Understanding of tribocorrosion and corrosion characteristics of304L stainless steel in hot concentrated nitric acid solution

Spent fuel reprocessing plays a pivotal role in achieving efficient recycling of nuclear fuel.Among thedifferent forms of failure encountered in spent fuel reprocessing,tribocorrosion stands out as a critical concern.Herein,the tribocorrosion behavior,as well as the corrosion behavior,of 304L stainless steel(SS)in high-temperatureconcentrated nitric acid was investigated.The results indicated that 304L SS formed a thin(1.54 nm)and stable passivefilm on the surface,imparting high resistance to nitric acid corrosion.Meanwhile,it was found that the synergistic effectbetween corrosion and wear accounted for a high total tribocorrosion weight loss of over 85%,implying the dominantrole of the synergistic effect in the tribocorrosion process.Furthermore,the wear of 304L SS in deionized water revealedboth abrasive and adhesive wear characterizations,whereas the tribocorrosion in nitric acid only exhibited abrasive wearfeature.Eventually,the tribocorrosion and corrosion models of 304L SS in hot concentrated nitric acid were proposedbased on the comprehensive experimental findings.

Influence of Nitric Acid Concentration on Characteristics of Olive Stone Based Activated Carbon

In this work we investigated the effect of nitric acid concentration on the pore structure,surface chemistry and liquid phase adsorption of olive stone based activated carbon prepared by mixing process using phosphoric acid and steam as activating agents.Chemicals and textural characterization show that the increase of HNO3concentration increases considerably the total acidic groups but decreases specific surface area and pore volume.The study of adsorption in aqueous solutions of two organics,phenol and methylene blue,on raw and oxidized activated carbon indicates that the treatment of mixed activated carbon with different concentrations of nitric acid improves the adsorbent capacity for methylene blue at HNO3concentrations less or equal to 2 mol·L 1,while it has a negative effect on phenol adsorption.

Microwave pretreatment for enhanced selective nitric acid pressure leaching of limonitic laterite

As clean energy,the microwave is commonly used to pretreat various ores.In this work,the microwave dielectric properties of limonitic laterite ore were measured by resonant cavity perturbation technique and the effects from microwave were systematically investigated.Results indicated that limonitic laterite had high microwave absorbance.After microwave pretreatment,the microstructure of the laterite became less aggregated and more porous and the main phase transformed from goethite to hematite that improved leaching in nitric acid(1.2 kg HNO3/kg ore);Ni,Co,Fe,and Mg extraction ratios were 95.2%,98.1%,1.8%and 15%,respectively,after leaching for 60 min at 200°C and 500 r/min.Furthermore,in the process of goethite to hematite by microwave pretreatment,the nickel-containing mineral is activated,which makes nickel be leached easily.The leaching process has high Ni extraction ratio compared to that without microwave(82%)and conventional pretreatment(90.4%).Therefore,microwave pretreatment of limonitic laterite before nitric acid pressure leaching is an effective way to improve the selectivity and extraction of the leach.

Kinetic study on leaching of nickel from Turkish lateritic ore in nitric acid solution

Dissolution kinetics of nickel from lateritic ore in nitric acid solution was investigated. Experimental parameters used were stirring speed(100-600 r/min), temperature(40-96 °C), nitric acid concentration(0.1-2 mol/L) and particle size(<106 μm). The shrinking core model was applied to the results of experiments investigating the effects of leaching temperature in the range of 40-90 °C and nitric acid concentration in range of 0.1-2 mol/L on nickel dissolution rate. The kinetic analysis shows that the nickel dissolution from lateritic ore could be described by diffusion model. The activation energy(E_a) for the dissolution reaction is calculated as 79.52 kJ/mol.

