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This answer affirms that reacting aluminum with HCl is a (seemingly convenient) way to produce hydrogen for use in other experiments, but the byproduct, AlCl3, is rather nasty. What's the best way to dispose of it? My naive guess is that reaction with baking soda would produce carbon dioxide and aluminum hydroxide, which would be fairly harmless. Is this correct?

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Sure, you can react the $\ce{AlCl3}$ with $\ce{NaHCO3}$ solution, and you'd also get $\ce{NaCl}$, in addition to $\ce{CO2}$.

Though $\ce{AlCl3}$ is toxic, it reacts readily with water, forming the less toxic chlorohydrate (used in antiperspirants!), and the baking soda should leave an innocuous sludge, safe to dispose of in a sink.

N.B.: The reaction is exothermic and bubbly, so use care when mixing in the $\ce{AlCl3}$ to avoids spatters.

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  • $\begingroup$ If it reacts readily with water, why does the initial reaction of Al with HCl produce it rather than yielding the chlorohydrate immediately? Or does it? $\endgroup$ – R.. GitHub STOP HELPING ICE Apr 12 '19 at 20:04
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    $\begingroup$ @R.. It obviously doesn't, really. You get a solution of aluminium chlorohydrate, which you shouldn't drink. $\endgroup$ – Karl Apr 12 '19 at 20:27
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You should begin by consulting the safety data sheet (SDS) provided by the manufacturer and Prudent Practices in the Laboratory to understand the hazards.

The laws of your jurisdiction and the policies of your organization will determine what amount (if any) and by what method neutralization is permitted. Environmental health and safety (EH&S) groups in some organizations deal with authorities who view quenching any regent as illegal unlicensed hazardous waste processing, justifying significant fines. EH&S might insist that you have a special pickup from your hazardous waste provider.

It is possible to quench AlCl3 cautiously in stirred ice water while keeping the pH to within the permissible range to bulk with your aqueous waste stream. Keep in mind the quench is highly exothermic and can get out of control quickly. From a practical standpoint, the volume of aqueous waste generated might make this approach more costly than having a LabPack pickup of the solid aluminum chloride waste.

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  • $\begingroup$ According to the other answer and Karl's comment on it, there is no solid aluminum chloride waste unless you go out of your way to make it, so perhaps my question is now somewhat mismatched with my intent. $\endgroup$ – R.. GitHub STOP HELPING ICE Apr 13 '19 at 0:16
  • $\begingroup$ @R.. Jup. Unless you use dry HCl gas instead of dilute hydrochloric acid. ;-) $\endgroup$ – Karl Apr 13 '19 at 22:52

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