{then it is cheaper to use dollar to purchase stuffs from australia in the first place. Using yuan then convert it to dollar again will incur unnecessary exchange costs, it is inefficient and put burden to businesses.}

I did not suggest using RMB to buy and then exchange it for USD. Predicate mentioned the use of RMB in iron ore pruchase from Australia. My RHETORICAL suggestion of exchanging it for USD, that China is already holding, was to repeat my original aim of unloading the USD.