Coordination leaching of tungsten from scheelite concentrate with phosphorus in nitric acid

A hydrometallurgical process for tungsten extraction and recovery from scheelite is reported.The technology includes leaching scheelite using phosphoric acid as chelating agent in nitric acid solutions,extracting tungsten by solvent extraction and reusing leaching agent.In the leaching process,affecting factors,such as temperature,leaching time,nitric acid and dosage of phosphoric acid,were examined on recovery of tungsten.Results show that more than 97%of tungsten could be extracted under conditions of leaching temperature of 80-90°C,HNO3 concentration of 3.0-4.0 mol/L,liquild-to-soild ratio of 10:1,H3PO4 dosage of 3 stoichiometric ratio and leaching time of 3 h.Solvent extraction was then employed for the W recovery from the leachate with a organic system of 40%(v/v)N235,30%(v/v)TBP,and 30%sulfonated kerosene.Approximately 99.93%of W was extracted and ammonium tungstate solution containing 193 g/L W was obtained with a stripping rate of 98.10%under the optimized conditions.

Kinetics of nitric acid leaching of low-grade rare earth elements from phosphogypsum

Phosphogypsum(PG)is a potential resource for rare earth elements(REEs).Several studies have been carried out on REE leaching from PG.However,few in-depth studies have investigated the kinetics of this leaching process.In this study,the leaching kinetics of REEs from PG in nitric acid at different temperatures were explored in depth.The experiments show that the maximum leaching recovery for ΣREE was 58.5%,75.9%and 83.4%at 30,60 and 80℃,respectively.Additionally,among La,Ce,Y and Nd,Y had the highest leaching rate.A new shrinking core model(SCM)based on the dissolution reaction of a cylindrical solid particle with interfacial transfer and diffusion across the product layer as the rate-controlling step was deduced and could well fit the leaching process of REEs from PG.The activation energies for the leaching of La,Ce,Y and Nd were determined on the basis of the new cylindrical SCM.In summary,the cylindrical SCM was a more suitable fitting model than the spherical SCM,and the interfacial transfer and diffusion across the product layer were the rate-controlling step for REE leaching from the PG sample.

Extraction of cerium(Ⅳ) using tributyl phosphate impregnated resin from nitric acid medium

Tributyl phosphate （TBP） solvent was used for impregnation into Amberlite XAD-16 nonionic polymeric resin beads using the wet method to prepare solvent impregnated resin （SIR）. Undiluted TBP in a ratio to the resin support （volume to mass） of 6.0 at room temperature （RT） in 24 h was impregnated the resin with a mass ratio of 1.944, while the prepared gross sample of SIR at the ratio of solvent to resin of 3.0 was impregnated with a mass ratio of 1.88. Cerium（Ⅳ） oxide concentrate, prepared from crude Egyptian monazite sand, containing 37% cerium, 1.6% thorium and about 40% the other trivalent rare earth oxides, was used to prepare cerium（Ⅳ） nitrate solution for extraction using the prepared SIR. The impregnated resin was satisfactory for Ce（Ⅳ） extraction from nitric acid medium at room temperature. Cerium loading capacity of the impregnated resin reached 95.6% of the calculated theoretical capacity （173 g/kg （Ce/SIR）） under the conditions of 51.57 g/L cerium and 2.48 g/L thorium, 5.0 mol/L free nitric acid, solution to resin ratio of 10.0 and contacting the phases for 5.0 min. The loading capacity reached 98.75% when cerium concentration was increased to 91.43 g/L under the same conditions.

Mechanism of oxidation of low rank coal by nitric acid

The pretreatment of low rank coal with nitric acid oxidation can promote its bio-liquefaction. However, the detailed mechanism of which remains an unresolved problem. In the present work, the characteristics of Fushun coal before and after oxidation by nitric acid were investigated combined with elemental composition, pore volume and pore size, Zeta potential, FT-IR, and 13C solid NMR spectrum analysis. The results show that the inorganic substance inlaid in coal are dissolved by ni- tric acid, which results in the decrease of coal ash content and increase of pore volume and pore size. Furthermore, there exist obvious chemical reactions between nitric acid and the functional groups of coal including aromatic ring carboxylation, side chain alkyl of aromatic ring oxidation and aromatic ring nitration. Among these reactions, some led to the increase in content of carboxyl, aliphatic carbon connected with O and humic acid carbon, while others caused the reduction of aromaticity, methyl carbon, substituted aryl carbon and side chain.

