Microwave Dielectric Properties and Reduction Behavior of Low-Grade Pyrolusite
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https://doi.org/10.1007/s11837-019-03522-8 2019 The Minerals, Metals & Materials Society
SUSTAINABLE PYROMETALLURGICAL PROCESSING
Microwave Dielectric Properties and Reduction Behavior of Low-Grade Pyrolusite FEI HE,1 JIN CHEN,1,2,6 GUO CHEN,1,2,3,7 JINHUI PENG,1 C. SRINIVASAKANNAN,5 and ROGER RUAN2,4 1.—Key Laboratory of Unconventional Metallurgy, Ministry of Education, Faculty of Metallurgical and Energy Engineering, Kunming University of Science and Technology, Kunming 650093, People’s Republic of China. 2.—Key Laboratory of Green-Chemistry Materials in University of Yunnan Province, Yunnan Minzu University, Kunming 650500, People’s Republic of China. 3.—Hunan Provincial Key Laboratory of Efficient and Clean Utilization of Manganese Resources, Central South University, Changsha 410083, Hunan, People’s Republic of China. 4.—Center for Biorefining, Bioproducts and Biosystems Engineering Department, University of Minnesota, 1390 Eckles Ave., Saint Paul, MN 55108, USA. 5.—Chemical Engineering Department, Khalifa University of Science and Technology, Abu Dhabi, UAE. 6.—e-mail: [email protected]. 7.—e-mail: [email protected]
Manganese ore is an important mineral having a strategic role in the development of the national economy and society. In this study, the dielectric properties, heating curve, crystal structure, and reduction ratio of a low-grade pyrolusite were investigated. The dielectric constant, dielectric loss factor, and loss tangent coefficient of low-grade pyrolusite at room temperature were evaluated using the resonant cavity perturbation method, yielding values of 5.854, 0.146, and 0.0249, respectively. Owing to the excellent microwave absorption properties of low-grade pyrolusite with 10% coal (22 g), it could be heated to a temperature of 800C within 200 s. X-ray diffraction results confirmed that MnO2 was partially transformed into MnO at 450C, while, at 650C, no diffraction peak of MnO2 was observed. At a reduction temperature of 550C, a reduction ratio of MnO2 to MnO of 96.65% could be achieved within a holding time of 50 min. This study demonstrates that the microwave carbothermal reduction of a low-grade pyrolusite is efficient, and thus could promote the clean production and sustainable development of the manganese industry.
INTRODUCTION The content of manganese in the earth’s crust is approximately 0.1%, mainly in the form of oxides, carbonates, and marine manganese nodules.1–4 They are available in various valence states, predominantly Mn2+ and Mn4+, and hence exhibit a high oxidizability.5,6 Manganese ore as an important raw material has a strategic role in the development of the national economy and society. 90% of the manganese is used in the manufacture of steels, 3% for batteries, 2% for chemicals, and approximately 5% for nonferrous metal smelting, electronic materials, building materials, environmental protection, agriculture, animal husbandry,
and national defense.7–9 Owing to its wide application in various industries, its demand continues to increase. A total of 0.5
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