Figure A in below shows the schematic diagram for an aluminum can manufacturer”s wastewater treatment system, which used surfactants to wash oil off aluminum sheets and hydrofluoric acid to separate the oil from the surfactant.
Figure B shows how this process leveraged the acid used for etching the cans to avoid having to add more acid during the separation phase. The reuse of acid was accomplished by adding Biomin’s (www.biomininc.com) Organoclay followed by a vessel of activated carbon during the separation phase. The Organoclay removed the surfactant and oil and the activated carbon functioned as a polisher, removing traces 1 PPM or less of dissolved oil.
Surfactants used for this application should be non-ionic, like Union Carbide’s Triton 150, which provides pH 3-5 maximun breakage of the oil-surfactant binding. Organoclay has a high capacity for oils and surfactant and activated carbon removes the traces. Anionic and cationic surfactants interfere with oil removal capacity. Laboratory studies with "Column Test Methods" have demonstrated these oil capacity changes.
For a tutorial on the column treatment test noted above, click here.