HNO3 System Research Articles

Silver cementation mechanism for leaching silicon solar cells in nitric acid

Silicon solar panels are often overlooked in e-waste recycling technology, even though they contain precious silver (Ag). In order to help meet future global Ag demands and prevent contamination of the environment, all the Ag from end-of-life modules must be recovered instead of landfilled. The most mature Ag recycling recipes use high concentration nitric acid (HNO3) solutions often in combination with heating and agitation. After the Ag is leached, chemical precipitation or electrochemistry is used to recover metallic Ag. However, the process of Ag leaching in the HNO3 system with competing elements from silicon solar cells is not well understood. In this paper, we investigate the thermodynamics governing Ag leaching in low-concentration HNO3 without agitation or heating to expand fundamental knowledge in support of Ag recovery efforts from end-of-life solar panels. ICP-OES is used to quantify the amount of Ag leached in the HNO3 solution over time. Scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) are used to study the changes on the silicon solar cell surface. Our results suggest when trace tin (Sn) is used in solar cell fingers, it causes Ag to cement in dendritic form.

New Features of the H2SO4–HNO3 System in the Synthesis of Adamantanecarboxylic Acids

New Features of the H2SO4–HNO3 System in the Synthesis of Adamantanecarboxylic Acids

Selective removal of Fe(Ⅲ) from HNO3 leach liquor of saprolitic laterite ore: Precipitation efficiency, hydrolysis mechanism, and removal strategy

HNO3 leach liquor of saprolitic laterite ore contains Fe3+, Al3+, Sc3+, Ni2+, Co2+, Mg2+, etc. Efficient removal of Fe3+ while reducing the loss of valuable metals is the key to solution purification. In this paper, a detailed study was carried out on the removal of Fe3+ by hydrolysis precipitation. First, thermodynamic calculations were conducted to analyze the precipitation pH changes and possible hydrolysis products at different temperatures. Subsequently, the experimental results show that more than 99 % Fe can be removed via low-temperature hydrolysis at 25–80 ℃ and pH = 3.0–3.5, but over 40 % Al and 30 % Sc also precipitate together, causing valuable metals losses. Differently, under high-temperature conditions (180 ℃, pH = 1.0, 0.5 h), 99.49 % of Fe can be selectively removed as Fe2O3 product, while other valuable metals hardly precipitate. It was found that the low-temperature Fe removal residue exhibits irregular agglomeration and uneven particle size, and contains 9.48 % NO3– and 25.86 % Fe. The high-temperature Fe removal residue presents a nanoscale spherical shape with uniform particle size and only contains 0.087 % NO3–, and the Fe content is up to 69.07 %. Finally, the Fe3+ hydrolysis mechanism was analyzed and an efficient Fe removal process from the HNO3 system including pH adjustment of leach liquor, selective Fe removal at high temperature, flash evaporation to recover free HNO3, and solid–liquid separation to obtain Fe2O3 products was proposed.

A Portable Microplasma Optical Emission Spectrometric Device with Online Digestion Function for Field and Sensitive Determination of Lead in Biological Samples.

Accurate detection and screening of Pb in biological samples is helpful to assess the risk associated with lead pollution to human health. However, conventional atomic spectroscopic instruments are bulky and cumbersome, requiring additional sample pretreatment equipment, and difficult to perform field analysis with. Herein, a portable point discharge (PD) microplasma-optical emission spectrometric (OES) device with online digestion function is designed for field and sensitive determination of lead in biological samples. With rice as a model, online digestion of a batch of six 50 mg samples can be achieved in the HNO3 and H2O2 system within 25 min by a temperature control and timing module. Compared to the conventional microwave digestion, the digestion efficiency of this device reaches 97%. Pb in digestion solution is converted into volatile species by hydride generation (HG) and directly introduced into PD-OES for excitation and detection by a self-designed rotatable and telescopic cutoff gas sampling column. Six samples can be successively detected in 2 min, and argon consumption of the whole process is only <800 mL. Under the optimized conditions, the detection limit of Pb is 0.018 mg kg-1 (0.9 μg L-1) and precision is 3.6%. The accuracy and practicability of the present device are verified by measuring several certified reference materials and real biological samples. By virtue of small size (23.5 × 17 × 8.5 cm3), lightweight (2.5 kg), and low energy consumption (24.3 W), the present device provides a convenient tool for field analysis of toxic elements in biological samples.

