In-situ electrochemical study on the eff ects of Fe(Ⅲ)on kinetics of pyrite acidic pressure oxidation

Fe(Ⅲ)has been proved to be a more eff ective oxidant than dissolved oxygen at ambient temperature,however,the role of Fe(Ⅲ)in pyrite acidic pressure oxidation was rarely discussed so far.In this paper,in-situ electrochemical investigation was performed using a flow-through autoclave system in acidic pressure oxidation environment.The results illustrated that increasing Fe(Ⅲ)concentrations led to raising in redox potential of the solution,and decreased passivation of pyrite caused by deposition of elemental sulfur.Reduction of Fe(Ⅲ)at pyrite surface was a fast reaction with low activation energy,it was only slightly promoted by rising temperatures.While,the oxidation rate of pyrite at all investigated Fe(Ⅲ)concentrations increased obviously with rising temperatures,the anodic reaction was the rate-limiting step in the overall reaction.Activation energy of pyrite oxidation decreased from 47.74 to 28.79 kJ/mol when Fe(Ⅲ)concentration was increased from 0.05 to 0.50 g/L,showing that the reaction kinetics were limited by the rate of electrochemical reaction at low Fe(Ⅲ)concentrations,while,it gradually turned to be diffusion control with increasing Fe(Ⅲ)concentrations.

Co-oxidation of arsenic(Ⅲ) and iron(Ⅱ) ions by pressurized oxygen in acidic solutions

The co-oxidation of As(Ⅲ) and Fe(Ⅱ) in acidic solutions by pressured oxygen was studied under an oxygen pressure between 0.5 and 2.0 MPa at a temperature of 150℃. It was confirmed that without Fe(Ⅱ) ions, As(Ⅲ) ions in the solutions are virtually non-oxidizable by pressured oxygen even at a temperature as high as 200℃ and an oxygen pressure up to 2.0 MPa. Fe(Ⅱ) ions in the solutions did have a catalysis effect on the oxidation of As(Ⅲ), possibly attributable to the production of such strong oxidants as hydroxyl free radicals (OH ) and Fe(Ⅳ) in the oxidation process of Fe(Ⅱ). The effects of such factors as the initial molar ratio of Fe(Ⅱ)/As(Ⅲ), initial pH value of the solution, oxygen pressure, and the addition of radical scavengers on the oxidation efficiencies of As(Ⅲ) and Fe(Ⅱ) were studied. It was found that the oxidation of As(Ⅲ) was limited in the co-oxidation process due to the accumulation of the As(Ⅲ) oxidation product, As(Ⅴ), in the solutions.

Selective recovery of lithium from spent lithium iron phosphate batteries using oxidation pressure sulfuric acid leaching system

Oxidation pressure leaching was proposed to selectively dissolve Li from spent LiFePO_(4) batteries in a stoichiometric sulfuric acid solution.Using O_(2) as an oxidant and stoichiometric sulfuric acid as leaching agent,above 97% of Li was leached into the solution,whereas more than 99% of Fe remained in the leaching residue,enabling a relatively low cost for one-step separation of Li and Fe.And then,by adjusting the pH of leachate,above 95% of Li was recovered in the form of the Li_(3)PO_(4) product through iron removal and chemical precipitation of phosphate.

INFLUENCE OF HEAT TREATMENT ON OXIDATION PROPERTIES OF C/C COMPOSITES FABRICATED BY HIGH PRESSURE IMPREGNATION CARBONIZATION

Felt base carbon/carbon composites fabricated by super-high pressure impregnation carbonization process (SPIC) were heat treated at high temperature 2773K. The oxidation properties of felt base carbon/carbon composites were investigated at different temperatures (773-1173K), and the microstructures of carbon/carbon composites were studied by SEM and X-ray diffraction. The experimental results showed that the inter-laminar distance of (002) plane (d002) deceased while the microcrystalline stack height (Lc) increased. The oxidation rate of felt base carbon/carbon composites was invari-able at certain temperatures. The oxidation mechanism of carbon/carbon composites changed remarkably at the oxidation temperature 973K. At the initial oxidation stage of carbon/carbon composites, carbon matrix was oxidized much more rapidly than carbon felt.

