Drying kinetics and energy efficiency of soot ash of smelting silicon manganese alloys under microwave heating.

When smelting silicon manganese alloy in an industrial electric furnace, it will produce smoke and dust waste gas, which can be utilized again back to the furnace and improve the utilization rate of raw materials after a particular trapping device and collection treatment. However, at higher moisture levels, they are prone to explode. Effects of various initial masses, initial moisture contents, and microwave output powers on the soot ash of smelting silicon manganese alloy were studies. The findings indicate that the microwave drying rate increases with all three variables. The time for complete microwave drying is directly proportional to the sample's initial moisture content and the sample's initial mass, and the time for complete microwave drying is inversely proportional to the microwave output power. The results demonstrate that the Modified Page model can accurately describe the microwave drying process. The experimental data were fitted experimentally by drying kinetic models. Microscopic characterization of soot ash from refining silico­manganese alloys before and after drying was carried out using FTIR and SEM. Through FTIR characterization, the peak value of the -OH absorption peak decreases upon drying, and SEM results in no agglomeration caused by microwave drying and better dispersion of the soot ash of the dried smelted silica­manganese alloys, all of which proved that microwaves could effectively remove water. It was discovered that the diffusion coefficient increased gradually with increasing power when it was computed using Fick's second law. The diffusion coefficient increases and then decreases as the moisture content increases. The diffusion coefficient decreases as the initial mass increases. Activation energy of microwave drying of soot ash from the refining of silicomanganese alloys was calculated to be -1.4467 W/g. Its purpose is to offer a detailed guide for the industrial drying of soot ash from silicomanganese alloy refinement using microwave drying technology.

Recent developments on the removal of zinc from electric arc furnace dust by using microwave heating.

Electric arc furnace dust (EAFD) is a hazardous by-product of steel production. As global steel output increases, substantial amounts of EAFD are produced, which causes significant environmental issues. EAFD contains quantities of Fe and Zn, which could be reused as raw materials in the steelmaking process. However, zinc oxides can be reduced and vaporized during this process, forming zinc vapor that contaminates equipment surfaces and causes damage. Consequently, various pyrometallurgical methods have been proposed for zinc removal from EAFD. Due to the extensive usage of carbonaceous materials, these methods contribute to significant CO2, raising concerns about greenhouse gas emissions. Microwave heating offers an efficient, energy-saving, and environmentally friendly alternative to pyrometallurgical approaches. EAFD can generate heat under microwave irradiation without carbon addition, which means the CO2 emissions can be reduced by replacing the reductant in the microwave heating process. Furthermore, microwaves enhance zinc removal reactions to a certain extent, resulting in higher efficiency. Thus, employing microwave heating for EAFD processing has significant potential for future development. This paper reviews recent research on using microwave heating for zinc removal from EAFD, focusing on the heating behavior of EAFD in microwaves and the mechanisms of zinc removal. This review will be crucial for researchers working on processing EAFD using microwave heating and could help guide the development of more sustainable and efficient methods.

Drying Kinetics of Microwave-Assisted Drying of Leaching Residues from Hydrometallurgy of Zinc.

In the hydrometallurgical process of zinc production, the residue from the leaching stage is an important intermediate product and is treated in a Waelz kiln to recover valuable metals. To ensure optimal results during the Waelz kiln process, it is necessary to pre-treat the residues by drying them first due to their higher water content. This work studies the residue's drying process using microwave technology. The study results indicate that microwave technology better removes the residue's oxygen functional groups and moisture. The dehydration process's effective diffusion coefficient increases as the microwave's heating power, the initial moisture content, and the initial mass increase. The Page model is appropriate for imitating the drying process, and the activation energy of the drying process for the residues is -13.11217 g/W. These results indicate that microwave technology efficiently dries the residues from the leaching stage. Furthermore, this study provides a theoretical basis and experimental data for the industrial application of microwave drying.

Microwave drying method investigation for the process and kinetics of drying characteristics of zinc-leaching residue.

