Sulfuric Acid Dilution

Q. How do you get sulfuric acid of 25 percent concentration down to 32°? The lowest we can get it is to 56°. Is there any material that can withstand 25-percent sulfuric acid? —M.S.

A. The Baumé system of acid concentration can be confusing and non-intuitive. If you are starting with a 56° Baumé concentration of sulfuric acid that equates to an approximate concentration of 71 percent. If you want to get it to a 32° Baumé, that would result in a concentration of about 37 percent. A 25-percent concentration would result in a Baumé concentration of about 28 percent.

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You may first want to find a good reference to convert degrees Baumé to percent concentration. The CRC Handbook of Chemistry or the Encyclopedia of Corrosion Technology are two potential references that can assist you in making this conversion. Once you have a good conversion reference, you then calculate how to dilute your tank from the higher to lower concentration tank.

A simple means to do this is C₁V₁=C₂V₂ where C equals concentration and V equals volume and 1 and 2 can be the two different systems you have. For instance, if you have 100 gallons of a 35-percent solution and you want a 25-percent solution you will need to dilute the mixture up to 140 gallons (200 × 35% / 25% = 140). This would best be done by adding 40 gallons of water to an empty tank and then slowly adding the 35-percent mixture to it, stirring until all 100 gallons are added.

There are several materials that can withstand a 25-percent concentration of sulfuric acid. High grades of well alloyed stainless steels and several plastic materials are compatible with sulfuric acid.