Pickling of stainless steel is a chemical operation for removing the oxide scale of the stainless steel after annealing treatment. The most commonly used pickling baths contain HNO3/HF acids, or H2SO4/HF acids in the case of NOx free haths developed during the last years. This project is concerning both kind of baths.
During the pickling operation acids are consumed and metals are dissolved in the bath. When a critical metal concentration is reached, some kinds of fluoride precipitation could appear, and the pickling bath is considered as spent. Therefore from time to time a part of the pickling liquor has to he replaced. This stream is neutralized producing sludges that represent a serious environmental problem because the use contains nitrates, flurides, acids and solid materials rich in heavy metals.
On the basis of information provided by European producers of stainless steel and alloyed steel, the total amount of spent pickling baths produced in EU countries is estimated at 300 000 m3/y and the stockpiled is about 150,000 t/y. For the total stainless steel production of 6 000 000 tons per year.
Apart from the severe environmental problems of the spent pickling baths, important deficiencies appear in a normal operation because of the non stable pickling conditions and of shut down periods for cleaning and bath adjustements. The annual losses in acids and metals as well as,the treatment cost of the spent baths represent a total amount of 121.6 million ECU per year for the European stainless steel industry.
Based on these facts we conclude that there is an urgent need in Europe on the topic that we propose in this project in order to develop and integrate a novel process to deal with spent pickling baths from stainless steel. The new process would eliminate a waste disposal problem while regenerating and recovering valuable by products which could well contribute to the economic feasibility of the process.
The proposed process is a combination of novel and existing
technologies, including the follwing steps: Acid recovery, Metal separation and refinning, Chemicals recovery and Rinse water treatment. The final process will be a prototype process, developed and proved at pilot plant level which will he available for commercial exploitation.
Funding SchemeCSC - Cost-sharing contracts
3144 NA Maassluis