How do I remove a rust stain off a comcrete driveway?

Try CLR. Lay a cloth down over the stain, soak it with the CLR and leave it. Keep it wet for 2-3 days. I know it works on a bathtub this way. Another option would be muriatic acid but I have no experience with it.

WD-40 ***** Did a leaky oil pan leave a big ugly spot in the middle of your concrete driveway? To get rid of an unsightly oil spot, just spray it with a generous amount of WD-40 and then hose it down with water. ***** Soda (Coca Cola) ***** Here’s how to remove oil stains from concrete drive-ways and garage floors: Gather up a small bag of cat litter, a few cans of cola, a stiff bristle broom, bucket, laundry detergent, bleach, eye protection, and rubber gloves. Cover the stain with a thin layer of cat litter and brush it in. Sweep up the litter and pour cola to cover the area. Work the cola in with a bristle broom, and leave the cola for about twenty minutes. Mix 1/4 cup laundry detergent with 1/4 cup bleach in 1 gallon (3.7 liters) warm water and use it to mop up the mess. ***** Oven Cleaner ***** Get those unsightly grease, oil, and transmission fluid stains off your concrete driveway or garage floor. Spray them with Easy Off No Fume Oven Cleaner in the BLUE can. Let it settle for 5-10 minutes, then scrub with a stiff brush and rinse it off with your garden hose at its highest pressure. Severe stains may require a second application. ***** Kool-Aid ***** Nasty rust stains on your concrete? Mix unsweetened lemonade Kool-Aid with hot water. Scrub and the rust stain should come right out. ***** Baking Soda ***** Salt and commercial ice-melt formulations can stain — or actually eat away — the concrete around your house. For an effective, but completely innocuous, way to melt the ice on your steps and walkways during those cold winter months, try sprinkling them with generous amounts of baking soda. Add some sand for improved traction. ***** Ammonia ***** Tired of those annoying discolorations on your concrete work? To get rid of them, scrub with 1 cup ammonia diluted in 1 gallon (3.7 liters) water. Hose it down well when you’re done.

Make a mixture of cream of tartar and lemon into a paste.Apply and leave on long enough for the rust to breakdown.

A power washer should take that right off

Try a can of coke it works on grease ..let sit and scrub and wash away with water

I use a product called "Iron Out" which is available in most grocery stores and Home Depot. It come in powder form. Wet the area down and sprinkle the powder on the stain and wait about 30 minutes and then rinse. Your stain will be gone. Repeat the process if it's not. It works on toilets, dishwashers and laundry.