Gibbs Energy Of Formation Research Articles

Empirical Analysis of Stability of An+1BnO3n+1 Ruddlesden–Popper Phases Using Reciprocal n-Values

Layered An+1BnO3n+1 (n = 1…∞) Ruddlesden–Popper (RP) phases are a promising system for a variety of applications. Within the RP family, the thermodynamic properties of the phases are essentially additive with variation in the n value, but at present, there are no general approaches that would allow one to evaluate the individual stability of the RP phases and the possibility of their interconversion. The aim of this paper is to present a novel concept for performing a thermodynamic analysis of RP phases using the reciprocal values of the index n. We present an empirical equation ΔG1/n = ΔGP + B1/n + B2/n2, where ΔG1/n and ΔGP are the molar Gibbs energies of formation of the Ruddlesden–Popper (RP) phase (AO)1/nABO3 and the parent ABO3 perovskite, respectively, and n is a stoichiometry index of An+1BnO3n+1 RP phase. The correlation was validated using available thermodynamic data for the systems Sr-Ti-O, Ca-Ti-O, Sr-Zr-O, La-Ni-O, and La-Co-O. For all A-B combinations, the equation quantitatively describes the Gibbs energy of RP phase formation. Predicted values for the non-linear approximation lie within the experimental uncertainty in determining ΔG1/n. The proposed correlation was used to analyze the relative stability of the RP phases and to determine the feasibility of synthesizing new compounds.

Destinezite: physicochemical and calorimetric study

Destinezite (Fe3+ Al0.02)(PO4)0.99(SO4)0.90(OH)1.20 ⋅ 5.97H2O (Czech Republic) has been studied by thermal and electron-microprobe analyses, X-ray powder diffraction, IR, Raman, and Mössbauer spectroscopy. The enthalpy of formation of destinezite Fe3 +(PO4)(SO4)(OH)⋅6H2O from the elements ∆fH0(298.15 K) = −4258 ± 12 kJ/mol was determined by the method of solution calorimetry in melt lead borate 2PbO ⋅ B2O3 on a Calvet microcalorimeter Setaram (France). The value of its absolute entropy S0(298.15 K) = 462.0 J/(mol⋅K) was estimated, the entropy of formation ∆fS0(298.15 K) = −2054 J/(mol⋅K) and the Gibbs energy of formation from the elements ∆fG0(298.15 K) = −3646 kJ/mol.

Investigation of metal-H2O systems at elevated temperatures: Part III. solubility data and new Zr Pourbaix diagrams at 298.15 K and 373.15 K.

Abstract The fuel bundles in coolant systems of CANDUTM reactors operate between 533 to 583 K (260 to 310°C). Given these extreme conditions and because of its neutronic properties, zirconium and Zircaloy-4 are used in these applications which require corrosion resistance at elevated temperatures. However, thermodynamic and hydrolysis properties of aqueous zirconium species have not been measured above standard conditions, making prediction using standard thermodynamic tools, such as the Pourbaix (E-pH) diagram difficult. This lack of information is addressed through solubility measurements and the development of elevated temperature Pourbaix diagrams for zirconium and Zircaloy-4. These Pourbaix diagrams of zirconium and a multi-element diagram (Sn, Zr, Cr) of Zircaloy-4 were developed at 373.15 K (100°C) and are presented in this work. Solubility measurements were made using a batch-style pressure vessel and concentration measurements were made using ICP-OES and ICP-MS, for zirconium and Zircaloy-4, respectively. For Zr(OH)6(2-); Zr(OH)4 (aq); Zr(OH)3+; and Zr(OH)2(2+) the Gibbs energy of formation (ΔG(°f,373.15 K)°) were found to be: -2177.4±8.5 kJ/mol, -1704.9±1.5 kJ/mol, -1808.8±8.9 kJ/mol, and -1095.1±2.7 kJ/mol, respectively.

Additive single atom values for thermodynamics III: Formation entropies and Gibbs energies for ionic solids – Hydrate and anhydrate data, and a correction

In the initial two publications in this series we established predictive additive Atom Sum thermochemical quantities for inorganic solids for each of the chemical elements. With the chemical elements being a finite set, these data cover the whole of the domain of inorganic solids so far as reference data is currently available.We here introduce a dataset augmented in hydrates, and divide our analysis between the hydrates and anhydrates. The Atom Sum terms are better directed independently to these disparate inorganic groups thus providing improved estimates of the corresponding predicted thermochemical quantities. In this paper we provide both updated formation reaction entropies and previously unpublished Gibbs energies.