Preferential Corrosion in Cold Sprayed Cu Induced by Oxide Inclusions

Cold spray (CS) deposition is a solid-state deposition technique that finds applications in additive manufacturing, coating, and repairing damaged components. During the cold spray deposition process, feedstock particles are accelerated by compressed gas and impinged onto the substrate at high velocity. Bonding between particles and the surface being coated is established by the high kinetic energy released during collision rather than by added thermal energy. As the particles remain in the solid state during spraying, oxidation is minimized. Despite the partial removal of the native air-formed oxides by the jetting effect, residual oxide debris often remains along the particle boundaries within the sprayed objects as inclusions [1]. The oxide inclusions have attracted attention concerning their influence on the inter-particle bonding strength in the deposit [2]. However, little is known about whether they affect the material’s corrosion behavior.In this work, we report a preferential corrosion phenomenon observed in a CS Cu-diluted HNO3 system that is caused by the remaining oxide inclusions. A mechanism that integrates Cu-NO3 – catalytic corrosion cycles with confined geometry resulting from the dissolution of the oxide inclusions is proposed. Furthermore, we find that this corrosion phenomenon may be mitigated through microstructure engineering. Annealing the CS Cu at 600 °C consolidated the oxide inclusions with their distribution changed from continuous thin films to isolated spherical particles [3]. The propagation of the preferential corrosion is hence interrupted by the lack of interconnected pathways. Counterintuitively, Cl– can function as an inhibitor for this preferential corrosion. Preferential corrosion did not initiate when 1 mM Cl– was initially present in the solution and slowed down when Cl– was added after the preferential corrosion occurred. Reference [1] S. Yin, X. Wang, W. Li, H. Liao, H. Jie, Deformation behavior of the oxide film on the surface of cold sprayed powder particle, Applied Surface Science, 259 (2012) 294-300.[2] Y. Ichikawa, R. Tokoro, M. Tanno, K. Ogawa, Elucidation of cold-spray deposition mechanism by auger electron spectroscopic evaluation of bonding interface oxide film, Acta Materialia, 164 (2019) 39-49.[3] J. Tam, B. Yu, W. Li, D. Poirier, J.-G. Legoux, J.D. Giallonardo, J. Howe, U. Erb, The effect of annealing on trapped copper oxides in particle-particle interfaces of cold-sprayed Cu coatings, Scripta Materialia, 208 (2022) 114333.

Behavior of Surface-Active Substances in a Nitric Acid Medium and Prospects for Using Them in Hydrometallurgy

The behavior of surface-active substances (surfactants) is studied using the examples of lignosulfonate (LS) and sodium dodecyl sulfate (SDS) in aqueous and nitric acid media as promising additives for the nitric acid leaching of refractory ore concentrates. The effect the temperature (15–70°С) and concentrations of the surfactant (Csurfactant = 0.02–200 g/dm3) and nitric acid (CHNO3 = 0.1–10 g/dm3) have on the surface tension, critical concentration of micelles (CMC), electrical conductivity, pH, and optical density of solutions is established. The critical association of concentration is determined for lignosulfonate: CLS ~ 0.13–0.14 mol/dm3. An increase in the surface activity of lignosulfonate is noted upon raising the temperature of and adding nitric acid to an LS–H2O system. The established effects (a drop in σl–g) are explained by an increase in the coefficient of diffusion of LS macromolecules and a change in the intensity of the associative-dissociative processes of counterions and the LS polyanion. The positive effect nitric acid has on the surface activity of SDS is noted and found to reduce surface tension at the liquid–gas interface and CMCs. Associative processes in SDS–HNO3 systems are also confirmed by measuring the optical density of the considered systems.

Behaviors of actinides in chromatographic separation by using TBP resin in nitric acid solution and hydrochloric acid solution

ABSTRACT We are developing a simple actinide separation method for a pre-treatment process of actinide analysis by mass spectrometry such as thermal ionization mass spectrometry or inductively coupled plasma mass spectrometry. The actinide separation was conducted by using Tributyl phosphate (TBP) impregnated resin commercially supplied by Triskem International. TBP is commonly used in the PUREX system as a solvent for the recovery and recycling of uranium and plutonium from spent nuclear fuels through liquid–liquid separation in the HNO3 system. In this study, TBP-impregnated resin is employed as a solid extractant for the mutual separation of uranium, plutonium, thorium, and trivalent actinides through solid–liquid separation by combination with nitric acid (HNO3) and hydrochloride acid (HCl), with divalent iron ion as a reductant for valence control of plutonium. We confirmed that uranium was extracted with a recovery rate of more than 96%.

