Behavior and mechanism of pre-oxidation improvement on fluidization in the fluidized reduction of titanomagnetite

The direct reduction process is an important development direction of low-carbon ironmaking and efficient comprehensive utilization of poly-metallic iron ore,such as titanomagnetite.However,the defluidization of reduced iron particles with a high metallization degree at a high temperature will seriously affect the operation of fluidized bed reduction.Coupling the pre-oxidation enhancing reduction and the particle surface modification of titanomagnetite,the behavior and mechanism of pre-oxidation improvement on fluidization in the fluidized bed reduction of titanomagnetite are systematically studied in this paper.Pre-oxidation treatment of titanomagnetite can significantly lower the critical stable reduction fluidization gas velocity to 0.17 m/s,which is reduced by 56%compared to that of titanomagnetite reduction without pre-oxidation,while achieving a metallization degree of>90%,Corresponding to the different reduction fluidization behaviors,three pre-oxidation operation regions have been divided,taking oxidation degrees of 26%and 86%as the boundaries.Focusing on the particle surface morphology evolution in the pre-oxidation-reduction process,the relationship between the surface morphology of pre-oxidized ore and the reduced iron with fluidization properties is built.The improving method of pre-oxidation on the reduction fluidization provides a novel approach to prevent defluidization by particle surface modification,especially for the fluidized bed reduction of poly-metallic iron ore.

Properties of Activated Carbons from Sugarcane Leaves and Rice Straw Derived Charcoals by Activation at Low Temperature via KMnO_(4)Pre-Oxidation-Hydrolysis

Activated carbon preparation from sugarcane leaves and rice straw by carbonization(250℃–400℃)and activation at 500℃were studied.The effects of pre-oxidation,hydrolysis of derived charcoals by boiled KMnO4 aqueous solution were evaluated.The derived charcoals products were pretreated using oxidation-hydrolysis with 1–5 wt.%KMnO4 at 100℃and then activated at 500℃.The derived charcoal and activated carbon products were characterized by FTIR,XRD,SEM-EDS and BET.Iodine number and methylene blue number of derived products were also used for the analysis of the products.It was found that fabricated charcoal materials made at 350℃–400℃possess good characteristics with low content of surface functional groups and high carbon content.After pre-oxidation-hydrolysis and activation at 500℃,the resulting derived activated carbon materials from charcoals with 400℃carbonization temperature have high content of oxygen containing surface functional groups such as Mn-O,Si-O,Si-O-Si,C-O,or O-H.In addition,MnO_(2) accumulated on the surface of the derived activated carbon products.The surface area and pore volume of the activated carbon products have also increased with increasing of KMnO_(4) concentration from 1 to 3 wt.%and then decreased with 5 wt.%used during activation.Therefore,activated carbon products made by pre-oxidation-hydrolysis with 3 wt.%KMnO_(4) were used for Fe(Ⅲ)adsorption experiments.It was found that Fe(Ⅲ)adsorption on the activated carbon materials can be fitted with both the Freundlich and the Langmuir models.The calculated maximum Fe(Ⅲ)adsorption capacities of sugarcane leaves derived activated carbon and rice straw derived activated carbon products were 50.00 and 39.37 mg/g,respectively.It was shown that the effect of pre-oxidation-hydrolysis by KMnO_(4) and activation at 500℃are beneficial for activated carbon preparation with environmentally friendly and low-cost simplified operation.

Prediction of pre-oxidation efficiency of refractory gold concentrate by ozone in ferric sulfate solution using artificial neural networks

An artificial neural network model was developed to predict the oxidation of refractory gold concentrate （RGC） by ozone and ferric ions. The concentration of ozone and ferric ions, pulp density, oxygen amount, leaching time and temperature were employed as inputs to the network; the output of the network was the percentage of the ferric extraction iron from RGC. The multilayered feed-forward networks were trained by 33 sets of input-output patterns using a back propagation algorithm; a three-layer network with 8 neurons in the hidden layer gave optimal results. The model gave good predictions of high correlation coefficient （R2=0.966）. The predictions by ANN are more accurate when compared with conventional multivariate regression analysis （MVRA）. In addition, calculation with ANN model indicates that temperature is the predominant parameter and ozone concentration is the lesser influential parameter in the pre-oxidation process of refractory gold ore. The ANN neural network model accurately estimates the ferric extraction during pretreatment process of RGC in gold smelter plants and can be used to optimize the process parameters.

