TITLE	Development of the effective recycling technology of stainless steel pickling agent (Joint Program to Promote Technological Development with the Private Sectors)
AUTHOR	RITE - CHIBA No. 5 LABORATORY in JFE Steel Corporation RITE - TOKYO CHIYODA LABORATORY in JFE Steel Corporation RITE - CHIBA No.6 LABORATORY in JFE Techno-Research Corporation RITE - TOKYO CHIYODA No. 2 LABORATORY in JFE Techno-Research Corporation RITE - SYUNAN LABORATORY in ASTOM Corporation RITE - OSAKA NISHI-YODOGAWA No. 2 LABORATORY in Sasakura Engineering Corporation
SOURCE
ABSTRACT	We have developed the process for recovery and recycling of valuable metal and nitric-hydrofluoric acids from waste pickling solution for stainless steel. There are 3 objectives for this process. (1) The first process is the recovery of valuable metal by neutralization of the waste pickling solution with KOH, followed by metal separation as sludge and then a water rinse. The recovered metals are re-used as raw material for stainless steel. (2) The second process is condensation of the neutralized and rinsed solution mixture with RO(Reverse Osmosis) membrane, followed by separation of acids and alkali with bipolar membrane electro dialyzer. The recycled alkali is re-used as neutralizer for waste pickling solution. (3) The third process is the vacuum-distillation of the acids, which were separated by bipolar membrane electro dialyzer.  The condensed acids are re-used as pickling for stainless steel. Experiments were conducted sequentially process(1)→(2)→(3) to develop these three process by bench plant  (the treatment of waste pickling solution was 454 L/month). The following results were obtained. (1) The concentrations of K and F in the sludge were decreased when waste pickling solutions were neutralized PH>11 with KOH、and then the rinse by water or KOH solution with sludge circulation. This sludge with low concentration of K and F can be re-used as raw materials for stainless steel. (2) The SS(suspended solid) of neutralized and rinsed solution mixture could be removed by MF(micro filtration). The life-time of RO and bipolar membrane can be maintained over 2 years by removal of SS. (3) The electrical efficiency of acid and alkali by bipolar membrane electro dialyzer were over 77 %.  The degradation of membrane was not observed in this experiment. (4) The 95% of nitric-hydrofluoric acids could be recovered in the process of vacuum distillation. The material of distillation equipment with fluoridized resin-lining had good resistance to nitric and hydrofluoric acids (5) The recycled acids were evaluated as pickling of stainless steel. The good surface of stainless steel could be obtained. From these results, we have developed a successful process for recovery and recycling of valuable metal and nitric-hydrofluoric acids from waste pickling solutions for stainless steel.