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New insights into the promotion mechanism of (NH4)2SO4 in sulfidization flotation: a combined experimental and computational study

Chen Daixiong, Liu Mengfei, Hu Bo, Dong Yanhong, Xue Wei, He Peng, Chen Fang, Zhu Jianyu, Zhang Chenyang

Physicochemical Problems of Mineral Processing

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2021

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Vol. 57, iss. 5

57--70

EN

Ammonium sulfate ((NH4)2SO4) exhibits promoting effects in malachite sulfidization flotation. However, the promotion mechanism remains poorly understood. In this study, micro-flotation tests, zeta-potential measurements, scanning electron microscopy coupled with energy-dispersive spectroscopy (SEM-EDS), atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and materials studio simulation (DFT) were used to investigated the promotion mechanism of (NH4)2SO4. Micro-flotation test demonstrates that the recovery of malachite from 73% increased to 83%, when the (NH4)2SO4 was added. Contact angle and zeta potential test results indicate that addition of Na2S•9H2O changes the surface properties of malachite and provide the conditions for adsorption of butyl xanthate (BX). After promoting the sulfidization by (NH4)2SO4, BX is more effective in improving the hydrophobicity. SEM-EDS and AFM results show that (NH4)2SO4 can improve performance and stability of sulfidization. X-ray photoelectron spectroscopy indicates that after sulfidization, polysulfides and cuprous were appeared in malachite surface, infers that a redox reaction occurs between sulfur and copper on the surface of malachite. After addition of (NH4)2SO4, the percentage of polysulfides and cuprous were increased, it implies (NH4)2SO4 can accelerate the redox reaction. Computational results show that after adding (NH4)2SO4, the adsorption energy of HS- on the malachite surface is reduced, implies that (NH4)2SO4 can improve the stability of HS-adsorption on the surface of malachite.

2

Wide-angle infrared plasmonic perfect absorber based on graphene-silica grating

Chen Fang

Optica Applicata

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2021

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Vol. 51, nr 1

87--95

EN

In this paper, wide-angle infrared perfect absorption has been demonstrated by using a double-layer graphene strip grating coupled with a silicon dioxide grating. Numerical simulation of the finite-difference time-domain method indicates that the perfect absorption can be achieved due to the effective impedance matching, and all the incident electromagnetic energy is confined in the Al2O3 layer between the silver substrate and the graphene strip grating. Dual-band perfect absorption is achieved with the change of strip width or chemical potential of the bi-layer graphene strip grating. It is found that the spectral position of the absorption peak can be tuned by the chemical potential or the width of the graphene strip, and additionally by the size of the proposed absorber. Moreover, the proposed perfect absorber shows excellent absorption stability for a wide range of the incident angle up to ±65°. The proposed absorber may find potential application in tunable double band perfect absorbers in the mid-infrared range.

3

An empirical study on system dynamics model for sustainable development of air traffic control units

Chen Fang, Chen Xi, Zhang Xinjian

Ecological Chemistry and Engineering. S

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2021

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Vol. 28, nr 1

101--116

EN

With the rapid growth of flight volume, the contradiction between insufficient support capability of air traffic control (ATC) units and large demand for development ultimately hinders their sustainable and safe development. The article aims at the leverage point of the contradiction between supply and demand so as to provide scientific safety policies. Based on the system archetype "growth and underinvestment", from the perspective of the feedback relationships between support capability, safety, and development, the causality of the dynamic factors of control, communication, navigation, and surveillance, as well as meteorology and information subsystems was studied. Then, a system dynamics model for the sustainable and safe development of ATC units was established. Taking the Tianjin ATC sub-bureau as an example, policy suggestions for sustainable and safe development were put forward according to the scenario simulation results.

4

Optical bistability in double quantum dot molecule with inter-dot tunnelling

Yu Chunchao, Sun Lihui, Zhang Huafeng, Chen Fang

Optica Applicata

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2019

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Vol. 49, nr 2

293--301

EN

We have theoretically studied the optical bistability behaviors under an external electric field and a coupling laser field in double quantum dot molecule system with π-type four energy levels. It can be adjusted by the system parameters such as the electronic cooperation parameter, the tunneling strength, the coupling laser field, the probe and coupling laser detuning. These results may be useful in the experiment and provide new types of all-optical switching.