Electrolyte Purification

The Steuler Electrolyte Purification (SEP) process is based on the reduction of chrome(VI) compounds

and extends the lifetime of an electrolyte.

 

For the pretreatment in pickling plants for stainless steel wire an electrolytic pickling process is often employed using a solution of approx. 20% sodium sulfate. 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, also the chrome(VI) compounds formed by oxidation, which cannot be removed directly as suspended solids, have to be eliminated from the electrolyte.

 

Process description:
The reduction process is based on the reduction of chrome (VI) by employing such reduction agents

as hydrogen peroxide or sodium bi-sulfite at a low pH value.

 

First there occurs a pH-controlled addition of sulfuric acid to lower the pH value. At the same time, the reduction agent is dosed rh-dependently to reduce the chrome (VI) to chrome (III).

 

After that, the liquid is neutralized using caustic soda and the dissolved metals are precipitated out as metal hydroxides. The particles form flakes, precipitate and are then dewatered in a chamber filter press.
The dose-added caustic soda and sulfuric 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.

 

The main benefits are:
— High regeneration rate of the neutral electrolytes
— Savings in operational costs due to less formation of residue sludge that has to be disposed in the waste water treatment plants
— Simple construction of plant and use of tried-and-tested equipment