Recovery of nickel from waste in stainless steel industry (RECONI) : final report

Pickling processes in stainless steel industry produce large amounts of waste which contain a lot of valuable nickel. In Europe more than 2500 t/a of nickel with a current value of 35 million €/a are deposited. The objective of the project was to recover this nickel from waste acid as well as from neutralisation sludge for re-using it in the steelmaking process. Therefore, two main processing routes with several well-coordinated unit operations were investigated. For the recovery processes both main pickling systems, HF/HNO3-pickling and HNO3- free pickling were considered. The first processing route for the treatment of the waste acid contains the following unit operations: first precipitation (removal of the non-nickel substances), resin/chemical treatment (purify the nickel solution); second precipitation (to precipitate nickel hydroxide) and briquetting the sludge for re-use in EAF and AOD processes. The second processing route for the treatment of the neutralisation sludge contains the following unit operations: leaching of the sludge and precipitation of iron and chromium, filtration, extraction (to purify and concentrate the nickel solution) and electrodeposition of metallic nickel. The technical feasibility of both processing routes has been demonstrated by pilot scale trials. Cost estimations considering the current nickel prize show that nickel recovery from waste acid is economically valuable, whereas the nickel recovery from neutralisation sludge is economically valuable only with a nickel content of more than 3 wt.-% with respect to the dry mass of the sludge.