Research into Uncertainty in Measurement of Seawater Chemical Oxygen Demand by Potassium Iodide-Alkaline Potassium Permanganate Determination Method

Using the glucose and L-glutamic-acid to prepare the standard substance according to the ratio of 1：1, and the artificial seawater and the standard substance to prepare a series of standard solutions, the distribution pattern of uncertainty in measurement of seawater COD is obtained based on the measured results of the series of standard solutions by the potassium iodide-alkaline potassium permanganate determination method. The distribution pattern is as follows： Uncertainty in measurement is big and not constant at the high end, but small and constant at the low end.

Effects of vacuum pre-oxidation process on thermally-grown oxides layer of CoCrAlY high temperature corrosion resistance coating

The influence of the certain specific vacuum pre-oxidation process on the phase transformation of thermally-grown oxides（TGO） was studied.The CoCrAlY high temperature corrosion resistance coatings were produced onto the nickel-based superalloy substrate by high velocity oxygen fuel（HVOF）.It suggests that the TGO usually consists of a great number of chromium oxides,cobalt oxides and spinel oxides besides alumina during the initial period of the high temperature oxidation if the specimens are not subjected to the appropriate vacuum pre-oxidation process.Furthermore,the amount of alumina is strongly dependent on the partial pressure of oxygen;while the CoCr2O4 spinel oxides are usually formed under the conditions of higher partial pressure of oxygen during the initial period and the lower partial pressure of oxygen during the subsequent period of the isothermal oxidation.After the appropriate vacuum pre-oxidation process,the TGO is mainly composed of alumina that contains lower Y element,while alumina that contains higher Y element sporadically distributes,and the spinel oxides cannot be found.After a longer period of the isothermal oxidation,a small amount of porous CoCr2O4 and the chrome oxide sporadically distribute near the continuous alumina.Additionally,after the appropriate vacuum pre-oxidation process,the TGO growth rate is relatively slow.

Oxidation of As(Ⅲ) by potassium permanganate

The oxidation of As（Ⅲ） with potassium permanganate was studied under conditions including pH, initial As（Ⅲ） concentration and dosage of Mn（Ⅶ）. The results have shown that potassium permanganate was an effective agent for oxidation of As（Ⅲ） in a wide pH range. The pH value of tested water was not a significant factor affecting the oxidation of As（Ⅲ） by Mn（Ⅲ）. Although theoretical redox analyses suggest that Mn（Ⅶ） should have better performance in oxidization of As（Ⅲ） within lower pH ranges, the experimental results show that the oxidation efficiencies of As（Ⅲ） under basic and acidic conditions were similar, which may be due to the adsorption of As（Ⅲ） on the Mn（OH）2 and MnO2 resulting from the oxidation of As（Ⅲ）.

Chemiluminescence detection of permanganate index (COD_(Mn)) by a luminol-KMnO_4 based reaction

A novel chemiluminescence （CL） system for determination of permanganate index （CODMn） combined with flow injection analysis has been proposed in this study. On the basis of the chemiluminescent reaction of luminol-KMnO4 system, light emission caused by luminol-KMnO4 system was detected by the photomultiplier tube, and its intensity caused by the appearance of KMnO4 after sample digestion was inversely proportional to CODMn. Effects for CODMn determining such as pH, concentrations and interference were investigated in detail. A detection limit of 0.3 mg/L CODMn with a linear range of 0.3-200 mg/L for its theoretical CODMn was obtained under the optimized experimental conditions. The relative standard deviation was 4.3% for 5.0 mg/L CODMn （n = 11）. This CL flow system for determining CODMn was simple, rapid, and suitable for automatic analysis. The data obtained by the present method were fairly in good agreement with those obtained by the standard titrimetric method. It has been applied to determine real samples with satisfactory results.

