We recently bought a home and found about 2 litres of hydrochloric acid 20% (also known as muriatic acid) that was used to manage acidity in a swimming pool that no longer exists. I would like to dispose of it but our local recycling centre is unfortunately not accepting this substance.
Is there a safe way to dispose of it? I have done limited research and here are the 3 ways I could think of:
- Diluting the acid in water and dispose in a sewer when pH is above something like 5-6. I have testing bands so I can ensure that the water solution is not too acid.
- Neutralize with a basis, like baking soda or garden lime. Basically, it's similar to solution 1 except that it uses less water but produces dangerous gaseous chlorine as a side product.
- Use a solid metal (like iron or aluminum) to produce a precipitate and gaseous hydrogen. This might be safer (no toxic chlorine is produced as gas) but I have the problem of getting rid of the precipitate. I am not sure if that's simpler.
I am not a chemistry expert but I do remember some basic concepts. I can find online that the pH of HCl is 0 for a concentration of 3.647%. From there, I compute that the theoretical pH of my solution is -0.74. This means that, to reach a pH of 5, I believe that I need to dilute by solution by more than 500'000 times, assuming that the pH of the water in our pipes is around 7 (which is the case). That means that I would need to use 1 million litres of water, which is insane!
That leaves me with the last 2 solutions. Is it reasonable to consider using a metal to form a precipitate or is really the only option to use a basis? Also, what amount of garden lime or baking soda should I expect to need to bring my pH to around 5?