Kayla, pictures would help a lot here! Also if you could fill in your profile to tell us where you are (city/state/country) that would also help to figure out what might be going on.
Ants generally don't harm plants (except leaf-cutter ants which are tropical species) but they do "farm" other insects that live on citrus, like aphids.
If your tree has a wound that is leaking sap, the ants would be there eating the sap, but they are not the cause of the damage. You don't want to use any toxic insecticide on a tree that is growing something you want to eat. So non-toxic methods are indicated here. Diatomaceous earth (available at HD or Lowe's) will deter the ants, and may also kill other bugs that may be in the tree.
I'd advise also as Philip said, to wash off the area with the hose, and let it dry thoroughly then get out a magnifying glass and try to figure out why the sap is leaking out of the tree. A picture would help us to help you with this, if you're able to post one.
Is the sap weeping from the tree low down on the trunk? I don't want to alarm you but there is a very serious fungal disease known commonly as "foot rot" that kills a lot of citrus trees here in Florida. Again, I'd need to see a picture of the area you're talking about.
