I used to sand it down on my belt sander and re-use it, however I split 12 dozen with my dad and so now I just pitch them
You remind me of a funny story. I used to play in a bowling alley when I was a teen. It had 10 GC tables and 24 lanes. Really nice family run place. One day the owner who played billiards and had a table there for his own use gets an idea.
He see all this used chalk and has the kid who was kind of the goofer there collect it all up. There was at least a few hundred pieces. He has the kid go behind the machines where there was like a workshop that the bowling mech used.
The kid puts a belt sander in a vice and starts sanding down all the used chalk. Even the ones that were not that low. He gets done and comes out looking like one of those guys in the Blue man troupe
https://pbs.twimg.com/profile_images/450417292707635201/INGRyxSH_400x400.jpeg
This kid was not too bright anyway and being all blue was funny enough but it was not till later that night we found what he had actually done.
About half way through the first league on about 8 of the lanes near where he had worked grinding the chalk the pins were turning blue.
By the end of the night it was a mess, so much of that chalk had gotten into the machines. They had to take all the pins out and clean them as well as the machines. Like everyone who worked in the bowling alley spent all night there doing this.
I guess since we didn't have to pay for it we all found it really funny. We played pool all night as they working cleaning the machines. At that time you could buy a gross of chalk for like $4.00.