In The Netherlands, the cost of waste disposal is increasing fast. Moreover, government policy forces companies to research, develop and implement new techniques aimed at the recovery of the waste streams they produce. WTN Water Treatment reacted very early on this new trend in developing new techniques to remove Zn from hydrochloric acid pickling baths, without producing any additional waste products.
The ReZn process offers several major advantages:
It has been developed by and for galvanizers
It is a flexible process.
It involves very low disposal costs
No extra manpower is required
It represents a saving on basic chemical cost
In this case, flexibility refers to the final concentration of zinc which is easy to control. If a final zinc content of 2 g/l is required it can be achieved, likewise for 0,5 g/l, and so on. Thus it is a process designed for the future, easily adapting changing zinc-limitations in waste pick- ling acid.
Process description
The ion-exchange material, specially developed for the ReZn-process, separates Zn and Fe in a highly selective way. The process is divided into 4 stages:
1. Loading phase.
After filtration of solid particles with a plate-filter zinc is separated from the pickling acid and absorbed by the special ion-exchange material. Zinc-free pickling acid is pumped back into the pickling bath.
2. Rinsing phase
After saturation of ion-exchange material with zinc, it is rinsed to remove any re- maining pickling acid. Rinse solution later be used to adjust the concentration of the pickling bath.
3. Stripping phase
Zinc is stripped from the ion-exchange material with stripping solution, which may be used to adjust the composition of the flux bath. It contains nothing more than ZnCl2 and NH4Cl (flux-salts).
4. Rinsing Phase
Traces of the (flux) solution are removed by rinsing the column with tap water. Now the system is ready for the next run. The unit can be supplied fully skid- mounted and is able to run fully auto-
