Iron filings are the only magnetic component - use a magnet under the dish & pull sideways slowly to pull the filings out of the mix.
Salt is soluble in water, so add water (hot will dissolve the salt more easily) to your mix and strain through filter paper - evaporate the water from the salt water solution that comes through the filter
Sand & pepper is a bit harder - is it peppercorns or ground? If peppercorns a strainer the right size would do it. If ground - try adding water again & letting it settle, the sand will sink and the pepper float to the top - both would need evaporating to get the excess water out once you separate them