I have read the ants will not cross a chalk line.
It would be worth a try hitting chalk over the ant nest, which is calcium.
I recently in my flower bed mixed a half a cup of blue down with a half a cup of baking soda and the rest water, of course 3/4 of the way full I shook it up waited on the bubbles to go down to finish filling and then check the top of the ant mount off with a stick and poured the mixture in. So far, no ants.
This was in an area with flowers at this time but with all the rain it will not be long before it is washed deeper in the soil and I will put my flowers in.
