Hemoglobin is a protein, so you can use standard protein purification techniques to isolate it. You can start with a cation or anion exchange, then purify it further with a size exclusion column.

Alternatively, hemoglobin has a high affinity for zinc. You can buy zinc IMAC resin and use it for affinity purification (see a link for one source below).

Article Purification of Hemoglobin from Red Blood Cells using Tangen...

https://us.vwr.com/store/product/8085124/zinc-chelating-resin-for-immobilized-metal-affinity-chromatography-purification-g-biosciences

Human hemoglobin was isolated and purified by anion exchange chromatography. To isolate hemoglobin, outdated red blood cells (RBC) were transformed into carbonylhemoglobin, by reaction with carbon monoxide, and submitted to washing/centrifugation procedures, to eliminate other plasma proteins.

Andrade et Al., 2004.

Thank you so much guys. That was quite useful.