You have a few options:
1. In bucket(s), soak in mixture of bleach and water (15-30mins.), rinse using a sifter, dechlorinate in bucket(s), rinse in sifter (repeat), and let dry. There should be no bleach smell or "sliminess" to the texture.
2. Soak in freshwater-tap water (30-60mins.), rinse in sifter (repeat), and let dry.
3. Rinse in sifter.
A sifter, for lack of a better name that I can think of at the moment, is just a box (can be made of wood) with an appropriate screen that won't allow the sand to pass through.