Novel mesoporous submicron SO42−/FeCu-ZrO2 catalyst for highly selective liquid-phase nitration of 1-nitronaphthalene with NO2 to 1, 5-dinitronaphthalene under mild conditions

An efficient approach for highly selective preparation of 1,5-dinitronaphthalene from liquid-phase nitration of 1-nitronaphthalene with NO2 over mesoporous submicron sub-SO42−/Fe1.5Cu0.5-ZrO2 (s-SFCZ) superacid catalyst prepared by the two-step hydrothermal impregnation (THI) method has been developed. The results showed that the enhanced 1-nitronaphthalene conversion and 1,5-dinitronaphthalene selectivity were attributed to the synergistic catalysis of s-SFCZ combined O2-Ac2O. 94.8% of 1-nitronaphthalene conversion and 62.1% 1,5-dinitronaphthalene selectivity were achieved under optimal conditions. The characterization results unveiled that s-SFCZ had a uniform morphology, lower nano-crystallite size along with more number of accessible acid sites as compared to SO42−/Fe1.5Cu0.5-ZrO2 (SFCZ) and SO42−/Fe1.5Cu0.5/ZrO2 (SFC/Z) catalysts prepared by conventional methods. Furthermore, the density functional theory calculation revealed the cause of the favorable selectivity to 1,5-dinitronaphthalene in NO2-O2-Ac2O compares to HNO3 system. This work affords a novel strategy for preparing mesoporous submicron catalyst used in the nitration of 1-nitronaphthalene with NO2 to 1,5-dinitronaphthalene, and has potential application prospects.

GO-anchored imidazolium based cross-linked composite anion exchange membranes for the enhancement in acid recovery via diffusion dialysis

To break the “trade-off” limitations regarding the acid reclamation and selectivity of the commercially available anion exchange membranes (AEMs), herein we report the preparation of specially designed 2D material incorporated dense AEMs to achieve high dialysis coefficient (UH+) and high separation factor (S) for separation of inorganic acids from its corresponding metal salt mixture by diffusion dialysis (DD). The composite AEMs were fabricated by incorporating graphene oxide (GO) into N-alkylated polyacrylonitrile-co-polyvinyl imidazole copolymer followed by crosslinking with hydrazine hydrate. The composite membranes exhibit higher hydrophilicity and increases the water uptake of the membranes. The combined effect of the impregnation of GO and the imidazolium ion on the acid recovery performance have been evaluated. The membrane B3 prepared by the quaternization of the copolymer with butyl bromide having 1.5 % (w/w) of GO in the polymer matrix exhibits the highest acid recovery performance with a UH+ and S value of 48 × 10−3 m/h and 87, respectively during the acid reclamation study of 1 M HCl + 0.2 M FeCl2 mixture. It also showed UH+ values of 37.11 × 10−3 m/h and 16.22 × 10−3 m/h for HNO3 and H2SO4 systems, respectively, with their respective salt mixtures. GO provides a well-organized slit like channels which intensifies the migration of H+ and increases the selectivity of the AEMs towards metal cations. We believe this engineering strategy can be employed to fabricate better AEMs for acid recovery (HCl, H2SO4 and HNO3) by DD process.

Efficient removal of Se-79 from highly acidic solution using SiO2 particles functionalised with iron hydroxide

Due to its high solubility, radioactivity and toxicity, the separation of selenium from spent fuel reprocessing waste and industrial wastewater has attracted much attention. In this study, a novel adsorbent FeOOH@SiO2 with particle size of ∼100 μm was successfully prepared by loading FeOOH on micron-sized silica with emulsion methods. FeOOH@SiO2 with good acid resistance, γ-irradiation and thermal stability exhibits excellent adsorption abilities for Se(IV) and Se(VI) including fast adsorption kinetics, great adsorption capacities (11.0 mg/g for Se(IV) and 6.04 mg/g for Se(VI)) and preferable adsorption selectivity. It is worth noting that FeOOH@SiO2 can still remove nearly 90 % of Se(IV) and 80 % of Se(VI) even in 3 mol/L HNO3 system. Combined with the observations from X-ray photoelectron spectroscopic characterization and surface potential measurement, the adsorption mechanism caused with electrostatic attraction and the formation of inner complexes for Se(IV), and reduction reaction and partial formation of outer complexes for Se(VI) can be deduced. After 4 adsorption–desorption cycles, FeOOH@SiO2 still exhibits satisfactory reusability. Dynamic column experiments also demonstrated that FeOOH@SiO2 exhibited excellent removal capabilities towards Se(IV) and Se(VI) from real water samples. The present work demonstrates that FeOOH@SiO2 has great potential application for 79Se removal in highly acidic nuclear waste.

