grind onvi phrasalphrasal verb, intransitive: Verb with adverb(s) or preposition(s), having special meaning and not taking direct object--for example, "make up" [=reconcile]: "After they fought, they made up."
([sth] unpleasant or boring: continue) (令人不快或无聊的事)
持续 chí xù
The negotiations ground on for several weeks without success.