You are in the freshwater forums, but consider this...
Beaches are the planet's skimmers. All the crud gets washed up onto them and into the sand.
Consider also that most beach sands are silicate sands and will do nothing to help maintain and buffer your pH. Some may even say that silicate sand in a salt tank may contribute to diatom issues.
Not saying it can't be done. Proper cleaning of the sand and care of the tank will be necessary. You will need to research how to properly clean it.
I support the right to arm bears.