a rotating disk instrument to measure dissolution rates of dolomite rock samples in retarding acid systems and straight acid. A rotating disk system is used at 30–75°C under a pressure of 8MPa and rotational speeds up to 1200rpm.

Wet creep of hardened hydraulic cements — Example of gypsum plaster and implication for hydrated Portland cement

Gypsum plaster exhibits a dramatic creep when placed in a very humid environment. We have combined mechanical tests of wet bending creep of set plaster and holographic interferometry measurements of dissolution rate and diffusion coefficient to look for the origin of this wet creep. Both these experiments have been performed in the absence and presence of various known anti-creep admixtures. It appears that the creep rate and dissolution rate are strongly correlated. This correlation has allowed to propose surface-driven pressure solution creep as mechanism of wet creep of gypsum plaster, i.e., the sequence dissolution in the grain boundary water/diffusion/precipitation at the grain surface. An order of magnitude analysis shows that this dissolution–diffusion–recrystallization series can also contribute to the creep of hydrated Portland cement.

Response of acid mobilization of iron-containing mineral dust to improvement of air quality projected in the future

Abstract. Acidification of dust aerosols may increase aerosol iron (Fe) solubility, which is linked to mineral properties. Combustion aerosols can also elevate aerosol iron solubility when aerosol loading is low. Here, we use an atmospheric chemical transport model to investigate the deposition of filterable iron and its response to changes in anthropogenic emissions of both combustion aerosols and precursor gases. By introducing three classes of iron-containing minerals into the detailed aerosol chemistry model, we provide a theoretical examination of the effects of different dissolution behaviors on the acid mobilization of iron. Comparisons of modeled Fe dissolution curves with the measured dissolution rates for African, east Asian, and Australian dust samples show overall good agreement under acidic conditions. The improved treatment of Fe in mineral dust and its dissolution scheme results in reasonable predictive capability for iron solubility over the oceans in the Northern Hemisphere. Our model results suggest that the improvement of air quality projected in the future will lead to a decrease of the filterable iron deposition from iron-containing mineral dust to the eastern North Pacific due to less acidification in Asian dust, which is mainly associated with the reduction of nitrogen oxides (NOx) emissions. These results could have important implications for iron fertilization of phytoplankton growth, and highlight the necessity of improving the process-based quantitative understanding of the response of the chemical modification in iron-containing minerals to environmental changes.

Selection of acid for weak acid processing of wollastonite for mineralisation of CO2

Typically, mineral carbonation comprises aqueous phase reactions involving the dissolution of naturally occurring magnesium and calcium silicate rocks, such as olivine, serpentinites and wollastonite, followed by the precipitation of magnesium and calcium carbonate minerals. In this report, we evaluated the effect of formic, acetic and DL-lactic acids on the calcium-leaching process from wollastonite between 22°C and 80°C and at atmospheric pressure. OLI Analyzer Studio 3.0 predicted equilibrium conversions of calcium and its speciation in the aqueous phase. Additionally, we measured dissolution rates, for a constant pH system, as a function of temperature for the three organic acids. All experiments involved the reaction of 17±1μm (volume mean diameter) ground rock samples with the acids in a stirred batch reactor equipped with in situ pH measurements. Inductively coupled plasma-optical emission spectrometry (ICP-OES) analysed the concentration of calcium ions in the leaching medium while scanning electron microscopy/energy dispersive spectroscopy (SEM/EDS) examined the morphology and surface chemical composition of the residual solid phase from dissolution experiments. We estimated the maximum dissolution rates of wollastonite in the limit of low but achievable pH and in the absence of diffusion limitation in pores and cracks of the SiO2 skin. At 80°C, these rates correspond to 26(±7)×10−5, 14(±3)×10−5 and 17(±4)×10−5molm−2s−1 for formic, acetic and DL-lactic acids, respectively. The apparent activation energies amount to 11±3, 47±13 and 52±14kJmol−1 for dissolution in formic, acetic and DL-lactic acids, respectively. These values indicate the initial diffusion limitation in the film around wollastonite particles for formic acid, and kinetic limitation for acetic and DL-lactic acids. The rates of dissolution rapidly decline for acetic and DL-lactic acids, but remain high for formic acid. The findings are altogether indicative of high performance of formic acid for extraction of Ca2+ for storing CO2. Further experiments are needed to assess the recycling of formic acid to determine its overall suitability as a Ca2+ carrier for the weak acid process.