Hydrazine Radiolysis by Gamma-Ray in the N2H4-Cu+-HNO3 System.

Radiolysis of chemical agents occurs during the decontamination of nuclear power plants. The γ-ray irradiation tests of the N2H4–Cu+–HNO3 solution, a decontamination agent, were performed to investigate the effect of Cu+ ion and HNO3 on N2H4 decomposition using a Co-60 high-dose irradiator. After the irradiation, the residues of N2H4 decomposition were analyzed by Ultraviolet-visible (UV) spectroscopy. NH4+ ions generated from N2H4 radiolysis were analyzed by ion chromatography. Based on the results, the decomposition mechanism of N2H4 in the N2H4–Cu+–HNO3 solution under γ-ray irradiation condition was derived. Cu+ ions form Cu+N2H4 complexes with N2H4, and then N2H4 is decomposed into intermediates. H+ ions and H● radicals generated from the reaction between H+ ion and eaq− increased the N2H4 decomposition reaction. NO3− ions promoted the N2H4 decomposition by providing additional reaction paths: (1) the reaction between NO3− ions and N2H4●+, and (2) the reaction between NO● radical, which is the radiolysis product of NO3− ion, and N2H5+. Finally, the radiolytic decomposition mechanism of N2H4 obtained in the N2H4–Cu+–HNO3 was schematically suggested.

Comparison of the hydraulic characteristics of the 30%TRPO/kerosene―HNO3 and iPr-C[4]C-6/n-octanol―HNO3 systems in an annular centrifugal extractor

The hydraulic characteristics of the 30% TRPO (trialkylphosphine oxide)/kerosene―1.0 M HNO3 and 0.025 M iPr-C [4]C-6 (25,27-bis(isopropoxy) calix [4]-26,28-crown-6)/n-octanol―1.3 M HNO3 systems were systematically investigated in a φ20 ACE (annular centrifugal extractor) to find the cause of the hydraulic performance problem of the CECE (calixcrown ether extraction) process operated in ACEs. The results show that the operating and structure parameters have different influences on the F (A/O) (phase ratio (A/O)) and V (liquid hold-up volume). Moreover, the Vr (V of the rotor) of the 30%TRPO/kerosene―HNO3 and iPr-C [4]C-6/n-octanol―HNO3 systems are almost same, while the Vm (V of the mixing zone) and Vt (total V of the ACE) for the former are slightly higher than those for the latter under the same experimental conditions. Meanwhile, both the Fm (A/O) (F (A/O) of the mixing zone) and Fs(A/O) (F (A/O) of the separating zone) for the 30%TRPO/kerosene―HNO3 system are also higher than those for the iPr-C [4]C-6/n-octanol―HNO3 system under the same experimental conditions. Moreover, the Fs(A/O) of the iPr-C [4]C-6/n-octanol―HNO3 system is less than 1.5 under most of the present experimental conditions, which shows organic phase entrainment may easily occur in the outlet aqueous phase. This may be the cause of the hydraulic performance problem of the CECE process operated in ACEs.

A Study of the Radiolysis Products of the Tri-n-Butyl-Phosphate–Isopar-M–HNO3 System before and after Regeneration with Carbonates of Organic Bases

By measuring the hydrodynamic characteristics (viscosity, density of extraction mixture, and interfacial tension) and determining the composition of degradation products by the IR, CMS, and nuclear magnetic resonance methods, the efficiency of using solutions of methylamine and guanidine carbonates at the stage of intracycle regeneration was evaluated. It has been experimentally proven that, when using these solutions, the same efficiency is achieved as when using a sodium bicarbonate solution. The main products of radiation destruction of the 30% Tri-n-butyl-phosphate in Isopar-M extraction mixture irradiated after saturation with nitric acid are determined: dibutyl phosphoric and monobutyl phosphoric acids, carboxylic acids, ketones, carbonyl compounds, and hydrocarbons.

