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Selective removal of Calcium from wastewater


Q. From our waste water we want to concentrate our zinc level by means of electrodialysis or reverse osmosis. We want to achieve a zinc concentration 80 times as high as the starting level. The problem is that there is too much Ca in our wastewater (240 mg/L) and it will precipitate as CaSO4. Does anyone know of a possibility to remove the calcium and not the zinc?

Koen Joris
- Belgium


A. I'll offer 2 suggestions:
1) If the source of the Ca is hard water used for rinsing, switch to using de-ionized water for your zinc drag-out rinse, or
2) Use a heavy metal selective (chelating) ion exchange resin to extract the Zn but not the Ca.

Ken Vlach
- Goleta, California
contributor of the year honored Ken for his countless carefully
researched responses. He passed away May 14, 2015.
Rest in peace, Ken. Thank you for your hard work
which the finishing world continues to benefit from.

December 16, 2016

Q. CaSO4 precipitated in outlet of pipe and we could not pass rinse water to our ETP plant because pipeline choked. Give me advice for that?

yogini kalambhe
- Nagpur,Maharashtra, India

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