Development of Recycling System for Sludge from the Stainless Steel Nitric-hydrofluoric Acid Pickling Process
The sludge produced from the pickling of stainless bands settles to the bottom of the pickling tank and becomes an impediment to the operation. In this research, a very high concentrations of Cr, Ni, and Fe were found in the sludge. In particular, the concentration of Cr was more than 40 mass%. It was also found that the particle size of the sludge is as small as 9.2 μm. The diameter increases by coagulation and the sedimentation velocity of the sludge is 1.4 m/h. <br>Based on these results, a study was made on an ejector capable of preventing the sludge precipitation in the pickling tank and moving the sludge, and a sedimentation tank where the sludge would precipitate.<br> First, 14 groups of ejectors were installed on the two sides of the pickling tank. Two circulation tanks connect with the pickling tank and each group of ejectors was installed in different circulation tanks. Continuous action of the ejectors causes the sludge to remain afloat and prevents it from settling out in the pickling tank. The sludge is moved to the circulation tank, which is also equipped with the same type of ejectors as the pickling tank to prevent the sludge from settling. <br>Next, precipitation and separation of the sludge are performed in this sedimentation tank. After separation in the sedimentation tank, the sludge was neutralized by mixing with hydrated lime using kneading device. The neutralized sludge is loaded into a lugger bag and can be used as a raw material for steel making.
- ISIJ international
ISIJ international 37(4), 391-398, 1997-04-15
The Iron and Steel Institute of Japan