Mining “clean” blocks is a euphemism for selective or censored mining where only transactions from non-criminal or non-sanctioned entities are included in a block. The term has no applicability to the type of energy consumed by mining.
The US Office of Foreign Assets Control maintains lists of foreign individuals and entities that US companies are barred from doing business with. “Clean” block miners wish to apply this list, which includes a few cryptocurrency addresses, to their transaction selection. To be clear, mining only “clean” blocks are a self-imposed obligation created by certain miners.
“Clean” block mining centers around an ethos that prioritizes regulatory compliance over fungibility by opting to not treat all transactions as equally valid and mineable, and instead creating two classes of bitcoins and transactions: the “tainted” and the “clean.” Many bitcoin investors view the practice of “clean” mining as an attack on the Bitcoin network.
Problems for “clean” mining
Because on-chain data allows limited visibility into which real-world entities are behind Bitcoin transactions, correctly labeling all transactions as either “clean” or “tainted” is incredibly difficult. Of course, connections between many addresses and their real-world owners have been made. But this is not the case for all or even most addresses. Thus, including any transactions in a “clean” block risks polluting it entirely and ruining the whole endeavour.
To ensure a completely clean block, miners would have to exclude all transactions and simply mine empty blocks, claiming no network fees and only earning the mining subsidy. This would result in only the newly minted coins from the mining subsidy being sent directly to the mining pool.
Opting to claim no transaction fees puts “clean” block miners at a significant financial disadvantage compared to other miners, especially as fees become an increasingly important source of revenue while the mining subsidy continues to decrease.