How many horns can be fired from Alicorn Lance during its duration?

I am somewhat confused by the wording of Alicorn Lance as stated in Elminster’s Guide to Magic. The text states:

Duration: Concentration, up to 1 minute

A transparent alicorn (unicorn horn) forms about 2 inches from your brow. Starting the turn you cast this spell, for the duration you can use a bonus action during each of your turns to launch the horn at a creature you can see within range.

I am confused about the supposed contradiction between "during each of your turns" and "launch the horn".

Does it return between launches? Does it reappear? Does it ever leave your head in the first place?

Can you launch a new horn each round?

Or is it just a single-shot effect that you can use on one bonus action that occurs during the spells duration?