plating, anodizing, & finishing Q&As since 1989
Phosphate removal from chrome solution
Does anyone know how to remove phosphates from a standard chromic acid plating solution? We are trying to remove the phosphates in our treatment system prior to chrome reduction and recovery of the chrome as a metal precipitate. I understand there's a relatively simple chemical process but I haven't been able to figure it out. (The phosphates are a source of phosphorous in the recovered chrome precipitate. Phosphorous is very detrimental in the recycling of chrome back to the stainless steel industry).Jim Sullivan
metal recovery - Paterson, New Jersey
That's tough. Chrome solution is pretty acidic. I would say your best bet would be to neutralize most of the acidity with lime or magnesium hydroxide, then drop the phosphate with aluminum sulphate. With experiment, you may be able to find a level of neutralization that will still leave enough acid for the metabisulfite (I presume that's what you're using) to work.
If not that, then the only thing would be to neutralize *all* the acidity, drop the phosphate with Ca, Mg, or Al, then reacidify the waste for the reduction step. Or, live with the problem.
Consultant - The Bronx, New York
Why wouldn't you reduce and precipitate the chrome, allowing soluble phosphates to just wash away? I haven't done this, as I've never seen a problem of phosphates in chrome, but it sounds like it would work.
Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
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