The Obama administration is set to give protection to one of the world's natural wonders, by banning uranium mining on 1m acres of land around the Grand Canyon.

The interior secretary, Ken Salazar, is due to make a formal announcement on Monday of the 20-year ban on new mining claims, at a film screening at the National Geographic Society in Washington.

The move, praised by conservation groups, is sure to bring the wrath of the mining industry as well as some Republicans, who argue the ban will cost jobs. The measure does not affect some 3,000 existing mining claims around the canyon, however.

Conservation groups said Barack Obama had shown political courage in going ahead with the ban in the face of that opposition. "Despite significant pressure, the president did not settle for a halfway measure," said Jane Danowitz of the Pew Environment Group.

In the final years of the George Bush presidency, when uranium prices were rising worldwide, mining companies filed thousands of new claims in northern Arizona, on lands near the Grand Canyon. They also proposed reopening old mines adjacent to the canyon.

Salazar ordered a temporary halt to new claims in 2009, after Obama came to office.

Government officials proposed the 20-year ban in October last year, after an environmental review, calling for the preservation of an "iconic landscape".

"It is appropriate to pause, identify what the predicted level of mining and its impacts on the Grand Canyon would be, and decide what level of risk is acceptable to take with this natural treasure," Bob Abbey, the director of the US bureau of land management, said at the time.

Republicans, including former presidential candidate John McCain, condemned the move to withdraw lands from new mining claims as an emotional over-reaction.

"This withdrawal is fuelled by an emotional public relations campaign designed by some of the same environmental groups whose long-time mission has been to kill mining and grazing jobs on the Arizona Strip, as well as tourism jobs at the Grand Canyon," McCain told a hearing in Congress last year.

Conservation groups have long argued that mining laws in the west are antiquated – giving companies free access to vast swathes of iconic public lands.

In the case of the Grand Canyon, the concerns go far beyond just conserving a spectacular view. At least one creek in the national park is known to be contaminated by uranium, and the government's environmental impact review found high levels of arsenic from old uranium operations.

• This article was amended on Tuesday 10 January. The original picture showed Monument Valley. This has been corrected