Why should on earth any miner accept your dirty coins and give you their fresh mined coins? What's the benefit for the miner? Well, if you give them the double money, then they might think about it but otherwise, I think no miner will accept such an offer.
With a interest of a few percent, why would a miner not exchange his coins for others of the same value? After all, that's what mixers do. What do you think miners do with fresh coins, keep them forever for themselves?
Also, who is reliable enough to claim that some coins are 'dirty'? Whitebit AML checker?