Due to the high moisture content in the zinc-leaching residue, it is easy to cause safety problems when directly entering the kiln. Microwave drying can minimize particle agglomeration and promote cracks on the mineral surface, which benefits the subsequent recovery and smelting of zinc-leaching residue. The results showed that increasing microwave power and particle size range could improve the maximum drying rate and reduce the drying time. The maximum drying rate of 20 g zinc-leaching slag with a microwave power of 700 W, a particle size of 1-10 mm, and a moisture content of 20% can be higher than 0.365%/s and reach complete drying within 120 s. The drying results were fitted and statistically analyzed using nine common kinetic models of drying, the surface diffusion coefficient changes were further analyzed at four levels, and the reaction activation energy (Ea) was calculated. According to Fick's second law, when the average particle size increased from 0.044 to 5.5 mm, the surface diffusion coefficient increased from 6.2559 × 10-9 to 3.8604 × 10-6 m2/s, which showed that the effect of particle size change on microwave drying process was significant. The Ea of the drying reaction was 18.1169 kJ/mol. This method provides an idea for efficiently treating secondary resources containing valuable metals.

Microwave-enhanced reduction of manganese from a low-grade pyrolusite ore using pyrite: process optimization and kinetic studies.

The inefficient leaching of manganese is the main factor hindering the commercialization of the reduction process during manganese recovery using pyrite as the reducing agent. Hence, a new method for improving recovery efficiency and reducing the cost is required. This study uses microwave heating as a strengthening method to extract Mn2+ from pyrolusite and the leaching conditions are optimized. It was found that the extraction rate of Mn2+ could reach 95.07% under microwave heating through the conditions of H2SO4 is 1.2 mol/L, m(pyrolusite)/m(pyrite) equals to 10:2, leaching temperature is 90 ℃, and a liquid-solid (L/S) ratio of 10:1. The achieved extraction rate was higher than that of 75.08% under the conventional heating achieved at the same conditions. Besides, experimental studies have found that microwave heating can change the process and direction of chemical reactions, shorten the reaction time, and reduce sulfuric acid. Finally, the kinetic study indicates that the leaching process under microwave heating is controlled by surface chemical reactions. The equation of leaching kinetics is 1 - (1 - x)1/3 = 3425.32/r0·[H2SO4]1.316·[FeS2/MnO2]0.907·exp(- 45.03/(RT)·t. The activation energy is 45.03 kJ/mol. Meanwhile, through a scanning electron microscope and particle size analyzer, microwave heating has a significant influence on reducing the ore diameter and increasing the specific surface area of the sample. This study aims to provide an experimental trial case for studying the mechanism of microwave-enhanced leaching process during manganese recovery using pyrite as the reducing agent. The reported kinetics research may guide the development of the industrial application for Mn recovery.

Investigations on the Thermodynamics Characteristics, Thermal and Dielectric Properties of Calcium-Activated Zinc-Containing Metallurgical Residues.

An activate pretreatment of zinc-containing metallurgical residues were proposed by adding CaO and introducing microwave heating approach into the CaO activation pretreatment process to realize the conversion of refractory ore phases into pre-treated ore phase. Thermodynamic characteristics analysis indicated that adding CaO can realize the conversion of refractory ore phases, with the same effect as the carbon additives. Thermal conductivity properties analysis denoted that the thermal conductivity properties of ZnS and ZnFe2O4 were relatively poor. Meanwhile, the thermal conductivity properties of the residues sample added with 25% CaO were significantly superior to the residues added with other CaO contents, with the maximum specific heat value of 1.348 J/g·K at 350 °C. Dielectric properties analysis highlighted that adding CaO with the dielectric constant properties significantly higher than that of other substances can enhance the microwave absorption capacity of zinc-containing residues. The decrease in dielectric loss and loss tangent value with the increase of temperature and the residues having large microwave penetration depth guaranteed to obtain better uniformity of microwave heating. Furthermore, adding 25% CaO promoted the microwave penetration depth of the residues sample increased in the range of 300-500 °C. This work can lay a theoretical research foundation for solving the key difficulty for efficient Zn recovery from complex zinc-containing metallurgical residues.

