What's the best way to remove rust surface stains from concrete ?

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.

Soda (Coca Cola). 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.

Muriatic acid is supposed to work you can get it at Lowes and Home depot in the paint department

Iron Out. Available at hardware stores.

Whink. It's by CRL in cleaning aisle at Walmart. This stuff is a miracle