Hassan,
it depends on the other metal. Pity, you did not mention this important fact. You also did not mention explicitly whether Zn is present in the catalyst in its elementar form, or as part of an alloy. But OK, if the "other " metal is more noble than Zn you may dissolve Zn by gradual addition of 0,1 M HCl or 0.05 M H2SO4, after achieving a stabile drop in the pH of your suspension below approx. 2. In that case dissolution of zinc should be finished.
Prior to "extraction" of elementary Zn from the spent catalist you should remove possible impurities from it by washing with dilluted NaOH /0.1M/. After rhinsing the catalyst with hot distilled H2O and ethanol you might use CHCl3 or other non polar solvent for its final cleaning /removal of fats and other non polar derivatives of hydrocarbons /.
Note: instead of HCl and H2SO4 it is possible to dissolve zinc with acetic acid. Due to slower rate of reaction, the concentration of acid in this case can be for 1 to 2 orders higher.
I hope, this answer might help you a bit. Regards,
R.S.
You can also dissolve Zn from your catalyst via extraction with NaOH, or other strong base. In this case hawever, the reaction proceeds slowly. This method you could use when the other metal dissolves well in the acid, too.
Good luck,
R.S.
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