What is the scientific principle behind why ice cream turns gritty ? Once it has reached this stage, other than throwing it out, what can be done with it ?

I realize that it’s caused by partially thawing and re-freezing, but still curious as to why it develops that obnoxious sandy texture.

Would melting it totally, or perhaps even heating it a little, get rid of the grittiness and enable it to be used in a milkshake or as a dessert sauce ?

It seems a shame to just toss it, but that sandy texture is just too awful for words.

I’m hoping some of you scientific genius types can provide some help here :)