Rio Tinto has won a regulatory battle in the US after staring down a big Utah power company, paving the way for its copper mine to obtain cheaper power.

Rio's Kennecott Utah Copper convinced politicians in Salt Lake City to change the law to allow it to tap alternative energy providers for its troubled Bingham Canyon Mine.

The project has been under pressure since a huge landslide in April last year interrupted operations, cutting its production capacity by about a third and forcing the miner into an expensive salvage and rehabilitation effort.

The huge clean-up as a result of 165,000 tonnes of earth slipping into the open-cut mine - the biggest collapse in mining history - has so far recovered 16 pieces of buried equipment, including trucks, a giant electric drill and a massive shovel about six-storeys tall.

Amid a global push by Rio to slash its expenses by more than half to about $US8 billion ($8.65 billion) by 2015, the miner told Utah politicians it needed to lower Kennecott's operating costs or otherwise investment in the Bingham Canyon Mine would be jeopardised.

Kennecott delivered 10 per cent of Rio's earnings before the mine collapse and it was desperate to cut its energy costs by becoming less reliant on the local regulated energy monopoly, Rocky Mountain Power.

The Rio subsidiary urged Utah politicians to pass legislation to let it buy energy on the wholesale market.

The old law prevented Rocky Mountain Power's customers, such as Kennecott, buying electricity directly from third-party suppliers.

Rocky Mountain Power fiercely objected, arguing it would still have to provide the mine back-up power, forcing it to maintain a big reserve of power at the expense to the public utility, consumers and taxpayers.

The Utah State Legislature in March passed legislation to support Rio's desired changes.

Senator Stuart Adams, the majority whip who tabled the bill in the Utah State Senate, said a compromise had been reached and the change would help encourage Rio to invest and support local jobs.

''The bill was an effort to allow Kennecott Copper to attract capital,'' Senator Adams said.

''In any mining operation it's really important that you have the ability to attract capital and that is contingent upon long-term viability.''

The 110-year-old Rio-owned mine employs about 800 workers and provides nearly a quarter of the United States' copper needs.