I agree with Benjy that 'to be ground' is better, although both are possible. I think with 'to grind' the emphasis is on the grinding, as if that is the objective in itself, whereas 'to be ground' suggests that the grinding is just a means to an end.
[…]
1 ton of material to be ground

1 ton of material to grind

(but with the distinction mentioned above)
The ton of material is to be ground

The ton of material is to grind

(because the material is not doing the grinding)