1 private key is for one single address so just like the above said it won't work if you want to recover your seed using private key and if you want to recover your Bitcoin including ETH wallet.

ETH wallet on Mycelium still on beta testing and it is new and it is not recommended wallet to save a large amount of ETH.
So, If you still have access to the ETH wallet much better transfer it right now to your new wallet. I suggest you use MEW or Coinomi wallet as an alternative wallet to save Ethereum.

But if you don't have access to your wallet anymore and only private key you have then there's no way to recover your ETH because like the above said the private key you have is the Bitcoin private key.

You must have seed backup to be able to recover your old wallet including ETH wallet.