Thermodynamic Properties of Phases and Phase Equilibria in the H2O–HNO3–UO2(NO3)2–Th(NO3)4 System

A set of Pitzer parameters was obtained to accurately describe the thermodynamic properties of solutions in the H2O–UO2(NO3)2–Th(NO3)4–HNO3 system at 25°С and represent the thermodynamic properties of liquid phases in the H2O–Th(NO3)4–HNO3 subsystem in the temperature range 25–50°С. Solubility products were calculated for crystal hydrates Th(NO3)4 · 6H2O and UO2(NO3)2 · 3H2O to predict the solubilities of these compounds in those solutions over a wide concentration range.

Direct oxidative pressure leaching of bismuth sulfide concentrate in methanesulfonic acid medium

As the prevalent extraction technology of bismuth sulfide concentrate, the precipitation smelting process has disadvantages of SO2 emission and inefficient recovery of associated metals. Hydrometallurgical alternatives to traditional pyrometallurgical techniques have obtained continuously growing attention in recent years. In this paper, methanesulfonic acid (MSA) was proposed as the reaction medium to extract bismuth from bismuth sulfide concentrate under pressure leaching conditions. It was found that more than 95% of Bi could be leached out in 2.70 mol/L MSA + 28.6 g/L ferrous ion solution at 110 °C and 0.4 MPa oxygen pressure for 2 h. Cu and Fe from chalcopyrite and pyrite can be slightly leached out with ratio of 26.67% and 30.51%, respectively. Scheelite and molybdenite basically remained in the leaching residue. Galena was partially dissolved to generate lead ion and elemental sulfur, which could be further oxidized to sulfate as the leaching temperature and oxygen pressure raised, and then reacted with dissolved lead ion to form insoluble lead sulfate. The produced leaching residue was mainly composed of sulfur, lead sulphate, quartz, molybdenite, and unleached chalcopyrite and pyrite. Compared with the traditional FeCl3, HCl-NaClO3, HNO3 system, the proposed MSA medium is proved to be biodegradable, low toxic, less volatile, and thus has broad application prospects in bismuth green hydrometallurgy.

Recovery of cerium(IV) in acidic nitrate solutions by solvent extraction with a novel extractant tris(2-ethylhexyl)phosphine oxide

The extraction of cerium(IV) (Ce(IV)) from a nitric acid (HNO3) system using a novel extractant, tris(2-ethylhexyl)phosphine oxide (TEHPO), was studied. The separation factors of Ce(IV)/Th(IV) and Ce(IV)/Ln(III) (La3+, Gd3+ and Lu3+) were found to be in the range of 60–127 and 121–827, respectively, in the HNO3 concentration range of 0.5–5.0 mol/L, showing high selectivity with TEHPO. The experimental results showed that TEHPO can effectively extract Ce(IV) from a HNO3 system quantitatively in a 2:1 form (molar ratio of TEHPO: Ce(IV)), which is unrelated to the experimental conditions, that is, factors such as HNO3 concentration, extractant concentration, and temperature. The loaded Th(IV) could be stripped efficiently using H2O, but Ce(IV) should be stripped using H2O2. The extraction mechanisms of HNO3 and Ce(IV) with TEHPO were determined through the slope analysis method, infrared spectroscopy (FT-IR), and electrospray ionization mass spectrometry (ESI-MS), and the extracted complexes were found to be HNO3·TEHPO and Ce(NO3)4·2TEHPO. Comparison of their extraction performances revealed that TEHPO shows a better interfacial phenomenon and higher extraction ability and saturation loading capacity than those of Cyanex923.

Cesium and Strontium Contamination of Nuclear Plant Stainless Steel: Implications for Decommissioning and Waste Minimization.