Calculation of the formation enthalpies of charge-transfer complexes with iodine from the binding constants at 298.15 K

There is a continuing interest in charge-transfer complex chemistry, particularly in their formation thermodynamics. Nowadays, the binding constants and Gibbs energies of formation are available for many complexes. However, the experimental determination of the complexation enthalpies is a more difficult procedure, as it usually requires the establishment of the temperature dependence of the binding constant. Our recent studies of the compensation relationship in the thermodynamics of solvation in hydrogen-bonded systems opened the way to the calculation of the enthalpies of specific (i.e., localized donor-acceptor) interactions (Δint(sp)H) directly from the Gibbs energies at 298.15 K (Δint(sp)G). The calculation procedure is based on the following equation: Δint(sp)G/(kJ·mol−1) = 0.66·Δint(sp)H/(kJ·mol−1) + 2.5n (n corresponds to the coordination number of a solute).In the present work, we checked whether the above relation can be applied to the complex formation between halogens (primarily iodine) and organic electron donors. For 152 complexes with aromatics, nitrogen, oxygen, sulfur, selenium, and phosphor-containing compounds, the formation enthalpies were estimated using the data on equilibrium constants at 298.15 K. In most cases, agreement with the experimental binding enthalpies within the expected measurement error was observed (RMS = 1.4 kJ·mol−1, AD = –0.4 kJ·mol−1).

1-Ethyl (butyl)-3-methylimidazolium methanesulfonaties: Low-temperature heat capacity and standard thermodynamic functions of formation

A comprehensive study of the thermodynamic properties of two ionic liquids 1-ethyl-3-methylimidazolium (EmimMS) and 1-butyl-3-methylimidazolium methanesulfonate (BmimMS) was carried out. The isobaric heat capacity of the crystal and liquid phases of EmimMS and BmimMS was determined in the temperature range from 80 to 380 K by vacuum adiabatic calorimetry. The heat capacities of EmimMS and BmimMS were assessed at temperatures from 5 to 80 K by the Kelly method. The temperature dependencies of EmimMS and BmimMS main thermodynamic functions were determined in the temperature range from 5 to 380 K (isobaric heat capacity Cp,m(T), standard entropy Som(T), heat content Hom(T) – Hom(0), Gibbs energy content Gom(T) – Hom(0). Melting points and fusion enthalpies of EmimMS and BmimMS have been refined by DSC. The enthalpies of dissolution in water of EmimMS and BmimMS at 298.15 K were measured by the dissolution calorimetry. The standard enthalpies, entropies and Gibbs energies of EmimMS and BmimMS formation in the crystal and liquid state at 298.15 K were calculated from the experimental data. Comparison of the obtained thermodynamic characteristics with the literature data was carried out.

Quantum chemical modeling of alkane 2D monolayer formation on graphene

The paper presents a quantum chemical approach for assessment of the thermodynamic parameters of association for alkanes CnH2n+2 (n = 6–14) and polyaromatic hydrocarbons (PAH) of the coronene series as model structures of the graphene surface within the framework of semiempirical methods. The enthalpy, entropy and Gibbs energy of formation and binding for alkanes with PAH were calculated using the PM3 and PM6-DH2 methods. It is shown that an adequate description of the interactions in the regarded complexes requires the use of PM6-DH2 method, since it contains corrections for dispersion interactions and hydrogen bonds. The parallel orientation of the alkane molecule relative to the coronene plane is proved to be more energetically preferable than perpendicular one, which is consistent with experimental data.Intermolecular C–H/π interactions are revealed to be crucial in the 2D film formation of alkanes on graphene/graphite. While interactions between alkane molecules make a destabilizing contribution due to the implementation of energetically unfavorable types of intermolecular CH/HC interactions. This stipulates a threshold chain length of alkanes capable of film formation on the graphene/graphite surface at standard temperature: 14 and 19 carbon atoms for parallel and perpendicular oriented alkanes, respectively. The obtained threshold values of the alkane chain length, as well as the geometric parameters of their orientation in 2D monolayers on the graphene/graphite surface are consistent with available experimental data.

