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What is the proper way to dispose of used hydrochloric acid (e.g. Sureklean 600)? My municipal waste station does take toxic waste periodically but I was wondering if it can be safely flushed down the toilet. It is very corrosive to metal and I know there is cast iron sewer pipe below the basement leaving the house to the street. Also, is it safe to flush it from the environmental standpoint?

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up vote 9 down vote accepted

HCl can be combined with baking soda to form salt water and CO2.

NaHCO3 + HCl = NaCl + H2O + CO2

NOTE this is exothermic and effervescent, mix slowly, adding the soda to the acid. In a wide-mouth container.

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According to the MSDS, use Soda Ash or Lime to neutralize, 2.5 Lbs. of lime per gallon. The usual requirement is neutralize to 6-8 pH (neutral) and then dilute. Per their words "Neutralized materials may be discharged to a sanitary sewer with approval of the receiving treatment plant." –  Fiasco Labs Feb 13 '13 at 6:20
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Watch for heat production. Mix Chemicals slowly. –  Chris Cudmore Feb 13 '13 at 14:40
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NEVER add baking soda to acid. Always add acid to baking soda (slowly and carefully). A baking soda splash is harmless. An acid splash can cause a lot of damage. Basic high school chemistry safety. –  Philip Ngai Feb 13 '13 at 18:47
    
@PhilipNgai I might typically agree with you, but in an effervescent reaction like this I think you'll get better results by carefully adding the soda. –  Matthew Feb 13 '13 at 20:21
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With bicarb, the stuff's going to bubble and foam horribly no matter how you mix things. If you have it, it's better to use slaked lime (calcium hydroxide, pickling lime, nixtamilization lime) to neutralize. No carbon dioxide-> no foaming. –  Wayfaring Stranger Feb 14 '13 at 15:24

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