Study of an Organic Binder of Cold-Bonded Briquettes with Two Different Iron Bearing Materials.

The aim of this study was to investigate the properties of an organic binder used in cold-bonded briquettes (CBBs) prepared from two different iron bearing materials. The applied binder is a type of starch as indicated by chemical analysis, iodine-starch staining and Fourier transform infrared analyses. Thermogravimetric differential scanning calorimetry showed that the binder pyrolysis undergoes four stages: moisture desorption, ash volatilization, pyrolysis of organic matter and decomposition of materials with high activation energy. The difference between the dry and heat-treated samples during the macroscopic failure process is the instability propagation of the crack. The CBB shows a low decrepitation index at 700 °C. The returned fines of CBBs used with the organic binder were applied in two blast furnaces. The industrial trials showed that the CBBs do not influence the performance of the blast furnace and can reduce the fuel consumption rate. The curing rate of the binder decreases, and the growth rate of compressive strength decreases during the curing process. Iron ore particles are bonded together and exist in the form of aggregation after mixing with water and binder. The edges and corners of the particles become blurred, and the original surfaces of the particles are covered with binder film, the surface of which is covered with fine particles. The multi-branched structure of amylopectin provides omnibearing adhesion sites, thus forming binder agglomeration and film leading to a strong adhesion between binder and iron ore particles. Binder film and binder agglomeration work together to make the CBB perform well.

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.

Investigations on the microwave absorption properties and thermal behavior of vanadium slag: Improvement in microwave oxidation roasting for recycling vanadium and chromium.

Vanadium slag contains high contents of vanadium and chromium with complex and dense structures, hence microwave heating instead of conventional methods is expected to destroy the dense structure and further to improve the extraction rate of vanadium and chromium, and exploring its dielectric properties is the prerequisite work. Microwave absorption properties and thermal behavior of vanadium slag were investigated. Results indicated that vanadium slag endowed excellent microwave absorption properties, with minimum εr' value of 34.447 (F/M). Dielectric properties of vanadium slag varied with temperature, which changing trend was matched to the three stages of microwave heating characteristics identified by heating rates. Meanwhile, the changing process of dielectric properties also corresponded to the three processes of thermogravimetric characteristics: dehydration stage (30 °C-280 °C), oxidation decomposition of olivine phase and normal spinel phase (280 °C-650 °C), and oxidation decomposition of vanadium chromium spinel (650 °C-950 °C). Moreover, the maximum dielectric constant and highest microwave heating rate of vanadium slag both appeared at the temperature regime of 500 °C-550 °C, which was also the main temperature regime for oxidation decomposition of olivine phase and normal spinel phase in vanadium slag, demonstrating the appropriate process temperature for microwave heating technology to recycle vanadium slag.

Simultaneous removal of Cr(III) and V(V) and enhanced synthesis of high-grade rutile TiO2 based on sodium carbonate decomposition.

Rutile TiO2 is widely applied as the raw material to produce titanium dioxide and titanium sponge, whereas the Cr (III) and V (V) impurities in rutile TiO2 significantly affect the performance of related products. In the present work, the sodium carbonate decomposition treatment on Panzhihua titanium slag was attempted, to improve the preparation process of rutile TiO2 with high crystallinity and simultaneously reduce the chromium (Cr) and vanadium (V) content as hazardous elements. Effects of sodium carbonate decomposition treatment on the crystal composition, microstructure of rutile TiO2 were determined using XRD, SEM and Raman characterization. The recovery of Cr(III) and V(V) was achieved through leaching the roasted titanium slag by dilute sulfuric acid, with the chromium and vanadium content in the residue decreasing up to 0.03 % and 0.04 %, respectively, followed by the final product rutile TiO2 was produced by the leaching residue calcined at 1323.15 K with a duration time of 120 min, with 85.56 % of TiO2 grade. The work highlights the feasibility of synchronously preparing rutile TiO2 and removing hazardous Cr (III) and V (V) impurities from titanium slag using sodium carbonate decomposition.