Multi-Pollutant Formation and Control in Pressurized Oxy-Combustion:SO_(x),NO_(x),Particulate Matter,and Mercury

Oxy-combustion is a promising carbon-capture technology,but atmospheric-pressure oxy-combustion has a relatively low net efficiency,limiting its application in power plants.In pressurized oxycombustion(POC),the boiler,air separation unit,flue gas recirculation unit,and CO_(2)purification and compression unit are all operated at elevated pressure;this makes the process more efficient,with many advantages over atmospheric pressure,such as low NO_(x)emissions,a smaller boiler size,and more.POC is also more promising for industrial application and has attracted widespread research interest in recent years.It can produce high-pressure CO_(2)with a purity of approximately 95%,which can be used directly for enhanced oil recovery or geo-sequestration.However,the pollutant emissions must meet the standards for carbon capture,storage,and utilization.Because of the high oxygen and moisture concentrations in POC,the formation of acids via the oxidation and solution of SO_(x)and NO_(x)can be increased,causing the corrosion of pipelines and equipment.Furthermore,particulate matter(PM)and mercury emissions can harm the environment and human health.The main distinction between pressurized and atmospheric-pressure oxy-combustion is the former’s elevated pressure;thus,the effect of this pressure on the pollutants emitted from POC—including SO_(x),NO_(x),PM,and mercury—must be understood,and effective control methodologies must be incorporated to control the formation of these pollutants.This paper reviews recent advances in research on SO_(x),NO_(x),PM,and mercury formation and control in POC systems that can aid in pollutant control in such systems.

High temperature oxidation of powder metallurgy two phase Cu Cr alloys under low oxygen pressure

The oxidation of two phase Cu Cr alloys containing 25% and 50% Cr prepared by powder metallurgy (PM) with a rather uniform two phase microstructure has been studied at 700～900 ℃ under oxygen pressure below the stability of the copper oxides. The two PM alloys oxidized very slowly and formed only external Cr 2O 3 scales rather than undergoing an internal oxidation of chromium. This result is attributed mainly to a supply of chromium from the small Cr rich particles dispersed within the Cu rich phase. The oxidation kinetics of the two PM Cu Cr alloys approximately followed the parabolic rate law. The scaling rates are of the same order as those measured for pure chromium under the same oxygen pressure, but smaller than those for the alloys of similar composition prepared by normal arc melting techniques, whose compositions were largely non uniform. The results are interpreted in terms of the two phase nature of these alloys.

Acid leaching decarbonization and following pressure oxidation of carbonic refractory gold ore

Carbonate decomposition of carbonic refractory gold ore and the following pressure oxidation were studied.In the carbonate decomposition procedure,the effects of liquid-to-solid ratio and reaction time on decomposition ratio of carbonate were investigated.The experimental result shows that the decomposition ratio of carbonate is 98.24%under the conditions of liquid-to-solid ratio of 5:1,Fe^(3+)concentration of 20 g/L,sulfuric acid concentration of 20 g/L,reaction temperature of 80 ℃ and reaction time of 2 h.Then,the slurry obtained from carbonate decomposition was put into the titanium autoclave for pressure oxidation leaching.Effects of liquid-to-solid ratio,temperature,time and oxygen partial pressure on sulfur oxidation ratio were studied during pressure oxidation.With the prolonged time,pyrite and arsenopyrite are oxidized to ferric subsulfate,hydrated ferric sulfate and jarosite,resulting in the increasing residue ratio.The residue ratio and the sulfur content in the residue can be decreased by ferric subsulfate dissolution.The oxidation ratio of the sulfur is 99.35% under the conditions of oxidation time of 4 h,temperature of 210 ℃,oxygen partial pressure of 0.8 MPa and stirring speed of 600 r/min.