Measurement of Stress Changes during Growth and Dissolution of Anodic Oxide Films on Aluminum

While stress is thought to play an important role in the development of self-organized porous films, mechanisms of stress generation during anodizing are not yet understood. In order to reveal depth distributions of stress in anodic films, phase-shifting curvature interferometry was used to monitor force transients (in-plane stress integrated through the sample thickness) during formation of anodic oxides on aluminum in phosphoric acid, as well as subsequent open-circuit dissolution. The measurements were not influenced significantly by electrostatic stress, internal stress in the metal samples, thermal stress, or stress induced by open-circuit dissolution. At typical current densities, the force became more compressive during anodizing, while a net tensile force change was measured after anodizing followed by complete oxide dissolution. Thus, it was revealed that anodizing generates both compressive stress in the oxide and tensile stress near the metal-oxide interface. Analysis of the open-circuit stress change revealed separate contributions from diffusional stress relaxations, and removal of residual oxide stress by dissolution. Residual stress distributions in the oxide, at nanometer depth resolution, were determined from measurements of dissolution rate and stress at open circuit, and validated through variations of the open-circuit dissolution rate.

木炭の炭素結晶性と灰分が溶鉄への炭素溶解と鉄−木炭コンポジットの浸炭反応に及ぼす影響

Charcoal use instead of fossil fuel is one of the possible technologies for mitigation of CO2 emission in the steel industry because charcoal can be considered as “carbon-neutral” material. In this study, the possibility of utilization of charcoal as carbon source for carburization reaction was examined; more specifically effects of carbon crystalinity and ash in charcoal on carbon dissolution into molten iron and iron carburization reaction in iron-charcoal composite were investigated. Two kinds of experiments were carried out. One is measurement of charcoal carbon dissolution rate in iron bath. Another is observation of isothermal reaction between iron and charcoal in a composite sample. Several kinds of charcoal with relatively low ash content were applied as experimental samples. Charcoal samples were treated with several heating patterns to control their carbon crystallinity. Additionally, charcoal samples were treated with acid solutions, HCl and HF, to control the ash content in them. From these investigations, following results were revealed. Charcoal heat-treated at low temperature, 1 273 K, has advantage for carbon dissolution reaction into iron bath. Charcoal ash strongly prevents the carburization reaction between iron and carbon in the composite sample.

In situ measurements of dissolution rates of Vendian Aluminosilicates

In situ measurements of dissolution rates of Vendian Aluminosilicates

Batch Reactor experimental Results for GaMin’11: Reactivity of Siderite/Ankerite, Labradorite, Illite and Chlorite Under CO2 Saturated Conditions

A series of batch reactor experiments were conducted to measure the rate of dissolution of four mineral specimens under conditions of CO saturation at 200 bar and 80oC in NaCl brines. Comparing the results within individual experiments and against those of eleven different laboratories participating in an interlaboratory comparison study (GaMin’11) shows wide variability, up to two orders of magnitude, in measured dissolution rates of individual minerals. In general, elevated pCO2 appears to have little effect on mineral dissolution rates other than the expected increase in dissolution rate induced by the increase in acidity of solutions.

