Continuous-flow microwave heating stands out for its ability to rapidly and uniformly heat substances, making it widely applicable in chemical production. However, in practical applications, the permittivity of the heated liquid changes dramatically as the reaction progresses, affecting the efficiency and uniformity of continuous-flow heating. Herein, this work presents a novel microwave heating device based on a coaxial structure for high-performance heating. Our approach commenced with the development of a multiphysical field model, incorporating spiraled polytetrafluoroethylene (PTFE) as a water channel and the coaxial waveguide as a container. The analysis shows that the uniform distribution of the sectional electric field of electromagnetic waves in the TEM mode within the coaxial structure can enhance heating uniformity. Then, a continuous-flow microwave heating system for different liquid loads was established, and experimental measurements were conducted. The heating efficiency for all loads exceeded 90%, which basely matched the simulation results, validating the accuracy of the model. Finally, the heating efficiency and uniformity under different permittivity loads were analyzed, as well as the impact of channel radius on heating efficiency. The device exhibits high heating efficiency under different loads, with uniform radial electric field distribution and stable heating uniformity. This continuous-flow microwave device is suitable for chemical research and production because of its high adaptability to the large dynamic range of permittivity, contributing to the promotion of microwave energy applications in the chemical industry.

Silicon tetrafluoride (SiF4), being a toxic gas, contains abundant fluorine and silicon resources. However, at present, the extraction of these resources from SiF4 remains a significant challenge for current technologies. Microwave plasma emerges as a promising technology with considerable potential in this area. Nevertheless, the majority of research endeavors concentrate on the silicon production through microwave plasma treatment of SiF4, while the resultant tail gas, rich in fluorine resources, is neglected and subsequently wasted. In this paper, a low-pressure microwave plasma is employed to process SiF4 and H2 for the synthesis of hydrogen fluoride (HF). The microwave power reflection ratio, electron density, and produced HF concentration in varying microwave power levels and gas flow rates are obtained. The results demonstrate that all the processing parameters have a direct impact on the HF concentration. The maximum HF concentration of 11200 ppm is achieved under the specific condition: an H2 flow rate of 2.5 sccm, a SiF4 flow rate of 2 sccm, and a microwave power level of 1100 W. Notably, this condition also results in the lowest energy cost. This work presents fundamental process guidance for the production of HF using microwave plasma, facilitating the scalability of this technology in industry.

Silicon tetrafluoride (SiF₄), being a toxic gas, contains abundant fluorine and silicon resources. However, at present, the extraction of these resources from SiF₄ remains a significant challenge for current technologies. Microwave plasma emerges as a promising technology with considerable potential in this area. Nevertheless, the majority of research endeavors concentrate on the silicon production through microwave plasma treatment of SiF₄, while the resultant tail gas, rich in fluorine resources, is neglected and subsequently wasted. In this paper, a low-pressure microwave plasma is employed to process SiF₄ and H₂ for the one-step synthesis of hydrogen fluoride (HF). The microwave power reflection ratio, electron density, SF₄ conversion rate, and produced HF concentration in varying microwave power levels and gas flow rates are obtained. The results demonstrate that all the processing parameters have a direct impact on the HF concentration. The maximum HF concentration of 11,200 ppm is achieved under the specific condition: an H₂ flow rate of 2.5 sccm, a SiF₄ flow rate of 2 sccm, and a microwave power level of 1100 W. Notably, this condition also results in the lowest energy cost. Moreover, the underlying reaction mechanism of the conversion from SiF₄ to HF is thoroughly analyzed. This work presents fundamental process guidance for the production of HF using microwave plasma, facilitating the scalability of this technology in industry.

The separation of ultrafine apatite from quartz through reverse flotation is a challenge due to its low mass and high specific surface area. In this work, xanthan gum–Fe³⁺ (XG–Fe³⁺) was explored as a novel and efficient depressant–flocculant for the selective flotation separation of apatite and quartz. The flotation performance and separation selectivity of XG–Fe³⁺ were systematically assessed using micro-flotation tests. The mechanisms were revealed through turbidity analysis, microscopic observation, contact angle measurement, zeta potential, and Fourier Transform Infrared Spectroscopy (FTIR) analysis. Flotation results illustrated that XG-Fe³⁺ strongly depressed the flotation of apatite, while it hardly affected the flotation of quartz. Turbidity analysis and microscopic observation indicated the flocculation of fine apatite in the presence of XG-Fe³⁺, while no flocculation was found for quartz. Contact angle, zeta potential and FTIR results indicated that XG-Fe³⁺ was chemically adsorbed onto the apatite surface, hindering the adsorption of dodecylamine (DDA) and maintaining the hydrophilicity of apatite. XG-Fe³⁺ enhanced the flotation separation of ultrafine apatite from quartz by maintaining the hydrophilicity of ultrafine apatite while simultaneously reducing its entrainment into the froth via selective flocculation.

The conversion of carbon dioxide (CO₂) driven by microwave plasma has garnered extensive attention due to its capability to recycle carbon resources and mitigate the greenhouse effect. However, the existing microwave plasma technologies suffer from cumbersome system setups and relatively low energy efficiency. This work investigates the CO₂ conversion using a portable atmospheric microwave plasma source, which requires low plasma-generating power. When the working gas is a mixture of CO₂ and Ar, the minimum plasma-generating power required for the proposed portable microwave plasma source is only 50 W. A Fourier transform infrared spectrometer is used to quantify both the CO₂ and CO concentrations, and the C₂ Swan bands of the plasma are measured to determine the gas temperature. The maximum CO₂ conversion rate is approximately 12.7%. Furthermore, the maximum energy efficiency reaches 87.9%, which exceeds that of most of the state-of-the-art atmospheric microwave plasma configurations. Owing to its simplicity of operation, portability, and high energy efficiency, this method is well-suited for distributed CO₂ conversion systems.

The conversion of carbon dioxide (CO₂) driven by microwave plasma has garnered extensive attention due to its capability to recycle carbon resources and mitigate the greenhouse effect. However, the existing microwave plasma technologies suffer from cumbersome system setups and relatively low energy efficiency. This work investigates CO₂ conversion using a portable atmospheric microwave plasma source, which requires low plasma-generating power. When the working gas is a mixture of CO₂ and Ar, the minimum plasma-generating power required for the proposed portable microwave plasma source is only 50 W. A Fourier transform infrared spectrometer is used to quantify both the CO₂ and CO concentrations, and the C₂ Swan bands in the plasma are measured to determine the gas temperature. The maximum CO₂ conversion rate is approximately 12.7%. Furthermore, the maximum energy efficiency reaches 87.9%, which exceeds that of most state-of-the-art atmospheric microwave plasma configurations. Owing to its simplicity of operation, portability, and high energy efficiency, this method is well-suited for distributed CO₂ conversion systems.