Stainless steels can become contaminated with radionuclides at nuclear sites. Their disposal as radioactive waste would be costly. If the nature of steel contamination could be understood, effective decontamination strategies could be designed and implemented during nuclear site decommissioning in an effort to release the steels from regulatory control. Here, batch uptake experiments have been used to understand Sr and Cs (fission product radionuclides) uptake onto AISI Type 304 stainless steel under conditions representative of spent nuclear fuel storage (alkaline ponds) and PUREX nuclear fuel reprocessing (HNO3). Solution (ICP-MS) and surface measurements (GD-OES depth profiling, TOF-SIMS, and XPS) and kinetic modeling of Sr and Cs removal from solution were used to characterize their uptake onto the steel and define the chemical composition and structure of the passive layer formed on the steel surfaces. Under passivating conditions (when the steel was exposed to solutions representative of alkaline ponds and 3 and 6 M HNO3), Sr and Cs were maintained at the steel surface by sorption/selective incorporation into the Cr-rich passive film. In 12 M HNO3, corrosion and severe intergranular attack led to Sr diffusion into the passive layer and steel bulk. In HNO3, Sr and Cs accumulation was also commensurate with corrosion product (Fe and Cr) readsorption, and in the 12 M HNO3 system, XPS documented the presence of Sr and Cs chromates.

A novel extractant 2-Ethylhexyl Bis(2-ethylhexyl)phosphinate for cerium(IV) and fluorine extraction from nitric acid system

A novel extractant, 2-ethylhexyl Bis(2-ethylhexyl)phosphinate (EHBEHP, abbreviated as B), was synthesized for the extraction of Cerium(IV) (Ce(IV)) and fluorine (F(I)) from nitric acid (HNO3) media. The effects of HNO3 concentration, extractant concentration, F(I) concentration and the temperature on the Ce(IV) and F(I) extraction were studied and discussed. The experimental results show that EHBEHP has a strong ability to extract Ce(IV), while the presence of F(I) decreases the extraction ability of Ce(IV). The extraction process had nothing to do within the studied temperature range. The extraction of HNO3, Ce(IV) and Ce(IV)-F(I) were studied respectively, and the extracted complexes were found to be 2HNO3·EHBEHP, Ce(NO3)4·2EHBEHP and Ce(HF)(NO3)4·EHBEHP, individually. The extraction mechanisms were determined according to slope analysis method. Saturation loading capacity of Ce(IV) and F(I) extracted by 0.867 mol/L EHBEHP in HNO3 system was about 50.98 g/L and 5.67 g/L, respectively. The stripping experiment shows that 95.3% of stripping efficiency of Ce(IV) can be obtained with 2.4% H2O2. The FT-IR of extracted complexes were measured and characterized. EHBEHP shows higher extraction ability and saturation loading capacity compared with DEHEHP.

Reactive thermal hazards of irradiated tributyl phosphate with nitric acid

Red oil incidents reported worldwide are attributed to the reactive thermal reactions between Tributyl phosphate (TBP) and nitric acid. The vigor of thermal behavior may be influenced by various factors including irradiation, presence of metal nitrates etc. This work is focused to study the influence of irradiation on the reactive thermal behavior of 30% TBP with varying strengths of HNO3 for the first time. The Accelerating Rate Calorimetry (ARC) studies reveal that irradiated 30% TBP reacts exothermically with 4 mol/L–16 mol/L HNO3 and contributes to rise in system pressure. A lower onset temperature for exothermic reaction was noticed in irradiated TBP compared to the non-irradiated 30% TBP with acid. From the Zero-Order kinetic model, the TMRad for irradiated and non-irradiated TBP 4 mol/L HNO3 system was been determined for thermal hazard assessment. FT-IR, NMR and GC–MS characterization of the residues of ARC clearly suggest that conversion of butanol to butanoic acid is the exothermic red-oil forming reaction.

Effects of temperature on the extraction of U(VI) and Pu(IV) by tris(2-methylbutyl) phosphate from nitric acid media

Abstract Extraction behavior of tris(2-methylbutyl) phosphate (T2MBP), a higher homologue of tri-n-butyl phosphate (TBP), in the extraction of U(VI) and Pu(IV) from nitric acid media has been evaluated in the present study. Distribution ratios for the extraction of these metal ions by T2MBP were measured as a function of equilibrium aqueous phase nitric acid concentration, extractant concentration and temperature to understand the temperature effects on extraction. Enthalpies of extraction of T2MBP/n-dodecane-U(VI)-HNO3 and T2MBP/n-dodecane-Pu(IV)-HNO3 systems were calculated from the distribution ratio data using “second law” method. The data reveal that the extraction of U(VI) by T2MBP is exothermic in nature, whereas that of Pu(IV) is endothermic.