Nontronite dissolution rates and implications for Mars

The Fe-rich smectite nontronite M+1.05[Si6.98Al1.02][Al0.29Fe3.68Mg0.04]O20(OH)4 has been detected using orbital data at multiple locations in ancient terrains on Mars, including Mawrth Vallis, Nilli Fossae, north of the Syrtis Major volcanic plateau, Terra Meridiani, and the landing site of the Mars Science Laboratory (MSL), Gale Crater. Given the antiquity of these sites (>3.0Ga), it is likely that nontronite has been exposed to the martian environment for long periods of time and therefore provides an integrated record of processes in near surface environments including pedogenesis and diagenesis. In particular, nontronite detected at Mawrth Vallis is overlain by montmorillonite and kaolinite, and it has been previously suggested that this mineralogical sequence may be the result of surface weathering. In order to better understand clay mineral weathering on Mars, we measured dissolution rates of nontronite in column reactors at solution pH values of 0.9, 1.7, and 3.0, and two flow rates (0.16ml/h and 0.32ml/h). Solution chemistry indicates stoichiometric dissolution at pH=0.9 and non-stoichiometric dissolution at pH=1.7 and 3.0. Mineral dissolution rates based on elemental release rates at pH=1.7 and 3.0 of Ca, Si and Fe follow the order interlayer>tetrahedral>octahedral sites, respectively. The behavior of all experiments suggests far from equilibrium conditions, with the exception of the experiment performed at pH 3.0 and flow rate 0.16ml/h. A pH-dependent dissolution rate law was calculated through Si release from experiments that showed no dependence on saturation (far from equilibrium conditions) under both flow rates and is r=10−12.06 (±0.123)·10−0.297 (±0.058)·pH where r has the units mol mineral m−2s−1. When compared to dissolution rates from the literature, our results indicate that nontronite dissolution is significantly slower than dissolution of the primary phases present in basalt under acidic conditions, suggesting that once nontronite forms it could remain stable at or near the surface of Mars for extended periods of time. Nontronite dissolution rates are faster than dissolution rates of montmorillonite (Rozalén et al., 2008) and kaolinite (Huertas et al., 1999), suggesting that chemical weathering of a mixed clay deposit would enrich the proportions of montmorillonite and kaolinite through the preferential dissolution of nontronite. Vis–NIR analyses of our reacted products and thermodynamic modeling of our experimental conditions both indicate the precipitation of amorphous silica within columns, and amorphous silica has also been observed in association with phyllosilicates on the martian surface (Mustard et al., 2008; Ehlmann et al., 2009; Murchie et al., 2009a). Therefore, chemical weathering of strata containing mixtures of montmorillonite, nontronite and kaolinite provides a potential formation mechanism for the mineralogic stratigraphy observed at Mawrth Vallis and other locations on Mars.

Anticorrosion mechanisms of aluminized steel for hot stamping

An improved corrosion resistance of aluminized press hardened steel Usibor® AlSi compared to untreated 22MnB5 steel is observed in cyclic corrosion tests even though cracks are present in the coating after the hot stamping resulting in the simultaneous corrosion of the coating and the steel beneath. The coating shows a poorer performance in continuous salt spray test than in cyclic corrosion test. Electrochemical measurements and in situ measurement of the elemental dissolution rates combined with the characterization of the corroded surface are used to argue in favor of an anticorrosion mechanism related to the barrier protection by corrosion products formed. Al and Fe oxides were formed in continuous test and aluminosilicates and a mixture of hydroxides after the cyclic test. The formation of specific corrosion products is assumed to be due to a specific surface pH evolution during corrosion testing.

Measuring Tablet Dissolution: An Experiment for Teaching Quantitative Ultraviolet Absorption Spectroscopy

Dissolution testing is a quantitative analytical technique used to measure the release rate of ingredients from tablets and capsules. This instrumental analysis lab experiment teaches students how to compress tablets from a mixture of powders and challenges students to build their own apparatus to measure dissolution rates of their tablets. Each group of students was able to complete the experiment successfully and elucidate two predicted trends in dissolution rates from a set of five tablets. Students learned the fundamentals of UV spectroscopy, data handling, calibration, and sampling, while gaining insight and experience regarding an important test used in the pharmaceutical and dietary supplement industries.

