Not sure why you need a Terram requisite to evaporate the water, as I said, this process was understood by the Romans. So if the Romans were evaporating water naturally, it stands to reason that a spell that evaporates water would just evaporate water and leave the salt.
I just don't like using PeAq to destroy the water and leave the salt, because it's using Perdo to dry/make something better. I'll note, if you're personally fine with that, the gudeline to completely dry something out (the size of a small house) is a PeAq Base 4 guideline. It doesn't fit with my aesthetic, but I can see others going this way. I would still do a separate ReAq spell to move the salt water into ponds, because I don't like combining spells to do separate and distinct effects into one spell and then saying it's a requisite. Sometimes it is necessary, but I'm not sure that's the case here.