Not sure about the cheapest ...
Published by Suhasini Bhatnagar, Employee at swaroop enterprises and biotech private limited.
Not sure about the cheapest and the best method, but one word of caution that there must be no residue remaining to tackle later. For one such reason can offer a method bioremediation and my patent to do the needful.No infrastructure required.
wish to offer using my patent-
· Patent no.IN 201811011885 titled BIOREMEDIATION SYSTEMS AND METHODS FOR REMOVING DAMAGING HEAVY METALS FROM INDUSTRIAL EFFLUENTS as a Inventor
to remove both iron and magnesium in one go.