Membrane electrolysis is a well-known process, used at the chloride-alkali industries. Slight changes made this process also suitable for the treatment of liquid flows in several surface technologies.
During the last years, a process for regeneration of used solutions of pickling baths (e.g. chromic acid and iron chloride) has been developed. The regeneration of alkaline pickling solutions has been developed successfully, too.
Physical processes like membrane separation, electrolysis, membrane electrolysis, evaporation and so on become more and more important for the environmental technologies.
No chemicals are needed for this processes. The usage of this processes enables the recovery of recyclables (e.g. heavy metals) out of wastewaters of the galvanic industries and the regeneration of the activated baths so that wastewaters will not come up. Very often, this processes will avoid the usage of chemicals for wastewater treatment and so, no hydroxide sludges and no neutral salts will occur.
The named processes can be used as follows:
- Rinse water recycling which means a reduction of the wastewater volume
- Recovery of recyclables in terms of concentrated solutions or even directly metals which means a reduction of the accruing sludge amount
- Regeneration and recycling of electrolytes, hence a reduction of disposal costs and accruing sludge amount
- Electrolysis and membrane electrolysis are suitable especially for the separation of metals out of rinse baths and semi concentrates as well as for the regeneration of electrolytes.
Electrolysis processes are known from extractive metallurgy and galvanic industries, where open and non-split electrolysis cells are used. Anodes and Cathodes are installed in the same tank. Thereby, metals are deposited at the cathode according to the following chemical equation:
E.g.: Cu2+ + 2e- à Cu0
At the cathode side electrochemical reduction reactions (e.g. metal deposition) and at the anode side electrochemical oxidation reactions (e.g. Oxidation of cyanide) can proceed.
This reactions are already used in the environmental technologies to reduce detoxification costs and the amount of sludge.
For membrane electrolysis cells are used, where anodes and cathodes are installed in separate chambers which are divided by ions exchange membranes. Thereby, it is possible to use different solutions on anolyte and catholyte side; so, different electrochemical reactions can proceed on the different sides of the membranes.
The most popular process, based on membrane electro dialysis, is the so-called chlorine-alkaline-electrolysis; here, chlorine gas is produced at the anolyte side and sodium hydroxide is produced at the catholyte side. At the environmental technologies, this process can be used very economically for the regeneration of process baths and for the wastewater conditioning.
The plants are based on a modular design and can be adjusted in size and recovery very easily.
Field of applications of the membrane electro dialysis
- Regeneration of FeCl3-etching solutions
- Regeneration of CuCl2-etching solutions
- Regeneration of chromic acid pickling solutions
- Regeneration of hard chromic electrolytes
- Regeneration of alodine baths
- Conditioning of nickel electrolytes
Advantages of the membrane electro dialysis
- Recycling of recyclables
- Recirculation of regenerated solutions
- No costs for neutralization
- No landfill costs
- Fully-automated process control
- Low maintenance costs
- High profitability
- Short payback period