Novel-structured Mo-Cu-Fe-O composite for catalytic air oxidation of dye-containing wastewater under ambient temperature and pressure

A novel‐structured Mo‐Cu‐Fe‐O composite was successfully prepared by co‐precipitation and impregnation method.The properties of the as‐prepared samples were determined using X‐ray diffraction,temperature‐programmed reduction by H2,cyclic voltammetry,and temperature‐programmed desorption by O2.The results showed that Mo6+diffused into the Cu‐Fe‐O crystal lattice and then formed a new crystalline phase of CuMoO4.The Mo‐Cu‐Fe‐O catalyst had redox properties,and its surface contained active sites for oxygen adsorption.In addition,the catalytic activity of the Mo‐Cu‐Fe‐O composite was evaluated by the degradation of Cationic Red GTL,Crystal Violet,and Acid Red in catalytic wet air oxidation(CWAO)at ambient temperature and pressure.The Mo‐Cu‐Fe‐O catalyst showed excellent activity at basic conditions for the degradation of Cationic Red GTL.High removal efficiencies of91.5%and92.8%were achieved for Cationic Red GTL and Crystal Violet,respectively,in wastewater,and the efficiency remained high after seven cycles.However,almost no degradation of Acid Red occurred in the CWAO process.Furthermore,hydroxyl radicals were formed in the CWAO process,which induced the decomposition of the two cationic dyes in wastewater,and the toxicity of their effluents was decreased after degradation.The results indicate that the Mo‐Cu‐Fe‐O composite shows excellent catalytic activity for the treatment of wastewater contaminated with cationic dyes.

Atmospheric-Pressure DBD Cold Plasma for Preparation of High Active Au/P25 Catalysts for Low-Temperature CO Oxidation

Cold plasma generated by dielectric barrier discharge （DBD） at atmospheric pressure was adopted for preparation of commercial TiO2 Degussa P25 supported Au catalysts （Au/P25- P） with the assistance of the deposition-precipitation procedure. The influences of the plasma reduction time and calcination on the performance of the Au/P25-P catalysts were investigated. CO oxidation was performed to investigate the catalytic activity of the Au/P25 catalysts. The results show that DBD cold plasma for the fabrication of Au/P25-P catalysts is a fast process, and Au/P25-P （4 min） exhibited the highest CO oxidation activity due to the complete reduction of Au compounds and less consumption of oxygen vacancies. In order to form more oxygen vacancies active species, Au/P25-P was calcined to obtain Au/P25-PC catalysts. Interestingly, Au/P25- PC exhibited the highest activity for CO oxidation among the Au/P25 samples. The results of transmission electron microscopy （TEM） indicated that the smaller size and high distribution of Au nanoparticles are the mean reasons for a high performance of Au/P25-PC. Atmospheric- pressure DBD cold plasma was proved to be of great efficiency in preparing high performance supported Au catalysts.

Oxidation of Fe-Cr-Ni Alloys in a Low Oxygen Partial Pressure Atmosphere to Mitigate Coke Formation

Anti-coking oxide films were prepared on a 25Cr35Ni and 35Cr45Ni alloy surface under the low oxygen partialpressure atmosphere of a H2-H2O mixture. The composition and phase structure of the oxide films were analyzed by energydispersive spectroscopy (EDS), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The anti-cokingperformance of a mini tube made of a HP40 (25Cr35Ni) alloy was evaluated on a bench scale pyrolysis and coking test unit.The results showed that the surface Fe and Ni content decreased after the oxidation of the two alloys in a low oxygen partialpressure atmosphere. The oxide films were mainly composed of MnCr_(2)O_(4) and Cr_(2)O_(3). The average mass of coke in the minitube with oxide film decreased by 87% relative to that of a tube without an oxide film when the cracking temperature was 900℃. The ethylene, propylene, and butadiene yields in the pyrolysis tests were almost the same for the mini tubes withand without an oxide film. The oxide film on the alloy surface effectively inhibited catalytic filamentous coke formation.An industrial test showed that the run length of the cracking furnace with the in-situ coating technology was significantlyextended.

Complete Maps for the Internal Oxidation of Ideal Ternary Alloys Forming Insoluble Oxides under High Oxidant Pressures

This paper presents an analysis of the conditions of stability of the different forms of internal oxidation of ideal ternary A-B-C alloys,where A is the most noble and C the most reactive component, forming insoluble oxide and exposed to high pressures of a single oxidant.The treatment,based on an extension to ternary alloys of Wagner' s criterion for the transition from internal to external oxidation in binary alloys,allows to predict the existence of three different forms of internal oxidation.In fact,in addition to the most common kinds of internal attack,involving the coupled internal oxidation of B+C beneath external AO scales and the internal oxidation of C beneath external BO scales,a third mode, involving the internal oxidation of C beneath external scales composed of mixtures of AO+BO,becomes also possible under special conditions.A combination of the boundary conditions for the existence of these different types of internal oxidation allows to predict three different kinds of complete maps for the internal oxidation in these systems,one of which involves only two modes,while the other two involve all the three possible modes of internal oxidation.

