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

Abstract

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 CaF₂, CaSO₄, Me(OH)_n (M: Fe, Cr, Ni), and the content of CaF₂ 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 SiF₄ and AlF₃ generated through the reactions of CaF₂ with SiO₂ and Al₂O₃. 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.

Keywords

stainless steel / pickling sludge / characterization / recycling / sulfur / fluorine

References

[1] LiL F, CaenenP, JiangM F. Electrolytic pickling of the oxide layer on hot-rolled 304 stainless steel in sodium sulphate [J]. Corrosion Science, 2008, 50(1): 2824-2830

[2] WangH L. Process conditions, exhaust gases and waste acid treatment in cold rolling stainless strip steel picking [J]. China Metallurgy, 2009, 19(6): 40-43

[3] BraunE. How to improve pickling of stainless steel strip [J]. Iron and Steel Engineering, 1980, 57: 79-81

[4] ShiL, ChenR-h, WangR-yi. Two-stage treatment process of pickling wastewater in the cold-rolling production of stainless steel [J]. Baosteel Technical Research, 2010, 4(2): 16-22

[5] GaoLiang. Sludge reduction technology in stainless steel acid cleaning wastewater treatment [J]. China Water and Wastewater, 2009, 25(10): 83-85

[6] MaG, Garbers-CraigA M. A review on the characteristics, formation mechanisms and treatment processes of Cr(VI)-containing pyrometallurgical wastes [J]. Journal of the Southern African Institute of Mining and Metallurgy, 2006, 106(11): 753-763

[7] MaP, LindblomB, BjörkmanB. Experimental studies on solid-state reduction of pickling sludge generated in the stainless steel production [J]. Scandinavian Journal of Metallurgy, 2005, 34(1): 31-40

[8] ItoM, TachibanaR, FukushimaK, SeinoY, YamamotoA, KawabataY. Characteristics and production mechanism of sulfuric acid and nitric-hydrofluoric acid pickling sludge produced in manufacture of stainless steel [J]. Journal of Chemical Engineering of Japan, 1998, 31(4): 589-595

[9] IslamM Z, CatalanL J J, YanfulE K. Effect of remineralization on heavy-metal leaching from cement-stabilized /solidified waste [J]. Environmental Science and Technology, 2004, 38(5): 1561-1568

[10] AsavapisitS, ChotklangD. Solidification of electroplating sludge using alkali-activated pulverized fuel ash as cementitious binder [J]. Cement and Concrete Research, 2004, 34(2): 349-353

[11] MaJ, ZouZ. Resource usage and new technical evolution of discard solid materials from iron and steel enterprises at home and abroad [J]. Metallurgical Economics and Management, 2006, 4: 32-33

[12] ChenQ-songRecycling method of nickel-chromium in stainless steel sludge [P], 2009

[13] LiuF-q, YangC-j, LiL-j, HouP, WangJ-n, LiA-m, DaiJ-junHarmless disposal and resource utilization of neutralized sludge from stainless steel pickling wastewater [P], 2010

[14] HanewaldR H, DombrowskiD E. Recovery of metals from steel wastes and production of DRI by the Inmetco process [J]. Iron and Steel Engineering, 1985, 62(3): 62-67

[15] LiX-m, ZhaoJ-x, CuiY-r, YangJun. The comprehensive utilization of EAF dust and pickling sludge of stainless steel works [J]. Materials Science Forum, 2009603-606

[16] XuKeRecycling of chromium from wastewater sludge in steel plant [D], 2006, Shanghai, Tongji University

[17] MaG, Garbers-craigA M. Cr(VI) containing electric furnace dusts and filter cake from a stainless steel waste treatment plant: Part 1-Characteristics and microstructure [J]. Ironmaking and Steelmaking, 2006, 33(3): 229-237