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Hello everybody. I’m working in the probably smallest zinc facility of the world… We do Zn recycling from fly ash of an incineration plant, means 100% secondary input. The process is like this: leaching of fly ash with HCL > Cementation with Zn-Powder > SX > Electrowinning of Zn. So our SX chances the medium from chloride to sulphate.
The PLS has about 12 g/L Zn. To take it out at once (3 counter current extraction states) we add NaOH in the mixer. We cannot put the raffinate/acid of SX extraction back to the leaching. This because our HCl is "produced" by our wet flue gas treatment of the incineration plant. So we give our raffinate to the wastewater treatment. This is the reason, because we add a base (NaOH) in the SX extraction, to get out all the Zn in one “cycle”.
The addition of NaOH in the SX-Extraction on the one hand induces some saponification reactions with/of our complexing agent Cyanex 272 (means a lot of cleaning work) and on the other hand creates some serious entrainment (HCl in direction of electrowinning…).
Does anyone out there is working with a similar (add of a base in the SX Extraction) system and has some hints for me, who to reduce entrainment and saponification reaction?
Best regards