Crystal structure and catalytic performance for direst oxidation of propylene to acrylic acid of MoVTeNbO_(x) prepared by high-pressure hydrothermal synthesis

MoVTeNbO_(x) catalysts were prepared through a high-pressure hydrothermal method,in which the crystalline structure and properties of the catalysts were tuned by varying the system pressure(0-12.0 MPa).Results showed that the system pressure had a significant influence on the structure and catalytic performance of MoVTeNbO_(x).Under 3.0 MPa,MoVTeNbO_(x) prepared possessed the highest content of M1 phase(90.6%)and V5+content(60.7%),exhibiting a uniform short and thick needle-like morphology.Also,it showed excellent selectivity(79.1%)and yield(52.8%)to acrylic acid at the catalytic temperature of 380℃.However,under 4.4 and 11.6 MPa,the characteristic peaks of M1 shifted to a certain extent and the morphology changed from short and thick to slender.As a result,the V5+content of M1(001)plane decreased,resulting in a remarkable decline of the selectivity to acrylic acid.Moreover,DFT simulation results showed that the anti-bond orbital energy of V-O bond is the highest under 3.0 MPa,while further increase of pressure leads to obvious extrusion between atoms in the internal structure of MoVTeNbO_(x).Moreover,it was clear that the lower the anti-bond orbital energy of V-O bond,the lower the selectivity to acrylic acid.

Formation mechanism and oxidation behavior of MoSi_2-SiC protective coating prepared by chemical vapor infiltration/reaction

In order to protect C/C composites from oxidation, SiC-MoSi2 composite coating was synthesized by chemical vapor infiltration /reaction （CVI/CVR） technology. A porous Mo layer was prefabricated on SiC coated C/C composites, and then MoSi2 and SiC were subsequently prepared in a CVI /CVR process using methyltrichlorosilane （MTS） as precursor. The deposition and reaction mechanism of the MoSi2-SiC composite coating was investigated by X-ray diffraction （XRD） and scanning electron microscopy （SEM）. The oxidation behavior of SiC-MoSi2 coated specimens was tested. The results show that the porous Mo layer can be densified with SiC phase decomposed from MTS, and transformed into SiC-MoSi2 by reacting with MTS as well. A dense composite coating was prepared with optimized deposition parameters. The coated specimen exhibits a good oxidation resistance with a little mass loss of 1.25% after oxidation at 1500 °C for 80 h.

Indium recovery from zinc oxide flue dust by oxidative pressure leaching

Indium was recovered from zinc oxide flue dust(ZOFD)with sulfuric acid by oxidative pressure leaching in an autoclave, and the effects of different technological conditions on indium leaching were studied.Potassium permanganate and hydrogen peroxide were used as oxidants.The atmospheric pressure leaching experiments were also carried out.The experimental results show that the leaching rate of indium can be effectively improved by oxidative pressure leaching.The optimum conditions of pressure leaching are determined as sulfuric 5.10 mol/L acid,leaching time 150 min,temperature 90℃,and the H2O2 dosage of 0.5 mL/g or 2.5%KMnO4.The leaching rate of indium is more than 90%,which is increased by 13%compared with that of atmospheric pressure leaching process without oxidant under the optimum conditions.

Continuous Positive Airway Pressure Effectively Alleviates Arrhythmias in Patients with Obstructive Sleep Apnea:Possible Relationship with Counteracting Oxidative Stress

