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Title

The regeneration of HNO<sub>3</sub> and MgO via multistep pyrolysis of Mg(NO<sub>3</sub>)<sub>2</sub>⋅6H<sub>2</sub>O and thermodynamic analysis of critical intermediate product.

Authors

Zhao, Ding; Ma, Baozhong; Wang, Chengyan; Chen, Yongqiang

Abstract

The extraction of Ni from limonitic laterite by the NAPL (nitric acid pressure leaching) process has received significant attention. However, how to achieve continuous and suitable acid–base regeneration restricts the industrialization of the NAPL process. In this paper, spray pyrolysis technology promises to solve this problem. Hence, the phase evolution of the sample during the spray pyrolysis was studied, which is Mg(NO3)2·6H2O → Mg(NO3)2·2H2O → Mg3(OH)4(NO3)2 → MgO. Raman spectra of Mg3(OH)4(NO3)2 were recorded for the first time and further prove the conclusion of the phase evolution. In addition, the thermal analysis of the critical intermediate product (Mg3(OH)4(NO3)2) was performed, which indicates that the endothermic in the pyrolysis process is 194.35 kJ/mol, and is divided into two stages. The two stages both include the process of dehydration and denitration and the amount of dehydration and denitration in the second stage is relatively small. The reaction rate of stage two is slow and the temperature requirement is higher. Thermodynamic calculation results show that the R3 and An models could describe the whole process well. The related kinetic equations were obtained and the thermal stability of Mg3(OH)4(NO3)2 was predicted. Based on the above research, a two-step pyrolysis process is proposed by combining spray pyrolysis (~ 823 K) and calcining pyrolysis (≥ 693 K, 0.5 ~ 1.5 h). This route is simple, efficient, and continuous, which is conducive to industrialization and can successfully reduce at least 58.31% of NOx entering the compressor, thereby making the compressor smaller and less electricity consumption.

Subjects

PYROLYSIS; CRITICAL analysis; ELECTRIC power consumption; RAMAN spectroscopy; MAGNESIUM oxide

Publication

Journal of Thermal Analysis & Calorimetry, 2023, Vol 148, Issue 17, p9047

ISSN

1388-6150

Publication type

Academic Journal

DOI

10.1007/s10973-023-12284-0

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