Regular Article

Crystalline-selected synthesis of ferrous oxalate dihydrate from spent pickle liquor

¹ Yunnan Provincial Laboratory for Advanced Materials and Batteries Application, Faculty of Metallurgical and Energy Engineering, Kunming University of Science and Technology, 650093 Kunming, Yunnan, PR China
² Research & Development Center, China Tobacco Yunnan Industrial Co. Ltd, 650093 Kunming, PR China
³ State Key Laboratory of Physical Chemistry of Solid Surfaces, Collaborative Innovation Center of Chemistry for Energy Materials, College of Chemistry and Chemical Engineering, Xiamen University, 361005 Xiamen, PR China
⁴ Yunnan Provincial Energy Investment Group Co. Ltd, 650000 Kunming, PR China

^* E-mail: 438616074@qq.com; zyjkmust@126.com

Received: 11 April 2017
Received in final form: 2 June 2017
Accepted: 8 June 2017

Abstract

Ferrous oxalate dihydrate with different crystalline structures, polymorphs and sizes have been synthesized through a facile precipitation reaction from spent pickling liquors (SPL) by controlling synthesis conditions. The β-FeC₂O₄ · 2H₂O in orthorhombic phase can be formed at room temperature, whereas α-FeC₂O₄ · 2H₂O with a monoclinic unit cell can be obtained after aging at 80 °C. With the increasing aging temperature, the morphology of samples can be tailored from flower-like to prismatic-like and the particle-sizes are decreased. Innovatively, thermal decomposition behaviors of products have been investigated in details by X-ray diffraction pattern (XRD) and thermal gravimetric-differential scanning calorimetry (TG-DSC). The results show that both FeC₂O₄ · 2H₂O samples can be transformed to α-Fe₂O₃ in air atmosphere and Fe₃O₄ in argon atmosphere at T ≧ 400 °C. In air atmosphere, there are two sharp exothermic peaks for β-FeC₂O₄ · 2H₂O (250 °C) and α-FeC₂O₄ · 2H₂O (239.5 °C) correspond to the decomposition reactions. In argon atmosphere, the decomposition end temperatures are 500 °C and 430 °C for β-FeC2O4 · 2H2O and α-FeC2O4 · 2H2O, respectively. This indicates that β-FeC2O4 · 2H2O has higher thermal stability in comparison with α-FeC2O4 · 2H2O.