There are a number of areas with lockers in the Zurich Airport, all of them at or adjacent to the train station I believe. The train station is attached to the terminal, and one need only walk a few minutes to get there, over an enclosed bridge. There are a number of lockers just above the main concourse of the train station. As you come over the bridge, you will see an information counter to your left, on the mezzanine level. The lockers are located just to the left of the information counter in an alcove.

A;lternatively, there are lockers near the ticket sales windows. As you face the ticket windows, the lockers are to the left. You can ask there. The lockers are of various sizes, but none will accomodate a really large suitcase. I believe there is also a bag check counter somewhere upstiars near the station, but I don't recall exactly where. You could, of course, leave a bag of most any size there.

finally, silly as this sounds, don't forget to put in the coins and take the key after closing the locker (or take the key code slip in the case of some of the automated lockers). Otherwise, your locker will be closed and not locked and will present a tempting discovery for someone opening it to put their bag in an apparently empty locker. It may seem hard to believe, but many peopkle, especially those jet lagged or distracted, forget to lock the locker.