Enhanced Leaching of Zinc from Zinc-Containing Metallurgical Residues via Microwave Calcium Activation Pretreatment

Given the shortage of zinc resource, the low utilisation efficiency of secondary zinc resource, and the crucial problem that the synchronous dissolution of zinc from different mineral phases, an activation pretreatment method merged with calcium activation and microwave heating approach was proposed to enhance the zinc leaching from complex encapsulated zinc-containing metallurgical residues (ZMR). Results indicated that under the optimal pretreatment conditions, including microwave activation temperature of 400 °C, CaO addition of 25% and activation time of 20 min, the zinc leaching rate reached 91.67%, which was 3.9% higher than that by conventional roasting pretreatment. Meanwhile, microwave heating presents excellent treatment effects, manifested by the zinc leaching rates, all exceeding that of conventional roasting under the same conditions, while the process temperature is decreased by 200 °C. In addition, XRD and SEM-EDS analysis denoted that microwave calcification pretreatment can effectively promote the transformation of the refractory zinc minerals like Zn2SiO4 and ZnFe2O4 into the easily leachable zinc oxides. The distinctive selective heating characteristics of microwave heating strengthened the dissociation of mineral inclusion, and the generated cracks increased the interfacial reaction area and further enhancing the leaching reaction of zinc from ZMR.

Particle-in-cell Simulation of 3He Enrichment in Solar Energetic Particle Events

3He enrichment is one distinctive feature of impulsive solar energetic particle events. This study is designed to investigate the process of plasma wave–particle resonance, which plays a key role in selectively accelerating heavy ions. We apply a 1.5 dimensional particle-in-cell simulation to model the electron-beam–plasma interaction that generates electron and ion cyclotron waves, namely proton and 4He cyclotron waves, whose dispersions are dependent on the magnetization parameter α = ω pe/Ωce and the temperature ratio τ = T e /T p . The background particles, e.g., 3He and 4He, resonate with the excited cyclotron waves and experience selective heating or acceleration. Specifically, the resonant modes of 3He ions lead to a more effective acceleration rate compared to those of the 4He ions. The simulation results provide a potential solution for understanding the abundance of heavy ions in the solar wind.

Pengaruh Temperatur Pada Microwave Pirolisis Cangkang Kelapa Sawit dan Low Density Polyethylene Dengan Katalis Zeolite/Kalsium Oksida

In general, the use of oil palm parts can be utilized by industry, but it is different from oil palm shells which become waste. The high use of plastic is proportional to the waste generated. So far, both types of waste are problems that have not been resolved. The utilization of waste shell waste and low-density polyethylene using the pyrolysis method. Microwave technology has been widely used as a heat source in the pyrolysis process. The advantages of using microwaves in pyrolysis are fast and selective heating, efficient energy use, and control of pyrolysis products. This study aimed to determine the characteristics of Pyrolytic-oil from the pyrolysis of waste oil palm shells and Low-density polyethylene. The research was conducted using a microwave with temperature variations of 400oC, 450oC, 500oC, 550oC and 600oC. The composition of the main ingredients consisted of 75 grams of palm shells, 75 grams of low-density polyethylene plastic, 56.25 grams of a zeolite catalyst, 56.25 grams of calcium oxide and 131.25 grams of charcoal carbon absorber. The results showed the effect of temperature on pyrolytic-oil productivity; as the temperature increases, the product gas increases. The lowest density value at a temperature of 400oC is 966.8 Kg/m. The lowest viscosity at a temperature variation of 500oC is 2.1 Mpa.s. The highest acidity value is at a temperature of 550oC.

Thermally Assisted Grinding of Cassiterite Associated with Pollimetallic Ore: A Comparison between Microwave and Conventional Furnaces

We investigated the influence of microwave and conventional heating pretreatments on the grinding of cassiterite associated with pollimetallic ore. The minerals that exhibited a stronger microwave absorption ability crushed first, which is the main difference between the microwave and the traditional heating pretreatments. The distribution of Fe, Pb, Zn, and Sn increased in the fine size range (−0.425 mm). The Fe and Pb grades in the size ranges of −3.2 + 2 mm and −2 + 1 mm after the microwave pretreatment (6 kW, 1 min) were lower than those of the traditional heating (12 kW, 400 °C, 20 min), indicating that the microwave selective heating was beneficial for pyrite and jamesonite. The grade and distribution of Sn decreased significantly in the size ranges of −3.2 + 2 mm and −2 + 1 mm and increased in the size ranges of −0.425 + 0.15 mm and −0.15 + 0.074 mm. Microwave heating treatment promoted the grinding of sulfide ore and reduced the cassiterite overgrinding.