Experimental and theoretical studies on thermodynamic activities of binaries ferric and magnesium chlorides in aqueous solutions at various temperatures

The investigation of the thermodynamic properties of binary systems of ferric and magnesium chlorides in aqueous solutions was reported at various temperatures using both the hygrometric method and thermodynamic modeling. Water activities were measured over a molality range of 0.100 up to mmax(FeCl3)= 2.500 mol·kg−1 and to mmax(MgCl2)=(5.798, 6.090, 6.394, and 6.839) mol·kg−1at temperatures from 298.15 K to 353.15 K, respectively. From the new measurements, the osmotic coefficients of water were evaluated and compared with the existing literature data at ambient temperature. These coefficients were treated at various temperatures using established thermodynamic models of the Pitzer, Filippov–Charykov–Rumyantsev, extended ion interaction, and Clegg–Pitzer–Brimblecombe. The relevant properties of ferric and magnesium electrolyte solutions were determined in the temperature range. Indeed, the parameterizations of FeCl3(aq) and MgCl2(aq) were evaluated and employed for the computation of solute activity and osmotic coefficients. Based on literature emf data for MgCl2(aq) at a temperature of 298.15 K, the consistency of the activity coefficients was evaluated using an adequate model, and an excellent description of the prediction activity coefficients is obtained by the extended ion interaction model. Then, the recommended activity coefficients were given at various temperatures by extending this procedure. An experimental investigation was also carried out to evaluate the solubility equilibrium of MgCl2 in aqueous solutions at different temperatures. The solubility product and standard Gibbs energies of dissolution and formation were also calculated at different temperatures and compared with those existing in the literature.

Thermodynamic insights of ternary compounds of NiO - V2O5 system

We present the first experimental investigation on thermochemical stability of three ternary nickel vanadates, namely, NiV2O6(s), Ni2V2O7(s) and Ni3V2O8(s) in the NiO-V2O5 system. The standard molar entropies of formation of the compounds were determined by low temperature heat capacity measurements from 2 to 300 K using relaxation calorimetry. The standard molar enthalpy of formation and molar heat capacities were determined employing high temperature oxide melt solution calorimetry in conjunction with differential scanning calorimetry. Using the experimentally obtained thermochemical data, the standard molar Gibbs energy of formation of these compounds were derived and the corresponding expressions are given as follows:∆Gf,m°<NiV2O6>±1.4kJmol−1=−1839.4+0.5132(T/K)(T:298.15−1000K)∆Gf,m°<Ni2V2O7>±1.4kJmol−1=−2101.8+0.5971(T/K)(T:298.15−1000K)∆Gf,m°<Ni3V2O8>±3.2kJmol−1=−2360.5+0.6538(T/K)(T:298.15−1000K)

Interaction between hydroxymethanesulfonic acid and several organic compounds and its atmospheric significance

The interactions of the micro-mechanism of hydroxymethanesulfonic acid (HMSA) with the typical small organic molecule in atmospheric (X = methanol, formaldehyde, formic acid, methyl formate, dimethyl ether, acetone) has been investigated by density functional theory (DFT), quantum theory of atoms in molecules (QTAIM), Generalized Kohn-Sham Enery Decomposition Analysis (GKS−EDA) and the atmospheric clusters dynamic code (ACDC). The results of DFT show that the stable six− to eight−membered ring structures are easily formed in HMSA−X clusters. According to the topological analysis results of the AIM theory and the IRI method, a strong hydrogen bonding interaction is present in the complex. GKS−EDA results show that electrostatic energy is the main contributor to the interaction energy as it accounts for 51 %–55 % of the total attraction energy. The evaporation rates of HMSA−HMSA and HMSA−HCOOH clusters were much lower than those of the other HMSA complexes. In addition, the Gibbs energy of formation (ΔG) of HMSA−X dimers is investigated under atmosphere temperature T = 217–298 K and p = 0.19–1.0 atm, the ΔG decreased with decreasing of the atmosphere temperature and increased with the decrease of atmospheric pressure, indicating that the low temperature and high pressure may significantly facilitate to the formation of dimers.

