Reduction Of Pyrolusite Research Articles

CFD simulation for reduction of pyrolusite in fluidized beds

In this study, a CFD model coupled with heterogeneous flow structure, mass transfer equations, and chemical reaction kinetics is established to forecast the pyrolusite reduction reaction behavior. Compared with the previous studies which ignore the volume change of solids phase, the influence of volume shrinkage on reaction and flow behavior is explored in this research. Volume shrinkage of pyrolusite is proved to be non-negligible in predicting the conversion rate. The negligence of volume shrinkage leads to the overestimation of conversion rate for its inaccurate estimation of surface area for reaction. Besides, the influence of volume shrinkage on the reaction is found smaller in the scaled-up reactor.

Study on Microwave-assisted Reduction of Pyrolusite

Abstract: Manganese is a vital metal resource, and increased consumption of manganese is leading to the shortage of high-grade manganese ore resources. However, a large number of low-grade manganese ore resources ((Mn<30%) accounts for about 60% of the total manganese resources) have not been effectively utilized because of the lack of efficient industrial utilization methods. Researching new technologies for reducing low-grade pyrolusite is an urgent problem to be solved. Microwave is an effective and environmentally friendly heat source widely used in mining, metallurgy, and chemistry. Different substances have different dielectric constants. The difference in dielectric constant affects the absorption rate of substances, resulting in different heating rates for different substances when heated by microwaves. Microwave is widely used in the metal smelting process because of its unique heating method. So far, few works have been done to verify that microwave heating can effectively promote the reduction of pyrolusite. This article summarizes some current methods of reducing low-grade pyrolusite and compares them with the method of reducing pyrolusite by microwave heating. In addition, this article introduces the principle of microwave- enhanced reduction of pyrolusite and discusses the opportunities and challenges faced by microwave heating technology in its subsequent development. The aim is to analyze and study the promoting effect of microwave heating technology on the reduction of pyrolusite, further improve the utilization of low-grade pyrolusite, and provide new methods and approaches for the comprehensive utilization of mineral resources and provide assistance in industrial production.

Dielectric characterisation and reduction properties of the blending mixtures of low-grade pyrolusite and waste corn stalks in the microwave field

Recently, pyrometallurgical reduction of low-grade pyrolusite is one of the potential techniques for expanding the resources for manganese. However, the process has a high cost on fossil energy and produces a large amount of greenhouse gases. This work proposed a novel method of using biomass, namely corn stalks, to reduce and roast low-grade pyrolusite under microwave field to provide positive alternatives for fossil energy. The microwave-assisted reduction was studied systematically, and the corresponding mechanism was also studied by thermodynamic analysis and dielectric properties analysis. Results indicated that co-pyrolysis reduction characteristics of the mixtures were mainly divided into three stages: the pre-reaction stage (25 °C–196 °C), activated pyrolysis reduction stage (196 °C–480 °C), and carbonisation stage (>430 °C). The mechanism of MnO2 reduction is attributed to reductive volatiles (H2, CO, CH4) and the fixed carbon (C) produced by biomass pyrolysis. Meanwhile, the reduction efficiency of Mn can achieve 97.2% at 650 °C for 60 min with 25% corn stalks, indicating efficient pyrolusite reduction by microwave heating. These results enrich the fundamental knowledge on the corresponding industrial technology development.

Research Status of Microwave-assisted Reduction Technology of Pyrolusite

Manganese ore is an important metallurgical raw material that holds an important strategic position in the national economy of China. However, the grade of manganese ore in the country is mostly low, and the utilization efficiency of low-grade manganese ore resources is low, which seriously restricts the healthy and stable development of China’s metallurgical industry. As a new green heating method, microwave is expected to address the problems of conventional methods and realize the effective utilization of low-grade manganese ore. In this paper, the research status of the microwave composite reduction of pyrolusite in recent years is reviewed. Microwave plays an important role in metallurgy, and it is the current direction pursued to improve the research level of microwave heating and extend it to actual industrial processes.

