Corn is often ground up into a meal consistency called corn meal. If they grind it up more it is called corn flour. If they grind it up less, it is called cracked corn. All ground or cracked corn materials work the same and are applied at the same rate of 10-20 pounds per 1,000 square feet. I have been using corn meal since 2001 and have not seen any ants in my yard. If you have fire ants, they seem to hate sweets, so if you dissolve 3 tablespoons of table sugar or molasses in a gallon of water and drench their mound with it, they should go away. The theory is that the sugar breeds bacteria on their underground food supply that makes the food inedible for them, so they go away. You might also spray a 10 foot circle around the mound so they don't just move a few feet and set up a new camp. Some people have fortified the sugar mix by adding a few ounces per gallon of orange oil. Orange oil softens the exoskeleton on the ants which seems to hasten their demise.

Any remaining corn meal will still be good, but you might find them full of bugs. If so you could still compost it with some browns (leaves). Because of bugs I always suggest people not buy more organic materials than they can use in one season. If you have a big freezer, you could kill any bugs or eggs in the corn meal before you open the bags.

To answer you question: Sure you could use Corn Gluten now, unfortunately most of use have found it doesn't work very well as a pre-emergent. However it is an excellent fertilizer. The pre-emergent results vary greatly and for the cost, I think you will be disappointed. With an organic approach your going to have some weeds, thats a fact. Now, there are some things you can do to limit the amount of weeds you have. Proper management practices that encourage a dense, thriving turf are the best method of weed control. Healthy turf shades the soil so sunlight can't reach weed seeds ready to germinate. A thick turf also minimizes the physical space available for weeds to become established. There are several management practices that will promote a healthy, dense grass. Proper management begins with selection of the best turf species or variety for a particular area. For example, heavily shaded areas will support only a few turfgrass species. This results in thin, weak turf that is very susceptible to weed invasion. Do some homework before you overseed this fall and find the best variety of seed for your area and "shade situation". Proper fertilization, watering and mowing are required to produce a dense turf that will prevent weed infestation. If turf is over-or under-watered, over-or under-fertilized, or mowed too low or too infrequently, the turf is weakened and cannot compete with weeds. Damaged areas resulting from using unsharpened mowers increase time needed for turf recovery, allowing for weed invasion. It is very important to understand that weeds don't create a void, they fill a void. So, first, Set your mower to its Highest setting and leave it there. Always use a Sharp blade Irrigate with 3/4" of water when 30-50% of the lawn shows signs of stress. In the shady areas you might be able to go weeks between waterings. The general rule of thumb is no more than once a week in the middle of summer. This is the most important step IMO. To determine how long to run your sprinkler system to apply this much water, set out several straight-sided, same-size cans (tuna cans work best) at random in each irrigation zone and see how long it takes to fill them to the desired depth. Be sure to check your irrigation system for uniform coverage at the same time. In the meantime get yourself a Weedhound(google it) or hand pull the weeds. You could also CAREFULLY spot spray the weeds with vinegar.

Corn Gluten Meal should be applied to prevent seed germination about 6 weeks before that is to happen and it has a fairly limited life for that prevention, so applying CGM now to prevent seed germination next spring would be a waste of your money, time, and energy. Burning might be illegal in your area of the world, or may require a permit with strict limitations. Some people with prairies for yards do burn, because their plants need that for some of the seeds to germinate. Burning would not be a solution for "weed" control.