Steuler Electrolyte Purification (SEP)

For pretreatment in pickling plants for stainless steel wire, an electrolytic pickling process is often employed using a solution of approx. 20% sodium sulphate. The electrolyte itself is not used up during this process. Such metals as iron(III), nickel(II) and chrome(III) are precipitated out into the neutral solution as metal hydroxides. To achieve a longer service life for the electrolytes, the chrome(VI) compounds formed by oxidation, which cannot be removed directly as suspended solids, have to be eliminated from the electrolyte. This is achieved with the help of the Steuler Electrolyte Purification (SEP) process through the reduction of chrome(VI).

  • High regeneration rate of the neutral electrolytes
  • Savings in operational costs due to formation of less residue sludge for disposal in waste water treatment plants
  • Simple construction of plant and use of tried-and-tested equipment

Description of the process

The reduction process is based on the reduction of chrome(VI) by employing such reduction agents as hydrogen peroxide or sodium bi-sulphite at a low pH value. 
First there occurs a pH-guided addition of sulphuric acid to lower the pH value. At the same time, the reduction agent is dosed using rH guidance to reduce the chrome(VI) to chrome(III).

After this, the liquid is neutralised using caustic soda and the dissolved metals then precipitate out as metal hydroxides. The particles form flakes, precipitate and are then desiccated in a chamber filter press.

The dose-added caustic soda and sulphuric acid form new electrolytic solution to compensate for losses in the filter cake water and for those caused by dissipation on the surface of the belt.