A Review on the Treatments and Minimization Techniques of Stainless Steel Pickling Sludge

Abstract

Pickling sludge is the deposits that generated from the neutralization of pickling waste water with calcium hydroxide in stainless steel pickling process. The main composition of pickling sludge is CaF2, CaSO4, Me(OH)n (M:Fe,Cr,Ni). Solidification /stabilization method is believed to a most economical way to dispose these wastes at present. But the process caused serious compatibilization, it not only took up the scarce land resource, but also wasted nickel, chromium and other resources, in addition, the potential harm of Cr6+ to the environment still existed. A new thought to recycle the sludge was as following. After drying the sludge, it contained mainly calcium fluoride and metal oxides. The calcium fluoride could replace fluorspar, so the sludge could be used as a raw material for AOD process, where the metal oxides were reduced into the bulk of the metal. This would not only save fluorite, but also could reduce metal oxide of sludge. With more stringent environmental demands and increasingly output of the sludge, the most effective way to reduce the sludge from source is recycling the valuable elements from waste water directly. Solvent extraction combined with vacuum evaporation, spray evaporation and resin absorption coordination were all the effective methods. The resin adsorption process would be another promising method as ion exchange resin was continuously successfully developed. It had been found that treating the waste water with positive resin can remove the metal ions, but how to completely resolve the metal from the resin was still a problem.