Optimum pH for precipitation of zinc as zinc hydroxide is 9.45 from my experience. Above this pH zinc effectively comes 'back' into solution as a zincate Zn(OH)4 - - ...thus causing a rise in zinc concentration in your effluent outfall. Ferric chloride alone is not the best way for metal precipitation, I would use an anionic polymer after you add the ferric chloride and adjust pH. And most important: 1 - First add ferric chloride 2 - Adjust pH 3 - Add polymer Ferric chloride is always acid, so if you adjust pH before adding it, pH values will be not consistent and you will have problems again..
Published by Ing.Tiziano Zampollo, Employee at Water Engineers & Consultants - WEnCo
Optimum pH for precipitation of zinc as zinc hydroxide is 9.45 from my experience. Above this pH zinc effectively comes 'back' into solution as a zincate Zn(OH)4 - - ...thus causing a rise in zinc concentration in your effluent outfall.
Ferric chloride alone is not the best way for metal precipitation, I would use an anionic polymer after you add the ferric chloride and adjust pH.
And most important:
1 - First add ferric chloride
2 - Adjust pH
3 - Add polymer
Ferric chloride is always acid, so if you adjust pH before adding it, pH values will be not consistent and you will have problems again..