Thank you for the opportunity to help you with your question!
You can put it all in water. The salt will dissolve into the water but
the diamond dust will not. Then pour the mixture through one of those
coffee filters. This should let the salt and water solution pass through
and leave behind the diamond dust. Then again the chance of this
working depends on how fine the dust is.
Please let me know if you need any clarification. I'm always happy to answer your questions.