Corrosion behavior of porous Ti_3SiC_2 in nitric acid and aqua regia

Porous Ti3SiC2with high purity was synthesized using TiH2,Si and C powders with mole ratio of Ti to Si to C being3:1.2:2by reactive synthesis method.The corrosion behaviors of porous Ti3SiC2in nitric acid and aqua regia were investigated byimmersing test.Scanning electron microscope(SEM),X-ray diffractometer(XRD),energy dispersive spectrometer(EDS)and X-rayphotoelectron spectroscopy(XPS)were used to analyze the morphology,compositions and element contents of the samples beforeand after corrosion to determine the corrosion product and corrosion mechanism.The mass loss values of porous Ti3SiC2are26.9and132.5μg/cm2,respectively after immersing in nitric acid and aqua regia for600h.The results indicate that Ti3SiC2transforms toTi5Si3which has better corrosion resistance in nitric acid and aqua regia with mass loss values of9.34and7.06μg/cm2under thesame immersing time,respectively.The dramatic dissolution of porous Ti3SiC2in the acids is due to its special microstructure.

Chlorine inclusion mechanism in high purity copper electrorefining from nitric acid system

A practical approach was introduced to study the inclusion mechanism of chlorine in high purity copper electrorefining from nitric acid system via cyclic voltammetry(CV) combined with electrodeposition experiments. The CV curves display an obvious reduction peak of Cu Cl intermediate, which can provide an insight into the electrochemical behavior of this inclusion. Experimental results show that the increase of HNO3 concentration is favorable to reducing the quantity of chlorine inclusion although there is a slight decline in cathodic current efficiency. The optimum conditions for copper electrorefining in nitric acid system are HNO3 concentration in solution of 1-2 mol/L, moderate temperature of ~35 ℃ with current density not exceeding 25 m A/cm2. Based on the theoretical studies, an optimized copper electrorefining experiment was designed to simulate the industrial electrolysis, by which high purity copper can be obtained with chlorine inclusion less than 10 μg/g and current efficiency higher than 90%.

A Durable Catalyst for Vapor Phase Nitration of Benzene with Nitric Acid

Experimental results in this work demonstrate that PW12-H2SO4/SiO2 catalyst is a good and durable catalyst for vapor phase nitration of benzene to nitrobenzene (NB) using 65% nitric acid at normal pressure. It retains the advantages of using H2SO4 as catalyst and the addition of phosphotungstic acid holds back the effusion of sulfuric acid. This new catalyst keeps high activity (the conversion of HNO3 is more than 92%), high selectivity of NB (more than 97%) and high space time yield (STY 1.5 kg NB/kg cat.h) even after 150 h on stream, under condition of 423 K, SV=3200 ml/g h.

Solvent extraction equilibrium of dysprosium(Ⅲ) from nitric acid solutions with 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester

In view of the importance of solvent extraction of rare earth metals with the acidic organophosphorous reagent,the development of a chemically based model applicable to high concentration is desired.In the present study,the equilibrium distribution of dysprosium(Ⅲ)between an aqueous nitric acid solution and 2-ethylhexylphosphonic acid mono-2-ethylhexyl ester (PC88A)was measured in the range of an initial aqueous dysprosium(Ⅲ)concentration from 1.0×10-3to 1.0×10-1kmol/m 3and PC88A concentration from 0.16 to 0.65 kmol/m3in Shellsol D70 as the diluent.The obtained data were analyzed using the chemically based model in order to correlate the equilibrium distribution ratios.In this model,dysprosium(Ⅲ)was assumed to be extracted with the PC88A dimer as a 1:3 complex,the activities were considered for the aqueous species,and the effective concentration of the PC88A dimer was calculated using Alstad's empirical equation.As a result,the apparent extraction equilibrium constant was determined to be 253(kmol·m- 3)-2with an excellent correlation between the experiment and calculation results in the wide range of the logarithm of the distribution ratio from-2 to 3.5.In conclusion,the methodology in this model would be effective for quantitative description of solvent extraction behavior of general rare earth elements as well as dysprosium.