Electrode potentials involving atoms and ions of metals in intermediate oxidation states in aqueous solutions

The electrode potentials of metal atoms (M+/M0 and M2+/M0 couples) were calculated from their standard electrode potentials in water minus the standard molar Gibbs energy of formation of the atoms in the gas phase, ΔfG0(Mgas0), and the Gibbs energy of hydration in solution, ΔhydG°. Electrode potentials are appreciably shifted (by 2.0–2.5 V) toward negative values relative to the potentials of the solid metals. For the univalent metals Cu0, Ag0, and Au0 (d10s1 electronic configuration), the electrode potentials of M+/M0 couples are –2.73, –1.90, and –1.82 V; for Ga0, In0, and Tl0 (d10s2p1 electronic configuration), they are –3.14, –2.45, and –1.99 V, respectively. For bivalent transition metals of period IV with the d5+ns2 configuration, the potentials of M2+/M0 couples are –2.50 V for Mn0, –2.45 V for Fe0, –2.33 V for Co0, –2.34 for Ni0, –1.29 V for Cu0, and –1.34 V for Zn0. For Cd0 and Hg0 (d10s2 configuration), the potentials are –0.87 and + 0.42 V. Estimation of the electrode potentials of bivalent metals in the intermediate and unstable oxidation states (M2+/M+ and M+/M0 couples) revealed their significant difference. In the case of Zn, Cd, and Hg, this difference is particularly noticeable, as large as 2–3 V, because of different configurations of the M+ (d10s1) and M0 (d10s2) electronic shells. Regular trends in variations of the electrode potentials in the periods and groups of the periodic table were revealed. In going from the atomic-molecular to the solid state, the chemical activity of the metals decreases. The metal surface catalyzes the reactions that are thermodynamically unfavorable in the solution volume.

Oxidative breakup of cemented carbide scrap by CuO-flux roasting

Tungsten carbide‑cobalt (WC-Co) composites are widely used in industry as hardmetals with superior properties and performance; however, these qualities make it difficult to recycle components made of WC-Co at their end-of-life. Herein, we present a one-step CuO-flux roasting process in which a solid-state flux supplies sufficient oxygen for the full oxidation of a hardmetal tool piece when melted. Computational assessments of the Gibbs energy of formation and its tendency to form alloys reveal that CuO is suitable for oxidizing WC cutting tools at high temperatures. After roasting a WC-Co cutting insert covered with CuO powder at 1048 °C, the insert loses its shape and changes into a friable solid oxide mass. As the oxidation reaction is highly exothermic and sustainable, the temperatures of the reactants can exceed the melting points of the oxides produced. Meltable oxide-flux roasting can be applied to the recycling of hardmetals, such as carbides and nitrides.

Stabilisation of solid-state cubic ammonia confined in a glass substance at ambient temperature under atmospheric pressure.

Ammonia, a widely available compound, exhibits structural transitions from solid to liquid to gas depending on temperature, pressure, and chemical interactions with adjacent atoms, offering valuable insights into planetary science. It serves as a significant hydrogen storage medium in environmental science, mitigating carbon dioxide emissions from fossil fuels. However, its gaseous form, NH3(g), poses health risks, potentially leading to fatalities. The sublimation pressure (psub) of solid cubic ammonia, NH3(cr), below 195.5 K is minimal. In this study, we endeavoured to stabilise NH3(cr) at room temperature for the first time. Through confinement within a boric acid glass matrix, we successfully synthesised and stabilised cubic crystal NH3(cr) with a lattice constant of 0.5165 nm under atmospheric pressure. Thermodynamic simulations affirmed the stabilisation of NH3(cr), indicating its quasi-equilibrium state based on the estimated standard Gibbs energy of formation, . Despite these advancements, the extraction of H2(g) from NH3(cr) within the boric acid glass matrix remains unresolved. The quest for an external matrix with catalytic capabilities to decompose inner NH3(cr) into H2(g) and N2(g) presents a promising avenue for future research. Achieving stability of the low-temperature phase at ambient conditions could significantly propel exploration in this field.

Accurate complex-stacking-fault Gibbs energy in Ni3Al at high temperatures

To gain a deeper insight into the anomalous yield behavior of Ni3Al, it is essential to obtain temperature-dependent formation Gibbs energies of the relevant planar defects. Here, the Gibbs energy of the complex stacking fault (CSF) is evaluated using a recently proposed ab initio framework [Acta Materialia, 255 (2023) 118986], accounting for all thermal contributions—including anharmonicity and paramagnetism—up to the melting point. The CSF energy shows a moderate decrease from 300K to about 1200K, followed by a stronger drop. We demonstrate the necessity to carefully consider the individual thermal excitations. We also propose a way to analyze the origin of the significant anharmonic contribution to the CSF energy through atomic pair distributions at the CSF plane. With the newly available high-temperature CSF data, an increasing contribution to the energy barrier for the cross-slip process in Ni3Al with increasing temperature is unveiled, necessitating the refinement of existing analytical models.

General Equation to Estimate the Physicochemical Properties of Aliphatic Amines.

