Hi again,
I bet all of these solutions will kill them on the surface, but they won't get them all the way. Fires ant mounds are at least 1 foot deep, and if you attack them from the surface, the majority of the ants will retreat to the bottom of the mound, then tunnel to somewhere safe, and your problem starts all over again. Like bees, ants reproduce through the queen, so ants put her in the most fortified part of the mound, the bottom. The trick to fire ants is the queen, if you kill the queen, you kill the mound. The problem with this grits trick, is that it isn't liquid enough to seep down into the mound, it will just sit on top and roast the surface layer, which is unimportant. All the ants will just stay down low and wait until the grits cool, then they will rebuild their mound and use the cold grits as a food. then your problem is worse because your feeding them.
I would suggest the Dawn solution, or gasoline ( I prefer a gasoline, but I have had some squabbles over the matter with other members, so I will say no more about it)