Biorelevant characterisation of amorphous furosemide salt exhibits conversion to a furosemide hydrate during dissolution

Biorelevant dissolution behaviour of the amorphous sodium salt and amorphous acid forms of furosemide was evaluated, together with investigations of the solid state changes during in vitro dissolution in medium simulating the conditions in the small intestine. UV imaging of the two amorphous forms, as well as of crystalline furosemide salt and acid showed a higher rate of dissolution of the salt forms in comparison with the two acid forms. The measured dissolution rates of the four furosemide forms from the UV imaging system and from eluted effluent samples were consistent with dissolution rates obtained from micro dissolution experiments. Partial least squares-discriminant analysis of Raman spectra of the amorphous acid form during flow through dissolution showed that the amorphous acid exhibited a fast conversion to the crystalline acid. Flow through dissolution coupled with Raman spectroscopy showed a conversion of the amorphous furosemide salt to a more stable polymorph. It was found by thermogravimetric analysis and hot stage microscopy that the salt forms of furosemide converted to a trihydrate during dissolution. It can be concluded that during biorelevant dissolution, the amorphous and crystalline furosemide salt converted to a trihydrate, whereas the amorphous acid exhibited fast conversion to the crystalline acid.

A flow-through method for measuring the dissolution rate of alite and Portland cement clinker

A flow-through method for measuring dissolution rates of cement minerals is described. The quantity of dissolved material is measured after the dissolution experiment from SEM-BSE images. This makes it possible to measure dissolution rates of individual phases in multiphase cements. The SEM images also directly show if precipitation (hydration) occurred and how the surface roughness changed during dissolution. Furthermore, the method is designed for the purpose of determining if dissolution rate is reaction- or diffusion-controlled, by changing water flow rate or by calculating expected diffusion fluxes. Dissolution rates of flat-ground Portland cement clinker and synthesized alite in deionized water were measured to demonstrate the potential of the method. Initial dissolution rates at lower flow rates were transport-controlled as indicated by the flow rate dependency and predicted diffusion fluxes. The highest alite dissolution rate measured in this study was 93μmol/m2/s.

Pitfalls in the Measurement of the True Dissolution Kinetics of Soft Minerals

The study of dissolution can face pitfalls at all length-scales, other phenomena being able to blur the investigated reaction. We present here two situations where an a posteriori analysis of the experimental results enables recovery of the true dissolution behavior free from external influences. In standard solution chemistry dissolution experiments, the measured dissolution rate is the result of a combination of the reaction kinetics and of mass transport due to the convection of the flowing solvent. We show here how to circumvent this mass transport contribution to recover the true dissolution rate constant. Moreover, in AFM dissolution experiments, the stress applied by the tip to the surface modifies the velocity of the atomic steps, the migration of which is at the origin of dissolution. We show here how to obtain stress-free, true dissolution velocities.

The effect of a new formaldehyde-free binder on the dissolution rate of glass wool fibre in physiological saline solution

The in-vitro dissolution rate of fibres is a good predictor of the in-vivo behavior and potential health effects of inhaled fibres. This study examines the effect of a new formaldehyde-free carbohydrate-polycarboxylic acid binder on the in-vitro dissolution rate of biosoluble glass fibres. Dissolution rate measurements in pH 7.4 physiological saline solution show that the presence of the binder on wool insulation glass fibres has no effect on their dissolution. There is no measurable difference between the dissolution rates of continuous draw fibres before and after binder was applied by dipping. Nor is there a measurable difference between the dissolution rates of a production glass wool sample with binder and that same sample after removal of the binder by low-temperature ashing. Morphological examination shows that swelling of the binder in the solution is at least partially responsible for the development of open channels around the glass-binder interface early in the dissolution. These channels allow fluid to reach the entire glass surface under the binder coating. There is no evidence of any delay in the dissolution rate as a result of the binder coating.