Novel Application of Vacuum Sealing Drainage with Continuous Irrigation of Potassium Permanganate for Managing Infective Wounds of Gas Gangrene

Summary： Traumatic gas gangrene is a fatal infection mainly caused by Clostridium perfringens. It is a challenge to manage gas gangrene in open wounds and control infection after debridement or amputa- tion. The aim of the present study was to use vacuum sealing drainage （VSD） with continuous irrigation of potassium permanganate to manage infective wounds of gas gangrene and observe its clinical effi- cacy. A total of 48 patients with open traumatic gas gangrene infection were included in this study. Am- putations were done for 27 patients, and limb salvage procedures were performed for the others. After amputation or aggressive debridement, the VSD system, including polyvinyl alcohol （PVA） foam dress- ing and polyurethane （PU） film, with continuous irrigation of 1：5000 potassium permanganate solutions, was applied to the wounds. During the follow-up, all the patients healed without recurrence within 8-18 months. There were four complications. Cardiac arrest during amputation surgery occurred in one pa- tient who suffered from severe septic shock. Emergent resuscitation was performed and the patient re- turned to stable condition. One patient suffered from mixed infection of Staphylococcal aureus, and a second-stage debridement was performed. One patient suffered from severe pain of the limb after the debridement. Exploratory operation was done and the possible reason was trauma of a local peripheral nerve. Three cases of crush syndrome had dialysis treatment for concomitant renal failure. In conclusion, VSD can convert open wound to closed wound, and evacuate necrotic tissues. Furthermore, potassium permanganate solutions help eliminate anaerobic microenviroument and achieve good therapeutic effect on gas gangrene and mixed infection. VSD with continuous irrigation of potassium permanganate is a novel, simple and feasible alternative for severe traumatic open wounds with gas gangrene infection.

Effects of chlorine content and position of chlorinated phenols on their oxidation kinetics by potassium permanganate

Chlorine content and position of chlorinated phenols have many significant effects on the reactivity of oxido-reduction. The effects of chlorine content and position of chlorinated phenols on their oxidation kinetics by potassium permanganate were evaluated through different kinetics studies. Since chlorine was an electron withdrawing atom, the substitution of chlorine on the aromatic ring decreased the oxidation rate constant by σ-electron withdrawing conductive effect. The substitution of chlorine at ortho or para position on the aromatic ring increased the oxidation rate constant by π-electron donating conjugative effect, and the conjugative effect could counteract the negative impact of the conductive effect to some extent. On the other hand, the substitution of chlorine at ortho position on the aromatic ring decreased the oxidation rate constant by steric hindrance effect. The oxidation rate constants of phenol and chlorinated phenols studied decreased as follow order: 4-chlorophenol>2,4-dichlorophenol>phenol>2,6-dichlorophenol.

Flow-injection chemiluminescence determination of tryptophan using galangin-potassium permanganate-polyphosphoric acid system

A high sensitive flow-injection chemiluminescence （FI-CL） method for the determination of tryptophan has been developed. The method is based on the chemiluminescence reaction of galangin-potassium permanganate-tryptophan in polyphosphoric acid （PPA） media. Under the optimized conditions, tryptophan was determined in the range 0.05-10 μg/mL with the detection limit （3tr） of 5.0 × 10^-3 μg/mL. The relative standard deviation （RSD） was 1.0% for 11 replicate determinations of 1.0 μg/mL tryptophan. Three synthetic samples were determined selectively with recoveries in the range from 99.6% to 102.0% in the presence of other amino acids.

Sulfidization regulation of cuprite by pre-oxidation using sodium hypochlorite as an oxidant

The direct sulfidization of cuprite is inefficient because cuprite is a copper-oxide mineral with a strong surface hydrophilicity.In this study,oxidant was used to modify cuprite surfaces to regulate the sulfidization of cuprite.Microflotation tests showed that the flotation recovery of pre-oxidized cuprite was nearly25% higher than that of direct sulfidization flotation,which indicates that the cuprite surface activity was enhanced after pre-oxidation by Cu(Ⅰ) species(weak affinity with sulfur ions) transformation to Cu(Ⅱ)species(strong affinity with sulfur ions).Zeta potential,scanning electron microscopy-energy dispersive X-ray spectroscopy,X-ray photoelectron spectroscopy,and time-of-flight secondary ion mass spectrometry results showed that pre-oxidation improved cuprite sulfidization and promoted the formation of copper-sulfide species on the cuprite surfaces.The mineral surface stability and thus,xanthate species adsorption on the cuprite surfaces were improved.The surface-adsorption measurements and infrared spectroscopy showed that a large amount of xanthate species was adsorbed onto the sulfidized cuprite surfaces after pre-oxidation,which enhanced the cuprite hydrophobicity and improved the cuprite flotation.

