ADVION Fire Ant Bait. 1.5 lbs per acre, broadcast. Or, use it for mound-treatments. 1-3 days later, any active mounds will be dead.
Best of all, the active-ingredient is relatively non-toxic until after it passes through the ant-larvae gut; at which point it becomes very lethal to the colony after it is underground.
Available in 2# shaker-jugs and 12# bags. But, once either container is opened, make sure to keep it well-sealed to prevent the bait from losing its freshness (attractiveness). In fact, try not to keep it stored too long after opening the container. Consider it like a bag of potato chips. Once opened, the clock begins ticking for when it becomes stale.