Characterization and recycling of nickel- and chromium-contained pickling sludge generated in production of stainless steel

• Published in: Journal of Central South University Vol. 21; no. 8; pp. 3241 - 3246
• Main Authors: Li, Xiao-ming, Xie, Geng, Hojamberdiev, Mirabbos, Cui, Ya-ru, Zhao, Jun-xue
• Format: Journal Article
• Language: English
• Published: Heidelberg Central South University 01.08.2014
• Subjects: Engineering; Metallic Materials; recycling; sulfur; stainless steel; pickling sludge; characterization; fluorine
• ISSN: 2095-2899; 2227-5223
• DOI: 10.1007/s11771-014-2296-6

Pickling sludge generated during the neutralization of pickling wastewater with calcium hydroxide in stainless steel pickling process was characterized using X-ray fluorescence spectrometry, X-ray diffractometry, scanning electron microscopy, thermogravimetry and differential scanning calorimetry, etc. The major compositions of pickling sludge are CaF 2 , CaSO 4 , Me(OH) n (M: Fe, Cr, Ni), and the content of CaF 2 is high in the sludge. The melting point of pickling sludge is about 1350 °C and the viscosity is about 0.14 Pa·s at 1450 °C, which are comparatively lower than those of normal refining slag. After heat treatment, the contents of sulfur and fluorine in the pickling sludge were reduced, confirming the thermal decomposition of sulfate in the sludge. Fluorine in the sludge is reduced by the gaseous SiF 4 and AlF 3 generated through the reactions of CaF 2 with SiO 2 and Al 2 O 3 . The preliminary results from the reduction test indicate that the sulfur content in the steel is not affected by the presence of sulfur in the sludge. The recovery of nickel is about 40%, and the chromium content changes marginally due to the protective atmosphere under the reduction condition of chromic oxide. The pickling sludge is a potential auxiliary material for the production of stainless steel.