This work is aimed at exploring the clinical efficacy of continuous positive airway pressuie(CPAP)in treatment of patients with arrhythmias combined with obstructive sleep apnea(OSA).Through evaluating serum native thiol,malonaldehyde(MDA)and nicotinamide adenine dinucleotide phosphate oxidase(NADPH oxidase)in these patients and describing the effects on oxidative parameters of CPAP therapy for 3 months,we confirmed the impact of oxidative stress on arrhythmias.A total of 64 patients with OSA combined with arrhythmias were collected from April 2014 to April 2017 with full clinical information.Patients were divided into two groups(paired experiment design):32 patients in group A(control group),who received unchanged anti-arrhythmia treatment and 32 patients in group B,who were subjected to unchanged pharmacological anti-arrhythmia therapy combined with CPAP.OSA related parameters were compared between the two groups after 3-month therapy.And the levels of parameters of oxidative stress in patients were measured before and after CPAP therapy.After 3 months of CPAP therapy,compared with the control group,the percentage of sage N3(NREM 3)and stage R(REM)in total sleep time was significantly increased,while apnea-hypopnea index(AHI)and the Epworth Sleepiness Scale(ESS)score were evidently decreased.Meanwhile,the lowest oxygen saturation(LSpCh)was also elevated after CPAP treatment for 3 months.The CPAP therapy significantly prevented the occurrence of arrhythmias(P<0.05).Both the MDA level and NADPH oxidase levels were significantly lower in the group B than in the group A(P<0.05).But serum native thiol was improved by CPAP treatment(P<0.05).In conclusion,proper use of CPAP therapy provides significant benefits for the treatment of arrhythmia in patients with OSA.

Homogeneous catalytic wet air oxidation for the treatment of textile wastewaters

An extensive series of experiments was carried out in order to identify suitable catalysts to boost the reaction rate of wet air oxidation of real textile wastewaters at relatively mild temperature and pressure. Experimental results indicated that all catalysts tested in this investigation had shown an impressive increase in the initial COD and TOC removal rate as well as the COD and TOC removal levels in two hours reaction. Among all the catalysts tested, copper salts were more effective than the rest. Anions of the salt solutions also played a role in the catalytic process with nitrate ions having better effect than sulfate ions. Hence copper nitrates were more effective than copper sulfates. It was also found that a mixture of salts with different metals performed better than either of the component single salt alone.

Effects of operating parameters on oxidative coupling of methane over Na-W-Mn/SiO_2 catalyst at elevated pressures

The effects of operating parameters on oxidative coupling of methane （OCM） over Na-W-Mn/SiO2 catalyst have been studied at elevated pressures of 0.2, 0.3 and 0.4 MPa under low gaseous hourly space velocity （GHSV） and low temperature conditions. Experimental results show that when the operating pressure is increased, C2＋ yield slightly decreases, while the maximum ratio of ethylene to ethane remains unchanged. Moreover, it has been found empirically that increase of pressure does not affect the catalyst behavior permanently, the catalyst recovers its original low pressure performance without hysteresis behavior by reducing the pressure. Under the investigated conditions, when oxygen is completely consumed, the increase of GHSV leads to improvement in C2 selectivity, while C3＋ and COx selectivities decrease slightly. The C2＋ selectivity increases by increase of nitrogen diluent in the feed, but the C3＋ hydrocarbons selectivities decrease with increase of nitrogen since it is possible that further dilution at high pressure may reduce the probability of collision between CH3 and C2＋ hydrocarbons. During the stability test at high pressure, the catalyst performance remains unchanged throughout the 20 h running. The fresh and used catalysts were characterized using XRD, SEM and N2 adsorption-desorption methods. It was found that the phase transformation of the support from α-cristobalite to tridymite and quartz does not have obvious effect on catalyst performance at high pressure.

Changes of Nitric Oxide and Its Relationship with Clinical Features,Intracranial Pressure and Outcome in Acute Head Injury

To investigate the content and dynamics of nitric oxide (NO) in the cerebrospinal fluid (CSF) of patients with acute head injury and to clarify the relationship of NO with clinical features and intracranial pressure (ICP) as well as outcomes, 38 adults with acute head injury were studied. Glasgow Coma Scale (GCS) obtained at admission and Glasgow Outcome Scale (GOS) 3 months after injury was assessed. ICP was surveyed via intraventricular catheter and lumbar puncture and CSF samples were obtained simultaneously. NO was determined with Griess reagents. Results showed that NO peak content in the head injury group was significantly higher than that of the control group. During dynamic research, no peak content of mildly injured cases and severely injured ones appeared in different time windows respectively. The peak value of NO was distinctly higher in the severe group than in the mild group. NO peak value of the raised ICP group was remarkably higher than that of the normal ICP group. The peak value of NO was considerately higher in the poor outcome group than in the good outcome group. When the content of NO was over 6. 5 μmol/L, the rate of poor outcome was increased. There existed a correlation between NO and GCS, ICP and GOS. It is concluded that the content of NO was increased in patients with acute head injury and the changes of NO had different time windows in severely injured patients and mildly injured ones. The more sever the injury, the higher the NO content; and the more serious the secondary brain injury and brain edema, the worse the outcomes. When NO is combined with GCS, GOS and ICP, it increases the accuracy of judgement to the degree of head injury and outcome.