Changes in various physicochemical properties (P(n)) of aliphatic amines (including primary, secondary, and tertiary amines) can be roughly divided into nonlinear (P(n)) and linear (PLC(n)) changes. In our previous paper, nonlinear and linear change properties of noncyclic alkanes all were correlated with four parameters, n, SCNE, ΔAOEI, and ΔAIMPI, indicating number of carbon atoms, sum of carbon number effects, average odd-even index difference, and average inner molecular polarizability index difference, respectively. To date, there has been no general equation to express changes in the properties of substituted alkanes. This work, based on the molecular structure characteristics of aliphatic amine molecules, proposes a general equation to express nonlinear changes in their physicochemical properties, named as the "NPAA equation" (eq 12), ln(P(n)) = a + b(n) + c(SCNE) + d(ΔAOEI) + e(PEI) + f(APEI) + g(GN), and proposes a general equation to express linear changes in the physicochemical properties of them, named as the "LPAA equation" (eq 13), PLC(n) = a + b(n) + c(SCNE) + d(ΔAOEI) + e(PEI) + f(APEI) + g(GN). In NPAA and LPAA equations, a, b, c, d, e, f, and g are coefficients, and PEI, APEI, and GN represent the polarizability effect index, average polarizability effect index, and N atomic influence factor, respectively. The results show that nonlinear and linear change properties of aliphatic amines all can be correlated with six parameters, n, SCNE, ΔAOEI, PEI, APEI, and GN. NPAA and LPAA equations have the advantages of uniform expression, high estimation accuracy, and usage of fewer parameters. Further, by employing the above six parameters, a quantitative correlation equation can be established between any two properties of aliphatic amines. Using the obtained equations as model equations, the property data of aliphatic amines were predicted, involving 107 normal boiling points, 10 refractive indexes, 11 liquid densities, 54 critical temperatures, 54 critical pressures, 62 liquid thermal conductivities, 59 surface tensions, 56 heat capacities, 55 critical volumes, 54 gas enthalpies of formation, and 57 gas Gibbs energies of formation, a total of 579 values, which have not been experimentally determined yet. This work not only provides a simple and convenient method for estimating or predicting the properties of aliphatic amines but can also provide new perspectives for quantitative structure-property relationships of substituted alkanes.

Thermal and Thermochemical Study of Thaumasite

A sample of natural thaumasite Ca3.0Si(OH)6(CO3)0.9(SO4)1.1·12.3H2O (N’Chwaning mine, Kalahari manganese ore field, South Africa) was studied by powder X-ray diffraction, infrared absorption and Raman spectroscopy, thermal analysis, and microcalorimetry. The process of thermal transformation of thaumasite was studied using the results of FTIR and Raman spectroscopy. The enthalpy of formation from elements ΔfH0(298.15 K) = −8816 ± 30 kJ/mol was determined by high-temperature melt solution calorimetry. The value of the absolute entropy was estimated, and the enthalpy and Gibbs energy of formation of thaumasite of theoretical composition were calculated: 945.4 ± 1.8 J/(mol K), −8699 ± 30 kJ/mol, −7577 ± 30 kJ/mol, respectively.

Optimized thermodynamic properties of REE aqueous species (REE3+ and REEOH2+) and experimental database for modeling the solubility of REE phosphate minerals (monazite, xenotime, and rhabdophane) from 25 to 300 °C

