Working in 2 batches, place 1 quart ice cubes in a blender. Add 1/2 can limeade, 6 ounces tequila and 2 tablespoons Cointreau. Blend at highest speed until drink is almost smooth. Pour into a pitcher and repeat with remaining ingredients. Store in the freezer.
To salt the margarita glasses, pour a single layer of salt on a salad plate. Moisten each glass rim with lime; dip each rim in the salt. Pour margaritas into each glass; garnish with lime. Serve immediately.