Can ricotta cheese be frozen? If yes then how long it keep in freezer?
I would not recommend freezing ricotta as-is. My concern is the freeze-thaw cycle would deteriorate the lovely delicate texture of the curds. 

However, freezing a ricotta filling (example: a spinach ricotta filling for a pasta shell or cannelloni) seems to work well (bound with egg, breadcrumbs, parmesan, spinach, etc).