Question

How can you separate a mixture of shampoo and sand?

Answer 1

Use the universal solvent water.
See below

Explanation:

Pour mixture into a funnel lined with filter paper, run water into the mixture.
The sand is left behind.
Collect liquid from the funnel : this is diluted shampoo.

Trying to eliminate the water content to concentrate the shampoo can be very tricky as the shampoo is a complex combination compounds typically:
Ammonium Chloride,Sodium Chloride, Ammonium lauryl sulfate,Glycol, derivatives of coconut oil etc.