Microwave catalyzed carbothermic reduction of zinc oxide and zinc ferrite: effect of microwave energy on the reaction activation energy.

Recently, more attention has been paid to the use of microwave (MW) energy in accelerating chemical reactions. The effect of microwave energy on the reduction of zinc oxide and zinc ferrite was investigated. The results indicated that the temperatures required to initiate zinc oxide and zinc ferrite reduction under MW heating were 550 and 450 °C, respectively, while under conventional thermal (CT) heating, were 950 and 850 °C, respectively. Apparently, the MW reaction had a negative standard Gibbs free energy (ΔG) at a lower temperature (∼400 °C) when compared to the CT reaction. Additionally, the activation energy (E a) substantially decreased from 223.7 and 221.1 kJ mol-1 under CT heating to 64.8 and 32.9 kJ mol-1 under MW heating for Zn oxide and zinc ferrite, respectively. The enhancement in zinc reduction under MW energy was due to the rapid and bulk heating phenomena of MWs as well as the interactions occurring between the electromagnetic MW pattern and the molecules of heated materials.

Dielectric properties and thermal behavior of electrolytic manganese anode mud in microwave field.

Exploring the dielectric properties of a material can provide guidance for applications of microwave technology to the material. In this work, dielectric properties and thermal behavior of manganese anode mud and pure MnO2, CaSO4 and PbSO4 components were systematically investigated. Results indicated that manganese anode mud showed excellent responsiveness to microwaves, with εr' value of 17.971 (F/M) at room temperature and a maximum value of 20.816 (F/M) at 150 °C, rendering it took only 5.5 min for manganese anode mud to be heated from room temperature to 1000 °C. The dielectric properties of manganese anode mud were related to its thermal behavior, mainly affected by MnO2 component. Moreover, the heating process of manganese anode mud was divided into four stages identified by temperatures: less than 200 °C, 200 °C-700 °C, 700 °C-900 °C, greater than 900 °C, corresponding to the five stages of thermal behavior: the removal of absorption water and combined water, the decomposition reaction of Pb2Mn8O16, and the deoxidation reactions of PbO2, MnO2 and Mn3O4. The work highlights the feasibility of processing manganese anode mud by microwave heating.

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.

Microwave absorption properties of steelmaking dusts: effects of temperature on the dielectric constant (ε') and loss factor (ε'') at 1064 MHz and 2423 MHz.

The microwave absorption properties of a material depend largely on the dielectric properties of the material being heated. Therefore, the influences of temperature on the dielectric constant (ε'), loss factor (ε''), loss tangent (tan δ d) and penetration depth (D P) of steelmaking dust at frequencies of 1064 MHz and 2423 MHz were measured. Three steelmaking dust samples were studied. The effects of temperature on the dielectric properties of the samples were insignificant at temperatures below 600 °C. However, above this temperature, a rapid rise in the values of the dielectric properties of the samples was observed. Comparing the thermogravimetric analysis and differential scanning calorimetry (TGA-DSC) results and mass spectra (MS) of the dusts with their dielectric properties revealed that the changes in the dielectric values of the dusts were associated with the thermal decomposition of calcium carbonate and the release of CO/CO2 gases. Furthermore, the increase in the electrical conductivity of the samples at high temperature resulted in increased dielectric values. The behavior of the loss tangent of the samples with increasing temperature coincided with the behavior of the loss factor. The penetration depth decreased with an increase in temperature at both frequencies, while an increase in the dielectric properties caused a significant decrease in the penetration depth. The results indicated that steelmaking dusts have good microwave absorbing properties owing to their carbon and iron oxide contents.

Dielectric properties and carbothermic reduction of zinc oxide and zinc ferrite by microwave heating.