Study on thermochemical characteristics properties and pyrolysis kinetics of the mixtures of waste corn stalk and pyrolusite

As an alternative energy source for fossil energy, use of biomass pyrolysis to reduce pyrolusite is of great significance for energy conservation, emission reduction and environmental protection. Kinetics and thermodynamics of reducing pyrolusite using biomass pyrolysis was studied using thermogravimetric analysis analysis. Five non-isothermal methods, Flynn-Wall-Ozawa, Kissinger-Akahira-Sunose, Distributed Activation Energy Model, Starink and Friedman, were employed to calculate the pyrolysis kinetics and thermodynamic parameters. The results showed that pyrolusite reduction by biomass pyrolysis can be divided into four stages: drying stage (30–175 °C), rapid pyrolysis reduction stage (175–350 °C), slow pyrolysis reduction stage (350–680 °C) and char formation stage (680–900 °C). The apparent activation energy, reaction enthalpy, Gibbs free energy and entropy change of pyrolusite reduction by biomass pyrolysis was calculated ranges from 170 to 180 kJ/mol, 164 to 174 kJ/mol, 136.97 to 137.25 kJ/mol and 45.67 to 61.91 J/mol·K, respectively. This work provides theoretical basis and practical guidance for the reduction of pyrolusite by waste corn stalk.

Kinetics characteristics and microwave reduction behavior of walnut shell-pyrolusite blends

Combining biomass pyrolysis with microwave heating technologies provides a novel and efficient approach for low-grade pyrolusite reduction. The microwave reduction behavior and pyrolysis kinetic characteristics of walnut shell-pyrolusite blends were explored. Results indicated the optimal reduction parameters were: reduction temperature of 650 °C, holding time of 30 min, Mbio/More of 1.8:10, and microwave power of 1200 W. The co-pyrolysis characteristics of the blends included four stages: dehydration, pre-pyrolysis, intense pyrolysis and reduction, and slow pyrolysis and reduction. Fitting analysis based on Coats-Redfern method revealed that chemical reaction was the control step of the process of reducing pyrolusite by biomass, which the finding matched to the isothermal kinetic analysis results determined through unreacted shrinking nuclear model. The activation energies and pre-exponential factors were determined at 5.62 kJ·mol−1–16.69 kJ·mol−1 and 0.0426 min−1–0.515 min−1. The work provides sound references for promoting the industrial application of the combined method on minerals reduction.

Pilot-scale study on enhanced carbothermal reduction of low-grade pyrolusite using microwave heating

Microwave heating through materials' dielectric loss endows energy saving and consumption reduction and production clean characteristics. Pilot-scale study was initiated to evaluate the enhanced effect of microwave heating on carbothermal reduction process of pyrolusite. Results indicated that carbothermal reduction process for low-grade pyrolusite was divided into three stages identified by temperatures: <145 °C, 145 °C–400 °C, >400 °C. Meanwhile, ƞMn value of 95.38% can achieve at 650 °C for 60 min with 15% coal addition, with low Fe2+ content, indicating efficient pyrolusite reduction by microwave heating. Moreover, MnO2 peaks disappeared and MnO peaks were detected and product surface became loose and porous with numerous cracks and holes, meanwhile grain shape became more regular with a smaller particle size after further microwave treatment. The study highlights that the non-conventional technology by microwave heating to reduce low-grade pyrolusite is very promising and could be considered for full scale applications.

High-temperature dielectric properties and pyrolysis reduction characteristics of different biomass-pyrolusite mixtures in microwave field

Exploring the dielectric properties of mineral-biomass mixtures is fundamental to the coupled application with biomass pyrolysis and microwave technology to mineral reduction. In this work, the microwave dielectric properties of five pyrolusite-biomass mixtures were measured by resonant cavity perturbation technique and the pyrolysis reduction characteristics were systematically investigated, including poplar, pine, ageratina adenophora, rapeseed shell and walnut shell. Results indicated that the dielectric properties commonalities of five mixtures with temperature represented by increasing firstly, dropping intensely and finally rising slightly, with excellent responsiveness to microwaves; which the change trend was mainly attributed to the crystal transformation of amorphous MnO2 and pyrolusite reduction reactions by biomass pyrolysis. Meanwhile, the heating characteristics successfully matched the dielectric properties of the mixtures, and the pyrolusite reduction process by biomass can be divided into two stages: biomass pyrolysis and pyrolusite reduction. The work highlights the universal feasibility of the novel coupled method for mineral reduction.