Recovery of Lead from Sulfide Concentrate after Mechanochemical Activation Using Nitric Acid

Decomposition of lead sulfide concentrates in nitric acidic solutions after ferric(Ⅲ)nitrate addition and mechanical preparation has been investigated.It was found out that the decomposition can be achieved in HNO_(3) solution(>1.5 mol·L^(-1))at the temperature above 85℃.The leaching rate of lead can be increased by means of mechanochemical activation.The use of[Fe(NO_(3))_(3)-HNO_(3)-H_(2)O]aqueous salt system allows the decomposition of lead sulfide concentrate at room temperature and in this case the concentration of HNO_(3) does not exceed 0.05-0.1 mol.L^(-1),The degree of lead recovery into solution from PbS concentrate reaches 99.3%-99.6c70 with the mechanochemical activation of this concentrate.The insoluble residues after the leaching contain SiO_(2),S^(0),FeCO_(3) and PbSO_(4).

Kinetic study for the oxidation of cyclohexanol and cyclohexanone with nitric acid to adipic acid

The adipic acid is an important intermediate in the production of nylon,polyurethane and polye ster resin s.The industrial approach for preparing adipic acid is through the liquid catalytic oxidation of KA oil with nitric acid.In this work,a comprehensive model is developed for this reaction based on the kinetic study conducted in a continuous flow tubular reactor.The kinetic model fits well with the experimental results across the experimental conditions,and the average relative error between the calculated and experimental values is 5.7%.Results show that there was an induction period at the early stage of reaction.Moreover,it is found that at temperature range of 328-358 K,the formation rate of adipic acid strongly dependents on the temperature and nitric acid concentration.The developed model is used to predict the yield of adipic acid at 359-368 K.The work in this study could provide much knowledge for industrial tubular reactor design.

A New Process Study on Comprehensive Utilization of NO_x from Nitric Acid Plant

Based on studies of controlling NOx from nitric acid exhaust gas domestic and abroad, this paper has developed a new technique on removal of NOx and production of aby-product with high added value-MnO2. Experimentshows, pyrolusite, whose valid composition is MnO2 , of absorbing NOx has the following characteristics: quick, low cost, no secondary pollutant. Moreover, exhaust gas can attain the required standards. If the temperature of the pyrolusite serum is 30℃ , pH = 4, containing 90 g/L MnO2, the absorptivity for 3 000 mg/m3 NOx is 89. 2%. Furthermore, few of the impurities in pyrolusite dissolve in the absorption mother solution. The purification cost of product is very low. The purity of end product MnO2 is more than 99. 995% after purifying. Therefore, it is workable for the new technique on economy and technology. There are also obvious environmental benefits and marked economic returns.

Corrosion Behavior of a Titanium Alloy in Hot Nitric Acid Condensate

The corrosion behavior of a titanium-5% tantalum alloy （Ti-STa） in hot nitric acid condensate was investigated to understand aging behavior ofreprocessing equipments. On the basis of long-term immersion tests, it was determined that the corrosion of Ti-STa in nitric acid condensate is accelerated with an increase in the concentration. The corrosion rate was nearly constant during the immersion test and the coupons suffered from uniform corrosion. In addition, it is important to note that the nitric acid concentration in the condensate increased on addition of metal salts to the heated nitric acid solution. The larger valence of metal ions was contributed to the increase in the concentration of nitric acid condensate. Consequently, the metal salt in the heated nitric acid solution accelerates the corrosion of Ti-STa in the condensate. Therefore, the nitric acid condensate condition should be carefully considered for the corrosion environment of titanium and its alloys.

