Lots of people wonder if you can reuse grit. You can but it takes a lot of sorting and cleaning. A low (coarse) grit breaks down into a finer grit but it is still useable. If you are not doing huge projects probably the sorting and sifting is not worth the time. Also you really don't know the state of your recovered grit so your timing will be off. What did the grit break down into 100, 200, or more. So really there goes the planning.