The government of the day did not and never used the word "tax". They essentially turned pollution into a commodity, which could be traded between companies who wanted to pollute more and rewarded companies who transitioned to clean energy. See the primary Wikipedia article on emissions trading schemes[0] for more information.

The political opposition continuously spun it as a "tax", in an attempt to stir outrage and win the next election, which they succeeded in[1]. The incoming government was and still is largely funded by fossil fuel companies, so they repealed the scheme.

[0] https://en.wikipedia.org/wiki/Carbon_emission_trading

[1] https://en.wikipedia.org/wiki/2013_Australian_federal_electi...