Controlled-Release Analysis of Potassium Permanganate Using PMMA Matrix

Excess amount of potassium permanganate has often been used in-situ for chemical oxidation of contaminated sites. The consequences are not limited to secondary contamination and cost but also inefficient remediation. Encapsulation of permanganate using PMMA enables controlled dissolution of the oxidant and aids long-term processes. This paper focuses on the oxidant release efficiency from polymer matrix and analysis of data using existing models for glassy polymers. The efficiency profile obtained using mass ratios of 2:1, 4:1, and 8:1 of PMMA to KMnO4 showed a decrease in the extent of release with increasing mass ratio with 79%, 55.35% and 33.59% respectively. Patches were noticed on the surfaces of PMMA after the release of KMnO4, these were attributed to crevices created by the non-fickian diffusion of the oxidant.

Wet carbon-based solid acid/potassium permanganate as an efficient heterogeneous reagents for oxidation of alcohols under mild conditions

Wet carbon-based solid acid and potassium permanganate were used as new reagents for oxidation of alcohols to their corresponding aldehydes and ketones in heterogeneous mixtures. The experiments were done moderately at mild condition and high yields in suitable times were obtained.

Enhanced treatment of water with low turbidity:Combined effects of permanganate, PAM and recycled sludge

The effectiveness of enhancing treatment of water with low turbidity through combined effects of permanganate oxidation, PAM aiding coagulation and sludge recycling was investigated through continuous bench scale studies. In comparing with ferric chloride coagulation, only recycling sedimentation sludge was ineffective in enhancing treatment of water with low turbidity. PAM with recycled sludge showed positive effects, and the additional permanganate dosing exhibited the best potential of favoring coagulation, which leaded to much lower effluent turbidity and CODMa. Additionally, it was observed that the optimal permanganate dosage was 0. 4 mg/ L and the higher permanganate dosage exhibited inhibiting effects for pollutants removal. SEM analysis indicated that the floes were loosely formed and the particle diameter was critically low for ferric chloride coagulation process. Comparatively, the addition of PAM and permanganate with recycled sludge facilitated the aggregation of tinny particles onto compact PAM polymer chains, therefore contributing to the formation of compact floes with high particle diameter. The combined employment of recycled sludge, PAM and permanganate showed the best potential of favoring coagulation, mainly through synergistic effects between seeding, polymer bridging and increasing effective collision in mechanism. Additionally, the variation of Fe and Mn concentration after recycling and sedimentating units was studied for the processes, and the main species was also investigated for elements Fe and Mn. Sludge recycling and permanganate addition did not increase Fe and Mn concentration in the sedimented water.

Complete stabilization of severely As-contaminated soil by a simple H2O2 pre-oxidation method combined with non-toxic TMT-15 and FeCl3·6H2O

The stabilization of severely As-polluted soil has been a challenge, especially for the extremely toxic As(Ⅲ) contaminants. In this study, soil with a high As concentration(26084 mg/kg) was availably stabilized by a H2O2 pre-oxidation assisted TMT-15(Na3S3C3N3 solution with a mass fraction of 15%) and FeCl3·6 H2O stabilization method. The results showed that the combination of the two stabilizers(i.e., TMT-15 and FeCl3·6 H2O) presented a better stabilization behavior than either stabilizer used individually. The use of the H2O2 pre-oxidation assisted TMT-15 and FeCl3·6 H2O stabilization approach not only converted the As(Ⅲ) to As(Ⅴ) but also reduced the toxic leaching concentration of As to 1.61 mg/L, which is a safe level, when the additions of TMT-15 and FeCl3·6 H2O were 2 mL and 0.20 g, respectively. Thus, using only a simple H2O2 pre-oxidation to combine clean stabilization with non-toxic stabilizers TMT-15 and FeCl3·6 H2O could render the severely As-contaminated soil safe for disposal in a landfill.