This paper aims to study the dielectric properties and carbothermic reduction of zinc oxide (zincite, ZnO) and zinc ferrite (franklinite, ZnFe2O4) by microwave heating. To achieve this aim, the dielectric properties were measured with an open-ended coaxial method to understand the behaviour of the samples under microwave irradiation. The effects of microwave power, duration time and sample mass on the heating rate, and the effects of the stoichiometric amount of graphite on the reduction of ZnO and decomposition of ZnFe2O4 were investigated. The results show that ZnFe2O4 has significantly higher dielectric properties compared to ZnO. Generally, for both samples, the dielectric values at room temperature were quite low, indicating that both ZnO and ZnFe2O4 are poor microwave absorbers. It was found that the temperatures have a more significant effect on the imaginary permittivities than on the real permittivities. The heating rate showed that the sample temperature increased with increase in microwave power and sample mass. Using 700 W of microwave power and two times the stoichiometric amount of graphite, almost complete reduction of ZnO was achieved in 12 min, while ZnFe2O4 completely decomposed to zincite and wustite in 3 min.

Long-term follow up of surgical repair of late bleb leaks after glaucoma filtering surgery.

PURPOSE: To study the long-term outcomes of surgical revision of leaking blebs after trabeculectomy and identify possible risk factors for failure. PATIENT AND METHODS: A retrospective, nonrandomized, noncomparative interventional study of 34 eyes with late bleb leaks after trabeculectomy that underwent bleb excision with conjunctival advancement. The primary outcome measure was successful repair and control of intraocular pressure (IOP). The other measures evaluated included change in visual acuity from baseline and complications such as recurrence of bleb leak, endophthalmitis or the need for additional antiglaucoma medication to control IOP. RESULTS: After a mean follow up of 36.2+/-23 months, the mean IOP at the last visit was 14.5+/-7.6 mm Hg. IOP in 58.8% of eyes was controlled without medication. Complications included early leaks (7/34), late recurrent or persistent leaks (1/34), and endophthalmitis (1/34). In all, 41.2% patients required additional medication at the last visit. Survival analysis at 22 months the probability of total and qualified success was 52% and 72%, respectively. However, this dropped to 10% and 15%, respectively, at 5 years. The probability of total and qualified success further dropped to 2.5% and 5% at 5 years when the IOP cut-off was lowered from 21 to 15 mm Hg. Cox regression analysis failed to identify risk factors for bleb failure. CONCLUSIONS: Surgical bleb revision seems to be effective in treating late bleb leaks with few postoperative complications. However, patients should be followed carefully as late failure of bleb function beyond 2 years is a significant possibility.

Side-effect profile of brimonidine tartrate in children.

PURPOSE: To investigate brimonidine-related side effects and the efficacy of brimonidine in lowering intraocular pressure (IOP) in children with primary infantile and secondary glaucoma. STUDY DESIGN: Single-center, prospective, interventional, noncomparative case series. PARTICIPANTS: Eighty-three children (mean age, 7.84 years) met the inclusion criteria. METHODS: Medical records were reviewed to identify children with primary infantile or other forms of secondary pediatric glaucoma from birth to 15 years who received brimonidine as adjunctive therapy for glaucoma. The parents of the children who met the inclusion criteria completed a detailed questionnaire-based interview. The children were examined to assess weight, major systemic effects, and efficacy of adjunctive brimonidine therapy. MAIN OUTCOME MEASURES: Questionnaire-based interview of parents to assess side effects of brimonidine and IOP-lowering effect of adjunctive brimonidine. RESULTS: Parents reported symptoms in 70 of 83 children (84%). The most common side effects were excessive sleepiness and lethargy (76%), eye itching and rubbing (49%), and stinging and burning of the eyes (39%). Logistic regression analysis showed a statistically significant independent association between age and weight with lethargy and sleepiness. In symptomatic patients, symptoms' frequency increased with low weight (<20 kg) and in the young (<6 years). Mean IOP reduction after initiation of brimonidine, mainly as an adjunct, was 5+/-6.7 mmHg (P<0.001). CONCLUSIONS: Side effects after the use of brimonidine in children were frequent. The weight and age of the child were important factors in predicting central nervous system side effects, especially excessive sleepiness and lethargy. Although brimonidine is effective in lowering IOP in children, alternative glaucoma therapy should be considered especially in children weighing <20 kg and those younger than 6 years.