Search for the Microwave Nonthermal Effect in Microwave Chemistry: Synthesis of the Heptyl Butanoate Ester with Microwave Selective Heating of a Sulfonated Activated Carbon Catalyst

The heptyl butanoate ester was synthesized from butanoic acid and heptanol in a heterogeneous medium in the presence of sulfonated activated carbon (AC-SO3H) catalyst particles subjected to microwave irradiation, which led to higher conversion yields (greater product yields) than conventional heating with an oil bath. The advantage of the microwaves appeared only when the moisture content in the butanoic acid batch(es) was high, suggesting that, unlike conventional heating, the reverse reaction caused by the moisture content and/or by the byproduct water was suppressed by the microwaves. This contrasted with the results that were found when carrying out the reaction in a homogeneous medium in the presence of the 2,4,6-trimethylpyridinium-p-toluene sulfonate (TMP-PTS) catalyst, as product yields were not improved by microwave heating relative to conventional heating. The removal of moisture/water content in the reaction solution was more pronounced when the reactor was cooled, as the reaction yields were enhanced via selective heating of the heterogeneous catalyst. A coupled electromagnetic field/heat transfer analysis gave credence to the selective heating of the AC-SO3H catalyst, which was further enhanced by cooling the reactor. It was deduced that unforeseen impurities and local high-temperature fields generated on the surface of small fine catalyst particles may have had an effect on the microwave chemistry such that the associated phenomena could be mistaken as originating from a nonthermal effect of the microwaves. Accordingly, it is highly recommended that impurities and selective heating be taken into consideration when examining and concluding the occurrence of a microwave nonthermal effect.

Research into Silicon Nanoparticles as Agents for UHF Hyperthermia In Vitro

The current approaches to cancer treatment, including surgery and high-energy beam irradiation, do not always give satisfactory results for a number of oncological neoplasms. One of the promising areas in oncology is the use of nanoparticles selectively heated by external action as agents for hyperthermia of some types of tumors. In this work, we performed selective heating of suspensions of silicon nanoparticles using a device for electromagnetic high-frequency therapy (UHF-60).

Efficient Iron Removal to Produce High Purity Quartz Sand by Micro-Inclusion Bursting Using Microwave Pretreatment Combined with Different Acid

The one of major impurities in quartz is iron, which has a great impact on the properties of the material and should be be strictly removed in many applications. In this study, a low-energy consumption, simple, fast processing is introduced by combination microwave treatment with different acid leaching. Selective heating of microwaves is used to process quartz, causing local phase changes to improve the purification effect. Acid leaching was used to remove the iron in the quartz matrix. Under optimized conditions, the iron content can be reduced to below 0.167 ppmw with one single purification pass.

Thermal Effect in the Microwave-assisted Aminolysis of Benzoates and Amines

Background: Microwave selective heating thermal effect is obvious in unimolecular organic reactions. However, it is unclear whether it exists in bimolecular organic reactions under strictly controlled reaction temperature conditions. Objective: To determine whether microwave selective heating effect exists in the microwave-assisted bimolecular reactions. Methods: Hammett linear relationships in “one-pot” aminolyses of mixed 4-nitrophenyl substituted benzoates with benzylamine and 4-nitrophenyl benzoate with mixed substituted anilines were selected as molecular level probes to explore the thermal effect in the microwave-assisted bimolecular reactions. Results: In less polar solvent, there is an obvious “hot spots” effect. “One-pot” aminolyses of mixed 4-nitrophenyl substituted benzoates with benzylamine and 4-nitrophenyl benzoate with mixed substituted anilines were performed in less polar solvent toluene under oil-bath and microwave heating conditions. Generally, slopes of Hammett plots or effect of substituents on reaction rates decrease along with temperature increases under oil-bath heating conditions. Under microwave irradiation conditions, slopes of Hammett plots or effect of substituents on reaction rates decrease in comparison with those under oil-bath heating conditions at the same setting temperature, revealing that higher temperature regions (“hot spots”) still exist in intermolecular organic reactions. Conclusion: Microwave selective heating thermal effect still exists in bimolecular organic reactions under strictly controlled reaction temperature conditions, revealing that higher temperature regions (“hot spots”) do exist in intermolecular organic reactions.