does Sodium persulfate evaporate at room temperature I use Sodium persulfate to etch a copper board to manufacture home made Printed Circuit Board (PCB), and I use the same etching tank on the below photo which has no cover on the top. I wonder if it is okay to keep it like that at the room temperature or would it evaporate?
Regardless of evaporation, it is an oxidizer and unhealthy so it is recommended to keep it in a closed container. 

With that being said, you most likely have a solution of sodium persulfate in water.  Water will evaporate so again, yes, keep it closed.