Reduction and subsequent carburization of pre-oxidation magnetite pellets

Magnetite is a kind of iron ore that is difficult to carburize.In order to improve the carburizing performance of magnetite pellet,pre-oxidation treatment was carried out,and the oxidation,reduction and carburization behaviors of magnetite pellet were investigated in this study.The magnetite pellet was oxidized in the air and carburized in CO-CO_(2)-H_(2) gas mixtures,the oxidation,reduction and carburization behaviors were demonstrated by detecting phase change,microstructure,carburizing index via thermogravimetry,X-ray diffraction(XRD),infrared carbon-sulfur analyzer,and scanning electron microscope(SEM).The results show that the dense magnetite particles inside pellet are oxidized to porous hematite particles,and the Fe_(3)O_(4) transforms to Fe_(2)O_(3) with high lattice defect concentration during the pre-oxidation process.Then the porous hematite particles and newly formed Fe_(2)O_(3) significantly promote the reduction efficiency.Porous metallic iron particles are produced in the reduction process.Finally,both high reduction efficiency and the porous structure of metallic iron particles dramatically enhance the carburization efficiency of pellet.High preoxidation temperature favors to the carburization of magnetite pellet.However,the carburized index decreases due to the recrystallization of iron oxide when the temperature extends to 1000℃.The optimum pre-oxidation temperature for magnetite pellet carburization is 900℃.

Preliminary Analyses of Controlled Release of Potassium Permanganate Encapsulated in Polycaprolactone

Potassium permanganate (KMnO4) has been used widely as an oxidant for remediation of contaminated soil and water systems. The present study evaluates the release of this oxidant from Polycaprolactone (PCL) polymer as part of a patented controlled release process (CRP) to be applied for targeted removal of contaminants from water. KMnO4 was encapsulated into PCL at a 1:5 oxidant to polymer ratio and placed in batch reactor systems with reagent water to be evaluated over a 96 hour period. SEM images showed that over time, the number of cavities and their sizes increased on the waxy surface of the PCL polymer. The experimental data from the release of KMnO4 from PCL was found to fit non-Fickian diffusion model after dissolution (R2 = 0.93) similar to other systems that describe the dispersal of other oxidants from wax matrices. In addition, the model parameters for data of this present study were also found to be comparable to previous release studies with the same oxidant encapsulated in different wax matrices at similar ratios. Overall, the similarity of release data between the diversity of polymers shows that the controlled release biodegradable polymer utilizing PCL provides effective release of the KMnO4 with the added benefit biodegradable nature of PCL.

Effect of chloride ion on bacterial pre-oxidation of arsenic-containing gold concentrate

The bacterial pre-oxidation process of arsenic-containing gold concentrates and the bacterial activity under different chloride ion concentrations were studied by using a mixture of thermophilic strains TCJ domesticated in production.The experimental result shows that with different samples and leaching systems,the adaptability and Cl- tolerance of bacteria are different,and that appropriate chloride ion concentration is conductive to bacterial oxidation,while higher chloride ion concentration will inhibit the bacterial activity and affect the pre-oxidation performance.Under the present production conditions,TCJ can adapt to the changes of water quality in the source of water and its critical chloride ion tolerance value is 2.7 g/L.

Study on contrast test of PPC pre-oxidation and coagulation for algae removal and deodorization

The effect of treating algae-bearing water and induced odor by use of permanganate potassium composite （PPC） pre-oxidation was investigated, and was compared with the effect of treatments by pre-chlorination, permanganate petassium pre-oxidation and simple coagulation. The results showed that simple coagulation and pre-chlorination were less effective in removing algae and its odor, whereas PPC pre-oxidation was the most effective in algae removal and deodorization. Upon oxidation with PPC, the cells of Oscillatoria agardhic were inactivated and some intra-cellular and extra-cellular components were released into the water, which may help the coagulation by their bridging effect. The efficient removal of algae by PPC pre-oxidation is believed to be the joint contribution of several mechanisms.

Effect of pre-oxidation on strength and thermal shock behavior of ZrB_2-SiC-graphite ceramic composites

A novelty technique,namely,pre-oxidation,has been proposed to improve the strength and thermal shock behavior of ZrB2-SiC-graphite ceramic composites,which is a promising candidate for ultra-high temperature ceramics (UHTCs) in aerospace engineering. The composite is pre-oxidized at temperatures of 900 ℃ and 1100 ℃ for 1 h and 3 h in air. A theoretical model considering surface heat transfer has been given and analyzed. A water-quenching technique is adopted at different temperatures from 300 ℃ to 600 ℃ in order to investigate the thermal shock behavior of pre-oxidized composites. The critical thermal shock temperature improves more than 40% after pre-oxidizing at 1100 ℃ for 3 h. However,the composites strength is not improved as a result of the insensitivity to surface defects.