What is the process for purifying KOH?

I'm partnered with a jewelry production company whose plating baths require KOH. We're located in Indonesia, where import fees are absurdly high, and reliable suppliers are rare. A local shop sells KOH at \$5 / Kg, but whatever impurities are present in their mix cause enough problems to spoil the entire bath. (Expensive mistake when doing gold plating...) The only alternative we can find is a Merck redistributor, who sells KOH at close to$100/Kg, which is ridiculous.

Is there a relatively simple process we could learn (of the DIY variety) for removing impurities, turning non-lab-grade KOH into lab-grade KOH?

-

1 Answer

According to Armarego, et al. (Purification of Laboratory Chemicals, 6th edition), they only provide a procedure to purify a solution of $KOH$, likely owing to its very high solubility. Further, the only impurity of note they cite is carbonate (from standing in contact with air), so if this is not your impurity then this procedure will not help.

If this is your impurity, they recommend adding a saturated solution of a barium salt, either $BaCl$ or $Ba(OH)_2$, shaking, and then setting aside to allow the insoluble $BaCO_3$ to settle. It sounds like you are working on large scale, so it is important to recall that the procedure just described should be done in several small batches to work best.

Not certain this is what you are looking for, but I hope it's a start.

-
I read somewhere that non-lab-grade KOH usually contained heavy metals. We'll try a barium salt process and see if things improve :) Thanks! –  neokio Dec 29 '12 at 9:43