Muriatic/Hydrochloric acid is easily obtainable as it is the acid they use for swimming pools, also called pool acid. Its about pH1 and super acidic can eat through even cement. It will just acid burn/turn white any organic material it comes into contact with and "bleach" it much like chlorine does in pools or to your clothes. Havent tried it myself as I just dig the weeds out and feed em to the chickens
I reckon putting on a layer of cement is still the best way to go. Just pour once and forget about the weeds. Can always put in self watering garden beds over the cement if you ever need to expand grow space.
