If fairly small amount I would suggest diluting it as a first step - pour
slowly into a large container of water - about 10 times the volume - with
stirring. This will give a faily vigourous reaction. Obviously wear
goggles and gloves.
When this has cooled to around room temp, you could add washing soda in
small quantities - it will fizz vigourously. Keep adding until there is
no fizzing and you then have a pretty harmless solution.
Large amounts I suggest you get someone else to deal with it.