Rare earth elements (REE) are critical elements found in monazite, xenotime, and hydrated REE phosphates which typically form in hydrothermal mineral deposits. Accurate predictions of the solubility of these REE phosphates and the speciation of REE in aqueous fluids are both key to understanding the controls on the transport, fractionation, and deposition of REE in natural systems. Previous monazite and xenotime solubility experiments indicate the presence of large discrepancies between experimentally derived solubility constants versus calculated solubilities by combining different data sources for the thermodynamic properties of minerals and aqueous species at hydrothermal conditions. In this study, these discrepancies were resolved by using the program GEMSFITS to optimize the standard partial molal Gibbs energy of formation (ΔfG°298) of REE aqueous species (REE3+ and REE hydroxyl complexes) at 298.15 K and 1 bar while keeping the thermodynamic properties fixed for the REE phosphates. A comprehensive experimental database was compiled using solubility data available between 25 and 300 °C. The latter permits conducting thermodynamic parameter optimization of ΔfG°298 for REE aqueous species. Optimal matching of the rhabdophane solubility data between 25 and 100 °C requires modifying the ΔfG°298 values of REE3+ by 1–6 kJ/mol, whereas matching of the monazite solubility data between 100 and 300 °C requires modifying the ΔfG°298 values of both REE3+ and REEOH2+ by ~15–31 kJ/mol and ~ 2–10 kJ/mol, respectively. For xenotime, adjustments of ΔfG°298 values by 1–26 kJ/mol are only necessary for the REE3+ species. The optimizations indicate that the solubility of monazite in acidic solutions is controlled by the light (L)REE3+ species at <150 °C and the LREEOH2+ species at >150 °C, whereas the solubility of xenotime is controlled by the heavy (H)REE3+ species between 25 and 300 °C. Based on the optimization results, we conclude that the revised Helgeson-Kirkham-Flowers equation of state does not reliably predict the thermodynamic properties of REE3+, REEOH2+, and likely other REE hydroxyl species at hydrothermal conditions. We therefore provide an experimental database (ThermoExp_REE) as a basic framework for future updates, extensions with other ligands, and optimizations as new experimental REE data become available. The optimized thermodynamic properties of aqueous species and minerals are available open access to accurately predict the solubility of REE phosphates in fluid-rock systems.

Critical systematic investigation of the Cd–Ce system: phase stability and Gibbs energies of formation and equilibria via thermodynamic description

Abstract The CALPHAD (CAlculation of PHAse Diagrams) technique is used in the critical remodeling of the Cd–Ce system. On the basis of new experimental data in the literature, the excess Gibbs energies of the solution phase expression (liquid, bcc, fcc, and hcp_A3) are described using the Redlich–Kister equation. Four compounds (Cd3Ce, Cd6Ce, Cd11Ce, and Cd17Ce2) are treated as stochiometric compounds. Two intermetallic compounds (Cd2Ce and Cd58Ce13), which exhibit a little homogeneity range, are treated as a two-sublattice model. Two thermodynamic models are used for the CdCe and bcc. Model I is to model the compound CdCe and bcc-Ce separately. Model II is to use the formula (Cd, Ce)0.5(Cd, Ce)0.5(Va)3 to describe the compound CdCe with a CsCl-type structure (B2) and cope with the disorder–order transition from bcc-A2 to bcc-B2. The present work shows that four eutectic reactions, three peritectic reactions, two eutectoid reactions, one peritectoid transformation and three congruent reactions are observed, and the stoichiometric compound Cd17Ce2 is only stable from 804 to 882 °C in the Cd–Ce system.

Estimation of the Thermophysical Properties of Pentaalkylguanidinium-Based Magnetic Ionic Liquids with Unusual Thermal Expansion Coefficient.

The thermal expansion coefficient (αexp. ), the molecular volume (Vm ), the entropy of surface formation (Sa ), and the Gibbs energy of surface formation (Ea ) of four pentaalkylguanidinium-based MILs [Cn TMG][FeCl3 Br] (n=2, 4, 6, 8) were calculated based on the density and surface tension data determined from 278.15 to 323.15 K. In terms of classical semiempirical methods, the standard molar entropy (S0 ), the lattice energy (UPOT ), the molar enthalpy of evaporation ( , (298 K)), and the thermal expansion coefficient (αest. ) of the MILs were further estimated. The estimation results indicate that the classical semiempirical methods are suitable for estimating the thermophysical properties of the MILs, except the unusual αexp. , which were extremely larger than those of representative non-magnetic ionic liquids (ILs). We further optimized the estimation methods and discussed the potential reasons for the unusual thermal expansion coefficient of the MILs.

Colloid-chemical properties of surfactant–nitric acid–water systems

The behavior of the surfactants Tween 80, SaS and alkyl betaine in aqueous and nitric acid environments as promising additives for nitrate leaching of hard-to-process ore concentrates of non-ferrous metals was studied. The influence of surfactant concentration (0.04–1.28 g/dm3), nitric acid concentration (0.1–10 g/dm3) and temperature (295–343 K) on the surface tension, critical micelle concentration (CMC), pH and optical density of aqueous surfactant solutions and surfactant–HNO3–H2O systems was found. The critical micelle concentration of the surfactants used was estimated. A positive effect of nitric acid on the surface activity of surfactants was discovered, which manifests itself in a decrease in both the CMC and the surface tension at the liquid–gas interface. The values of surface activity and Gibbs energy of surfactant micelle formation in aqueous and nitric acid media were calculated. Associative processes in the solutions and compositions were confirmed by measuring the optical density of the systems under study.