1. What SS are you starting with? The 300-series contains Ni, while 400-series does not. That's the first question. If you're just starting with a
piece of scrap metal off the shop floor, it's probably 304SS (cheap) or maybe 316SS (expensive). But there are many other alloys, and some do not
contain any Ni at all.
2. You stated you added NaOH until you "got a thick goo". I don't even know what that means in english. What was the pH at that point? All 3 of these
metals precipitate at different pH's. In fact, that's one way you could try to separate them.
3. Okay, so turn them into their Cl salts like you did. Then *carefully* add NaOH (or other base) to selectively ppt them.
4. Just trying to brainstorm here, but sulfide precipitation is another well-known approach used in the water treatment industry. Bubble H2S into the
soup, and selectively ppt them as the sulfide. I'm just throwing out ideas, here.
5. Use selective ion exchange. Pretty complicated, but this is another separation technique used in removal of heavy metals from wastewater streams.
6. Just buy Cr metal online.
7. Just start with 400-series SS. That eliminates the Nickel, anyway.
That's just my 25 cents worth
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