Effect of advanced milling on carbothermal reduction of pyrolusite (MnO2) by carbonized tea plant waste

This study examined the effect of advanced milling on carbothermal reduction of oxidized manganese ore using carbonized tea plant waste as reductant.For the carbothermal reduction of manganese oxide, the ratios of Mn/Fe, C/(MnO2+Fe3O4) and ball/mixture were 8/1, 2/1 and 10/1, respectively. Samples were subjected to advanced milling in an attritor mill for 10, 15, 20, 30, 60, 90 and 120 h. The rotation speed of the mill shaft was 350 rpm during the processes performed in the attritor. DTA-TG, SEM and XRD analyses were carried out to characterize the samples. When XRD peaks were compared for different grinding times, it was seen that all of the diffraction peaks gradually decreased in parallel with the increase in grinding time. The DTA-TG analysis of the samples subjected to mechanical activation for 120 h shows a symmetrical change, which is similar to the Gaussian function. The activated samples obtained from advanced milling were treated at 1000, 1100, 1200 and 1300 °C for 30, 60, 90 and 120 min in an argon atmosphere. The results of the experimental studies indicate that a 58.76% reduction occurred in the 120 h advanced milled samples subjected to treatment at 1300 °C for 2 h.

Microwave pyrolysis of walnut shell for reduction process of low-grade pyrolusite

Replacing fossil energy by utilizing biomass as carbon source to convert metal oxides has meaning for reduction of minerals. Microwave pyrolysis of walnut shell for reduction process of low-grade pyrolusite was proposed. Thermogravimetric analysis indicated biomass pyrolysis process for reduction of pyrolusite was divided into four phases identified by temperatures: dehydration stage (<150 °C), pre-pyrolysis stage (150 °C–290 °C), curing decomposition stage (290 °C–480 °C) and carbonization stage (>480 °C), and manganese recovery reached 92.01% at 650 °C for 30 min with 18% walnut shell. The strongest preferential orientation of MnO was appeared, with good crystalline structure and no MnO2 and FeO peaks detected. The product surface became loose and porous with numerous cracks, pits and holes, and molten granules were interconnected and stacked with regular shape. The methods propose new idea of selective reduction of pyrolusite based on biomass pyrolysis by microwave heating.

TG–FTIR analysis of pyrolusite reduction by major biomass components

Pyrolusite reduction processes by three major biomass components cellulose, hemicelluloses and lignin, represented by CP, HP and LP, respectively, were investigated by thermogravimetric analyzer coupled with Fourier transform infrared spectrometry (TG–FTIR). The Šesták–Berggren (SB) equation was used to evaluate the kinetics of reduction processes. TG analysis reveals that the main reduction processes occur at 250–410°C, 220–390°C, and 190–410°C for CP, HP, and LP, respectively. FT-IR and XRD results indicate that various reducing volatiles (e.g. aldehydes, furans, ketones and alcohols) are produced from the pyrolysis with the three major components, which directly reduce MnO2 in ore to MnO. The processes are described by the SB equation with three parameters (m, n, p). Their non-zero values suggest that pyrolusite reduction is controlled by the diffusion of reducing gaseous products through an ash/inert layer associated with minerals. The apparent activation energies for pyrolusite reduction by CP, HP and LP are 40.48, 25.70 and 40.10kJ·mol−1, respectively.

Halocarbons in the environment: estimates of thermodynamic properties for aqueous chloroethylene species and their stabilities in natural settings

