The foam separation of colloidal ferric oxide with an anionic and a cationic surfactant

An experimental investigation is presented of the foam separation of colloidal ferric oxide over the pH range 3 to 12 by using an anionic and a cationic surfactant. A sol containing 1.67 mmole/ liter (93 mg/liter) of trivalent iron can be reduced in concentration to 0.09 mmole/liter by 0.17 mmole/liter dodecyl sodium sulfate (anionic) over pH 4.5 to 8; and to 0.18 mmole/liter by 0.17 mmole/liter ethylhexadecyldimethylammonium bromide (cationic) over pH 10 to 12. Soluble iron species produce poorer separations. Between pH 8 and pH 10 the charge of the colloid is reversed from positive to negative, and for an efficient separation a two‐step process should be used, first with an anionic surfactant and then with a cationic. The charge of the particulates has little effect on the foam separation of the surfactants although the presence of the particulates has a significant effect, as evidenced by residual surfactant concentrations and collapsed foam volumes.