I have several pending transactions which I want to get rid of because they are holding up other txns. Using Bitcoin-qt client....
I have heard that these can take days to disappear.
If I export my private key associated with these hung txns, can I import it into blockchain.info and initiate a large txn fee spend that will invalidate the other transactions?
Please advise
Search the blockchain.info website for the transactions. If blockchain.info is already aware of the transaction, then they will not allow you to send "a large txn fee spend that will invalidate the other transactions". You'll need to wait until the original transaction no longer shows up on their website.
If you used Bitcoin Core to send the original transaction, then it will continue to resend the transaction every few days to make sure that the network doesn't forget about it. You'll either need to shut down Bitcoin Core until the network has forgotten about the transaction, or you'll need to remove the transaction from Bitcoin Core with the zapwallettxes command line option.