Recovery of the metals from pickling liquors of stainless steel by precipitation methods

Pickling liquors are still one of the main environmental concerns of the st ainless steel industry. Most of the processes designed to recover these was tes focus on the recovery of their acid content (mixtures of HF and HNO3), but also produce metals (iron, nickel, chromium and molybdenum) as a low qu ality by-product that sometimes must be treated as a residue. This paper pr esents the development of a process to obtain commercial products from the metal content of these liquors. To this end, three precipitation methods (t otal, sequential and modified) were tested. The proposed procedure is the l ast one, i.e., modified precipitation. It consists of two stages each resul ting in the recovery of solids. The first product is mainly composed of iro n and chromium hydroxides and oxides, along with molybdate, while the secon d is mainly composed of nickel hydroxide. In addition, this method allows a n almost total recovery of the acids.