The Effect of Nitrous Oxide on the Intraocular Pressure in Patients Undergoing Abdominal Surgery under Sevoflurane and Remifentanil Anesthesia

Introduction: Although inhalational anesthesia and nitrousoxide (N2O) are known to affect the intraocular pressure (IOP), little is known about the effect of nitrousoxide on the IOP during sevoflurane and remifentanil anesthesia. In the present study, we examined the effect of balanced anesthesia on the IOP. Materials and Methods: After obtaining informed consent, the patients undergoing abdominal surgery under general anesthesia were divided into two groups: N2O group (n = 10) and control group (n = 12). General anesthesia was maintained with remifentanil (0.05 - 0.3 μg/kg/min), 33% O2 and 1.2% sevoflurane to keep ETCO2 of 35 - 40 mmHg following tracheal intubation. After baseline measurement of IOP (T0, 20 minutes after injection of anesthesia), the patients in the N2O group received 67% nitrousoxide, and the patients in the control group received air, with O2 and 1.2% sevoflurane. Then, IOP was measured at 1 hour (T1), 2 hours (T2), and 3 hours (T3) after anesthesia induction in the supineposition. Blood pressure and heart rate were recorded at the same time interval. Results: There was no significant difference in the IOP at any period between the two groups. In both groups, the IOP at the T3 was significantly higher than that at T0. Conclusion: These results suggest that N2O does not affect the IOP in patients undergoing abdominal surgery under sevoflurane and remifentanil anesthesia.

Dynamic changes of inducible nitric oxide synthase expression in rat's retina and its role on blood-retinal barrier injury after acute high intraocular pressure

AIM: To clarify the role of inducible nitric oxide synthase(i NOS) in blood-retinal barrier(BRB) injury after acute high intraocular pressure(IOP) in rats.METHODS: Forty-two Sprague-Dawley(SD) rats were randomized into 7 groups [control(Cont), 3, 6, 12, 24, 48, and 72 h, n=6]. Except Cont group, other groups’ retina tissue was obtained at corresponding time points after a model of acute high IOP have been established in rats. The expression of i NOS and tight junction protein zonula occludens(ZO)-1 was detected by Western blotting. Evans blue(EB;3%) was injected into the great saphenous vein to detect the leakage of EB by spectrophotometer. Nine rats were divided into Cont, 6 h, 12 h groups, the expression of i NOS was localized by immunofluorescence. In order to verify the role of i NOS in the damage to BRB, thirty-six rats were randomly divided into 4 groups [Cont, Cont+inhibitor(Inh), 6 h and 6 h+Inh, n=9]. After treatment with the i NOSspecific inhibitor 1400 W, the expression of i NOS and ZO-1 and the leakage of BRB were detected again.RESULTS: The immunofluorescence results showed that the expression of i NOS was observed in the Cont group and 6 h group, but not in the 12 h group. i NOS was mainly expressed in the retinal nerve fiber layer, ganglion cell layer and inner nuclear layer and that it did not colocalize with the retinal ganglion cell marker Neu N but was co-expressed with the vascular endothelial cell marker CD31. Western blotting showed that in the early period(3 h, 6 h) after acute high IOP, the expression of i NOS was upregulated, then the down-regulation of i NOS were tested in the follow-up timing spots. ZO-1 expression showed a continuous downregulation after 6 h. The quantitative results for EB showed that the amount of EB leakage began to increase at 3 h after acute high IOP. At 6 h, the leakage of EB was lower, but at 12 h, the leakage of EB was highest, after which it gradually recovered but remained higher than that in the Cont group. The expression of i NOS was down-regulated after 1400 W treatment. ZO-1 expression was not significantly changed in the Cont+Inh group and the 6 h group, and significantly down-regulated in the 6 h+Inh group, and the leakage of EB was significantly increased after 1400 W treatment.CONCLUSION: These results suggest that the upregulation of i NOS expression in the early stage after acute high IOP may have a protective effect on BRB injury.