Standard partial molal thermodynamic parameters for the aqueous chlorinated-ethylene species, perchloroethylene (PCE), trichloroethylene (TCE), 1,1-dichloroethylene (1,1-DCE), cis-1,2-dichloroethylene (cis-1,2-DCE), trans-1,2-dichloroethylene (trans-1,2,-DCE), and vinyl chloride (VC) have been estimated by using experimental gas-solubility data and correlation algorithms. The provided thermodynamic values may be used to calculate properties of reactions involving the aqueous chloroethylene species at a wide range of temperatures and pressures. Estimated values for the chloroethylenes were used, along with published values for minerals, gases, aqueous ions, and aqueous neutral organic species, to calculate the stability of chloroethylene species in equilibrium with the minerals magnetite, hematite, pyrite, and pyrrhotite in the subsurface. Estimated values for the aqueous chloroethylenes were also used to calculate reduction potentials for microbially-mediated reductive dechlorination half-reactions at elevated temperatures. Calculations indicate that all aqueous chloroethylene species are energetically favored to decompose to ethylene(aq) under a wide range of conditions in the subsurface, by both abiotic and biotic pathways. Anaerobic microbially mediated degradation is especially favored under conditions at least sufficiently reducing to promote sulfate-reduction, but not under conditions sufficient for microbial denitrification, pyrolusite reduction, or ferric-iron reduction.

5543128 Regeneration method for process waste containing sulfur and phosphorus : Tuovinen Heikki; Saari Jorma; Roine Antti; Holma Hannu; Kalliokoski Matti Ulvila, Finland assigned to Oy Neste

Standard partial molal thermodynamic parameters for the aqueous chlorinated-ethylene species, perchloroethylene (PCE), trichloroethylene (TCE), 1,1-dichloroethylene (1,1-DCE), cis-1,2-dichloroethylene (cis-1,2-DCE), trans-1,2-dichloroethylene (trans-1,2,-DCE), and vinyl chloride (VC) have been estimated by using experimental gas-solubility data and correlation algorithms. The provided thermodynamic values may be used to calculate properties of reactions involving the aqueous chloroethylene species at a wide range of temperatures and pressures. Estimated values for the chloroethylenes were used, along with published values for minerals, gases, aqueous ions, and aqueous neutral organic species, to calculate the stability of chloroethylene species in equilibrium with the minerals magnetite, hematite, pyrite, and pyrrhotite in the subsurface. Estimated values for the aqueous chloroethylenes were also used to calculate reduction potentials for microbially-mediated reductive dechlorination half-reactions at elevated temperatures. Calculations indicate that all aqueous chloroethylene species are energetically favored to decompose to ethylene(aq) under a wide range of conditions in the subsurface, by both abiotic and biotic pathways. Anaerobic microbially mediated degradation is especially favored under conditions at least sufficiently reducing to promote sulfate-reduction, but not under conditions sufficient for microbial denitrification, pyrolusite reduction, or ferric-iron reduction.

The reduction of pyrolusite in a hydrogen atmosphere

The isothermal reduction of pyrolusite, β-MnO 2, in a hydrogen atmosphere has been studied. Under these conditions the reduction product is Mn 3O 4. The kinetics of the reaction were determined and the activation energy for the process was calculated to be 140.0 kJ mole −1.

Bacteriology of Manganese Nodules

MnO 2 reduction by aerobic growing cultures of Bacillus 29 and coccus 32, isolated from ferromanganese nodules, was assessed for 7 days. A 1-day lag was observed before the onset of MnO 2 reduction by either culture. Addition of HgCl 2 to a final concentration of about 10 -3 M caused a rapid cessation of MnO 2 reduction by the growing cultures. Neither culture reduced MnO 2 when grown under continued anaerobiosis from the start of an experiment. However, if conditions were made anaerobic after MnO 2 reduction was initiated, reduction continued at a rate only slightly lower than that under aerobic conditions. Resting-cell cultures reduced MnO 2 equally well aerobically and anaerobically, provided that ferricyanide was present to serve as electron carrier. These findings showed that oxygen is needed for culture adaptation to MnO 2 reduction, and that oxygen does not interfere with microbial MnO 2 reduction itself. Both cultures caused sharp drops in the p H of the medium during MnO 2 reduction: with coccus 32, during the entire incubation time; with Bacillus 29, for the first 3 days. The E h of the medium fluctuated with either culture and never fell below 469 mv with Bacillus 29 and below 394 mv with coccus 32. The rates of glucose consumption and Mn 2+ release by Bacillus 29 and coccus 32 were fairly constant, but the rates of lactate and pyruvate production were not. Although acid production undoubtedly helped in the reduction of pyrolusite (MnO 2 ) by the bacteria, it did not appear to be important in the reduction of manganese oxide in ferromanganese nodules, as shown by the results with a nodule enrichment.