Crystal architecture and physicochemical properties of felodipine solvates

Solvates of the calcium-channel blocking agent felodipine with three structurally related high-boiling point solvents, dimethylacetamide (DMAA), dimethylethyleneurea (DMEU) and tetramethylurea (TMU), are described. The solvates can be formed either by solution crystallisation or solvent-drop mechanical grinding. In all of the crystal structures, the solvent molecule accepts an N–H⋯O hydrogen bond from felodipine. Analysis of the conformational preferences of the felodipine molecule in the crystal structures shows that it adopts a higher-energy conformation in the solvate with TMU. Hot-stage microscopy shows that the solvates decompose below the boiling point of the solvent, then the solvent condenses and dissolves the desolvated felodipine. The decomposition temperature of the solvate is correlated with the van der Waals molecular volume for the solvent molecule within the crystal structure. Measurements of the aqueous dissolution rate show that the concentration of felodipine during the first hour is increased by 4–6 times for dissolution of the solvates compared to pure felodipine.

Planned Experimental Studies into the Nucleation and Precipitation Kinetics of Sulfate-bearing Minerals under Conditions Relevant to CO2 Geological Storage

Carbon Capture and Storage (CCS) has been widely recognized as one of the main technologies to mitigate climate change. Deep-saline aquifers are among the preferred potential repositories for CO2 currently being emitted to the atmosphere from burning of fossil fuels. Large-scale injection of supercritical CO2 into subsurface reservoirs induces a complex interplay of multiphase flow, capillary trapping, dissolution and chemical reactions that may have significant impacts on both, short-term injection performance and long-term fate of CO2 storage. To ensure the viability of geological CO2 storage, a holistic understanding of reactions at supercritical CO2-water-rock interfaces and the environmental factors affecting these interactions is required.The major objectives of this contribution are to study the kinetics of CO2 brine-rock interactions and derive respective chemical reaction rate expressions under the typical conditions of CO2 storage sites. These rate laws may be used in modeling the storage sites and operating them in a way that will minimize scaling and thus potential reduction of injectivity.A new experimental system was set up at the Water-Rock interaction laboratory, Ben-Gurion University of the Negev that allows studying the interaction between CO2, brine, and minerals under CO2 supercritical conditions. All equipment is fully capable to deal with adjustable PTX conditions enabling continuous and computerized data acquisition of various variables including pressure, temperature, stirring speed, in-situ measurement of pH and redox potential. The experimental setup allows the measurement of dissolution and precipitation rates of diverse minerals under a wide range of environmental conditions as found in CO2 storage sites offering the possibility to collect liquid and solid samples for further chemical and morphological analyses.

Influence of CO2 dynamics on the longitudinal variation of incision rates in soluble bedrock channels: Feedback mechanisms

We use measurements of dissolution rates of limestone tablets placed along a cave stream to estimate rates of modern incision. Dissolution rates within the stream display a systematic decrease with downstream distance. We discuss a variety of mechanisms that could be responsible for the longitudinal decrease in dissolution rates and develop simple mathematical models for each. The dissolutional length scales that arise from each model allow a first-order estimate of the plausibility of each mechanism and motivate further field studies to test each possibility. Water chemistry and other field data suggest that a decrease in the concentration of CO2 along the cave stream is responsible for the observed decrease in dissolution rates. We propose two potential mechanisms that could trigger this reduction in dissolved CO2 and discuss the plausibility of each mechanism in light of the field data collected. Either of these mechanisms introduces a feedback loop whereby the stream profile of a channel in soluble bedrock indirectly influences CO2 concentrations in the water, via either microbial or hydraulic processes. The CO2 concentration in turn effects the incision rates and therefore the future stream profile. This study illustrates the importance of CO2 dynamics in determining incision rates in a soluble channel and points to further modeling and field work that are needed in order to enable the development of realistic stream incision models in soluble strata.