Mix salt and zest in a bowl; work zest into salt with your fingers to release oils and flavor.
A mortar and pestle works well if you have one....
Spread out the salt on strips of parchment paper to dry in any of the these ways
Spread it on parchment paper-lined racks of your food dehydrator and set the temp at about 100 degrees. Four or five hours should take care of it
Spread on a baking tray. Air-dry until dried completely, 8 hours to overnight.
Set the cookie sheet in an oven heated to 225 degrees for about an hour and a half. The citrus zest is easy to burn, so keep an eye on your project....
Make ahead: 2 months, kept airtight at room temperature.
Note: Zest's color will fade over time, but this won't affect taste.