Macroscopic,thermodynamic,kinetic and microscopic study of nitric acid pickling of Elektron 21(EV31A)magnesium alloy

The study of pickling of the EL21T6 substrate in a nitric acid bath firstly provided knowledge of the influence of the different experimental parameters(concentration of acid,temperature and stirring of the solution)in relation to the etching rate.This experimental part led to the choice of standard pickling(T_(bath)=25℃,moderate stirring(250 rpm),[HNO_(3)]=1.20 mol/L,duration of 2 min)so as to obtain constant removal of material,even after several uses of the pickling bath.SEM observations also confirmed that in these operating conditions,pickling concerns both the grains of the matrix and the precipitates of type Mg3(Nd,Gd),leading to uniform removal of material from the surface.Working from a number of assumptions,thermodynamic and chemical kinetic studies then allowed a pickling mechanism to be proposed and led to obtaining values for the corresponding kinetic parameters(order of reaction,constant of mean rate,activation energy)to be obtained.

UV Photodissociation Dynamics of Nitric Acid： The Hydroxyl Elimination Channel

Sliced velocity mapping ion imaging technique was employed to investigate the dynamics of the hydroxyl elimination channel in the photodissociaiton of nitric acid in the ultraviolet region. The OH product was detected by （2＋1） resonance enhanced multiphoton ionization via the D^2∑^- electronic state. The total kinetic energy spectra of the OH＋NO2 channel from the photolysis of HONO2 show that both ：NO2（X2A1） and NO2（A2B2） channels are present, suggesting that both 1^1A″ and 2^1A″ excited electronic states of HONO2 are involved in the excitation. The parallel angular distributions suggest that the dissociation of the nitric acid is a fast process in comparison with the rotational period of the HNO3 molecule. The anisotropy parameter β for the hydroxyl elimination channel is found to be dependent on the OH product rotational state as well as the photolysis energy.

Study on effect of crosslink structure on decomposition of epoxy resins in nitric acid

One chemical approach using nitric acid as the solvent to decompose thermosetting epoxy resin was discussed. The samples were prepared by using different kinds of curing agents, namely polyamide (PA651), isophorone diamine (IPDA), 4,4'-diaminodiphenylmethane (DDM) and 2-ethyl-4-methy-imidazole (EMI-2,4) and different kinds of epoxy resins, namely bisphenol-A epoxy resin(E-44), bisphenol-A epoxy resin(E-51), N,N,N',N' teraglycidy 4,4' diaminodiphenyl methane (AG-80) and diglycidyl-4,5-epoxycyclohexane-1,2-dicarboxylate (TDE-85). Their effects on decomposition rate were investigated and the decomposition products were analyzed by Infra-red (IR) spectra, and Gas Chromatography-Mass Spectrometry (GC-MS). Based on conclusions drawn from experiments, the mechanism of degrading thermosetting epoxy resin with nitric acid was envisaged tentatively.

Alpha radiolysis of nitric acid aqueous solution irradiated by 238Pu source

Alpha radiolysis of nitric acid aqueous solution by a ^(238)Pu source is investigated experimentally and theoretically.The time dependence of the nitrous acid yield on dose rate,nitric acid concentration,and nitrate ion concentration is studied.A novel kinetic model for the α-radiolysis of nitric acid aqueous solution is established,by considering the direct and indirect effects.The simulation results agree well with the experimental data,indicating the validity of our model to treat the reaction paths for generation and consumption of nitrous acid.It is shown that the redox reactions involving Pu cannot be neglected in theα-radiolysis of the solution.The results provide a better understanding of the α-ray radiolysis of aqueous nitric acid.